Iris Publishers Engineering Sciences

Abstract

In southeastern Nigeria, soil and gully erosion and landslides are responsible for the widespread destructions of human, animal and plant lives, domestic, industrial and commercial property, transportation and communication systems, degradation of arable lands, contamination of surface and groundwater supplies, isolation of settlements and migration of communities. This account presents some of the results of research and studies of gully erosion and landslides carried out over the years in parts of southeastern States of Abia, Anambra, Enugu, Ebonyi and Imo States. Gully erosion is attributed to natural and anthropogenic causes, with the latter being most prevalent. Gully initiation is the result of localized erosion by surface runoff and soil eluviation associated with rainfall events of high intensity. Erosion is frequently concentrated where the forest cover has been removed for agricultural, urbanization and construction purposes and also at sites of uneven compaction of surface soils through surficial changes and movements. Based on rigorous reviews and research, interactions and personal experiences, the gullying mechanisms and processes were evaluated and the control measures suggested includes: avoiding human induced Soil/gully erosion initiation; public awareness; planting of vegetation on flood plains to be encouraged; laws guiding construction and building codes should be enacted by governments and relevant agencies; construction of special road infrastructure must be emplaced on solid engineering structures for soil and gully erosion control as well as regular maintenance of roads and drainages. Federal and State governments and community leaders should, therefore, inform and engage the inhabitants of the communities within the study area to successfully halt the initiation of gully erosion and landslide.

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Abstract

In atmospheric conditions, most of the metals and alloys are unstable and prone to corrosion. The corrosion potentially affects industrial equipment, reduce the shelf life of the infrastructure assets and the quality of the environment. Therefore, it is essential to control the corrosion to save considerable expenses in materials, equipment, and structure. This review article provides a brief overview and impact of corrosion, recent incidence related to corrosion, incurred cost, and mitigation methods of corrosion.

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Increasing Durability of Weak Lime Mortars Using Saturated Solution of Calcium Hydroxide or Barium Hydroxide, Aachen City Wall, Germany, Case Study

Authored by Serdar Koltuk

Introduction

Lime mortars have been broadly used in the Medieval period in building as it has been considered as friendly mortar to the building stones as well as to the environment. Chester City walls at Chester City, UK as well as other Medieval structures had been built from natural sandstone blocks cemented with such hydraulic lime mortar [1]. Not only that but also the ancient Medieval Aachen City walls, Germany have also been built from fine grained sandstone cemented with such type of mortars [2]. Recently, such type of mortars become week and easily weathered by the severe and aggressive weathering processes (particularly salts created from acid rains, de-icing salt ...etc.) acting on all building materials [2-5].

Increasing durability of such weak mortars using some additives becomes a must. Unfortunately; a lack of experimentally supported publications and detailed information about the impact of lime water treatment on lime mortars particularly the weak ones have been found. Some previous literatures regarding hardening weak mortars presented only marginal data [6,7] or the results attained under certain limited conditions may be broadly interpreted. It may be extrapolated into conditions where no enough information is available, and so, no precise information or evidence can be found regarding this point of view [8] Consequently, the number of relevant articles is quite not enough to understand this topic i.e. it still requires several investigations to cover it for the best of archaeological conservation Angeli et al 2007 [9]. Only the most relevant experimental studies have been mentioned, theoretical works analyzing very important questions of binding mechanisms [10] analso literatures illustrating confusions in terminology (limewater against lime wash) [11] or presenting discussions against the application of limewater for consolidating mortar and/or building stone.

The efficacy of limewater applied in situ for conservation of wall paintings on lime mortar rendering has been previously studied [12]. Those researchers tested limewater treatments from the following points: the application procedure, the number of applications that are ranging from 20 – 60 cycles, dosage and maturation.

They concluded that continuous “wet” applications ended with a consolidation effect, unlike applications with “drying” breaks, which do not consolidate the wall paintings. However, the observed consolidation tended to consider fixation of a released surface paint layer, for which limewater was recommended to be applied in some publications [13]. Previous literatures had not considered measuring of mechanical characteristics of the treated mortars before and after treating with limewater. On applying limewater for 40 cycles on stone as well as on crushed limestone, a very small increase in calcite content has been observed in the material, no observable change in the mechanical characteristics (particularly compressive strength), and no consolidation effect on the crushed material have been recorded [13]. Limewater effects and the use of meta-kaolin as an additive in limewater were investigated [14]. The limewater wasapplied for 40 cycles on stone and also on crushed limestone sand, and it has been found a very limited increase in the amount of calcite in the material, no observable change in the mechanical characteristics, and no consolidation effect on the tested crushed material [14]. Applying the limewater and limewater with meta-kaolin for consolidating old rendering with low cohesion at both of laboratory and in situ tests had been conducted [13]. It was concluded that the tested consolidates increase the mechanical resistance only of the superficial layers [14]. Based on the previous investigations in this field of render consolidation. The current study aimed to conduct an experimental program to reveal the fundamental behavior of weak lime mortars when subjected to multiple saturations and evaporation of distilled water, a saturated solution of calcium hydroxide in water (“limewater”), limewater with added meta-kaolin, and saturated solution of barium hydroxide.

Simply, the main aim of the current study is to offer an objective evaluation of the impact of adding limewater to friable mortar, and to ascertain the degree of consolidation. The consolidating effects not only of limewater but also of multiple applications of some other treatments e.g. distilled water, limewater blended with meta-kaolin, and barium water (a barium hydroxide saturated solution in water). Barium hydroxide was considered as an alternative consolidating agent to calcium hydroxide and is expected to be more effective as it is much more soluble in water than calcium hydroxide[13].

Methodology

To conduct and achieve the aims of the current study, a well performed plan of research has been structured as shown in Flow chart (1). The following sections are detailed explanation of the methods, tests and results of the measurements conducted for the control and treated mortar samples to find out which one of the suggested treating materials with which regime of applying we get the ultimate enhancement in hardness and durability of the weak lime mortar.

Lime mortar test specimens

Surveying the previous literatures, it has been indicated a very slight effects of multiple wetting of historic mortars or stone with limewater, regarding its penetration depth and strengthening of the material under consolidation. Test specimens have been prepared in the form of short tubes for applying and testing compressive strength for these samples. The specimens were made of lime mortar prepared in the laboratory from powdered lime hydrate and sand. It is the same composition as that of the mortar composing a binding material in the walls of ancient Aachen City (Figure 1).

For this purpose, the historic lime render with quartz aggregate was sampled from the medieval Aachen City walls and the sample of about 200g was dissolved by the acid dissolution. The aggregate separated from a disintegrated mortar by filtration was dried at 60 °C till reaching constant weight. In accordance with the historic render, the sand was mixed and used for preparation of the model laboratory mortar’s samples in a ratio of 1:8 by volume were accurately mixed in the laboratory to prepare a weak lime mortar.

The steps of mixing lime-mortar components have been listed as follows: First, water was poured into the mixing bowl then the lime hydrate was added, and the lime mixture was mixed for about 25 minutes in a laboratory mortar mixer to ensure perfect mixing of these components. After that, the sand was poured into the lime and finally, the mortar was properly mixed for about 40 minutes to ensure complete mixing and preparation of this created lime mortar. The fresh mortar was stored in a closed plastic bag to keep it away from carbonation process. The specimens were prepared by casting of the fresh mortar in a stainless-steel cast, and they were well compacted. This enabled the specimens to be safely pushed out from the cast immediately after molding and prevented the development of shrinkage defects in the prepared mortar samples.

The tubular cast shape of specimens for the compressive test increased the ratio of surface/cross section area and intensified the measurable compressive strength. As the study was focused mainly on compressive strength of the consolidated mortar, Eight tubes for compressive strength testing were prepared for each mode of consolidation treatment (consolidation agent, application regime, and number of applied cycles). The specimens were cured by slight spraying of distilled water, for about one month, to support carbonation process for these samples. All specimens were kept in a conditioned room before testing at a controlled environment (i.e. temp.20 °C, and Rh 70%). After that, the consolidation agents were applied, and on completion of the consolidation treatment, the specimens were left to mature for another 60 days, which was sufficientto allow carbonation of the calcium or barium hydroxides applied into lime mortar specimens. The other tests (Pore size distribution “PSD”, microscopic examination and durability investigation) were carried out on samples prepared as a copy of that used for conducting compressive strength testing. Therefore, the tests follow a sequence from destructive to non-destructive ones.

The micro-texture of the created weak mortar can be noted, with its components, under the magnification power of the transmitting polarizing microscope (Figure 2) and for more clarification on the texture of this mortar, it has been examined under the high magnification power of scanning electron microscope (Figure 3).

Consolidation of mortar specimens

In the current study, four consolidating substances were applied, for the created mortars, they are namely: distilled water, calcium hydroxide saturated solution in water (known as “lime water”), limewater mixed with meta-kaolin and barium hydroxide saturated solution in water (known as “barium water”). Water solutions of calcium hydroxide and barium hydroxide were prepared, i.e., for the limewater solution 3g of Ca(OH)2 were dissolved in one liter of distilled water; while for the barium water solution, 6g of Ba(OH)2·8H2O were dissolved in one liter of distilled water. The solubility of barium hydroxide in water made it possible to prepare “barium water” with a higher concentration of barium hydroxide (6% weight) than for the limewater (0.18% weight) [15-18]. The limewater with meta-kaolin was prepared by mixing 3g of calcium hydroxide and 3g of meta-kaolin in one liter of distilled water. Meta-kaolin used in the current study for modification of the limewater was a finely ground burnt clay-stone with relatively high amount of alumina (52.5% SiO2, 43.3% Al2O3). The meta-kaolin has the particle diameter at 40% of particles equal 4μm and 60% of particles size was less than 12μm. Limewater, barium water and limewater with added meta-kaolin were prepared and stored in closed glass barrels at controlled laboratory conditions (temp. 25 °C, and 40% RH) throughout the experiment. For consolidation treatments, a solution above the solid sediment was poured off and used. Each agent was applied, on the created weak mortar, by continually dripping it from a syringe on to tubes fixed in a horizontal position on a rotating shaft (Figure 4).

The mortar specimens were fully saturated during each application of each consolidating agent. The treatment by limewater has been conducted by means of many applied cycles of sprayed limewater into the created lime render samples. The same schedule was used for the distilled water treatment to find out the difference between effects of limewater and distilled water. In respect to other two studied agents (limewater with meta-kaolin and barium water), the applications were realized with a purpose to compare the obtained effects with limewater applied at the same condition.

Two different regimes of the drying time interval between two following saturations were tested for the limewater: first regime, two applications per day were conducted, and the mortar tubes were allowed to dry completely before the following saturation (wet to dry alternative); and second regime, three applications per day were performed. The new dose of the lime or distilled water was applied to the created mortar once the mortar was capable to absorb it, but before it dried out completely (wet to wet alternative). However, the intended number of application has been precisely managed in the experimental work and actually the applied cycles of console dating agents have slightly varied from the original schedule (60 cycles were realized for the wet to wet alternatives and 200 cycles for the wet to dry alternative). The main aim of this study is to examine the influence of lower and higher repeated applications number for the consolidating materials on the created render that imitate that of Aachen City walls.

Mechanical characteristics

The mechanical measurements for the created mortar samples have been conducted, in the current study at laboratory conditions (Rh 60%, Temp. 20 °C), the crosshead velocity movement of 0.45 mm/min. The short mortar tubes were loaded along the tube axis as shown in Figure 5.

The attained compressive strengths had been checked for the untreated reference (control) specimens of tube shape (of dimensions 40mm diameter and 60mm length). The average compressive strength was calculated as an average value, from tests conducted, for eight samples of the created mortar at each regime of the considered consolidating material (fresh water, lime water, limewater with meta-kaolin; and barium water). The results of the mechanical tests conducted in the current study are presented in Figure 6 and listed in Table 1. Mostly, five specimens had been tested, in few cases, the fragile mortar samples had not sustained treatment and was damaged before testing, then, only four specimens were tested. The amount of new calcite after limewater treatment is sufficient to make a slight improvement in the shear cohesion characteristics, not only that but also in the surface cohesion characteristics. Regarding data listed in Table 1 and graphically presented in Figure 6, it can be noted that barium water treatment is about three times (particularly for wet/dry regime applying it 200 cycles) as that of the control samples. Not only that but also, it is two times more efficient than lime water treatment that corresponds to a higher concentration and the high solubility of the barium hydroxide in the solution. Increasing number of applied cycles (for each of limewater and barium water) from 60 cycles (at wet/wet regime as three applications/day) to 200 cycles (at wet/dry regime as two applications/day), an increase in the compressive strength of the created mortar sampleshas been noted (Figure 6). The results show that there is no apparent difference in compressive strength between distilled water application and limewater application mixed with meta-kaolin (wet/wet application for 60 cycles) (Figure 6). There is a considerable increase in the compressive strength of a poor lime mortar after 200 cycles (in the case of two saturations regime, wet/dry regime either for limewater or barium water, Figure 6). The combination of limewater with meta-kaolin did not provide any noticeable input or advance in the mortar’s strength (Figure 6). This indicates that the products of the pozzolanic reaction of meta-kaolin and calcium hydroxide in limewater were not water-soluble, i.e., did not penetrate throughout the mortar under investigation, and therefore did not improve its compressive strength (Figure 6). The lime presents in the lime meta-kaolin suspension was partially consumed due to a pozzolanic reaction with meta-kaolin, and the following consolidation treatment of the mortar with lime–meta-kaolin water was less effective than treatment with simple limewater. Samples undergoing the same number of treatments show a higher compressive strength when barium water was employed regarding to limewater.

The observed improvement in mechanical properties is not high as it is expected considering the higher concentration of Ba(OH)2 in the saturated solution. In fact, the strength after consolidation, using Ba(OH)2, was three times higher than that of the untreated (control) mortar. Distilled water did not show any consolidating effecton the tested mortar with a low lime content. In this case, only compressive strength was measured, and the difference from the control specimens was insignificant (Figure 6). Probably the repeated dissolution and precipitation of the calcium carbonate presented in the treated mortar with a low content of lime, was not associated with a significant re-distribution within the volume of the specimen and no relevant micro-structural changes was occurred.

Change in structure

Solutions with higher content of the active agents are considered as enough salt sources to a given building material e.g., brick, concrete, mortar. Such agents act as binding material for the unit components at the beginning till the whole pores and fractures are completely filled with such salt then, such agents (particularly the salts) start exerting stresses on the unit structure leading to its deformation [19-21]. Figure 7 (a-b) illustrates the basic differences between untreated (control) mortar and mortars treated with limewater and barium water, respectively, at the high power of magnification using the scanning electron microscope.

It has been noted that calcium carbonate has grown in the columnar form within the texture of the untreated mortar, together with tabular crystals. The mortar’s matrix is quite thin, with weak bridges. After 200 cycles of limewater treatment in the regime of full drying between subsequent applications, the matrix is filled with layers of newly formed discontinuous clusters of calcium carbonate. The difference between the consolidating matrices of lime and barium water can be noted (Figure 7). Barium water obviously resulted in a denser and better-connected microstructure, i.e., barium hydroxide presents higher efficiency as consolidating material compared with limewater.

A microscopic study of the cross-sections conducted in the created and treated mortar samples, focused on the distribution of consolidates into the texture of the created mortar specimen through a depth profile starting from sample’s surface to its deep inside. It has been noted that calcium carbonate on the surface layer of the created mortar, in the first case for the reference mortar, and in the second case for the mortar treated with 200 cycles of lime water, where a much thicker layer of calcium carbonate is visible. Barium carbonate presents dense structure on the treated mortar surface. Only the mortar samples treated with barium water presented a significantly higher deposition of barium (in the form of barium carbonate) mainly on the surface of created and treated mortar samples.

Change in porosity

The pore size distribution had examined for the reference and consolidated mortars using Mercury intrusion porosimetry (MIP AutoPore IV 9500) with pressure range of 13,000 to 30,000 MPa to achieve all pores within the examined samples. This test aims to find out the impact of different consolidating materials on the pore size distribution (PSD) of the created mortars and such PSD has been previously reported to be the main culprit behind material durability to weathering particularly by salts [22,23]. Five mortar samples copying those used for measuring each consolidation treatment (followed by calculating average values) for more data accuracy were also used for PSD measurements. The MIP results of the examined mortar samples indicated a slightly reduction for the porosity of the mortars particularly treated with limewater and barium water (Table 2a). For the lower number of consolidates (limewater or barium water) applications (60 cycles; wet/wet application; 3 apps./day), the porosity has been slightly shifted from mega-pores to meso-pores and micro-pores and the total porosity has been slightly decreased regarding its original porosity (Table 2a). While for the higher number of applications (200 cycles; wet/dry deposition; 2 apps./day), the porosity had been noticeably shifted from mega-pores to almost meso and micro-pores and the total porosity had been noticeably reduced regarding its original value (Table 2a). No significant difference, in reduction of samples’ porosity, was noted for limewater with meta-kaolin compared to simple limewater consolidating materials (Table 2a). The shifting of mortars’ pore size distribution at each consolidating material at each regime of application, regardless water and limewater mixed with meta-kaolin that haven’t result in any progress in mortars durability, has been noted on the MIP curve (Figures 8a - 8e). The MIP enabled defining the salt susceptibility index (SSI) based on the PSD of the given mortar samples, and the interpretation of the SSI values has been based on [23] classification (Table 2b). It indicated a progress in mortars durability (by shifting SSI to salt resistance trend, Table 2a) particularly for those treated with barium water (wet/dry regime).

Durability test

It is a measure of materials resistance to weathering/damage on its exposure to artificial weathering at conditions as those dominate at the study area but with condensed limits to highly reduce time from years scale to days scale [24]. The durable material is that expresses low weight loss percentage at the end of the test and vice versa. The weight loss percentage has been computed, at the end as well as every two cycles of the sixteen cycles of artificial salt weathering, for each mortar before and after treatment with each consolidating material following the equation of [25] given below:

Weight loss (%) = ((W1 – Wn) / W1)* 100 where W1 is the initial weight of a given sample, Wn is the sample’s weight at the end of the test, the results are listed in Table 3, and graphically represented (Figure 9).

From the graphical representation of the sample’s weight through the sixteen cycles of artificial weathering (for the control and the treated mortar samples, Figure 9), it is clear that the first three cases of mortar behave nearly the same. In another words, they present slight increase in their weight as salt ingresses and fills mortars’ pores in the first four cycles of durability test, then, anoticeable weight loss (decrease in samples’ weight) has been reported (Figure 9 and Table 3). On the other hand, the mortar samples treated with either lime water or barium water at each of the two (wet/wet or wet/dry) regimes of application, present a noticeable withstand against weathering (particularly for barium water applied for 200 cycles, wet/dry regime) till the 12th cycle of attack.

