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Development of Alternative Wood-Post MGS Approach Guardrail Transition

REPORT NUMBER

TRP-03-243-11

AUTHORS

Scott Rosenbaugh, Kevin Schrum, Ronald Faller, Karla Lechtenberg (Polivka), Dean Sicking, John Reid

PUBLICATION DATE

2011-11-28

ABSTRACT

The objective of this study was to develop a wood-post MGS approach transition system that is equivalent to the simplified steel-post, MGS stiffness transition recently developed at the Midwest Roadside Safety Facility. An extensive literature review was conducted on wood and steel post performance comparisons through either dynamic component testing or full-scale crash testing. This review concluded that 6-ft (1.8-m) long W6x9 (W152x13.4) steel posts and 6-in. x 8- in. (152-cm x 203-mm) wood posts provide similar force vs. deflection characteristics during rotation through soil. However, no such data was available concerning dynamic testing on larger transition posts located adjacent to the bridge rail. Therefore, a dynamic testing program was undertaken to evaluate W6x15 (W152x22.3) steel posts and various sizes of wood posts. At the conclusion of the testing program, an 8-in. x 10-in. (203-mm x 254-mm) wood post was chosen as the best equivalent to the W6x15 (W152x22.3) steel post due to similar post-soil resistances as well as a reduced propensity to fracture when compared to smaller post cross sections. A BARRIER VII computer model was then used to evaluate the wood-post stiffness transition against a calibrated model of the original steel post transition system. When subjected to identical impacts, the wood-post system was shown to reduce system deflections, vehicle pocketing angles, and the potential for wheel snag. Therefore, the wood-post MGS stiffness transition was recommended for use as a MASH TL-3 safety barrier.