The objective of this project was to develop a long-span guardrail design that meets NCHRP Report 350 evaluation criteria and is less expensive to construct than the existing design.
The researchers reviewed design details of the long-span guardrails previously developed, especially the design presented by Mak, to evaluate expected behavior of the guardrail when subjected to NCHRP Report 350 tests. Design features that have been found to be important in terms of capacity of the guardrail to contain and redirect a vehicle are the structural strength and geometrics of the guardrail. Lateral stiffness of the guardrail system is the primary design feature that determines maximum deflection of the guardrail during a collision and changes in lateral stiffness of the guardrail system along its length are the key features influencing pocketing of the vehicle.
The BARRIER VII computer program was used to evaluate expected performance of the proposed design in NCHRP Report 350 tests. This program models a collision in two dimensions with a simple characterization of a vehicle and a detailed characterization of the guardrail. It was used to evaluate the expected deflections of the barrier and to predict any potential of the barrier to allow any unacceptable pocketing of the vehicle.
Reported herein are the details and results of the full-scale crash test performed on the long-span guardrail. The rail element ruptured and allowed the vehicle to penetrate the rail system. The vehicle subsequently rolled onto its side. Therefore, the rail failed evaluation criteria for NCHRP Report 350 test 3-11. The abrupt change in stiffness of the rail element where it changes from two layer of W-beam (nested) to a single layer may have contributed to rupture of the single layer rail element.