Development of a MASH TL-3 Transition Between Guardrail and Portable Concrete Barriers

Author/Presenter: Bielenberg, Robert W.; Faller, Ronald K.; Lechtenberg, Karla A.; Gutierrez, David; Reid, John D.
Abstract:

Often, road construction causes the need to create a work zone. In these scenarios, portable concrete barriers (PCBs) are typically installed to shield workers and equipment from errant vehicles as well as prevent motorists from striking other roadside hazards. For an existing W-beam guardrail system installed adjacent to the roadway and near the work zone, guardrail sections are removed in order to place the portable concrete barrier system. The focus of this research study was to develop a proper stiffness transition between W-beam guardrail and portable concrete barrier systems. The research objectives were to determine performance and design constraints and to develop a stiffness transition between PCBs and W-beam guardrail that will significantly improve safety for the motoring public and workers within construction zones. The stiffness transition was designed and simulated according to the AASHTO MASH Test Level 3 (TL-3)impact safety standards.This research effort was accomplished through development and refinement of design concepts using computer simulation with LS-DYNA.The research methodology began with a literature review performed on PCB and transition designs. Next, performance and design criteria were developed to allow the researchers to evaluate design concepts. Design concepts for guardrail-to-PCB transitions were developed, discussed, and prioritized. A computer simulation effortwas undertaken to analyze, refine, and evaluate the design concepts under TL-3impact scenarios. Finally, conclusions pertaining to the potential success of each proposed design were made, and recommendations for full-scale crash testing were provided.Two preferred design concepts with a total of fourteen different transition configurations were evaluated using LS-DYNA computer simulationto determine the optimal transition design for evaluation through full scale testing. These design variations included overlapping and offsetting of the PCB segments relative to the guardrail, attachment of the guardrail to the PBCs, use of kicker beam to initiate motion of the PCBs, and use of thrie beam in lieu of W-beam guardrail. Each design configuration was simulated at a variety of impact points and compared based on specific safety performance criteria for the transition, including vehicle snag, barrier pocketing, vehicle stability, and occupant risk criteria. Following the analysis, the design configurations were ranked based on their potential safety performance and presented to the Technical Advisory Committee (TAC). The TAC selected a preferred design configuration that used Midwest Guardrail System (MGS)guardrail with nested W-beam for the transition.Afterselection of the preferred design, the researchers used simulation analysis to determine Critical Impact Points (CIPs) for full-scale testing, evaluate additional impacts along the transition, and analyze impacts on the transition from opposing traffic. This information was combined with the previous analysis to develop the final transition design and recommendations for full-scale testing and evaluation of the transition.Based on this research, the nested-MGS configuration was recommended for evaluation using a full-scale crash testing program. The nested-MGS configuration connected the barrier systems with the W-beam end-shoe attached to the upstream end of the fourth PCB segment with a minimum of three PCB segments extending behind the nested MGS. A minimum of five 12-ft 6-in. long, W-beam sections should be nested upstream from the end-shoe. For testing purposes, the transition should consist of at least a twenty-five post MGS system and an eleven segment PCB system at a 15H:1V flare. The critical impact point should occur at the centerline of the fifth guardrail post upstream from the end-shoe attachment for test designation no. 3-21. The reverse-direction test scenario should use an impact location 12 ft –6 in. longitudinally upstream from the end-shoe attachment for test designation no. 3-21. A simulation effort involving impacts with the 1100C small car was not conducted. The 2270P test vehicle was deemed more critical than the 1100C small car for the concept development phase, due to the likelihood of increased barrier deflections, rail and anchor loads, rail pocketing, and wheel snag. Therefore, test designation no. 3-20 for the full-scale crash testing program should use MASH procedures for determining a critical impact point.