 Investigators from the National Bureau of Standards for the Occupational Safety and Health Administration (OSHA) discovered several errors that caused the collapse of the bridge section.The most likely cause of the collapse was "the cracking of a concrete pad supporting a leg of the shoring towers".The failure of the concrete pad, built too thinly, led to another finding; bolts that were supposed to connect key stringers to cross-beams instead were replaced with frictional clips, but investigators did not find any documentation that supported this substitution.