【摘要】 通过开展离心机动力模型试验,深刻地揭示桩筏基础与土之间的动力相互作用将造成基础和土体运动的非一致性,土体的运动不能代表基础的运动,两者在加速度时程、反应谱特征、共振周期等方面均存在显著的差异,传统结构抗震设计中采用自由场土体的动力参数直接作为基础的动力参数是极不严格的;基础与土之间的动力相互作用将导致周围土体发生重塑软化,且基础附近的土体(近场)软化程度明显高于远场土体(自由场土体),加之土体自身的应变软化和强度降低的内在机制将共同导致土体的周期明显延长;然而,在地震作用下,桩筏基础几乎不发生软化,这与土体有着本质的区别;在相同条件下,基础的共振周期小于土体周期(近场和远场),远场土体(自由场土体)周期小于基础附近的土体周期(近场土体);土体的动力软化对结构的影响甚微。更多还原

【Abstract】 By conducting dynamic centrifuge model tests on the clay-pile-raft system,this paper investigated that a kind of dynamic interaction non-coincidence between soil and pile-raft foundation.This suggested that soil motion can not be representative of foundation motion,and that adopting free field soil seismic parameters directly as foundation parameters in traditional building aseismic design is unreasonable;differences on the acceleration time histories,response spectra,as well as resonance period between soil and pile-raft foundation are very obvious and can not be neglected in engineering aseismic design.The effects of modulus reduction and stiffness degradation are manifested as an increase in the resonance periods of the clay layers with the level of shaking and with successive earthquakes,while this is not the case for the pile-raft foundation since its resonance period is hardly affected by earthquake loadings.Furthermore,raft period is always lower than corresponding clay period and period of far field clay is lower than that of near field clay because of remolding softening effect under the same condition,and pile-raft dynamic behavior is hardly affected by the stiffness degradation of surrounding clay.更多还原