Abstract
Certification crash test experiments conducted in controlled laboratory environments play a crucial role in the product development cycle of roadside safety hardware by linking analysis, design, and real-world in-service performance along low-volume roads (LVRs). The AASHTO Manual for Assessing Safety Hardware worst-case testing philosophy prescribes a commonsense approach to ensuring reliable real-world performance in designing certification crash test experiments for W-beam guardrails. Literature of the past two decades establishes extreme rail-to-post connection strength variability as a component-level trigger mechanism of guardrail system-level failure modes that degrade the reliability of guardrail safety performance. A range of primary and secondary release mechanisms with their associated variability sources is examined from the perspective of characterizing the worst case for each release mechanism. A case is made to support a recommendation that worst-case connection strength be systematically represented in designing certification crash test experiment matrices that are intended to ensure adequate performance of guardrails along LVRs. A systematic general methodology is introduced for defining compounded worst-case connection strength. The standard button head mounting bolt of the modified G4(1S) and Midwest Guardrail System family is considered as an example. Detailed evaluation of variability extremes in button head bolt connection strength indicates that optimizing the existing button head bolt release mechanism is not possible, even with the use of mid-span splices. Thus, it is recommended that an optimized release mechanism solution—such as the Gregory Mini Spacer guardrail fastener—be considered, consistent with the award-winning science of release for guardrail optimization to improve roadside safety along LVRs and other roadways in the United States, Europe, and developing countries.
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