Fragility analysis for reinforced concrete sections in an in-service nonlinear hysteretic system subjected to seismic actions

Hysteresis is a phenomenon that characterizes the structural behavior of typical reinforced concrete (RC) structures that undergo load reversals beyond their elastic limits. For an RC structure constructed in an earthquake-prone zone, seismic actions are routinely considered as one of the most commonly encountered situations that may lead to hysteresis. This paper is concerned with the seismic structural safety in relation to a hysteretic RC system. Specifically, the fragility of the RC system at a given level of seismic intensity is quantified. The seismic fragility quantification of this kind is often accompanied by two issues, i.e., incomplete structural appraisal data and prolonged computing time. The former is addressed by using a contemporary statistical technique referred to as the expectation-maximization algorithm, while a surrogate model is rolled out to help resolve the latter. A salient feature of the study presented herein is that the hysteretic system being investigated is presumed to have been in service for a considerable period of time so that its up-to-date, degraded health condition needs to be allowed for