TTI Research Supervisor: Sofokli Cakalli Associate Research Scientist Texas A&M Transportation Institute Texas A&M University System TAMU 3135, College Station, Texas, 77843-3135 (512) 998-6039 [email protected]
Pooled Fund Technical Representative: Derwood C. Sheppard, Jr., M.Eng., P.E. Roadway Standard Plans Administrator State Standard Plans Engineer Roadway Design Office (850) 414-4334 [email protected]
Background (and Problem Statement)
Problem Statement: When site conditions, such as work zones, result in exposed barrier ends that are different or cannot otherwise be connected due to spacing limitations, a common practice is to overlap barrier segments in the direction of traffic. Overlap length and offset of portable concrete barriers (PCBs) must be adequate to protect workers and redirect errant vehicles without excessive deflections into opposing traffic and avoid the need of anchoring barriers ends. Even though this is a widespread practice in many Departments of Transportation throughout the nation, there is no research conducted to evaluate its crashworthiness. The purpose of this research is to investigate the crashworthiness of the barrier overlap practice for different PCB profiles and produce Manual for Assessing Safety Hardware (MASH) compliant guidelines for the member states (1). A survey will be conducted to identify the common barrier overlap practices and standards used by the member states. Finite element analysis (FEA) will be used to evaluate the performance of different configurations with different barrier profiles. Based on FEA results, two critical configurations will be selected for full-scale crash testing under MASH test 3-11 conditions. A final report recommending MASH compliant guidelines for overlapping precast concrete portable barriers will be delivered
Background: The 2016 MASH edition is the latest in a series of documents that provided guidance on testing and evaluation of roadside safety features. The original MASH document was published in 2009 and represents a comprehensive update to crash test and evaluation procedures to reflect changes in the vehicle fleet, operating conditions, and roadside safety knowledge and technology. The MASH documents supersede the NCHRP Report 350, ‟Recommended Procedures for the Safety Performance Evaluation of Highway Features” standards (2). Overlapping of PCBs is a commonly used roadside safety practice to terminate exposed barrier ends in work zones by many DOTs, predominantly in work zones. Current practices and standards of such practice are not based in research and not MASH crash tested. This study will develop MASH guidelines for overlapping the free ends of two runs of portable concrete barriers when connection of the barriers is not possible due to having different connection types or a gap that is smaller than the barrier segment length. This research will consider the different portable concrete barrier types used by the member DOTs.
Objective
The research objective is to evaluate produce MASH compliant guidelines for overlapping of portable concrete barriers based on full-scale crash testing and finite element analysis. The research will consider different PCB profiles in different configurations as used by the member DOTs.
Benefits
Work zone safety is a major mission for the Roadside Safety Pooled Fund member states. The current practices for overlapping PCBs have not been investigated or evaluated for crashworthiness by any previous study and pose an unknown risk to the safety of motorists and workers. The development of MASH compliant guidelines for overlapping PCBs will significantly increase safety to both motorists and work zone personnel when such practice is needed.
Products
This project will provide a final report presenting MASH compliant guidelines for the practice of overlapping PCBs
Work Plan
The proposed work plan consists of three tasks as described below.
Task 1 – Literature Review & State of Practice | The TTI research team will perform a literature review of previous relevant research for overlapping PCBs. In addition, the TTI research team will conduct a survey among Roadside Safety Pooled Fund members to identify current standards and configuration details for the common practices. Examples of such details are the barrier type, segment length, overlap length, gap between barriers etc. Based on the Task 1 results, the TTI research team will determine the most critical and representative barrier profiles for further evaluation.
Task 2 – Finite Element Simulation Analysis The TTI research team will initially develop detailed finite element models for the barrier profiles selected in Task 1. These profiles will be used to configure FE overlapping barrier systems with multiple segments. The TTI research team will conduct parametric studies to identify the effect of the overlap length and barrier offset to the system crashworthiness. The TTI research team will develop a chart relating the overlap length and the gap between the barrier segments to the maximum deflection of the system based on the parametric studies. MASH does not explicitly recommend a critical impact point for nontraditional roadside safety features such as the overlapping of PCB runs. Therefore, the TTI research team will conduct a parametric study to identify the critical impact point of the system. For the parametric studies, the TTI research team will perform the FE impact simulations with the pickup truck (2270P) and small car (1100C) models according to MASH test level 3 (TL-3) conditions. Based on the FE simulations, the TTI research team will recommend the two most critical configurations for full scale crash testing under MASH test 3-11 conditions with the pickup truck.
Task 3 – System Installation & Full-Scale Crash Testing In Task 3, the TTI research team will perform one full-scale crash test on both configurations recommended in Task 2. Specifically, MASH test 3-11 will be conducted on each of the critical configurations. • MASH Test Designation 3-11: A 5000-lb vehicle impacting the roadside safety system at a nominal impact speed of 62 mi/h at 25 degrees from the normal direction. The research team considers that performing only one full-scale crash test will be sufficient to indicate MASH crashworthiness of this roadside safety feature.
Task 4 – Final Report The TTI research team will generate a final report summarizing the work effort and research findings. The report will present MASH compliant guidelines for overlapping precast concrete portable barriers.
