Seismic Analysis and Reliability-based Design of Secondary Systems

Abstract

Seismic qualification of secondary systems such as piping is performed using the response spectrum method. Structural responses evaluated using response spectrum method are used for checking the design equations specified by the ASME Section III Boiler and Pressure Vessel (ASME BPV) Code. This dissertation addresses the topics of combining modal responses in response spectrum method and the reliability associated with the ASME design equations. In the method for combining modal responses, the validity of the existing expressions for rigid response coefficient is evaluated for the case of floor motions which represents earthquake input to the secondary systems. A closed-form formulation is proposed for the rigid response coefficient and is verified using time history analysis for both the cases of ground and floor motions. The closed-form expression is then extended to response spectrum method by developing a simplified procedure for evaluating relative Fourier amplitudes of few significant pulses from the floor response spectrum. In the reliability-based design of piping systems using ASME BPV code design equations, performance functions are formulated to characterize the different failure modes in a straight pipe segment. These performance functions are then used to determine the implicit reliability levels associated with the design equations in ASME-BPV code. This calibration of the existing design equations is intended to provide an input for future studies related to the development of Load and Resistance Factor (LRFD) design equations which require an estimate of implicit reliability levels in existing equations in order to establish the target reliabilities.