Construction Technology and Management

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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.
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.
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.
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.
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
Constitutive Model for the Red Clay Soils of Addis Ababa
(Addis Ababa University, 2003-07) Firew, Tezera; Boled, Girma(PhD)
Key words: constitutive equations, strains, stress, elastic-plastic theories. An associative constitutive model originally developed by C. S. Desai based on rateindependent elastoplasticity concepts is validated for the Red Clay Soils of Addis Ababa. The basic concept of the model used herein was proposed and developed by Desai (1980). The yield function is expressed in terms of the state of stress, while the evolution or strain hardening process is characterized by using internal state variables such as the irreversible strain. Laboratory tests are conducted to determine the material constants. The material constants that are associated with the model are found based on four different states of a material deformation process: the elastic, plastic accompanied by hardening, phase change from contraction to dilation and the ultimate state. The model is then validated by comparing predictions with laboratory tests from which the constants were found, and also with tests not used for finding the constants. Comparison of observed and predicted response show that the model yielded predictions that compared remarkably well with the observed behavior.
Investigation Into Some of The Engineering Properties of Red Clay Soils In Bahir Dar.
(Addis Ababa University, 2003-11) Abagena, Fasil; Worku, Asrat (PhD)
Despite Geotechnical research has not been done in Bahir Dar, from reconnaissance, the majority of the town is covered by red soils comparing to the black soils. The red clay soils are dominantly found in the eastern and western parts of the town. An investigation has been made on the properties of red soils obtained, from locally called 'Abay mado' (Kebele 11), in the eastern part of the town where the expansion is very high for development. Hence the present research is intended to investigate some of the engineering properties of red clay soils in Bahir. After visiting the proposed site, six test pit points were selected. The numbers of test pits were limited because of the constraint in budget and time. Representative disturbed and undisturbed soil samples were collected from open pits by direct excavation manually. The laboratory tests that were carried out includes mineralogical analysis, index properties, consolidation, and shear strength tests and with the aid of these results an analysis is made to determine some characteristics of red clay soils. 10 The laboratory result shows the red clay soils in Bahir Dar contain the clay mineral kaolinite predominantly. The data resulted from the test is inadequate to provide correlation that relate index properties with shear strength parameters and compressibility characteristics.
Performance of Piled Raft Foundations for Addis Ababa Soils
(Addis Ababa University, 2004-03) Mekbib, Metsihafe; Boled, Girma (Associate Professor)
This thesis presents the investigation of the performance of the concept of piled raft foundation compared to the conventional pile and raft foundation for Addis Ababa soils. The investigation has been carried out using soil profiles in Addis Ababa where highrise buildings are going to be constructed and have been already constructed. To support the results of the investigation, soil profile from Wabe Shebele River bridge site has been also considered. In this work, first, different design philosophies and method of analysis have been discussed. From already available methods of analysis, the hybrid method of analysis has been chosen for its computational efficiency. The program is validated by anaysing examples available in literature and has already been analyzed using 3D finite element code (FLAC 3D). Then, two case studies have been made to explore the performance of the piled raft for Addis Ababa soils. The first case is the Awash bank head quarter building, which is going to be constructed near national theater. The second case considered is the soil profile on which the former marine transport authority building is constructed. For both cases, comparison has been made among raft, pile, and piled raft foundation based on settlement and bending moment. Another case study, conducted to supplement the out come of the foregoing two cases, is the abutment foundation of Wabe Shebele River Bridge. This case specifically conducted aiming at reducing the total settlement of the foundation that is above the permissible limit for masonry abutment. For the this case, the results have shown that v two fifth of the number of piles required for conventional piles can be reduced using piled raft design concept. When raft alone is used, the settlement exceeds the permissible value. Generally, it has been observed that piled raft concept is very advantageous in minimizing the total and differential settlements as compared to the conventional raft foundation. It also reduces number of piles required as compared to the conventional pile foundation. For the cases investigated in this work, the reduction in number of piles ranges from 25% to 45% of that required for conventional pile foundation, though the variation in raft bending moment and other issues are no considered in detail.
