Development of a MASH TL-4 Open Concrete Bridge Rail

Abstract

A new open concrete bridge rail was developed to satisfy the safety performance criteria of AASHTO’s (American Association of State Highway and Transportation Official’s) Manual for Assessing Safety Hardware (MASH) Test Level 4 (TL-4). The railing design was optimized to minimize vehicle snag, contain large openings for drainage and aesthetics, minimize installation costs, and have the capacity to withstand MASH TL-4 impacts. Additionally, the railing was designed to be crashworthy before and after roadway overlays up to 3 in. thick. The new barrier was designed with a height of 39 in. and a width of 14 in. Posts were 36 in. long, by 10 in. deep, by 12 in. tall, and were set back 4 in. from the face of the railing to minimize the risk of vehicle snag. The inelastic post-and-beam method found in Section 13 of AASHTO LRFD Bridge Design Specifications was modified to account for differences in failure shapes between steel and concrete post and beam railings. The modified method also adjusted the height for the applied design load to match the recommended 30 in. height for tall TL-4 barriers. This modified analysis method was used to optimize the barrier geometry and reinforcement. The new open concrete bridge rail was then subjected to crash testing in accordance with MASH TL-4. All three tests, MASH Tests 4-10, 4-11, and 4-12, resulted in successful capture and safe redirection of the vehicles. Thus, the new open concrete bridge railing was deemed MASH TL-4 crashworthy.