The Pennsylvania Department of Transportation is working on eight more bridges to correct rocker-bearing problems similar to those that caused a southbound span of the Birmingham Bridge to collapse onto a pier Feb. 8.

Although 241 bridges in PennDOT's District 11, encompassing Allegheny, Beaver and Lawrence counties, rely on rocker bearings to allow for structural expansion, contraction and flexing, it identified only eight others as needing quick attention.

Some measures are minor, such as shoring up several areas of the Highland Park Bridge with large wood blocks, while some are more complicated, such as resetting the bearings on a Parkway West/Interstate 279 overpass in Carnegie, work that's being done under an existing repair contract.

In no case is the traveling public in danger, PennDOT District 11 engineer Dan Cessna said yesterday, when he authorized release of a forensic engineering analysis that confirmed earlier reports about why the span on the Birmingham Bridge over the Monongahela River suddenly failed.

The analysis determined that rocker bearings "froze" over time, mainly from debris and water seeping through deteriorated expansion dams. When the pier moved slightly from the extra pressure, the bearings tipped over, causing the span to drop 8 inches onto the pier cap.

"Many lessons are being learned through this incident, both here and across the nation, that will allow bridge engineers and inspectors to take steps to ensure [this] does not happen elsewhere," he said. "The events of February have changed how we inspect, maintain and repair rocker bearing systems.

"Preventive bridge maintenance was not always our focus, due to limited funding, but fortunately, that philosophy has shifted."

The other six bridges getting PennDOT's immediate attention carry Route 28 over Squaw Run; the Crosstown Boulevard/Interstate 579 over Seventh Avenue; Route 422 over the Shenango River; the 62nd Street Bridge over railroad tracks on the northern approach; Route 28 over Route 8 as part of the Etna bypass; and the ramp from Route 51 north to the Parkway West outbound.

Of the other bridges in District 11 with rocker bearings, PennDOT has determined that 121 have "nonemergency maintenance issues" that will be closely monitored and corrected, when necessary. Ninety-five of them are in Allegheny County.

The forensic engineering analysis noted that the rocker bearings on the Birmingham Bridge had not been properly maintained over the years. It said periodic cleaning and lubricating would have enabled them to function properly.

It said the frozen bearings put different horizontal and vertical forces on Pier No. 10, a land pier between Second Avenue and the north shore of the river, causing the pier to move enough to initiate a tipping sequence. The force from 2.1 million tons of concrete and steel deck further jarred the pier when it fell 8 inches. The pier is to be replaced later this year for an estimated cost of $5 million.

Mr. Cessna said a series of small events over the 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 Birmingham Bridge was reopened to single-lane traffic using the southbound side on March 3. Meanwhile, PennDOT is replacing the rocker bearings on the adjacent northbound pier. Once that is finished, traffic will be shifted and Pier 10 will be rebuilt.

All work is expected to be finished and all lanes of traffic are to be restored later this year on the link between East Carson Street on the South Side and Forbes and Fifth avenues between Oakland and Downtown.

Mr. Cessna and other PennDOT officials appeared before Allegheny County Council last night to explain what happened and to assure members that they're not dealing with a new bridge crisis.