Then, slight to very slight weight loss can still be noted till the end of this test (Figure 9). This regime of weight loss is corresponding with the microscopic investigation of the treated samples that indicated noticeable ingress of barium water (more than limewater) within mortar’s pore reducing pore size distribution (as indicated from MIP measurements conducted for these samples, Table 2a). This indicated the efficacy of barium water and limewater particu larly limewater as well as barium water at wet/dry regime of application for that weak mortar. By plotting the weight loss percentage of the control and treated mortar samples (Table 3) on [26] (Figure 10), the difference in durability can be noted among these cases. The three cases (control, treated with water, treated with limewater mixed with meta-kaolin) of the mortars have nearly the same durability without any impact of treating with water or limewater mixed with meta-kaolin, they are in durability class E i.e. very low durability class (Figure 10). While the mortar treated with limewater at its two regimes are falling within Class D i.e. low durability class which is better than class E [27]. Lastly, the mortar samples treated with barium water at its two regimes are within class C i.e. moderate durability class (Figure 10). This progress in cohesion/durability class of these treated mortars to the limewater and barium water trend (Table 3) is highly matching with SSI determined by MIP (Table 2a) (Figure 11).

Conclusion

Limewater treatment of a specific lime mortar had proved to be effective after a considerably large number of immersions (200 cycles of immersion) into a weak lime mortar. Some poor mechanical characteristics (compressive strength) were improved substantially after a large number of saturations. No consolidating effect of distilled water on the compressive strength of tested mortars with a low lime content (1:8) was observed. The higher concentration of barium hydroxide in its saturated solution resulted in higher limits of compressive strength than in specimens treated in the same mode with limewater, but the increase was not as large as would have been expected according to the concentration of the barium water. The improvement in compressive strength after consolidation was more than three times higher than the strength of the untreated (control) mortar samples. A microscopic study verified differences between the consolidating matrices of lime and barium water, where barium water clearly built a denser and better coherent substance. There was no detectable benefit of modifying limewater with meta-kaolin in terms of the mechanical characteristics of the treated mortar. The evaluated consolidating materials, in particular the barium water, reduced the porosity and pore size distribution of the investigated mortar. Concerning the distribution of the consolidates into the mortar specimens, a higher deposition of barium carbonate on the surface layer of the mortar was detected by scanning electron microscope. This finding corresponds with the results of the durability test conducted for these mortars over sixteen cycles of artificial weathering. The research reported here did not aim to optimize the application of various agents, only to make a comparison under specific conditions. This should be considered in order to avoid misinterpretation of the results.

Acknowledgement

The authors are greatly thankful for the intensive reading and discussion of the results with Prof Martin Derek and his remarkable editing of English language of this work. They are also thankful for the financial support of DAAD during the fellowship at Aachen University (RWTH).

Conflict of Interest.

No conflict of interest.

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Biological Processes In Urban Mines

Authored by Navarro Hidalgo

Keywords: Critical elements; Microorganisms; Urban mines; Biological processes; Recycling

Introduction

The innovation and development of high technology have demanded the exploration of some chemical elements in greater quantity. These elements have physicochemical properties of high economic interest. Some countries have larger amounts of the reserves of these elements, creating an imbalance in world supply.

An example of the use of these materials are rare earth elements widely used in equipment with greater energy efficiency and magnets in wind generators. They are also present in increasingly modern computers, cell phones and televisions. Given this reality, thiswork proposes to recover critical elements from alternative sources (electronic waste - REE) using a biological process as a tool for solubilization of waste elements with subsequent recovery.

The proposed technique is bio-hydrometallurgy, already used to obtainelements from mineral deposits where the solubilization of elements by microorganisms occurs. These are capable, due to their small size (on a micrometric scale), of reaching cracks and providing elements in solution even if they are combined with other elements in the structure, facilitating recovery. This tool is being studied by the Mineral Processing Laboratory of the Federal University of Rio Grande do Sul as a complement and aims to explore and reuse elements that are combined not by natural processes but by human-industrial processes in the form of urban mining.

The material used in the recovery methodology are printed circuit boards (PCB) from computers, cell phones, lamps, among other electronic devices. Among the elements of greatest interest are the lanthanides (15 elements), yttrium, scandium, gallium and indium, all considered critical elements. These wastes are considered urban mines, with complex structures for recycling and that often make recovery unfeasible, however, the concentration of these residues and the consolidation of a technique that facilitates recovery are of great interest. The methodology consists of dismantling, classifying and characterizing these equipment’s and subsequently using the biological process under different conditions of temperature, agitation, pH and nutrients, accelerating the interaction and solubilization of the elements. One of the microorganisms to be used is the bacterium Acidithiobacillus ferrooxidans, with properties already known for extracting elements from mineral deposits.

The experiments are conducted and monitored by techniques/equipment such as atomic absorption (AA), scanning electron microscopy (SEM), X-ray fluorescence (FRX). Some initial results obtained from some electronic equipment showed the recovery of indium, gallium in initial experimental conditions with specific culture medium for A. ferrooxidans. In view of the encouraging initial results, the progress of the work follows.

Acknowledgement

None.

Conflict of Interest

No conflict of interest.

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Study Regarding Input Data Consideration (Required Accelerograms) for Experimental Test of The Optimal Moment Resisting (MR) Reinforced Concrete(RC) Frame Model on The Seismic Platform

Authored by Sococol Ion

A significant number of reinforced concrete (RC) frame models have been studied for seismic (ductile) performance purpose through nonlinear static analyses (using ATENA software). In these conditions, it was chosen the optimal models for experimental test on the seismic platform. In next stage, it was used the existing pushover curves to establish the ground acceleration values for five performance requirements (objectives). Thus, it was generated for each performance requirement an artificial accelerogram with which optimal RC frame model can be tested on the seismic platform. Consequently, it will be possible to study the complex cracking mechanism and failure/ split/ rupture/ expulsion material process of the RC frame model at each experimental test for either performance objective. Also, it will be possible test results superposition proceeding with existing theoretical studies.

Keywords: Static Pushover bilinearization; performance requirements (objectives); response spectra; Fourier spectra

*Corresponding author: Sococol Ion, Doctoral School, Faculty of Civil Engineering

and Building Services, “Gheorghe Asachi” Technical University of Iasi, Nr. 1, 700050,

Romania. Received Date: September 25, 2021 Published Date: October 07, 2021

Introduction

Complex analytical studies it were performed with nonlinear [1-7] static analyses [8-15] for a multitude of pure [16] moment resisting RC frame models (“reduced to ½ scale [17] with the same inter-axis distances and story height” [11] (see Figure 1 - Figure 5 and Table 1) in order to identify the optimal ductile (and realistic) seismic response [18-25].

Global Journal of Engineering Sciences Volume 8-Issue 4Citation: Sococol Ion, Mihai Petru, Budescu Mihai. Study Regarding Input Data Consideration (Required Accelerograms) for Experimental Test of The Optimal Moment Resisting (MR) Reinforced Concrete (RC) Frame Model on The Seismic Platform. Glob J Eng Sci. 8(4): 2021. GJES.MS.ID.000692. DOI: 10.33552/GJES.2021.08.000692. Page 6 of 22 Figure 5: “Representation of steel reinforcement car case in pure MR RC frame models with : (a) longitudinal rigid RC beams (structural system type 1); (c) normal RC beams (structural system type 2); (e) ductile RC beams (structural system type 3). Representation of structural mesh discretization for pure MR RC frame models with: (b) longitudinal rigid RC beams (structural system type 1); (d) normal RC beams (structural system type 2); (f) ductile RC beams (structural system type 3)” [11].

Thus, it has been reached the input data stage for experimental test on the seismic platform [26] of the optimal (unique) RC frame model. In these conditions, it was proposed to “generate artificial ac- celerograms” [27-31] (associated with “target spectra” [30-32]) whose PGA values (see Table 6 - column two (from left to right)) reach the absolute acceleration values assigned for each consid- ered performance requirement [33-43] (see Table 5 - column three (from left to right)) [27,32], [44-51]. Thus, it is desired artificial accelerograms implementation in the pre-test stage of experimental study to verify the structural seis- mic response [18-23], [25,43] in accordance with achieved perfor- mance objectives [52-53] in the post-test stage. Determination of Spectral Acceleration Values For M_8, K_5, K_7 And Z_8 Moment-Resisting RC Frame Models Depending on Performance Objectives Analytical study conducted by Sococol et al. [9] demonstrates the superior concrete strength class effectiveness on ductile seis- mic response for MR RC frame structural models. Thus, it was con- sidered valid for the next research stage M_8, K_5, K_7 and Z_8 RC frame models.

Citation: Sococol Ion, Mihai Petru, Budescu Mihai. Study Regarding Input Data Consideration (Required Accelerograms) for Experimental Test of The Optimal Moment Resisting (MR) Reinforced Concrete (RC) Frame Model on The Seismic Platform. Glob J Eng Sci. 8(4): 2021. GJES.MS.ID.000692. DOI: 10.33552/GJES.2021.08.000692.Global Journal of Engineering Sciences Volume 8-Issue 4 Page 7 of 3 In these conditions, it were drawn the “F-d” capacity curves (where: “F” - Base Shear; “d” - horizontal Roof Displacement) (see Figure 6- Figure 9 and Table 2) in order to establish the absolute spectral accelerations values for this series of RC frame models depending on the performance requirements (objectives) [34-43], [52-53] (see Table 3).

Also, it was obtained the ultimate lateral forces “Fu” and later- al displacement requirements “du” of the structural systems [54], [21-25] (see Table 2) following nonlinear static analyses performed with ATENA software [13-14]. Lateral forces “F*y” and lateral dis- placements “d*y” corresponding to the global yielding mechanism [18-22], [25], were obtained after bilinearization process (method, procedure) [19-20] of the pushover curves for equivalent SDOF sys- tems [53]. Thus, it were established elastic - perfectly plastic fits com- patible with EC8 indications [20] (see Figure 10 - Figure 13) using SPO2FRAG software [55] (where “SPO2FRAG (Static Push-Over to FRAGility) is introduced, a MATLAB® [56] - coded software tool for estimating structure-specific seismic fragility curves of buildings, using the results of static pushover analysis” [53]). In these conditions, it was indicated position of the perfor- mance requirements (Figure 14 - Figure 17) through “RDR” indica- tor (Roof Drift Ratio) (see Equation 1) for each “F-d” capacity curve, establishing the absolute spectral accelerations values (see Table) where: “RDR - Roof Drift Ratio [%]; hi - denotes the height of the i-th storey [m]; Γeff - effective modal participation factor; μ = δmax/δy - displacement ductility (structural ductility) [18]; * Y δ – equivalent SDOF yield displacement [m]” [53]. In current seismic design norms [19-20], [57] and engineer- ing literature [21-25], [52,58] is practiced performance objectives consideration in different forms (with qualitative implications and quantitative enumeration [59]). Thus, five performance objectives are considered in current research (analytical) study (see Table 3). Four performance objectives were considered according to SEAOC recommendations [52]. The fifth limit state, labeled “side- sway collapse”, is added by SPO2FRAG [53,55] when the SPO.

(Push-Over) curve exhibits strength degradation in the form of a negative-stiffness branch (this limit state corresponds to dynamic instability) [53,55] (Table 3). Generation of Target Spectra and Artificial Accelerograms for K_7 Moment Resisting RC Frame Model Depending on Performance Objectives The principal parameters regarding optimal RC frame model determination for target spectra [30-32] generation process with the corresponding artificial accelerograms [27-31] (depending on performance objectives) are:

• “F-d” capacity curves values (with focused attention on the ul- timate lateral displacements “du” and structural yielding dis-placements “d*

y” [19-20], [53]);

• bilinearized curves [19-20], [53];

• “RDR” (%) values for five performance objectives [52-53];

• MR RC frame deformation mechanisms

[19-25] for either lat- eral loading stage or absolute spectral acceleration values “Sa” (see Table 4). In these conditions, Z_8 MR RC frame model presents optimal results, without inclusion in a legal design norm [19]. Thus, it was performed the generation of the artificial accelerograms [27-31] according to the performance objectives for K_7 MR RC frame model. The analytical process of artificial accelerograms generation [27-31] (in correspondence with performance objectives [52-53]) for K_7 moment resisting RC frame model includes the knowledge of the “normalized elastic response spectrum of absolute accelera- tions for horizontal components of the ground motion with Tc=0.7 s” (according to P100-1 [19] norm - Iasi area) (see Figure 18), in addition to knowing the absolute spectral acceleration values for each performance objective (see Table 4 and Table 5).

Thus, it was calculated (with Equation 3) the absolute acceleration values necessary for target spectra generation and comparison of these values with subsequently PGA values related to generated artificial accelerograms. An important condition in the comparison process is the proximity of the PGA values in Table 6 to the GA values in Table 5, preferably being as PGA>GA.

The elastic response spectrum of absolute accelerations for horizontal components of the site ground motion, Se(T)=Sa(T), is defined according to P100-1 norm [19] (see Equation 2):

Accelerogram sets compatible with target acceleration spectra (Figure 19), it was generated with (using) MSIMQKE software [62-63]. Graphical representation of these artificial accelerograms and their elastic response spectra, was performed through PRISM soft- ware [64] (where: “PRISM® is a free program for seismic response analysis of structures idealized as single-degree-of-freedom systems. The main features of the program include modification of earthquake records, calculation of response time histories of various hysteresis models, and generation of elastic and inelastic response spectra” [65]). In these conditions, it was generated a number of artificial accelerograms (Figure 20 - Figure 24) for K_7 moment resisting RC frame model, depending on performance objectives.

Accelerogram PGA values presented in Table 6, reach the absolute acceleration values enumerated (listed) in Table 5. Elasticspectra of these artificial accelerograms are represented in Figure 25, Figure 26, Figure 27, Figure 28, Figure 29, following the form

Conclusion

In current research practice exist a major necessity for clear methodology regarding required accelerograms consideration for experimental moment resisting RC frame structures/ systems/ prototypes/ models in experimental tests on seismic platforms.

In these conditions, it was presented a method of the input data consideration for the experimental test, have as a reference point the performance objectives necessary to be achieved in terms of the global seismic response of the RC frame structure. Thus, it was considered this form of input data for experimental seismic analysis of the K_7 moment-resisting RC frame model (system). Basically, it can be verified the theoretical considerations in RC seismo-engineering literature through the real seismic response of the reinforced concrete frame structure. If artificial accelerograms cannot be used for any technical reason, it can be used PGA values for a standard lateral loading protocol.

Acknowledgement

None.

Conflict of Interest

This research paper is sponsored by “Gheorghe Asachi” Technical University of Iasi with grant number GI/R16_Drd/2021.

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CUDA-based Accelerated FEM Calculation

Authored by Cankun Zheng

The Finite Element Method (FEM) had been widely used in engineering applications. There are two bottleneck issues in the FEM calculation. The first one is how to minimize computer memory demand so that to be able to run large-scale simulations using limited computational resources. The second one is how to carry out simulation as fast as possible to complete a large-scale simulation job. A standard finite element analysis always results in solving simultaneous linear equations. Overall, a global stiffness matrix of a finite element simulation often has sparse, symmetric, and positive definite characteristics. To overcome the first issue, we proposed integrating and storing stiffness matrix using the Compressed Sparse Row (CSR) format in this paper. We proposed to carry out parallel computing to solve simultaneous equations using the cuBlAS, cuSPARSE, and cuSOLVER libraries on the Compute Unified Device Architecture (CUDA) platform to overcome the second issue. The aim of this article is to explore the possibility to solve simultaneous equations with sparse matrix using CUDA libraries. Three algorithms of cuSOLVER libraries were evaluated through case studies. The three algorithms include the QR factorization, incomplete LU factorization, and the conjugate gradient methods. We have evaluated the efficiency, accuracy and capacity of the algorithms. Two type of case studies were investigated in the numerical experiments. First type of sparse matrix were downloaded from the Florida Sparse Matrix Collection and second type of matrix were assembled from truss structure using FEM. Numerical experiment results showed that, the accuracy of incomplete LU factorization is unacceptable, the capacity of the QR factorization is weak, since the GPU memory demand is higher. The efficiency, capacity and accuracy of the conjugate gradient methods all are satisfied. However, it may break down for some particular cases.

Keywords: FEM; cuSPARSE; cuBLAS; cuSOLVER; Compressed sparse row format matrix; QR Factorization; Incomplete LU Factorization; Conjugate gradient

Introduction

For many large-scale FEM calculations, solving sparse linear equations takes up most of the computing time and resources. Taking the static analysis of structures using the finite element method as an example, the solution of sparse linear equations usually accounts for more than 70% of the whole analysis time [1]. With the continuous expansion of engineering scale and the continuous improvement of engineering complexity, higher requirements are put forward for the scale and speed of solving sparse linear equations. Therefore, the use of high-performance computing is a critical way to solve sparse linear equations.

Nowadays, the direct method and the iterative method are the two most popular methods to solve sparse linear equations. The direct process is to transform the coefficient matrix of the equationsinto a triangular matrix and then use the back-substitution method or the pursuit method to get the solution of the equations. The iterative approach is a process of constructing an infinite sequence to approximate the exact solution from an approximate initial valueof the solution. The rest of the paper is organized as follows: Section 2 gives a brief description of the CUDA platform. We focus onthree essential libraries of CUDA Toolkit, cuBLAS, cuSOLVER, and cuSPARSE. Section 3 defines the CSR storage format, which was used in this paper. Section 4 demonstrates how cuBLAS, cuSOLVER and cuSPARSE were implemented in detail and error analysis. Section 5 shows two types of case studies to solve sparse simultaneousequations. In the first type of case study, the matrix was download from the Sparse Matrix Library [2]. The second type of case study is an example to analyze truss structure using FEM. Section 6 is the Global Journal of Engineering Sciences Volume 8-Issue 4Citation: Cankun Zheng, Wenhao Lin, Jiujiang Zhu. CUDA-based Accelerated FEM Calculation. Glob J Eng Sci. 8(4): 2021. GJES.MS.ID.000690. DOI: 10.33552/GJES.2021.08.000690.Page 2 of 8 conclusion.

CUDA Platform

The CUDA platform allows developers to use the C language as a development language and also supports other programming languages or interfaces. Under the CUDA architecture, a program is divided into two parts: the Host side, which is executed serially on the CPU, and the Device side (also known as the kernel), which is implemented in parallel on the graphics card. Usually, the execution model of a complete program is that the host side prepares the data and copies it to the graphics card’s memory. The GPU executes the kernel program of the device side for parallel calculation. After the calculation is completed, the result is sent back to the host side from the memory of the graphics card [3]. The cuBLAS library implements BLAS (Basic Linear Algebra Subprograms) on top of the NVIDIA ®CUDATM runtime [4]. The cuBLAS library is mainly used for matrix operation. It contains two sets of API. One is the commonly used cuBLAS API, which requires users to allocate GPU memory space and fill in data according to the specified format. The other one is cuBLASXT API, which  an assign data at the CPU end, then call function. It will automatically manage memory and perform computation [5]. In practice, the first set of APIs is usually used.

