FAST NONLINEAR SEISMIC SSI ANALYSIS USING A HYBRID TIME-COMPLEX FREQUENCY APPROACH FOR LOW-RISE NUCLEAR CONCRETE SHEARWALL BUIDLINGS

摘要

The paper presents a highly efficient nonlinear SSI approach based on a hybrid time-complex frequency approach using an iterative procedure. The hybrid approach uses a piece-wise equivalent-linearization for computing the FEA solution in complex frequency. The local linearized hysteretic models are calibrated based on the "true" nonlinear concrete wall behaviour in time domain. Sophisticated shear deformation hysteretic models with pinching were implemented. Comparative results of the hybrid approach and the true nonlinear time-integration approach showed very good matching. The hybrid approach is applicable to nonlinear SSI analysis for i) design level for correctly including the concrete cracking in structures as a function of stress levels in accordance to the new ASCE 04-2015 standard (Sections 3.2.2 and 3.3.2) and the USNRC SRP requirements, and ii) beyond design level in accordance with the ASCE 43-2005 recommendations, to properly compute the inelastic absorption factors for structural fragility analyses. The paper presents a validation case study of a typical low-rise shearwall nuclear structure for which the hybrid approach results are compared with the "true" nonlinear time-integration approach results. Nonlinear SSI analyses performed for rigid rock and soft soil sites demonstrate the capabilities of the hybrid approach. The nonlinear SSI hybrid approach is also much faster and robust than the "true" nonlinear SSI time-integration approach.