Investigation reveals cause of cracked bridge girder

Stantec has been hired by the City of Prince Albert, Saskatchewan to undertake an expedited repair of the Diefenbaker Bridge, after an investigation reveals the cause of a cracked girder.

“The City is able to report that the nature of the crack is considered to be a brittle fracture or constraint induced fracture (CIF),” said a City of Prince Albert press release.

“Several contributing factors lead to this type of crack including the steel type, connection geometry of the bridge and fatigue. The research surrounding CIF’s is relatively new, but the research does suggest that the failure occurs without warning and the details are essentially non-inspectable.”

The preliminary results of an investigation, which involved visual and Magnetic Particle/Ultrasonic testing, were reported to the City by a bridge engineer on Sept 27.

Stantec is working in cooperation with experts in the field of CIF to expedite an effective repair of the bridge.

“Work is proceeding to determine the repair of the bridge as a whole and measures to mitigate this from occurring at other locations on the bridge,” said the press release. In the meantime, Prince Albert City Council has expedited the repair process by authorizing City administration to approve the necessary investigative or consulting work as needed.”

The City of Prince Albert was made aware of a crack in one of four support girders of the Diefenbaker Bridge on Aug 29, and initiated the closure of the southbound lanes the next day.

Two-lane traffic was redirected to the northbound lanes and a weight restriction of 15,000 kg (33,000lbs) was been implemented to ensure the integrity of these lanes. It is considered too early in the analysis to increase the weight restrictions.

The northbound and southbound sides of the Diefenbaker Bridge are separate structures, which means what happens on the south side does not affect the north side.

This is why northbound traffic is still permitted.

Work is proceeding to determine the repair of the bridge as a whole and measures to mitigate this from occurring at other locations on the bridge. A repair schedule will be released when available.

In the meantime, Prince Albert City Council has expedited the repair process by authorizing City Administration to approve the necessary investigative or consulting work as needed. City Council will be provided with information reports as the work progresses. .

The Diefenbaker Bridge is owned by the City of Prince Albert, but through a new funding agreement, announced on Thursday, Sept. 15, 2011, with the Ministry of Highways and Infrastructure, the current and future repairs of the bridge will be 100 per cent funded by the provincial government.

The agreement is part of the Urban Highway Connector Program. Previously the maintenance of the Diefenbaker Bridge was cost shared 50/50 with the provincial government. Discussions regarding the designation of the Bridge as a level one, national highway system began in March of this year with confirmation from the provincial government in July 2011 and final approval from City Council on Sept. 12, 2011.