Adaptation and Development of NCHRP 350 TL-2 Low-Profile, Concrete Bridge Railing System for AASHTO MASH TL-1 Concrete Bridge Decks
REPORT NUMBER
AUTHORS
PUBLICATION DATE
ABSTRACT
In 2002, the Midwest Roadside Safety Facility (MwRSF), in partnership with the Midwest Pooled Fund Program (MPFP), developed, crash tested, and evaluated a low-height, reinforced concrete bridge railing to meet the TL-2 impact safety standards published in the National Cooperative Highway Research Program (NCHRP) Report No. 350. The 20-in. tall bridge railing was configured with a top width of 14 in. and base width of 11 in., which resulted in a crashworthy system. The low-height, concrete bridge railing system was also configured with a sloped end treatment. More recently, the United States Department of Agriculture - Forest Service – National Technology and Development Program expressed interest in adapting the NCHRP Report No. 350 TL-2 bridge railing for use on reinforced concrete bridge decks where it would be deemed crashworthy according to the American Association of State Highway and Transportation Officials (AASHTO) Manual for Assessing Safety Hardware (MASH) TL-1 impact safety standards. The modification process involved determining the capacity of the NCHRP Report No. 350 TL-2 bridge railing using yield-line and punching shear analytical methods published in the AASHTO Load Resistance Factored Design (LRFD) Bridge Design Specifications. Appropriate modifications were incorporated into the bridge railing, which included changes in width and steel reinforcement to ensure that it would withstand MASH TL-1 impacts scenarios but provide MASH TL-2 structural capacity. A literature review was conducted to obtain common design parameters for bridge deck overhangs, and different combinations of overhangs were evaluated for compatibility with the modified bridge railing system using three design cases corresponding to extreme limit state and strength limit state load combinations. Based on this analysis and design effort, a recommended bridge railing configuration was provided along with example designs for the transverse steel reinforcement used within bridge deck overhangs ranging from 6 to 10 in. thick.
KEYWORDS
USDA-FS, NDTP, Bridge Rail, MASH 2016, Crashworthy, AASHTO, Yield-Line, Punching Shear, Redirective Capacity, Bridge Deck