Impact response of overhead sign bridges mounted on breakaway supports. Paper presented at the 50th Annual Meeting of the Highway Research Board HRB, 1971.

Most modern roadways employ overhead sign bridges to relay information to the motoring public efficiently. Collisions with these massive structures have caused serious injuries and fatalities as current installations do not employ safety features that limit impact forces incurred during a collision. The general design considerations and the results of the mathematical simulation of vehicle collision with overhead sign bridges mounted on breakaway supports are presented. The results were obtained through the use of a mathematical model verified by seven full- scale crash tests. A comparison of model and test results is shown and indicates good agreement. The study was performed on a high-speed electronic computer. The findings and the results of the crash tests are: (1) the application of the breakaway concept to the supports of an overhead sign bridge is feasible. (2) the prototype truss possessed the ability to withstand the torsional loads imparted to it by the rotating support, and the structure as a whole remained stable under the impact forces. (3) vehicle-velocity changes and deceleration rates increase as breakaway base and uppe-shear connection resistance increase. (4) occupants of small to medium-size vehicles could possibly suffer injury in a collision with the prototype support. (5) larger vehicles were not severely damaged in collisions with the prototype support. /author/