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Item An Integrated Approach to Sustainable Construction Through Recycling, Co2 Capture and Artificial Intelligence(Addis Ababa University, 2026-07-01) Hintsa Gebrezgiher Gebremariam; Abrham GebreThe construction industry is one of the largest contributors to climate change, driven largely by carbon dioxide (CO₂) emissions from anthropogenic activities. In addition to putting tremendous strain on natural resources through aggregate extraction, the production of cement and concrete alone is responsible for over 8% of global CO2 emissions. Concurrently, the construction sector produces enormous amounts of construction and demolition (C&D) waste, which exacerbates resource and environmental problems. Recycling this waste into recycled concrete aggregates (RCA) provides a sustainable path forward by conserving raw materials, reducing pressure on landfills, and enabling the sequestration of CO₂. However, RCAs' limited range of applications is due to their lower quality when compared to natural aggregates (NAs). While many studies have explored not only how to enhance RCA performance but also how to effectively incorporate it into construction applications, several important gaps still remain. These include, inconsistencies in results on the influence of parent concrete (PC) strength on RCAs and RAC (recycled aggregate concrete) characteristics, the interaction between carbonation treatment and aggregate characteristics, and the effect of natural preprocessing carbonation on the carbonation potential of the accelerated carbonation. In addition, predictive modelling frameworks capable of linking CO₂ uptake with the mechanical performance of concretes containing carbonated aggregates are still unexplored. This dissertation addresses these gaps through a comprehensive experimental and data driven programs. RCAs were obtained from both laboratory produced concretes of varying strengths and demolished structures. Their physical and mechanical properties were characterized under controlled crushing, ambient carbonation, and pressurized accelerated carbonation conditions. Custom built carbonation chamber with controlled environment and 99.5% purity CO2 gas purchased from local suppliers was used in the pressurized carbonation process. Advanced analytical techniques, including thermogravimetric analysis (TGA-DTA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTiR), were employed to assess microstructural and chemical changes before and after carbonation. Concrete mixes produced with these aggregates were evaluated for compressive, split tensile, and flexural strength. Complementary regression based machine learning models were developed using 108 datasets to predict compressive strength, explicitly incorporating aggregate quality parameters, mix proportioning parameters, carbonation degree, and percent replacement of natural aggregates by RCAs. The results demonstrated that PC strength has an effect on the characteristics of RCAs and RAC. Higher strength PCs produced aggregates with improved abrasion resistance, impact resistance, crushing resistance, and specific gravity, alongside reduced water absorption, although mortar content increased. Carbonation treatment further enhanced performance, with natural storage achieving up to 7.5% CO₂ uptake by mortar mass and accelerated carbonation achieving up to 12% CO₂ storage in the form of calcium carbonate polymorphs. Concrete produced with carbonated aggregates exhibited strength improvements of up to 12.5% in compression, 8.6% in tension, and 3.3% in flexure. Replacing normal strength aggregates with those from high strength concretes yielded further gains of 18%, 26%, and 30% respectively. Microstructural analyses confirmed that carbonation refined pore structures and improved durability, although dense aggregates from high strength concretes limited CO₂ penetration and resulted in incomplete carbonation. The machine learning models provided robust predictive capability, with ensemble methods such as Random Forest achieving the highest accuracy within a ±13% maximum error ranges. Sensitivity analysis identified mix proportioning, carbonation degree, and aggregate performance as the most influential factors. While the controlled laboratory environment ensured systematic testing, real world demolition waste presents greater variability due to the presence of impurities and weak segregation practices, which remains a limitation of this study for large scale application. In the Ethiopian context, both challenges and opportunities exist for mainstreaming RACs. Establishing national guidelines, improving demolition and waste segregation practices, and integrating CO₂ utilization with industrial emitters such as cement and steel plants will be critical for adoption. With the current trend in corridor development and city renewals in Addis Ababa and other cities of Ethiopia, embedding RACs into the construction sector can establish a circular economy model that reduces reliance on virgin materials, diverts waste from the demolition processes, and supports the country’s climate commitments. To establish waste materials as a sustainable building material and a pillar of low carbon development, legislators, researchers, industry, and contractors must work together.Item Assessment of Material Characteristics, Mechanical Performance, Durability, and Shrinkage of Bamboo Fiber Reinforced Concrete for Sustainable Construction(Addis Ababa University, 2026-06) Muluken Awulachew Asres; Girma Zerayohannes; Adil Zekaria (Co-Advisor); Denamo Addissie (Co-Advisor)Concrete is the dominant structural material used worldwide in most infrastructures. While it has commendable engineering properties, including compressive strength and the ability to attain the various shapes desired, concrete is known to be relatively weak in resisting tensile forces and brittle. Finite resources and synthetic fibers were exploited to address the weakness of concrete. These fibers are found to be unfavorable for the environment and questionable from a sustainability perspective. Therefore, researchers aimed to utilize the vast bamboo plantation wealth as a fiber source. However, research on the engineering properties of bamboo fiber in concrete is limited. Moreover, those studies were conducted for a very short duration, a maximum of 90 days. Conversely, the existence of thousands of bamboo species and their variability necessitates further investigations into the fibers of the other species and how they affect the range of concrete properties. Therefore, this research is designed and carried out in two phases. The first phase assesses the impact of extraction methods on the bamboo species, Yushania alpina. The second phase investigates the impact of incorporating these fibers on various concrete properties, including slump, compressive strength, split tensile strength, flexural