School of Civil and Environmental Engineering

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Comparison of Pseudo-Static and Dynamic Response Analysis of Sibilu Dam
(Addis Ababa University, 1979) Getachew, Fantahun; Haile, Messele(PhD)
Dynamic loads induced by earthquakes are often major factors in the design of earth dams. Earthquake induced stresses are major factors in determining the angles of the dam slopes and significantly influence the selection of materials, the zoning of the dam, and the construction method. Awareness about more rigorous seismic stability analysis is also growing during recent years. In Ethiopia dams are being constructed for various purposes. The analysis and design of dams has been carried out by taking many factors in to account. Among these factors earthquake effect is considered mainly for major dams. One of these dams is the Sibilu Dam, which is under design for the Addis Ababa water supply. Until the present, in Ethiopia, seismic effect is commonly considered by the pseudo-static analysis method. But representation of the complex, transient and dynamic effects of earthquake shaking by constant pseudo-static forces is obviously not accurate. In this thesis an attempt was made to compare the pseudo-static and dynamic response analysis by taking the Sibilu Dam as a case study. The main purpose of the study is to show the shortcomings of the pseudo-static analysis method as compared to the dynamic response analysis when applied to the analysis of earth/ rock fill dams. The thesis is organized as follows: initially a background is given on seismicity and seismic hazards in general and Ethiopia in particular. The second chapter covers summary of previous works related to this study. In the third chapter some description is given about the Sibilu Dam, the dam under the case study. In chapter four, the definition of the expected seismic excitation for the dam site is presented. The historical records of earthquake events are collected and geotechnical data of the dam site are reviewed 2 paying special attention to the location of active faults. The obtained data set is analyzed to give the required earthquake parameter for two different return periods. In fifth chapter, the pseudo-static slope stability analysis is done with the conventional limit equilibrium method by using the design ground motion as an input. The analysis is performed for the upstream and down stream slopes of the dam by varying the possible critical cases. In chapter six, analysis and design is done based on permissible deformation. The dynamic response analysis is done by varying the material behavior. Non-linearity is considered by the Equivalent Linear Method. Finally, comparison of the different analysis methods is made and conclusions and recommendations are drawn.
Prefabrication of Structural Elements: A CaseStudy
(Addis Ababa University, 1998-06) Bulto, Gutema; Adamu, Asnake (PhD)
The back-log of housing units in Ethiopia was so immense that all efforts made by the Government and inhabitants could not wipe out the shortage of housing in the early 1980s. To promote the building industry and to alleviate the housing shortage prefabrication technology was introduced. The Prefabricated Building Parts Production Enterprise (PBPPE), which makes use of IMS precast concrete system (a patent of the Institute for Testing Materials for prestressed concrete), was established in 1984 with a technical assistance from the former Yugoslavia. The objectives of the enterprise are to promote the building industry through mass production of precast concrete elements, to alleviate the shortage of housing and to reduce the construction cost. Since its foundation the enterprise has carried out the production of building parts and the erection of residential and public buildings. The IMS framework of precast concrete constitutes one of the widely applied industrialized building technology, because it provides for cost-effective mass production of buildings. In the research work, a review of the experiences of other countries and a comprehensive literature survey on prefabrication was conducted. Then, the Ethiopian experience in the use of precast concrete especially the IMS system was assessed. The use and development of the IMS precast system were found slow and far below our expectation. To identify the sole cause that contributed to this effect, a sample survey was carried out and from the analysis of the survey conclusions were drawn. After a thorough evaluation of the existing modules, to demonstrate the flexibility and the possible modification to the existing modules of the IMS system, a proposal was made for a G+1 dwelling building. Comparative analysis between the existing and the proposed modules was made and recommendations were forwarded. The study also considers the application of precast concrete to other special structures. Finally, conclusions and recommendations were forwarded to promote the development of the IMS system. Essentially, great efforts should be done to disseminate technical information through brochures, manuals, design guidelines and advertisement to support the industrialization of the building industry in Ethiopia.