The cuSPARSE library contains a set of basic linear algebra subroutines used for handling sparse matrices. The goal of the standard library is a matrix with a certain number of (structurally) zero elements that represent >95% of the total entries. It is implemented on top of the NVIDIA ®CUDATM runtime (part of CUDA Toolkit). And it is designed to be called from C and C++ [6].

cuSPARSE is acollection of column interfaces. And the main advantage is that itonly needs to call the corresponding API when the users write the host code. So, it can save a lot of development time, and this library also supports many data formats. cuSlOLVER is an advanced library. It is based on the cuBLAS and cuSPARES library and includes matrix factorization and solving equations. It contains three independent library files, including cuolverDN, cuSolverSP, and cuSolverRF. The cuSolverDN can performdense matrix factorization (LU, QR, SVD, LDLT), while the cuSolverSP is a new toolset to manipulate sparse matrices, such as to solvesimultaneous equations with sparse matrix. The cuSolverRF is asparse refactoring package [7].

Storage Format

In solving the simultaneous sparse linear equation, the coefficient matrix is sparse. Therefore, the selection of storage format is crucial to reduce the storage of unnecessary zeros, and it is also imperative to improve the performance of its operation. We mainly introduce the compressed sparse row format used in this paper. CSR format is a mainstream general sparse matrix representation format, which stores column indices and nonzero values in array columns and array values [8].

Implementation Method and Relative Error Analysis Based on cuBlAS, cuSPARSE, and cuSOLVER

The solution methods of large sparse linear equations usually include the direct method and the iterative method. QR Factorization QR factorization is based on matrix factorization. Based on elimination, the linear equations are transformed into several equivalent sub-problems, which are easy to be calculated and solved in turn. Theoretically, the exact solution of the system of equations can be obtained by the direct method in a fixed number of steps without considering the accumulative numerical error.

• Apply for variable memory space on the GPU and transfer Col, row, Val and b from the CPU to the GPU.

• Find the final X value by calling cusolverSpDcsrlsvqr.

• Return the X value from the GPU side to the CPU side.

Incomplete LU Factorization

Incomplete LU factorization is an iterative solution method, which is related to the LU factorization method. The LU factorization method is a direct solution method. When the matrix A is asparse matrix, the matrix L and U lose the sparse characteristics of the matrix A. The storage cost of the matrix that loses the sparse property will increase, so the incomplete LU factorization method Citation: Cankun Zheng, Wenhao Lin, Jiujiang Zhu. CUDA-based Accelerated FEM Calculation. Glob J Eng Sci. 8(4): 2021. GJES.MS.ID.000690. DOI: 10.33552/GJES.2021.08.000690.Global Journal of Engineering Sciences Volume 8-Issue 4 Page 3 of 8 is proposed in [9], so that the iterative matrix K in A = K – R satisfies:

K = L X U and the matrices L and U have the sparse property. The algorithm of incomplete LU factorization can be described as follows: Operations on sparse matrices stored in CSR format have been provided in the cuSPARSE library. Call the cusparseDcsrilu02 function to decompose the matrix into a unit lower triangular matrix Land an upper triangular matrix U. Call the cusparseDcsrsv2 _ solve function to find the value of the matrix Z, and then repeat the call to find the final value X. In this way, the algorithm of incomplete LU factorization is completed by calling the corresponding function through the cuSPARSE library. This article refers to this algorithm as cuSPARSE_LU. The specific algorithm flow is as follows:

• Apply for variable memory space on the GPU and transfer Col, row, Val and b from the CPU to the GPU.

• By calling cusparseCreateMatDescr, cusparseSetMatIndex Base, cusparseSetMatType, cusparSESetMatFillMode, CusparseSetMatDiagType creates descriptors of matrix A, matrix L, and matrix U, and opens the corresponding memory by calling csru02Info_t and csrsv2Info_t.

• Analyze the LU by calling cusparseDcsru02_analysis, cusparseDcsrsv2_analysis.

• The matrix K is decomposed into a lower triangular matrix Land an upper triangular matrix U by calling cusparseDcsrilu02 and cusparseXcsrilu02_zeroPivot.

• Solve the value of matrix Z by calling cusparseDcsrsv2_to solve.

• Find the final X value by calling cusparseDcsrsv2_to solve.

• Return the X value from the GPU side to the CPU side.

Conjugate gradient method

The conjugate gradient method is one of the most commonly used iterative methods for solving linear equations [10]. The conjugate gradient method uses successive approximation, generally using the iterative formula to get a series of approximate solutionsgradually approaching the real solution, and finally get the approximate solution satisfying certain error tolerance.

The conjugate gradient algorithm is described as follows:

1) Set Initial guessed value X0.

The solution of this conjugate gradient method calls the cuBLAS and cuSPARSE libraries. Although each step of the conjugate gradient method is serial, it mainly involves sparse matrix and vector multiplication, vector and vector dot multiplication, vector update, and scalar division in the whole algorithm process. These operations can all involve data-level parallelism, thus enabling GPU parallel computing. That is to say, GPU is responsible for the parallel calculation between matrix and vector, vector and vector before iteration and in each iteration, and CPU is responsible for the control of iteration loop and convergence condition, as well as the operation of scalar multiplication. Operations on sparse matrices store in CSR format have been provided in the cuSPARSE library. By calling the cusparseSpMV function in the cuSPARSE library, a sparse matrix stored in CSR format can be multiplied by a vector. The operation of two-vector dot multiplication can be realized by calling the cublasDdot function in the cuBLAS library. The vector update is implemented by calling the cublasDaxpy function in the cuBLAS library. In this way, the cuSPARSE library and the cuBLAS library can be used to call the corresponding functions for the conjugate gradient algorithm. This article refers to this algorithm as cuSPARSE_CG.

The specific algorithm flow path is as follows:

Global Journal of Engineering Sciences Volume 8-Issue 4Citation: Cankun Zheng, Wenhao Lin, Jiujiang Zhu. CUDA-based Accelerated FEM Calculation. Glob J Eng Sci. 8(4): 2021. GJES.MS.ID.000690. DOI: 10.33552/GJES.2021.08.000690.

Page 4 of 8

• Apply memory space for variables on the GPU, and trans-

Comparison of QR Factorization, Incomplete LU Factorization and Conjugate Gradient Method for Solving Truss Structure using FEM

The overall stiffness matrix of the truss elements in this test is simple, the length L, cross-sectional area A and elastic modulus E of the truss are all set as 1, and the relative residual error is set at 10-6. The simple overall stiffness matrix results in that the QR factorization and incomplete LU factorization method have break neck calculation speeds. For example, to solve 100000 orders matrix equations, the computational time of the conjugate gradient is about 4.07 times more than that of the incomplete LU factorization, while the conjugate gradient computational time is about 2.64 times more than that of the QR factorization. Table 4 compares the computation time of solving the global stiffness matrix of the truss elements using the QR factorization, incomplete LU factorization, and the conjugate gradient method. The relative error analysis and comparison are shown in Table 5. The accuracies of both QR factorization and incomplete LU factorization are satisfied. For large-scale simulation, the conjugate gradient method was not convergent, i.e. the iteration steps are less than the total freedom of the system. For this particular structure, the conjugate gradient method only convergent when iteration steps equal the total freedom of the system. If the iteration steps equal the total freedom of the system, iteration solution equals exact solution. Table 4: Comparison of calculation time of three algorithms for truss structure.

Reason analysis: Although the computational efficiency of the conjugate gradient method and QR factorization in the Florida sparse library is slower than the incomplete LU factorization, the relative error of QR factorization and the conjugate gradient is much smaller than the incomplete LU factorization. Due to in incomplete LU factorization, some elements of the matrix R in Eq. (5) were dopped off; this causes incomplete LU factorization to be just an approximate method. Our testing results demonstrate that the accuracy of incomplete LU factorization is unacceptable for accurate engineering simulation. In practice, usually, incomplete LU factorization is only suitable to be used as a preprocessing. Although

both efficiency and accuracy of QR factorization are satisfied, our numerical experiments show that the GPU memory consumption of QR factorization is much higher than the other two methods. It means QR factorization is not suitable for large scall simulation, at least for some cheap GPUs. Our testing shows that, in most cases, the efficiency, accuracy, and capacity of conjugate gradient all are good enough for FEM simulation; however conjugate gradient may break down for some particular cases. For example, in our truss structure FEM simulation, if the iteration step is less than the total freedoms of the system, the residual error keeps as constant without change. If and only if when the iteration step equals the freedoms of the system, the residual error becomes zero, i.e., the iteration solution reaches the exact solution. For large-scale simulation, it is not feasible to make iteration steps equal the freedoms of the system. It needs a very long iteration time.

Conclusion and Future Work

In this paper, we have compared the computational efficiency, accuracy, and capability of three algorithms: QR factorization, incomplete LU factorization, and conjugate gradient method using cuBlAS, cuSPARSE, and cuSOLVER libraries. We have reached the following conclusions:

 In terms of computational efficiency, the incomplete LU factorization is the fastest, and the conjugate gradient is the slowest. The running speed of the incomplete LU factorization is 11.6 times faster than that of the conjugate gradient. The running speed of the QR factorization is 3.3 times faster than that of the conjugate gradient.  In terms of computational accuracy, both the QR factorization and the conjugate gradient methods are good enough for accurate engineering simulation. The incomplete LU factorization method is unacceptable. In terms of computational capacity, both the incomplete LU factorization and the conjugate gradient methods are acceptable. The QR factorization method requires too much GPU memory, so it is not suitable for large-scale simulation. To compare all three algorithms, we will find the conjugate gradient method is the best candidate for large-scale FEM simulation. However, the conjugate gradient method may break down for some particular cases. We proposed to combine the incomplete LU factorization and the conjugate gradient method in our future work. To use incomplete LU factorization as a preprocessing to carry out the precondition conjugate gradient simulation.

Acknowledgment

This research is supported by the project of “High Education funding of Guangdong Province: 2018KZDXM072”; the College Students’ Innovation and Entrepreneurship Project: 5031700602O6; the Natural Science Foundation of Guangdong Province:

Conflict of Interest

No conflict of interest.

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Renewable Energy in Architecture “Used Techniques to Achieve Green Net Zero Energy Buildings”

Authored by Ashraf A Gaafar

There are various negatives to use non-renewable energy resources, it consumes the exhaustible resources, as well as their use produces emissions that affect and pollute the environment and cause major changes in global climate. On the global level, we find the construction field is a key consumer of energy and natural resources, therefore, its participation is essential to achieve the sustainable development. The buildings and constructions are mainly responsible for the gas emissions that cause the global warming. Therefore, the importance of keeping and saving the energy, to keep resources from running out and reduce CO2 emissions which cause the global warming. The research reviews current techniques in addressing energy problems in buildings. The research consists of three parts; Part one reviews the concept of new and renewable energy in general, the second part reviews the concept of new and renewable energy in buildings, and then we end with the third part which reviews successful case studies that have been built in the world, studying and analysing the examples, and studying technologies and methods of reducing energy consumption and production to achieve green net Zero Energy Buildings (ZEB).

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Potentials of Commercialization of Smallholder Farming in Kigoma Region, Tanzania: Gross Profit Margin Analysis of selected Crops in Selected Districts, Kigoma Region

Authored by Chami Avit A

Commercialization of smallholder farming (SF) is of paramount importance for African rural economic transformation. This study was undertaken to reveal the less known potentials of commercialization of SF in Kigoma Region. The Gross Profit Margin Analysis of beans, maize and cassava in Kasulu, Kakonko and Kibondo districts from Kigoma Region was performed. Descriptive cross-sectional research design was employed and both primary and secondary data were utilized. The target population of 10,708 smallholder farmers (SFs) resulted to the sample size of 400 SFs (at 95% confidence level and 5% confidence interval (0.05 sampling error)). The study revealed majority of households were male-headed households, 57% of the households had the household size ranging from 6 to 10 members while 96.5% of all respondent’s own land. Through the overall mean yields, the study also revealed Kibondo and Kasulu as capable districts of producing both maize and beans while cassava was highly produced in Kakonko district. The study further revealed majority of SFs were non-users of improved seeds, fertilizers and pesticides. The Gross Profit Margin Analyses of all three crops revealed high profitability under ideal farming conditions compared the prevailing farmers’ traditional practices. The study concludes all opportunities in the ideal farming conditions as the major potentials for commercialization of SF. The study urges SFs, business community and the government to put deliberate efforts towards investing on the agriculture sector to enable ideal farming conditions to majority of farmers, hence enhancing agricultural productivity and profitability among SFs in Kigoma region.

Keywords: Commercialization; Smallholder Farming and Gross-Profit-Margin-Analysis

Introduction

Smallholder agriculture continues to play a key role in African agriculture. According to FAO [1] smallholder farming is the type of farming with limited resource endowments, relative to other types of farming in the agriculture sector. Approximately 80% of agriculture in sub-Saharan Africa is managed by families cultivating less than 10 hectares of land, which makes smallholder production the backbone of agriculture sector in sub-Saharan Africa [1-3]. Food supply and the livelihood of billions of people depend largely on the productivity of these systems [4]. Although smallholder farming systems have proven to be resilient and viable in risk-prone environments, climate change is likely to outpace their current coping capabilities; with less commercial opportunities in majority of areas in the world [5].

Smallholder farmers in sub-Saharan Africa have historically been confronted with numerous bottlenecks including high climate variability, low levels of income and technology, coupled with isolation from markets and lack of institutional support [1,2]. Among the widely envisaged common characteristics of smallholder farming systems include the vulnerability to changes in external conditions which result to low income producers often who do not have the means to invest in adaptive technologies and strategies under increasing climatic risks [3]. However, confronted with unprecedented risks and uncertainties, the need to incorporate new information and technologies into the traditional farming systems becomes imperative (Steenwerth et al., 2014). Taking no action towards availing commercial opportunities to the entire smallholder farming practices means jeopardizing the efforts of the past decades to improve livelihoods and reduce the number of undernourished people while enhancing farmers’ standard of living [1,6,7].

According to FAO [1], commercialization is defined as production for the market with profit objectives. Commercialization further refers to the process by which products, services, and technologies are introduced to the market for purchase (USAID, 2017). From an international development perspective, agricultural commercialization is an important pathway to providing smallholder farmers access to transformational innovations in the entire farming practice (USAID, 2017). A commercial approach to various food crops farming contrasts with subsistence farming in majority of rural areas in sub-Saharan Africa. Marketing process plays a pivotal role in the commercialization pathway. Marketing involves finding out what customers want and supplying it to them at a profit [8,9]. The fact that smallholder farmers’ empowerment decisions are based on the principles of commercialization, the need of efficient agricultural marketing systems can efficiently save the cost of exchange of agro-produce. In the agri-food systems, an efficient marketing assures adequacy and stability of food supply in ways that reward farmers, agro-traders and consumers. The major challenges underlying agricultural markets that would hamper commercialization of subsistence agriculture include poor infrastructure, inadequate support services and weak institutions, increasing transaction costs and the volatility of prices [1,10].

In Tanzania, the agriculture sector contributes 50% of the country’s GDP. The sector accounts for over 50% of the country’s exports [11-13]. Majority of Tanzanian agriculture like any other African agriculture is predominantly carried out on small-scale family farms. The big question about such family farms which are subsistence in nature is whether they can be successfully commercialized within their current structures, or whether they should give way to commercial medium and large-scale farm enterprises. In more detail, the following questions arise about the experience of commercialization of small farming in Tanzania and Africa at large and their prospects, various initiatives have been in place [14]. In all facets, commercialization of smallholder farming seems as a main vehicle in any national economic strategy to combat poverty and enhanced agricultural productivity.

Kigoma region; the region found in the North-Western Tanzania which has a rich base of land and water resources, with high crop diversity including maize, beans, cassava, rice etc [15-17]. Agriculture is mainly an economic mainstay of the Kigoma Region, with over 85% of the total population of the region depending on agriculture for its livelihood [18]. Despite the fact that maize, beans and cassava stand as the major staple crops grown by the majority of smallholder farmers in the Kigoma region, other food crops are highly grown in the region including rice, sorghum, banana, sweet potatoes, groundnut, oil palm and various fruits and vegetables. The main export crops include tobacco, coffee and cotton. Livestock kept in the target area including cattle, goats and poultry (mainly local chicken). The rationale of significant policy commitments to commercialize Tanzanian agriculture are clearly made in KILIMO KWANZA declaration [19]. Some commercialization initiatives related action points in this declaration include agricultural commoditization, implementation of incentives to ensure competitiveness and address market barriers, price stabilization mechanisms, industrialization and infrastructure development which have been advocated in the earlier times [16].

Despite the widely known challenges, roles, merits and usefulness of smallholder farming in the entire spectrum of climate change, food security and the livelihoods of smallholder farmers [1,4,20] less remains to be known on the existing potentials of commercialization of smallholder farming in Kigoma Region. This study performed Gross Profit Margin Analysis of selected three crops namely beans, maize and cassava in selected three districts namely Kasulu, Kakonko and Kibondo in Kigoma Region. The fact that, the agricultural sector in Kigoma region is dominated by smallholder farming systems which accounts for the 75% of national food production, the majority of smallholder farmers lack access to inputs, knowledge on sustainable technologies, finance, commercial markets, as well as business and market orientation [14,21]. For the sake of revealing the actual growth or decline in performance of smallholder farming particularly beans, maize and cassava in Kigoma region compared to the previous period or the industry, the Gross Profit Margin Analysis will be undertaken. The study envisaged to avail significant findings which will be useful inputs to the agricultural market actors and institutions which are at the core of agrarian revolutions which have been pursued ever since [22]. This was attributed by the three objectives; firstly to assess the average annual yield for the three crops among smallholder farmers in the study area, secondly to examine the level of adoption of modern farming methods among smallholder farmers in the study area and thirdly was to assess profitability of maize, beans, and cassava per acre in the study area.

Methodology

Description of the study location

The study was conducted in three districts of Kigoma Region, the North-Eastern located region in Tanzania East Africa namely, Kasulu, Kakonko, and Kibondo. The selected three districts are generally from the North-Eastern part of the Kigoma region. For the sake of revealing the actual growth or decline in performance of smallholder farming in the region, three staple crops were selected namely beans, maize and cassava. Data on the said crop production were collected from three districts in Kigoma region. The Gross Profit Margin Analysis of the three selected crops of the annual production was undertaken.

Research Design

Descriptive cross-sectional research design was employed in the course of undertaking this study. The design is preferred because due to the fact that data on the variables of interest were collected and examined only once and the relationship between variables determined [23]. The design was further preferred because, it concerns with answering questions such as who, how, what, which, when and how much respondents (smallholder farmers) had accrued in the previous farming season [24]. The selected study design was found useful due to the fact that, apart from managing the data collection process to clearly avail quantitative information, the selected research design ensures minimum bias in data collection that was helpful in reducing errors in data collection process and henceforth its interpretation [25].

Types of data and collection techniques

The study gathered both primary and secondary data. Primary data were collected using a questionnaire which was selfadministered through enumerators who were deployed to gather data from the smallholder farmers in the designated study area. Other sources of primary data were value chain players including agro-dealers, operators of aggregation centers, processors and various financial service providers. These stakeholders were consulted through scheduled interviews which were guided by checklists of issues related to their thematic areas of operations. Secondary data were collected through desk review of different reports including various agriculture project documents, progress reports; government documents and several other reports from district extension officers and relevant literature from regional and district levels. Data was largely collected through close ended questionnaire which was self-administered through enumerators. Nine enumerators were deployed into collecting data across the three target districts. The data were then imported to Excel and SPSS software for cleaning analysis.

