Large civil structures such as concrete dams, nuclear power plants, high-rise buildings and bridges are massive enough that their vibration due to earthquake excitation affects the motion of the soil or rock supporting them, which in turn further affects the motion of the structure itself. This interaction between the structure and the soil needs to be modelled accurately in order to design earthquake resistant structures and to correctly evaluate the earthquale safety of existing structures.
Historically, engineering analysis of such soil-structure interaction has had several impediments: (i) limited knowledge of the relevant earthquake faults and of the regional geological features required to fully characterize the incoming earthquake ground motion, (ii) lack of accurate earthquake input methods in existing analysis software, and (iii) inability to efficiently model the unbounded soil domain.
LS-DYNA now has a novel method for soil-structure interaction analysis that applies the earthquake forces in an efficient and rational manner and models the unbounded domain accurately at low computational cost, given a free-field ground motion characterizing an earthquake. It uses the effective seismic input method to incorporate the earthquake forces into the soil-structure model, using only the free-field ground motion at the soil-structure interface, and not requiring any deconvolution down to depth unlike older methods of earthquake input. The unbounded domain is modeled using perfectly matched layers, which absorbs the outward-propagating waves almost perfectly with only a slight increase in cost from the classical Lysmer dashpot boundaries. These pages explain and demonstrate these techniques for seismic soil-structure interaction analysis in LS-DYNA.