Establishing Water Release Rules for Koka Reservoir for Wet Seasons.
(Addis Ababa University, 1998-12) Shemeles, Paulos; Seleshi, Yilma (PhD)
Koka is the only single Reservoir found in the Upper Awash River Basin being utilised both for Hydropower and Irrigation uses. The current maximum capacity of the reservoir is estimated at 1,000 million rrr'. Up to the inlet to the Reservoir, the Upper Awash River Basin drains a catchment area close to 11,300 Km2. A number of important schemes found at the flood prone areas, downstream of the reservoir, are in need of a workable operation rule for Koka which can give them some protection against flooding during wet seasons. In this research an operation rule curve is established. The operation rule curve is established in such a way that all important variables for the hydropower operation and flood control are optimised subject to the constraints. Linear programming in MS-FORTRAN language is used to develop the optimisation model for Koka reservoir operation. The dry season water requirements of downstream irrigation schemes are implicitly guaranteed since the optimised rule curve will ultimately lead to a full storage at the end of every wet season which is desirable by those schemes. Emphasis was also given on the flexibility of the model to allow adaptive operation rules responding to the changing constraints and boundary conditions which are quite noticeable in the Koka reservoir system. The Real-Time operation procedure is formulated to be used in conjunction with the established rule-curve to enable the reservoir operators to make decisions, regarding releases for various purposes, in a considerably shorter period of time (e.g.,daily) using the current hydrometeorological information. The most important component in Real-Time reservoir operation is the Rainfall-Runoff model. These models enables, for a known rainfall, to predict the expected runoff which is an important information for the Real-Time operation of the reservoir and for assessing the possibility of flood hazards well in advance of its catastrophic consequences. It is, however, unfortunate that most models are data intensive that the scarcity of data is the major bottleneck in using them. In this research, a rainfall-runoff model is established employing the SCS
Evaluation of Approximate Methods for the Design of Biaxiall Y Loaded Reinforced Concrete Columns
(Addis Ababa University, 1999-05) Desta, Tefera; Chane, Bayou(PhD)
The ultimate capacity of reinforced concrete sections under normal force and biaxial bending moments can be represented by a three dimensional interaction surface in terms of the normal force and biaxial moments. The surface can be conveniently represented by a family of curves either on a plane of constant normal force relating the two moment components or as interaction diagram on a plane of constant angle relating the normal force and the resultant of the two moment components. However, the curves can not be described by exact and closed form mathematical expressions due to a wide variety of parameters involved in the determination of ultimate biaxial moment capacity of crosssections with normal force. Thus the systematic generation of such curves to be used for design involves obtaining sufficient number of suitable points by iteration which normally requires use of computer programs. In the absence of such facilities, the use of approximate methods becomes mandatory. There are different approximate methods adopted in different codes for the design of biaxially loaded reinforced concrete columns and the purpose of this thesis work is to assess and evaluate the proximity of some of these approximate methods with the exact solution. The approximate methods evaluated include those recommended by EBCS-2 [1), CPllO [2,3) and ACI [4,5).
