Development of a Surface-mounted Strong Post for the Midwest Guardrail System

This research investigated the development of a surface-mounted strong post for the Midwest Guardrail System (MGS), designed to replicate the behavior of the standard MGS post, a W6 x8.5, 72-in. long post embedded 40 in. into strong soil. The MGS is a strong post, W-beam guardrail system that has been successfully evaluated in many applications using crashworthiness criteria described in the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH). However, in some locations, conventional soil-embedded posts are impossible to install due to subgrade obstructions like concrete slabs, mow strips, utilities, and limited right-of-way. Although weak-post alternatives have been tested, they may not suit all installation sites. To address these limitations, this study proposed a surface-mounted, strong post design as a cost-effective alternative for MGS for applications in soil-restricted environments. Computer simulations conducted using LS-DYNA revealed that the optimized surface-mounted post consisted of a W6x8.5 post with a 13/16-in. x 2-in. vertical slot in the compression flange with average forces of 10.35, 9.21, 8.77, and 8.39 kip through 5, 10, 15 and 20 in. of displacement, respectively. This was determined to be comparable to 40-in. soil-embedded W6x8.5 post’s force-displacement response of 9.41, 9.16, 9.55, and 8.92 kip over those same displacements. A testing matrix and fabrication plan were developed to guide bogie impact testing, including configurations with upper and lower deviations from the selected 13/16-in. x 2-in. vertical slot, to account for uncertainties in simulation results. Designs were recommended for bogie testing to investigate potential failure modes and to calibrate simulation models. Preliminary full-scale simulations of the surface-mounted MGS resulted in a dynamic deflection of 38.5 in., which suggested similar performance to the standard 40-in. soil-embedded MGS crash tests with dynamic deflections between 42 and 43 in. The standard MGS to surface-mounted MGS transition critical impact point (CIP) study showed no significant potential for snagging or pocketing with an identified CIP location 22 ft – 4 in. upstream from the transition point between the two systems, which maximized dynamic deflection and pocketing angle at 43.2 in. and 20 degrees, respectively. Advisor: Cody S. Stolle