Improvement to Linear Elastic Procedures for Seismic Performance Assessment

Abstract

Nonlinear modelling and analysis of complex structures is generally considered a difficult area in structural engineering practice due to many reasons. Firstly, it requires a detailed understanding of various complex interactions and phenomena. Secondly, nonlinear dynamic analysis also demands significant computational effort and the use of specialized computer software which are complex and time consuming. In some cases, the obtained results can be significantly sensitive to nonlinear modelling assumptions and inelastic properties of components which may not always be well-defined. For most practical cases, the linear elastic analysis may serve the purpose of estimating design demands within their required degree of accuracy. But in recent times due to the advent of latest “Performance-based Design methodology, the need for nonlinear modelling and analysis is growing rapidly. The seismic simulation is more realistic and meaningful compared to a linear elastic model. But because of complex and time-consuming nature of nonlinear dynamic analysis, in this report we have tried to developed some modifications over linear dynamic procedures so that our results and analysis can be somewhat approximated near to the nonlinear dynamic analysis which can reduce the overall complexity and time of our analysis. Considering the current practice of structural engineering in implementing linear-elastic analysis with standard analysis tools, an improved linear procedure is developing in this study for the seismic performance assessment of MDOF systems. It is based on a single, global iteration step for updating the stiffness of members that exceed their flexural capacities, as predicted from the initial linear-elastic analysis. The fragility function obtained from the proposed procedure is evaluated comparatively using incremental dynamic analysis results. ESDOF approximation is adopted as the basis for approximating the inelastic behaviour of the building. YFS is used as an approximation method, to incorporate and propagate all source uncertainty related to the seismic hazard, structure modelling and analysis framework.