Structural Engineering
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Item Replacement of River Sand by Idaga Hamus Crushed Sandstone Sand in Reinforced Concrete and Hollow Concrete Block Production(Addis Ababa University, 2024-05) Fitsum Reda; Girma Zerayohannes (PhD)This study aims to investigate crushed sandstone sand (CSS) in Concrete and hollow concrete block (HCB) properties as replacement of RS material. It was conducted by taking samples of CSS from Idaga Hamus, and RS from Gereb Giba quarry sites. The significance of blending CSS with RS materials using several laboratory tests were investigated. Total 36 samples of 15cmx15cmx15cm cubic concrete at 7th, 14th, and 28th days of curing period for compressive strength of concrete, 9 samples 50cmx15cmx15cm beams for flexural strength of concrete with mix ratio of 1:2:3, and water to cement ratio 0.50 for 0% and 50% replacement of CSS and 0.55 for 75% and 100% replacement of CSS, and 24 samples of HCB at 7th day curing period were prepared and tested. The test results on the specimens showed that the concrete and HCB manufactured using CSS as a partial and full replacement of RS have all strength, and density requirements specified in Ethiopian Standard ES 596:2001. It can be concluded from the study that CSS can readily to be used as a replacement for RS, in Concrete and HCB as far as the quantity and procedures in this study are followed. Commercial sand production from the sandstone could also be taken as a potential solution for RS shortage. The RS replaced by 100% of CSS greatly improves the physical and mechanical behaviors of concrete and HCB. The amount in percentage of silt content, and clay content in CSS and RS has been widely investigated. The significance of the replacement of CSS to RS concrete with the characteristic strength of concrete C-25 and HCB were studied in mixtures prepared with constant workability. Compared to RS, CSS has better quality consistency and higher Strength in concrete. The manufactured CSS that is available in Idaga Hamus is well-graded. The strength properties of concrete were investigated with 0%, 50%, 75%, and 100% replacement of RS by CSS for C-25 mix proportion of concrete and 40cmx20cmx20cm, dimension of HCB. There is a 15.4927% increment in the relative compressive strength of concrete, and a 13.226% increase the relative flexural strength of concrete with 100% replaced of CSS at the 28th day of curing period compared with conventional concreteItem Investigation of Mechanical Properties of Concrete with Aspect Ratio of Pineapple Leaf Fibers(Addis Ababa University, 2023-09) Tewodros Tilahun; Adil Zekaria (PhD0The paper aims to investigate the influence of incorporating PALF (pineapple leaf fiber) on the mechanical properties of concrete, with a particular focus on the aspect ratio of PALF. This study has to search thoroughly into how varying the aspect ratio of PALF affects the overall performance of concrete as a construction material. The research methodology involves incorporating different aspect ratios of PALF into concrete mixtures, followed by a thorough examination of the resulting mechanical properties. The aspect ratio, which is the ratio of the length to the diameter or width of the PALF fibers, is a critical parameter to study because it can significantly impact the behavior of the composite material. The study will employ various mechanical tests, such as tensile strength, compressive strength and flexural strength, to assess how the different aspect ratios of PALF affect these properties. Additionally, the work will investigate the durability and long-term performance of concrete with PALF reinforcements, considering factors like moisture absorption and aging. Furthermore, the paper will investigate into the implications of the findings for practical applications in the construction industry. Understanding how the aspect ratio of PALF influences concrete's mechanical properties can provide valuable insights for designing sustainable and highperformance concrete composites. In addition to the investigation of PALF's impact on concrete properties, this research shows the influence of sodium hydroxide (NaOH) treatments on enhancing PALF's properties. These treatments are important to mitigate the hydrophilic nature of the fibers, thereby improving their compatibility with hydrophobic fibers within the concrete matrix. The study systematically analyzes the effects of different concentrations of NaOH on the PALF fibers, specifically Alkali 1 wt., Alkali 2 wt., Alkali 4 wt., and Alkali 8 wt. The concrete samples are subjected to testing at different time intervals: the 7th day (representing the initial stage) and the 28th day (representing the final settling period). Moreover, this investigation is carried out in conjunction with varying aspect ratios of PALF, which include 150, 450, 750, and 1050. the result show that 150 is shown an incremental improvement when compared to the control mix and 450 is the optimum amount of PALF to enhance all three mechanical properties in the other way 1050 aspect ratio showing a significant decrease in strength and the 750 aspect ratio exhibiting a decline compared to the control mix.Item Investigation of Mechanical Properties of Concrete with Aspect Ratio of Pineapple Leaf Fibers(Addis Ababa University, 2023-09) Tewodros Tilahun; Adil Zekaria (pHd)The paper