strength, brittleness, cracking, performance in adverse environments, volume of voids, absorption capacity, and time-dependent behavior, specifically drying shrinkage of concrete. The impacts of mechanical, chemical, and combined extraction techniques on the absorption, chemical composition, morphology, thermal properties, and tensile strengths of the bamboo fiber were examined. On the other hand, the mechanical and durability properties were examined for 365 days, while the shrinkage was examined for 197 days. For this purpose, concrete specimens containing bamboo fiber in amounts of 0%, 0.25%, 0.5%, 0.75%, and 1.0% by volume of concrete were prepared. The results of the investigations of bamboo fiber revealed that chemically extracted fibers showed the highest tensile strength, the removal of attachments on the surface of the fibers, the reduction of lignin content, reduced water absorption capacity, reduced diameter, increased surface roughness, and improved thermal properties. The composite of bamboo fiber and concrete showed results that are correlated with the dose of bamboo fiber. Accordingly, concrete with a bamboo fiber content of 0.5% or higher exhibited less performance in compressive, split tensile, and flexural strength, as well as durability. The study revealed that when the bamboo fiber dose in the concrete is 0.25%, it has comparable compressive strength and durability properties to plain concrete. The highest split tensile strength, the highest flexural strength, the lowest drying shrinkage, and reduced crack width were attained in specimens containing 0.25% bamboo fiber. The existing shrinkage prediction models were not satisfactorily able to trace the drying shrinkage development. Therefore, a new model is formulated and proposed for the use of bamboo fiber-reinforced concrete. Finally, bamboo fiber with a low dose can be utilized in construction.Item Suitability of Crushed Hintalo Wejerat Sandstone as a River Sand Alternative for Normal Grade Concrete Production(Addis Ababa University, 2025-09-01) Tekestebrhan Gebreslassie; Adil ZekariaThe potential of substituting Hintalo Wejerat Sandstone for regular river sand in the production of regular grade concrete is investigated in this study. The building industry of Ethiopia is expanding rapidly,, with the resultant increased demand for concrete. River sand has been the main fine aggregate: however, overexploitation has resulted in environmental degradation in the form of riverbank erosion and loss of habitat. The study examines particle size distribution, specific gravity, water absorption and strength of concrete that consists of Hintalo Wejerat sandstone and compares it with the properties of natural river sand. River sand substitution with different percentage of Hintalo Wejerat Sandstone was used to produce concrete mix, C-25. The workability of the fresh concrete was checked by slump tests, and the compressive and flexural strength of hardened concrete was checked at 7,14 and 28 days. Results indicate that Hintalo Wejerat Sandstone can be used successfully as a river sand substitute in the production of concrete with all replacement levels satisfying the compressive strength requirement. Although concrete mix containing 100% river sand was indicated to possess higher compressive strength, use of Hintalo Wejerat Sandstone also facilitated proper workability, and hence, its suitability towards sustainable construction. The flexural strength tests indicated that higher percentage of Hintalo Wejerat Sandstone had a positive influence on the bending strength of the concrete, demonstrating improved durability. In conclusion, this study recommends Hintalo Wejerat sandstone as a substitute to river sand in concrete production to construction sector's need for green operations. The study recommends the establishment of standard practices in Hintalo Wejerat sandstone quarrying and processing to further enhance its usefulness as a building material. Additional studies should also involve the long term strength of Hintalo Wejerat Sandstone concrete under different environmental conditions and its use performance in practice.Item Eggshell Powder and Waste Soda-Lime Glass Powder as a Partial Cement Replacement Material in Mortar(Addis Ababa University, 2026-02-01) Faiza Yasin; Esayas G/YohannesIn current situation where the need for cement is scaling up and the world is wisely using waste materials in to useful products, this research proposes potential poultry and domestic waste (Eggshell) and industrial and domestic waste (Soda-lime glass) as a partial cement replacing material for the construction industry. The eggshell samples were collected from Mojo and the soda-lime glass where collected from households then grinded until all the particles passed 150 µm sieve and then their chemical properties were investigated. From the complete silicate analysis test result it is found that eggshell is reach in calcium oxide or lime and soda-lime glass is reach in silica. And the XRD test result showed, the eggshell has 47.87% crystalline and 52.13% amorphous property and the soda-lime glass has pure amorphous property. For the flow and compressive strength test a total of 414 mortar cubes were utilized. The mortar cubes were done by replacing OPC with eggshell powder and soda-lime glass powder in 23 different mixes according to the ASTM using 0.485 water to cement ratio and 1:2.75 cement to sand content. The property of mixes at fresh state showed that, workability increases as ESP and SLGP increases. The results of mortar at hardened state also showed that, 2.5%SLGP + 7.5%ESP, 5% SLGP + 5%ESP, 7.5%SLGP + 2.5%ESP and 10% SLGP replacement with OPC have applicable compressive strength value relative to the control sample throughout the tests period i.e. 7, 28 and 56 days curing in 20°c. The result also shows 2.5%SLGP + 7.5%ESP, 5% SLGP + 5%ESP, 7.5%SLGP + 2.5%ESP and 10% SLGP replacement with OPC have applicable compressive strength value relative to the control sample throughout the tests period i.e. 7 and 28 days curing in 60°c. However the control still shows higher value at 56 days curing in 60°c. Even if the control tends to have a higher compressive strength at later age, 2.5%SLGP + 7.5%ESP, 5% SLGP + 5%ESP, 7.5%SLGP + 2.5%ESP and 10% SLGP replacements could be used as an optimum mix.Item Probabilistic Impact Assessment of Traffic Overload on Bridge Structural Capacity: a Case Study Approach(Addis Ababa University, 2025-12-01) Gebyaw Amare; Abrham GebreThis study investigates the effects caused by traffic overload on bridge superstructures, especially with regards to heavy vehicles. The critical thresholds with regards to heavy traffic are discussed, taking into consideration parameters such as traffic flow and characteristics and types and patterns of overload. The work also considers design standards and bridge materials. The methodology would commence with identification of some bridges in Ethiopia that are faced with varying degrees of traffic overload. And to get this study off the ground, data was collected from 38,188 truckloads of traffic at weigh stations managed by the Ethiopian Roads Administration in those regions that record high traffic flow of heavy vehicles. Using the R statistical software, a probabilistic loading process was generated. This involved the examination of the material properties of key components as well as the design parameters of a chosen bridge. Probabilistic axle loads were analyzed to assess the impact on the existing bridge’s capacity. A simulation program was developed to determine static overload influence on a particular type of three-span simply-supported box-girder bridge (Mille. 