Experimental Analysis on Effectiveness of Crash Beams for Impact Attenuation of Overheight Vehicle Collisions on Railroad Bridges: Fid-Bau Portal

Experimental Analysis on Effectiveness of Crash Beams for Impact Attenuation of Overheight Vehicle Collisions on Railroad Bridges

Ozdagli, A. I. / Moreu, F. / Xu, Dan / Wang, Tao

Abstract

Collisions between overheight semitrailer trucks with low-clearance railroad bridges are one of the leading causes for railroad traffic interruptions on bridges in the United States. Current sensing efforts to inform drivers to avoid low-clearance bridges are not effective, and the number of bridge impacts is not decreasing over time. Railroad bridge owners are interested in attenuating the impact by adding crash beams. Furthermore, crash beams can establish safer transportation operations for railroads, roadways, drivers, and pedestrians, especially in congested cities and communities with several transportation modes. Additionally, crash beams can reduce the damage caused by highway strike incidents and can be easily replaced in those low-clearance bridges that are frequently impacted. This paper presents an experimental study for assessing the effectiveness of various crash beams in attenuating the impact consequences of overheight vehicle collisions against railroad bridges. The experimental test setup includes a 1:5 scaled model of a ballast deck through plate girder (TPG) steel bridge. TPG is a common bridge type utilized frequently in the North American rail transportation system, and this study is the first experiment of this size for railroad bridges impact attenuation. The testing setup consists of a pendulum mass impacting the TPG. A realistic collision event is simulated when the steel block attached to the tip of the pendulum swings and hits the bridge girder. The drop height is adjusted to vary the velocity of the collision and the input force to the TPG. Researchers tested three different crash beam configurations under various impact loads to evaluate their ability in attenuating the consequences of collisions compared with a no-crash beam configuration. To achieve this objective, researchers measured total and permanent displacements of the impacted girder, also known as the outside girder, and permanent crash beam displacements. In general, all crash beams attenuate permanent displacements efficiently, which protects the bridge and its ability to carry railroad traffic after impact. This study designs and validates experimentally three different types of crash beams to protect the bridge serviceability and railroad operations after impacts. Further analysis shows that weak crash beams perform better in reducing outside girder permanent displacements for a low-intensity impact compared to strong beams. Conversely, strong crash beams can sustain high-intensity impacts where weak beams are unable to resist. Overall, there is a trade-off between the ability of the crash beam to dissipate impact energy and to sustain impact loads. Thus, engineers should consider the intensity of the expected impact and design crash beams accordingly. In conclusion, this research experimentally quantifies the efficiency of different crash beam configurations, which establishes new methods to inform different designs for the impact attenuation of overheight vehicle–railroad bridge collisions. Future research includes the experimental testing of larger forces and a larger pool of crash beams toward design recommendations.