Mainshock-aftershock Risk Analysis And Assessment Of RC Frame Structures Based On Bivariate Intensity Measures

In recent years,there are lots of strong earthquakes occurred in China.There are many aftershocks after the corresponding mainshock and it is necessary to pay attention to the“incremental damage”for the aftershock.However,the current seismic codes and engineering practice did not consider the aftershock.This greatly affects the safety of structures in real earthquake events.To evaluate the seismic response and performance of the structure under earthquake,the framework of performance-based earthquake engineering was proposed by the Pacific Earthquake Engineering Research Center.The framework is aiming for the seismic risk evaluation for the structure and composed of seismic fragility and hazard analysis.Therefore,this thesis focuses on the damage potential,seismic fragility analysis,seismic hazard analysis and seismic risk evaluation of a RC structure under mainshock-aftershock sequences.Main contents are shown as follows:（1）The research of damage potential under mainshock aftershock（MS-AS）sequences.A prediction model for the damage potential is developed under mainshock-aftershock sequences.A set of classical intensity measures（IMs）are considered to represent the intensity of a specific MS-AS sequence.The single degree of freedom system with varying hysteretic behaviors are subjected to real MS-AS sequences to estimate structural damage.The correlation between the MS-AS ground motion intensity and damage potential is evaluated and the best-correlated IM is selected based on the correlation coefficient.The prediction model for the damage potential is conducted with the best-correlated IM.（2）Univariate fragility analysis for MS-AS sequences.Based on the classical univariate MS fragility analysis,the MS-AS fragility analysis is conducted with MS-AS sequences.The intensity of a specific MS-AS sequence is represented by a single IM.To illustrate the influence of the AS to a MS-damaged structure,an AS fragility（also called“damage state dependent AS fragility”）analysis is studied in this section.With the AS fragility,we examined the damage state for the structure before and after the AS and evaluated the probability of damage state transition.（3）Bivariate fragility analysis for MS-AS sequences.We proposed a framework for the bivariate fragility analysis under MS-AS sequences.Single IM could not well represent the MS-AS ground motion intensity.According to this disadvantage,we use a bivariate IMs form in MS-AS fragility analysis.The total probability thermos is used to consider the structural collapse in MS-AS fragility analysis.The Bayesian updating is used to evaluate the confidence intervals for parameters in demand model.The fragility band is computed based on the confidence intervals of parameters.（4）Bivariate hazard analysis for MS-AS sequences.We proposed a framework for the bivariate hazard analysis based on the Copula theory.The nonlinear correlation between MS intensity(IM_MS)and AS intensity(IM_AS)is evaluated by Copula technique.The joint distribution of the IM_MS and IM_AS is computed through Copula function.Based on the classical vector hazard analysis,we examined the bivariate hazard analysis for MS-AS sequences,in conjunction with the scalar MS hazard analysis.（5）Seismic risk analysis for MS-AS sequences and uniform risk-targeted definitions and decision-making of four seismic design levels considering very rare earthquake.Based on the results from bivariate fragility analysis and bivariate fragility analysis for MS-AS sequences,the seismic risk analysis under MS-AS sequences is conducted for a case structure.We evaluate the collapse risk for existing structures in China using gathered data from huge number of papers and theses.Following the concept of“Uniform Risk”and decision-making of four seismic design levels,we proposed a framework for evaluating four seismic design levels considering very rare earthquake and finished an initial analysis for the determination of four seismic design levels considering very rare earthquake.