3 bridge). The extreme values of the load effects for various return-period values were computed with statistical extrapolation methods. By using the First Order Reliability Method (FORM), reliability indices (β) can be determined in order to calculate the probability of failure regarding flexural and shear modes. The findings contribute to performance-based management in bridges, considering the impact of real-life overloaded traffic on structural reliability in relation to the life cycle maintenance approach in accordance with AASHTO LRFD/ERA.Item Effects of Soil-Structure Interaction on the Seismic Response of Building Considering Three Categories of Soil(Addis Ababa University, 2025-05-01) Miskir Tadesse; Esayas G/YohannesThe primary aim of this study was to investigate the influence of soil-structure interaction (SSI) on the seismic performance of a building under three different soil categories. To achieve this, the behavior of a structure placed on three categories of soil—hard, medium, and soft—was assessed. A comprehensive literature review was conducted to understand the fundamental concepts of SSI, the techniques used to analyze it, and its influence on the seismic demands of buildings. The adopted methodology began with site assessment and gathering the geometric data of the building. Subsequently, a standard 11 story hospital building was analyzed following European standards. The underlying soil was modeled using the direct approach to account for soil flexibility. The building was then subjected to the 1952 Hollywood Storage earthquake, utilizing Midas Gen and Midas GTS NX for structural and geotechnical analysis, respectively. The results were evaluated and compared based on vibration period, lateral deformation, inter-story drift, bending moment, and shear force, across different soil conditions. Findings indicated that as the stiffness of the subsoil decreases, the influence of SSI on the building's seismic response becomes more significant and adverse. Specifically, SSI led to an increase in vibration period, lateral displacement, and inter-story drift, especially on soft soil. These results emphasize the importance of considering SSI in the dynamic design of buildings on soft soil to ensure structural safety.Item Truss Reinforcement vs. Conventional Arrangements of Stirrup for Enhancing Shear Capacity of Slender Beams.(Addis Ababa University, 2025-12-01) Tamrat Ali; Esayas G/YouhannesThis study investigates the importance of using truss reinforcement stirrup arrangement as an alternative to Conventional vertical stirrups as the shear reinforcement in slender reinforced concrete (RC) beams. The goals of the study are to experimentally investigate the shear behavior and failure modes of slender RC beams with stirrups arranged in truss form compared to beams reinforced with Conventional stirrups, and to develop numerical models using Abaqus that would simulate beam shear behavior and to verify the numerical models with the experimental results of the beams based on comparisons of load capacity, crack patterns, and failure modes and to select the best inclination angle. The experimental phase involves castings of three slender RC beams with the same dimensions, same materials and same load configurations, but with different stirrup configurations (Conventional vertical stirrups, non-staggered Warren truss stirrup, staggered Warren truss stirrup). And set the surface monitoring system with transducers to monitored shear strain at the left side of the front face of each beam. This study investigated the effectiveness of truss reinforcement to replace conventional vertical stirrups as shear reinforcement in slender reinforced concrete (RC) beams. The study objectives: experimentally investigating shear behavior and failure modes of slender RC beams with stirrups configured in truss form in comparison to beams using conventional stirrups. In the FEM study, five different models were used, including the conventional stirrup model and truss types with two different inclination angles of 45° and 57°. The findings revealed that all beams failed by shear mode, where the beams with the truss stirrups with 570 inclined exhibited higher ultimate shear strength than the beams with conventional stirrups. The non-staggered truss stirrups with 570 inclined had 18.25 % improvement for experimental ultimate load and 31.09 % improvement predicted using FEM. The staggered truss configuration with 570 inclined was shown to have the largest improvement with experimental ultimate load improvement of 26.75% improvement and FEM capacity increment of 32.89%. The staggered truss stirrups with 570 inclined were determined to be the most beneficial stirrup arrangement for improving shear strength. In FEM analysis, non-staggered and staggered truss stirrups inclined at 45° exhibit lower shear capacity than all other truss types and conventional stirrups, as observed in both experimental and FEM results.Item Seismic Evaluation of Cost-Effective Houses around Addis Ababa Due to Current Earthquakes in Awash Region (Case Study of Condominium Building)(Addis Ababa University, 2025-09) Suleyman Mohammed; Edom Adane (PhD)Ethiopia, particularly the Afar region, has experienced a significant increase in seismic activity, including frequent tremors in the Awash region. This heightened seismic risk necessitates a comprehensive evaluation of seismic performance of buildings, especially low-cost housing structures. Seismic evaluation of constructed buildings is mandatory especially in Ethiopia region where the great east African rift valley crosses our country Ethiopia. Studies shows or predicts that the country Ethiopia inclusive of Africa will bisect into two different continents. Recently starting from September to end of October 2024 unusual weekly repeating earthquakes making its initial (epicenter) from awash region is occurring and the ground shake vibration is felt in 10km radius including in Addis Ababa. The performance of existing building in seismic evaluation area mainly affected by ground excitation. Ground acceleration is the principal cause of collapse in