Rockfall Impact Resistance And Damage Assessment Criterion Of Hollow Thin-Walled High Pier

China is a mountainous country,and bridge structures located in mountainous areas are easy to suffer from the impact of rockfalls caused by heavy rainfall,earthquake and debris flow,resulting in serious bridge damage and destruction.Hollow thin-walled high piers are widely used in continuous rigid frame bridges across deep canyons because of their strong supporting capacity and low construction cost.However,at present,the research on rockfall impact resistance of bridge pier is mainly focused on rectangular or circular piers,and the research on hollow thin-wall high pier is relatively limited.In order to better serve the rockfall impact design of thin-walled high piers in mountainous areas,the damage,dynamic response characteristics and damage assessment method of hollow thinwalled high piers subjected to rockfall impact were studied by combining numerical simulation and theoretical methods.The main research contents and conclusions are as follows:(1)ANSYS/LS-DYNA was used to establish a refined "rockfallhollow thin-walled high pier" collision model.The element types,element mesh sizes,steel and concrete material models and contact algorithms of each part of the bridge were reasonably selected.The accuracy of the model was verified based on the simulation of the falling weight test and the principle of energy conservation.(2)Based on the verified impact model,the impact force and damage characteristics of hollow thin-walled high pier under rockfall impact were studied by changing the impact height,velocity,size and strength grade of pier concrete.The results have shown that the peak impact force is most obviously affected by the velocity and size of rockfall.The main damage modes of collision surface,side and cross-section of bridge pier are strip,radial and corner shear failure respectively.(3)The influence of each parameter on the internal force response and displacement response of the pier and the corresponding energy mechanism are analyzed.The bending moment of bridge pier increases with the increase of rockfall speed,rockfall size and concrete strength grade.The impact of rockfall size on bending moment is the most significant.When the diameter of rockfall increases from 1.5m to 2.5m,the bending moment of pier bottom section increases by 357.3%.The maximum displacements of the pier all occur on the back of the pier within the height range of 40 m to 60 m,and the maximum displacements increase with the upward movement of the impact position,the increase of the size and speed of the rockfall,and the decrease of the concrete strength grade.(4)Based on Box-Behnken design method,multi-factor and multilevel test design was carried out,and corresponding response surface prediction model of volume damage index was established,and two main control parameters affecting pier damage were identified.The damage assessment curve and partition diagram based on the main control parameters are established,which can realize the rapid damage assessment of the impacted pier.