This report summarizes the research efforts of using finite element modeling and simulations to evaluate the performance of NCDOT double-faced W-beam and Thrie-beam guardrails at different installation heights under Manual for Assessing Safety Hardware (MASH) Test Level 4 (TL-4) and Test Level 5 (TL-5) impact conditions. A literature review is included on performance evaluation of W-beam and Thrie-beam guardrails as well as applications of finite element modeling and simulations in roadside safety research.
The modeling and simulation work was conducted on six double-faced W-beam and Thrie-beam guardrails (with placement heights of 29 and 31 inches) placed along a six-lane 46-foot wide flat median. Two types of Thrie-beam guardrails, one utilizing a wood blockout and the other with a steel blockout, were evaluated. Under MASH TL-4 conditions, the guardrails were impacted by a 1996 Dodge Neon and a 2006 Ford F250 at 62 mph (100 km/h) and an impact angle of 25° and by a 1996 Ford F800 single-unit truck at 56 mph (90 km/h) and an impact angle of 15°. Under MASH TL-5 conditions, the guardrails were impacted by a 1996 Dodge Neon and a 2006 Ford F250 at 62 mph (100 km/h) and an impact angle of 25° and by a 1991 GMC day-cab tractor-trailer at 50 mph (80 km/h) and an impact angle of 15°. The guardrail's performance was determined by evaluating the guardrail deflection and vehicular responses based on the MASH exit box criterion, MASH evaluation criterion F, exit angles, yaw, pitch, and roll angles, transverse displacements, and transverse velocities.
The simulation results demonstrated the effectiveness of the double-faced 29- and 31-inch W-beam guardrails and Thrie-beam guardrails, with wood- and steel-blockouts, placed on a flat median under MASH TL-4 and TL-5 impact conditions. Under impacts from the passenger vehicles (i.e., Dodge Neon and Ford F250) the W-beam and Thrie-beam guardrails with 29- and 31-inch placement heights were shown to effectively redirect the vehicles in all cases, although in some scenarios, a large exit angle was observed. Under impacts by heavy trucks (i.e., single-unit truck and tractor-trailer), the W-beam and Thrie-beam guardrails with 29- and 31-inch placement heights were shown to be effective at containing the vehicle on the impacting side, but exhibited a high likelihood for vehicle rollover. Finite element modeling and simulations were shown to provide an effective means for studying crash scenarios that are difficult and/or extremely expensive to investigate with physical crash testing.