The Reliability Analysis Of Flexible Guardrail By Finite Element Method

Road accident is a commonly faced problem in worldwide,with the flourish developed traffic system,the accidents ratio also grow rapidly. In the year 2005 the direct property losses caused by traffic accidents is up to 1.88 billon. One third of the fatal accident occurred in the road-side collision of single accident annually. As the most important traffic safety appurtenance on expressway,guardrail plays a key role in reducing the severity and property losses in road accident.At present the commonly used guardrail form are rigid guardrail,semi-rigid guardrail and flexible guardrail. For flexible guardrail,seldom research have been carried on,may it can be say no study have been conducted. So the relative principle is mostly based on foreign studies and the experience gained from the using on HE-NING expressway. In this paper,firstly I give a summarization of the phylogeny,current research situation and commonly used research method of road side barrier,then make a decision for the content of this paper. I choose the digital simulation method as the research direction for this paper,by FEA software HYPERMESH and LS-DYNA,I give the mainly factor that should be considered in structure design through changing the structure parameter.Analyzing the results,we found that the flexible guardrail is a kind of safety facilities of partial breakage during the impacting process,the post nearest to the crash point damaged firstly,sequencely the others. Also we found the block's stress is far less the other parts composite the flexible guardrail,and it doesn't share any loads after the post which it's constrainted on yield,so when choose the material for block we can consider the material with less strength. The cable work in it's elastic range and seldom damaged. During the impacting process the cables'tensional stress distributed uniformly and the maximum stress point is near the impacting point.The maximum dynamic displacement of the guardrail is an important criterion to evaluate the roadside barrier,during the impacting process we found that it changes with the initial tension stress of the cable,the guardrail's installation length and the space between the posts,it is sensitive to the last factor,then to the cable's initial stress,and the sensitivity to the installation length less than formers. When reference to the acceleration,it's sensitive to all the factors above. Also the impacting force is another important standard to evaluate the guardrail,for it's directly affluent the vehicles'damage and people's safety. The results reflect the impacting force far less than the car impact to a rigid guardrail with same kinetic energy. During the impact process,most of the car's kinetic energy convert into the guardrail's internal energy and seldom other energy form were converted. The internal energy of the guardrail is mainly distribute by the post and cable , and the distribution not sensitive to the factor above. In the figure of resultant force, we found that the value changed with the initial condition and far less than that of a vehicle impact rigid guardrail.To sum up,the conclusion of this paper is when reference to the safety to design a flexible guardrail one should consider the factors'sequence as follows:1,The space between the post;2,The cable's initial stress;3,The installation length.