Method of Reliability-Based Seismic Design. I: Equivalent Nonlinear Systems

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Abstract
This is the first part of a two-part investigation on the method of reliability-based seismic design. In reliability analysis and reliability-based design under stochastic loads such as seismic excitations, repeated time-history solutions of multi–degree-of-freedom (MDOF) inelastic structures are often required, which can become computationally expensive. To alleviate this difficulty, an approximate method is developed by replacing the MDOF system with a simple equivalent nonlinear system (ENS) that retains the dynamic characteristics of the first two modes and the global yielding behavior of the system. The equivalence is achieved by the use of two empirical response modification factors based on regression analyses of responses to a large number of actual ground accelerations recorded in past earthquakes. Numerical examples on reliability analysis of the special moment resistant space frame (SMRSF) under seismic excitations are given. The computational advantage and accuracy of the method are demonstrated.