ON THE IMPROVEMENT OF NONLINEARSTATIC PROCEDURES FOR STRUCTURES SUBJECTED TO NEAR-FAULTGROUNDMOTIONS CONSIDERINGVARIOUS FAULTING MECHANISMS

This paper investigates inelastic seismic demands of the normal component of near-fault (NF) pulselike ground motions, which differ considerably from those of far-fault (FF) ground motions and also parallel component of near-fault ones. The results are utilized to improve the nonlinear static procedure (NSP) called Displacement Coefficient Method (DCM). 96 NF and 20 FF ground motions and the responses of various SDOF systems constitute the dataset. A comprehensive set of Nonlinear Time-history (NTH) analyses are conducted to produce benchmark responses against the predictions of NSPs are compared. Considerable influences of different faulting mechanisms are observed on inelastic seismic demands. The demands are functions of the strength ratio and also the ratio of pulse period to structural period. Simple mathematical expressions are developed to consider the effects of NF motion and fault type on nonlinear responses. Modifications are presented for the DCM by introducing a NF modification factor, CN. In locations, where the fault type is known, the modifications proposed in this paper help to obtain a more precise estimate of seismic demands in structures. The second objective is the verification of the probable differences in seismic demands of MDOF structures, including steel moment-resisting frames, and also inefficiencies of current lateral load patterns. The family of structural models used in this study is composed of nine and twenty-story 2-D moment resisting steel frames, considering medium to tall frame models. Two basic types of ground motions are used as the input: 10 FF and 10 NF ground motions. NTH analyses as the output, which are utilized to demonstrate the differences in seismic demands for each set, including interstory drift ratios and peak roof displacement ratios.