Structural Engineering

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Assessment of Load Carrying Capacity of Arch Bridge: Case study on Odie Bridge
(Addis Ababa University, 2020-06) Abiyu, Awoke; Abraham, Gebre (PhD)
Arch bridges possess an enormous capacity that can carry larger load than assessed through the application of limit state analysis and experimental methods. In the case of arch bridges, accessing detailed information of the structure is a bit difficult. In this study, load carrying capacity of Odie bridge, which is non-reinforced concrete arch bridge found in Ethiopia Federal Road Network, is carried out. Nonlinear finite element analysis was adopted using the total strain crack model in Midas FEA. Arch Bridge can manage load even with the formation of hinges. The study is focused on identification of the formation of cracks in arch barrel due to its own weight and vehicular loads applied at the quarter and crown point of the arch. Moreover, an influence surface along the top surface of the bridge was generated. Using the influence surface, the vehicular axle load positions were identified. Crack formation and stress in the arch due to a moving load is captured. To validate the numerical model, verification on Prestwood Bridge was used. The study revealed that the comparison between the numerical model and the full-scale test of Prestwood Bridge is applicable to estimate load carrying capacity of non-reinforced concrete arch bridges.
Assessment of Shear Strength of Reinforced Concrete Beam-Column Joints
(Addis Ababa University, 2017-12) Garomsa, Fikadu; Abraham, Gebre (PhD)
Even though beam-column joint is one of the most critical regions in reinforced concrete frames, a little attention is paid to the design of beam-column joints in Ethiopian practice. In this study shear strength of beam-column joints RC building frames designed to old EBCS is investigated. Shear strength of selected beam- column joints of a G+5 building has been assessed. The building is analyzed for seismic actions and the shear strength of the beamcolumn joint is estimated using both empirical expressions and analytically by using VecTor2 finite element computer program. Joints in the fourth story are selected to be assessed under monotonic loading for a constant column axial load. The study showed that there is a significant variation between result from analysis in VecTor2 and provisions in EBCSEN1998-1 (2013). From the investigation on the interior joints, the interior joint satisfies both ductility and shear strength requirement after column jacketing The maximum shear stress occurred at a story drift angle of 1.01% before column jacketing and it occurred at a story drift angle of 4.63% after column jacketing. This study is not enough in exposing the problems regarding design and detailing of beam-column joints in Ethiopian practice. Laboratory investigation is highly recommended due to its accuracy compared to software simulations.
Characterization And Grading Of Some Potential Timber Based On EN-338(2009
(Addis Ababa University, 2020-08) Samuel, Mulugeta; Abraham, Gebre (PhD)
The paper is aimed at the characterization and grading of two potential timbers species in Ethiopia using EN-338 (2009) strength classification for Euro code 5 timber design. The timber species namely Cupressus lusitanica mill and Eucalyptus globulus labill were obtained from Gullele Botanic Garden (GBG). Physical and mechanical properties of the selected timber species were determined in according with EN 13183-1 (2002), EN-373 (1957) and EN 408(1995) on small clear specimens. Three point bending tests based on EN 373 (1957) with specimen size 2x2x38 cm was carried out using a universal testing machine (UTM). Mechanical properties of timbers such as bending strength, modules of elasticity and compressive strength of each timber species were determined. Strength grading of timber species was conducted by adjusting the material property value at 12 % moisture content equivalent. Forty five samples from each species, 15 sample from bottom, 15 from middle and 15 from top for each species were tested. Compression stress parallel to the grain samples were prepared and tested. The experimental results were compared with the analytical values. The analytical compressive strength value was derived by the formula from EN-338 and these values were used to verify the test results. Finally, the timber species were then graded according to EN 338 (2009). And hence Cupressus lusitanica mill and Eucalyptus globulus labill were assigned to C-16 and D-24 class, respectively.
