Study On Shear Failure Behavior And Mechanism Of Segmental Beam Under Impact

The act of impact loads such as vehicle falling objects on the bridge structure will lead to a more prominent shear failure mechanism of the beam.Because of the discontinuity of the ordinary reinforcement and concrete at the joints,the segmental fabricated beams also show prominent shear failure characteristics.With the rapid development of Precast Segmental Bridges,the research on the effect of impact load such as vehicle falling objects on the assembled segment beams is still insufficient.It is urgent to carry out relevant research,especially the research on the shear failure mechanism of assembled segment beams under impact action.In this paper,the shear performance of assembled segment beams under impact load is taken as the main objective,and the systematic research is carried out by means of finite element simulation analysis and falling weight impact test.The main research contents and achievements are as follows:(1)Numerical simulation and experimental study on shear failure of assembled segment beams under impact loading action.Through the finite element software(ANSYS / LS-DYNA)simulation and five groups of falling weight impact test of unbonded prestressed concrete assembled segment beams,this paper analyzes the crack development form,ultimate failure form and related characteristics of the impact loading action on the middle of the segmental beam and near the joint.The result shows that when the impact load acts on the middle of the segment,the beam will produce inclined cracks from the joint to the point of action and the width of the inclined cracks will eventually increase and develop into the main failure cracks,and the segmental beam will have inclined section failure;when the impact load acts near the joint of the segment beam,it will produce inclined cracks from the joint to the point of action,and then the inclined cracks gradually develop into vertical cracks,which will be destroyed main crack with the increase of the width,making the segmental beam damaged by direct shear.Under the impact loading action,due to the hysteresis of force transmission,the reaction force of both sides of the support,which is about half of the second peak value of the impact force,will reach the peak value after the impact force.(2)Shear failure mechanism of assembled segment beams under impact loading action.With the combination of numerical simulation and shear test,this paper compares the failure forms of segmental beam and whole beam under the impact action,the shear failure forms of segmental beam under dynamic and static action,and analyzes the influence of different concrete normal stress levels on the shear crack development of segmental beam.The result shows that the main failure cracks of assembled segment beams and integral reinforced concrete beam under impact action both occur at the initial stage of impact action.The failure mode of segmental beam under impact action is different from that of the whole beam because of the weak connection of joints;the failure cracks occur at the joint surface.The different normal stress level of concrete does not change the failure mode of segmental assembled beam,but the larger concrete strength will inhibit the development of inclined cracks.The closer the joint surface is to the loading point,the closer the crack angle is to 90 degrees,and the main crack distribution is more concentrated.