Seismic Risk Transfer And Control Of High-speed Railway Multi-span Simply Supported Bridge In The Longitudinal Direction

In order to ensure driving smoothness,control project cost and protect environment,a large number of multi-span simply-supported bridges are used in high-speed railway construction in China.Due to the need of national strategic development,more and more high-speed railways are built in the west of China where seismic zones are widely distributed.Therefore,it is very important to control the earthquake risk of multi-span simply-supported bridges for the current development of highspeed railways.The research on the seismic disasters in recent years shows that the existing bridge Earthquake Resistance System(ERS)and design strategy play a limited role in the high-speed railway multi-span simplysupported beam bridge(HSRSB).At present,the important reason why there is still room for improvement in anti-seismic strategies for HSRSB is that the research on the track constraint effect under earthquake is not deep enough.The complex integrated track-bridge model leads to the low efficiency of obtaining seismic response samples and makes it difficult to carry out parameter analysis.By combining theoretical analysis and numerical simulation,this thesis carries out research from four aspects:improving numerical analysis model,exploring the principle of track constraint action,proposing and verifying reasonable anti-seismic design strategy,and proposing technical means and design methods to achieve the strategy,in order to propose a reasonable ERS for HSRSB.The main research work is as follows:(1)A new track-bridge integrated simplified modeling method is proposed,which can effectively reduce the number of track structure elements in finite element model without changing the fine modeling of bridge structure,while retaining the constraint effect of track structure on bridge structure,and can be flexibly applied to bridge models with different structural parameters.The dynamic characteristics and seismic response of the refined model and the simplified model(SM)of the full bridge are compared to verify that the SM proposed in this thesis can simultaneously take into account the computational accuracy,computational efficiency and modeling efficiency,and has significant advantages over the traditional simplified model.(2)Study the influence of track constraints on bridge structural characteristics and seismic risk.Based on the Quasi-static method,the influence of the constraint degree on the internal force and displacement of each bridge span in HSRSB is revealed,and the relationship between the number of bridge spans and the system constraint degree is established.By comparing the peak value of longitudinal seismic response of HSRSB and trackless bridge,the influence of constraint degree on longitudinal seismic response of bridge structure is revealed.According to the phenomenon of constraint degree difference,an appropriate seismic risk evaluation index is proposed,including damage risk and damage scale.Based on sufficient seismic samples,the influence of rail structure constraints on seismic risk of bridge structures is evaluated from two perspectives of damage risk and damage scale.(3)Based on the relationship between system constraint degree,adjacent-span constraint and subgrade constraint,the "bridge constraint reinforcement" strategy and "subgrade constraint softening" strategy are proposed to control the seismic risk of bridge structure and the seismic risk of track structure respectively.The feasibility of the two strategies is illustrated by the Quasi-static method,and the minimum stiffness to reach the rigid limit state and the minimum length of the friction plate to reach the soft limit state are proposed.Based on a large number of seismic samples,the seismic risks of four kinds of track-bridge systems(common track-bridge system,"reinforcement" strategic track-bridge system,"softening" strategic track-bridge system,and track-bridge system with both two strategies(RTCS))are evaluated,and the advantages of RTCS in controlling seismic risks are verified.A new type of ERS," Risk transfer and control",which breaks through the existing seismic design concept of Bridges,is proposed.(4)The design framework based on performance matching is proposed to optimize the material usage and reduce the engineering construction cost on the premise of meeting the rigidity requirements of the "reinforcement" strategy.At the specific optimization level of the design framework,a polynomial feature mapping genetic algorithm is proposed to achieve the differential configuration of adjacent-span constraint stiffness in different spans,thus further reducing the amount.By comparing with the standard code method and the traditional "single parameter" genetic algorithm,the superiority of the optimized design method in narrowing the search space,controlling the search direction,maintaining a good global search ability and satisfying the differentiated demand is verified.