The Ore Bridge Collapse

The Ore Bridge was a moveable crane built around 1920. The main span was a steel box truss structure with a 365-foot span length that was supported by two 100-foot tall steel "legs". Its two supports or legs rested on platforms that traveled simultaneously down two parallel railroad tracks. The bridge suffered severe structural damage in 1991 during a windstorm when the brakes on one of its support platforms failed causing one end of the structure to continue moving down its track while the other end came to a halt. The resulting twisting and skewing of the structure caused significant inelastic deformations in numerous structural members and resulted in one of the bridge's support legs being pulled off its track. During repairs to the structure, the entire bridge and a 125-foot high support tower being used to lift it back into place collapsed. This paper evaluates several different (and rather contradictory) potential failure scenarios advocated by various eyewitnesses and engineers who investigated the collapse, and proposes a scenario which we believe represents the most likely cause of the collapse.