Vibration Characteristics of Buildings in Addis Ababa
(Addis Ababa University, 1999-06) Kebede, Tadesse; Halle, Messele (PhD)
Dynamic loading acting on structural systems may result from several sources such as wind and vehicular motions, etc. The type of dynamic input, which is of greatest importance to the structural engineer undoubtedly is the one that is induced by earthquakes. Buildings constructed in Seismic Zones are subjected to earthquake ground motion in addition to other types of loads. If one tries to generate response spectrum curves of a structure for different recorded ground motions, large variations will be obseIVed in both the response spectral values and the shape of the spectrum curves. These variations depend on many factors, such as magnitude, source, and variation in geological formation along the path, local site condition and the nature of the building. The recent trend of increasing height and scale of building structures accelerated the research and investigation activities in the area of Earthquake Engineering, with the aim to get rational and safe earthquake resistant design criteria. Consequently, one n of the current problems in evaluating earthquake response of a building is how 1D find out period of vibration of a building. Recent developments in the techniques for measuring period of vibration of building have permitted us 1D obtain important experimental information reganling the dynamic behavior of a building during earthquakes. The fundamental period of buildings can be obtained by one of the following methods: - 1) Microtremor measurements: here ambient building vibrations are measured by using microtremors. These ambient VIbrations called microtremors operate at a very low strain level. Properly interpreted, microtremors give the fundamental period of vibration of the building. 2) Code Method -or-Equivalent Static Analysis: this gives an approximate formula that can be used to determine the first mode period of a building. 3) Dynamic Analysis: is a sophisticated level of analysis available for finding period of vibration of buildings, that employs Dynamic Time-History Analysis or Response Spectral Analysis. III The comparison of experimental results with the results obtained by empirical formulas and dynaJnic analysis will facilitate the engineers' understanding of the an a lysis and design of building structures subject to dyn amic loading. In the "Introduction", the background and the purpose of this study are described. In the second chapter Period of vibration of selected buildings are determined by u s ing Microtremor. In the third chapter Period of vibration of buildings a re determined by using the Code Method. In the fourth ch apter periods of buildings are determined by using Dynamic Analysis. In the fifth chapter Comparison of results obtained by Microtremor, CodeMethod and Dynamic Analysis are done. In the last chapter, Conclusion was made ba sed on the results obtained.
Computerized AnalysisofFrames with Non-Prismatic Members
(Addis Ababa University, 2002-04) Takele, Samson; Taye, Shifferaw(PhD)
Optimal Design for Prestressed Concrete Box Girder Brigde
(Addis Ababa University, 2002-06) HaileMichael, Samuel; Taye, Shifferaw(PhD)
This thesis concerned with optimization of simply supported prestresed concrete box girder bridge. Usually, the design of prestressed concrete bridges is done based on codes on prestressed concrete bridges. The code requirement is generally concerned with the safety of the structure in its lifetime. Apart from satisfying the code requirement, the design should be economically chosen. For a given condition, there might be a large number of alternatives that satisfy the requirements imposed by codes. But the designer must be in position to choose the one, which is optimal against certain measure of optimality. Therefore, the designers have to do some optimization to arrive at such design. The objective of this thesis work is to show how the optimal design of a prestressed concrete boxgirder bridge can be obtained. It will established a general relationship among different design variables at optimum and will recommend a simple procedure to identify an the optimum design. The presentation is divided in to six chapters. In chapter one, a detail discussion on the theory of prestressed concrete is presented. Great emphasis is given for analysis of sections for flexure both in elastic and plastic ranges. It also explains the usual trends to be followed in the design of a pre stressed concrete section under service and over loads. In chapter two, application of pre stressed concrete on bridge is discussed. Conditions favoring pre stressed concrete application for such type of structural systems Chapter three discusses about optimization theory and general formulation of an optimization problem. Emphasis will be given numerical optimization theory and techniques. Chapter four deals with the methods used to solve an optimization problem. An extended complete coverage is given on linear programming and feasible direction methods, as they will be used later in chapter six to solve an optimal design problem for box-girder bridge. In chapter five, an optimal design problem is formulated for simply supported rectangular box-girder bridge based on AASHTO 96 Code. 2 In chapter six, the optimal design problem formulated in (chapter five) is solved for 40m span bridges using a Fortran program written for the method of Feasible Direction. The program is developed for this particular purpose. Concluding remark is also given The source code of developed program along with a flow chart outlining the program logic to this work is included in an appendix.
