Investigation of the Relationship Between Bridge Rail Geometrics and AASHTO MASH Compliance

Abstract

National Cooperative Highway Research Program (NCHRP) Report 350 “Recommended Procedures for the Safety Performance Evaluation of Highway Features” was superseded by the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH) in 2009. MASH contains revised criteria for safety-performance evaluation of virtually all roadside safety features. Changes included new design vehicles and impact conditions that place greater safety-performance demands on many types of roadside safety hardware, including bridge rails. While research has been conducted to understand structural loading demands for bridge rails under MASH, little is known regarding bridge rail geometrics and its’ effect on MASH compliance. To investigate this relationship, finite element computer simulations were utilized to evaluate various bridge rail systems. A critical event in these computer simulations was interaction between the vehicle wheel and bridge rail post. Efforts were made to improve the capabilities of vehicle models to have proper load and failure response to these impact events. The computer simulation results were used to evaluate the current AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications bridge rail geometric design guidelines.