Analysis Of Effects Of Near-Field Ground Motion On Structures And Seismic Response Of Moment Resisting Steel Frames

The near-field earthquake causes the destruction of structures because of its special effects, which will lead to a large number of casualties and huge economic losses. Advanced seismic design methods should have the function of protecting the structures in near-field area.The characteristics of near-field ground motion and its influences on the structure have attracted more and more scholars’ attention. According to CODE FOR SEISMIC DESIGN OF BUILDINGS (GB50011),if structures locate close to the causative fault within 10km on both sides, ground motion parameters should be taken account for the near-fault effects;if structures locate close to the causative fault within 5km,ground motion should be multiplied by amplification factor 1.5;if beyond 5km,ground motion should be multiplied by amplification factor which is not less than 1.25.This provision does not consider the particularity of near-field response spectra.The values of far-field response spectra are only roughly magnified in order to improve the effects of near-fault ground motion.There’s no foundation for the interpretation.In addition,few literatures are discussed amplification factor’s safety and rationality.Moment Resisting Steel Frames(MRSFs) are studied in this paper.A 3-story and a 6-story frame structure which consider the near-fault effects are designed by following the standard design code strictly.And ground motion is multiplied by amplification factor 1.5 and 1.25.15 near-field earthquake records with velocity pulse are selected in this paper. The response spectra of 15 near-field earthquake records is established and compared with the design spectra of Chinese seismic code. It is indicated that the response spectra of near-field earthquake records has wilder acceleration-sensitive region.It is necessary to revise the design response spectra of Chinese seismic code.Nonlinear time-history analysis is used to evaluate the seismic response of the MRSFs.It is indicated that roof displacement,story displacement, base shear and story shear are increased because of near-field effects; When ground motion is multiplied by amplification factor 1.5,it is conservative for the 3-story frame structure and is unsafe for the 6-story frame structure; When ground motion is multiplied by amplification factor 1.25,it is unsafe for the 3-story and 6-story frame structure.It is suggested that different amplification factors should be adopted by corresponding to structures with different periods,or the design response spectra of near-field earthquake should be adopted.