Prestressed Concrete Bridge Design and Construction Practices and Prospects in Ethiopia
(Addis Ababa University, 2002-07) Berhane, Beruk; Tebedge, Negussie(Prossefor)
The problems and achievements on the design and construction of prestressed concrete bridges in Ethiopia is assessed through distributing Questionnaires to be filled by professionals currently working on design and construction of bridges. A seminar is also organized to collect ideas from the participants and also to convey the basic concepts of prestressed concrete bridge design and construction. The basic concepts, principles and advantages of prestressed concrete bridge design are discussed. The different construction methods of prestressed concrete bridges with the detail of anchorages are included. Design example based on simple procedures is shown including its cost comparison with normally reinforced concrete bridge. Standard sections are prepared based on PCI (prestressed Concrete Institute) for different simply supported spans with design flow chart.
Ameliorated Design and Construction Techniques of Pavements on Expansive Soils.
(Addis Ababa University, 2003-02) G.hiwot, Tekeste
The main cause of the economic losses incurred for pavements built on swelling subgrade is the lack of appropriate selection of the design and construction method adopted to alleviate the swelling phenomena. The extent of the problem depends mainly on the degree of expansiveness of the soil and the corresponding climatic conditions. Current situation Ethiopia shows that random selection of design & construction methods is widely practiced despite the various soil and climatic condition. Most of the practices aim at undefined use of the design and construction method that results in uneconomical and unsafe pavement design. The effectiveness of the methods depends also on the selection of the design depth, a design depth that suits the technical and economical conditions. Chapter two consists the review of the performance and suitability of the various design and construction method adopted in most part of the world including Current practices in this country. In Chapter three, an attempt has been put to see the consideration of potential expansiveness and assessment of the various prediction methods of heave and swelling pressure for the existing experimental values.
Claims in Ethiopian Construction Industry
(Addis Ababa University, 2003-02) Dessa, Abdissa
Claim in general term is defined as a demand or request for some thing, which one has right to have. In the context of this thesis claim means a demand by a contractor for extension of time or for an extra payment of an item or items of work carried out by him on behave of employer for which a readily identifiable amount can not be ascertained under the term of contract. The right of entitlement for a contractor to his intention depends on the provision of condition of contract on which the contracting parties depend for their agreement. These conditions could be FIDIC, BaTCoDA, ICE or others. The conditions of contract provide specific clauses for making and settlement of claims for extra cost and for grant of extension of time. In Ethiopian construction industry, claims are normally inevitable because of the traditional project procurement system widely practiced in the country. Moreover, majority of local construction organizations manage their construction projects by employing engineers who have little or no training on construction project management. This results in improper claim administration. In addition to the complexity of projects being undertaken, these days, the type of project procurement system and improper claim administration raises more problems. For instance, among 15 completed projects studied during the thesis work, project delay up to 500 % of its contractual time and cost increase of greater than 80 % of its contractual sum were encountered. The main causes for these problems are thought to be the improper project management and claim administration. Therefore, the research is aimed to describe the general nature of claims and to identify the type of claims widely raised by local contractors. In addition the thesis is expected to create awareness with the major construction parties i.e. contractors, owners and consultants about the level and significance of claims in Ethiopian construction industry. Even though, there are many bases on which claims may be raised legally, claims that are based on contractual provisions are emphasized in this research work. viii Contractual claims in the industry can be raised due to variations, breach of contract from contractor(s) or employer(s) side, delay/disruption and third party. The thesis is mainly devoted to identify the main causes of claims in Ethiopian construction industry, among the aforesaid types of claims. For this purpose different data collection techniques like constructive interviewing and questionnaires were designed and utilized. Conclusions and recommendations are forwarded based upon statistical analysis of data collected during the study period. For the sake of comparisons of the experience of local contractors and foreign (international) contractors in processing claims, case studies were conducted. The cases are: Lalibela to Sekota rural road project undertaken by local contractor called SUR construction Share Company, Sodao to Chida access road project undertaken by international (foreign) contractor called Salini construttori S.P.A and the 500 special housing project undertaken by international (foreign) contractor called C.M.C-di- Ravenna. The detail analyses of the case studies along with copies of questionnaires are annexed in the appendix of the thesis.
