PROBABILISTIC ASSESSMENT OF SEISMIC DRIFT DEMANDS FOR FRAME STRUCTURES IN NEAR-FAULT REGIONS

The purpose of this paper is to provide engineers with a rapid procedure to assess the maximum inter-story drift for generic moment-resisting frame (GMRF) structures in near-fault regions. In this procedure, the maximum inter-story drift demand of a structure can be evaluated by starting from the median value of elastic spectral displacement at the first period of the structure, and then amplifying it with some modification factors. Statistical parameters (medians and dispersions) of the distributions of these factors are obtained by performing linear, and nonlinear, dynamic simulations on code-compliant steel GMRF structures, to near-fault ground motions during Taiwan's Chi-Chi earthquake in 1999. Statistical equations that use the obtained medians and dispersions are provided for engineers to evaluate the maximum inter-story drift. Through the study on the simulation data of medians and dispersions of these factors, it is found that the dispersion of alpha(u) - which has been neglected in the previous study by Gupta and Krawinkler - has a great effect on determining the maximum inter-story drift demand of structures. In addition, care must be taken when buildings being designed are less than 2 km from the fault, since the medians (alpha) over cap (theta) of structures in this region are relatively larger than those of the other regions (2 km < r < 12 km). All statistics obtained in this study are steady and reliable, regardless of the number of stories. Therefore, this rapid method for evaluating seismic demands should be valuable and helpful for engineers in doing the preliminary design.