aims to investigate the influence of incorporating PALF (pineapple leaf fiber) on the mechanical properties of concrete, with a particular focus on the aspect ratio of PALF. This study has to search thoroughly into how varying the aspect ratio of PALF affects the overall performance of concrete as a construction material. The research methodology involves incorporating different aspect ratios of PALF into concrete mixtures, followed by a thorough examination of the resulting mechanical properties. The aspect ratio, which is the ratio of the length to the diameter or width of the PALF fibers, is a critical parameter to study because it can significantly impact the behavior of the composite material. The study will employ various mechanical tests, such as tensile strength, compressive strength and flexural strength, to assess how the different aspect ratios of PALF affect these properties. Additionally, the work will investigate the durability and long-term performance of concrete with PALF reinforcements, considering factors like moisture absorption and aging. Furthermore, the paper will investigate into the implications of the findings for practical applications in the construction industry. Understanding how the aspect ratio of PALF influences concrete's mechanical properties can provide valuable insights for designing sustainable and highperformance concrete composites. In addition to the investigation of PALF's impact on concrete properties, this research shows the influence of sodium hydroxide (NaOH) treatments on enhancing PALF's properties. These treatments are important to mitigate the hydrophilic nature of the fibers, thereby improving their compatibility with hydrophobic fibers within the concrete matrix. The study systematically analyzes the effects of different concentrations of NaOH on the PALF fibers, specifically Alkali 1 wt., Alkali 2 wt., Alkali 4 wt., and Alkali 8 wt. The concrete samples are subjected to testing at different time intervals: the 7th day (representing the initial stage) and the 28th day (representing the final settling period). Moreover, this investigation is carried out in conjunction with varying aspect ratios of PALF, which include 150, 450, 750, and 1050. the result show that 150 is shown an incremental improvement when compared to the control mix and 450 is the optimum amount of PALF to enhance all three mechanical properties in the other way 1050 aspect ratio showing a significant decrease in strength and the 750 aspect ratio exhibiting a decline compared to the control mix.Item Resistance to Chloride Penetration of Mortar Using Eggshell as a Partial Replacement of Sand(Addis Ababa University, 2024-06) Betelhem Aziz; Abrham Gebre (PhD)Concrete became more in demand as the building sector grew. Which leads to ongoing quarrying and causes the depletion of natural resources due to excessive mining of natural sand. Also the increase in demand and consumption of egg leads to waste production which will impact the environment. Utilizing of waste materials will reduces the need for natural aggregate, energy, and environmental damage. This study explores the possibility of substituting sand partially with eggshell in mortar production, with a focus on its effects on compressive strength, flexural strength, and chloride penetration resistance. Eggshells, a readily available waste material, offer a sustainable alternative to traditional sand, addressing both environmental and resource depletion concerns. Mortar samples with varying percentages of eggshell powder replacing sand (0%, 10%, 20%, 25%, and 30%) were prepared and subjected to standard testing procedures. The experimental results indicate a decrease in both compressive and flexural strengths with the inclusion of eggshell, compared to control samples. Specifically, the compressive strength decreased by up to 16%, 38% 44% and 49% with 10%, 20%, 25%, and 30% replacement respectively the flexural strength saw a reduction of up to 7.8%, 22%, 31% and 43% with 10%, 20%, 25%, and 30% replacement respectively. Despite these reductions in mechanical properties, a replacement up to 5% is acceptable. For flexural strength 25% is acceptable. The resistance to chloride penetration increases as the percentage of eggshell increases with 0% and 10% replacement showing similar results and 30% showed the highest increase in chloride penetration. And also, there is a decrease in the density of mortar samples with eggshell than the controlled samples because of the light weight of eggshell which can be used for redaction of the overall weight of the structure.Item Shear Strength Analysis of RC Exterior Wide-Beam-Column Joint(Addis Ababa University, 2024-02) Betelhem Desalegn; Abrham Gebre (PhD)In seismically active areas where lightweight constructions are recommended, buildings with long-span floors and heavy self-weight create huge platforms. Ribbed slabs are commonly used to address this issue. Unlike conventional beams, wide beams in ribbed slab supporting frames often exceed framing column widths. Most design codes generally allow following a similar approach to the conventional beam-column joint with some additional beam width limitation which varies among those codes. Research suggests that relying solely on these limitations cannot guarantee adequate joint performance, as the seismic behavior of the joint is significantly influenced