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场地液化除引起场地失稳和沉降外,也会对场地加速度反应产生重要作用。基于Finn模型实现自由场液化数值模拟试验,研究典型液化场加速度反应问题。研究结果表明:液化场加速度反应幅值与输入加速度幅值有关,液化场加速度放大倍数随输入地震动的增大而减小;液化场加速度反应大小与输入频率有很大关系,可液化场加速度反应的频率特征为:低频输入加速度反应幅值放大、高频输入反应幅值缩小,低频强化效应明显大于高频弱化效应;干砂弹性场也有低频放大高频滤波效应,但没有液化场显著;对于低频激振,若可液化场加速度经过放大且场地发生液化,场地加速度则衰减,若可液化场加速度经过放大但场地仍然未液化,场地加速度则维持稳态受迫振动状态;弹性场加速度反应从下到上逐渐增大,地表面放大最显著,液化场加速度放大在场地腰部最显著;高幅值输入易掩盖液化场加速度反应频率特性,低加速度幅值、低频输入下液化场的频率特性较明显。液化场地下结构抗震设计采用常规弹性场加速度反应系数,则会导致地下结构处于不安全状态。研究成果为液化场地下结构动力分析提供理论及试验基础。
Site liquefaction in addition to cause site instability and settlement, but also on the site acceleration response has an important role. Based on the Finn model, a free-field liquefaction numerical simulation experiment is carried out to study the acceleration response of a typical liquefied field. The results show that the magnitude of the acceleration response of the liquefaction field is related to the amplitude of the input acceleration, and the acceleration magnification of the liquefaction field decreases with the increase of the input ground motion. The magnitude of the liquefaction response has a great relationship with the input frequency, The frequency characteristics of the reaction are as follows: the amplitudes of the low frequency input acceleration responses are magnified, the amplitude of the high frequency input responses is reduced, the low frequency enhancement effect is significantly greater than the high frequency attenuation effect; dry sand elastic field also has low frequency amplification and high frequency filtering effect, but no liquefaction field is significant; For low-frequency excitation, if acceleration of liquefied ground is enlarged and liquefaction occurs on site, acceleration of site will be attenuated. If acceleration of liquefied ground is magnified but site is still not liquefied, acceleration of site will maintain steady state forced vibration state. Acceleration of elastic field The amplitude of the liquefaction field is the most significant at the waist of the liquefaction field. The high-amplitude input easily masks the frequency response of the liquefaction field, the frequency characteristic of the liquefaction field with low acceleration amplitude and low frequency input More obvious. The seismic design of underground structure of liquefied ground using the conventional elastic field acceleration response coefficient will lead to the underground structure in an unsafe condition. The research results provide theoretical and experimental basis for the dynamic analysis of subsurface structure of liquefied field.