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Works continues on the damaged Nipigon River Bridge in Nipigon, Ont., on Jan. 14.Martine Laberge/The Canadian Press

The regulating body for professional engineers in Ontario is investigating the possibility of incompetence in the failure of the Nipigon River Bridge last January, which severed a critical link on the Trans-Canada Highway.

Two engineering reports found that improperly tightened bolts on one portion of the first suspension bridge ever built in Ontario had snapped, causing the steel decking to lift about 60 centimetres.

Other factors that contributed to the failure of the $106-million bridge just six weeks after it opened were the design of the shoe plate and its flexibility, and a lack of rotation in the bearing.

Professional Engineers Ontario says it can initiate investigations in the absence of a complaint being filed "on the reasonable and probable grounds ... of professional misconduct or incompetence."

The regulator says it has a responsibility to investigate "any possible engineering practice deficiencies related to the failure and determine if engineering work was carried out by appropriately licensed people and companies."

The failure of the bridge in Northwestern Ontario forced up to 1,300 trucks – carrying an estimated $100-million worth of goods – to detour each day for several weeks.

One lane of the bridge was reopened to light vehicles one day after the failure when engineers placed huge concrete blocks to lower the deck to road level, but it was nearly a month and a half before a second lane was open to traffic.

The engineering reports released in September found the bearing design for the suspension bridge did not comply with the requirements of the contract.

The shoe plate, the bolted connection between the shoe plate and girder, the bolted connection between shoe plate and bearing, and the bearing design all failed to meet the Canadian Highway Bridge Design Code. The bolts were both too long and not properly tightened during installation, the reports found.

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.

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