Transportation officials in Ontario believe that 40 bolts securing the deck to beams on one span of the two-span cable-stayed Nipigon River Bridge at Thunder Bay, Canada, failed under uplift forces, which pulled the deck up about two feet. The breech halted traffic on the Trans-Canada Highway, a new $106-million structure that went into service in November. The deck and framing consists of steel beams, plate girders and a precast-concrete deck.

Gerry Chaput, assistant deputy minister in Ontario’s Ministry of Transportation, said the suspect bolts were on the western span of the bridge, which, at 113 meters, is shorter and lighter than the eastern span. Provincial officials say they have verified “the tensioning of the cables” and that the bridge design conformed to code provisions covering wind and temperature. The bearings of the bridge deck, which has been weighted with highway dividers to allow one lane of traffic to remain open, are being monitored