Analysis of the Effects of Construction Tolerances on Bridge Rail Performance

Bridge rails are a type of longitudinal barrier that serves the important purpose of keeping vehicles on the bridge structure. Many different designs have evolved for bridge rails, including some based upon the cross sections used for rigid concrete safety shapes. These designs need to conform to the crashworthiness requirements of NCHRP Report 350 or MASH to be acceptable for use on U.S. highways. This analysis investigates the effects on crashworthiness when construction practices result in the bridge rail taking a cross-sectional shape that varies from the designed and tested version. Crash simulation was utilized to assess the dynamic impact performance for a specific case. The simulations were conducted using trusted vehicle and barrier finite element models from the NCAC models array. A validation exercise was conducted to demonstrate that the simulations provide good representations of vehicle impacts into bridge rails. The barrier model was varied to reflect the as-built features of the bridge rail. Crash simulations were undertaken to replicate NCHRP and MASH tests 4-11 and 4-12 to evaluate the differences in performance. The results were compared both visually and statistically under both NCHRP 350 and MASH criteria and the results suggest that there is little effect on the crashworthiness of the as-built bridge rail. Working Paper NCAC 2011-W-003 September 2011