Abstract
This study investigates characteristics of vertical dynamic responses of a seismically isolated 9-storey building in Kushiro City considering dynamic interaction of soil and pile-group foundation. Records during small earthquakes and their simulation analyses reveal that vertical motions at ground observatory sites 29m away from the building are contaminated by soil responses induced by vertical responses of the building, resulting in an apparent increase of magnification factors of vertical responses in resonant frequency. Effects of soil nonlinearity during the 2003 Off-Tokachi earthquake are small in terms of vertical response characteristics considering dynamic impedance. The static or maximum value of the real part in dynamic vertical soil spring is preferable as a constant soil spring used in the time-domain earthquake response analyses for safety-margin based structural design.
