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近场地震动是具有长周期、短持时、高能量的速度脉冲运动,其对基础隔震的减震性能产生不利影响。建立一幢10层钢筋混凝土框架基础隔震的有限元模型,分析其在近场脉冲型强震与常规强震作用下的非线性反应,探讨速度脉冲对层间弹塑性位移、层间剪力、隔震层变形及隔震结构塑性铰分布的影响。提出在隔震层增设黏滞阻尼器,形成混合隔震方案,分析其对隔震层的限位保护效果及其对隔震结构非线性反应的减震效果。结果表明:基础隔震在速度脉冲近场强震作用下的非线性反应较常规强震显著增大;隔震层最大变形显著增加,远超过了隔震支座容许变形值。考虑近场影响系数不能有效反映长周期速度脉冲对隔震结构的不利影响。混合隔震能有效控制隔震层上部结构的非线性反应与隔震层最大变形,避免隔震支座破坏而导致上部结构倾覆失稳。
Near-field vibrations are velocity pulse motions with long period, short period and high energy, which adversely affect the shock absorption performance of base-isolated. A 10-story finite element model of base-isolated RC frame was established and its nonlinear response to near-field impulsive and conventional strong earthquakes was analyzed. The effects of velocity impulses on interlayer elasto-plastic displacement, interlayer shear force , The deformation of the isolation layer and the plastic hinge distribution of the isolation structure. It is proposed that a viscous damper be added to the isolation layer to form a hybrid isolation scheme. The effect of the limit protection on the isolation layer and its damping effect on the nonlinear response of the isolation structure are analyzed. The results show that the nonlinear response of foundation isolation to velocity pulse near-field strong earthquakes is significantly larger than that of conventional strong earthquakes, and the maximum deformation of isolation layer significantly increases, far exceeding the allowable deformation of isolation bearings. Considering the near-field influence coefficient can not effectively reflect the adverse effects of long-period velocity pulses on the isolated structure. Hybrid isolation can effectively control the nonlinear response of the superstructure and the maximum deformation of the isolation layer to avoid the collapse of the isolation bearings and the instability of overturning of the superstructure.