Failure Modes,Seismic Fragility And Risk Assessment Of Rail-cum-road Cable-stayed Bridge Under Earthquake Excitation

At present,the applications of long-span rail-cum-road cable-stayed bridges are few,a small amount of literature studied earthquake resistance for this type of cable-stayed bridges and no literature is about the research on damage modes of long-span rail-cum-road cable-stayed bridges,the seismic fragility and seismic risk assessment.Based on the present situation,combined with the characteristics of deep-water long-span rail-cum-road cable-stayed bridges,damage modes,probabilistic seismic fragility and probabilistic seismic risk are carried out by numerical simulation and probability analytic method.The main research contents are as follows:(1)The whole process simulation analysis theory of seismic response of long-span cable-stayed Bridges based on explicit dynamic analysis method is studied.The realization process of explicit dynamic analysis theory is expounded,including the explicit integral solution method based on central difference method,and large deformation theory,and material nonlinear theory.The material models,element types and failure criterion of cable-stayed bridge components are discussed.A rail-cum-road cable-stayed bridge is taken as an example,the simulation model is established based on the explicit integral method,revealing the impact on failure mode of long-span railway cable-stayed bridge under strong earthquake by the different bearing categories between main pylon and girder,and the pile-soil interaction,and the traveling wave effect,and setting damper.(2)A three-dimensional nonlinear finite element model of rail-cum-road cable-stayed bridge based on implicit integral is established.The incremental dynamic analysis method(IDA)is used to analyze the nonlinear dynamic response.Ten far field seismic waves are selected belonging to II soil site type,and the peak ground acceleration of the seismic waves are adjusted from 0.15 g to 1.5g according to the increment of 0.15 g.Multiple seismic wave analysis method with the same peak ground acceleration of 1.5g combining with the incremental dynamic analysis method of single seismic wave is used to study the nonlinear seismic response of the rail-cum-road cable-stayed bridges with considering pile-soil interaction and without considering pile-solid interaction.(3)Basing on the existing structure damage criterion and structural damage state,the damage states of pier column components,the sliding bearing components and the cable components are carried out.Then the whole process simulation of eccentric compression failure for all the pier column cross-sections is obtained by using the fiber model with considering 6 different axial compression ratio and without considering material parameters uncertainty and geometric parameters uncertainty.P-M-f curves are obtained under 6different axial compression ratios and deterministic seismic capacity models of pier column cross-sections are established with the variable of axial compression ratio.According to the design standard of the cable-stayed bridge,the deterministic damage index of sliding bearing and cables is determined.(4)The probabilistic damage limit state of pier column cross-section is analyzed basing on Monte Carlo method.From the aspect of sampling efficiency and sampling accuracy,the simple random sampling method and the Latin hypercube sampling method are compared and studied.An efficient random sampling method,which is Latin hypercube sampling method combining with antithetic variable method,is proposed.The method to eliminate pseudo-correlation is introduced when considering multiple random variables.The efficient sampling method to eliminating pseudo-correlation is used to obtain 100 random samples of every side pier cross-section,auxiliary pier cross-section and main pylon cross-section under considering material parameters uncertainties and geometric parameters uncertainties.P-M-(?) analysis for 100 random samples of every cross-section from transverse direction and longitudinal direction is carried out considering 6 different axial compression ratio.The longitudinal and transverse curvature indexes of different axial compression ratio are obtained,and the logistic regression analysis of cubic polynomials is carried out,and probabilistic seismic capacity models of pier column cross-section are established.(5)The rail-cum-road cable-stayed bridge is taken as an engineering example.Under transverse seismic excitation and longitudinal seismic excitation,elasto-plastic time-history analysis is carried out for 330 structure-ground motion random samples considering pier bottom fixed,pile-soil interaction,pier-water interaction,and railway of structure model respectively.Probabilistic seismic demand models of pier column cross-section based on curvature index,and side pier sliding bearing based on relative displacement index,and cables based on cable force under four different situations are established.(6)From the viewpoint of uncertainty propagation,seismic fragility formulations considering aleatory uncertainty and epistemic uncertainty are studied.The analytical formulation for seismic fragility considering aleatory uncertainty is obtained and the analytical formulation for seismic fragility considering aleatory and epistemic uncertainty is obtained.Probabilistic seismic fragility curves of the components of rail-cum-road cable-stayed bridge are obtained.Then,the system damage probability of the cable-stayed bridge structure is estimated by first-order boundary method,and the probabilistic seismic fragility curves of structural system are obtained.Meanwhile,the impact on seismic fragility curves of rail-cum-road cable-stayed bridge by pile-soil interaction,pier-water interaction,and railway constrains is studied.(7)Based on developed analytical seismic fragility functions,the probabilistic seismic risk functions considering both aleatory and epistemic are derived incorporating the generally used power-law seismic hazard function.Using these analytical functions,the seismic damage risk analysis and the seismic demand risk analysis of rail-cum-road cable-stayed bridge are carried out.The probabilistic seismic risk during the service life(100)is studied from component level and structure level respectively,and then the seismic performance of rail-cum-road cable-stayed bridge is evaluated according to the seismic fortification standards.