ON THE IMPROVEME NT OF NONLINEARSTATIC PROCEDURES FOR STRUCTURES SUBJECTED TO NEAR-FAULTGROUN DMOTIONS CONSIDERINGVARIOUS FAULTING MECHANNISMS

This paper investigates inelasstic seismic demands of the normal component of near-fault (NF) pulse-like ground motions, which differ c onsiderably from those of far-fault (FF) ground motions and also parallel component of near-fault ones. The r esults 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-hist ory (NTH) analyses are conducted to produce benchmark responses against the predictions of NSPs are compared. Considerable influences of different faulting me chanisms are observed on inelastic seismic dem ands. The demands are functions of the strength ratio and also the ratio of pulse period to structural perio d. 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 modifi cations 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, incl uding steel moment-resisting frames, and also inefficiencies of current lateral load patterns. The family of s tructural 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 differen ces in seismic demands for each set, including interstory drift ratios and peak roof displacement ratios.

Keywords:

Pulse-Like Ground Motion , Near-Fault Earthquakes , Nonlinear Static Procedure , Displacement Coefficient Method , Lateral Load Pattern