Structural Engineering

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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.
Alternative Approach for The Analysis of Suspended Slab Panels Under Partition Wall Load
(Addis Ababa University, 2005-06) Seyoum, Thomas; Zekeria, Adil(PhD)
Analysis techniques for most structural elements with different arrangement of externally applied loads are well developed and sufficiently covered with modern analysis theories. Further more, the application of today’s high-speed computers enables the analysis of complex structures with different load arrangements. In addition to these effective analysis tools, building design codes provide table of values and analysis charts for the analysis of different elements of structural systems. As one of the structural element in building structure, different analysis methods were proposed for the analysis of suspended slab panel subjected to non-uniform loads. Among the possible arrangement of externally applied loads on suspended slab panel a line load is the one which can best represent the weight of partition wall on it. Different simplified analysis methods were proposed to consider the contribution of this load to the design action effects. The current practice of accounting this partition wall loads in the analysis of suspended slab panel is to change it to the 'equivalent' uniformly distributed load. The analysis of regular slab panel subjected to uniformly distributed load may be carried out using computer softwares or using coefficients which are presented in many design codes (including the Ethiopian Building Code of Standards for concrete structures, EBCS 2 – 1995). The Swedish method and Reynolds method can be referred as some of the examples which are used to obtain equivalent uniformly distributed load. These methods analysis need to be investigated whether they can represent the actual load or not. Therefore, as it is important to address this problem, comparative analysis has been carried out. A new simplified method which considers the actual scenario has been developed. This newly proposed method makes use of coefficients derived from the basic principle of elastic analysis of plate. The results have been verified by comparing it with results of the finite element analysis. It enables us to make elastic analysis of suspended slab panel subjected to the weight of partition wall and avoids the uncertain use of approximate methods.
Analysis Aid Preparation for Self Supporting Fixed Ended Helical Stairs
(2015) Gizaw, Yonathan; Habte, Bedilu (PhD)
As amazing its appearance is, spiral stair has complex geometric configuration. As a result of this complexity, its analysis is challenging. And our Building Code of Standard doesn’t have analysis aid for these special structures, like the ones we have for slabs. Hence, the purpose of this study is to come up with a convenient and user friendly analysis tables and charts for the analysis of spiral stairs. This research follows analytical and finite element approach interdependently. The out come of the research is perceived by accompanying the comparative assessment of the two approaches. The analysis of spiral stairs is done in different approaches. First detail formulation is derived for the stair using strain energy concept considering the stair as twisting girder and in plane curved beam. Secondly, modeling and analysis is carried out using finite element technique as 3D twisting beam and 3D twisting shell stair slab separately. Then, graphical and tabular comparison is done between all approaches. In addition, modification factors are formulated considering variation of internal actions along stair width. More over, valid width is demarcated to limit the acceptable width for the applicability of centerline model for stain energy solution of helical stairs. Hence, the analysis tables and charts that are annexed in the write up together with the modification factors presented are very crucial tools for the analysis of these spectacular complex structures.
Analysis and Design of Assembled Steel Truss Bridges
(Addis Ababa University, 2007-10) Tihitina Siyoum; Tebedge, Negussie(Prossefor)
Analysis and Design of Prestressed Concrete Sleeper
(Addis Ababa University, 2014-11) Fisseha, Desalew; G.Youhannes, Esayas (PhD)
The track system consists of structural components like sleeper that has to be designed to accommodate the maximum tonnage. The main function of sleeper is to transfer the load from the rail to the ballast via the rail pad and to the under laying formation. The analysis and design of concrete sleepers requires the assessment of load on the sleepers, ballast pressure distribution, selection of the dimensions of the sleeper followed by bending moment calculations at rail seat and center section of sleeper and finally checking of the stresses in sleeper ensuring the factor of safety. The aim of this paper is to analyze and design a pre-stressed pre-tensioned concrete sleeper having an optimal shape, strength and tendon type and profile with reference to the current sleeper type which is used by ERC. The existing sleeper length, fastening system, spacing and area of reinforcement are maintained constant. The research is done by conducting literature review related to this paper work, design data and input parameters are collected from ERC, analysis of the existing sleeper have been made, proceeding the parametric optimization of new model with respect to geometry (shape), concrete grade, pre-stressing tendon type and profile. The optimization output shows that increasing the concrete grade results an increase in sleeper capacity but has no more effect on moment capacity which is largely dependent on the section dimension of the sleeper, tendon strength and eccentricity. Increasing the diameter of the tendons has direct relation on sleeper capacity and inversely related to pre-stresses losses which exceed the maximum limit beyond a certain magnitude (9mm diameter). The shape of the sleeper is investigated based on the ballast pressure which shows wider dimension at the end and tapering to the center; the reduction is gradual to avoid stress concentration. The final optimized design outputs and analysis result of the existing sleeper are compared with respect to raw material consumption for production and its capacity. The analysis and design of turnout sleepers, sleepers with additional rails, the effect of the length and spacing of sleeper on its capacity, and the fastening system with relation to lateral and longitudinal loading are recommended for further researches. Keywords: Analysis and Design, current (existing) sleeper, modeling, optimization, prestressed concrete sleeper
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.
