Effectiveness of vector intensity measures in probabilistic seismic demand assessment

The vector intensity measures (IMs) has been recommended by many researchers for probabilistic seismic demand assessment (PSDA) because they claimed that using vector IMs could reduce the uncertainty in engineering demand parameters (EDPs) estimates. However, the inclusion of additional vector elements in vector IMs also increases the IM uncertainty, which in return brings additional uncertainty to the EDPs estimates. Thus, the benefit of implementing the vector IMs for PSDA is unclear. The objective of this study will clarify the effectiveness of vector IMs for PSDA. The study discusses the framework of PSDA using scalar IM and vector IMs. Based on the uncertainty in EDPs estimates involved in the framework, we applies theoretical derivative to clarify the hidden aleatory uncertainty in EDPs estimates, which offers a fresh view on PSDA. Using numerical examples of three buildings and Monte Carlo simulation, we further investigate the effectiveness of vector IMs in EDPs estimates by comparing structural response hazards determined by vector IMs and scalar IM. Our study reveals that, for cases when collapse effect is not considered, the use of vector IMs cannot benefit PSDA. Under cases when the collapse effect should be considered in PSDA, the use of vector IMs may improve accuracy of structural response hazard curves. Such improvement is associated with the capability of vector IMs to predict the structural collapse.