Importance of time step discretisation for nonlinear dynamic finite element analysis

Abstract

The behaviour of saturated soils subjected to earthquake loading has been investigated using the finite element method in the time domain. Such analyses are able to capture the excess pore pressure generation and subsequent nonlinear behaviour of the soil. It is important, however, when carrying out such analyses to use adequately small time steps. It has been recognized by previous researchers that small time steps are needed for the numerical solution of wave propagation problems, whereas in this technical note, the importance of using very small time steps for the analysis of nonlinear liquefying soil is demonstrated. It is shown that satisfactory results can only be obtained from finite element analyses when the time steps used are shorter than one twentieth of the time taken for a shear wave to travel across the smallest element in the finite element mesh.Key words: dynamic finite element analysis, liquefaction, time discretisation.