A forensic engineering analysis released today has confirmed previous information suggesting "frozen" rocker bearings caused a southbound approach span of the Birmingham Bridge to collapse onto a pier on Feb. 8.

The force also caused the concrete land pier on which the span sat to shift slightly. It is to be replaced starting this fall at an estimated cost of $8 million.

Dan Cessna, head of Pennsylvania Department of Transportation District 11, said a series of small events over a period of years led to the failure as opposed to a single, major event.

"The report indicated that excessive movement in one direction of the rocker bearing system, caused by corrosion and debris from leaking expansion dams, led to the incident," he said. "Rocker bearings are designed to allow the bridge to flex with traffic and weather and, unfortunately in this case, those bearings were not able to return to an upright position due to the corrosion and debris."

The Post-Gazette reported shortly after the incident that has closed the southbound side of the tied-arch bridge over the Monongahela River that "frozen" rocker bearings were suspect.

PennDOT confirmed the information in preliminary findings that Mr. Cessna discussed with the newspaper one month ago.

He also said 241 bridges have the same of similar type of rocker bearing systems in District 11, encompassing Allegheny, Beaver and Lawrence counties. While some have what he called "issues," none of them are in imminent danger and they will remain open.

However, PennDOT is taking "corrective action" on eight of them, including a Parkway West overpass in Carnegie, where the bearings are being reset as part of a current bridge repair project; the Highland Park Bridge, where wooden shoring has been installed; and the Crosstown Boulevard/I-579 Bridge over Seventh Avenue, where bearings there are also being reset as part of current construction work.

PennDOT said it will continue to inspect, monitor and repair the remaining bridges, including 200 in Allegheny County with the same or similar rocker bearings.

"Many lessons are being learned through this (Birmingham Bridge) incident, here and across the nation, that will allow bridge engineers and inspectors to take steps to ensure this does not happen elsewhere," Mr. Cessna said. "Preventive bridge maintenance was not always our focus due to limited funding but, fortunately, that philosophy has shifted."