Dynamic Response Of Bridge Under Flood-induced Scour And Vessel Impact

Flood-induced scour and vessel impacts are the major reasons leading to the damage of bridge crossing over navigable river.A scoured b ridge will be damaged more severely under vessel impacts,and few works focused on this issue.Based on scoured bridge pier-barge impact tests,we aimed to study the dynamic response and impact force of bridge systems under combined hazards scour and vessel impacts.(1)Experimental study on scoured pier-barge impacts.The influence of scour depth on impact force and pier displacement is studied through impact tests.Based on the barge-pier impact tests,the finite element model of the scoured pier-barge model is created,and the numerical results are compared with that recorded from the tests.The results show that the effects of scour depth on the impact force and pier displacement extracted from numerical simulation are consistent with that recorded from the impact test.Based on relative and absolute error analysis,it is found that displacements from numerical simulation match with that in the tests.By comparing the accuracy and calculation cost of soil spring method and solid element method,it can be found that soil spring method can effectively reduce the calculation cost and improve the calculation efficiency.The feasibility of the soil spring method is verified,which provides a reliable base for the application of the soil spring method in the whole bridge model.(2)Study on the dynamic response of continuous reinforced concrete bridges under scour and barge collision.Based on AASHTO code,a barge model was created to study the effects of scour depth on impact force,bow crush depth,pier displacement,pile deformation and pier damage.The results show that scour has small effects on the maximum impact force,it significantly affects the impact force time-history curve and the bow impact depth.For example,the maximum horizontal displacement at top of pier is about 64%higher than that without scour at 3.09m/s collision speed,567ton barge and with 9m scour depth.(3)Study on the dynamic response of cable-stayed Bridge under the combined hazards Scour and ship collision.The effects of scour and Bulbous bow impact on impact force,bow crush depth,displacement of pile cap,bending moment at pile top,deformation of pile body and damage of bridge tower are studied.The results show that scour has small effect on the maximum impact force,however,it significantly affects the crush depth of bow.For example,the crush depth is about 0.37m for the pristine structure with impact velocity 1.03m/s,and the crush depth is 0.32 m with 20 m scour depth under the same impact condition,which decreases about 14%.The maximum crush depth and residual crush depth decrease with scour depth.Scour significantly increases bearing platform displacement and pile deformation.For example,under 2.06m/s impact velocity,the maximum displacement of cap with 20m scour depth is about 0.08 m,which is 4 times of that of the bridge without scour.It is also found that scour depth increases the damage severity of the pylon,and the increase of velocity also increases the damage severity of the bearing platform.This study provides a theoretical base for the bridges crossing over navigable waterways to resist the Flood induced Scour and vessel collision,and has important theoretical value and social economic benefits.In addition to the impact force,it is suggested that the structural displacement,deformation and damage of the bridge should be taken as important indexes in the safety evaluation of the bridge under the combined hazards of scour and ship collision.