Impact Fragility Analysis Of A Bridge Under Scour And Vessel Impact

In recent years,with the development of society and economy,the demand for the construction of cross-river and cross-sea bridges has increased day by day,and bridges have become an important pivot project in China’s transportation lifeline system.However,instability and collapse of bridges caused by scouring and vessel impact occurs frequently.At present,few researchers have studied the impact fragility of bridge structures under the combined hazards:scour and vessel impact.In this paper,taking a continuous girder bridge as the engineering background,through the scale test and finite element numerical simulation,the fragility analysis is carried out to evaluate the safety of the bridge structure under the combined action of double disaster erosion and ship collision.(1)Based on the finite element software ABAQUS,the influence of the scour depth on the bearing capacity and the maximum bending moment of the single pile foundation are analyzed,and the vertical and horizontal ultimate bearing capacity and the change law of the pile body displacement with the scour depth are obtained.(2)Though the vessel-bridge impact test,collect vessel collision force,bridge pier local displacement and bridge pier damage under various cases,and then establish a finite element model,and perform nonlinear dynamic analysis to compare the simulation results with the test results.The results show that the displacement of the bridge under vessel collision increases with scour depth.Under the same impact speed and ship tonnage,the local scouring has little effect on the peak impact force of the pier structure.(3)Relying on the actual project as the background,a finite element model of a continuous beam bridge and barge across the river is established.The pile-soil interaction is simulated by the p-y method,and the nonlinear dynamic analysis is performed to obtain the structural displacement response and determine each damage state(slight damage,medium Destruction,severe destruction and collapse),through vulnerability analysis,the probability of impact failure under different scouring and impact conditions is obtained.The results show that:under the same barge tonnage,when the impact velocity is greater than a certain critical value,as the scouring depth increases,the bridge structure’s probability of surpassing increases in each damage state.When the barge tonnage is 500t and the impact velocity is 4m/s,the probability of collapse of a bridge system with a erosion depth of 15m is about 11 times that of an intact bridge system.Under the same erosion depth,when the impact velocity is greater than a certain critical value,the failure probability of the bridge structure in each damage state increases with the increase of the barge tonnage.When the barge tonnage is 500t and the impact speed is 3m/s,the probability of serious damage is 60%.At the same impact speed,when the tonnage of the barge is increased to 1000t,the probability of serious damage is increased to 95%.Therefore,the formation of local erosion of the bridge foundation will seriously affect the safety of the bridge structure.