DYNAMIC RESPONSE OF SYMMETRICAL REINFORCED CONCRETE BUILDINGS
(Addis Ababa University, 2004-03) Usmail, Abdulwasi; Haile, Messele(PhD)
The effect of soil-structure interaction on the dynamic response of reinforced concrete buildings of regular and symmetrical geometry is considered in this study. The structures are presumed to be generally embedded in a homogenous soil formation underlain by very stiff material or bedrock. The structure-foundation–soil system is excited at the base by an earthquake ground motion. The superstructure is idealized as a system with lumped masses concentrated at the floor levels, and coupled with the substructure. The substructure system, which comprises of the foundation and soil, is represented and replaced by springs and dashpots. Frequency-dependent impedances of the foundation system are incorporated in the discrete model in terms of the springs and dashpots coefficients. The excitation applied to the model is field ground motions of actual earthquake records. Modal superposition principle is employed to transform the equations of motion in geometrical coordinates to modal coordinates. However, the modal equations remain coupled with respect to damping terms due to the difference in damping mechanisms of the superstructure and the soil. Hence, proportional damping for the coupled structural system may not be assumed. An iterative approach developed by Worku [13,14] is adopted and programmed to solve the system of coupled equations of motion in modal coordinates to obtain the displacement responses of the system. Parametric studies for responses of building structures with regular and symmetric plans of different structural properties and heights are made for fixed and flexible base conditions, for different soil conditions encountered in Addis Ababa. Soil borehole log data of three representative sites in Addis Ababa were used for the computation of the stiffness and damping of the soil. iv The displacement, base shear and base overturning moments are used in the comparison of different types of structures for various foundation embedment depths, site conditions and height of structures. These values are compared against those of fixed base structure. The study shows that the flexible base structures, generally exhibit different responses from those structures with fixed base. Basically, the natural circular frequencies, the base shears and the inter-story displacements for the flexible base are less than those of the fixed base structures. This trend is particularly evident when the flexible soil has large thickness. In contrast, the trend becomes less predictable, when the thickness of the flexible soil decreases. Moreover, in the latter case, the iteration undulates significantly making the prediction difficult. This is attributed to the highly jagged nature of the impedance functions of frequencies for such formations. In this particular case, it is difficult to conclude whether the conventional fixed-base approach yields conservative design forces, as is the case for soil formations of large thickness.
Assessment Of Causes and Cost Impact of Change Order on Road Projects in Ehtiopia
(Addis Ababa University, 2005) Behsah, Mekonnen; Dinku, Abebe(Professor)
This research makes assessment on the causes and cost impacts of change orders on road projects in Ethiopia. Emphasis is given to the identification of the root causes of change order categories from seventeen road project with a total of 123 reasons of causes of change order. As a result the most common reasons of causes of change order are categorized as: design errors and omissions, scope change, unforeseen conditions, value engineering, force majeure and others. Of the total reasons of causes of changes orders included in the study, 40.8% were caused by design errors and omissions, 29.3% by change of scope by owner, 15.8% resulted from other causes, 7.5% were caused by unforeseen conditions, 5.8% by value engineering and 0.8% due to force majeure. In addition to identifying the major categories of change orders, the consequential cost impacts of these change orders were analyzed. As a result, those reasons of change order categorized under value engineering have a decrement cost impact which saves an amount of birr 23,861,361.94. The reasons of change orders in this category have positive cost impact on the total project cost as they are a saving to the project owner. However, the rest categories of causes of change order have increment or negative cost impacts with a total change order amount of birr 410,596,232.76. From this total cost increment 52.4% is caused by change of scope; 38.6% by design errors and omissions, and 7.6% contributed other causes. Though they are minor, 1.2% and 0.2%, the rest are contributed by unforeseen conditions and force majeure respectively in descending manner of their contribution. Spearman rank order correlation analysis was used to evaluate whether consensus of opinions exists between groups of respondents. From the analysis of the results it can be concluded that the correlation between the attitudes of the respondents in all the three Assessment of Causes and Cost Impact of Change Orders on Road Projects in Ethiopia AAU, School of Civil and Environmental Engineering Construction Technology and Management 9 groups is relatively weak. This is so, because two third of the groups assure the absence of significant consensus. Key words: change, change order, change order categories, cost impacts of change order.
