Study On Seismic Performance Of Damaged Girder Bridge Using Displacement-based Approach

In earthquake-prone areas,some girder bridges still have a certain bearing capacity after being damaged by earthquakes,and at this time whether the seismic performance still meets the relevant requirements after earthquakes needs to be further studied theoretically and experimentally.How to evaluate the seismic performance of damaged girder bridges scientifically in earthquake-prone areas is an important subject in the current seismic bridge research.In the performance-based seismic design method,displacement is the main seismic performance index of the regular girder bridges.which can be used to evaluate the seismic performance of regular girder bridges accurately and complete the seismic design.Therefore,it is necessary to know the change of the loading force-displacement skeleton curve of damaged bridges with the damage degree.It is generally believed that the lateral deformation of the pier is composed of three parts: bending deformation,shear deformation and slip deformation.For piers with bending failure,the bending deformation can be calculated by the equivalent plastic hinge formula,and the method is relatively simple.The shear deformation proportion is not large,but in the nonlinear stage,sliding deformation accounts for a large proportion of the total deformation.Therefore,the proportion of the sliding deformation and the change during the movement have become the important content in the research of seismic damaged girder bridges.According to the Japanese standard,the residual displacement ratio is used to measure the seismic performance of girder bridges.Based on the pseudo static test results of piers,combined with the numerical simulation,design parameters of piers(such as the shear span ratio,axial compression ratio,concrete strength,,longitudinal reinforcement strength,longitudinal reinforcement ratio and stirrup spacing)for residual displacement ratio are studied.In order to verify the effectiveness of the slip ratio,residual displacement ratio and research methods,in the thesis,a concrete continuous girder bridge is numerical simulated,to analyze the displacement requirements of the damaged bridge with the main and aftershock sequences,investigate the effect of sliding deformation on the displacement performance of girder bridges,and discuss the design measures to reduce the residual displacement ratio and optimize the seismic performance of structures.The main work and achievements in this thesis can be drawn as follows:(1)Numerical simulation is carried out on piers with common section forms;damage parameters are selected to represent the damage state of each component with different displacement;the force-displacement skeleton curve of components with different damage state is calculated,and the changes of peak displacement and limit displacement of components with damage are analyzed.The results show that,with the increase of the damage degree,the peak displacement increases,the limit displacement change little,and the peak and ultimate bearing capacity decrease gradually;(2)The pseudo-static test is carried out on round-end hollow piers,and finite element models are established.By comparing the calculated and measured hysteresis curves,the validity of the numerical models is verified,and numerical models are extended to analyze,so as to get the slip deformation in proportion to the total deformation,residual deformation(i.e.,slip ratio),and the change rule of the ratio during the movement.The results show that,for damaged components,the slip ratio is about 6%-38% in the maximum deformation,and 13%-66% in the residual deformation.The proportion of slip deformation decreases first and then increases in the process of loading,and the proportion of slip displacement gradually increases in the process of unloading.(3)The pseudo-static test of rectangular solid piers is carried out to verify the correctness of the numerical models,and based on the numerical models for extended analysis,the influence law of design parameters on the residual displacement ratio,such as shear span ratio,axial compression ratio,concrete strength,longitudinal reinforcement strength,longitudinal reinforcement ratio,stirrup spacing and so on,is studied.The results show that,the residual displacement ratio decreases with the increase of shear span ratio,axial compression ratio and longitudinal reinforcement strength,and increases with the increase of concrete strength,but the ratio of longitudinal reinforcement and stirrup spacing have no effect on the residual displacement ratio.(4)To a three span prestressed concrete continuous girder bridge as an example,the numerical model is established,and series of main and aftershock sequence seismic wave that are constructed by some actual recorded seismic waves to form bridge seismic damage are selected as conditions,to explore the residual displacement and aftershock type girder bridge to the damage of the influence law of seismic performance,clarify the slip deformation influence on the seismic displacement capacity of seismic damaged bridges,and then some design measures to reduce the residual displacement ratio and optimize the seismic performance of the structure are analyzed.The results show that,the residual displacements of the damaged bridges tend to amplify its displacement response(maximum displacement and residual displacement)in subsequent ground motions;if the slip deformation is ignored,the bridge displacement demand will be underestimated,and reducing the residual displacement ratio can improve the seismic capability of the damaged bridge.