reinforced concrete structures developed in seismically active zone. This might be owing to either the unanticipated nature of the seismic excitation or due to lack of suitable structural design, detailing and construction. It is mandatory to accurately assess the response of the structure during seismic excitation. Codes are unable to foresee the real-time reaction of structures when it comes to response determination. Therefore, the existing structural performance assessment should be done using a reliable and easily applicable analysis procedure. The revised Ethiopian building code shows a major change on Ethiopia’s hazard map in terms of peak ground acceleration. The expected peak ground acceleration (from 0.05g to 0.1g) for Addis Ababa [1]. And also incorporate two types of spectra that depends the surface wave magnitude (Type 1 and Type 2) that happen recently earth quick fluctuate in those two ranges. Many buildings have been designed and build in accordance with the previous building code for the past few years. This change has the significant impact on these structures’ performance. Therefor it is necessary to evaluate the effectiveness of the current structures using the revised code’s provisions. Because condominiums are built on a large scale across the nation and are places where people congregate, this study focus on them. Premature failures are not anticipated to occur, according to the study's premise. The main objective of the study is to assess the seismic performance of residential condominium buildings that have been built in Addis Ababa for earthquake design. The existing residential condominium buildings have been chosen for the study.From the existing 40/60 high rise condominium houses located in Addis Ababa, four samples (Building Typology of B+G+7, B+G+9,2B+G+12 and 2B+G+18) were chosen for the assessment. Architectural, structural as built structural detail and some design reports were taken from CITY GOVERNMENT OF ADDIS ABABA SAVING HOUSING HOUSE DEVELOPMENT ENTERPRISE for modeling purposes. The structural modeling was analyzed and designed by linear static and nonlinear static pushover analysis using ETABS 22.0.0 (cracked) Engineering software. Furthermore, damage limitation limit state and ultimate limit state have been considered for the linear static analysis. Base shear, story displacement, story drift, and design spectra were compared in this study in order to analyze the building; The findings base shear, story displacement and story drift significantly changed as the result of revision but spectrum type in the performance evaluation did not significantly change. Lastly, push over analysis was used to evaluate the case study building's performance level. All four typologies used for the study—Building TypologyB+G+7, B+G+9, 2B+G+12, and 2B+G+18)—had sufficient capacity to withstand damage limiting earthquakes, according to the results of linear static analysis. And going additional investigation on nonlinear static analysis showed Only two structures (structure Type B+G+9 and 2B+G+18) had sufficient capacity to ensure life safety but 2B+G+18 has good performance in Y direction between (A and Io), while the other one building (Building Type B+G+7 and 2B+G+12) had inadequate for IO it is in the range of LS(life safety) near Cp (collapse preventive). But the most important discovery was that every type of building did not pass ultimate limit state evaluation, which is a crucial criterion outlined in the code. The majority of house construction in the town area is from this construction type and the performance of the buildings against earthquake forces was shown to be poor. Accordingly, it is important to seismically retrofit the existing buildings to mitigate potential disasters to be caused by future earthquakes.Item Parametric Study of Reinforced Concrete Beams Strengthened in Flexure by Fiber Reinforced Polymer(Addis Ababa University, 2025-05) Kaleab Teshome; Abrham Gebre (PhD)This study examines the effect of parameters on damaged Reinforced Concrete (RC) beams by using Finite Element Analysis (FEA) method. A software verification was conducted for the ABAQUS software by using an experimental result that is found in a literature review. The result shows that the FEA method gives approximately similar results to the experimental results. A Latin Hypercubic Sampling (LHS) method was used to create 32 samples that have 7 parameters. The FEA software was used to conduct a non-linear analysis for 32 samples of damaged RC beams that are strengthened with Carbon fiber Reinforced Polymer (CFRP) on the sides. The non-linear FEA results indicated that the stiffness of strengthened RC beams increased compared to un-strengthened beams. An equation that can be used to determine the extent of flexural strengthening that can be applied on the side of a damaged RC beams has been formulated by using regression analysis. According to a sensitivity analysis conducted to determine which parameter affects most amongst the parameters of degree of damage, ratio of length of CFRP to length of beam (LCFRP/Lbeam), ratio of width of CFRP to depth of beam (bCFRP/hbeam), number of layers of CFRP, compressive strength of concrete, yield strength of reinforcement and tensile reinforcement ratio (ρ) in a strengthening method, it is shown that the tensile reinforcement ratio (ρ) and the ratio of the length of the CFRP to the length of the beam (LCFRPP/Lbeam) have showed the highest direct effects on the load carrying capacity of strengthened RC beams. While the degree of damage showed an inverse effect. A verification of the equation was conducted using both strengthened and un-strengthened RC beams. The results showed that the equation should only be used for strengthened RC beams. The equation was also compared with other analytical equations provided by researchers and codes such as ACI 440.2R-08, Bai Y-L et al., Stephen Lee and CEB-FIP technical report [1, 2, 3, 4]. The comparison shows that the FIB technical report and the ACI440.2R-08 are in good agreement with the proposed equation. The comparison also showed that the proposed equation is conservative than the researches conducted by Bai Y-L et al. and Stephen Lee.Item Study on Local Steel Profiles in Steel-Concrete Composite Bridges(Addis Ababa University, 2009-08) Dawit Hailemariam; Asnake Adamu (PhD)Building a functional transportation infrastructure is a high priority for a nation, particularly for developing country like ours. Currently, the Ethiopian government has given special attention for road construction sector and is to invest billions of dollars. Parallel to road construction, there is also a demand of construction of bridges as most of the existing ones are getting older as they are constructed, during colonization by Italians. Construction of such bridges naturally occupy longer construction time where the time required may be farther exacerbated