Sampling technique

This study employed random sampling technique. A multistage cluster sampling technique was applied where the population of target farmers was first clustered into three target districts, then into wards according to the proportion of farmers in each district and ward. The individual farmers, organized in groups at ward level, were then randomly selected from villages to ensure that each had equal chance of being selected.

Sample size and distribution of farmers

The sampling frame of the study was the list of all smallholder farmers in the three districts namely Kibondo, Kakonko and Kasulu. From the target population of 10,708 smallholder farmers (listed in groups by various intervention projects had been carried out in the selected districts), the sample size was determined to be 371 individual farmers (at 95% confidence level and 5% confidence interval (0.05 sampling error)). The sample was weighted, and farmers apportioned to districts according to their numbers per district (Table 1). Working out the calculation (last column), the proportions of farmers allocated to Kakonko, Kibondo and Kasulu were 43%, 28% and 29% respectively, which is similar to 161 framers in Kakonko, 103 in Kibondo and 107 in Kasulu.

The respective number of farmers per district was changed from the original plan to that indicated in Table 2: 114 farmers in Kibondo, 120 in Kakonko and 166 in Kasulu. The sample was increased by almost 8% to 400 farmers above the planned 371 farmers to take care of potential missing data. The distribution of farmers who were interviewed in three districts is presented in the Table 2.

Table 1: Distribution of smallholder farmers’ population and their groups in three districts.

Data analysis

Data analysis for each perspective was aided by the application of Microsoft Excel and Statistical Package for Social Sciences (SPSS 22.0) computer programs. Analysis entailed descriptive statistics which generated frequencies/percentage and means for the required information. Qualitative data were mainly used to triangulate quantitative information. In particular Gross Profit Margin Analysis (GMA per acre) was undertaken. The fact that gross profit can be used as a proxy for assessing land productivity, the test assumes all (100%) of the harvested crop was sold at the market. The revealed findings on profitability of maize, beans, and cassava respectively per acre were calculated by consultations with field extension staff, taking practical data from smallholder farmers themselves. Gross Profit Margin Analysis considered two sides; namely ideal farming conditions (demo plots) and farming practice in the study area.

Results and Discussion

The results and discussion section entails basing findings regarding the potential and useful demographic attributes of the study respondents as well as the designated three study objectives. The findings on the first objective which was meant to assess the average annual yield for the three crops among smallholder farmers in the study area were presented in line with other findings for second and third objective; to examine the level of adoption of modern farming methods among smallholder farmers in the study area and to assess profitability of maize, beans, and cassava per acre in the study area respectively.

Characteristics of respondents

The useful socio-economic characteristics of the 400 respondents who were involved in this study namely sex, household size and Ownership and access to land among smallholder farmers in the study area. The respondents’ relevant characteristics were sought important in providing a snapshot on the background of the respondents and their suitability for this inquiry. The characteristics are summarized, presented in percent using bar charts and possible implications to the populations discussed in the following subsections.

Sex of respondents: Most of the households were male headed. Overall, 82.5% of households were headed by men and 17.5% by women. The female household heads indicated either that they were divorced, widowed, unmarried or married to polygamous husbands. Variation in three districts surveyed was visible. For example, there were more female-headed households in Kibondo (28.5%), followed by Kakonko (19.7%) and Kasulu (10.8%). Traditionally, households in the three districts are headed by males. Female-headed households are fewer and considered abnormal in this community.

Household size: It was found, among interviewed households that, household size ranged from 1 to 16 members, with an average of 7 persons per household. Most of the households (57%) had members ranging from 6 to 10 and 0 to 5 members (35%). Only a few households (about 9%) had over 10 members. Figure 2 depicts the general picture of household size in the three districts (Figure 1).

The household sizes differences among districts can be drawn from the study findings as follows: Kasulu had more households with family size ranging from 0 to 5 years (7.3%); while Kakonko had the largest number of households with 6 to 10 members (12.6%). The same district also had a relatively large number of household sizes above 10.

Ownership and access to land among smallholder farmers: In terms of land ownership, about 96.5% of the interviewed respondents indicated that they own land; 1.2% reported that they both owned and hired land and the remaining 2.3% indicated that they don’t own land but share the land with others such as their parents, other relatives, and friends. In terms of access, all interviewed respondents indicated that they have access to agricultural land. No farmers failed to grow crops because of the lack of access to land. The size varied widely as some farmers owned small areas such as 1 acre (0.4 hectares) while only 2 farmers mentioned to having above 60 acres. However, the mean was 5.3 acres (2.12 hectares). The ownership among districts did not differ much from general ownership; only 3.6% and 2.4% of farmers in Kibondo and Kasulu respectively said that they share ownership with others. There was no big difference in land ownership by sex; about 98.8% of males owned land while 96.6% of females indicated that they own land.

Average annual yield for the three crops among smallholder farmers

In the course of underscoring the effective participation of smallholder farmers in agricultural activities in the study area, the average annual yield for the three selected crops namely maize, cassava and beans in three districts were revealed. Crop yield per unit area is key productivity index. The average yield values for the three crops are indicated in Table 3. The presented data in the Table has disaggregated yields of the three crops per district. However, the overall mean yields of maize, beans and cassava for the three districts are 371 kg, 400 kg, and 53 kg per acre respectively.

With exception of beans, the yields in Table 3 are below the average figures cited in literature and those recommended by local extension staff. An average yield of maize in Kigoma ranges from 1200 to 1600 kg per ha (480 to 640 kg per acre) [5]. However, discussions with local extension staff in the three target districts indicated that the average yield of maize ranges between 2,000 and 2,500 kg per acre depending on the variety planted.

Table 3: Acreage and yield of maize, beans and cassava for target districts.

In beans, FAOSTAT (2006) showed the average yield for Tanzania is 741 kg/ha which is a little bit below Africa’s average (799 kg/ha). This national average is equivalent to 296.4kg/acre, which is less than the average yield of beans reported in Table 3. With exception of Kakonko, the average yield of beans in the target districts seems to be higher than the National average. The widely planted Kigoma yellow variety produces an average of 715 Kg/Ha, while the highest producing variety, Lyamungu 90, produces 1,430 Kg/Ha under the same conditions [18].

In cassava, it is estimated that, under ideal conditions, cassava varieties yield up to 7 MT per ha or 2.8 MT/acre [5]. Discussion with local extension staff indicated that under ideal field conditions as per demo plots, cassava gives yield of up to 300 bags (of 90 kg each) per acre. The yield figures are below this average regional figure.

Level of adoption of modern farming methods among smallholder farmers

The fact that more than 80% of Tanzania’s population depends on climate sensitive rain-fed agriculture as a source of livelihood, these smallholder farmers who control a large part of the country’s agricultural production are currently experiencing adverse climate change impacts due to traditional methods in their farming practices [15]. The understanding of the level of adoption of modern farming methods among smallholder farmers in the study area can help in reducing vulnerability of the agriculture sector hence envisaged to significantly contribute to socio-economic development and ensure food security among the farming communities. In the course of shedding light on the level of adoption of modern farming methods among smallholder farmers in the study area three parameters were put forward mainly; the application of primary farm inputs including improved seeds, fertilizers and pesticides.

The fact that demonstration of modern farming methods implies mostly the application of farm inputs in the farming practice stands as one of the key factors for increasing farm productivity (yield). According to agro-dealers in three districts, inputs required by most farmers in the project area include seed, fertilizers and pesticides. Most farmers use traditional seed, there is limited tendency to buy improved seeds. The role of input suppliers in production is mainly limited to agro-chemicals. Farmers use seeds kept from the previous harvest or buy from fellow farmers who could store enough to sell, or from food kiosks. There are no improved, certified, beans seed sold by any of the village input suppliers interviewed. Farm inputs may also refer to tools, equipment and technologies which are used to enhance the effectiveness of farm operations. The study found out that most farmers across the three target districts practice low-input agriculture which is characterized by no or inadequate use of recommended inputs. Based on the study findings; three parameters were put forward; the use of the primary farm inputs including improved seeds, fertilizers and pesticides.

Prevalence of application of improved seed against traditional seeds: Figure 2 shows that about 72.7% of maize farmers used traditional maize seeds, 93.6% and 85.3% of bean and cassava farmers respectively use traditional seeds. This means that the majority of maize farmers use traditional seeds.

Traditional (indigenous) low-yielding verities generally have inferior genetic potential in terms of yield, time to maturity and susceptibility to diseases and pests. In this era of climate adversity which is associated with short rains, high prevalence of plant pests and diseases and degrading soil, farmers need to use improved seed varieties because most of them are adaptive or resilient to these adverse effects of climate change (Figure 2).

• Maize: USAID (2014) saw that although improved maize hybrids have diffused rapidly in high potential areas of Tanzania, a large proportion of resource-poor farmers in marginal areas still use local varieties and prefer improved open-pollinated varieties (OPVs) over hybrids. Recent reports estimate the area under improved OPVs to be 9% (USAID, 2014).

• Beans: In terms of variety preference, farmers in Kigoma seem to prefer Lyamungo 90 and Jesca beans. The reasons given by farmers are high yielding and short cooking time. These traits need to be incorporated into the breeding processes. A study by Bucheyeki & Mmbaga [18] indicated that Kigoma yellow rank last in terms of yield. The common bean varieties available include Lyamungo 90, Jesca, Uyole 94, Kablanketi and Kigoma yellow. Despite lowest yield, farmers seem to prefer Kigoma yellow because it suits Kigoma agro-climatic conditions long and short cropping seasons. It can be planted in both seasons. Under traditional planting practice, bean farmers’ plant in lines or broadcast. They sow 3-4 debe1 per acre (each debe weighs 20-21 kg). Unlike in past years, currently, farmers have started planting using fertilizers.

1Swahili word for a metallic (tin) container, usually measuring 20 liters

• Cassava: Despite the release of several new cassava varieties, cassava landraces remain predominant in Kigoma. Most farmers still grow traditional varieties and practice recycling. It is estimated that only 2% of cassava is planted with improved planting materials while 98% is planted with recycled or shared cuttings. This practice has led to severe yield decline due to the spread of diseases, especially Cassava Brown Streak Disease (CBSD) and Cassava Mosaic Disease (CMD) which are common in most of the cassava growing ecologies.

Fertilizer: Results indicate that the majority of farmers are non-users. From Figure 3, only 1.5% of farmers indicated that they use fertilizers, while 26.5% and 1.5% of bean and cassava farmers respectively indicated that they use fertilizers. As majority of target community does not keep livestock; use of organic fertilizers is also uncommon. The fewer farmers who apply fertilizers don’t use the recommended rates resulting into low crop productivityIn terms of amount of fertilizers applied, maize farmers used an average of 22 kg/ha (range 0 to 250 kg per hectare); bean farmers used and average of 24 kg/ha (range 0 to 500 kg/ha). These are lower application rates. According to local extension staff, the recommended application rate in both maize and bean crop is 125 kg/ha for both planting and topdressing. This rate is applicable for both phosphate (planting) and nitrogenous (top-dressing) fertilizers. Generally, farmers don’t use fertilizers in cassava farms. Table 4 shows use of fertilizers disaggregated per district.

Pesticide application: Similarly, the study identified that most farmers don’t use pesticides. Low or non-use of pesticides results into crop loss due to the vulnerability of crop plants to pest attacks. Farmers indicated that there were pests and diseases that attack their crops; however, there were no documented records for the last few years even from the government officials. Most of the farmers indicated that they don’t use pesticides, mainly because they are high prices of chemical pesticides; only few farmers could buy the chemical pesticides. For example, 84.8% of farmers indicated that they didn’t apply pesticides in their farm in the last farming season. At the district level, about 88.1% of farmers in Kasulu did not apply pesticides; 84.4% and 80.0% of farmers in Kakonko and Kibondo respectively indicated that they did not apply pesticides in bean and maize farms in last farming season. Some farmers indicated that they combat the challenge of pests using traditional pesticides extracted from plants such as the locally known ntibuhunwa (Tephrosia vogelii) and vitembwatembwa which may be with pepper leaves. Some farmers reported that they use same pesticides in both crops (beans and maize). The study findings indicated in Table 4 apply to only few farmers who could afford chemical fertilizers.

In line with the study findings, the presence of agro-dealers in the study envisages the access to farm inputs among farmers. Basing on the study findings, among the three districts studied, most agrodealers are found in Kasulu. The consulted 8 agrodealers in Kasulu town were selling several agro-inputs, mainly fertilizers pesticides and herbicides. The team found only 3 agrodealers in Kakonko and 3 in Kibondo. The common characteristics of these agrodealers are the fact that they usually stock a variety of fertilizers, pesticides, and veterinary drugs. Pesticides are widely used, to control farm insects or during post-harvest handling (storage) to control insects such as Stophilus trancatus.

The primary farm inputs, in essence, include improved seeds, fertilizers and pesticides. Farm inputs may also refer to tools, equipment and technologies which are used to enhance the effectiveness of farm operations. The study found out that most farmers across the three target districts practice low-input agriculture which is characterized by no or inadequate use of recommended inputs. In line with the findings from Rwehumbiza [21] that in order to improve the productivity of smallholder farming there is need for government to subsidize and enhance the availability of inputs mainly farm inputs. However, it is impetus to train, equip and deploy adequate numbers of extension officers and land use planners at grass root level to reduce unplanned land management improper farming practices.

Profitability of maize, beans, and cassava per acre

Gross profit can be used as a proxy for assessing land productivity. This assumes all (100%) of the harvested crop was sold at the market. This can give a smallholder farmer deeper insight into farming practice management efficiency. In the course of revealing gross margin profit, the ideal conditions were calculated with the aid of field extension staff as well as taking practical data from demo plots. The study findings presented in Tables 5, 6 and 7 show profitability of maize, beans, and cassava respectively per acre under ideal (demo plots) and farmer conditions (as recorded during the undertaking of study) [26]. Basing on the study context, the ideal conditions refer to the plots which accessed all necessary farm inputs during the whole season while farmer condition data where the collected information from the common farming practice from the study area.

Gross profit margin analysis for maize: Maize (Zea mays, L.) is the main staple crop in Tanzania and Kigoma in particular. Food security information indicates that maize is the main staple and source of calories (carbohydrate) in the Kigoma region. Overall, 98.8% of farmers indicated that they grow maize in the last farming season. District data show that about 97.6% of farmers in Kasulu grew maize; 99.1% in Kibondo and all farmers (100%) in Kakonko grew maize in the last farming season. Majority of maize farmers were reported to sell maize as whole grains, packaged in bags, unpackaged flour or packaged flour.

The gross profit margin per acre of maize under ideal practices recommended by extension staff could be 50% per acre. However, under farmers’ condition, it is about 13% per acre. Farmers still have a long way to go to attain the ideal gross margin.

Gross profit margin analysis for beans: Bean (Phaseolus vulgaris, L.) is the main protein source in the three districts. The production of beans in the target districts is characteristically dominated by smallholder farmers. Beans in the target districts are a critical crop for two reasons: first, it is the main supplier of protein and second, it is a source of income. It is estimated that about 50% of small-scale farmers do intercrop beans with maize or cassava, usually in the first season and grow the crop in monoculture during the second season. In terms of yield, pure stands are better than the intercropped crop. Through Gross Profit Margin Analysis for beans could inform the potential area for investment. The two sides of the collected data including demo plots with ideal conditions compared to farmers traditional farming conditions. By undertaking the gross margin per acre is higher for ideal farming practices, as demonstrated in demo plots. The findings in the Table 6 entail Gross Profit Margin Analysis of beans under ideal conditions was about 70% as opposed to bean farming under farmers’ conditions. Similarly, the ideal production figures as demonstrated at demonstration plots showed a great difference from farmers’ real practice on the ground.

Like maize, the gross margin per acre is higher for ideal farming practices, as demonstrated in demo plots. Since beans production under ideal conditions was about 70% as opposed to bean farming under farmers’ conditions, investing in the ideal farming conditions is envisaged to be highly potential towards commercializing smallholder farming.

Gross profit margin analysis for cassava: Cassava (Manihot esculanta, L.) is the third crop, in terms of importance in Kigoma region. Cassava contributes significantly to household food security in Kigoma region. Compared to maize and beans farmers in the surveyed districts grow less cassava. Out of about 54.8% of the interviewed farmers indicated that they grow cassava. The crop seems to be grown much more in Kakonko district, where about 68.9% of farmers indicated to have planted the crop in their farm in the last farming season, compared to 53.6% and 40.9% in Kibondo and Kasulu respectively. In terms of acreage per household, the overall mean was 1.54 acres, which differed slightly from district mean acreage. For example, the largest acreage was in Kakonko where households grew an average of about 1.71 acres. Kasulu and Kibondo nearly had the same average land size; that is 1.49 acres and 1.45 acres per household respectively. Gross Profit Margin Analysis for Cassava was envisaged to be highly useful in unleashing the potential for commercialization among smallholder farmers. This could inform the ongoing initiatives towards enhancing the agriculture productivity and food security strategies in rural areas.

Similarly, GM analysis indicates that growing cassava under demo plot conditions a farmer get more profit than growing cassava under the current practice of most farmers. GM% for the ideal demo plot conditions and farmers practice on the ground was 83% and 42% - the difference is almost twice. Farmers practicing ideal farming are likely to get twice as much profit as what they get currently, hence calling for more investment in improving farming conditions.

Conclusions and Recommendations

Conclusion

Basing on the study findings, it was concluded that majority of households in the three districts are headed by males. Also, majority of the households (57%) had the household size ranging from 6 to 10 members. The study concludes that majority (96.5%) of the interviewed respondents own land. However, the concluded overall mean yields of maize, beans and cassava for the three districts are 371 kg, 400 kg, and 53 kg per acre respectively, Kibondo and Kasulu were capable of producing high quantity of maize and beans while cassava productivity was high in Kakonko district. On the other hand, the study concludes that majority of smallholder farmers were used to traditional seeds such that (72.7%) of maize farmers in the study area were reported using traditional maize seeds, 93.6% and 85.3% of bean and cassava farmers respectively use traditional seeds. This means that the majority of maize farmers use traditional seeds. Results further concluded that the majority of farmers are fertilizers non-users. Similarly, the study concluded that most farmers in the study area don’t use pesticides. Finally, the study concluded the results from the Gross Profit Margin Analyses of all three crops that; since the study findings revealed Gross Profit Margin for maize under ideal farming conditions being 50% compared to 13% that under farmers traditional practices, Gross Profit Margin for beans under ideal farming conditions being 70% compared to 62% that under farmers traditional practices while Gross Profit Margin for cassava under ideal farming conditions being 83% compared to 42% that under farmers traditional practices. Basing on the Gross Profit Margin analyses findings, the study concludes high Gross Profit Margin on all demo-plots/ideal farming conditions. High investment on farming practices including availing farming inputs on time to enable ideal farming conditions to majority of farmers was postulated as the major potential of commercialization of smallholder farming in Kigoma region.

Recommendations

Based on the study findings, the following recommendations have been put forward: -

To the smallholder farmers: They should embrace modern farming practices for enhanced agricultural productivity and profitability among smallholder farmers in Kigoma region.