Development of Live Load Model for Ethiopian Short to Medium Span Bridges
(Addis Ababa University, 2020-12) Binyam, Wesenseged; Abraham, Gebre (PhD)
This thesis assesses the development of a new live load model for Ethiopian bridges that reflects the actual developments of the growing traffic. To have a clear idea of the research idea different countries' experiences and models were explored to have the best benchmark practice that helps to replicate to our context. The subject of interest of this paper is to explore the existing traffic loading model in Ethiopia and have contributed to its role in identifying the strength and weaknesses of this model. A Quantitative research design used to be applied for the study and efforts were made to use data from Static Weighing Stations obtained from the Ethiopian Roads Authority from three sites, which consists of 35,000 truck loading data in total. A simulation program was developed for the calculation of static load effects for simply supported bridges spanning up to 50m. Extreme 75-year loads obtained using different statistical extrapolation methods and the data was used to compare the loading effects generated from the actual trucks with the loading effects of the trucks used in the Ethiopian Bridge Design Manual. The result shows that the traffic loading effects obtained from the analysis vary from the currently adopted practice of the Ethiopian bridge design manual that demands to increase either the design load or the factor of safeties indicating the need for further research to reflect the existing reality.
Enhancing Strength in Concrete with Partial Replacement of Cement by Fly ash and Basaltic Dust
(Addis Ababa University, 2021-01) Wakayo, Gemeda; Abraham, Gebre (PhD)
Owning to its local resource availability and its adaptability to prevailing environment, construction industry using concrete is common here in our country, Ethiopia. Therefore, enhancing strength in concrete structures has a lot of advantages over prevailing country’s socio- economics. Presently large amount of fly ash is generated in thermal power plants as a waste material with an improper impact on environment and humans. Fly ash, a waste generated by thermal power plants is as such a big environmental concern like ‘Reppi Electric power Station’ here in our country, Ethiopia. Therefore, economic concern and green environment issue should be addressed as many last studies shows as reduction of CO2 emissions and waste materials like fly ash and basaltic dust are being used instead of cement as cementations materials recently. Hence, using waste materials, fly ash and basaltic dust will improve structural strength of concrete than the conventional concrete production one in addition to its cost and make green environment by depleting above mentioned wastes, fly ash and basaltic dust. The cement has been replaced by fly ash and basaltic dust accordingly in the range of 0% (without fly ash and basaltic dust), 10%, 20%, 30%, 40% and 50% by weight of cement for OPC, C-30. These tests were carried out to evaluate the mechanical or structural properties of the concrete for the test results of Compressive Strength, Split Tensile Strength and Flexural Strength for 7days, 14days and 28days respectively. Based up on the test result obtained, Cement partial replacement by both fly ash and basaltic dust with 30% with slump test of 35-36.5mm induced best result in Compressive strength (42.47MPa) and attractive structural properties of the concrete with respect to the conventional one and higher results of Split tensile strength (2.94MPa) and Flexural strength (4.63MPa) were obtained with 20% partial replacement of cement with fly ash and basaltic dust while maintaining constructability by using water to cement ratio of 0.54. Hence it would minimize construction cost, avoid delay in construction as early strength can be obtained earlier, and enhance structural strength of the prevailing concrete and keeping the environment green from CO2 emissions and fly ash disposal pollutions.
Experimental Investigation of the Effect of Steel Slag Aggregate on the Bond Strength of Reinforced Concrete Member
(Addis Ababa University, 2022-01) Melkam, Gubay; Abraham, Gebre (PhD)
The demand of concrete has increased due to expand of the construction industry. To protect the natural concrete making materials and to sustain the environment, reused of waste products as ingredients of concrete is becoming an inevitable option. From those Steel slag was selected due to its properties, which has almost similar properties to natural coarse aggregate, and it is easily accessible as a by-product from steel production industry. The mechanical property of the concrete with steel slag aggregate has been studied in different literatures. However, literature is limited on the bond behavior of steel slag concrete with steel bar. In this research, the effect of steel slag aggregate on the bond strength of reinforced concrete was investigated experimentally using cylindrical specimens (300 mm ×150 mm) with centrally embedded 12 mm, 14 mm and 16 mm deformed bar. The bond strength test was conducted with pullout test on short embedment length (5db) for 45 specimens. A total of five concrete mixes with 25% interval replacement of steel slag aggregate as coarse aggregate was carried out up to fully replaced for the normal strength concrete C-30. In addition to the bond strength test compressive and splitting tensile strength of the concrete were studied by using (150 mm size cube) and (300 ×150 mm) cylinder, respectively. Experimental test results shows that the compressive strength and splitting tensile strength of concrete increased up to 50% replacement of coarse aggregate by steel slag aggregate, and also the ultimate bond strength was increased up to 50% replacement. For all bar diameters, fully replaced steel slag aggregate concrete has compatible bond strength value with control concrete. On the other hand as the bar diameter increased the bond strength decreased due to the decrement of concrete cover. Additionally, this study proposed an empirical equation for ultimate bond strength based on the experimental results. ACI 318 and ESEN 1992 1 codes are more conservative and underestimated the bond strength values of all specimens.
