Study On Seismic Performance Of Bridge Structures Based On Probabilistic

The uncertainty of structural capacity and seismic demand make it necessary to consider the seismic performance of structure from the probabilistic points. Ongoing this progress, the Pacific Earthquake Engineering Research Center (PEER) is developing a probabilistic framework for performance-based design and evaluation. The goal of the framework is to utilize the Total Probability Theorem to de-aggregate the complicated PBEE problem into decouple the complicated PBEE problem into four stages: hazard analysis, structural analysis, damage analysis, and loss analysis. And the framework assume that these stages are independent and discrete Markov process, where the conditional probabilities between parameters are independent, which making it as robust methodology for performance-based earthquake engineering to research and resolve the logical elements of process in a rigorous and consistent manner. In this paper, it is focused on the investigations of seismic hazard analysis methods with total probability theory and fragility analysis methods for reinforced concrete bridge structure, in which seismic demand model and seismic capacity model are mainly involved. The major studies and creative intents are as follows:1. The correlation between ground motion intensity measures (IM) and bilinear single-degree—of-freedom (SDOF) structure systems deformation demand is studied. In the Pacific Earthquake Research Center's probabilistic performance-based design and evaluation framework, the structure seismic response analysis and the ground motion predictions are related by an interface variable referred as the ground motion intensity measure (IM), IM should be correlated strongly to the seismic demand placed on the structure. In this paper, using a suit of 40 horizontal ground motions records referred to as LMSR_N, the correlation between the common IMs used in engineering practice and bilinear SDOF structure systems deformation demand is studied through nonlinear dynamic analysis. The numerical results obtained by nonlinear dynamic analyses have shown good correlation between S_a(T₁)(the spectral acceleration for the fundamental period of the structure) and bilinear SDOF structure systems deformation demand.2. The effect of adopted IM on structural responses is investigated through dynamic nonlinear analysis for several SDOF systems with different periods and different strength reduction factors. It was shown that the vector IM is more efficiency than scalar IM, and the proposed IM is the most efficiency of the three IMs adopted in this study. Moreover, by performing the analyses of prediction of structures response conditional IM, using the proposed vector IM only need one regression analysis as opposed to the vector IM proposed by Jack W. BAKER, which will reduce computational effort.3. Through the use of moment-curvature analysis of circular bridge columns, dimensionless serviceability and damage control curvature are investigated for different values of the axial load ratio, longitudinal reinforcement ratio and percentage of confinement. A constant value of section diameter 1.0m was used as reference column to study dimensionless curvatures. Furthermore, diameter modified factor to estimate dimensionless curvatures for other section dimensions are developed by regression analysis.4. The probabilistic dimensionless serviceability and damage control curvature limit state of circular reinforced concrete bridge column are investigated. Material and geometric parameters are modeled as random variables, using the LHS simulation, the probabilistic parameters of the two levels of curvature limit states are calculated for different values of the axial load ratio, longitudinal reinforcement ratio and transverse reinforcement ratio. Furthermore, the characteristic values of the curvature ductility factors for serviceability and damage control limit states are obtained respectively. Finally, two equations to estimate the curvature ductility factors are developed through the use of regression analysis.5. The programs of generate fragility curves for bridges through nonlinear static analysis (capacity spectra method) and nonlinear dynamic RHA (total probability theorem method) is developed. And the fragility curves of viaduct structure are developed by capacity spectra method and nonlinear dynamic RHA method, respectively. The results from structural fragility curves computed by two methods are shown that there's no big difference between two analysis methods for the serviceability limit state, and the rightward excursion of the fragility curve developed by nonlinear static analysis because of the damage control and collapse limit states, which reveals that nonlinear static analysis underestimates the probability of the specific damage state that structure reaches under a given ground motion intensity.6. The structural seismic risk analysis method based on probability is investigated systematically for the uncertainty of structural capacity and seismic demand. A procedure is provided to separate the structural seismic risk analysis logically into two stages, seismic hazard analysis and structural fragility analysis, with parameters of ground motion intensity measure as interim variables. An analytical expression is presented based on total probability theory to describe the mean annual rate of structural performance level reaching or exceeding a specific limit state, and the analytical solutions are adopted to analyze the seismic risk of a three-span rigid-frame bridge in a specific hazard environment.