• Basing on the study findings, smallholder farmers are urged to widely use improved seeds, modern fertilizers, and pesticides. This among other things could transform the current traditional farming practices into improved one with high agricultural production and productivity among smallholder farmers in Kigoma region, hence getting turned into a real commercial farming with absolute profitability.

Business community: They should enhance the availability of inputs for transforming traditional farming practices into more enhanced agricultural practices among smallholder farmers in Kigoma region.

• Basing on the study findings, inadequate agro-dealers in various areas of Kigoma including the study districts, Business community is urged to widely extend their services to a more accessible and affordable stage. This among other things could transform the current traditional farming practices into improved one with high application of improved inputs for improved agricultural production and productivity among smallholder farmers in Kigoma region, hence getting turned into a more commercial and profitable farming.

The government: Should avail political, institutional and infrastructural support to enhance the agricultural environment for transforming traditional farming practices into more profitable agricultural among smallholder farmers in Kigoma region.

• Basing on the study findings, inadequate political, institutional and infrastructural support in the area of agricultural development in particular in various areas of Kigoma including the study districts, the government through her instrumental actors including the Ministry of Agriculture is urged to enhance the agricultural environment through availing more political, institutional and infrastructural support including supporting policies, subsidies and other related interventions. This will be useful in the course of enhancing agricultural production and productivity among smallholder farmers in Tanzania.

Acknowledgement

This study has been accomplished by dedicated efforts of the smallholder farmers of Kigoma region in Tanzania. Their support, courage and cooperation rendered to me in the course of realizing this study were incredible. Smallholder farmers will always remain my teachers and distinguished experts in generating agriculture knowledge. Indeed, I appreciate every kind of support I got from all actors and leaders in the study area in the course undertaking this study.

Conflict of Interest

No conflict of interest.

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The thermal comfort in buildings is one of the most characteristic and important aim that architecture must provide, as the typical way to achieve the thermal comfort in buildings is the intensive use of energy consumed, but this is of course not an ideal approach because it leads to waste of energy. High consumption rates of electric energy and non-renewable energies are among the most serious problems facing Egypt and the whole world at the present time, as the deficit is increasing continuously.After analyzing and updating the international, local examples, studies and measurements that were developed by specialists in this field, we found that under the great development in methods of urban planning and design and access to finishing materials and thermal insulation of buildings has become a significant impact in the reduction of 40-50% of the total energy used in buildings of mechanical machines and reduce the total energy consumption.The goal of this research is to Reformulate the methods of reducing energy consumption, Clarify the process of thermal protection from buildings planning to finishing, analyzing sustainable strategies, objectives and Execution, & Clarifying the global standards & specifications to follow in buildings.Theoretical approachThis is achieved through a detailed study on the development of thermal protection systems and the creation of the internal spaces climates and passive designs.Practical approachThis is achieved through an analytical study and analysis of many local and international cases that have been implemented in accordance with the standards and technical studies to develop recommendations avoiding mistakes [1-6].At first the paper starts with a briefing about Energy saving & Rationalization Consumption, then Items & Factors to achieve thermal protection, Methods of Execution thermal protection systems, afterwards the paper introduces analysis of practical local & international Case studies and ends up with Conclusions & recommendations.Energy saving & rationalizing consumptionOverview: The problem of energy is due to the fact that its sources are decreasing with increasing consumption in line with technological development and modern industries with the impact of increasing in energy prices from fossil fuels.Historical environmental thought in architecture: If we look at the evolution of architecture through the ages, and by studying the architectural character, we find that it has always been a sincere reflection of the environment surrounding all elements of construction and the available materials.Ancient egyptian architecture: The ancient Egyptian architecture is one of the first examples where external factors had a clear impact on their buildings, for example (Figures 1a & 1b):Greek architecture: The Greeks cared for nature, making the entrances of their temples to the east to receive sunlight during the day (Figure 1c & 1d).Roman architecture:• The use of natural materials available in the surrounding environment.• Making openings in the ceiling for ventilation & lighting inside the building (Figure 1e).Byzantine architecture: Presented a new idea by gradient in the roof level and the skyline of the building in addition to use overhead windows in natural lighting, especially in domes (Figures 1f & 1g).Gothic architecture: Is expressive and distinctive image as they used rose windows in the facade to introduce lighting have a special character inside the building (churches) (Figures 1h & 1i).Islamic architecture:• Follow the idea of the integrated urban fabric by use different vertical heights to shade the low building parts, which helped to shade large parts of the roofs of neighboring buildings and protect them from the sun [7-13].• The use of specific external vents and a small proportion of the interface, to maintain the internal temperature and reduce the heat load (Figures 1j & 1k).Energy saving: The process of building design should be based on scientific methods to reduce the need for fossil fuels, as the protection of buildings from exposure to sunlight is very important methods to reduce thermal loads & reduce energy consumption (Figures 1l & 1m).Climatic designThe building is highly integrated with the environment, integrates with its location and consumes less energy, emphasizes the use of natural light and uses recyclable ecological materials from sustainable sources as using natural materials available in the environment.• The use of internal courtyards, including the shades provided during the day and stored for cold air at night.• Use air clamps to vent the voids that are not directly facing the prevailing winds or ventilate the basements.• The use of wooden mashrabiya in facades helped break the intensity of sunlight while providing a privacy factorFactors affecting energy consumption:a. Factors associated with the human: The rates of thermal energy produced by the human body’s bioreactor are dissipated in the atmosphere.b. Factors related to surrounding environmental:• Air temperature.• Relative humidity.• Air movement or speed.• Average radiant heat.Items & Factors to Achieve Thermal ProtectionIntroductionThe external climate has a direct impact on the human condition and a sense of comfort or tightness. Man’s adaptation to the external climate is not flexible enough to always feel comfortable, but its adaptation to the surrounding climate does not protect it from distress or discomfort due to exposure to these inappropriate weather conditions [14-19].The outer atmosphere of the buildingThe outer atmosphere of the building is the link between the inside and outside, whether, such as the vision or the entry and exit of the building, and whether influencing noise or heat or other external factors that affect the interior space (Figure 2a).Elements of the building’s exteriorThe outer envelope of the building consists of three main elements• Roofs• External Walls• Openings (Windows and doors)The role of urban design elements to reduce thermal loads• planting green areas around the building.• Use evergreen trees.• Usage water features next to the building.Planting green areas around the building: These areas help to absorb as much of the radiation and not reflected from the surface of the earth, and this helps to humidify the air in this area (Figure 2b).Usage water features next to the building: Water features near buildings are helping to break the sunlight falling and reduce the heat load resulting from them, And to avoid the surface of the water to be a heat-reflective surface on the building must be undulating water to lead to the dispersion and refraction of sunlight on them, such as the use of fountains (Figure 2c).Usage of trees: Surrounding buildings with trees and shrubs helps to provide shadows on the building, then protecting it from direct sunlight (Figure 2d).Building External ItemsExternal Walls:• Usage of thermal insulating materials in the walls, Figure (A).• Construction of walls from slow thermal gain materials, Figure (B).• Create double walls to generate air cavity insulator, Figure (C).• Double walls allow the ventilation of air & renewal, Figure (D).• Usage of heat-reflective materials for wall cladding, Figure (E).• Shading parts of the outer walls with projections, Figure (F) (Figure 2e).Openings:a. Use of sun breakers: The main purpose is to prevent sunlight from falling on the building’s outer shell or accessing the interior spaces (Figure 2f).b. Use of Mashrabiyat: They are commonly used, not only for the purpose of preventing sunlight, but for aesthetic reasons and to achieve privacy and distribution of natural lighting [20- 24].c. The position of the openings in the vertical section: The level of the windowsills has a significant impact on the level of movement of air inside the building and has an impact on the users accordingly (Figure 2g).Roofs:Roofs treatments are very similar to walls in addition to the following: treatmentsa. Use of curved roof shapes: It is known that the study of the corners of the sun is not exposed completely bent roofs to the sun, but there is a shaded part of it (Figure 2h), b. Create the roof from two separate tiles: The roof is constructed from two separate tiles, which leads to the movement of air between the layers as the heat across the upper roof and not run out through the lower roof (Figure 2i).Definition of thermal insulation Thermal insulation can be defined as the use of materials that have heat-insulating properties (low heat conductivity), which help to reduce heat leakage and transfer from outside the building into the interior in the summer and vice versa, where the rate of heat leakage from the ceilings and walls is estimated at 60-70% and the rest of Windows and vents [25-27].Advantages of thermal insulation for buildings:• Reduces Electrical power consumption.• Making air inside the building without air conditioning is relatively acceptable on hot summer days.• Reduce the thickness of walls and ceilings required to reduce heat transfer to the building.Methods of Thermal Protection Execution SystemsFactors affecting energy reduction at External wall Sectiona. The design of the external wall as a double wall contain air cavity, to be 45 cm thickness.b. Control the different alternatives to the wall section through several variables and alternatives such as:• The type of interior wall construction material.• Interior wall thickness.• The type of thermal insulation material used.• Type of exterior wall finishing material.Example of the main section - building’s external wallDouble wall and air cavity 5 cm thick. Each wall shall be composed as follows (Figure 3a):a. Interior wall: From the inside to the outside: Plaster thickness 2 cm and then cement hollow block thickness 20 cm.b. External wall: From outside to inside: sandstone thickness 15 cm and polystyrene sheet 5 cm thickness.Basic variables in the external wall sectionThe variables and alternatives in the mentioned before wall section are determined to study the effect of each variable on the thermal performance of the wall and compare between different sections of the wall, according to the u-values achieved [28-32]. Table shows the effect of the internal wall thickness on u-values (Table 1).Analysis results based on changing wall thickness:• As the thickness of the buildings increases, the u- value decreases and the thermal efficiency of the wall increases.• When the thickness of air cavity inside the double wall increases, however it has little effect on the thermal performance of the wall and u- values.Basic variables in different wall finishing material: The external finishing material of the wall shall be changed with the remaining components and thickness of the main wall.• Basic section: external cladding of sandstone with thickness 15 cm.• From the outside: sandstone cladding with thickness 4 cm, cement bricks 10 cm.• From inside: plaster with thickness 3 cm - cement bricks with thickness 12 cm (Table 2).Table 2:The effect of the difference in the material of the exterior wall finish on the thermal performance of the building.Analysis results based on changing finish materials: There is little effect of different finishing components in the exterior wall according to the previous alternatives.Change the thickness of the thermal insulation layer:b> Polystyrene sheets is used in different thicknesses (2:5cm) with the other components of the main wall with thickness, the table shows the analysis (Table 3):Table 3:The effect of changing the thickness of the thermal insulation layer on the thermal performance of the building.Analysis results using heat insulation thickness 2-5cm :The changes of polystyrene insulation sheets thickness values reach more than 50% when using layer of 5 cm thickness, as well as when Change the thickness of layer to thickness 3 cm and 2 cm.Basic variables in using of heat insulation material:• Case 01: The air cavity of the wall contains a heat-insulating layer of polystyrene with a thickness of 5 cm.• Case 02: Air cavity of 10 cm thickness without heat insulation layer (Table 4).Table 4:The effect of the presence or absence of a thermal insulation layer on the thermal performance of the building.Climatic zonesClimate is one of the elements of the natural environment in which human beings live, and it affects human comfort and production capacity, therefore, we must identify the nature of the climate environment, and the extent of its impact on the human and determine the limits and scope of the sense of comfort through them and try to reach the stage of thermal and environmental balance between human and the environment (Figure 3b).Urban climatic regionsExtract four main regions that constitute the climate map:• Coastal climate region.• Desert Climate region.• Semi Desert Climate region.• Highlands climate region (Table 5).Table 5:Climatic regions according to the climatic design of Egypt.When designing a building of any kind, in order to achieve the required thermal comfort inside the building, it is necessary to identify and study the different climatic factors that affect the building either positively or negatively, depending on the geographic location of building, which will be according to the following:• Global climate• Regional climate.• Local climate• Partial climate.• Internal climate.Analysis of Practical Case StudiesExample 01 - Credit Agricole, New Cairo, EgyptBuilding description: Crédit Agricole Egypt’s main building, which is located on an area of about 27,000 square meters, is considered a commercial center with many customers, employees and employees, with a capacity of 3000 people.Reasons of choosing the building: The location of the building, which is located in the middle of Cairo, which represents the semi-desert region, which is exposed to high temperatures in summer and exposure to sunlight for long hours up to (14 - 15) hours a day.• The building was awarded the title of “Green Bank”.• The building obtained LEED certificate from the American Center for Buildings and the Platinum evaluation.Building Analysis:• Clear and distinctive sign in front of the street.• Establish an indoor garden as the focal point of the site.• The main facades approach the site boundaries, especially at street intersections to ensure the best possible visibility of the roads (Figures 4b & 4c).Citation: Ashraf A Gaafar. Thermal Protection Systems for Buildings in Egypt. Glob J Eng Sci. 8(3): 2021. GJES.MS.ID.000689. DOI: 10.33552/GJES.2021.08.000689. Page 12 of 20 LEED strategy: The harsh environmental conditions of the site as well as the requirements for working comfort in the headquarters building pose a sustainable design challenge [33-35]. The project was originally designed for a LEED Silver rating, but in March 2016, the building received LEED Platinum certification from the US Green Building Council with a score of 81/110 as follows:Sustainable strategies:a. Top shading system / Windows shading:b. High efficiency lighting / passive system:(Figure 4e)Example 02 - AUC, New Cairo, EgyptLocation: The building is located in the New Cairo area in Cairo Governorate, where it is bordered to the south by Gamal Abdel Nasser Road and the southern ninety Street from the north and east, and the southern investors area from the west (Figures 4f & 4g).Building Description: These principles of environmental improvement can be translated into architectural works and landscapes through the use of a series of sustainable strategies, the master plan from its conception to its resulting plan is a form of site environment improvement (Figure 4h).Mechanical loads deduction:Table 6:Mechanical loads & comfort zones loads.Example 03 - Commerzbank, Frankfurt, GermanyLocation: The building is located in Frankfurt, Germany, bounded to the north by the main tower and south of the Opera House and bordered by Frankfurt Central Station to the west, and the Museum of Modern Art from the east side (Figures 4l & 4m).Building description: The idea of the building is made up of three separate segments grouped around the entire central atrium. The four-story gardens are located on different levels on each side of the tower, rising around the building (Figure 4n).LEED strategy: The building was designed with the aim of providing an eco-friendly design that resulted in the building being awarded LEED Platinum certification by the US Green Building Council with grade 83/110 (Figure 4o).Wind & Ventilation study: The design of the building responds to prevailing winds and solar orientation, ensuring optimal ventilation and penetration of daylight (Figure 4p).Form & shape / Passive system: The building is designed to be naturally ventilated for most of the year, allowing sky gardens to be naturally ventilated during the day, This approach reduced energy consumption by up to 50% compared to an equivalent office air conditioner (Figure 4q).Opening solution: In the following figure, flexibility in dealing with sunlight is explained in summer and winter, where umbrellas and breakers are used on surfaces and facades in the summer to maintain the internal temperature, While not used in winter to give the opportunity to warm indoor air and in both cases the goal is to reduce dependence on mechanical means to adjust the temperature (Figure 4r).Conclusions & RecommendationsArchitectural design recommendationThe role of the architect does not only design these architectural elements, but also includes the design of the elements surrounding the building, for its role in coordinating the site as well as for its climatic role. Here is some recommendation• The green spaces around the building help to absorb the greatest amount of solar radiation.• Use trees to purify the wind from dust and plankton and cast shadows on the facade of the building in the summer.• Finding water bodies next to the building helps to break the sunlight falling on them and reduce the resulting convec tion.• Use the idea of the building with the inner courtyard as a temperature regulator and also for privacy.• Direct most rooms on the inner courtyard and convenient to give privacy to man.• Use of water and greenery in public yards and yards.• Exploitation of roofs of flat buildings as open areas “roof garden”.• Reduce solar radiation, increase shadows and increase humidity.• Use of mashrabiya.• Use the idea of indirect entrance to avoid climate factors from winds loaded with dust.• The use of arches in corridors and shaded bouquets to provide them with shadows.• The installations do not face the direction of the wind and direct the openings towards the northwest and southwest.• The biggest and most important impact in the previous analyzes and studies was the effect of the thermal insulation layer in terms of thickness, and its use or not used within the wall section.• The effect of the thermal insulation layer on the thermal performance of the wall is large according to the thickness of the thermal insulation layer. 3 cm of extruded polystyrene for the same previous wall.Urban planning recommendationsDivision of climate regions: When designing a building of any kind, in a specific region, to achieve the required thermal comfort according to region climatic conditions, it is necessary to identify and study the various climatic factors that affect this region, either positively or negatively [36].The main elements of the climate are influencing the design of the building to achieve the thermal comfort required for the users of the interior space.The designer should study the most important points that give him a clear picture of these factors, and these points are as follows:• Factors affecting the climate element.• Unit of measurement of climate element.• The data needed to give a clear picture of the climate element.The designer must collect the climate information of the area or city where the designer is doing the design.The design of green spaces: It has been proven that seeing the green and open spaces of the windows is important for meditation, relaxation and spiritual renewal and that the landscape provides benefit on many levels [37]. The active and varied shades of tree umbrellas contrast with the shadow of static buildings. All outdoor spaces should be shaded as the difference between asphalt and grass is usually up to 25 °F (about 14 °C).AcknowledgementNone.Conflict of InterestNo conflict of interest.To read more about this article: https://irispublishers.com/gjes/fulltext/thermal-protection-systems-for-buildings-in-egypt.ID.000689.phpIndexing List of Iris Publishers: https://medium.com/@irispublishers/what-is-the-indexing-list-of-iris-publishers-4ace353e4eeeIris publishers google scholar citations: https://scholar.google.co.in/scholar?hl=en&as_sdt=0%2C5&q=irispublishers&btnG=https://irispublishers.com/gjes/fulltext/thermal-protection-systems-for-buildings-in-egypt.ID.000689.php

Authored by Ashraf A Gaafar

Influence of Green Terraces in Evaluating the Action of Wind on Buildings

Authored by Isopescu Dorina Nicolina

The development of the construction sector, as a result of the special emphasis of recent years in the implementation of the principles of sustainability, has included various directions: from structural certification of environmentally friendly materials in terms of their durability and carbon dioxide emissions, and the innovation of building systems respecting the energy efficiency principles requirements, until to the innovation of the shape and volume concepts of buildings. All over the world there are recognized examples of nature-friendly architecture. The complexity of sustainable development in construction is increasingly becoming cross-cutting research, which covers the integrated techniques of materials science, building physics, with the circular economy, and with plant science. This challenge offers new opportunities for buildings to become less polluting and more resistant to climate change.

Green buildings, in fact, green roofs and facades, help to create viable and sustainable built spaces. The benefits are much more than the structural or environmental protection, green structural components in buildings can contribute to the well-being of occupants, such as noise reduction, and can improve indoor air quality.

This article examines the importance of green roofs in sustainable buildings and their effect on the strength and stability of buildings against wind action, based on design regulation in force. In addition to the general presentation of the literature, several recent applications of greenery in projects are presented, to illustrate the architectural added value.

