Effects of rupture forward directivity and fling step of nearfault ground motions on seismic performance of baseisolated building structure

Near-fault ground motion records from two different earthquakes,the 21 September 1999 Jiji (Chi-Chi), Taiwan,earthquake and 17 January 1994 Northridge earthquake,are selected as seismic input,and the influence of velocitypulse of nearfault ground motions with rupture forward directivity and fling step on the seismic performance of single degree of freedom (SDOF) system and baseisolated buildings with lead rubber bearings are examined. The response spectrum analysis illustrates that the effects of rupture forward directivity and fling step of ground motions on the seismic responses of engineering structure are perioddependent. In the range of short and medium period, the spectral acceleration of ground motions with forward directivity is larger than that with fling step. In the long period range, the spectral acceleration of motions with fling step is generally larger than that with forward directivity. Furthermore, compared with the nonpulse ground motions, the dynamic responses of base-isolated buildings under the ground motions with rupture forward directivity and flingstep pulses are increased significantly. Moreover, the velocity pulses from the effect of fling step remarkably amplify the interstory drift and shear force of baseisolated building at lower stories. This implies that the fling-step pulse causes more severe damage to long-period buildings than the forward directivity pulse does.