due to shortage of budget beside having bad construction management practice which is observed in many construction undertakings. Associated with this, the normal day to day traffic flow is affected and causes discomforts to the road users. This problem is serious especially in towns where there is high traffic volume and provision of detours is not simple. Thus, as alternate, steel-concrete composite bridge which obviously shortens the construction time and alleviates the problems with other added advantages is thought in this study. Therefore, in this thesis attempt is being made to compare the usage of locally produced steel profile in steel-concrete composite bridges with the conventional reinforced concrete deck girder bridges cost wise, beside evaluating other merits of such application. In the thesis work, relevant literatures are reviewed, assessment of availability of local steel profiles for such application has been made to local private and governmental companies that are engaged in manufacturing, supplying and installing of such steel profiles for different engineering purposes. Kality Metal Products Factory, Mesfin Industrial Engineering PLC and Maru Metal Industry are among some whose local products are considered. Accordingly, it is observed that there is local capacity and experience of manufacturing I-section profiles by welding steel metal sheets which are imported from abroad. The practices have been observed with application for buildings, steel bridges and manufacture of vehicle body parts. Thus, the study makes use of these I-section profiles, for design of steel-concrete composite bridge superstructures having span lengths of 12m, 15m, 20m and 24m. For the purpose of comparison, the same span lengths and width of reinforced concrete deck girder bridges are also designed. Finally, based on design out puts, quantities of each item are summarized and using appropriate unit rates, cost analysis and evaluation of the two bridge types is carried out. It is observed that relatively compact and lighter bridge cross-sections can be obtained by using steel-concrete composite structures than the reinforced concrete ones. The steel beams can also be manufactured in workshops prior to the start of the construction and this can reduce the required construction time. Nevertheless, it is concluded that with current market condition and work exposure of metal industries, cost required for steel - concrete composite bridge construction is higher than that of reinforced concrete deck girder bridges of the same span, for spans under consideration. During the study, it is noticed that there are few metal industries that are involved in the manufacturing of steel profiles specially those for steel-concrete composite bridge constructions. So, investors should be encouraged to the sector so that designers could have free choices both in quality and shapes. It is also suggested that as markets are demand driven, consultants and designers should initiate and direct the metal industry by designing steel structures as an alternative. As final recommendation, further studies should be carried out to check feasibility of such constructions in our country in line with the change in development of the metal industry and construction skills, as the time saving by itself is a promising and vital item to be considered in bridge construction.Item State-of-the-Art review of Numerical Methods in Structural Dynamics(Addis Ababa University, 2021-11) Betely Tamiru; Shifferaw Taye (PhD)In this paper, a state-of-the-art review is carried out on numerical methods comprising the Central Difference, Houbolt, Newmark, Wilson-𝜽, HHT-𝜶, WBZ-𝜶, Generalized-𝜶, Bathe and Piecewise Exact Methods. Three algorithms (related to Piecewise Exact Method and Power Series Method) are developed for linear and nonlinear systems. To analyze the performance of the methods, the stability and accuracy of the above-mentioned methods are studied and some solutions for illustrative examples are presented. The HHT-𝜶, WBZ-𝜶, Generalized-𝜶 and Bathe methods have controllable dissipation in higher methods. The piecewise exact method (method based on interpolation of excitation) and the proposed methods are effective in providing accurate results (compared to other methods) for the truncated modal space.Item Buckling Response Analysis of Concrete Circular Domes(Addis Ababa University, 2023-03) Birku Fentaw; Shifferaw Taye (PhD)Concrete circular dome roofs are widely used on large-diameter churches, mosques, houses, schools, storage and business facilities, industrial and commercial buildings, football-filled roofs and basketball stadiums, and so on, as they provide high strength for very limited amounts of material: buckling normally controls the design. The purpose of this study is to investigate the linear buckling behavior of a circular concrete shell with a constant span of 40m. To do so, the linear buckling response of a concrete circular dome under dead load, live load, seismic action, and combinations of these, the linear buckling response of a concrete spherical dome with pinned and fixed support conditions when subjected to the horizontal component of earthquake load, the linear buckling response of a concrete circular dome with variable thickness and rise are investigated. For analysis, analytical and SAP2000 version-21 finite element software is used. In this scenario, five distinct radius-to-thickness ratios are used to determine the linear buckling responses of a circular concrete shell under the action of dead load and the horizontal component of seismic action, and the effect of different dome support conditions is considered. The buckling behaviour of the circular shell roof changes as the radius-to-thickness ratio and span-to-raise ratio change. The numerical value of buckling pressure decreases as the radius-to-thickness ratios and span-to-thickness ratios increase, and vice versa. Different dome structures with different geometry designations are used to make results more reliable. Software results are almost the same as empirical results. Hence, the findings are reliable and valid.Item Effect of Aggregate Size on Shear Strength of Reinforced Concrete Beam-Column Joint(Addis Ababa University, 2025-05) Murad Musbah; Esayas Gebreyohannes (PhD); Sadik Muzeyn (PhD)The beam-column connection is an important area within reinforced concrete moment frames. Significant shear is likely to be experienced by this connection during strong ground shaking as the loads are transferred from the beam to the column, and the way in which the connection acts can have a significant influence on how the whole structure is going to perform. Much of the literature simplified the connection as behaving rigid, and did not take into account that we have high shear forces concentrated within the connection. Ultimately, failure in shear is very brittle at the connection and we