by the torsional behavior of transverse beams. This research analytically investigates the structural performance of RC wide beam-column joints with shallow transverse beams under cyclic loading. The accuracy of the FE model in predicting shear capacity performance was validated through comparison with experimental data. A parametric study using finite element analysis was conducted on 48 specimens with different LHS representative combination samples. The study primarily analyzed shear strength of the joints. Using regression analysis for specified range of values, a suggested formula considering transverse beam factors was proposed to be incorporated into the existing expected shear strength equation provided by ACI. An influential parameters of transverse beam were identified by sensitivity analysis. Concrete strength, longitudinal reinforcement ratio, stirrup yield strength, and spacing significantly affected the joint capacity. The shear capacity of the joint showed low sensitivity to changes in the yield strength of longitudinal bars. Smaller diameter bars in the transverse beam showed relatively reduced concrete damage. The study emphasized the importance of incorporating shallow RC transverse beams in the design process of wide beam-column joints. The study presents a systematic approach to improve and quantify shear capacity by considering various combinations of transverse beam parameters. The increased design options for improving shear capacity broaden the scope for practical decision-making, taking into account the availability of parameters and the ease of implementation.Item Structural Stability Analysis of Corrugated Reinforced Concrete Shell Structure(Addis Ababa University, 2024) Selamawit Abayneh; Shifferaw Taye (PhD)The structural stability performance of shell structure is advanced. Corrugated shells are among the most unique shell structures available. These shells are shells of translation made up of a series of barrels shells with opposite Gaussian curvature connected edge to edge. The structural stability and performance of these types of shell structures in variable geometry and support condition must be precisely identified to build them. Many researchers have studied the structural performance of different shell structures. Studies on corrugated shell structures are few. The structural performance of a corrugated reinforced concrete shells with various curvatures and support position is the focus of this study. This research has been started by modeling individual barrels and corrugated multi-span shells by using SAP2000 software. The shells are analyzed by using SAP2000 software using various parameters. The result gain from SAP2000 is validated by using ANSYS software. Then the results of the SAP2000 analysis have been collated and graphically presented. Finally, the behavior and performance of the shell structures have been discussed based on the numerical results. According to the research shortening the span length and radius increases the stability of cylindrical shell structures, in addition, increasing the thickness and number of corrugations increases the global stiffness of corrugated shell structures.Item Investigation of the Effect of Shear Wall Curtailment for Medium and High-Rise Buildings in Seismic Region(Addis Ababa University, 2024-04) Abel Beneberu; Adil Zekaria (PhD)In this thesis work, the effect of shear wall curtailment for medium and high-rise buildings in seismic region is investigated. When the shear wall frame system is loaded laterally in medium and high-rise buildings, the upper part of the shear wall takes a negative role in resisting the lateral loads because of the difference in the free deflected forms of shear walls and moment resisting frame. The discontinuity of shear walls may prove an effective technique in reducing this negative effect at the top. Consequently, in order to have good wall-frame interaction, a shear wall should be curtailed above a point on which the shear wall is not effective in reducing the seismic responses of shear walls. Analysis is done for six G+10, seven G+20, and ten G+30 models using finite element method (FEM) of response spectrum analysis with respect to the seismic response parameters such as top story displacement, story drift, story shear, base moment and fundamental time period. Moreover, the Finite element analysis (FEA) is tried to be supplemented by three continuum methods (algebraic solutions) which includes the Component Stiffness Method-Equation C, Alex Coull’s method and Marie-José Nollet’s method. In the FEA and continuum analysis results, the maximum top story (roof) displacement where the shear wall is curtailed above 8th, 14th and 22nd floor for the G+10, G+20 and G+30 building models respectively do not significantly vary with respect to that of the full height shear wall-frame models. Moreover, the other parameters (i.e., the story drift, story shear, story overturning moment, story stiffness and fundamental time period) also reveal that curtailment of shear wall above 70% - 80% of the height of the building will not much affect the performance of the building in resisting seismic loads. Therefore, even if ES-EN 1998: 2015 recommend shear walls to continue up to the roof level for the sake of regularity (i.e., the analysis will be simplified and the structure response will also be easily