Currently, one of the most debated issues worldwide is the relationship and mutual influence between the natural environment and the built environment. The built environment is an artificial environment created by mankind and, although it is the support of the civilization development, current research shows that this field of activity has several adverse effects, including the fact that it is responsible for 33% of total emissions of greenhouse gases and 20% of the total amount of waste produced globally. Also, the processes specific to the construction and use of buildings are responsible for 40% of global energy consumption [1,2]. All these observations based on substantiated analyses, emphasize the fact that the built environment has a negative major impact on the natural one, having a key role in achieving the requirements of the development of global sustainability.

Urbanization and the impact of this trend on climate change is one of the most analysed topics in global climate change debates. In the most developed countries, the urbanization process is expected to reach about 83% by 2030 [3]. Due to the accelerated economic development, the urbanization process shows accelerated growth in most countries, to the detriment of the natural landscape as well as the requirements of environmental protection [4]. An increasingly approached solution is the concept of greening the built environment as an integrated approach to achieving sustainable urban development, mitigating the impact of rapid urbanization, and improving the quality of life [5].

The Paris Agreement on Climate Change, as well as the policies and strategies promoted by the European Union, attach particular importance to increasing the green areas in cities, reducing carbon dioxide emissions and energy consumption, but also to developing new green technologies. A modern and viable solution for mitigating negative environmental effects is identified in greening systems, such as the horizontal green building components (roofs) and vertical green building components (walls) (Figure 1). By rehabilitating with these solutions, the existing built environment can become the support for the improvement of the urban micro-climate conditions. Even though they are currently hotly debated, these concepts are not new, being found in the concerns of society since ancient times [6].

Urban areas are characterized by a lack of land, and in response to this, in some densely built-up areas, the vertical green strategy has been introduced to increase the area of green space following the requirements of international regulations. Vertical green systems can be made in two technologies, loadbearing green walls and green facades (Figure 2). Both systems have the advantage of optimizing the energy consumption of buildings [7] and increasing thermal comfort [8]. Scientific debates about the benefits of greening systems for the environment are complex and varied. Some researchers believe that vegetation attenuates the effect of heat islands both on an urban scale and on the building. Other researchers argue that green roofs are no better than other cold roofs, such as white roofs, when it comes to the heat island effect [9]. Also, other criticisms refer to the aspects related to plant species that can be used on the green roof, which must be resistant and be able to survive winter conditions, where temperatures drop well below zero degrees Celsius.

However, the presence of greening systems in the built environment certainly ensures an improvement in air quality through the process of photosynthesis, which is largely responsible for producing and maintaining the oxygen content of the Earth’s atmosphere and provides all organic compounds and most of the energy needed for life on Earth [10]. In the process of photosynthesis, plants transform water and carbon dioxide into large molecules such as glucose, cellulose, etc., and the chemical reactions of the formation of these substances are endothermic [11]. This explains the important role of plants in reducing carbon dioxide and dispersing pollutants into the atmosphere, as well as in reducing local temperature or reducing rainwater runoff.

Investigating the mechanisms of the mutual relationship between the built environment and the environment, aim to analyse the energy consumption of buildings, the use of renewable energy resources, as well as indoor and outdoor thermal comfort and air quality. Quantifying the causes and prospects of mitigating negative effects leads to technologies with the potential to improve thermal comfort and reduce carbon dioxide emissions, with substantial interventions in the architectural and structural configuration of buildings.

In the construction sector, designers and policymakers are stimulated to seek effective strategies for the sustainable development of buildings, to avoid the consumption of natural resources, and solve environmental problems. Greening systems are considered a promising solution to make buildings meet sustainability requirements, but their realization in the set of structural components of the constructions conducts to additional loads that modify the behavior of the building to various actions, which impose, in addition to the increased costs, appropriate design methods. Therefore, the main purpose of this paper is to present a short analysis of terrace-type green roofs in terms of their impact on the strength and stability design of buildings.

The scientific literature presents various research on green roofs, research on the species used, the plant substrate, and the performance of this structure on various climatic parameters [12- 14]. It is also noted that the study on the influence of green roof structure on the parameters that define the action of the wind is an important part of the research on these structures, this study being the main object and will be detailed in the next chapters.

The Evaluation of Wind Force in Structural Design

As the wind blows against a building, the resulting force called the “wind load” [15], must be taken up by the building’s strength structure and transferred to the foundations to avoid structural collapse. Wind loads depend on wind speed, shape, and volume of the building and therefore can be difficult to accurately predict. The norm Eurocode 1: Actions on structures - Part 1 - 4: General actions - Wind actions [16], gives guidance on the determination of natural wind actions for the structural design of the building and civil engineering works for each of the loaded areas under consideration. This includes the whole structure or parts of the structure or elements attached to the structure. The wind forces for the whole structure or a structural component should be determined by calculating forces from surface pressures or by calculating forces using force coefficients.

The wind force, Fw, acting on a structure or a structural element may be determined by vectorial summation of the forces Fwe, Fwi and Ffr calculated from the external and internal pressures and the frictional forces resulting from the friction of the wind parallel to the external surfaces [16], according to equation (1):

The design standard [16] prescribes a second methodology to determine the wind force Fw acting on a structure or a structural component, directly by using force coefficients as in expression (2):

The force coefficient cf of structural elements of rectangular section with the wind blowing normally to a face should be determined by equation (3):

Where:

• ρ is the air density, 1.25 kg/m3.

Analysing the structure of equation (5) it can be seen that the force given by the action of the wind is composed of the force from the vertical structural elements, respectively from the walls, as well as by the force at the roof level. Therefore, to evaluate the influence of the green terrace roof, the wind force at the roof level is defined according to equation (6):

The computation form of the equation (6) will allow, in the next chapter, to identify the influence of the green terrace roof on the wind force only at the roof level, considering that the force component given by the wind action on the vertical element is the same regardless of the type of terrace roof.

The Influence of Green Terrace Roof on Wind Force – Case Study

The case study was selected due to the need to improve the environment in crowded urban areas, respectively in residential areas where buildings usually have a height of about 15 m. This situation is characteristic of old residential areas with multi-store collective housing. Urban rehabilitation in these areas must take into account some specific features of these buildings, which, on the one hand, cannot be demolished given the legal situation regarding property rights, and on the other hand suffer the most from environmental pollution by lack of green areas and the impossibility of extending them to ground level. In this situation, modernization solutions to improve the quality of the environment are related to the transformation of traditional terrace roofs into green terrace roofs.

The following analysis was made on a parallelepiped-shaped building model, which keeps its cross-sectional area constant, but where the number of floors is variable and consequently the height of the building is variable. The reference area at the roof level, Aref,roof, has been considered equal to the cross-sectional area, regardless of the height at which it is from the ground. In the case study, the reference area at the roof level is assumed to be equal to 500 m2 (b = 20 m and d = 25 m). Taking also into account the recommendation given in Eurocode 1 that for all elements without free-end flow and no round corners the value 1.0 is given for ψr and ψλ, then the value of cf0 is determined using the following equation, (7):

Where:

• k is the equivalent surface roughness which is equal to 0.2 mm for the traditional roof covering and may have the assumed value of 3.0 mm in the case of green roof covering;

• Re is the Reynolds number determined with the peak velocity pressure qρ(z), eq. (4), and

• with a diameter c of an equivalent cylinder having the volume equal to the parallelepiped shaped building model:

• ν is the kinematic viscosity of the air (15·10-6 m2/s).

The roughness length - z0 depends on the roughness of the site terrain and it is considered equal to 0.05 (terrain category II). Making some partial substitutions in the equation (7), it is obtained the expression (8) for the force coefficient:

According to equation (9) the wind force at roof level, Fw,roof, has three variables: the force coefficient -cf0, the reference height -z, and the fundamental value of basic wind velocity -vb0. The recommended value for the structural factor cscd is equal to 1.0, therefore this value was used in the analysis. The results obtained for the force coefficient, cf0, are presented in Figures 3 & 5 related to the reference height - z and the fundamental value of basic wind velocity -vb0. In Figure 3, the variation of the force coefficient is evaluated for the equivalent surface roughness of the traditional terrace roof, k = 0.2 mm, while in Figure 5. is considered the equivalent surface roughness value for the case of green terrace roof, k = 3 mm.

Using the force coefficients evaluated for the two equivalent surface roughness values, the wind forces at the roof level can be evaluated. Thus, Figure 4 shows the graph of wind force depending on the variation of the reference height -z and the variation of the fundamental value of basic wind velocity - vb0, for the traditional terrace roof. Figure 6 shows the graph of wind force variation for the green terrace roof.

Discussions

From the results obtained in the case study analysed, the following observations can be formulated:

• The value of the equivalent surface roughness, k, influences differently the force coefficient, cf0, when the fundamental value of basic wind velocity, vb0, increases, so for k = 0.2 mm the value of the force coefficient increases with increasing wind velocity (Figure 3), while for k = 3 mm the value of the force coefficient decreases when the wind velocity increases (Figure 5);

• The same phenomenon occurs when the reference height, z, increases, so for k = 0.2 mm the value of the force coefficient increases with the increase of the reference height (Figure 3), while for k = 3 mm the value of the force coefficient decreases when the reference height increases (Figure 5);

• The wind force, Fw,roof, at the roof level increases with the increase of the reference height and the increase of the fundamental value of basic wind velocity, Figure 4 and Figure 6;

• The wind force for green terrace roof increased by approximately 20% when the equivalent surface roughness of k = 3 mm, Figure 6, compared to the value obtained for the case of k = 0.2 mm, Figure 4;

• For values of the fundamental basic wind velocity lower than 5 m/s, even if the reference height increases, there are non-essential differences between the wind force evaluated for traditional terrace roof and for green terrace roof;

• In the case when the fundamental value of basic wind velocity is higher than 5 m/s and the reference height increases, the wind force values grow exponentially (Figure 7).

Conclusion

According to the methodology of evaluating the wind force at the roof level used in the case study, the following conclusions can be formulated:

• For buildings with up to four levels above the ground floor, at wind velocity of up to 5 m/s the traditional terrace roofs can be replaced with green terrace roofs without the need to evaluate the wind force at the level of the green terrace roof;

• The wind force at the roof level is influenced by the type of terrace roof, so for a reference height of 15 m and a speed of 15 m/s, the force increases compared to the initial value by approximately 20% when the roof is a green terrace;

• Considering the exponential way of increasing the wind force at reference heights of over 15 m, it is recommended to check the behaviour of the building with a green terrace roof to the action of the wind when building height is higher than 15 m;

• By the method presented synthetically in equation (2) it is not possible to identify at the roof level if it is suction or pressure, this detailing can be identified by the analytical model presented in equation (1). It is important to know the direction of peak velocity pressure qρ(z) at reference height, to design the execution details to meet the requirements of conforming behaviour of the building in operation, to ensure the strength and stability of the structure, and its parts;

• Considering the 20% increase of the wind force and implicitly of the peak velocity pressure for high buildings, in the areas with negative values of suction, they can cause major damages in the stability of the vegetal layer from the green roof structure, thus to change the roof solution from a traditional terrace roof with a green terrace roof must be analysed before the implementation.

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Numerical Computation of Separation Events

Authored by Kevin Murphy

Impacting systems possess stiffness discontinuities (nonlinearities) and integrating the system through these abrupt transitions in stiffness is numerically challenging. Henon’s method [1] for identifying numerically the instant of impact - and the associated values of the state variables - is well established. However, in cases where distinct components move together, there is not a well-developed technique for identifying when they separate because this separation event is not expressed in terms of the generalized coordinates. This work presents a numerical technique for doing just that. If one couples this method with Henon’s method, the time response of a system undergoing repeated impacts and separations may be obtained with a high degree of precision. Several specific examples are presented to demonstrate the utility of the method.

Impact oscillators give rise to nonlinear behavior through the abrupt, impulsive interaction between the distinct, interacting bodies. Modeling this behavior accurately is a challenge because the instant of impact is not known a-priori. Moreover, capturing the instant of impact is crucial because nonlinear systems can display an extreme sensitivity to initial conditions, i.e., an impact event can be viewed as an initial condition for a new trajectory. For cases where the motion is found numerically via a time-stepping algorithm, Henon [1] developed a simple numerical technique for ascertaining this instant of impact. This method has been used effectively in a number of impact problems and produces results that agree with other techniques and, more importantly, with independent experimental observations. It has also been incorporated into commercial software packages.

One common model for an impact oscillator uses the coefficient of restitution (CoR) [2]. Here, the normal component of the rebound velocity is given as a percent of the inbound (pre-collision) velocity. It is assumed that, provided e≠0, the interacting bodies come into contact and then immediately separate. When numerically timestepping a solution, Henon’s method is invaluable because it clearly indicates the instant when the impact event occurs, i.e., when the CoR model should be applied.

Another class problem that comes up from time to time is that of separation. One can imagine two (or more) contacting bodies moving together; in this case, the system can be modeled as a single degree of freedom problem with one combined mass. As the motion evolves, these bodies may separate. This requires a sudden change in the model from one degree of freedom to multiple degrees of freedom. Therefore, like the impact problem, determining the moment of separation is critical in order to generate the response accurately. However, unlike the impact problem, the separation event is more subtle. It is not dictated by a condition placed on one of the state variables. Instead, the system must be unpacked a bit before a Henon-like approach may be taken (Figure 1).

In this paper a numerical technique is developed to determine this instant of separation for these systems. This method takes its inspiration from Henon’s method. Consequently, Henon’s method is briefly reviewed. Next, the separation problem is described and a numerical technique for the instant of separation is developed. A number of examples are provided, which demonstrate the utility of the method.

The Numerical Technique

The numerical solution of nonlinear ordinary differential equations involves time-stepping. This process begins by writing the set of equations in first order form: ẋ = f(x(t), t). x is the unknown state vector and t is the independent variable. Solutions are obtained by starting at some initial condition and integrating the state variables through some discrete time step △t from to t0 to t1. This integration is accomplished by some numerical scheme, such as Runge-Kutta, Geer’s method, etc. [3]. Using x(t1) as a new initial condition, another time integration step △t may be taken to t2. This gives x(t2). This process continues and gives the timediscretized trajectory of the system.

As will be described, both of the impact and separation problems are nonlinear in the sense that there is a model change at the impact/separation event. So, it is critical to ascertain the instant of these events or else the computed trajectories will not faithfully reflect the system response. As motivation, the impact problem is outlined and a brief description of the Henon technique [1] is given in the next section. This is followed, in the subsequent section, by a description of the separation problem and the new numerical technique for handling that problem.

Impact events

For the moment, consider a single mass approaching a rigid wall along its normal direction; this is shown schematically in Figure (1a). The equations of motion for the ball may be integrated until the mass impacts the wall. At the moment of impact, the velocity is instantaneously changed. The post-impact velocity υ’ (which serves as the new initial condition for the next step in the integration) is found by reversing the direction of the pre-impact velocity v and multiplying it by the coefficient of restitution: υ’= -eυ. However, to apply this condition, it is assumed that the integration routine will land exactly at the impact event (the wall). In general, this does not happen.

To demonstrate this, again consider Figure (1a). The equations of motion for the mass have been integrated through i time steps to ti. This leaves the mass very near the wall, △x away from an impact. The integration routine steps to ti+1; the updated position of the mass is determined by the governing differential equations. This turns out to be on the other side of the impact condition, which is physically meaningless since the mass can’t penetrate the wall. Traditional routines would return to ti and proceed to take smaller time steps, in the hope of landing “close enough” to the impact condition. But this process of refining the time step is computationally laborious. Moreover, it won’t effectively find the moment of impact because the same issue will continue to crop up, just at smaller spatial and temporal scales (Figure 2).

Henon [1] came up with a practical and easy-to-implement technique to circumvent this problem. Here is an overview. Consider Figure (1b). The problem begins at the same instant ti and position xi as before. Because the distance to the wall is well known (but the time needed to get there is not), the problem is recast. Specifically, the equations are rewritten with x as the independent variable and ẋ and t as the dependent variables. Then, rather than taking a time step, the system undertakes a single displacement step of △x. This, by definition, lands the mass at the impact condition. The associated velocity and time are determined by the recast differential equations. At this instant, the velocity is changed to the post-impact value: υ’ = -eυ. Then the equations are returned to their original form (with t as the independent variable) and the time stepping algorithm is continued until the next impact event.

To integrate the system through an impact event, Eqs. (2) are time integrated until the position violates the impact condition (i.e., the two bodies pass through one another, similar to Figure (1a)). Taking a time step back, one then switches to Eq. (3) and takes a prescribed relative displacement step (r1) to the impact condition. The other dependent variables (including time, t) are obtained through the integration process. Once at the impact condition, the velocities are changed using the CoR model and time stepping may resume using Eq. (2).

Separation events

Various conditions may cause two (or more) bodies to move together. Initial conditions could be such that they all begin together. Or two objects may approach one another, and their velocities coalesce at impact, causing them to move together afterwards. Regardless of the cause, consider two contacting bodies that are moving together. This scenario opens the door to the possibility that they may separate. Normal time integration of the governing equations will typically step through the separation event - just as time integration usually steps through an impact event (see Figure (1a)). Now the parallel question is asked: can the equations be recast in such a way as to end up at the moment of separation? As a specific example, recall the two degree of freedom model of Figure (2a) with u1 = u2 (or r1 = 0). There is an interaction force Fi between the bodies, as shown in Figure (2b). Applying Newton’s law to each mass and ignoring the external forces (for the moment) gives:

This work presents a new technique for calculating numerically the moment of separation of two moving, contacting bodies. This approach builds off of the technique developed by Henon [1] for determining numerically the moment of impact for two moving bodies. Specifically, the governing equations are integrated numerically until the impact condition is violated (i.e., the last time step went beyond the impact condition, allowing the bodies to partially pass through one another). The system then goes back one-time step, where the distance to impact is known. The governing equations are recast so with the relative position of the two bodies being the independent variable.

Time t is a dependent variable to be determined by the integration routine. A single displacement step is taken exactly to the condition of first contact. The associated time is then computed from the recast equations, along with the other state variables. In a similar way, the onset of separation of two contacting bodies may be identified. The system may be integrated forward in time until a separation event takes place. Going back one-time step, the governing equations may be recast so that the independent variable is the interaction force between the two bodies. Then a single force step may be taken to the exact moment of separation (F → 0). The process of recasting the equations is demonstrated with a simple two mass problem. To highlight the implementation, a number of impact/separation cases are considered both numerically and analytically. In each scenario, the instant of contact/separation are precisely identified, and the ensuing motion found. In general, the method developed here is straightforward and effective. And it may be easily extended for systems containing more degrees of freedom.

