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FAST NONLINEAR SEISMIC SOIL-STRUCTURE INTERACTION (SSI) ANALYSIS IN COMPLEX FREQUENCY DOMAIN

The technical note introduces a novel approach for modeling nonlinear hysteretic behavior of reinforced concrete structures in the complex frequency domain. The new approach can be used to perform fast and accurate nonlinear SSI analyses, including sophisticated nonlinear hysteretic models, at a small fraction of the runtime of a time domain nonlinear SSI analysis. The technical note presents some key ideas that are behind the proposed approach. A case study of a typical low-rise shearwall nuclear plant structure is shown to demonstrate the proposed nonlinear SSI analysis approach. The in-structure acceleration response spectra (ARS) computed using both linear elastic and nonlinear SSI analyses are compared for a severe review level earthquake input with a 0.70g maximum ground acceleration. The new nonlinear SSI approach also eliminates the need to use simplified cascaded multistep approaches that loose physics by neglecting the effects of the structural degradation on the SSI system dynamic behavior.