Analysis of Mechanical Properties of Cellular Lightweight Concrete Containing Bagasse Ash
(Addis Ababa University, 2017-03) Nigussie, Fitsum; G/youhannes, Esayas (PhD)
The cellular lightweight concrete (CLC) or sometimes might often called that foamed concrete is either a cement paste or mortar, classified as lightweight concrete, in which air voids are entrapped in mortar by suitable foaming agent. This research study various mechanical properties of compressive strength, dry density and water absorption of cellular lightweight concrete (CLC), which made from ordinary portland cement, sand , bagasse ash and foaming agent admixture. Bagasse ash use to replace cement in different proportions from 5 to 30 percent by volume of cement. Optimum replacement percentage is determined using cement-sand mortar then applies in CLC. Optimum bagasse ash present is a percentage which gives same or higher performance compare with CLC without bagasse ash. Different mix of CLC with constant water to binder ratio of 0.5, 1.5% foaming admixture and target density of 1600 kg/m3 were tested. 10% replacement of cement with bagasse ash slightly increases compressive strength and dry density, while 15% replacement of cement gives almost same strength with the control mix. The study result shows that replacing cement with bagasse ash up to 15% improves mechanical properties of CLC such as compressive strength, dry density, water absorption and plastic shrinkage. Key Words: Cellular Lightweight Concrete, Bagasse Ash, Foaming Agent Admixture, Mechanical Properties
Analysis of Steel Frames Under Seismic Loads Accounting for Imperfections
(Addis Ababa University, 2019-10) Mekuriaw, Mihrete; Bedilu, Habte (PhD)
The study presented here is focused on the seismic analysis of moment-resisting steel frames accounting for imperfections. Geometrical and material nonlinear effects are considered in the modeling of steel frames. The objectives of this research are to identify the main parameters affecting the response of moment-resisting steel frames under seismic actions. The effects of modeling problems and their accuracy in analyzing isolated imperfect columns and a simple imperfect steel portal frame were also examined by varying the number of elements per member. Two types of seismic analyses have been carried out by OpenSees for the steel frames considered in this research, these are nonlinear static and nonlinear dynamic analysis. Force-based distributed plasticity approaches were used for modeling of beam-column elements and fiber sections were assumed for modeling steel sections. Initial sway imperfections, residual stresses, and geometric nonlinear effects were considered for the global analysis of frames. The effects of lateral load distributions on the results of nonlinear static analysis have also been investigated by considering three different patterns of lateral load distribution: linear, modal and triangular. The results of the pushover analysis for the frames under consideration show that the lateral load distribution patterns have a greater effect than the magnitude of the loads applied to the structure. The effects of imperfections for moment-resisting sway frames are less than that of the second-order effects. Three verification examples are performed to demonstrate the capability of the OpenSees program in solving nonlinear problems in comparison with experimental results. These examples were analyzed by both OpenSees and SeismoStruct and the results were presented against experimental results. The second-order elastic analysis results for isolated columns show that the number of elements needed per member to model the cantilever column is lower than the pin ended column. A simple portal frame analyzed by modeling imperfections directly to the frame geometry and by replacing imperfections to equivalent lateral loads has no considerable difference between the results from these types of modeling imperfections.
Analytical Investigation of Composite Column And RC Beam Joint With Integrated Joint Connections
(Addis Ababa University, 2022-01) Mahlet, Wondwosen; Girma, Zerayohannes (Prof.)
