Study On Rockfall Impact And Structural Optimization Of Flexible Protective Shed Tunnel Of Bridge

Due to the complex geological conditions in the western mountainous areas of China and the influence of earthquakes,precipitation and human engineering activities,rockfall disasters occur frequently.As an indispensable structure in the traffic construction in mountainous areas,bridges are often hit by falling rocks,which seriously threatens the safety of traffic operation and bridge structure.Therefore,it is necessary to study the rockfall protection of bridge.Flexible shed tunnel is a common passive protection measure,which is very suitable for the rockfall protection of bridge structure because of its light structure and convenient installation.At present,there are few researches on the application of this kind of shed in bridge at home and abroad,and the corresponding design technical specifications have not yet been formed.Therefore,this paper takes a simple supported beam bridge and the flexible protective shed tunnel on the bridge of a mountain highway as the background,and carries out the following research:Firstly,the movement characteristics of rockfall are studied,and the movement state of rockfall in a practical slope is analyzed by Rockfall numerical simulation and theoretical calculation.Then,the explicit dynamic analysis software-LS-DYNA is used to simulate the impact of rockfall on the flexible protective shed of bridge,and the effect of impact velocity,impact position and impact angle are analyzed.Finally,the structure of the shed tunnel is optimized,and a new type of flexible shed tunnel based on the prestressed simply supported T-beam bridge is proposed.The influence of the cross-section size of the arch ring,the arch support and the diameter of steel wire of the protective net on the impact resistance of the shed tunnel is studied.The results show that the impact response of the shed tunnel and bridge structure is positively correlated with the impact velocity when the rock impact different positions of flexible protective shed tunnel;the impact on the protective net has the least impact to the bridge,and it will not damage the bridge when its own strength is enough;the impact on steel arch ring has the greatest impact and the most destructive effect on the bridge,which will cause the concrete failure under the impact of lower energy level;the impact response of the shed tunnel and bridge increase with the increase of impact angle.The deformation and energy dissipation capacity of arch ring of the new flexible shed tunnel under impact is significantly enhanced,and because the number of bases is doubled,the local impact is smaller,and the bridge does not appear damage under the considered impact energy level;With the increase of the size and thickness of the arch ring,the plastic strain area at the impact position decreases and the strength of the arch ring increases,but the deformation capacity decreases and the impact force transferred to the bridge increases;The energy of rockfall impacting on arch ring can be effectively reduced by the arch support,and the impact of rockfall on steel transverse beam can be avoided at the same time;The impact strength of the protective net increases with the increase of the diameter of the steel wire,but the increase of the diameter of the steel wire will lead to the increase of the impact force transferred to the bridge.