P-Delta effects on nonlinear dynamic response of steel moment-resisting frame structures subjected to near-fault pulse-like ground motions

Abstract

The objective of this study is to explore the P-Delta effects on the steel moment-resisting frame structures (MRFs) subjected to the near-fault ground motions with large, medium, and small pulse periods. The 3-, 9-, and 20-story MRFs designed for the American SAC Phase II Steel Project are used as benchmark models. Three near-fault and one far-field ground motion groups, each with 11 different records, are selected for the nonlinear time-history analysis. The P-Delta effects are quantified based on peak inter-story drift ratio (PIDR) demands. When the near-fault ground motions act on the structures, even if the structures have the low height and the earthquake is weak, the P-Delta effects could not be ignored. The nonlinear response of the group with Tp near to T1 is the largest, but the largest P-Delta effects appear in the group with TP slightly larger than T1. P-Delta effects do not influence the prediction of the weakest floor and the PIDR demands due to the ground motions which can trigger higher-mode effects. However, for long-period buildings, P-Delta effects can sharply increase the components’ distortion at the low half of the structure and even change the structural collapse direction, although P-Delta effects would decrease the demands at the middle stories. The panel zones are significantly important components for the seismic performance of MRFs and not only the weakest floor but also all the floors at the low half of the building are worthy of attention in the seismic design of MRFs.