Method of Seismic Reliability Evaluation for Moment Resisting Steel Frames

Abstract

The objective of this study is development of a method for evaluation of performance of moment resisting steel frames under seismic loads. The emphasis is on modeling and quantification of the large uncertainties associated with the excitation, details in design according to current code specifications (UBC) , and the nonlinear inelastic response behavior of the structure. A site-specific seismic hazard.analysis is carried out to identify and quantify the uncertainties associated with· the source, the path and the site condition. Future earthquakes are treated as either characteristic (major event along a well-identified major fault segment) on non-characteristic (local events). Ground motions are modeled as nonstationary random processes with time varying amplitude and frequency content, whose parameters depend on the source, path and site conditions. A strong column - weak beam model is developed for the structural frame and with which response can be obtained with good accuracy and computational efficiency. The response statistics are obtained by method of random vibration based on an equivalent linearization solution procedure and a smooth differential equation model for the hysteretic restoring force. The accuracy of this method is verified by comparison with simulations. A fast integration technique is then used to evaluate the probability of limit state (interstory drift limit being exceeded) considering the uncertainties in the excitation parameters. The robustness of the proposed method is demonstrated in the numerical examples throughout this study. The method can be used in assessing the risk implied in current earthquake resistant design, and in developing reliability-based code procedures.