would not want to see this structurally in a seismic region. The performance of beam–column joint comes from proper detailing of reinforcement and the strength of concrete. General property of concrete, strength, and durability, comes from its ingredient. Aggregate is an important element in concrete mixing and the resultant compression and tensile strength. Concrete failure properties are significantly affected when the size of aggregate change. This research will focus on the effect of aggregate size and volume on shear strength of reinforced concrete beam column joint. Generally beam- column joint are areas with relative higher congestion of bars. Hence it will be difficult for concrete to pass. Fine aggregates can reach inside whereas aggregate with larger size difficult to reach inside core concrete. This may cause change in composition inside joint that may cause reduction on shear strength of beam column joint. This research identify how coarse aggregate size affect shear strength of reinforced concrete beam column joint. Based on experimental result of five RC beam–column specimen with 37.5mm, 25mm, 12.5mm, 4.75mm maximum nominal aggregate size and one additional specimen with 25mm but sieved with 9.5 mm sieve mesh at the joint to represent the effect of bar congestion. Using aggregate with a larger size, typically provides higher shear capacity for the joint. In addition to shear capacity, aggregate size also affects the joint behavior after the peak strength is reached. Specimens with larger aggregates typically fail in a more ductile way than those with smaller aggregate. In addition, there is also higher initial stiffness for larger aggregate size specimens. Generally, the roll of aggregate size and volume is found to be critical for the seismic performance of beam column joint.Item Study on Local Steel Profiles in Steel-Concrete Composite Bridges(Addis Ababa University, 2009) Dawit Hailemariam; Asnake Adamu (PhD)Building a functional transportation infrastructure is a high priority for a nation, particularly for developing country like ours. Currently, the Ethiopian government has given special attention for road construction sector and is to invest billions of dollars. Parallel to road construction, there is also a demand of construction of bridges as most of the existing ones are getting older as they are constructed, during colonization by Italians. Construction of such bridges naturally occupy longer construction time where the time required may be farther exacerbated due to shortage of budget beside having bad construction management practice which is observed in many construction undertakings. Associated with this, the normal day to day traffic flow is affected and causes discomforts to the road users. This problem is serious especially in towns where there is high traffic volume and provision of detours is not simple. Thus, as alternate, steel-concrete composite bridge which obviously shortens the construction time and alleviates the problems with other added advantages is thought in this study. Therefore, in this thesis attempt is being made to compare the usage of locally produced steel profile in steel-concrete composite bridges with the conventional reinforced concrete deck girder bridges cost wise, beside evaluating other merits of such application. In the thesis work, relevant literatures are reviewed, assessment of availability of local steel profiles for such application has been made to local private and governmental companies that are engaged in manufacturing, supplying and installing of such steel profiles for different engineering purposes. Kality Metal Products Factory, Mesfin Industrial Engineering PLC and Maru Metal Industry are among some whose local products are considered. Accordingly, it is observed that there is local capacity and experience of manufacturing I-section profiles by welding steel metal sheets which are imported from abroad. The practices have been observed with application for buildings, steel bridges and manufacture of vehicle body parts. Thus, the study makes use of these I-section profiles, for design of steel-concrete composite bridge superstructures having span lengths of 12m, 15m, 20m and 24m. For the purpose of comparison, the same span lengths and width of reinforced concrete deck girder bridges are also designed. Finally, based on design out puts, quantities of each item are summarized and using appropriate unit rates, cost analysis and evaluation of the two bridge types is carried out. It is observed that relatively compact and lighter bridge cross-sections can be obtained by using steel-concrete composite structures than the reinforced concrete ones. The steel beams can also be manufactured in workshops prior to the start of the construction and this can reduce the required construction time. Nevertheless, it is concluded that with current market condition and work exposure of metal industries, cost required for steel - concrete composite bridge construction is higher than that of reinforced concrete deck girder bridges of the same span, for spans under consideration. During the study, it is noticed that there are few metal industries that are involved in the manufacturing of steel profiles specially those for steel-concrete composite bridge constructions. So, investors should be encouraged to the sector so that designers could have free choices both in quality and shapes. It is also suggested that as markets are demand driven, consultants and designers should initiate and direct the metal industry by designing steel structures as an alternative. As final recommendation, further studies should be carried out to check feasibility of such constructions in our country in line with the change in development of the metal industry and construction skills, as the time saving by itself is a promising and vital item to be considered in bridge construction.Item An Experimental Investigation on The Effect and Mechanism of Side Cover for Deep Beams(Addis Ababa University, 2025-06) Muhammed Jemal; Esayas Gebreyouhannes (PhD)This study investigates the effect and underlying mechanism of side cover spalling in reinforced concrete deep beams subjected to shear. While prior research, such as that by [2], has focused on slender beams, this thesis addresses a critical gap by examining deep beams, whose shear behavior is governed by arch action rather than flexural beam theory. A series of six full-scale deep beams with varying side cover thicknesses and stirrup cage configurations were experimentally tested under three-point monotonic loading. Two configurations were explored: SA-series beams, which maintained a constant outer width and reduced the core with increasing cover, and SB-series beams, which preserved the core width while increasing total width by adding cover externally. The primary aim was to determine whether large concrete covers compromise shear performance