Energy Response of Building Structures with Foundation Uplift Subjected to Earthquake Motions

Abstract eng:
Previous studies by many researchers suggested that rocking vibration accompanied with uplift might reduce the seismic damage of buildings in 1995 Hyogo-ken Nanbu Earthquake. In this paper, reduction effect to the response is discussed by the energy into the foundation-superstructure system using time history analysis. The results from comparing with structures with uplift to that without uplift are follows. Natural period of foundation-superstructure system becomes longer when the uplift occurs, and total input energy into the system increase when the energy spectrum of input ground motion increase and total input energy decrease when the energy spectrum decrease. In many analytical results, the strain energy of the superstructure decreases by uplift even if the total input energy of the system increase by uplift. This result indicates that the seismic damage would be reduced by uplift in many actual cases. When the uplift occurs the strain energy of the superstructure becomes less than 80% of that without uplift in case of the Vs=300 m/s, so that the reduction effect of response caused by uplift on the hard ground is larger than the soft ground. The input energy and strain energy are reduced significantly because of combination with uplift and soil-structure kinetic interaction effect. That is to say, response reduction effect by the foundation uplift can be considerably expected in many actual situations.

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