水平地层地震动力反应分析

Seismic response characteristic of horizontal layer

根据Iai多重剪切机构塑性模型及边界面塑性模型的特点,建立了一个砂土多机构边界面塑性模型。该模型将土复杂的变形机理分解为体积机理和一系列简单的剪切机理。用边界面弹塑性模型模拟多重剪切机构塑性模型中虚拟单剪机构,避免了Iai多重剪切机构塑性模型在利用修正M asing准则模拟虚拟单剪应力应变关系时,确定比例参数的复杂性。根据大量试验资料,建立了液化面参数与归一累积剪切功的关系,能够用较少的参数很好地建立有效应力路径。由于多重机理的特性,模型能够模拟复杂荷载作用下主应力轴偏转的影响。用多机构边界面塑性模型对饱和砂土水平场地进行有效应力分析,对水平场地的地震反应特性进行了分析,由于多机构边界面塑性模型能同时考虑振动孔隙水压力的发展引起的有效应力降低导致饱和砂土抗剪强度和模量的降低。分析表明,结果是合理的。模型简单实用,将方便在工程实践中的应用。

According to the characteristics of Iair s multiple mechanism plasticity model and boundary su- rface plasticity model, a multiple mechanism boundary surface plasticity model of saturated sand was established. The concept of multiple mechanism was used as a vehicle for decomposing the complex mechanism into a set of simple shear mechanisms defined in one dimensional space. Each virtual simple shear mechanism was simulated by the boundary surface plasticity model in the virtual stress and strain space, with which the complexity of getting the scale parameters was avoided when each virtual simple shear mechanism was simulated by the modified Masing＇ s rule in Iai＇s multiple mechanism model. Based on a lot of test data, the relation between the liquefaction front parameter and the normalized shear work was presented. The effective stress path was well modeled by several parameters. The effect of rotation of principal stress axial directions and large shear displacement of sand in the earthquake induced liquefaction were taken into account at the same time in the model. The computed results were consistent with the laboratory results. Based on the multiple mechanism boundary surface plasticity model, an analysis of effective stress on the horizontal layer of the saturated sand and of the seismic response characteristics of the horizontal layer were given. The multiple mechanism boundary surface plasticity model simultaneously considered the decrease of shear strength and the modulus of the saturated sand by the development of vibration pore water pressure. The analysis shows that the results are reasonable, and the model is simple and practical which makes the engineering application much easier.