predictable), curtailment of the shear walls in the top floors is not necessarily detrimental to the performance of the structure. When building height increases, the stiffer the frames will be, the greater the interaction become between wall and frame and the lesser the contribution of the shear wall. So, if we curtail the shear wall for the increased building height (high rise), since the shear wall contribution is minimized, the curtailment become safe.Item A Comparative Study of Limits on Normalized Axial Loads of Es-En 1998:2015 With Other Current Major Building Codes on Columns(Addis Ababa University, 2024-04) Abel Negussie; Adil Zekaria (PhD)Axial loads highly affect the behavior of reinforced concrete members, such as failure mode, yield curvature, ultimate curvature, curvature ductility, beam-column joint, etc. In order to limit the adverse effects of axial loads, Ethiopian Standards based on Euro-Norms limits normalized design axial compressive loads. This research explores the basis for these limits and then compares them with other major codes and standards. The primary aim for these limits is for the axial loads not to exceed loads at balanced failure, . To study the balanced conditions, a series of interaction charts were constructed with the confinement effect of transverse reinforcement on concrete considered. The three main parameters for the charts are the distance of compression reinforcement from the extreme compression fibres normalised with respect to effective depth, ⁄ , mechanical reinforcement ratios, , and mechanical volumetric ratio of confining reinforcement, . Sectional properties, i.e., yield curvature, ultimate curvature and curvature ductility, under the obtained balanced axial loads were compared to their perspective limits. It was concluded that is highly affected by , and to a lesser extent by and . It has an inversely proportional relationship with both , and . Fifteen different column section was also considered as an example, and their results are in alignment with the interaction charts. From the results obtained, it can be concluded that the limits can be more directed for values of . This is especially the case for column sections having lower values of which show a greater load capacity than the set limits.Item Dynamic Analysis of Fluid Containing Cylindrical Tanks Using ANN(Addis Ababa University, 2024-04) Estifanos Bekele; Bedilu Habte (PhD)Cylindrical containers that store liquid are among those delicate structures that are impacted through dynamic loads. These structures that contain fluid are affected due to impulsive and convective pressures created by the liquid inside. This study utilized an artificial neural networking (ANN) model to analyze the dynamic response of fluid-containing cylindrical tanks. Six input parameters were selected to characterize the geometric and mechanical attributes of the cylindrical tank, including the properties of the fluid it holds. A combined dataset of 6,912 samples from Housner's approximate method was utilized to train and test the ANN model. The training and testing sets yielded R2 values of 0.9997 and 0.9991, respectively. The ANN model obtained results that were comparable to the results of Housner's approximate method show that ANN simulations can accurately predict the dynamic response of fluid-containing cylindrical tanks. The model can be enhanced to investigate additional parameters that impact the dynamic response of fluid-containing cylindrical tanks, such as the second-order impact caused by axial load, the effect of baffles, etc. In addition, factors that affect the accuracy and precision of the prediction of the ANN model were investigated and directions were put forward to get a more accurate and precise prediction from available data.Item Analysis Design and Cost Effectiveness of Precast Beam-Slab System(Addis Ababa University, 2009-07) Matheas Kebede; Girma Zerayohannes (PhD)Pre-cast beam-slab is made of pre-cast reinforced concrete beam together with hollow blocks. The pre-cast beams are spaced at certain intervals and the hollow blocks are placed on them to form a working platform with out the use of formwork. The slab HCB, hanging between the pre cast beams are functioning like a formwork. They give only a temporary support during the installation phase. Only the pre-cast beams and the slab concrete are load bearing parts of the slab. In our country pre-cast beam-slab system is not widely used for construction of most buildings. The conventional cast institu constructions require lots of formwork and construction time, which increase the total cost of a project. When pre-cast beam slab systems are introduced in the construction of buildings, an economical construction could be achieved. In the present study, two types of pre-cast beam elements are chosen. Experimental studies are made on these beam elements by casting them in the laboratory condition. From experimental observation, there tried to come up with a new theoretical model. Loaddeflection data was taken from the experiment and compared with the theoretical output. Furthermore cost comparison is made between the two systems of slab construction. For the arrangement of panels used to compare cost, the pre-cast beam-slab system of construction is more economical than the conventional system. Finally, the model gives a hint for future study in trying