A Study on The Suitability of Local Steel Profiles for The Production of Steel Deck Reinforced Composite Slabs for Building
(Addis Ababa University, 2003-03) Redie, Rufael; Adamu, Asnake(PhD)
Floor and roof slabs constructed using composite panels of steel deck and concrete in which the steel deck panels serve both, as formwork and reinforcement are the practice of developed nations. The steel deck manufacturers developed their own cross sectional profiles and provide detail manuals where the thickness of the sheets ranges between 0.8mm to 1.5mm. This new technology has not been yet practiced in our construction industry. Thus, this Thesis Paper aims at assessing the local profile steel sheet products and develop analysis and design techniques for steel deck concrete composite slab for building, which fit our local conditions. The organization of the study can be viewed to consist of four main components, the first being assessment of the physical and mechanical properties and production process of steel sheet profiles produced by local manufacturers as well as foreign practices. Analysis and design requirement based on local building code requirement, foreign code of practice such as British Standard and international published books on the subject matter are dealt in the second part of the text for various stages of loading. Laboratory test for the assessment of tensile strength of local sheet and chemical as well as mechanical shear interlock between profile sheet and concrete conducted in the capacity of the local laboratory facility can be very well grouped as the third part of the manuscript. Design example for composite slab together with cost comparison between composite system and conventional slab construction are elaborated in the last section of the text. In general, Serviceability, Strength and Economy aspects of such construction are the main concerns of the study.
Vibration Analysis and Design of Block-Type Machine Foundations Interacting With Soil
(Addis Ababa University, 2003-03) Anteneh, Mulugeta; Worku, Asrat (PhD)
Until recently, the design and analysis of block-type machine foundations did not properly consider impedance functions. This thesis aims at incorporating impedance functions by making use of recently compiled closed form expressions and dimensionless graphs for the purpose of determining dynamic stiffness and dashpot coefficients. Based on these expressions and the well-known solutions of the dynamic equations of motions, a computer programme is written in FORTRAN. The general requirements and criteria to be fulfilled for machine foundations are compiled. The input soil parameters essential for the design including shear modulus, G, Poisson’s ratio, , damping ratio, D, spring stiffness K, and shear wave velocity, Vs, are reviewed. The basic concepts in vibration of structures like frequency, free vibration (undamped and damped), forced vibration and foundation vibration are discussed. In addition, the performance requirements and the basic steps employed in the design of a machine foundation are presented. The older approaches of machine foundation analysis are also reviewed. The basic steps and relations used to calculate the uncoupled vertical and torsional vibration amplitudes as well as the coupled rocking and horizontal vibration amplitudes are provided. x Based on the basic relationships for the vibration amplitudes and the relatively simplified and well-compiled recent works of G. Gazatas [2] for the determination of static stiffness, dynamic foundation soil stiffness as well as radiation dashpot coefficient, a computer program in FORTRAN is written to analyze block-type machine foundations for the following four conditions in a rational approach. (a) Foundation on the surface of a homogeneous half space (b) Partially of fully embedded foundation in a homogeneous half space. (c) Foundations on the surface of a homogeneous stratum overlying the bedrock. (d) Partially of fully embedded foundations in a homogeneous stratum overlying the bedrock. Finally, practical examples are solved for the above four cases using the programme and the results are checked against each other. The same example is also solved using the classical method even though this method does not appropriately incorporate the impedance functions. A comparison of the results obtained using the classical approach and the more rational method adopted in this work indicates that the latter is a substantial improvement over the former. A comparison of the results obtained showed that embedding a foundation is a very effective way to reduce to the acceptable levels of the anticipated amplitudes of vibration, especially if these amplitudes arise due to rocking or torsion. Such an improvement would be effected mainly by the increase in radiation damping produced by waves emanating from the vertical sidewalls.
