Development and Implementation of the Simplified Midwest Guardrail System Stiffness Transition

Abstract

The varied lateral stiffness between bridge rails and approach guardrail systems may cause vehicle pocketing or wheel snagging to occur near rigid bridge rail ends. To mitigate this potential hazard, an approach guardrail transition (AGT) is used to provide a gradual increase in the lateral stiffness of the barrier between the W-beam guardrail system and the bridge railing. However, these transitions can also cause a propensity for vehicle pocketing or wheel snagging if the change in lateral stiffness occurs too rapidly. Recently, a stiffness transition based on NCHRP Report 350 was developed for use with the Midwest Guardrail System (MGS) and a stiff Thrie beam AGT, and successful testing was performed close to the upstream end of the AGT. The transition was designed with three sizes of steel posts, one of which was nonstandard for state departments of transportation. Thus, a simplified version of the original MGS stiffness transition that used two common sizes of steel posts was developed and was subjected to full-scale crash testing according to Test Level 3 as set forth in the Manual for Assessing Safety Hardware. Subsequently, dynamic post properties obtained from bogie testing and numerical simulations were used to develop an equivalent wood post version of the simplified MGS stiffness transition. Recommendations are made regarding the attachment of the stiffness transitions to FHWA-accepted Thrie beam bridge rail AGTs.

Evaluation of the Midwest Guardrail System stiffness transition with curb

“…tall curb. In 2010, the stiffness transition configuration, shown in Figure 10a, was successfully crash tested without a curb (Lechtenberg et al, 2012;Rosenbaugh et al, 2010). However, when a 102-mm (4-in.)…”

“…The full-scale crash test installation utilized the same guardrail transition installation (including upstream stiffness transition, downstream transition, and bridge rail) that was previously evaluated according to MASH (Lechtenberg et al, 2012;Rosenbaugh et al, 2010). Only this time, a 102-mm (4-in.)…”

“…The same impact point was utilized in previous testing (Lechtenberg et al, 2012;Rosenbaugh et al, 2010). The damage to the vehicle was moderate with most of the damage occurring on the left side of the vehicle.…”

“…upstream of the W-to-thrie segment. This impact point was identical to previous testing of the transition without curb and was selected to maximize the potential for pocketing, snag on guardrail posts, and loading to the transition element (Lechtenberg et al, 2012;Rosenbaugh et al, 2010). A summary of the test results and sequential photographs are shown in Figures 8 and 9.…”

“…In 2010, the Midwest Roadside Safety Facility (MwRSF) successfully developed and crash tested a simplified, upstream stiffness transition for connecting 787-mm (31-in. ) tall W-beam MGS to thrie beam guardrail transition systems (Lechtenberg et al, 2012;Rosenbaugh et al, 2010), as shown in Figure 1. The upstream stiffness transition consisted of standard 12-gauge Wbeam guardrail, an asymmetrical 10-gauge W-to-thrie segment, and standard 12-gauge thrie beam guardrail.…”