due to premature side cover spalling. Observations revealed that spalling initiates near peak load, particularly when the stirrup cage is confined by a reduced core, as in the SA-series. Despite observable spalling in all specimens, the presence of adequate core concrete and stirrup confinement significantly influenced the beams' ability to reach peak load without premature failure. Finite element modeling results from Vector2 were compared with the experimental findings. The Experimental findings highlighted the limitations of current two-dimensional analyses in capturing out-of-plane spalling. Importantly, the results demonstrate that increasing the concrete side cover does not enhance the stiffness (except for the initial stiffness) or peak load capacity of deep beams. This finding sharply contrasts with the assumptions in most building design codes, such as ACI 318 and Eurocode 2, which treat the entire crosssectional width—including the cover zones—as fully effective in resisting shear and flexure. The test results suggest that once the core (stirrup-confined zone) is sufficient, additional concrete cover adds little to structural performance and may even introduce weaknesses due to spalling risk. Additionally, SB-series beams display stable load-displacement behavior with limited post-peak softening, indicating improved ductility relative to SA-series specimens. This research contributes to a more accurate understanding of D-region behavior in deep beams and underscores the need to re-evaluate code provisions related to effective shear/flexure width, particularly in the presence of large concrete covers.Item Seismic Performance Evaluation of Wall Equivalent Frame System Reinforced Concrete Building Structure(Addis Ababa University, 2025-06) Danait Tsegaye; Bedilu Habte (PhD)These days, predicting inelastic seismic responses and evaluating a structural building's seismic performance are crucial topics. This thesis evaluates the seismic performance of wall equivalent frame system reinforced concrete building structures, categorized as low rise, medium rise, and high rise, with a particular emphasis on this idea. The pushover analysis approach is used to evaluate the nonlinear response of the RC buildings under consideration in this thesis. Various shear wall locations are used, along with the presence or absence of slab openings and the introduction of irregularities in plan and elevation. Twelve Wall equivalent frame system reinforced concrete building models with ductility class medium have had examined their performance using the finite element analysis program ETABS 2021.1.1. Every model has been analyzed (response spectrum analysis) and designed (capacity design) in compliance with Ethiopian building codes and requirements. The performance for the models (G+5, G+15 and G+30) has been evaluated by discussing the results of the nonlinear static analysis. The seismic performance evaluation is carried out for different shear wall location, presence of slab opening and introduction of irregularity. The building's top story displacement, inter-story drift, capacity curve and plastic hinge distribution are the parameters used to evaluate the seismic performance of the structures. Based on this, the Top displacement value shows increment in Y Direction for the parameters; placing shear wall at the center by 5% relative to the edge, effect of having opening increase the Top displacement by 2% and having a plan irregular building increase the result by 10%.Introducing Irregularity in the building decrease the performance level by 0.8%, 5%, 8% for low, medium and high rise building respectively and having shear wall at the center by 0.4%,4% and 6%, the least effect is shown for introducing opening which is 0.1%, 0.9% and 2% for the buildings under consideration.Item Partial Replacement of Cement with Municipal Solid Waste Incinerator Fly Ash in Concrete Production(Addis Ababa University, 2025-02) Merem Sualih; Girma Zerayohannes (PhD); Esayas Gebreyohannes (PhD) Co-AdvisorFly ash resulting from municipal solid wastes incinerator (MSWI) can be potentially reused as cement replacement in concrete. However, several researchers suggest that fly ash requires pre-treatment due to its high chlorine content to be used as partial substitute for cement in concrete. Currently large amount of fly ash is generated in thermal power plant as waste material with an improper impact on environment and humans in Ethiopia. Fly ash waste generated by Reppie thermal power plant is as such a big environmental concern. This research examines the potential of using treated and untreated MSWI fly ash as partial replacement of cement in concrete production for saving waste disposal cost, conserving natural resource and for mitigating the environmental impact of cement production. This study aim to investigate early and late age mechanical and durability properties of untreated and treated fly ash concrete. In this research, the fly ash was treated by washing with water only to reduce the chlorine and sulfur. Concrete mixture containing 0%, 10%, 15%, and 20% dosage of untreated and treated fly ash by volume were proportioned. The compressive and flexural based tensile strength result at three, seven, twenty-eight and fifty-six days and also the water permeability data for twenty-eight days are determined. The experimental outcome indicates that the compressive strength of treated fly ash is lower compared to untreated fly ash, but still fall with in an acceptable range when compared to the control mix. The compressive strength of washed fly ash concrete with 10% and 15% replacement ratio exceed the control group’s 28th-day strength by 0.15% and 3.78% respectively. However, the flexural strength decreases as the level of both washed and unwashed fly ash increase. Still, the washed fly ash at 10% and 15% replacement level exhibits acceptable result when compared to the control group. Moreover, the 10% and 15% washed fly ash replaced concrete sample possess a better water tightness performance than the controlled sample. Based on the result, the treated FA can replace cement up to 15%.Item High-Temperature Performance of Concrete Utilizing Waste Ceramic Coarse Aggregate as Partial Replacement(Addis Ababa University, 2025-02) Sarem Jezbu; Esayas Gebryouhannes (PhD)The increasing demand for sustainable construction materials, along with the growing need for improved fire resistance in structural elements, has accelerated research into alternative aggregate sources for concrete production. In this context, this study investigates the high-temperature performance of concrete in which waste ceramic coarse aggregate, sourced primarily from discarded tiles and sanitary ware, is used as a partial replacement for natural coarse aggregates. The core aim is to address two pressing challenges in modern construction: enhancing concrete’s resistance to elevated