DESIGN AND SIMULATION OF TWO WOODEN-POST W-BEAM GUARDRAILS TO ELIMINATE WHEEL SNAGGING.

Recent crash tests on strong-post round- and rectangular-wood W-beam guardrail systems demonstrate that wheel snagging can be a serious concern for vehicle stability and impact severity. There are several methods that exist to minimise wheel snagging in strong-post guardrail systems. This paper aims to investigate the effect of one of those methods: the increased offset distance between post and W-beam rail. Extensive simulation studies are performed to determine optimum offset distances between the post and W-beam in both systems. Different designs with varying offset block depths are evaluated and their impact performances are compared. LS-DYNA, a versatile, nonlinear, large deformation, finite-element program is utilised to analyse different alternatives. Guardrail models previously validated against full-scale crash tests were used in the analysis. Simulation findings suggest that tendency to wheel snagging reduces with increased offset depths. 260-mm depth was determined to be the optimum offset distance between the wooden posts and W-beam. Simulation results show that when a nominal 260-mm offset distance is provided, wheel snagging and associated vehicle instability and impact severity can be alleviated in wooden-post guardrail systems.