Colorado Type 7 and 10 Rails under High Test Level Loads

Colorado impact rail designs follow the AASHTO Standard Specification for bridge deck overhangs, where it uses a 44.5 kN equivalent service load. In the AASHTO LRFD 2000 Code, the impact load was changed to an ultimate static load of TL1 (60 kN) to TL6 (780 kN) without providing design details and the Colorado Department of Transportation (CDOT) began its research to establish design details. Colorado railings in bridge approach usually sit on mechanically stabilized earth (MSE) walls and the impact load transfer from rails to walls becomes critical to rail stability and MSE wall design. Nonlinear quasi-static and impact load finite element analyses were performed to evaluate the stability and impact transfer efficiency of Colorado Type 7 and Type 10 rails with concrete and steel barriers, respectively under TL4 (240 kN) and TL5a (516 kN) impact loads. The finite element modeling demonstrated that the current design was effective at resisting impact loads if the rails were long and continuous. However, the modeling indicated that the system might not perform adequately if the impact occurred close to the end of the rail. Further research is needed to simulate true dynamic loading and to validate the results with actual crash tests.