Hybrid structural frame systems, which combine the use of reinforced concrete and steel, are becoming a viable solution for high-rise buildings. But like all innovative solutions, this comes with the problem of connecting the reinforced concrete beam with these composite columns. In this study, the structural performance of concrete-encased composite columns and reinforced concrete beam joints for selected connection types are evaluated. The main objective of this research is to investigate the two common types of connection, passing through type and wing plate type, and the implementation of a combination of these connections at one joint on an interior steel-reinforced concrete composite column to reinforced concrete beam joint under repeated reverse cyclic loading. Furthermore, the effect of column axial load variation for the three connection types has been investigated under cyclic loading. Beam-column joint specimens are obtained from a published experimental study. A non-linear finite element model is then developed using a three-dimensional software, DuCOM-COM3, and validated using the experimental result. An interior steel-reinforced concrete composite column to reinforced concrete beam joint using the passing through and wing plate connection type has been validated and used as control specimens. A comparative study is conducted between the control specimens and the integrated type specimen. In addition, a total of 18 specimens are simulated by varying column axial load on the three connection types. The analytical result showed that the integrated type specimen exhibits increased ultimate shear capacity and ductility from the control specimens. The increase of column axial load up to 20% of the column capacity on the three connection types showed a slight enhancement in the ultimate storey shear capacity. However, the ultimate storey shear capacity decreased as the axial force increased because of the adverse effect of axial forces on the lateral stiffness of the column. Moreover, an increase in column axial load ratio showed a reduction in the ductility performance of the joints. For the wing plate type specimen, an increase in column axial load ratio showed a determinantal effect on the stiffness and the energy dissipation capacity of the joint.
Analytical Investigation on the Seismic Performance of Partially Prestressed Concrete Beam-column Joints
(Addis Ababa University, 2021-05) Hilina, Assega; Adil, Zekaria (PhD)
Prestressed concrete concept was initially established to develop the performance of concrete members under flexure. But nowadays researchers are pointing out its satisfactory performance under seismic action. In this study, the seismic performance of partially prestressed concrete (PPC) exterior and interior beam-column joint (BCJ) is evaluated. Joint specimens are taken from a published experimental research program executed in Kyoto and Chiba University, Japan. Both joint types are subjected to a reverse cyclic loading at the beam ends and are designed to fail in shear at the joints. A 2D finite element software program, VecTor2, is used to validate the non-linear response of the joints. A total of three interior joint specimens and one exterior joint specimen with variable prestress have been validated. The software sufficiently captured the response of the PPC interior BCJs. While in the exterior BCJ, the software’s capability in capturing the last cycle after peak response was questionable. Six PPC exterior BCJs with variable prestress levels and four PPC interior BCJs with variable column axial load ratio has been analyzed and assessed for further investigation of its performance. The hysteretic response of the PPC exterior BCJ specimens is evaluated based on the ultimate storey shear capacity, stiffness, ductility, strength degradation, energy absorption, and dissipation capacity. Furthermore, the premature failure, and pinching of the PPC interior BCJ specimens, subjected to high compressive stress from column axial load and prestressing force is studied. In the PPC exterior BCJs, Variation of prestressing force didn’t encounter a significant effect on the ultimate shear capacity of the joints. Stiffness, and ductility increased significantly with prestressing force level before remarkable shear crack formation and prestress loss at the joint. Strength degradation was severe with the prestressing level. This phenomenon undermined the inelastic energy dissipation capacity of the highly prestressed joints at the later cycles. Since the software’s capacity is questionable at the last loading cycles, further evaluation of results at this loading stages might be crucial to obtain a more reasonable value. The column axial load variation in the PPC interior BCJ resulted in a considerable effect on the pinching behavior. Premature failure due to concrete crushing at the joint was not observed in any of the specimens.
Application of BIM Using Revit and Other Conventional Structural Design Software: A Case Study on A High-Rise Building
(Addis Ababa University, 2019-06) Eyosias, Dawit; Bedilu, Habte (PhD)
Building information modeling or BIM is a workflow whose application on a construction project will enable all involved players to compile information on every aspect of the building in a central model/database. Through BIM adoption, the entire building can be virtually built on a computer. This research examines the experiences of some countries with BIM and use that insight to introduce BIM to Ethiopian design and construction industry. BIM touches every part of a building’s life cycle starting from the design phase well into the construction phase and beyond that into asset management. However, the research will focus on the design stage of a building. Adaptation of BIM during design stage will require all design team members to implement BIM. The research focuses on structural designers and how BIM can improve the quality of their design. The research demonstrates how all structural design activities can be integrated with each other and how cross-discipline collaboration with architecture can be achieved through BIM adoption. A sample building is taken and BIM is implemented using Revit along with conventional software package ETABS and SAFE. plugins and applications have been developed for all these software packages to facilitate interoperability amongst them so that they can act as a single platform. Modeling, analysis, design and clash detection were all facilitated by applying BIM. Through the research various benefits of BIM were illustrated.
