Assessment of guardrail systems with a stiff surficial layer via continuum and discrete simulations
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Mow strips are asphalt or concrete layers which are used in the design of roadside safety structures as vegetation barriers around guardrail posts. Asphalt mow strips have historically been modeled in simulations as a rigid layer. This assumption often results in unrealistic ground level restraint of the guardrail post. Recent experiments conducted in a parallel research effort have shown that asphalt rupture and other material behavior should be considered in the analysis of the response of guardrail posts embedded in mow strips. This study provides an accurate and efficient approach for simulating the guardrail system and investigates the effect of asphalt material properties and mow strip geometry on the guardrail system performance. In this research, several mow strip designs with various thicknesses, rear distances behind the posts, and asphalt pre-cuts are investigated to provide recommendations for retrofit techniques and new construction. The recommended retrofit and new construction techniques are evaluated with static and dynamic numerical simulations of guardrail posts embedded in asphalt mow strips, and full-scale crash simulations of the guardrail systems are performed. The results are compared with available data from experiments and material tests. The simulation results for guardrail posts are used to evaluate the level of restraint provided by the asphalt mow strips. Thereafter, full-scale crash simulation results are evaluated using guidelines in the Manual for Assessing Safety Hardware (MASH). Additionally, simplified analytical solutions are constructed to obtain the lateral capacity of posts embedded in asphalt mow strips. These solutions are further enhanced by combining finite element simulations and regression analysis to provide predictive equations for the lateral strength and stiffness of asphalt mow strips. The predictive equations are utilized to construct force-displacement curves (p-y curves) for asphalt layers with various rear distances and material properties. The p-y curves are then employed to efficiently model asphalt mow strips using nonlinear uncoupled springs.