Combined Asymptotic Method for Soil-Structure Interaction Analysis
Alexander G. Tyapin
OJSC “Atomenergoproject (Moscow),” 1-119 Slaviansky boulevard, Moscow 121352, Russia
The author upgrades the well-known impedance method for seismic soil-structure interaction (SSI) analysis. The author suggests accounting in the time domain for the frequency dependence of the “true impedances” by means of the modification of the seismic input on the platform. The criterion for this modification is that it must provide the same structural response with approximate “platform” impedances as for the “true” frequency-dependent impedances in case of a rigid base mat. The entire analysis is performed for the linear system (no nonlinear effects occur in the soil, in the structure, or on the contact surface). In the process of modification, one first obtains the “true” seismic response of the rigid contact surface. If the actual contact surface can be considered stiff (e.g., the base mat is reinforced by dense walls) and the internal forces in the base mat itself are not important, then this “true” motion may be applied directly to the base mat. This simplified option goes without the modification of the seismic input. Another option is to use the “platform” model with “soil” springs and dashpots but to put to the platform the excitation modified in such a way as to provide a response base mat motion similar to the “true” one. The proposed method is called “combined” because it combines frequency-domain and time-domain calculations. This method is also called “asymptotic” because it becomes rigorous for rigid base mats.
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