to simulate the actual pre-cast beam slab system.Item Experimental Characterization of Sisal Fiber Reinforced Adobe Bricks(Addis Ababa University, 2022-03) Mesay Haileyesus; Girma Zerayohannes (PhD)The paper presents the result of a research aimed at comprehensively characterizing the physical, chemical and mechanical performance of adobe bricks produced by blending soils from termite mound, clay obtained from brick producing companies and by reinforcing using sisal fiber. Adobe is a traditional building material made of soil mixed with or without fiber or it is a mud bricks baked using sun light. Due to it is less impact on the environment, the use of adobe bricks is getting more scientific attention. It is the fact that provision of adequate and affordable house is one of the greatest challenges of the Ethiopian government. In terms of the quality of construction material, over 50% of the housing units are categorized as substandard and poor quality. Specific to the use of wall material in urban areas over 70.8% are made of “Chika,” Wood plastered with mud mortar. It is practically possible to use traditional building material for at least domestic use so as to contribute by producing adobe bricks for the construction of affordable housing units. Unfortunately, the mechanical characteristics of the adobe bricks produced by local material and reinforced with sisal fiber as well as the use of termite mound blending with clay soil for production of adobe bricks not addressed yet. The target of this experimental investigation is to fill the gap in terms of experimental data on the material, show the possible use of termite mound for production of adobe bricks and minimize the possible formation of cracks by incorporating sisal fiber on the adobe bricks. The outcomes of this research depicted that the use of termite mound blended with red clay for the production of adobe brick soil gives improved compressive strength and the use of sisal fiber mixed with soil matrix can enhance deformation properties and facilitate the drying process.Item Sensitivity Study of Reinforced Concrete Beam Exposed to High Temperature: Finite Element Model(Addis Ababa University, 2021-07) Alayu Befekadu; Alayu Befekadu (PhD)Reinforced concrete structures significantly weakened their strength as a result of the fire. The behavior of concrete and RC-reinforced concrete elements at high temperatures has been extensively studied experimentally and analytically. This research paper, "Sensitivity Study of Reinforced Concrete Beam Exposed to High Temperature: A Finite Element Model", analyzed using the commercial software ABAQUS, refers to a three-dimensional (3D) nonlinear transient thermo-mechanical element (FE) analysis. The purpose of this research is to find out the effect of fire on concrete cover, the compressive strength of concrete, the intensity of the fire, and the duration of the fire, as well as the load arising from the fracture, to understand the effects of fire. Methodologically Numerical model simulation was employed with the aid of ABAQUS Software, which operated based on a finite element algorithm. The models were developed to analyze and understand the behavior of concrete and reinforced concrete beams with different intensities of fire, concrete cohesion, and compressive strength under different conditions. The analysis result showed that when the temperature is from 200 °C to 700 °C (OC is a degree Celsius), the failure load decreases while the temperature increases. On the other hand, the concrete cover increased from 15mm to 25 mm, significantly increasing the failure load. Generally, the results obtained from the nonlinear analyses of reinforced concrete beams under high-temperature duration and intensity are more sensitive compared to compressive strength and concrete cover. In addition, compared with the numerical and experimental solutions available in the literature, they were highly satisfactory.Item Experimental Investigation on Bond Strength Behavior of Reinforced Concrete Members Using Waste Marble as Coarse Aggregate(Addis Ababa University, 2023-12) Dereje Hirpa; Adil Zekaria (PhD)The expansion of the construction industry increased the demand for concrete. This results in the depletion of natural resources due to continuous quarrying. In another way, the waste generated from the marble industry will affect the environment. The use of waste in construction saves natural aggregate, energy and preserves the environment. Previous studies focused on the strength and durability properties of marble aggregate concrete and there is no sufficient literature that investigates the bond strength behavior marble aggregate concrete as it enables the use of marble aggregate in structural members. Therefore, in this research the bond strength behavior of reinforced concrete using waste marble as coarse aggregate was investigated via Pull-out test. Deformed bars of diameters 12 mm, 14 mm, and 16 mm and length 1000mm were centrally placed in the cylindrical molds of dimensions 150 mm ×300 mm with an embedment length of five times the diameter of the bar. The bars were embedded in five different concrete mixes varying the quantity of marble replacing coarse aggregate at a ratio of 25% in C-30 concrete mixed using constant water-cement ratio. At the test date, each specimen was initially setup carefully and then an axial