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

MGS Dynamic Deflections and Working Widths at Lower Speeds

The Midwest Guardrail System (MGS) has been full-scale crash tested in many configurations, including installations adjacent to slopes, with different types of wood posts, with and without blockouts, for culvert and bridge applications, and at high flare rates. Although the performance of the MGS and the dynamic deflection and working width of the barrier have been examined, little is known about the dynamic deflection and working width of the MGS when impacted at lower speeds. The MGS is a relatively low-cost barrier, and the Test Level 3 (TL-3) version could be installed for TL-2 and TL-1 applications. The barrier is expected to capture or redirect errant vehicles impacting at speeds less than or equal to those used for crash testing according to TL-3of the Manual for Assessing Safety Hardware (MASH). Accurate dynamic deflections and working widths of the MGS when impacted at lower speeds are critical for the safe placement of guardrail to reduce the likelihood of vehicle impact with a shielded hazard in the Zone of Intrusion (ZOI) for use on level terrain and in combination with curbs. LS-DYNA computer simulation models of a 2007 Chevrolet Silverado impacting both a tangent MGS and MGS in combination with a curb at a 6-ft 3-in. (1.9-m) post spacing (i.e., standard post spacing) were calibrated against previous crash tests. Then, the model was simulated with two lower speeds and at five impact locations with a conservative soil model to determine the maximum dynamic deflection and working width of the system at TL-1 and TL-2 impact conditions of MASH