The Ontario Provincial Police posted this photo on Twitter on the damaged Nipigon River Bridge on Sunday, Jan. 10, 2016. An engineering analysis has found that a combination of factors putting strain on bolts led to a bridge failure that severed a critical Trans-Canada Highway link this past winter. THE CANADIAN PRESS/ho-Ontario Provincial Police via Twitter

A combination of design and installation deficiencies of several key components caused a bridge in northwestern Ontario to fail over the winter, severing a critical Trans-Canada Highway link, reports have found.

Two engineering reports, released Thursday, found that improperly tightened bolts on one portion of the Nipigon Bridge snapped, causing the steel decking to lift about 60 centimetres.

Other factors that contributed to the failure were the design of the shoe plate and its flexibility and a lack of rotation in the bearing.

The bridge failure last January, 42 days after it opened, caused up to 1,300 trucks — carrying an estimated $100 million worth of goods — to detour each day for several weeks.

The government estimates the repair work at between $8 million and $12 million, though Transportation Minister Steven Del Duca said taxpayers might not end up footing all of that bill.

"The reports tell us why the bridge malfunctioned," Del Duca said in an interview from Nipigon. "What the reports don't tell us is the extent to which, or percentage of which, who was responsible for every single piece."

The government has had an "initial conversation" with the contractor, he said.

"I think it's fair to say that there's a lot of responsibility to go around for this one," Del Duca said. "Now we need to go through a process to make sure that the responsibility or the liability for what's taken place is apportioned in a manner that's appropriate."

The bearing design did not comply with the requirements of the contract, the reports said. And the shoe plate, the bolted connection between shoe plate and girder, the bolted connection between shoe plate and bearing, and the bearing design all failed to meet the requirements of the Canadian Highway Bridge Design Code.

Additionally, the bolts were both too long and were not properly tightened during installation, the reports found.

NDP transportation critic Wayne Gates put the blame on the Liberal government.

"(They) didn't take their project oversight responsibilities seriously," he said in a statement. "Any engineering and design installation failures should have been caught before the Ministry of Transportation opened the Nipigon Bridge to passenger traffic in the first place."

There were also bolt polish marks on another part of the bridge, "suggesting that it was also experiencing bolt bending and was prone to a fracture similar to the north-west bearing failure," according to one of the reports.

Lives were put at risk, said Progressive Conservative critic Michael Harris.

"This was clearly a disaster waiting to happen," he said. "I know (when) we're all at home and we do a little repair we look to the toolbox and we find a wrong sized bolt to patch up something — that shouldn't be happening in a $106-million infrastructure project in the province of Ontario."

A temporary fix was put in place in February, but the government says a permanent retrofit design has now been developed and that design will also be used on a portion of the bridge that is still under construction.

News from © The Canadian Press, 2016