Research On Optimization Of Anti-Crossing Ability Of Am-Grade Modified Guardrail On Expressway

Highway guardrail can effectively prevent vehicles from rushing out of the road and reduce the level of accident harm.With the increase of the number of trucks passing through the highway and the improvement of vehicle performance,the commonly used Am guardrail protection has been difficult to meet the requirements of truck protection performance.At present,some road sections still continue to use such guardrails,and many major traffic accidents have occurred when trucks cross the median guardrail to the opposite lane,causing mass casualties.Therefore,it is of great significance to study the anti-crossing ability of Am-grade modified guardrail under the condition of out-of-control collision of medium-sized trucks,and further optimize the anti-crossing ability of Amgrade modified guardrail on this basis,so as to improve the comprehensive protection ability of existing guardrail and reduce the economic cost.According to the computer simulation,the finite element model of vehicle guardrail collision is established.The models of 1.5t SUV car,10 t medium-sized truck and 12.5t medium-sized truck are established by Hypermsh.Based on the 2006 edition of "Specification for Design of Highway Traffic Safety Facilities," the Am-level corrugated beam guardrail and its three modified guardrail models are established.The collision conditions of 10 t medium-sized truck weight,60 Km / h,20 ° collision angle and 12.5t medium-sized truck weight,80 Km / h,30 ° collision angle are set up.The collision process,acceleration and displacement are evaluated.The protection ability of Am-level guardrail under different collision conditions is analyzed,and the anti-crossing and protection ability of the modified guardrail under out of control conditions is verified.According to the applicable characteristics of each modified guardrail structure,the optimal transformation form of anti-crossing ability is determined.On this basis,the relationship between the new components and the protection ability is analyzed,and the multi-objective optimization design is carried out to improve the comprehensive protection ability and reduce the economic cost.The research provides a reference for the selection of guardrail reconstruction structure form for roads with different safety levels,provides a solution for further rational utilization of expressway old guardrails,upgrades road safety level,and improves the popularization and applicability of modified guardrail structure.The main conclusions are as follows :(1)In view of the anti-crossing ability of Am-class modified guardrail,when the speed of road trucks is generally not high,only arch-shaped reinforced guardrail can be used.When the speed is high,double-layer waveform beam guardrail should be used and the strength of the column should be strengthened,or double-layer waveform beam archshaped reinforced guardrail should be used directly.(2)There is a significant relationship between the structural design of the modified guardrail and the protection ability.In the design of double-layer corrugated beam arch reinforced guardrail structure,the arch height is reduced and the guardrail protection ability is increased.The thickness of the upper beam plate and the arch thickness are based on the threshold of T = 3.0mm.When the thickness of the upper beam plate is > 3.0mm,the comprehensive protection ability of the guardrail does not change significantly,and the value is significantly improved.When the arch thickness is less than 3.0mm,all medium-sized trucks have rollover,and when it is greater than this value,they are effectively blocked.(3)After optimization,2460.8 kg steel consumption and 6.9 % steel consumption can be saved for every 1 km of double-layer corrugated beam arch reinforced guardrail.In the design of double-layer corrugated beam arch-reinforced guardrail structure,the arch height should be 80 mm,the thickness of the upper beam plate should be in the range of 2mm-3mm,and the arch thickness should be 3mm-5mm.The comprehensive protection ability of the guardrail is better.(4)The optimal design provides a solution for the disposal of the Am-level guardrail after demolition.The corrugated beam plate can be used as the upper beam plate with a thickness of T = 4.0 mm in the double-layer corrugated beam arch reinforced guardrail,and the overall protection ability of the guardrail can be reused by optimizing the thickness of the arch structure.