Browsing by Author "Gebre, Abrham (PhD)"

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    Computer Program for Comaprative Study of the Analasis and Design of Prestressed Concrete Box Girder and Plate Girder Highway Bridges
    (Addis Ababa University, 2016-11) Nigussie, Seyfe; Gebre, Abrham (PhD)
    Planning and designing of bridges is part art and part compromise, the most significant aspect of structural engineering. One of the initial choices the designer should make is to select the most appropriate bridge type for the site. While this choice is not always straight forward, selecting the right structure type is probably the important phase of designing a cost-effective bridge. The various types are ideally suited for different span lengths. For instance, on different standards, for spans ten to fifty meters cast in Place Post Tension Box Girder Bridges are usually chosen where as for spans ten to one hundred twenty meters Steel Plate Girder Bridge is preferred to be used respectively. This study focused on developing computer program for the analysis and design of Cast in Place Post Tension Box Girder and Steel Plate Girder Bridges, for solving the design problem of economical span and demarking on the base of cost analysis. A comparative study based on cost of materials is conducted to select and identify the economical span range of Cast in Place Post Tension Box Girder and Steel Plate Girder Bridges. The program is developed using visual Studio 2012. The developed program is illustrated using particular examples for both types of bridges. The study has come with solution based on the current construction prices. As per the study based on the current material cost seventy-meter span is the demarcation span for the two types of bridges. Within the overlap span length of the two bridges, Cast in Place Post Tensioned Box Girder Bridge is economical up to seventy-meter and beyond seventy-meter Steel Plate Girder Bride be economical. Keywords: Bridge, cost effective, cast in place post tensioned box girder, steel plate girder
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    Performance of Concrete and Unrestrained Reinforced Concrete Beam for Fire
    (Addis Ababa University, 2015-09) Gebremariam, Habtomm; Gebre, Abrham (PhD)
    Fire accident is one of the dangerous accidents that could happen to any service structures in unexpected times, it could be ignited intentionally to attack enemies among human being aggression, it could be from the result of terrorism attack which of course common nowadays or it could be from war among enemies. Fire accident by its behaviour a little source is enough to be ignited but its costs much to be controlled. In our country Ethiopia there were so many lives taking and damaging fire accidents occurring for instance in the near past an accident caused on TAITU HOTEL in piazza , an accident in Southern Ethiopia, Hawassa demolishing large number of homes and lives. A repeated and hazardous fire accidents causing loss of valuable human life, failure of structures and the difficult circumstance to make fire accident under control within a shorter time, increase an interest in the design of structures for fire. Now a day there is a good development in using advanced analytical models to determine fire growth within a compartment and have used finite element models of structural components to determine temperatures within a component by heat transfer analysis but the experimental way of determining the performance of structural members for fire is more realistic one. This paper focused in studying the performance of concrete and unrestrained reinforced concrete beams under fire. In this study different concrete surface temperature and duration of fire exposure was considered. Experimental investigation on fire performance of concrete and unrestrained reinforced concrete were carried out and it is discovered compressive strength of concrete reduces up to 30% from initial compressive strength up on exposure to fire causing concrete surface temperature to rise to 246 0c for four hour duration, and residual shear and moment strength of unrestrained reinforced concrete beam reduce to 80% for 246 0c concrete surface temperature sustained for four hours. Key words: Fire duration, Concrete surface temperature, Reinforced concrete beam, Fire rating, Bending moment capacity, deflection, Shear capacity, Compressive Strength, concrete cube.