砂土震陷分析中多维地震荷载等效循环周数计算

Computation of equivalent number of uniform strain cycles for seismic compression of sand subjected to multi-directional earthquake loading

借助有限元数值方法模拟不同砂土试样在多向和单向地震荷载输入条件下的动三轴试验,选取覆盖大震、中震、近场、远场及不同土质条件的155组多向地震输入时程对不同砂土试样分别进行单向和多向加载,建立考虑多向地震荷载作用的等效循环周数计算方法,并研究震级、震中距和砂土特性对等效循环周数比的影响。研究表明,震级和震中距对等效循环周数比影响不明显,砂土特性对等效循环周数比的影响具有主导作用,砂土相对密度为45%、60%、80%和100%时,其对应的等效循环周数比均值分别为1.58、1.75、1.93和2.08,相对密度越大,比值越大,结合该比值,可以较好地应用文中提出方法进行多维地震荷载等效循环周数计算。

Dynamic triaxial tests on different types of sand under multi-directional earthquake loading are simulated using finite element method.155 groups of ground motions with multi-components from far and/or near field of moderate and/or strong earthquake events at different site conditions are used as input motions for strain controlled dynamic tri-axial tests.A new method of computation of equivalent number of strain cycles for seismic compression of sand induced by multi-directional earthquake loading is developed.Effects of earthquake magnitude,site-to-source distance and properties of sand on the ratio of equivalent number of strain cycles are also studied.The study shows that the ratio of equivalent number of strain cycle is not affected much by earthquake magnitude and site-to-source distance,but is dominated by the properties of sand.Corresponding to the relative densities 45%,60%,80% and 100% of sands,the mean ratio is 1.58,1.75,1.93 and 2.08,respectively.The ratio of equivalent number of strain cycles increases with the relative density of sand,which is useful in the computation of equivalent number considering multi-directional earthquake loading.