temperatures and promoting the sustainable use of construction and industrial waste. A series of concrete mixtures incorporating waste ceramic aggregate at replacement levels of 10%, 20%, 30%, 40%, and 50% by volume were prepared and subjected to both ambient conditions and elevated temperatures up to 600°C. After heating, specimens were cooled either gradually in a furnace or by immersion in a limited volume of water to simulate post-fire scenarios. Comprehensive tests were carried out to assess residual compressive strength, mass loss, and workability. The results demonstrated that concrete with 40% ceramic aggregate achieved the best overall performance, retaining more than 70% of its original compressive strength after thermal exposure. Water-quenched specimens consistently outperformed those cooled in the furnace due to shorter exposure to damaging high temperatures and the moderated thermal shock effects provided by steam and rising water temperatures.The superior performance of ceramic-modified concrete is attributed to several synergistic factors. The angular and irregular shapes of the ceramic particles contribute to improve internal packing, which reduces porosity and enhances strength. Moreover, the pozzolanic reactivity of ceramic materials due to their silica and alumina content supports secondary hydration reactions, thereby enhancing matrix cohesion and long-term durability. A stronger interfacial transition zone (ITZ) is formed, further improving the mechanical integrity of the concrete. Additionally, ceramic aggregates exhibit low thermal conductivity and high heat resistance, properties that significantly enhance the thermal stability of concrete under high-temperature exposure. Workability is also improved due to the smooth surface texture and lower water absorption rate of the ceramic aggregates, simplifying the mixing and placing process. In Ethiopia, where construction activity is rapidly expanding and ceramic waste is increasingly abundant but underutilized, the application of ceramic aggregates offers a dual advantage: reducing environmental waste while supporting infrastructure development. The findings of this study suggest that up to 40% replacement of natural coarse aggregate with waste ceramic aggregate provides an optimal balance between mechanical strength, thermal resistance, and sustainability. This position’s ceramic-modified concrete as a viable solution for fire-resistant construction in hot or fire-prone environments. In conclusion, this research demonstrates that waste ceramic materials can be effectively repurposed into durable and thermally resilient concrete, offering an eco-friendly and cost-effective alternative to conventional aggregates. The use of waste ceramic in concrete not only enhances mechanical and thermal properties but also aligns with circular economy principles by minimizing industrial waste and promoting resource efficiency. These findings contribute meaningful insights into sustainable construction practices, particularly in regions where exposure to high temperatures is expected, and encourage the development of policies and recycling infrastructure to support broader implementation.Item Development and Using Carbon Fiber Reinforcing Polymer to Strengthen The Flexural Capacity of Damaged Post-Tensioned Beams(Addis Ababa University, 2024-10) Maraki Gedu; Abrham Gebre (PhD)Post-tensioning is a type of pre-stressing in which high-strength steel strands or bars; commonly referred to as tendons, are used to reinforce (strengthen) concrete or other materials. Carbon ber-reinforced polymers on the other hand are incredibly light and strong ber-reinforced plastics that are used to enhance concrete structures by bonding the polymer to the concrete member. Damage to structural members can occur due to di erent reasons in various real-world applications. Similarly, post-tensioned members can also be subjected to damage due to various reasons, such as accidental cutting or drilling into tendons, failures in anchorage and dead end zones resulting from issues like insu cient anti-burst reinforcement, mis- alignment of the anchor, and improper material utilization. These problems can lead to the loss of prestressing force in post-tension strands, which in turn can decrease the load carrying capacity of the elements, particularly their exural capacity. This thesis paper investigates the potential of Carbon Fiber-Reinforced Polymer (CFRP) strengthening in enhancing the exural capacity of damaged post-tensioned concrete beams. Employing an experimental program, the study compares the performance of control beams to beams strengthened with varying CFRP layers. Results demonstrate a sig- ni cant increase in exural capacity, averaging 41.5% per CFRP layer, highlighting the e ectiveness of this strengthening technique. How varying amount of post tensioning and CFRP wraps a ect cracks and delamination patterns of carbon ber were also stud- ied and discussed in detail. Further exploration into alternative ber types and testing con gurations is recommended. .Item Performance of Self Compacting Concrete Used in Congested Reinforcement Structural Element(Addis Ababa University, 2018-06) Asnake Kefelegn; Abrham Gebre (PhD)Self-Compacting Concrete (SCC) is a concrete which can be placed under its own weight without vibration. Whereas Vibrated Concrete (VC) is a concrete which is compacted by means of mechanical vibration. SCC exceeds the current limitations of VC in providing superior material properties, namely passing ability through dense reinforcement resulting in fewer material defects and increasing durability. SCC can be considered as a feasible option where limitations of VC in relation to achieving full compaction of congested reinforcement structural elements. This paper compares the structural performance of congested reinforcement beams cast with Self Compacting Concrete (SCC) and identical beams cast with Vibrated Concrete (VC). Two different geometric cross-section and length, different longitudinal reinforcement ratios, and same stirrup configuration for all specimens were used. A total of 12 beams: 6 were tested in the experimental investigation (4 were cast with SCC and 2 were cast with VC in reinforced sections) and 6 (3 for each type of concrete) were investigated using software simulation. The results were compared with design performance prediction as per Euro code2. All beam specimens were tested under monotonic mid-span concentrated loading to determine the overall structural behavior of reinforced concrete beams. The test results on reinforced beams showed that SCC concrete performed better in reinforcement congested beam element than the referenced VC concrete beam element. The study also showed that the difference in mix composition of SCC from that of VC concrete would have no effects on the overall load-deflection response of reinforced concrete (RC) beam.