Correlation Between Actual Reinforced Concrete Wall Behavior and Its Centerline Model
(Addis Ababa University, 2003-06) Biedebrhan, Medhanye; Taye, Shifferaw(PhD)
Key words: concrete shear walls, dual systems, ETABS, lateral loads, shear deformation. Concrete shear walls or structural walls are often used in multistory buildings to resist lateral loads such as wind, seismic and blast loads. Such walls are used when the frame system alone is insufficient or uneconomical to withstand all the lateral loads or when partition walls can be made load bearing, replacing columns and beams. The analysis of buildings with shear walls became simple using commercially available computer programs based on the finite element method (FEM) and subsequent implementation of stress integration techniques to arrive at generalized forces (axial, shear, and moments). On the other hand, design engineers without such facilities or those with computer facilities lacking such features use simple method of analysis by taking the entire dimensions of the walls. This is done by considering the shear walls as wide columns of high moment of inertia and following the same procedure as for columns, a structural modeling approach that leads to incorrect results. Therefore, it is the primary purpose of this research work to correlate the results obtained from the above simple but incorrect method of analysis and those from true wall behaviors with an ultimate goal of providing the analysts and the designers with correction factors in order to implement the centerline method of analysis for the analysis of walls. It is believed that structural engineers working in the analysis and design of high- rise buildings will be benefited from the results.
Claims In International Projects In Ethiopia
(Addis Ababa University, 2003-06) Kahssay, Girmay; Dinku, Abebe(PhD)
Claims are an inevitable fact of life in the construction industry. Whether in local or International contract projects, the issue of claims remains the same. In the context of civil engineering projects, claims are a demand for money or time extension or both to which one party rightly or wrongly assumes that he has a right. With the advent of the liberalization of the economy and availability of funds from international financers, there has been a surge of large-scale civil engineering construction in the Ethiopian construction industry. This is particularly evident in the road sector, where the Ethiopian government, has been investing a substantial amount of money with the assistance of International financers like the World Bank. While this large scale investment in the construction sector has been a major step in the right direction, this venture has been beset with unfortunate incidences of claims ranging in millions of birr and sometimes even in excess of 100% of the project costs. In this regard therefore, the objectives of this thesis are to investigate the causes of these claims and to propose a possible remedy as to the handling of similar incidents in the future. Whilst claims are an inevitable fact in the construction industry, future handling of such incidents will have to depend not on an attitude of resignation, but on developing a healthy understanding of their occurrence and formulating a strategy of minimizing risks associated with such occurrences. In this aspect one of the main observations of this research work has been the fact that the Ethiopian construction industry seriously lacks, qualified engineering professionals with an appropriate level of training in construction management, international contract administration and claims handling. xv It appears that the provisions of the FIDIC forms of contract may not be well understood within the circles of Ethiopian engineering professionals. This has led in many instances to avoidable cases of claims, costing the Ethiopian government millions of birr. It is, therefore, mandatory that the Ethiopian construction industry, especially those responsible for running international projects, take a serious step to institute better contract management, they should also initiate exposure to international contract procedures, enforce training, develop regulated pre-tender document preparation and better bid evaluation measures. It is also essential that the process of pre-qualification for both consulting and contracting firms be mandatory in the administration of international projects. The findings of this research indicate that of the 10 international projects surveyed, all of them have experienced claims related to late handing over of site, rights of way problems as well as design errors, or late submission of drawings by the supervising consultants. This is indicative of inadequate contract administration practices. 80% of them have also experienced claims related to weather conditions. It can easily be observed that a major portion of the claims could have been mitigated, had there been a coordinated effort to administer the contracts in accordance with the expressed terms and conditions stipulated in the agreement. In the future, the Ethiopian construction industry needs to focus on the development of adequate project management skills and enhance the contract administration capacity of its practicing professionals, with particular emphasis on international projects. The establishment of a “ think-tank” of experts with appropriate negotiation skills, overseeing international projects can also assist towards this objective.
