Structural Engineering

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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Experimental Investigation on Bond Strength Behavior of Reinforced Concrete Members Using Waste Marble as Coarse Aggregate
(Addis Ababa University, 2023-12) Dereje Hirpa
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.
Effects of Skewed Supports on Horizontally Curved Box Girder Bridges
(Addis Ababa University, 2024-01) Ermias Gezahegn
Reinforced 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.
Parametric Study on The Use of Additional Steel Plates for Confinement of Axially Loaded Reinforced Concrete Columns
(Addis Ababa University, 2023-12) Kassahun Tilahun
Ductility 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.
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.
Solid Waste Bottom Ash as A Partial Replacement of Cement in Concrete Production
(Addis Ababa University, 2023-06) Samrawit Yeshaw; Abrham Gebre (PhD)
Cement production is hazardous to the environment due to generation of high carbon dioxide (CO2) and heat. To reduce CO2 emissions and protect the environment, researchers have found a wide variety of waste products that can be used as additional cementitious materials for concrete. The most common supplementary cementitious materials are fly ash, blast furnace, silica fume, bottom ash and others. Solid waste bottom ash is one of the supplementary cementitious materials. Solid waste resources are increasingly being used in the production of concrete. Particularly, using recycled solid waste in place of cement, a key component of concrete, has appealed due to its ability to reduce greenhouse gas emissions. The purpose of this study is to investigate the use of Municipal Solid Waste Incinerator Bottom Ash (MSWI) as partial replacement of cement and study the properties of concrete. Concretes were casted to compare the compressive strength, splitting tensile strength, flexural strength. Moreover water permeability test is done on normal strength concrete when cement is partially replaced with municipal solid waste bottom ash at different percentages. The workability of concrete decreased with an increase of percentage replacement of cement by Bottom ash. The obtained results of compressive, tensile and flexural strength show decrement with an increase of BA. However, the replaced concrete samples possess a better water tightness performance than the controlled sample. Solid waste bottom ash can be used to partially replace cement in a normal strength concrete.
Parametric Study on Shear Capacity of Plate Girders with Web Openings
(Addis Ababa University, 2023-06) Mekdes Debir; Abrham Gebre (PhD)
This thesis studies parametrically the ultimate shear capacity of plate girders with web holes. The variables include the span length, the opening depth, the opening number, the opening location, and the opening form. This study will provide guidelines for which form of openings to use, how deep to cut the web, where to cut the web, and how many openings to use when web openings are required to pass utility lines and for inspection purposes without adversely reducing the plate girder's ultimate capacity. The finite element software, ABAQUS, was employed as a practical design tool. The accuracy of the developed model is evaluated by comparing its predictions with tests that were carried out experimentally on plate girders, which showed a good agreement in terms of deformations and ultimate loads. The results demonstrated that the behavior of plate girders with web openings is significantly influenced by the shape and depth of the opening, particularly when the opening depth exceeds 50% of the web depth and the opening takes on a square shape. SPGs with two holes each situated up to two times the web depth from supports showed no discernible impact on the ultimate capacity. Increasing the number of openings resulted in additional mid span deflections and a considerable reduction in ultimate capacity. The depth of the opening was found to be the most influential parameter in the sensitivity analysis. The ultimate capacity of the weakest SPGs with web openings is greatly increased by providing steel plates around the openings.
Development of Comprehensive Tool for The Structural Analysis, Design, And Detailing of Buried Box Culverts
(Addis Ababa University, 2023-06) Tewele Brhane; Bedilu Habte (PhD)
Box culvert design currently involves using a minimum of three software programs, including Microsoft Excel for load determination and structural analysis tools such as CSI SAP or MIDAS CIVIL for determining action effects. AutoCAD is then used for structural detailing. This approach can lead to project delays and an increased likelihood of mistakes. Furthermore, the current design approach uses a two-dimensional plane frame model that assumes beam elements are centered in concrete members and that the model is externally supported by pinned and roller supports, resulting in uneconomical designs that may compromise safety. Moreover, the ERA standard drawing has restrictions that do not account for all potential culvert sizes and fill heights. To address these issues, this research proposes a comprehensive software solution for structural analysis, design, and detailing of box culverts. The proposed software enables designers to analyze and design box culverts of any size and fill height while accounting for vertical displacement of the foundation soil using spring modeling. This approach streamlines the design process, saving time and increasing accuracy, while also improving safety. The software program developed in this research is a web application. As a result, users can easily access the software from any location at any time, using any device with an internet connection, without the need for installation. Design charts have been developed to illustrate how the bending moment varies at different locations for various opening sizes of a culvert. This is achieved by varying the fill height and number of openings.
