The Low Cycle Fatigue Of The Shock Absorber And Steel Restrainer Bar For Railway Bridge

In recent years,with the rapid development of railway construction in China,more and more attention has been paid to the seismic mitigation and isolation of railway bridges.In order to reduce the damage to the bridge caused by earthquake,many scholars have carried out the research and development of displacement type energy dissipators,among which the shock absorber and steel restrainer bar have become an effective way of earthquake response reduction for railway bridges in China.At present,the shock absorber and steel restrainer bar has been successfully applied to the projects of simple supported beam bridges,showing good economic value and broad development prospects.In this dissertation,the theoretical and experimental research on the prediction of low cycle fatigue life and low cycle fatigue damage of shock absorber and steel restrainer bar are carried out.First of all,two prediction methods of low cycle fatigue life of shock absorber are proposed,which are effective energy method and critical interface energy combination method.Then,based on the existing nonlinear damage accumulation theory,the low cycle fatigue damage accumulation method of shock absorber is studied.Finally,the low cycle fatigue performance test of steel restrainer bar applied to continuous girder bridge is carried out,its low cycle fatigue life and damage accumulation method are given.The main research work is as follows:1.Hysteretic characteristic analysis and low cycle fatigue life prediction of shock absorberThrough the cyclic loading test of two integral shock absorber specimens,the hysteretic characteristics and energy law of the shock absorber under single-stage loading and continuous loading are analyzed.Furthermore,it is found that the depth of plastic deformation is directly related to the ductility deformation ability and energy dissipation ability.Based on the above analysis,taking the effective energy of considering the influence of plastic deformation depth as the fatigue parameter,an fatigue life prediction model of shock absorber is proposed.The accuracy of the effective energy method model is verified by the low cycle fatigue test of the integral shock absorbers.The results show that the calculation results are in good agreement with the test results.In addition,the prediction accuracy of the effective energy method is higher than that of Masson Coffin formula.2.Low cycle fatigue life prediction considering shear stressThe plastic behavior of shock absorber in low cycle fatigue stage can be described by Von Mises yield condition and multi-linear follow-up hardening model.Considering the driving effect of shear stress on fatigue damage,the composite method of critical plane method and energy method is proposed to predict the low cycle fatigue life of the shock absorber,which takes the plastic strain energy on the maximum damage plane as the fatigue parameter.The accuracy of the predicted results is verified by the fatigue test of the integral shock absorber.The results show that the combination of the critical plane method and the energy method considering the shear stress has higher accuracy than other methods.Finally,based on the critical interface energy method,the power exponent curve between the displacement D of the shock absorber top and the low cycle fatigue life N_f of the integral shock absorber is obtained,which can provide the basis for the determination of the low cycle fatigue life of the movable bearing system of the shock absorber of the simple supported beam bridge under the earthquake.3.Research on nonlinear fatigue damage accumulation under multistage loadIn view of the nonlinear characteristics of fatigue damage accumulation of shock absorbers,the method of introducing damage accumulation influence function is adopted,and the influence of shock absorber type,load interaction between front and rear stages and load amplitude span on fatigue damage is considered comprehensively.The existing nonlinear damage Ye model is modified and an improved fatigue damage accumulation model is proposed.The accuracy of the improved damage model is verified by the multi-stage loading test of five separate shock absorber specimens.The results show that the accuracy of the improved model is greatly improved compared with the original model.In addition,based on the improved model,the effects of the interaction between adjacent loads and the span of displacement amplitude conversion on the fatigue damage accumulation are analyzed.Finally,taking a simple supported beam bridge with movable support as an example,the nonlinear damage accumulation of the bridge under the earthquake action is calculated.The results show that the shock absorber has a strong ability to withstand the earthquake action,and can have a long service period.4.Experimental study on low cycle fatigue of steel restrainer barThe steel restrainer bar is a kind of anti falling beam device with damping and energy dissipation function.It is the improvement and function expansion of the shock absorber structure.In order to study the plastic energy dissipation capacity and low cycle fatigue performance of the steel restrainer bar,four groups of specimens were tested by cyclic loading method.The results show that four groups of steel restrainer bar specimens have better ductility and damping capacity after the displacement load value exceeds the free space.At the same time,the specimens have higher cycle times under the action of limit displacement,which shows that the steel restrainer bar has better low cycle fatigue Labor performance.In order to study the damping performance of steel restrainer bar,the dynamic analysis of a three span and one joint railway continuous girder bridge under the earthquake action is carried out by using the time history analysis method.The results show that after the steel restrainer bars are used at the support,the relative displacement reduction rate of the pier and beam of the continuous girder bridge is up to 70%,and the stress at the pier bottom is also reduced,which indicates that the steel restrainer bars used for the continuous beam bridge have good damping effect.Finally,the combination of critical surface method and energy method is used to predict the low cycle fatigue life of steel restrainer bar,and the improved fatigue damage accumulation model is used to calculate the nonlinear damage accumulation of the steel restrainer bar,and the calculation results are in good agreement with the test results.