Discrete Element Method for Slope Stability Analysis
(Addis Ababa University, 2003-07) Kebede, Dawit; Boled, . Girma
A static DEM has been presented to solve slope stability analyses. The method consists of discretizing the soil mass into blocks which are joined by Winkler springs. From relation of forces with stiffness and displacement, sets of simultaneous equations are solved to find displacements and stresses. The local stresses are used to calculate factor of safety while the displacement fields are used for predicting the critical failure surface. Example problems have been solved using DEM and the results have shown the potential of the method for slope stability analysis. Comparisons of the present model between limit equilibrium methods, FEM and with DEM models by other authors are made .The results suggest that DEM methods can be used both to predict the critical slip surface and give a factor of safety and that these outputs closely agree with the conventional limit equilibrium methods and the more rigorous FEMs.
A Comparative Study and Computer Coding of Limit Equilibrium-Based Slope Stability Analysis Techniques
(Addis Ababa University, 2003-07) Amare, Yohannes; Worku, Asrat (PhD)
General slope stability concepts and the parameters and major considerations associated with slope stability problems are discussed. General features and theories of some of the available methods of analysis such as limit equilibrium methods, limit analysis methods, finite element method, etc. are reviewed. Special emphasis is made to the limit equilibrium slope stability analysis techniques based on the method of slices. The underlying principles, common features and assumptions employed by these methods are elaborated. The various commonly used methods of slope stability analysis based on the limit equilibrium principles are then thoroughly assessed, compared and contrasted. These common limit equilibrium based methods of analysis, including Bishop’s simplified method, Janbu’s simplified method, Bishop’s rigorous method, Spencer’s/Morgenstern and Price’s method, Janbu’s rigorous method, are formulated in a unified manner. A computer program is then written for these selected methods, using the Visual Basic language, on the basis of this unified formulation. The computer program has the capacity of analyzing slopes with general-shaped slip surfaces and general loading conditions. It is also capable of incorporating earthquake loading based on the pseudo-static analysis. Finally, example problems are solved to illustrate the computer program developed and to reflect on the discussions and conclusions in the literature review section. The results obtained for the example problems, using the computer program developed and the different methods of analyses are in close agreement with those obtained by the author’s of the original methods. Key Words: slope stability analysis; limit equilibrium; method of slices; factor of safety
Seismic Microzonation For Central Addis Ababa
(Addis Ababa University, 2003-07) Mengistu, Araya; Haile, Messele(PhD)
This study is conducted to prepare seismic microzonation map to central part of Addis Ababa City. The basic method used is the observation and analysis of microtremors. The first effort was made by Ayele (2001) based on 40 observation sites. Latter detailed study was initiated by dividing the city in to five parts namely the northeastern, northwestern, central, southeastern and southwestern parts of which the central part is the study area for this thesis. In this thesis seismicity and related hazard for Addis Ababa city and its locality, historic records, geologic conditions and effects on earthquake, and the theoretical background used in preparing microzonation maps are presented. The nature of microtremors, basic characteristics and their use in estimating site-effects is also discussed together with the method of measurement, equipments used and available tools to analyze collected data. The suitability of microtremor based site-effect study has been tested by comparison of results with solutions from one dimensional analytical model for selected sites
Developing Supporting Software for Analysis. Design and Cost Estimation of Commonly Used Reinforced Condrete Foundations
(Addis Ababa University, 2003-07) Shibru, Mekonnen; Haile, Mesele (PhD)
Key words: Supporting Analysis And Design Software;Supporting Cost Estimation Software; Foundation Selection. The choice of the most appropriate type of foundation for structures is one of the challenges a civil design engineer faces. Different structural systems and loads from the super structure, hetrogenous soil conditions and variations of soil strength parameters with change in soil moisture makes determining the most appropriate foundation type a tedious process. Besides engineering consideration ,the variation in cost of construction materials and labour for the different foundation types and for different locations of projects makes the choice of the most appropriate foundation (function and cost) an extremely time consuming process. This practical difficulty has led most design engineers to opt for one type of foundation based on engineering judgment and experience. This not so rational process is not expected to lead to optimal design , it may even end up with erroneous design. In this thesis an attempt is made to develop a computer program that requires super structural input as foundation reaction and soil data and does analysis. Once design is completed the quantity of material and labour is calculated and cost comparison is made. Ultimately the functional best and economical foundation type is chosen in a matter of minutes. This enables design engineers to get an optimal solution in the foundation system at the same time saving design time.
