Seismic Resilience Enhancement And Evaluation Of Railway Simply-Supported Girder Bridges Near Faults

In recent years,China’s high-speed railroad has developed rapidly,and with the continuous extension of railroad lines,the construction of many railroad bridges is inevitably close to faults,and more and more studies have found that near-fault Seismic can cause more serious damage to bridge structures,so it is important to improve the seismic capacity of near-fault railroad bridges.At present,with the development of bridge seismic design ideas,people have started to focus on the design of resilience of seismic resistance,but less resilience seismic research has been carried out for railroad simple girder bridges in China,and most of the seismic studies do not directly consider the post-earthquake recovery capability of bridges.To this end,the following work has been carried out:1.The properties of shape memory alloy(SMA)and its intrinsic structure model were analyzed,and accurate numerical simulation of SMA superelasticity was achieved by using the multi-cell method.The working principle of SMA-LRB composite bearing is investigated,and its mechanical model is derived.On the basis of this,a numerical model of SMA-LRB is proposed which can be simulated in the finite element software SAP2000,and the model is simulated with low circumferential reciprocating load,and the results are compared with the relevant test results.The results were compared with the relevant test results to verify the correctness of the numerical model simulation.2.In order to study the effects of three main factors,namely,SMA wire arrangement,SMA material selection,and SMA arrangement quantity,on the mechanical properties of SMA-LRB composite bearings,the LRB model suitable for seismic isolation of railway simple supported beam bridges was selected as the base bearing to cooperate with SMA wires.Through mechanical model derivation and numerical simulation in SAP2000,the change rules of mechanical properties of SMA-LRB bearings under the three influencing factors were analyzed.The main conclusions are as follows:(1)Compared to the linear and crossing arrangement,when using the double cross type SMA wire arrangement,the SMA wire strain increases steadily with the displacement of the support,and before the support reaches the maximum displacement limit,the SMA wire can reach its limit strain,maximizing the provision of additional horizontal restoring force.(2)Under the condition of adopting a double-crossing arrangement and having the same displacement of SMA-LRB bearings,Fe-based SMA can provide greater horizontal resilience compared to Ni-Ti alloy and Cu-based SMA,with a maximum of 1.96 times that of Ni-Ti alloy and 2.4 times that of Cu-based SMA.Moreover,the hysteresis pattern is stable and energy consumption is good.(3)When Fe based SMA materials are used and the SMA wires are arranged in a double cross pattern,the horizontal equivalent stiffness,yield stiffness,and energy consumption of the SMA-LRB composite bearing will increase with the increase in the number of SMA wires arranged,but the equivalent damping ratio will decrease with the increase in the number of SMA wires arranged.3.In order to study the improvement of seismic performance of railway simply supported beam bridges with SMA-LRB composite bearings,three bridge models with ordinary pot type rubber bearings,LRB bearings,and SMA-LRB composite bearings were compared with each other,and the seismic responses of the three models in the longitudinal and transverse directions under near-field and far-field earthquakes were analyzed.The main conclusions are as follows:(1)Compared to far field earthquakes,near field earthquakes have a significant impact on the longitudinal structure of railway simply supported beam bridges.The installation of SMA-LRB composite bearings can effectively reduce the longitudinal displacement of its pier top,with a maximum isolation rate of 57.8% and a minimum isolation rate of 26.2%.Under the same conditions,the isolation performance of the SMA-LRB bearings is further improved compared to that of the LRB bearings.(2)Under near-field earthquake action,the pier bottom shear force and moment response of railway simply supported beam bridges are affected by the energy consumption and stiffness of the bearings.When the SMA-LRB composite bearings have high energy consumption,they can effectively reduce the pier bottom shear force response.However,when the composite bearings have low energy consumption and high stiffness of the bearings themselves,the seismic force transmitted to the bridge pier will increase,ultimately leading to an increase in the pier bottom bending moment or shear response.(3)Under near-field earthquake action,compared to LRB bearings,the displacement of SMA-LRB composite bearings in the longitudinal or transverse bridge directions decreases in most cases,and the residual displacement of SMA-LRB after earthquake is basically negligible or directly zero,showing good resilience.Comparing the hysteretic curves of SMA-LRB bearings and LRB bearings,it can be seen that the shear force of composite bearings under the same displacement is greater,providing more resilience,The addition of SMA filaments further improves the energy consumption and recoverability of LRBs.4.In order to quantitatively evaluate the seismic resilience of railway simply supported beam bridges,an evaluation framework for seismic resilience of railway simply supported beam bridges was established.Two types of bridge models equipped with SMA-LRB and LRB bearings were set as a comparison.An improved seismic vulnerability analysis(cloud to IDA method)was performed on the two types of bridge models.The calculated damage exceedance probability was substituted into the evaluation framework to quantitatively evaluate the seismic resilience of the two types of bridge models.The main conclusions are as follows:(1)The seismic resilience of railway simply supported beam bridge piers and isolation bearings studied in this article will gradually decrease with the increase of PGA.When PGA is less than 0.38 g,the seismic resilience of the bridge pier is better,often rated as excellent or good,while the isolation bearings show good seismic resilience within the range of PGA less than 0.7g,often rated as excellent or good.Under the same PGA conditions,the addition of SMA wire can further improve the seismic resilience of LRB bearings.(2)When the seismic resilience of railway simply supported beam bridge systems equipped with SMA-LRB or LRB is within the range of 0.4g seismic motion PGA,both types of bridge model systems have good seismic resilience,with ratings mostly excellent or good.However,under the same PGA conditions,the resilience index value of railway bridge seismic systems using SMA-LRB is larger than that of LRB railway bridges,and the seismic resilience is further improved.