Vulnerability Of Bridge Structures Subjected To Vessel Impacts Considering Multi-hazard

The past studies primarily performed the deterministic dynamic analysis of vesselbridge collision for a given collision event,which hardly reflects the contingency and probability characteristics of ship collision,as well as the damage evolution of bridge under impacts with various energy.In addition,few previous studies have combined the effects of ship collision with other factors such as corrosion and scouring.For this reason,this study systematically investigated the vulnerability of bridge structures subjected to two typical vessel impacts considering multi-hazard where the residual capacity of bridge piers after vessel impacts and the maximum curvature of pile used as the damage assessment index.The main contents of this study are summarized as follows:(1)Based on the RC pier column drop weight impact test and axial loading test carried out by this research group,refined finite element simulation analysis was carried out.A direct finite element(FE)simulation method was established to predict the residual capacity of axially-loaded RC column after lateral impact.The rationality of the simulation method was verified by comparing the FE analysis results with the test results.(2)By combining the simplified model and the response surface method,the vulnerability analysis method of the vessel-bridge collision was established.Taking a typical fourspan continuous beam bridge as an example,a FE model of bridge piers considering nonuniform degradation caused by steel bar corrosion in the marine environment was established.The vulnerability curves of the bridge were obtained for the impacts of two kinds of typical ships.The results show that: 1.The established response surface has good accuracy and can replace the complicated nonlinear finite element calculation;2.The corrosion of the steel bar will obviously weaken the residual capacity of the pier;3.Different response characteristics were observed for barge collisions and ship collisions because of the difference in the shape of the vessel bow.The residual strength gradually reduced with increasing impact speeds under ship collisions,while critical impact speed was identified for barge collision,particularly for the sound bridge structure.The residual strength slightly changed with impact speeds when the initial velocity exceeded the critical one;4.In most cases,when the initial velocity of the vessels is not large,the damage caused by the barge impact is greater than that caused by the ship.However,the failure probability of ship collisions is higher than that of barge collisions when the kinetic energy is large and the bridge has experienced the corrosion deterioration for a long time.(3)The vulnerability analysis of continuous girder bridge pier is carried out,which considering the joint action of steel bar corrosion and barge inclined impact.The modeling process considered two different boundary conditions(fixed pier and non-fixed pier)and two different inclined impact angles(15°,30°).The following conclusions were obtained:1.When the barge inclined impact the pier with an angle,the displacement of the pier top along the bridge was much greater than that cross the bridge,which may cause the bearing to be emptied,posing a great threat to the stability of the overall structure of the bridge;2.The peak impact force decreases with the gradual increase of the inclined impact angle,which makes the residual capacity of the pier under oblique impact generally higher than that under normal impact;3.At small inclination angle(15 degrees),the overall characteristics of residual capacity are similar to that of frontal collision,except that it is less affected by small energy impact;the structural response of pier under impact of barge with large angle(30°)is no longer affected by the critical vessels speed;4.For continuous girder bridges with rectangular piers,frontal impact is the most dangerous condition from the perspective of residual capacity of piers,which requires special attention.However,we should pay attention to the problem of excessive displacement of pier top along bridge under inclined impact.(4)The vulnerability analysis of vessel-bridge collision under combined action of scouring,steel corrosion and ship impact is carried out.Non-linear fiber element is used to simulate pile foundation in the model,and p-y curve method is used to consider the nonlinear relationship of pile-soil interaction.Damage assessment index based on curvature of pile foundation is added to the vulnerability analysis.The following conclusions are drawn: 1.With the increase of scouring depth,due to the overall reduced stiffness,the shear demand of pile foundation decreases while the bending demand increases greatly;2.When the pier is subjected to lateral impact,the pile top is the position where the demand for bending resistance of the pile is greatest and where the plastic hinge of the pile foundation occurs.This is different from seismic action,mainly due to differences in input methods of ship collisions and seismic loads;3.Affected by load spectrum characteristics and dynamic characteristics of bridge structure,the impact speed is nonlinear to the damage of pile under the impact of barge,and there is a "danger zone" of impact speed.When the vessels speed falls within this zone,the damage of pile is obvious,and even can be completely destroyed under the combined action of corrosion and scour;4.The increase of scouring depth increases the structural flexibility and the displacement at the top of the pile under lateral impact,which significantly increases the damage to the pile.However,for piers,the relative deformation of the pier itself decreases due to the increase of displacement at the top of the pile,so the residual capacity of the pier does not decrease significantly or even rises slightly.