load was imposed on the bar at the loaded end and the slip was measured at free end. In this way pull-out test was conducted on a total of 45 specimens at the age of 28 days. Test result indicates that compressive and splitting tensile strength of the concrete increases as the quantity of marble replacing natural coarse aggregate increases up to 50% and then decreases. Bond strength is consistent with the result of compressive and tensile strength of the concrete. For all diameter 12mm,14mm and 16mm bars the average bond strength of marble aggregate concrete is comparable with the control concrete as the percentage of marble in the mix increases up to 75%. However, the average ultimate bond strength significantly decreased in 100% marble coarse aggregate concrete because of low tensile strength of marble compared to natural aggregates. Furthermore, bond strength decreases as the diameter size of the bar increased due to nonlinear stress distribution along the embedment length of larger diameter size bars. The experimental result exceeds the bond strength calculated using equations proposed by nine different researchers. Both ES EN 1992-1-1:2015 and ACI 318-08 codes underestimated the average bond strength values of all steel bars embedded in all concrete mixes.Item Numerical Investigation of the Effect of Aerodynamic and Seismic Load Interaction on the Stability of Land-Based Wind Turbine Towers(Addis Ababa University, 2023-06-13) Gossaye Mathewos; Bedilu Habte (PhD)Wind energy is one form of renewable energy and the utilization of wind energy is rapidly growing worldwide due to its a bundance. Wind turbines are a feasible, cost effective, and durable source of wind energy, and ensuring their safety is essential for proper service life operation to protect the investment. The installation of wind turbines in seismic regions is growing t o meet renewable energy demand around the world, and analyzing the stability of wind turbines in these regions is critical. This research analyzes the effect of aerodynamic and seismic load interaction on the stability of land based horizontal axis wind tu rbine towers built in seismic areas. The methodology implemented to conduct this study is a decoupling approach to analyze the effect of wind loads and seismic loads independently and combine results obtained from ANSYS Workbench 2022. A reliable finite el ement model is established by validating modal analysis results with experimental values. Then, global responses such as top tower displacement and second order (P Δ) effect, and local responses such as maximum Von Mises stress and eigenvalue buckling anal ysis of wind turbine towers were conducted. Earthquake loads are found to be dominant loads compared to wind loads for all wind turbines and earthquake induced emergency shutdown condition is found to be the most critical operation condition for all wind t urbines. In addition, the second order (P Δ) effect from analysis of wind turbine towers shows that 1.5MW and 5MW wind turbine towers are significantly affected, but P Δ is negligible for 65kW wind turbine. Moreover, a 1.5MW wind turbine has higher top tow er displacement and maximum Von Mises stress compared to a 5MW wind turbine which is due to the effect of the shell property of the tower and the weight of wind turbines. Furthermore, the characteristics of the acceleration vs time records are also found t o have a significant effect on the response behavior of the turbines rather than the magnitude and distance earthquake records are measured from the source alone. This study emphasizes the need to consider the impact of the second order (P Δ) effect for th e design of 1.5MW and 5MW wind turbines to avoid structural stability failure.Item Effective Automated Design of Building Models for Torsional Flexibility and Lateral Stability(Addis Ababa University, 2023-06) Kirubel Hailegeorgis; Bedilu Habte (PhD)Despite making rapid progress in the field of earthquake science, seismologists are still unable to forecast the occurrence of the big one. Earthquake forces are unpredictable by nature, and sophisticated analysis and design options cannot guarantee complete safety of a structure against an earthquake. Therefore, current and emerging design philosophies require regularity to be one of the main considerations when designing a structure. Regular structures are capable of withstanding earthquake forces much better than irregular structures. Torsional regularity is the most important criterion for determining regularity of a structure. The drift sensitivity coefficient (𝜃), a parameter that describes stability of a structure, is another parameter that needs due attention during design of buildings. However, calculating parameters that describe both torsional regularity and stability of a structure can be very tedious. For this reason, structural designers often tend to create approximate methods of calculating these parameters. Nonetheless, these parameters are of great importance, therefore it is essential to avoid using approximate methods and results. Moreover, it is a common trend to increase the cost of the structure just so that calculation of these parameters is omitted. To address these problems, a software program that can calculate these parameters effortlessly is developed. This program, unlike the conventional approach, is also capable of solving stability