Research On Time-dependent Seismic Vulnerability And Risk Assessment Of Prestressed Concrete Continuous Girder Bridges

The corrosion of reinforcing bars results in structural damage of the bridge construction in its design life.Moreover,it has become increasingly severe over time,which can directly cause the reduction in the bearing capacity,durability and seismic performance of structure.At present,the scholars have studied the seismic performance of reinforced concrete structure based on durability deterioration;however,they have just considered from one single factor:the corrosion of reinforcing bars;actually,they have ignored the impact of the bond-slip deterioration after the corrosion of reinforcing bars on seismic performance.In this paper,in combination with significant demands of China for high-speed railway construction in the new era,taking the representative long-span prestressed concrete continuous girder bridges in the high-speed railway engineering as the research object,the authors deeply explore the time-dependent vulnerability after the corrosion of reinforcing bars through comprehensively using the theoretical analysis,numerical analysis and other methods and carry out the seismic risk assessment.This study is conducted to provide necessary scientific basis and technical support for bridge risk management and decision makers to make correct judgments.The main research content is as follows:(1)Based on the consultation of a large number of domestic and foreign literatures,the development history and research status of study on seismic vulnerability of bridges are summarized,the shortcomings of the present researches are pointed out and the main research contents of the paper are introduced.(2)Through adopting the theoretical deduction,the constitutive relationship of the confined concrete after the corrosion of stirrups was derived.First,based on the existing experimental data,the theoretically derived results are verified to ensure the reliability and accuracy of theoretical deduction.And then,the comparative analysis is made in combination with numerical analysis method and theoretical derivation results.The result shows their good agreement,determining the constitutive relation of confined concrete under different stirrup corrosion rates.(3)Based on OpenSees,the dynamic nonlinear finite element model for continuous girder bridges for high-speed railway is constructed.According to the stress characteristics of each component in the bridge construction and their status under the seismic excitation,the corresponding element is adopted for simulation.Generally,the main girder structure is non-vulnerable components,which are basically within the structural elastic range;so the elastic element is used in simulation.The pier is an important vulnerable component,which will enter the elasto-plastic state under the seismic excitation;so the elasto-plastic fiber beam-column element is used in simulation.For the constitutive relationship of concrete,the constitution of the confined concrete after the corrosion of stirrups is adopted.At the bottom of the pier,a zero-length element is established;the bond-slip constitutive relationship of the concrete is used in simulation.(4)The time-dependent vulnerability curve is established.The material degradation has a certain impact on the damage index of piers.Therefore,in the assessment on performances of piers,the constitutive relationship of the confined concrete after corrosion of stirrups is used for concrete and the constitutive relationship of the reinforcing bars after corrosion is used for longitudinal reinforcement,obtaining more accurate capacity damage indexes.Through using the incremental dynamic nonlinear time-history analysis method,the probabilistic seismic demand model for the bridge structure is established;on this basis,the relationship between seismic demand and seismic capacity is further established.Moreover,based on the reliability theory,the vulnerability curve is drawn from the perspective of the effect of material degradation,which is the time-dependent vulnerability curve.(5)Based on the time-dependent vulnerability curve,the seismic risk probability of time-dependent bridge construction is assessed.The time-dependent parameters of the bridge construction are obtained through the material degradation(time-varying)time.Based on the annual average transcendental probability of earthquakes on the bridge site,the seismic risk analysis is conducted to determine the probability of seismic hazards.Based on the seismic risk analysis results,the assessment on the seismic risk probability of the time-dependent bridge construction is conducted in combination with the time-dependent vulnerability analysis curve.