Experimental on Dynamic Response of PHC Pipe Piles Under Near-field Pulsed Ground Motion
To investigate the dynamic response of PHC pipe piles under near-field pulsed ground motion,a shake table test was performed on the pile.The dynamic properties,supported superstructure response,acceleration response,dynamic strain response,damage characteristics,dynamic bending moment response,maximum curvature ductility demand and dynamic soil pressure response of PHC pipe piles were compared and discussed under the near-field pulsed ground motion and near-field normal ground motion.The results show that the decrease in natural frequency of PHC piles under near-field pulsed ground motion is higher than that of near-field normal ground motion,with a maximum of 20％.As the ground motion intensity increases,the pile stiffness decreases,which leads to an increase in the vibration period of the superstructure.At small earthquakes,the energy dissipation capacity of the superstructure is similar under near-field pulsed and near-field normal ground motion.During moderate and strong earthquakes,the energy dissipation capacity of the superstructure under near-field pulsed ground motion is significantly higher than that of near-field normal ground motion.Compared to near-field normal ground motion,the acceleration magnification factors of the pile under near-field pulsed ground motion increase by 43％for moderate earthquakes and by 117％for strong earthquakes.In addition,the peaks of acceleration,velocity and displacement time history of the pile under near-field pulsed ground motion are higher than that of near-field normal ground motion.Therefore,the seismic design should fully consider the adverse effects of near-field pulsed ground motion on the pipe pile.Under the influence of the inertia forces of the superstructure and soil resistance,the bending moment in the pile exhibits a distribution pattern with larger values in the middle-upper part and smaller values at the two ends.The maximum curvature ductility demand of the pile under near-field pulsed ground motion is higher than that under near-field normal ground motion.Under moderate and strong earthquakes,the hysteresis damping of the soil gradually decreases,resulting in the rate of increase in the maximum curvature ductility demand of the pile being greater than the increase in peak acceleration.Additionally,the main reason for the change in dynamic soil pressure is the relative displacement between the pile and the soil.The results of the study provide reference for the seismic design of PHC piles under near-field pulsed ground motion.
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