A Study of Undrained Behavior of Saturated Sand and The Concept of Steady State
(Addis Ababa University, 2005-01) Enawgaw, Abraham; Tadesse, Samuel(PhD)
It has been very common to see collapse of structures, slopes, and foundations due to flow of foundation soils without observing any structural failure during earthquake. This can also occur frequently and cause severe damages in this country following the occurrence of earthquake, particularly in the Rift Valley region where there is a considerable deposit of saturated sand and silty sand. This problem has been studied in various countries and attributed to Liquefaction Phenomenon. The phenomenon occurs in saturated sand, which either completely loses its strength and flow as a liquid (Flow Liquefaction, F.L) or shows a progressive softening (Cyclic Mobility, C.M.) under cyclic loading. Since liquefaction of sand is entirely related to its undrained behavior, the undrained behavior of saturated sand under cyclic or equivalent monotonic loading has been studied in the laboratory by different researchers, simulating field conditions properly for the better understanding of liquefaction phenomenon. The undrained behavior of saturated sand is useful to predict the occurrence of the probable type of liquefaction (C.M. or F.L) and to provide suitable solutions for liquefaction problem. The objective of this research is therefore to study the undrained behavior of saturated sand in relation to liquefaction phenomenon based on intensive literature survey. This is best explained by identifying factors affecting the behavior and studying their effects observing the resulting stress-strain and p-q diagrams. The concept of Liquefaction and steady state are then discussed based on the undrained behavior of sand. Finally, the application of Steady State Line (SSL) on the assessment of liquefaction potential and in the identification of partial liquefaction, limited liquefaction, and complete liquefaction is discussed.
Relationship Between Consolidation and Swelling Characteristics of Expansive Soils of Addis Ababa
(Addis Ababa University, 2005-03) Kassa, Mesfin; Haile, Messele(PhD)
Clay soils are usually subjected to a time dependant strain under load. This strain is mainly a function of the rate of pore water pressure dissipation which in turn depends on the permeability of the soil mass. Therefore, consolidation is a term used to describe the volume change of the soil mass due to pore water pressure dissipation. Among the clay soils in the world, expansive soils have a special mineralogical characteristic which leads to swelling when exposed to moisture change. This behavior is due to the presence of considerable amount of montmorillonite clay mineral. As a result of swelling, pressure is exerted by the soil on the structures built on it and causes an increase in volume of the soil mass which also lifts the structure. Consequently, cracking of buildings, breaking of pavements, damaging of utility pipes are common problems on structures built on such soils. But under the action of heavy loads, greater than the swelling pressure, the soil undergoes consolidation. Thus, this paper is mainly intended to evaluate the swelling and consolidation behavior of expansive soils of Addis Ababa and their interdependence using one dimensional consolidation theory of Terzaghi. In the course of the research work consolidation-swell test was carried out on a number of samples of expansive soil obtained from different parts of Addis Ababa. The swelling and consolidation characteristic of the soil is determined from the laboratory tests. Ranges of values of the consolidation parameters are also obtained. The swelling behavior is found to influence the consolidation characteristics of expansive soils.
Design Charts for Composite Slab of 80mm and 100mm Concrete Thicknesses
(Addis Ababa University, 2005-07) Abebe, Michael; Taye, Shifferaw(PhD)
The use of steel deck in the construction of floors began in the 1920’s. The concept of using steel deck to act compositely with the concrete slab began in the 1950’s. A composite slab comprises steel decking, reinforcement and cast in situ concrete. Modern profiled steel are mostly designed to act as both formwork and Composite slabs. Composite construction in Ethiopian has not yet developed. This can be due to many factors. But to name a few, unavailability of the profile sheet locally and limited exposure to composite steel decks are some factors. In this thesis work, three analytic methods to calculate the capacity of composites is used. These are the full flexural method, first yield method and ASCE appendix D method. The full flexural method assumes that full interaction is present between the concrete section and profile steel sheet. The First Yield Method predicts the slab capacity to be the load that causes the bottom flange of the deck to reach yield stress. The Alternate Appendix D Method considers the shear transfer ability of different decks by the application of relaxation factors that describe the deck and embossment properties. The design strength is the multiplication product of the first yield strength and the relaxation factor. Based on these three analytic methods, design charts for different combinations of cross sectional values and material properties are developed.