Application of Machine Learning Methods for Shear Capacity of RC Beams
(Addis Ababa University, 2021-12) Birhane, Gemeda; Bedilu, Habte (PhD)
Accurate determination of the capacity of reinforced concrete (RC) beams in shear remains a demanding problem due to its complex failure mechanism and the nonlinear relationship between different factors influencing the shear capacity. This research employs different types of single and ensemble machine learning (ML) based techniques; namely, decision tree, support vector machine, extremely randomized trees, gradient boosting, random forest, and extreme gradient boosting (xgBoost) to correctly predict the shear capacity of reinforced concrete beams. To this end, a dataset of experimental test results of RC beam with and without stirrups comprised of various beam geometry, concrete strength, reinforcing steel strength, longitudinal and shear reinforcement ratios, and shear span-toeffective depth ratio is used to develop the models. The proposed models were calibrated for different values of hyperparameters to achieve optimized ML models. The results of the analysis evidenced that the xgBoost model can be effectively utilized to predict the shear capacity of RC beams. The comparison of the predictions of the proposed and existing models evidenced that the efficiency of the proposed model is superior to the existing models and guidelines in terms of accuracy, safety, and economic aspects with significantly lowest bias and variability. A solid correlation exists between the shear capacities predicted using the proposed model and the corresponding experimental values as evidenced by the value of ��2 (��2 = 0.99) for RC beams without stirrup and (��2 = 0.995) for RC beams with stirrup. The proposed xgBoost model is deployed into a user-friendly web-based application to facilitate a quick and accurate prediction of capacity of RC beams in shear. The web-based application can be used by both practitioners and researchers to accurately predict the shear capacity of beams.
Approximate and Grillage Analogy Methods of Analysis of Rc T- And Box Girder Bridges - Comparative Study
(Addis Ababa University, 2016-04) Gezahegne, Samuel; Adamu, Asnake (PhD)
Bridges are one part of the Road Infrastructures which needs care during design stages, among which include analysis. The most common Bridge superstructures forms widely used are RC T- and Box Girder types. To analyze such forms the most widely used method of analysis is Approximate Method based on Distribution Factor concept. This method is preferred due to its simplicity for use. This method has limitation for not considering stiffness of components sufficiently and effect of provision of diaphragm on load distribution; these parameters have great impact on load distribution between Girders. The result of this method is also considered conservative as compared to more refined method of analysis. In this study, the result obtained by this method and refined method of analysis (Grillage Analogy Method) are investigated. Using these methods, RC T- and Box Girder superstructures are analyzed, considering different Traffic lanes and span length. This task involves examining the maximum Bending Moment and Shear Force using the two numerical models. Furthermore, the effect of Diaphragm on load distribution is also investigated. This study provided useful information about the variation of Bending Moment, Shear Force with respect to change in Traffic Lanes, Span Length and arrangement of Diaphragm. It is concluded that the results obtained from Grillage analogy method are smaller than approximate method, except for shear force of Interior Girder of T-Girder Bridge, which gives slightly higher result where, the percentage differences varies from case to case. For all other cases considered, approximate method gives conservative values. In addition, since approximate method does not consider effect of diaphragm, provision of more number of diaphragms has effect on load distribution is observed for T-Girder than Box Girder in Grillage Analogy method. Key words: T-Girder; Box Girder; Approximate Method (Distribution Factor Method); Grillage Analogy Method; Flexural Moment of Inertia; Torsional Moment of Inertia; Bending Moment; Shear Force; Vehicular Live Load; Traffic Lanes; Span Length
Assessing Code Based Shear Prediction Values of Reinforced Concrete Beams Using Modified Compression Field Theory
(Addis Ababa University, 2016-12) Tsegaye, Surafel; Gebreyohannes, Esayas (PhD)
Though different researches have been conducted so far on shear strength of reinforced concrete beam, it is yet not definite to predict it in accurate manner. As a result, different design codes use different empirical formulae based on truss analogy. The truss analogy which was developed independently in 1899 and 1902 by Swiss engineer Ritter and by a German engineer Mӧrsch respectively. This theory is still deficient in representing the actual response of reinforced concrete element that is subjected to shear. In recent years researchers at the University of Toronto came up with a more rational theory called “The Modified Compression Field Theory (MCFT)”; that can explain the response of a reinforced concrete elements subjected to shear. However, the complexity of this theory necessitate to convert it is procedure in to a computer program. Therefore this research transact code algorithm of MCFT and evaluated both American Concrete Institute (ACI) 318-11 (2011) and EuroCode 2 (2004) design codes procedures. Analysis and design of three different beams that are exposed to different types of loading is conducted using the above two codes. Results have been compared with those obtained from MCFT and have shown a safe results. Also a comparison between this two codes shows, EuroCode 2 gives more economical shear reinforcement spacing than ACI, for beams that require minimum shear reinforcement. Key words: shear; strength; reinforced concrete; computer program; design code.
