High Resolution Numerical Simulation And Post-collision Bearing Capacity Of Prestressed Concrete Hollow Slab Bridge Under Over-height Vehicle Collision

Frequent accidents of over-height vehicle colliding with the superstructure of overpass bridges brought a serious threat to the bridge structural safety.The bridge structures mainly undertake vertical loads under normal circumstances,which is not fully considered the external loads applied laterally.The bridge superstructure damage in the lateral side will affect the vertical load-bearing performance significantly under the impact loadings such as over-height vehicle collision.Therefore,it is necessary to carry out the research on the bridge superstructure collided by over-height vehicle and analyze the influence of damage on vertical bearing capacity of bridge superstructure.Based on high-resolution numerical simulation in study,the accuracy of numerical model was verified by experimental data reported in literature.The dynamic response and vertical bearing capacity of RC beam subjected to lateral impact were studied.Taking the over-height vehicle collided with prestressed concrete hollow slab bridge superstructure as an engineering example,the dynamic response and damage mechanism were studied under a standard biaxial truck collision,and the vertical bearing capacity of damaged girder was analyzed under different load cases.A composite protective device was proposed,and the anti-collision performance and parameters sensitivity were analyzed in depth.The specific research contents and significant conclusions are as follows:(1)The current research achievements of RC beam and bridge structure under vehicle collision were summarized systemically.Moreover,the specifications in European Code(BS EN1991-1-7),US Code(AASHTO LRFD-2017)and Chinese Code(JTG D60-2015)on the impact force of vehicle were compared.The deficiencies of current research were pointed out on the problem of bridge superstructure under collision of over-height vehicle.(2)By comparing the results of numerical simulation with the experimental dates of a drop hammer impact test reported in literature,the feasibility of establishment method of numerical model,material constitutive models,contact types and hourglass control technology adopted in study were verified by experiment.Meanwhile,the dynamic response and damage distribution of structure can be correctly reflected under impact loadings.(3)Taking the impact of a drop hammer on RC beam as an example,the dynamic response of structure was calculated under different load cases,and the decreasing regularity of vertical bearing capacity of damaged structure was discussed.Meanwhile,the damage grade of RC beam was classified based on vertical residual bearing capacity.The influence of different parameters was analyzed on damage of structure,and the M-V curves were proposed to evaluate the damage grade of RC beam.The results showed that the vertical bearing capacity of RC beam reduced once damaged by lateral impact,and the change of post-collision stress-strain relationship of concrete and reinforcement mainly caused decrease of vertical bearing capacity.(4)The high-resolution simulation of over-height vehicle collided with prestressed concrete hollow slab bridge was conducted,and the dynamic response of bridge superstructure was investigated under different load cases.Meanwhile,the damage of bridge was analyzed during the collision process,and the effects of different parameters on the vertical bearing capacity of damaged girder were discussed,such as vehicle impact speeds,vehicle impact masses,vehicle ultra-high heights,impact angles and concrete strengths.The results showed that the over-height vehicle collision mainly caused local damage,and the vertical bearing capacity of damaged girder reduced within 15%.However,the vertical bearing capacity and stiffness decreased greatly once the prestressed tendon failed,which seriously affected the safety of bridge superstructure.(5)A composite protective device named ECC-Thin-Walled Steel Tube was proposed to protect the bridge from the over-height vehicle collision,its anti-collision performance was deeply analyzed.Meanwhile,the parameters sensitivity analysis of protective device was discussed based on the response surface method.The results showed that the protective device could effectively reduce the damage of bridge superstructure under over-height vehicle collision.The response was sensitive to the thickness of ECC plate and the number of thin-walled steel tubes,while the thickness of thin-walled steel tubes had little effect on target response.