Determination of Minimum Height and Lateral Design Load for MASH Test Level 4 Bridge Rails

摘要

The Manual for Assessing Safety Hardware (MASH) prescribes higher design vehicle impact speed and mass for test level 4 barriers compared to its predecessor National Cooperative Highway Research Program (NCHRP) Report 350. This has resulted in a 56 percent increase in impact severity for test level 4. The current American Association of State Highway Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Specifications require test level 4 bridge rails to have a minimum rail height of 32 inches and to be designed for a 54-kip lateral load. These requirements were based on NCHRP Report 350 impact conditions and need to be revised for the higher impact severity under MASH. A recent MASH test 4-21 with a 32-inch tall New Jersey profile rigid concrete barrier, which performed acceptably under NCHRP Report 350 TL-4, resulted in the vehicle rolling over the barrier. This research had the objectives of determining the minimum rail height and lateral design impact load for MASH test level 4 bridge rails. Using parametric finite element analysis and subsequent crash testing, the researchers determined the minimum recommended rail height for MASH TL-4 impact conditions to be 36 inches. Lateral design impact load for MASH TL-4 test conditions was determined to be 80 kips. A 36-inch tall Single Slope Traffic Rail (SSTR) that meets these rail height and lateral load capacity requirements was crash tested. The 36-inch tall SSTR successfully contained and redirected the impacting vehicle.