INCREASED SPAN LENGTH FOR THE MGS LONG-SPAN GUARDRAIL SYSTEM

Long-span guardrail systems have been recognized as an effective means of shielding low-fill culverts while minimizing construction efforts and limiting culvert damage and repair. The current MGS long-span design provided the capability to span unsupported lengths up to 25 ft (7.6 m) without the use of nested guardrail. The excellent performance of the MGS long-span system in full-scale crash tests suggested that longer span lengths may be possible with the current design. A detailed analysis of the MGS long-span guardrail system was performed using the finite element software program LS-DYNA®. It was shown that the MGS long-span design had the potential for satisfying MASH TL-3 evaluation criteria at increased span lengths of 31¼ ft (9.5 m) and 37½ ft (11.4 m). Further increasing the span length led to questionable vehicle capture and severe impacts into the culvert wingwall. It was determined that the 31¼-ft (9.5-m) span MGS long-span system would proceed to full-scale crash testing. A critical impact study identified two impact locations that (1) evaluated the structural capacity of the guardrail system and (2) maximized the vehicle’s extent over the culvert and potential for vehicle instabilities. Ultimately, the sponsors decided to perform full-scale crash testing with Universal Steel Breakaway Posts in lieu of Controlled Release Terminal posts to determine their suitability with the MGS long-span guardrail system. Prior full-scale crash testing indicated that the post-to-guardrail bolt connections were sensitive to the MGS long-span design. A simulation study investigated several techniques to improve the modeling of these bolted connections. Advisor: John D. Rei