Viscoelastic boundary method of horizontal layered site based on equivalent zero-time point

An equivalent zero-time point iterative time delay method for horizontal layered strata is proposed to solve the problem of time delay calculation in ground motion input of layered strata under viscoelastic boundary. It assignes an equivalent zero-time plane to each generated seismic wave. An appropriate point on the plane can be selected as the equivalent zero-time point, and the time delay can be calculated. Based on the Snell equation and the continuity condition of seismic waves at the layered interface, the formula for calculating the equivalent nodal force of the artificial boundary is derived, and the viscoelastic boundary input method for oblique incidence ground motion of the layered strata under the viscoelastic boundary is deduced. The finite element model for a double-layer horizontal layered stratum is established for dynamic response analysis. The calculated results are compared with the theoretical values. The deviation between them is relatively small, which shows the effectiveness and practicability of the method. By using the method it can be solved directly according to the specific information of the seismic wave and the stratum, without analyzing all the sources of the desired seismic wave in turn, which makes the formula unified. It is a way to simplify the calculation without affecting the accuracy. Meanwhile, it can extend the application of the viscoelastic boundary to the oblique incidence ground motion of layered stratum.