Research On The Performance Of UHPC Piers Subjected To Rockfall Impact

In China,the terrain including lots of mountains and plateaus is complex,which leads to frequent natural disasters.With the increase of the number of bridges in mountainous areas,the impact accidents on bridges under rockfall also occur frequently.Rockfall impact accidents often destroy engineering structures,block traffic,and even endanger the personal safety of the people,resulting in huge economic losses.After the rockfall impacts the bridge,the normal strength concrete(NC)pier shows obvious insufficient resistance of impact.The NC pier is prone to serious shear failure,resulting in the inclination and even collapse of the superstructure.Ultra-high performance concrete(UHPC)developed in recent decades is a new type of concrete material with high strength and high durability.Scientific research and engineering practice show that UHPC can improve the static and dynamic performance of the structure.In this thesis,the resistance of UHPC pier under rockfall impact will be investigated.A new UHPC outsourcing reinforced pier structure will be proposed and the influence of different outsourcing thickness on crashworthiness is analyzed.The main research contents and results are as follows:(1)A refined "rockfall bridge" collision model is established to compare the dynamic response and damage law of UHPC pier with NC pier under rockfall impact.The results show that the failure mode of UHPC pier under the impact of rockfall displays local impact failure while NC pier displays shear failure.The impact resistance of UHPC pier is significantly higher than that of NC pier.When the rockfall speed reaches60 m/s,the NC pier appears through cracks and almost loses its bearing capacity.However,the damage of UHPC pier is mainly concentrated at the impact position and the pier could still sustain its integrity.(2)Under the impact of rockfall,UHPC pier can reduce the displacement at the impact position by at least 30%.At the same time,due to the increase of transverse stiffness of UHPC pier,the impact force of rockfall of UHPC pier is higher than that of NC pier.(3)The influence of different pier parameters on the impact resistance of UHPC pier is explored.The calculation formula of impact force of rockfall impacting UHPC pier is proposed.The formula comprehensively considers the parameters such as rockfall speed,rockfall mass,pier stiffness and rockfall impact area.The results show that the formula has high accuracy,and the maximum relative error of the calculation formula is 8.06%.(4)In order to improve the impact resistance of old piers,a new pier structure reinforced through outsourcing UHPC is proposed.According to the pier resistance,a calculation formula about UHPC outsourcing thickness is put forward in this paper and its correctness is verified.Moreover,the influence of different UHPC outsourcing thickness on the impact resistance is explored.The results show that UHPC outsourcing reinforced pier can improve the impact resistance of pier and effectively reduce the damage of internal concrete materials.This thesis contains 68 figures,10 tables and 76 references...