Seismic Probabilistic Fragility Assessment of Reinforced Concrete Shear Wall Structures in Nuclear Power Plants

A seismic fragility assessment framework is proposed to address the problem of evaluating and updating estimates of seismic fragility for reinforced concrete structures in nuclear power plants. The main objective of the framework is to enable (i) incorporation of fragility estimates from previous studies with the new fragility data from experimental testing and finite element simulations, (ii) modeling and characterizing uncertainties in material model parameters of concrete constitutive models used in finite element simulations for fragility data, (iii) developing fragility curves for different performance criteria and damage limit states using Bayesian updating techniques. Experimental seismic fragility assessment of large-scale reinforced concrete structures is cost intensive and impractical. A hybrid approach is proposed to estimate fragility of reinforced concrete structures like box shaped shear walls by performing Monte-Carlo simulations involving multiple nonlinear dynamic analyses using experimentally validated finite element models. Data collected from Monte-Carlo simulations is then used to develop new fragility estimates. The key step in conducting Monte-Carlo simulations is to model the uncertainties and randomness in the material properties and earthquake time histories. A framework is proposed to consider and characterize uncertainties in concrete material constitutive model like damage plasticity model, used in the finite element simulations for probabilistic risk assessment. A computational methodology based on Bayesian inference techniques is proposed to update the existing fragility curves using the failure data derived from nonlinear time history analyses. Performance of shear wall structures is characterized using multiple limit states that corresponds to no-damage, minor damage, moderate damage, and significant damage Qualitative performance functions are defined to assess seismic performance of shear walls in terms of engineering design parameters like maximum shear force, maximum shear deformation and maximum inter story drift ratio and maximum shear strains.