Nian, DX; (1992) Inelastic response and effective design of asymmetric buildings under strong earthquake loading. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Asymmetric building structures arise frequently in civil engineering practice as a result of architectural or other requirements. Collapse and widespread severe damage of buildings associated with the torsional response created by structural asymmetry or other forms of irregularity have been observed repeatedly in past strong earthquakes. This highlights the inadequacies in current earthquake resistant design and construction of asymmetric buildings in seismic prone regions. This thesis investigates the inelastic behaviour of asymmetric buildings under strong earthquake motions and provides guidelines and recommendations for their effective design. These guidelines are widely applicable, offer conservative estimates of design loadings for individual resisting elements, and retain simplicity for ease of code implementation. A comprehensive review and critical assessment of previous studies are presented in which the different approaches and contradictory conclusions reached are identified. Prior to inelastic dynamic studies, an inelastic failure mode analysis of single-storey asymmetric buildings under static monotonic loading is carried out. The latter analysis helps to explain the model dependency of the inelastic torsional response and clarifies the influence of key system parameters. Based on single-storey building models, the model dependency of the inelastic torsional response is studied further by carrying out inelastic earthquake response analysis. A suitable analytical model is developed, which provides conservative estimates of the inelastic torsional effects, represents a wide range of actual buildings, is simply defined and facilitates the straightforward interpretation of results. A thorough inelastic dynamic parametric study is carried out employing this model, leading to improved understanding of the inelastic behaviour of asymmetric buildings to strong earthquake motions and the influence of key system parameters on the inelastic seismic response. The torsional provisions of current earthquake resistant design building codes from Europe, New Zealand, Canada, Mexico and the United States are rigorously evaluated based on the analysis of the single-storey building model. In particular, an assessment is made of the adequacy of the linear elastic modal analysis procedure, which is specified in most codes as an alternative approach to the equivalent static force procedure for the design of asymmetric buildings when certain regularity conditions are not satisfied. Inadequacies in the code torsional provisions and the linear elastic modal analysis procedure are identified. Improvements to these code provisions are sought and a new unified approach for torsional design is proposed. A multistorey regularly asymmetric frame building model is also developed, and the code torsional provisions and the linear elastic modal analysis method are re-evaluated based on this model. The results of this study reinforce the conclusions obtained from analysis of the single-storey model and provide insight into the effect of inelastic torsional coupling in the various storeys of the building. A new equivalent static force procedure is proposed for the design of multistorey regularly asymmetric frame buildings. As a result of its inadequacies, it is suggested that linear elastic modal analysis be deleted as an alternative method for design of these buildings.

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