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Nuclear Detonation Radiative Heat Effects on Contemporary Building Structure

Authored by Danladi Slim Matawal

Introduction

The growing number of studies on the impact of COVID-19 is often chosen in the context of developed countries, highlighting a gap in the understanding of how the pandemic is impacting developing countries. There is need to acknowledge the effect/ impact on transportation in emerging economies where lockdowns and restrictions on movement may not be wholly ineffective but even more suited to the level of psychological response of the people. There is not just poor transportation infrastructure but also lack of a clearly defined transportation system that is effectively managed and regulated by operators while the economy is largely informal. The outbreak of the COVID-19 coronavirus was deemed a pandemic by the World Health Organization (WHO) on 11th March 2020. To date, there have been cases confirmed in at least 203 countries, areas or territories, causing unprecedented measures to be taken by many countries, such as travel restrictions and restrictions on social gatherings. Nigeria is a key regional actor in the African continent with over 200 million people, and it confirmed its first case in Lagos in February 2020.

The emerging economy faces institutional adversity with underlying and persistent economic challenges as it copes with the pandemic and both effect and responses have varied widely in the country. Virtual lives have essentially been instituted for the upper and middle class just like the global situation, more people are working from home. This has reduced travel needs; which before now was essential because inadequate power supply, internet connections and the large informal economy in Nigeria has often meant that people must travel daily to work. The road modal system is the most prevalent and extensively used form of transportation in Nigeria which grappling with challenges of inadequate fleets of public transport vehicles and dilapidated road networks, makes for significant concerns for the state. The population is growing fast and it has to struggle with the poor infrastructure leading to increased passenger cars and taxis on roads, which cause traffic congestion and gridlocks at peak periods; example, it is estimated the commuters lose up to 75% of their weekly working hours because of traffic congestion in Lagos [1], the busiest and commercial centre of the country.

Nigerian COVID-19 Update & Vulnerability

For situations of emergencies like epidemics, pandemics and any spontaneous or contagious situation, Nigeria is viewed as posing high vulnerability medically because of its large population; the coronavirus disease is one such situation. The dense population of some cities and thin density of facilities has led to overstrained infrastructure. All the 36 states in Nigeria had confirmed cases of COVID-19 but the number of cases and deaths varied with the highest in Lagos followed by Abuja. Earlier in 2021, following relaxation of lockdown measures round the globe, Nigeria also relaxed its tight supervision and it appeared all was getting back to normalcy on the road towards recovery. Currently, the 3rd wave of pandemic due to the Delta variant has hit many countries and figures of infections and isolations (especially from international travellers) have been rising and some panic measures and pronouncements are already being embarked upon, again primarily in Lagos. Overall, there was devastating impact on road transportation especially at the peak and immediate post-peak periods in 2020.

Commercial transportation comprising of Commuter Buses, Taxis, Tricycles also called Keke Napep) and Motorcycles (known as Okadas) comprised the main means of transportation in major Nigerian cities especially commercial hubs and state capitals. These form of transport was already one of the biggest challenges for all municipalities, especially in big metropolitan cities where people are highly concentrated at the same space at the same time before COVID-19 and in fact in some cities like the Federal Capital city of Abuja and most of Lagos, Keke Napeps and Okadas were banned because of the menace they had constituted leading to traffic congestion with high contribution to road accidents and crashes. However, though they were banned to instil organization and sanity, nonetheless they constitute essential commercial transport modes in some parts of state capitals and commercial towns/cities and almost the main transportation mode for Local Government and rural short distance movements. The BRT (Bus Rapid Transit) is a special intervention public road transport mode with a special reserved lane in Lagos while numerous agencies and organizations as well as major businesses and organizations (including construction companies) own staff buses that operate on specified routes to convey workers to and from work. With COVID-19 pandemic and social distancing consequences, proper organizational and logistical frameworks are required now that there is an ease down and workers and public commuters need to resume a measure of movements. It is not clear if commercial transportation unions, municipalities and transport operators have risen to the many challenges of organizing all passenger fluxes to serve all needs and new regulations without losing efficiency and profitability with adequate and acceptable prices for users.

Specific COVID-19 Road Transportation Impacts

Overall COVID-19 pandemic impact on transportation in Nigeria can be evaluated in the context of the developing countries bedevilled by economic and social difficulties that preceded the pandemic; and the experience may suggest a need for new and different policies in the sector. Experience clearly presents practical implications for public and private sector policymakers, as the country navigates this precarious time and charts a new path for individuals and Nigeria. The influence of COVID-19 extended from the economic to the social and religious activities which are the key factors that have confirmed why and how transportation in all highly affected towns and states became disruptive and consequential. The influence of COVID-19 on transportation can be assessed based on the dynamic changes to the commuters’ transport demands and relative fare prices during the pandemic, the operators’ expected revenue or income structures and the loss in government revenues, which is loss emanating from taxes, tickets and other related government transport income generations sources. At the peak periods, the scale of the global pandemic, as well as the limited social contact and government lockdown restrictions, dictates that research projects requiring fieldwork or sampling be based on convenient procedure as preferred method of gathering data such as gsm, e-mailing, audio phoning and other communication techniques. Convenience sampling procedure involves non-randomised experimentation and relies mainly on individual respondents or groups of respondents that are nearby or easy to reach. Economic activities, social activities and religious activities during COVID-19 were impacted differently by the disrupted transport services due to the pandemic.

Road transportation impact on the economy

As residents could not travel, as usual, a significant impact caused by the pandemic on their economic activities became a major consequence. The informal economic sector is enormous in Nigeria accounting for as much as 65% of the economy in some towns, cities and states. These economic activities include trading, transportation, construction, food preparation, mechanical and electrical work, fashion design and hairdressing, all dependent on travel and some form of road movements to undertake and they require some form of human physical presence. There are those who hawk and sell goods in traffic, operate Uber and other forms of transportation or must travel to provide services who can no longer engage in these activities, thereby impacting negatively on the economy. These businesses are managed by low-income selfemployed owners operating in a mostly cash-dominated society; and they must leave their homes daily to earn an income. To these, in addition to lockdown barring free movements, increased cost of transportation, shortage/lack of transportation mode and traffic congestion have been major impact of COVID-19 on Transportation. The scenario was that there were few fleets of public transport in periods of lockdown with many people wishing to travel. With the demand for transportation being greater than the supply, due to lock down and restriction, the transporters increased their fares. The chain-mail effect is that this high cost of transportation then added to the overall cost of living in towns and cities in particular. Similarly, the cost of food items increased.

Road transportation impact on social and religious activities

Religious activities, which seem such essential part of life, Nigeria being the 6th largest Christian population (87 million) and 5th largest Muslim population (90 million) in the world [2], suffered due to the challenges of COVID-19, especially the social distancing regulation. Regularly, thousands of worshippers travel to different worship centres, and due to the lockdown, this movement was affected. In 2020, the Christian Easter and Muslim Ramadan seasons both fell in the peak COVID-19 lockdown period and many worshippers could not typically travel to places of worship. In a secular sense, religion may be considered a social activity but then disruption in transport services due to the pandemic impacted badly on social and some essential activities like leisure, typical shopping and visits (example to friends and other family members). It may be recalled that at certain periods, partial curfews were required to curb movement. In typical social orientation of many Nigerians, many people like to socialise in the evenings and weekends, visit clubs and attend parties; which the restrictions on transportation impacted. Nigerian collectivistic society habits where there is a fundamental value in a long-term commitment to groups suffered. Many people who wished to check on their friends or volunteer to distribute palliative cares to friends and neighbours were prevented from their practices by restrictions and the lack of transportation impacted upon their desires.

Pandemic Research Challenges on Road Transport Research

Indeed, the Nigerian road transportation sector faced challenges especially on the need to cope with the potential disruption caused by the pandemic and a national lockdown that lasted from 4-6 months. Unfortunately, the provision of road services, and the requirement to ensure the proper operation and maintenance, often goes unnoticed even if disregarded by national authorities because until there is an emergency before fire-brigade interventions and approaches are designed. But we have discussed already that there were strong negative impacts of the pandemic on levels of traffic [3,4]. Strong spontaneous government regulatory response in line with WHO and other global dictations were quite visible primarily to stop spread of coronavirus, cure those infected and get as many vaccinated as possible. But then a large measure of road transportation response was left to the operators essentially characterised by panic reactions to government social distancing and lockdown measures, curfews and sets of related regulations and guidelines. Little road transportation engineering and management, internal business management, and overall economic impact measures may have been in the minds of the operators except complains about the devastating economic effects. Government itself and the transport operators were hardly prepared for such an event and became more focused on prioritising their survival strategies and lobbying for interventions and relief packages. However sustainable engineering approaches and responses must be made to learn and develop schemes that can be applied in case of new waves and future similar events in Nigeria and other emerging economies of Africa and the world. Challenges for public transportation should be viewed in terms of consequences and possible alternatives for the Covid-19 pandemic through strategic precision- application [5].

A lot of city/urban and even rural challenges have to do with coping with peak hour traffic periods when workers have to go to work and student/school children commute to school, and later return to their homes. With COVID-19 pandemic and social distancing consequences, mass transportation became actually the main barrier for students and workers who are all highly dependent on transport to go back to their daily routines with comfort and safety. Thus, the objective of a good research would be to determine a demand control able to equalize the number of passengers in each car, respecting the COVID-19 social distancing protocols. The number of passengers in each time-of-day range should be combined into suitable predictive models that include independent variables related to passenger’s behavior indicating that almost 90% of all passengers are following a very strict and straight daily routine that can be coordinated and scheduled creating enough time space one from the other to avoid undesirable concentrations inside buses and bus stops. In a sense therefore, a very accurate urban management tool can arise from the study and may be able to solve not only the pandemic issues but also to improve local public services efficiency, to attract private investments and to improve citizen’s quality of life [6,7].

In Nigeria, public transport being exclusively comprised of private bus operators with a measure of regulation by traffic control officers and the police, research needs to be planned by reorganizing daily routines and schedules to move people from their points of origin to their destinations in a real time demand coordination to avoid crowding and time and money losses. Therefore, studies should seek to answer such research queries that: Observe and find any patterns in passengers’ daily behaviour; and, determining the main variables responsible for passenger’s decision to take public transportation or ride in their own cars, with other modal systems relatively undeveloped. From these preliminary results, the research question would then arise whether it is possible to determine the demand for public transport to organize it so as not to create agglomerations in times of pandemic. Thus, the objective would be to determine a demand control able to equalize the number of passengers in each car, respecting the COVID-19 social distancing protocols. In the tight options available to commuters in Nigeria, it is possible that many passengers can switch from private cars to public transport to private cars and vice versa and some decisions are likely to cause instability in demand, leading to increasing traffic congestion, pollution and time loss. The Nigerian situation also proves that crowding in public transport systems have implications for the estimation of demand. Rider characteristics must also be considered and included in the model in order to stimulate coordinated supportive policies able to attract passengers to public transport.

Daily information must be collected and collated for the most critical routes susceptible to high traffic, congestion and road crashes/accidents. In terms of research methodology, the number of passengers in each day range time must be combined in different models that include independent variables like time of day, weather conditions, the structure of traffic especially bus and other vehicular type and other binary general variables like school day, pay day and crime; indicating that almost 90% of all passengers follow very strict and straight daily routine, mostly, from their houses up to school and work and back, that can be coordinated and scheduled creating enough time space one from the other to avoid undesirable concentrations inside buses and bus stops due to COVID-19 pandemic [8].

A project that must be adequate to be applied as the study objective will not only be to create a management tool capable to predict demand but also to organize passenger trips, scheduling it according to their daily appointments in order to have buses and other traffic capacity in an optimal usage level for users and operators. This way, the outcome can contribute to a sustainable public transport model and system in the future, respecting not only the number of persons allowed per car but also taking in consideration of other important indicators like fee and gas prices, weather conditions and other alternative transport offers. We must not also lose foresight that the use of gasoline may come to an end sooner than expected, like in 2035, so that we can factor in the place of e-vehicles in our researches [9].

Conclusion

Overall COVID-19 pandemic impact on transportation in Nigeria can be evaluated in the context of the developing countries bedevilled by economic and social difficulties that preceded the pandemic. The unique scenario is that there is overcrowding in urban centres usually likely with unhygienic communal or worksite accommodation and transported to and from the workplace packed in small buses or personal cars, the population presents vulnerable easy target for pandemics, especially the coronavirus. Yet the response, with Nigeria as case-study, has mostly simply been a government magnification of WHO and other countries’ suggestions that are spontaneously adhered to by the population without research and modifications to suit peculiar circumstances. In the end, there is hardly any analysis on how to balance economic interests and public health risks, public transport operators being on the receiving end. Indeed, the effect on the disproportionately dominant road transportation sector is devastating, translating to dramatic and devastating chainmail harm on the economy and social activities of the population. But if properly constructed research studies are articulated and conducted, results can be obtained whose outcomes will lead to earlier and faster transportation recoveries and application to solve future situations of similar proportions. Therefore as the current pandemic is being fought to conclusion, it is recommended that our traffic and transportation models be studied and prepared for emergencies, while specific route studies are initiated, convenient pandemic-suitable methodologies identified and schemes worked out for any future situation scale and devastation of the COVID-19 pandemic. The experience may suggest a need to examine the road transportation sector for new and different policies in place of a clueless and nonchalant attention

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Research Challenges for Nigerian Road Transportation Sector in Covid-19 Pandemic Era

Authored by Danladi Slim Matawal

Introduction

The growing number of studies on the impact of COVID-19 is often chosen in the context of developed countries, highlighting a gap in the understanding of how the pandemic is impacting developing countries. There is need to acknowledge the effect/ impact on transportation in emerging economies where lockdowns and restrictions on movement may not be wholly ineffective but even more suited to the level of psychological response of the people. There is not just poor transportation infrastructure but also lack of a clearly defined transportation system that is effectively managed and regulated by operators while the economy is largely informal. The outbreak of the COVID-19 coronavirus was deemed a pandemic by the World Health Organization (WHO) on 11th March 2020. To date, there have been cases confirmed in at least 203 countries, areas or territories, causing unprecedented measures to be taken by many countries, such as travel restrictions and restrictions on social gatherings. Nigeria is a key regional actor in the African continent with over 200 million people, and it confirmed its first case in Lagos in February 2020.

The emerging economy faces institutional adversity with underlying and persistent economic challenges as it copes with the pandemic and both effect and responses have varied widely in the country. Virtual lives have essentially been instituted for the upper and middle class just like the global situation, more people are working from home. This has reduced travel needs; which before now was essential because inadequate power supply, internet connections and the large informal economy in Nigeria has often meant that people must travel daily to work. The road modal system is the most prevalent and extensively used form of transportation in Nigeria which grappling with challenges of inadequate fleets of public transport vehicles and dilapidated road networks, makes for significant concerns for the state. The population is growing fast and it has to struggle with the poor infrastructure leading to increased passenger cars and taxis on roads, which cause traffic congestion and gridlocks at peak periods; example, it is estimated the commuters lose up to 75% of their weekly working hours because of traffic congestion in Lagos [1], the busiest and commercial centre of the country.

Nigerian COVID-19 Update & Vulnerability

For situations of emergencies like epidemics, pandemics and any spontaneous or contagious situation, Nigeria is viewed as posing high vulnerability medically because of its large population; the coronavirus disease is one such situation. The dense population of some cities and thin density of facilities has led to overstrained infrastructure. All the 36 states in Nigeria had confirmed cases of COVID-19 but the number of cases and deaths varied with the highest in Lagos followed by Abuja. Earlier in 2021, following relaxation of lockdown measures round the globe, Nigeria also relaxed its tight supervision and it appeared all was getting back to normalcy on the road towards recovery. Currently, the 3rd wave of pandemic due to the Delta variant has hit many countries and figures of infections and isolations (especially from international travellers) have been rising and some panic measures and pronouncements are already being embarked upon, again primarily in Lagos. Overall, there was devastating impact on road transportation especially at the peak and immediate post-peak periods in 2020.

Commercial transportation comprising of Commuter Buses, Taxis, Tricycles also called Keke Napep) and Motorcycles (known as Okadas) comprised the main means of transportation in major Nigerian cities especially commercial hubs and state capitals. These form of transport was already one of the biggest challenges for all municipalities, especially in big metropolitan cities where people are highly concentrated at the same space at the same time before COVID-19 and in fact in some cities like the Federal Capital city of Abuja and most of Lagos, Keke Napeps and Okadas were banned because of the menace they had constituted leading to traffic congestion with high contribution to road accidents and crashes. However, though they were banned to instil organization and sanity, nonetheless they constitute essential commercial transport modes in some parts of state capitals and commercial towns/cities and almost the main transportation mode for Local Government and rural short distance movements. The BRT (Bus Rapid Transit) is a special intervention public road transport mode with a special reserved lane in Lagos while numerous agencies and organizations as well as major businesses and organizations (including construction companies) own staff buses that operate on specified routes to convey workers to and from work. With COVID-19 pandemic and social distancing consequences, proper organizational and logistical frameworks are required now that there is an ease down and workers and public commuters need to resume a measure of movements. It is not clear if commercial transportation unions, municipalities and transport operators have risen to the many challenges of organizing all passenger fluxes to serve all needs and new regulations without losing efficiency and profitability with adequate and acceptable prices for users.

Specific COVID-19 Road Transportation Impacts

Overall COVID-19 pandemic impact on transportation in Nigeria can be evaluated in the context of the developing countries bedevilled by economic and social difficulties that preceded the pandemic; and the experience may suggest a need for new and different policies in the sector. Experience clearly presents practical implications for public and private sector policymakers, as the country navigates this precarious time and charts a new path for individuals and Nigeria. The influence of COVID-19 extended from the economic to the social and religious activities which are the key factors that have confirmed why and how transportation in all highly affected towns and states became disruptive and consequential. The influence of COVID-19 on transportation can be assessed based on the dynamic changes to the commuters’ transport demands and relative fare prices during the pandemic, the operators’ expected revenue or income structures and the loss in government revenues, which is loss emanating from taxes, tickets and other related government transport income generations sources. At the peak periods, the scale of the global pandemic, as well as the limited social contact and government lockdown restrictions, dictates that research projects requiring fieldwork or sampling be based on convenient procedure as preferred method of gathering data such as gsm, e-mailing, audio phoning and other communication techniques. Convenience sampling procedure involves non-randomised experimentation and relies mainly on individual respondents or groups of respondents that are nearby or easy to reach. Economic activities, social activities and religious activities during COVID-19 were impacted differently by the disrupted transport services due to the pandemic.

Road transportation impact on the economy

As residents could not travel, as usual, a significant impact caused by the pandemic on their economic activities became a major consequence. The informal economic sector is enormous in Nigeria accounting for as much as 65% of the economy in some towns, cities and states. These economic activities include trading, transportation, construction, food preparation, mechanical and electrical work, fashion design and hairdressing, all dependent on travel and some form of road movements to undertake and they require some form of human physical presence. There are those who hawk and sell goods in traffic, operate Uber and other forms of transportation or must travel to provide services who can no longer engage in these activities, thereby impacting negatively on the economy. These businesses are managed by low-income selfemployed owners operating in a mostly cash-dominated society; and they must leave their homes daily to earn an income. To these, in addition to lockdown barring free movements, increased cost of transportation, shortage/lack of transportation mode and traffic congestion have been major impact of COVID-19 on Transportation. The scenario was that there were few fleets of public transport in periods of lockdown with many people wishing to travel. With the demand for transportation being greater than the supply, due to lock down and restriction, the transporters increased their fares. The chain-mail effect is that this high cost of transportation then added to the overall cost of living in towns and cities in particular. Similarly, the cost of food items increased.

