Date of Award
Master of Science
Cable-stayed bridges are popular these days in spite of their complexity in shape and design. Cable-stayed bridges are ideal for a navigational channel due to their high clearance and long central span. These types of bridges also possess advantages over suspension bridges, especially when local site conditions are not suitable for anchoring the towers. In most of the cases, cable-stayed bridges are self-supportive or require less anchorage. Although symmetrical cable-stayed bridges are dominant, asymmetrical bridges are also common as well due to ground layouts and other restrictions like economy, aesthetic purpose. Added counter weight and eccentricity of asymmetrical bridge may highly affect the response of the structure under earthquake loading. For the same length span bridge, the response of the asymmetric one may have an amplified response compared to the symmetric one with the same span length and also, may not follow any predictable trend. This study presents a multi-support analysis for four models, which are, 200 m symmetrical, 400 m symmetrical, 200 m asymmetrical and 400 m asymmetrical bridges. Ground motions has been recorded by using accelerometers. The recorded ground motion depends on the direction of the accelerometer. To remove this dependency, the principal components of each ground motion were found and used for the analysis and the models were excited in the transverse direction. The models were run under both multi-support excitation and identical-support excitation for displacement time-history analysis using SAP2000. Ratio of stresses and deflections were compared for the bridges with the same span length. According to this study, on 200 m asymmetrical bridge, multi-support excitation factored responses up to 4%, while on 400 m asymmetrical bridge, responses are factored up to 20% compared to the identical-support excitation. It is noted that responses of asymmetrical bridges are factored up making identical-support excitation non-conservative.
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