Partial Replacement of Cement With Marble and Ceramic Waste Powders in Normal Strength Concrete
(Addis Ababa University, 2022-01) Rihanna, Nuru; Abraham, Gebre (PhD)
Production of cement is hazardous to the environment. Recycling wastes has been one of the most influential aspect affecting global conditions of the world. Fair amount of work has been done on the utilization of the wastes such as marble waste, ceramic waste, tiles waste, fly ash, glass, plastic etc. used as different forms of replacement to preserve the environment. The combined effect of marble waste powder and ceramic waste powder as a partial replacement of cement is observed and analyzed. 21 cement pastes for chemical shrinkage test, 60 cube samples for compressive strength test, 60 cylinder samples for splitting tensile strength test and 21 beam members for flexural strength test with different percentages of partial replacements were made. The workability of concrete decreased with an increase of percentage replacement of cement by marble and ceramic waste powders. All of the mixes do not possess an early age cracking due to the result obtained from the chemical shrinkage test. The obtained results for compressive strength, splitting tensile and flexural strength of concrete are in the acceptable range as compared to the conventional concrete values.
Performance Evaluation of Reinforced concrete Bridges without Plans: A case study on the assessment of Koka Bridge
(Addis Ababa University, 2019-06-12) Martha, Bimrew; Abraham, Gebre (PhD)
In Ethiopia, reinforced concrete bridges that were constructed in the early and mid of 20 th century exist in large numbers and are still in service. Due to the changing nature of vehicular load supported by these bridges and frequent permit trucks using the bridges, assessment of bridges to obtain their load carrying capacity is usually desired. The legal owner of the bridges, the Ethiopian Roads Authority, cannot provide necessary information such as as-built drawings, and properties of construction materials. The thesis demonstrates the assessment of load carrying capacity of old and deteriorated reinforced concrete bridges without plans (as built drawings or design drawings). Assessment codes give sufficient recommendations on how to load rate bridges that does not have sufficient data to be used in load rating. The safe live load carrying capacity of a highway structure is known as its rating. A case study has been conducted on one of the bridges along the heavily loaded route corridors bridges i.e. Koka River Bridge. Data obtained from historical records, field inspection and measurement besides design code existing by the time of construction of the bridge, 1953 G.C. has been used to prepare an effective Finite Element model on Abaqus/CAE 6.13-1. A moving tire load on the bridge deck has been used for the analysis, and the results obtained have been used to load rate the bridge for a permit load and ERA’s legal loads. The bridge was found to have sufficient capacity to withstand Legal loads and selected permit load, it has 50% and 8% reserve capacity respectively. However, it is recommended to maintain defects and distresses noticed on field inspection since they might lead to further deterioration of the bridge.
Seismic Behavior of High-rise Building having Symmetric and Asymmetric Setback with Steel Bracing
(Addis Ababa University, 2017-11) Tilahun, Hailegnaw; Abraham, Gebre (PhD)
Construction of vertical geometric irregular buildings is very common due to space, architectural and functional constraints. This paper is concerned with the behaviour of various vertical geometrical irregularities of symmetric and asymmetric setback by different types of bracing. For this study twenty five story buildings 12 modeling have been analyzed considering different types of vertical geometric irregularities and different steel bracings using response spectrum analysis with the help of ETABS 2015 software. The response of the these setback structures are obsereved with lateral displacement, story drift, shear force and bending moment. From addition of X type brace, V type brace and Inverted V type brace shows that use of X-type of bracing is found more efficent and significantly contributes to the structural stiffness and reduces the maximum interstorey drift and lateral displacement of the frames. This study may help the practicing engineers to improve and understanding about seismic susceptibility of setback buildings, and using steel bracing is one of the advantageous concepts which can be used to strengthen or retrofit the existing structures..

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