覆盖层上土石坝非线性动力响应分析的地震波动输入方法

Seismic wave input method for nonlinear dynamic analysis of earth dam built on overburden

较多已建和待建的土石坝直接修筑于覆盖层上,合理描述土石坝与覆盖层之间的动力相互作用对大坝抗震安全评价至关重要。基于等效荷载和人工边界的地震波动输入方法能较好地反映出结构-地基之间的相互作用并得到了广泛应用。等效荷载和人工边界参数在均质线弹性地基条件下易于获得,而对于覆盖层地基,土体动力非线性特性给求解带来很大困难。鉴于此,首先根据覆盖层侧向边界的位移模式,发展了能高效、精确地获取多向地震动垂直入射时均质或成层覆盖层自由场非线性动力响应的简化模型;结合能动态实时获取地基材料参数的非线性人工边界,发展了一套覆盖层上土石坝非线性动力响应分析的地震波动输入方法。算例表明,发展的地震波动输入方法可大大减小计算网格量,并能较好地反映覆盖层对地震动频谱特性的影响且具有较高的精度。

Since many earth dams were built and are to be built on overburden, it is essential to describe the dynamic interaction behaviour between earth dams and the overburden reasonably for the seismic safety evaluation of dams. The seismic wave input method is based on the equivalent load and artificial boundary. This method can well reflect the dynamic soil-structure interaction, and thus it has been widely used in dam engineering and underground engineering. Moreover, this method is easy to be realised in the homogeneous linear elastic foundation but difficult in the overburden foundation with the soil nonlinearity. In this study, a simplified finite element model for the free field is established according to the deformation mode of the free field at the lateral boundary. This simplified model can conveniently and precisely obtain the nonlinear dynamic response of homogeneous or layered overburden under the action of normal incidence of the multi-direction earthquake. Then, a seismic wave input method is developed for nonlinear dynamic analysis of earth dams built on overburden. Besides, the established method is combined with the dynamic real-time nonlinear artificial boundary of ground material parameters. The numerical examples show that this method can reduce the amount of calculation grid remarkably, meanwhile can reflect the effect of overburden on the spectrum of earthquake response with high accuracy.