Instructors' Provision of Written Responses to Students' Business Letter Writing
(Addis Ababa University, 2003-07) Mengistu, Araya; Haile, Messele(PhD)
This study is conducted to prepare seismic microzonation map to central part of Addis Ababa City. The basic method used is the observation and analysis of microtremors. The first effort was made by Ayele (2001) based on 40 observation sites. Latter detailed study was initiated by dividing the city in to five parts namely the northeastern, northwestern, central, southeastern and southwestern parts of which the central part is the study area for this thesis. In this thesis seismicity and related hazard for Addis Ababa city and its locality, historic records, geologic conditions and effects on earthquake, and the theoretical background used in preparing microzonation maps are presented. The nature of microtremors, basic characteristics and their use in estimating site-effects is also discussed together with the method of measurement, equipments used and available tools to analyze collected data. The suitability of microtremor based site-effect study has been tested by comparison of results with solutions from one dimensional analytical model for selected sites.
Computation of Soil Compressibility Using Tangent Modulus Approach
(Addis Ababa University, 2003-07) Sissay, Dessalegn; Tadesse, Samuel(PhD)
Keywords: tangent modulus, resistance, modulus number and strain There are several mechanisms causing settlement of a structure. Different structures have varying potential to withstand the settlement that takes place Thus, its determination has to be given due consideration by engineers as it affects these structures from functioning properly if not limited to a permissible value. Soils consist of solid particles and void space. Gas or water or combination of both occupies the void space. When loaded the water and air gets squeezed out resulting in settlement. Determination of settlement and the rate at which the expulsion takes place is determined from the theory of consolidation. The classical approach, which is widely used in our country and other parts of the world, has limitations. These limitations have contributed for the development of the tangent modulus approach. The tangent modulus approach provides better way of determining settlement for various types of soil ranging from hard to very soft soil. In the method the soil property, which is determined from laboratory soil deformation tests, are used. In the approach a compression modulus also called the constrained modulus, the tangent to a linear plot of stress versus strain curves determined from laboratory tests play a significant role. It is emphasized on this property of the soil, as it is a measure of resistance of the soil against deformation due to change in loading condition The compression modulus, measures of the resistance of a media or an isolated part of it against a forced change of equilibrium condition. It is based on the resistance concept, which is very well developed in other field of engineering, except that its application for settlement analysis in soil mechanics is new. 1 1. Introduction 1.1 General Construction scheme is advancing day to day. This has made possible construction of high rising buildings, heavy structures and highways. Due to this heavy loads are induced on to the soil underneath. Besides the use of undesirable construction site is increasing. The above factors results in compressive strains causing settlement of a structure. The resulting settlement has to be limited to a minimum to allow the structure function properly and maintain the required aesthetic value. Further cost of maintenance has to be limited to a minimum. For estimating the settlement that occurs in cohesive sols the classical approach is widely used in most parts of the world including Ethiopia. This approach assumes the compressibility of the soil remains constant. Further it was believed that the initial pore water pressure describes the consolidation characteristics of thick clay. These and other assumptions limit the validity of the approach. Thus, another method of settlement evaluation which amends at least the above mentioned drawbacks have to be adopted. This paper introduces another method as compared to classical method for the determination of settlement, which is known as the tangent modulus approach. 1.2 Background The probable settlement any structure undergoes on different types of soils is predicted by compressibility study. Thus, based on the compressibility characteristics the method which relies on the stress- strain analysis of soil for determining this property is dealt with. 1.3 Objective of the Present Work The objective of the research work is to: i) Introduce a recent and more practical way of determining settlement and compare the applicability with the existing and more popular classical approach. ii) To

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