Study On Impact Model And Service Performance Of Bridge System In Debris Flow Affected Area

With the extension of infrastructure construction to highland and mountainous areas,the operation conditions of bridge system become more and more complicated.In recent years,the accident number of bridge collapse and casualties caused by debris flow disasters has been increasing,so it is significant to explore the impact effect of debris flow on bridge and its failure mechanism.Previous studies on the impact force of debris flow and the impact resistance of bridges mainly focused on qualitative and estimation.Therefore,it is urgent to carry out researches on the dynamic action of debris flow impact and service performance of bridge.In this paper,a two-phase numerical model of the debris flow impacting on the bridge system is established,the impact force formula of debris flow is determined,and the vulnerability and dynamic responces of the bridge under debris flow impacting are analyzed.The main research contents of this paper are as follows:(1)Firstly,the feasibility of using the two-phase flow theory to establish the debris flow impact bridge pier model is discussed,and the domestic and foreign simulation analysis methods of debris flow are compared by modeling analysis and trial calculation,and then the Arbitrary Lagrange-Euler Method(ALE)and Smoothed Particle Hydrodynamics(SPH)algorithms are selected.Furthermore,the experimental data of debris flow impact force in China and abroad are collected,and the characteristics in time and frequency domains and analysis methods of debris flow impact process are summarized.(2)Based on flume impact test,a flume impact test model was established by using finite element software.Then the applicability of the ALE and SPH algorithms in two-phase flow calculation are compared with the relevant experimental data,and the reliability of fluid,solid and fluid-solid coupling calculation is verified respectively.Coupling characteristics between fluid and solid are analyzed,and the stress redistribution between the two phases is revealed.(3)On the basis of hydrodynamic formula,the formulas to calculate impact force on highway and railway bridge piers are derived respectively.The full-scale impact models of debris flow impacting two bridges are established as study cases.The correlation coefficients are determined according to 54 groups of numerical tests and related supplementary tests,and the mechanical model of debris flow impact bridge system is obtained.(4)The reliability calculation model of debris flow impacting bridge system is established,and the vulnerability analysis of the bridge is carried out by using Monte Carlo method.Thus,the critical velocity and impact point height of debris flow impact are determined by the failure probability and reliability index in three states.(5)By utilizing the calculation results of the full scale impact test,the failure surface and failure envelope of the highway bridge under the impact of debris flow are further determined.The train-bridge coupling model of railway bridge under debris flow impact is established,and the structural dynamic response of the bridge and running safety of the the train bridge are analyzed.