Road transportation impact on social and religious activities

Religious activities, which seem such essential part of life, Nigeria being the 6th largest Christian population (87 million) and 5th largest Muslim population (90 million) in the world [2], suffered due to the challenges of COVID-19, especially the social distancing regulation. Regularly, thousands of worshippers travel to different worship centres, and due to the lockdown, this movement was affected. In 2020, the Christian Easter and Muslim Ramadan seasons both fell in the peak COVID-19 lockdown period and many worshippers could not typically travel to places of worship. In a secular sense, religion may be considered a social activity but then disruption in transport services due to the pandemic impacted badly on social and some essential activities like leisure, typical shopping and visits (example to friends and other family members). It may be recalled that at certain periods, partial curfews were required to curb movement. In typical social orientation of many Nigerians, many people like to socialise in the evenings and weekends, visit clubs and attend parties; which the restrictions on transportation impacted. Nigerian collectivistic society habits where there is a fundamental value in a long-term commitment to groups suffered. Many people who wished to check on their friends or volunteer to distribute palliative cares to friends and neighbours were prevented from their practices by restrictions and the lack of transportation impacted upon their desires.

Pandemic Research Challenges on Road Transport Research

Indeed, the Nigerian road transportation sector faced challenges especially on the need to cope with the potential disruption caused by the pandemic and a national lockdown that lasted from 4-6 months. Unfortunately, the provision of road services, and the requirement to ensure the proper operation and maintenance, often goes unnoticed even if disregarded by national authorities because until there is an emergency before fire-brigade interventions and approaches are designed. But we have discussed already that there were strong negative impacts of the pandemic on levels of traffic [3,4]. Strong spontaneous government regulatory response in line with WHO and other global dictations were quite visible primarily to stop spread of coronavirus, cure those infected and get as many vaccinated as possible. But then a large measure of road transportation response was left to the operators essentially characterised by panic reactions to government social distancing and lockdown measures, curfews and sets of related regulations and guidelines. Little road transportation engineering and management, internal business management, and overall economic impact measures may have been in the minds of the operators except complains about the devastating economic effects. Government itself and the transport operators were hardly prepared for such an event and became more focused on prioritising their survival strategies and lobbying for interventions and relief packages. However sustainable engineering approaches and responses must be made to learn and develop schemes that can be applied in case of new waves and future similar events in Nigeria and other emerging economies of Africa and the world. Challenges for public transportation should be viewed in terms of consequences and possible alternatives for the Covid-19 pandemic through strategic precision- application [5].

A lot of city/urban and even rural challenges have to do with coping with peak hour traffic periods when workers have to go to work and student/school children commute to school, and later return to their homes. With COVID-19 pandemic and social distancing consequences, mass transportation became actually the main barrier for students and workers who are all highly dependent on transport to go back to their daily routines with comfort and safety. Thus, the objective of a good research would be to determine a demand control able to equalize the number of passengers in each car, respecting the COVID-19 social distancing protocols. The number of passengers in each time-of-day range should be combined into suitable predictive models that include independent variables related to passenger’s behavior indicating that almost 90% of all passengers are following a very strict and straight daily routine that can be coordinated and scheduled creating enough time space one from the other to avoid undesirable concentrations inside buses and bus stops. In a sense therefore, a very accurate urban management tool can arise from the study and may be able to solve not only the pandemic issues but also to improve local public services efficiency, to attract private investments and to improve citizen’s quality of life [6,7].

In Nigeria, public transport being exclusively comprised of private bus operators with a measure of regulation by traffic control officers and the police, research needs to be planned by reorganizing daily routines and schedules to move people from their points of origin to their destinations in a real time demand coordination to avoid crowding and time and money losses. Therefore, studies should seek to answer such research queries that: Observe and find any patterns in passengers’ daily behaviour; and, determining the main variables responsible for passenger’s decision to take public transportation or ride in their own cars, with other modal systems relatively undeveloped. From these preliminary results, the research question would then arise whether it is possible to determine the demand for public transport to organize it so as not to create agglomerations in times of pandemic. Thus, the objective would be to determine a demand control able to equalize the number of passengers in each car, respecting the COVID-19 social distancing protocols. In the tight options available to commuters in Nigeria, it is possible that many passengers can switch from private cars to public transport to private cars and vice versa and some decisions are likely to cause instability in demand, leading to increasing traffic congestion, pollution and time loss. The Nigerian situation also proves that crowding in public transport systems have implications for the estimation of demand. Rider characteristics must also be considered and included in the model in order to stimulate coordinated supportive policies able to attract passengers to public transport.

Daily information must be collected and collated for the most critical routes susceptible to high traffic, congestion and road crashes/accidents. In terms of research methodology, the number of passengers in each day range time must be combined in different models that include independent variables like time of day, weather conditions, the structure of traffic especially bus and other vehicular type and other binary general variables like school day, pay day and crime; indicating that almost 90% of all passengers follow very strict and straight daily routine, mostly, from their houses up to school and work and back, that can be coordinated and scheduled creating enough time space one from the other to avoid undesirable concentrations inside buses and bus stops due to COVID-19 pandemic [8].

A project that must be adequate to be applied as the study objective will not only be to create a management tool capable to predict demand but also to organize passenger trips, scheduling it according to their daily appointments in order to have buses and other traffic capacity in an optimal usage level for users and operators. This way, the outcome can contribute to a sustainable public transport model and system in the future, respecting not only the number of persons allowed per car but also taking in consideration of other important indicators like fee and gas prices, weather conditions and other alternative transport offers. We must not also lose foresight that the use of gasoline may come to an end sooner than expected, like in 2035, so that we can factor in the place of e-vehicles in our researches [9].

Conclusion

Overall COVID-19 pandemic impact on transportation in Nigeria can be evaluated in the context of the developing countries bedevilled by economic and social difficulties that preceded the pandemic. The unique scenario is that there is overcrowding in urban centres usually likely with unhygienic communal or worksite accommodation and transported to and from the workplace packed in small buses or personal cars, the population presents vulnerable easy target for pandemics, especially the coronavirus. Yet the response, with Nigeria as case-study, has mostly simply been a government magnification of WHO and other countries’ suggestions that are spontaneously adhered to by the population without research and modifications to suit peculiar circumstances. In the end, there is hardly any analysis on how to balance economic interests and public health risks, public transport operators being on the receiving end. Indeed, the effect on the disproportionately dominant road transportation sector is devastating, translating to dramatic and devastating chainmail harm on the economy and social activities of the population. But if properly constructed research studies are articulated and conducted, results can be obtained whose outcomes will lead to earlier and faster transportation recoveries and application to solve future situations of similar proportions. Therefore as the current pandemic is being fought to conclusion, it is recommended that our traffic and transportation models be studied and prepared for emergencies, while specific route studies are initiated, convenient pandemic-suitable methodologies identified and schemes worked out for any future situation scale and devastation of the COVID-19 pandemic. The experience may suggest a need to examine the road transportation sector for new and different policies in place of a clueless and nonchalant attention

To read more about this article: https://irispublishers.com/gjes/fulltext/research-challenges-for-nigerian-road-transportation-sector-in-covid-19-pandemic-era.ID.000685.php

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On Computational Modeling and Analysis of Transonic Aerodynamics

Authored by Jun Yu

Introduction

There has been considerable amount of researches conducted on the studies of transonic aerodynamics due to its use in airplane wing design. Using a general theory of expansion procedures, transonic flow past slender bodies and thin wings is investigated [1]. Asymptotic expansions with appropriate limiting procedures reduce the full equations to an approximation involving the steady transonic small-disturbance (TSD) equation. Expansion procedures of thin airfoil theory at various Mach numbers can be found in Section 5.3 of [2]. The TSD equation is mathematically interesting as the freestream Mach number approaching to unity it becomes a partial differential equation of mixed type (elliptic and hyperbolic). This creates a challenge for obtaining solution of the equation. There are several theoretical and computational methods based on the hodograph method. A series of interesting results for mixed subsonic-supersonic, shock-free flows are obtained in [3, 4]. Magnus and Yoshihara [5] computed mixed flows with shock waves by integrating the equations of unsteady compressible flow forward in time to approach a steady state. With a newly developed mixed finite difference method and a line relaxation algorithm, the transonic case of the equation is solved with shock waves that appear naturally [6]. Later, Murman [7] investigated the requirements for uniqueness of the calculated jump conditions across embedded shock waves and created the conservative Murman-Cole numerical method. The non-uniqueness of numerical solutions of potential equations at transonic speeds has been found to be related to the stability of the problem [8,9]. Kuzmin [10] reviewed all the solutions in detail where it was stated that all airfoils considered were long and flat with instability attributed to the rupture of supersonic regions.

Procedures have been developed for solving the TSD equations and full potential equations for two-dimensional and axisymmetric bodies and for the TSD equations for three-dimensional wings [11]. There are many notable extensions of the steady TSD equation model. We show just a few here. First, theoretical, and numerical studies of transonic flow of moist air around a thin airfoil are carried out [12-14]. In [14], steady TSD equation model with moist air and condensation on a thin airfoil is solved in order to investigate changes in the flow field by homogeneous nucleation of water and heat addition. Secondly, implicit methods, using successive line over-relaxation, alternating-direction and approximate factorization techniques, are adopted for solving the unsteady TSD equations [15-17]. Thirdly, a new small-disturbance model for a steady, lean, premixed combustion at transonic speeds in a channel of slightly varying area is presented in [18]. Finally, the TSD equations are coupled with aeroelastic solution in order to study the fluid-structure interactions [19, 20].

Approximate Factorization Algorithm

To solve the unsteady TSD equations, explicit time-marching schemes were found to impose severe restrictions on the time step due to stability. Implicit schemes are thus adopted. The approximate factorization (AF) technique in [17], for example, is a time accurate algorithm formulated for solution of the threedimensional unsteady TSD equation. The AF algorithm involves a time linearization procedure coupled with a Newton iteration technique. More specifically, for unsteady flow calculations, the solution procedure involves two steps. First, a time linearization step is performed to determine an estimate of the potential field. Second, Newton Iterations are performed to provide the time accuracy. To do that, the TSD equation is written in a general form as a nonlinear function of the unknown potentials at time level (n+1). The Newton iteration solution is then given by the first order Taylor series with the estimated potentials from the first step as the initial guess. Superior stability properties of the algorithm are demonstrated through applications to steady and oscillatory flows at subsonic and supersonic freestream conditions for an F-5 fighter wing. The AF algorithm is also shown to be efficient. It can provide accurate solutions in only several hundred-time steps, yielding a significant computational cost savings when compared to alternative methods. For reasons of practicality and affordability, an efficient algorithm and a fast computer code are requirements for realistic aircraft applications.

Several algorithm modifications have been made which have improved the stability of the AF algorithm and the accuracy of the results [21, 22]. A Computational Aeroelasticity Program - Transonic Small Disturbance (CAP-TSD) code permits the calculation of steady and unsteady flows about complete aircraft configurations for aeroelastic analysis in the flutter critical transonic speed range [19]. This CAP-TSD code uses the AF algorithm for solution of the unsteady TSD potential equation with five modifications: (1) an Engquist-Osher (E-0) [21] type-dependent switch to treat regions of supersonic flow, (2) extension of the E-0 switch for secondorder spatial accuracy, (3) nonisentropic effects to treat strongshock cases, (4) nonreflecting far field boundary conditions for unsteady applications, and (5) several modifications to accelerate convergence to steady state. Calculations are presented for several configurations including the General Dynamics one-ninth scale F-16C aircraft model to evaluate the modified algorithm. These modifications have been shown to significantly improved the stability of the AF algorithm and hence the reliability of the CAP-TSD code in general. Calculations are also presented from a flutter analysis of a 45” sweptback wing which agree well with the experimental data. The results and comparisons demonstrate the stability, accuracy, efficiency, and utility of CAP-TSD.

Conclusion

For steady TSD equations, mixed finite difference method with a line relaxation captures the embedded shock waves for the transonic case. For unsteady TSD equations, AF algorithm coupled with computational aeroelasticity program provided accurate and efficient solution for engineering design applications. Comparisons to experimental data serves as a check for the computational methods and it also provides clues for algorithm invention and modifications.

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The Contribution of Sedimentological Studies to River Engineering Projects in Khuzestan Province, Iran

Authored by A Barjasteh

Introduction

Khuzestan Province in the southwest of Iran has the longest and largest rivers of the country (Figure 1). Accordingly, river engineering studies including sedimentological and geomorphological investigations are of especial concern in the province. Erosion and weathering of easily erodible geological formations particularly evaporitic ones in the region is a significant problem that could affect the projects. This is due to the impact of erosion on river morphology. However, most of these studies are concentrated on hydraulic aspects of sedimentation and little has been devoted to sedimentary geology of river sediments. In this regard some of the related projects related could not attain their forecasted aims.

Geological Setting

The Zagros Fold Belt in the northeast of the Persian Gulf is a branch of the Alpine-Himalayan Orogenic belt divided into different structural or morphotectonic zones [1-3]. The study area is located in the middle of the Simply Folded Belt [4], being comprised of parallel, long anticlines and synclines; the former shows topographic crest lines, while the latter coincides with the trough lines. The most outcropped lithologies in the area as part of the Simply Folded Belt are of Post–Miocene age including, from older to younger, Asmari Limestones, Gachsaran Evaporites, Mishan Marlstones, Agha Jari Sandstones, Bakhtiari Conglomerates and Quaternary deposits. The folding trend is northwest–southeast and the system is composed of elongated whaleback or box-shaped anticlinal mountains. In addition to gently dipping over-thrusts, folds are dissected also by sub-vertical normal and strike-slip faults. From a geomorphological viewpoint, the anticlines can be divided into two sets: plain anticlines and mountain anticlines. The lithological exposure in the former is mostly limited to Post– Miocene formations while in the latter the outcrops are mainly of Pre-Miocene formations. Morphotectonic studies indicate a fairly relationship between the geologic structure and morphology of the region [5-8].

River Engineering Studies

River engineering projects in Khuzestan Province are mainly aimed at the following subjects: dam sedimentation, flood control, sand mining, protection and maintenance of river training structures and partly navigation purpose. Existence of five largest and longest rivers of country in the province namely, Karun, Dez, Marun, Karkheh and Zohreh rivers necessitated comprehensive sedimentological and geomorphological investigations in the region. Regarding to this fact, a good knowledge of erosion and weathering aspects of the outcropped formations is vital. As noted previously, some of the formations have very week and easily erodible lithology and produce a large amount of sediments annually. Among them, Gachsaran Formation is almost of most importance due to its evaporitic layers consisting of salt, gypsum, anhydrite and marl. It has been shown that river morphology and geometry of river course affect sedimentation process. The morphology of the streams in the Zagros Fold–Thrust Belt has been previously studied and its relation to the regional tectonics has been proved [3,6,8,10- 12]. Observation of satellite image, measurement of morphological parameters and field surveys show such a relationship. In the studied region, at least two main geomorphic features regarding to the channel course of the rivers can be seen [9]. The river trunks are mainly aligned with the Zagros trends (saying northwestsoutheast trend) whereas the small and much local parts mostly coincide with an east-west and partly the Arabian trends (that is predominantly north-south trending). Riverbank erosion is closely related to the velocity of flow in the river channel [13-15]. The alignment of the rivers with structural trends influences type of sediments as these river courses are mostly identified as straight channels and are deeper and narrower than others so their flow velocity is usually higher and less sediments can be deposited on the riverbed. On the other hand, these straight channels commonly have steeper walls and more potential to erosion and weathering. The amount of sediment load carried by the river is important as it affects riverbank erosion. If sediment load of river decreases below its transport capacity, the river tends to erode its banks and bed to keep its balanced regime. This is mostly seen in straight streams which run through structurally controlled courses.

Conclusion

Due to obvious role of formation lithology and river morphology on sediment type, petrographic and sedimentological investigations should be more considered in investigations related to river engineering projects. Erosion and weathering of easily erodible geological formations in the studied region is a significant problem that could affect the projects. Besides, riverbanks erosion is dependant on the velocity of flow in the river channel that is in turn influenced by geological structural trends. River engineering studies in Khuzestan Province of southwest Iran are more concentrated on sediment hydraulics and less attention has been paid to sedimentary petrology of river deposits Thus, more studies should be conducted to complement other relevant investigations.

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Disturbances of Ozone Layer and Radio Wave Absorption in D-Region of Ionosphere of the Earth During Solar Proton Event: Simulations with СHARM-I Model

Authored by Alexei Krivolutsky

As it is well known [1], the high-energy solar particles (mainly solar protons), with an energy of several to 500 MeV, enter into the Earth’s stratosphere and mesosphere only in polar regions. For the first time the sharp decrease of the ozone and ion content in e stratosphere was detected on board the American Nimbus-4 satellite in course of one of the strongest flares on the Sun (August 4, 1972) [2]. As the theoretical analysis has shown, the highenergy particles intrusion in polar atmosphere produced oxides of nitrogen (NOx), hydrogen (HOx), and some ions, which destroy ozone in catalytic chemical cycles and increases electron density in polar region. Important steps were made with satellite missions NASA UARS (with HALOE instrument) and European ENVISAT (with MIPAS instrument). Basing on the ENVISAT measurements of ozone and other small gas components, the international project HEPPA (High Energy Particle Precipitation in the Atmosphere) was arranged [3]. This project involved 10 research groups including Russian teams from the Central Aerological Observatory (CAO, Moscow). As a result, the model computations were fulfilled which have demonstrated the well correspondence with data of satellite measurements during the solar flare in October 2003.

In this work we used global 3D numerical photochemical model CHARM-I (Chemical Atmospheric Research Model with Ions) [4] and satellite observations of solar proton fluxes to investigate the response of neutral and ion composition to strong SPEs of July14 2000 and October28 2003.We should mention that changes in D-region of ionosphere induced by solar particles should leads to the changes in radio wave absorption in polar region

CHARM-I Model Short Description

Neutral chemical compounds

To describe the global photochemical processes taking place in the Earth’s atmosphere, the numerical Chemical Atmospheric Research Model with Ions (CHARM-I) was elaborated in the Laboratory of Atmospheric Chemistry and Dynamics of CAO. The CHARM-I model used the “splitting method” that makes it possible to describe independently processes of advective transport and photochemical processes. Ions are calculated under suppose that the sum of ions is zero. One of the most accurate methods, the Prater’s method, is applied to describe the transfer processes. The corresponding velocity components were calculated using the general circulation model [5]. The method of” chemical families”, proposed in the work [6], was used while integrating this system with equations of chemical kinetics, which belongs to the so-called “rigid systems”. The “rigidity” of systems of the chemical kinetics equations is manifested in this case in a large range of values of the characteristic “lifetimes” of chemical components (from fractions of a second to hundreds of years), which would require very small time steps of integration. The method of “families” makes it possible to significantly remove the “rigidity” of the system and considerably increase the time step. The photochemical block of the model describes the interaction between the 41st chemical components involved in 127 photochemical reactions. The following chemical components were calculated in the model.

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