Multi-objective Optimization of Post-tensioned Pedestrian Bridge
(Addis Ababa University, 2021-09) Metasebia, Dabi; Bedilu, Habte (PhD)
Multi-objective design optimization of post-tensioned box girder pedestrian bridge is presented in this study. The proposed design optimization incorporates some behavior and side constraints specified by the AASHTO Standard specifications. Multi-objective optimization is performed to minimize the cost and maximize the safety factor for the ultimate limit states. Considering stress and deflection limits as design constraints, and geometrical dimensions of the box-girder and shear reinforcements as design variables. Additionally, application of MATLAB routine gamultiobj algorithm for the design of posttensioned pedestrian bridge is presented, and a set of solutions in the pareto front are illustrated in graphical format. Then multi-criteria decision analysis method named TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) is used to determine the single optimal result from the Pareto set solutions by giving weight to the objective functions
Use of Waste Paper Sludge Ash as Partial Replacement of Cement in Mortar
(Addis Ababa University, 2022-06) Bonsa, Teshome; Adil, Zekaria (PhD)
Various industrial wastes were employed as supplemental cementitious materials to save the environment from filling with non-biodegradable wastes and to limit the consumption of existing limestone. Waste paper sludge makes up a significant component of the numerous materials produced as byproducts in the paper industry. The overall goal of this research is to determine the suitability of waste paper sludge ash as a partial cement replacement material by conducting compressive strength and reactivity tests while substituting cement in various quantities. The end-by-product of the paper manufacturing industry is paper sludge, which is a wet gray waste mud. This paper sludge is turned into ash and utilized as a partial cement replacement. This research is entirely based on the use of waste paper sludge ash (WPSA) as a cement replacement in mortar production. WPSA amounts of 0, 5, 10, 15, 20, 25, and 30% by volume of cement are used to make the mortar mix. At the ages of 7, 28, and 56 days after curing under ambient conditions, the compressive strength of mortar cube specimens was measured. The results suggest that increasing the replacement level up to a certain level increases the strength of mortar cubes incorporating waste paper sludge ash (WPSA). In terms of compressive strength, 15 percent replacement yielded the optimum results. WPSA reactivity was assessed using a variety of techniques. This was accomplished by assessing the reactivity of WPSA using a modified Chappelle test, estimating the amount of bound water, and characterization of pastes using XRD analysis was done for a sample at the optimum replacement level, i.e. 15%. The strength development was also compared to the test results. On day 7, reference sample had a bound water content of 4.18%, whereas blended sample had a bound water level of 5.20%. WPSA has a reactivity of -1244.89 mg Ca(OH) 2 per gram of WPSA. These findings suggest that the increase in compressive strength is entirely due to the filler effect.
The Role of Bond in Shear Transfer of Shear Critical Reinforced Concrete Slender Beams
(Addis Ababa University, 2022-01) Weyneshet, Getachew; Esayas, Gebreyouhannes (PhD)
Due to its complex nature, the effect of bond loss between concrete and longitudinal bar on the shear transfer mechanism lacks a complete framework. So far, all ranges of bond losses are considered as a total bond loss, leaving no gap to address intermediate ranges. Advancement in this area will aid in the assessment of the service life time of various structures and provide insight for rehabilitative engineers in their efforts. An experimental program was undertaken to investigate two ranges of bond losses, complete bond loss and bond losses induced by transversal cracks in relation to the effect of the location of the bond deterioration. In first set Pullout test was used to determine the best approach for bond cutting without compromising the cracking pattern. This set experimented on the location of the artificial bond cut. It included the control beam and two beams with artificial bond cutting material covering 75% of their shear span, with a sole difference being the location of the artificial bond cut. The second set experimented on bond losses induced by transversal cracks. The transversal cracks were induced by introducing slits and a water proof tape was wounded around the slits to simulate the bond deterioration zone. This set included four beams with 75% and 50% of their shear span designed to imitate transversal cracks. During testing, the shear strain at specified points of the 8 beams were measured to compare the two sets. A number of mold strain gauges were also used in the second set of specimens to monitor the transfer of shear force to the web. The results of the beam specimens in the first set have attained 90% up to 100% of their flexural capacity, while the control has attained 53% of the flexural capacity. It was also observed that the critical diagonal crack initiation, propagation and location is severely affected by the experimental variables. Finally, it was observed that the location of the bond cut or bond deterioration resulted in a different effect on the two sets.

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