Research On Seismic Failure Mechanism And Simulation Method Of Reinforced Concrete Rigid Frame Bridge

As the lifeline of rescue and disaster relief after earthquake,the health condition of bridge after earthquake will directly affect the rescue process.Therefore,it is important to accurately grasp the damage mechanism and seismic performance of bridge structure.It is undoubtedly that the physical test is the most accurate method to analyze the seismic performance of bridge structures.However,the expensive cost of money and time are result in the limitation application of this approach.In contrast,the numerical simulation of mechanical behavior of the bridge structure under earthquake can also provide a comparatively accurate results and reveal the damage and destruction pattern of bridge structure with a reasonable costs and time.In view of the above reasons,the damage and failure mechanism of RC high-pier rigid frame bridge under earthquake action will be studied in this paper based on the general finite element software ABAQUS.This paper will establish the elastic-plastic constitutive relation and relevant elastic-plastic model.In the meantime,numerical simulation approach is also studied systematically to ensure the calculation efficiency and accuracy of seismic response analysis of high-pier rigid frame bridges.The efforts of the study can provide some suggestions for performance-based seismic design of bridges.The main contents and the conclusions of this thesis are as follows:(1)Based on user material subroutine interface(UMAT)provided by ABAQUS,the sub-programs of steel hysteresis model,concrete hysteresis model and component hysteresis model are written in Fortran language.The numerical simulation results of reinforced concrete members are carried out by using the above three material hysteresis model subprograms and the material model provided by ABAQUS software.The results show that the developed material hysteresis model can well simulated the stiffness degradation of members under reciprocating loads,but cannot represent the strength degradation at the later stage of loading cycle,which result in the error up to 24.6%.However,the material model with ABAQUS software can neither simulate the stiffness degradation nor the strength degradation,leading to overestimate the energy consumption capacity of components and the calculation error up to 97.1%,which is seriously inconsistent with the actual situation.(2)Based on Park’s seismic damage model and regression analysis of relevant data provided by the column test database of the Pacific Seismic Engineering Research Center,a bearing capacity degradation model considering bond slip between reinforcement and concrete and spalling of concrete protective layer was established.By introducing this model into the developed steel bar hysteresis model,the strength degradation of members can be well simulated,and the calculation error of members can be reduced to 9.5%.It should be point out that the model also applicable for the specimens which is not contained in the regression data.(3)Since the macro model(fiber and beam unit)can not reveal the micro-failure mode of the bridge piers and the time cost for solid model is too expensive,a multiscale model of bridge pier is established to balance the efficiency and accuracy of simulation analysis.The interface connection of multi-scale model and the definition of the refine region are discussed in detail.By comparing the calculation results with the test results,it is found that the multi-scale model modeling method proposed in this paper can well reveal the damage and failure process of the plastic hinge area of the bridge pier,improve the calculation efficiency of the model.This approach will apply to the subsequent simulation analysis of the bridge structure.(4)Based on IDA method,the operating high-pier rigid frame bridge is simulated from intact to damage under earthquake action at different sites and different epicenter distances.The traveling wave effect is investigated systematically during the numerical simulation.In the meantime,the time history curve of structural displacement calculated is processed and its residual displacement drift is obtained.The results indicate that the effect of seismic action on the structure residual displacement of typeⅡ site is greater than that of type Ⅰ site.The residual displacement of the structure under near-field earthquake is significantly greater than that under far-field earthquake.Under the same PGA,the structure response considering traveling wave effect is much larger than that without traveling wave effect and the damage is more serious.The drift rate of residual displacement calculated can be used to evaluate the seismic performance level of High Pier Rigid Frame Bridge and its post-seismic damage.