Assessment and Application of Direct Displacement Based Design for Dual Frame–Wall Reinforced Concrete Buildings
(Addis Ababa University, 2016-06) Kassahun, Eskedar; Zekaria, Adil (PhD)
Assessment and Application of Direct Displacement Based Design for Frame –Wall Reinforced Concrete Buildings Eskedar Kassahun Addis Ababa University, 2016 In this thesis work Direct Displacement Based Design method is assessed in dual frame-wall reinforced concrete building. Traditional forced based design method compared with this method applying to different case studies. The effect of frame shear ratio, base shear shared by the frame, when DDBD design method is applied is studied in detail by taking frame base shear ratio 25%, 40% and 60%, in terms of base shear and displacement of the building. Also the effect of presence and absence of connected link beam which directly has an effect on moment profile of the wall is studied. The effectiveness of the method has been tested by designing a set of case studies. Dual frame-wall building with story 4, 8, 12, 16 and 20 is taken as case studies. From the study the base shear calculated using DDBD is less than FBD in all case studies considered. In low rise building, with storey 4 in this study, the base shear increases as frame shear ratio increase. However in building with higher stories the base shear decrease as frame shear ratio increases. Similarly the storey shear obtained from DDBD is less than FBD in all case studies. Considering building with and without link beam the moment profile with link beam has low moment than that beam without link beam in all case studies.
Assessment and Evaluation of Slab Analysis and Design Practice In Ethiopia
(Addis Ababa University, 2014-08) Gebreegziabiher, Mesgina; Zekaria, Adil (PhD)
The analysis and design of plate elements is too complex, for most cases there is no closed form of solution for these are highly intermediate structures which are full of assumptions, and uncertainty makes difficult for day to day application and become uneconomical during design. To tackle this, researchers and engineers developed simplified method with acceptable reliability and accuracy. Still the limitation is visible that some methods are only applicable to some particular problems. Hence to control this, codes were prepared and used in practical analysis and design practices and used to harmonize the application throughout the country. But many professionals claim that the practice is not to the standard and may damage the economy of the country as whole if some devastating earth quake happens. Moreover, these believes care shall be taken in design, construction and service of the buildings for the country is under development, projects are becoming cost intensive and massive in terms of size (in which large number of occupants may use it). It is clear that buildings shall be safe, economical and serviceable. But is very difficult to attain these requirements the same time , that is, these may need more time, finance and experience with knowledge. Almost all designers claim that the cost provided by most clients extremely unaffordable and time that they required for analysis and design is too short which leads for inexperienced and unqualified designers to join the practice on the contrast the well experienced go to large projects. For instance, in this research, it is identified mechanical engineers participate in design of buildings knowing the analysis software alone. Hence, this study focuses on the actual practice of slab analysis and design assessment and evaluation. It covers international and local challenges faced during analysis and design, approval and construction (partly) of slabs. It compares and clarifies our code of practice with respect to related international code practice and re-evaluates the country local practical (particularly Addis Ababa and Mekelle) practice with our code of standard. Moreover, present and clarifies the methods of slab design and analysis stated in our code
Assessment and Retrofitting Mechanisms of Existing Reinforced Concrete Buildings
(Addis Ababa University, 2017-11) Mesfin, Gizaw; Asmerom, Woldegerima (Mr.)