and torsional rigidity issues simultaneously. With the use of parametric data, the program is capable of suggesting strategic wall locations and making the necessary structural modifications that can address both issues. This approach prevents worsening of torsional rigidity behaviour while taking structural measures for solving stability issues, eliminating the need for excessive usage of structural members like walls. The software interacts with conventional structural design software to extract required data, to analyze status, detect problems and suggests solutions to create a sound structural system. Through the developed graphical user interface, the solutions are reported to the user, and capability of applying the solutions automatically is one of the features of the program. The program employs fuzzy logic to determine depth of detected problem, aiding designers foresee extent of required structural modifications. Proper functioning of the program is verified by replicating an example done by Eurocode designers guide.Item Experimental Characterization of Sisal Fiber Reinforced Adobe Bricks(Addis Ababa University, 2022-03-10) Mesay Haileyesus; Girma Zerayohannes (Prof.)The paper presents the result of a research aimed at comprehensively characterizing the physical, chemical and mechanical performance of adobe bricks produced by blending soils from termite mound, clay obtained from brick producing companies and by reinforcing using sisal fiber. Adobe is a traditional building material made of soil mixed with or without fiber or it is a mud bricks baked using sun light. Due to it is less impact on the environment, the use of adobe bricks is getting more scientific attention. It is the fact that provision of adequate and affordable house is one of the greatest challenges of the Ethiopian government. In terms of the quality of construction material, over 50% of the housing units are categorized as substandard and poor quality. Specific to the use of wall material in urban areas over 70.8% are made of “Chika,” Wood plastered with mud mortar. It is practically possible to use traditional building material for at least domestic use so as to contribute by producing adobe bricks for the construction of affordable housing units. Unfortunately, the mechanical characteristics of the adobe bricks produced by local material and reinforced with sisal fiber as well as the use of termite mound blending with clay soil for production of adobe bricks not addressed yet. The target of this experimental investigation is to fill the gap in terms of experimental data on the material, show the possible use of termite mound for production of adobe bricks and minimize the possible formation of cracks by incorporating sisal fiber on the adobe bricks. The outcomes of this research depicted that the use of termite mound blended with red clay for the production of adobe brick soil gives improved compressive strength and the use of sisal fiber mixed with soil matrix can enhance deformation properties and facilitate the drying process.Item Experimental Investigation on Bond Strength Behavior of Reinforced Concrete Members Using Waste Marble as Coarse Aggregate(Addis Ababa University, 2023-12) Dereje HirpaThe expansion of the construction industry increased the demand for concrete. This results in the depletion of natural resources due to continuous quarrying. In another way, the waste generated from the marble industry will affect the environment. The use of waste in construction saves natural aggregate, energy and preserves the environment. Previous studies focused on the strength and durability properties of marble aggregate concrete and there is no sufficient literature that investigates the bond strength behavior marble aggregate concrete as it enables the use of marble aggregate in structural members. Therefore, in this research the bond strength behavior of reinforced concrete using waste marble as coarse aggregate was investigated via Pull-out test. Deformed bars of diameters 12 mm, 14 mm, and 16 mm and length 1000mm were centrally placed in the cylindrical molds of dimensions 150 mm ×300 mm with an embedment length of five times the diameter of the bar. The bars were embedded in five different concrete mixes varying the quantity of marble replacing coarse aggregate at a ratio of 25% in C-30 concrete mixed using constant water-cement ratio. At the test date, each specimen was initially setup carefully and then an axial load was imposed on the bar at the loaded end and the slip was measured at free end. In this way pull-out test was conducted on a total of 45 specimens at the age of 28 days. Test result indicates that compressive and splitting tensile strength of the concrete increases as the quantity of marble replacing natural coarse aggregate increases up to 50% and then decreases. Bond strength is consistent with the result of compressive and tensile strength of the concrete. For all diameter 12mm,14mm and 16mm bars the average bond strength of marble aggregate concrete is comparable with the control concrete as the percentage of marble in the mix increases up to 75%. However, the average ultimate bond strength significantly decreased in 100% marble coarse aggregate concrete because of low tensile strength of marble compared to natural aggregates. Furthermore, bond strength decreases as the diameter size of the bar increased