Design Aid for Composite Columns (Concrete Filled Tubes)
(Addis Ababa University, 2005-07) Ketema, Ermiyas; Taye, Shifferaw(PhD)
Composite Columns Are In An Increased Usage For Construction Of Highrise And Medium-Rise Buildings, Bridges And Other Structures. However, Their Designs Involves Tiresome Calculations And Drawing Of Interaction Charts. In Addition, The Results Are Approximate. This Thesis Presents Design Aids For Concrete-Filled Steel Tubes To Simplify The Design And At The Same Time Increase The Accuracy Of Results. It Also Summarizes Important Behaviors Of Concrete-Filled Tube Columns As Compared To Other Column Types. General Approaches Have Been Presented On How To Prepare Design Charts And Such Charts Have Been Drawn For Selected Cross-Sectional Shapes. Uniaxial Charts Have Been Drawn For Square, Rectangular, Hexagonal And Octagonal Shapes Whereas Biaxial Chart Is Drawn For Square Section. This Thesis Also Provides Guidelines To Easily Develop Other Charts For Other Shapes And Material Types That Were Not Considered. Numerical Examples Have Been Presented To Illustrate The Application Of The Charts For The Design Of Composite Cross-Sections. Results Have Been Compared With Those Obtained Using The Procedure Outlined In EBCS 4-1995 And Have Shown Close Similarity. The Accuracy Of Viii Biaxial Charts As Compared With The Approximate Method In EBCS 4- 1995 Has Also Been Shown With The Help Of A Numeric Example. Keywords: Concrete-Filled Tubes, Uniaxial Bending, Biaxial Bending, Plastic Capacity, Interaction Chart
Response of Masonry Infilled Rc Frame Under Horizontal Seismic force
(Addis Ababa University, 2005-07) Degefa, Mekonnen; Zekaria, Adil(PhD)
Equivalent strut approach coupled with modified Bouc-Wen model for hysteretic behavior has been adapted for the analysis of masonry infilled RC frame. Modification of Bouc-Wen model includes stiffness and strength degradations as well as pinching in the infill panel. Default values for some of the parameters involved in the hysteretic model are adopted from the manual of IDARC-2D version 6.0. A simplified program developed in substitute of IDARC-2D is the backbone of this paper. The program assumes the beams as rigid elements embodied in the floor slabs and the deformation of columns in linearly elastic behavior. Four frames having the same number of stories but different number of bays are analyzed using the program. Only the first bay, whose aspect ratio (L/H) subject to variation from 1.0 to 3.0, has been infilled with masonry. Comparative analysis of shear in the left end column is performed for the infilled frame and corresponding bare frame. Static analysis using fundamental period and response spectrum curve based on EBCS-8 is carried out to compare the results of analysis of the program. Key words: Infill; Macro-model; Hysteretic; Degradation; Aspect ratio.
Alternative Dispute Resolution Methods in Construction Industry: An Assesment of Ethiopian Situation
(2005-07) bekele, Aberra; Dinku, Abebe(PhD)
The aim of every construction project stakeholder is the completion of a project that meets the objectives of time, cost and quality. However, the construction process is often fraught with disputes over the interpretation of construction documents, existing conditions, the legitimacy of variations, timely payments, etc. The emerging Alternative Dispute Resolution (ADR) methods which are non-litigation alternatives offer opportunities for effectively resolving disputes in the construction industry. Depending on the nature of the relationship between the parties involved in the disputes and the circumstances under which the dispute is evolved, different methods of dispute resolution mechanism may be preferable. This research reviews alternative dispute resolution methods in construction industry with an assessment of the Ethiopian situation. It provides insights into decisions making on appropriateness of dispute resolution method that suit their needs. These days both public and privately owned construction projects are increasing through out the country. The industry must change its treatment of conflicts, claims and disputes. Time should be used for works instead of wasting time for unnecessary litigation, and out-of-court dispute resolution methods need to be developed in the processing of construction management and project contract administration. The Ethiopian civil codes that deal with contract in general and construction contract in particular are reviewed in this thesis. Construction of public works made by the Statutory or other administrative authorities that is governed by administrative contract as stated in civil code is also considered in the research. Compromise and Arbitral Submission proceedings are addressed in the civil code with due procedure for detail implementation. The legal application of conciliation and arbitration relevant to public works and administrative contract, are examined in the research. The arbitrability of administrative contracts has controversial implications on the civil procedure code article 315 sub articles (2) and (4).

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