Shaking Table Test and Numerical Simulation on a Mega-Sub Isolation System Under Near-Fault Ground Motions with Velocity Pulses

Theoretical analyses show that the velocity pulse characteristics of ground motions adversely affect structural responses of mega-sub isolation systems. This study presents an extensive shaking table test conducted to investigate the seismic responses of a mega-sub isolation system under near-fault ground motions with velocity pulses. Two steel frames were used as test specimens, representing aseismic and seismic isolation models. Two representative groups of actual ground motion records with velocity pulse characteristics were selected as inputs, along with their corresponding synthetic counterparts with the same acceleration spectrum, but without velocity pulses. Test results showed that near-fault ground motions with velocity pulses had an adverse effect on the seismic responses of the mega-sub structure system, especially on the displacement of the isolation layer in the isolation structure. Compared with the mega-sub isolation system, more nonlinear behaviors were observed in the aseismic system. Finite element analysis of the mega-sub aseismic and isolation systems was conducted by using SAP2000. Satisfactory agreement was observed between the simulation and test results, and the differences between them were discussed in detail. The obtained conclusions can provide a scientific basis and valuable reference for the seismic design and safety evaluations of mega-sub isolation systems under near-fault ground motions with velocity pulses.