due to nonlinear stress distribution along the embedment length of larger diameter size bars. The experimental result exceeds the bond strength calculated using equations proposed by nine different researchers. Both ES EN 1992-1-1:2015 and ACI 318-08 codes underestimated the average bond strength values of all steel bars embedded in all concrete mixes.Item Effects of Skewed Supports on Horizontally Curved Box Girder Bridges(Addis Ababa University, 2024-01) Ermias GezahegnReinforced concrete overpass bridges are commonly used for modern highway bridges and large urban interchanges. However, in urban areas, space constraints and alignment requirements often make it difficult to use conventional bridge designs. Bridges with in-plan curvature that rest on skewed supports fall into this category, presenting a complex geometrical arrangement. The ERA bridge design manual and AASHTO LRFD design manual have limitations in addressing the combined effects of curvature and support skewness on bridges. They specify an Angle of Curvature below which neglecting plan curvature in determining the preliminary effects of curved bridges is acceptable, as well as shear correction factors for skewed bridges. To assess the structural response of a bridge when these conditions occur concurrently, a three-dimensional Finite Element Analysis was conducted on a multi-cell cast in situ reinforced concrete box girder bridge. Two hundred bridges were modeled with varying parameters. The analysis showed that the bending moment results of skewed bridges are not significantly affected by the incorporation of in-plan curvature. However, there was a significant (15%) difference between the shear response of the approximation method stipulated in design codes and the outputs of this research. To address this issue, a shear correction and magnification factor is proposed for the outermost girders of skew-curved bridges. Additionally, it was found that the girder at the acute corner of the bridge experienced a downward support reaction force, known as an uplift force. This force is magnified when one-lane traffic loading is applied. Furthermore, it was observed that incorporating skewed supports reduces the live load deflection of curved bridges.Item Parametric Study on The Use of Additional Steel Plates for Confinement of Axially Loaded Reinforced Concrete Columns(Addis Ababa University, 2023-12) Kassahun TilahunDuctility is the ability of a structure or its components to offer resistance in the inelastic domain of response. However, concrete is not a ductile material, and therefore, confinement is recommended to improve its performance. Confinement in concrete is achieved by the suitable placement of transverse reinforcement, which results in a significant increase in the strength and ductility of concrete. This paper focuses on the confinement effect induced by different arrangements of transverse reinforcement on axially loaded concrete columns. The aim of this research is to carry out a parametric study on the confinement action induced by a type of stirrup involving steel plates and different arrangements of transverse reinforcement on axially loaded concrete columns. To achieve this goal, numerical analysis was conducted using the finite element program, ABAQUS. The variables considered in this study were concrete compressive strength, spacing of transverse reinforcement, arrangement of transverse reinforcement, and influence of plate thickness. The results of numerical studies have shown that the effect of concrete compressive strength and longitudinal reinforcement ratio have the most impact on the column response, the spacing of transverse reinforcement has less impact and the effect of plate thickness almost negligible. Additionally, the configuration of transverse reinforcement involving steel plates has been found to improve a column's strength and its ability to withstand axial loads.Item Influence of Shear And Flexural Hinges Length And Ductility Class on Seismic Performance of Reinforced Concrete Structure.(Addis Ababa University, 2023-10) Abebaw Assefa; Esayas Gebreyouhannes (PhD)Seismic evaluation helps to identify structural and non-structural vulnerabilities in existing buildings. This includes weaknesses in the building's design, construction materials or foundation, which might make it susceptible to earthquake damage. Older buildings were often constructed using old codes that may not be as stringent as modern ones. Evaluating these buildings against current seismic design standards helps to determine if they meet contemporary safety requirements. The aim of this study is assessing how ductility class, flexural and shear hinge length, impact on the seismic performance of an existing reinforced concrete frame structure in a seismic zone three setting as per EN 1998-3:2004. The seismic performance evaluation of the proposed structure is carried out by using nonlinear static procedure (NSP) or pushover analysis as per EN1998-3:2004 guidelines. Seismo-structure v-2023 program is used for pushover analysis by providing user-defined nonlinear hinge properties. The study's findings suggest that the length of flexural and shear hinges and the chosen ductility class are important factors to consider when designing earthquake-resistant structures as they have a direct impact on base shear and inelastic displacement capacity.