In the past many cities around the world have been struck by a range of earthquakes which have resulted in the loss of many lives along with the destruction of properties. Cites have been turned into dust and rubbles. Earthquake causes different intensities of shaking at different locations and the damage induced in buildings at these locations is also different. In many countries, tools have been designed and incorporated in their national building codes to decrease the hazards caused by earthquakes starting from the inception of design to the final stage of construction to harmonize designs for the reduction of seismic risk. The goal of this study is to focus on the solution mechanisms to be addressed in strengthening of older and existing reinforced concrete framed building to ensure an appropriate level of safety for occupants in the event of an earthquake. As it is known, the earthquake design parameters have been revised in the new Ethiopian Building Code Standard. According to EBCS 8: 1995, Addis Ababa was categorized in zone 2 in the seismic hazard map. But the new revised code locates the city in zone 3, which doubles the peak ground acceleration. More over the city is expanding towards the outskirts of Addis Ababa like Akaki, Bole Arabssa. In this study, it is considered that the building stock designed earlier before the revision of the code will not survive an earthquake based on the new peak ground acceleration. This brings a question on how these buildings will be strengthened before this kind of destruction and loss of life and property occurs in the city. Therefore, the outcome of this study will benefit the owners as well as the authorities on the retrofitting procedures as well as solution mechanisms of reinforced concrete framed building structures are undertaken.
Assessment of Adjacent RC Buildings Against Free Pounding Distance in Consideration of Soil Structure Interaction
(Addis Ababa University, 2016-11) Asmare, Abayneh; Zekaria, Adil (PhD)
The pounding action mainly depends on the main character which is the peak lateral displacement of the structural systems due seismic action, the influence of soil structure interaction at seismic event in respect to avoid pounding between two adjacently constructed structures is investigated. The modeled structure buildings runs from 6 (G+5) to 26 (G+25) stories with realistic lateral force resisting system and they are studied with different ideal soil class units and with moderate peak ground acceleration value. The result of the structural model systems peak lateral displacement with and without consideration of the effect of soil structure interaction has been presented. Observations of peak lateral displacement regarding the consideration of different class soil type are discussed. The result of the study indicates providing minimum free pounding distance is something elegant to avoid the pounding action in any circumstance and consideration of the soil structure interaction significantly influence the pounding free distance in affirmative way by avoiding pounding that comes from additional peak lateral displacement of the systems.
Assessment of Behavior Factor recommended in EC8 for Reinforced Concrete Planar Frame Using Nonlinear Analysis
(Addis Ababa University, 2018-03) Omar, Nega; Adil, Zekaria (PhD)
According to current seismic codes the structures are calculated using the capacity design procedure based on the concept of at the shear base depending on several parameters including behavior factor which is consider to be the most important parameter. The behavior factor allows designing the structure when it is at ultimate limit state taking in to account its energy dissipation through its plastic deformation. The aim of the present study is to assess the basic parameters of the behavior factor among of these the reduction factor due to ductility, redundancy and over strength for reinforced concrete frames of different height and bays. Analysis are conducted on these frames using the nonlinear statics pushover analysis method where the effect of some parameters on behavior factor, such as the number of stories, the number of bays and the member section are taken in to account. The results show that the behavior factor is sensitive to the variation of the number of stories and bays. Also, the value of behavior factor recommended by the Euro Code 8 (EC8) is underestimated, mostly for low-rise (storey four) frames.
Assessment of Current Non-linear Analysis Models used in Earthquake Engineering
(Addis Ababa University, 2019-09) Anur, Oumer; Adil, Zekaria (PhD)
The study aims to evaluate existing numerical nonlinear modeling techniques used in the seismic analysis to provide a common ground for applications of the models in earthquake engineering. Comparative analysis carried out to further asses the existing nonlinear numerical finite element modeling techniques for beam-column elements subjected to lateral loading. First, experimentally tested RC bridge column specimens downloaded from peer structural performance database and modeled in OpenSees finite element software. The study shows, for sections exhibiting strain hardening behavior, the distributed forcebased fiber models provide a more accurate response. The response computed using the distributed displacement-based fiber models overestimate the capacity of the members. Therefore, to accurately describe the inelastic response, several displacement-based elements are required. For the section exhibiting strain-softening behavior, the localization issue affected both the displacement-based and force-based formulations. Therefore, material regularization is required to overcome mesh dependent response. Furthermore, for section showing softening behavior, the regularization of both concrete and steel materials is required. The concentrated force-based plastic hinge model adequately captures the nonlinear response. The lumped plasticity with zero-length hinge model captures the initial stiffness adequately, but, inadequate to capture the cracking and onset of overall yielding. Furthermore, the model underestimates the ultimate capacity in terms of base shear. Finally, to evaluate the numerical accuracy of the models, two-story and three-story RC frames modeled in OpenSees finite element software. For nonlinear analysis of the RC frames, the distributed force-based fiber models capture the inelastic response accurately. Increasing the axial load on the two-story RC frame exhibits mesh dependent results. For the frame under strain-softening behavior, the material regularization techniques successfully tackle the localization issue.

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