Thursday, August 14, 2003

By Joe Grata, Post-Gazette Staff Writer

The state will do remedial work on the welded plates fastening the steel beams of a dozen bridges in Allegheny County and two in Beaver County to guarantee that what happened in Wisconsin won't happen here.

That is, a Milwaukee bridge carrying interstate traffic sagged and nearly collapsed into a river after its plates fractured suddenly and set off a chain reaction of cracks in the superstructure.

The same type of welded plates exist on a total of 38 steel girder bridges in Pennsylvania, but minor cracking has been discovered on only one so far -- a Route 422 span near Pottstown, Montgomery County, that already has been repaired.

"We're being proactive," Pennsylvania Department of Transportation spokesman Rich Kirkpatrick said. "We're taking steps now to see that the welds hold and that the web plates won't crack and spread to the main girders in the future."

The remedial work, including drilling "stress relief holes" to stop the spread of cracks should they occur, will cost an estimated $12.5 million statewide and take the next six months to complete.

It will be the third time for weld repairs on the massive Interstate 79 bridge between Robinson and Glenfield that's actually two spans, a 3,700-foot steel arch bridge over the main channel of the Ohio River and a shorter box-beam bridge over Neville Island and the smaller river channel.

A 10-foot crack blamed on an electroslag welding process forced PennDOT to close the back-to-back, six-lane bridges in January 1977, only five months after it held a ribbon-cutting ceremony to open the last link in the 180-mile north-south interstate.

Hairline cracks that started showing up in other pieces of steel necessitated $1.8 million of repairs and preventive work to the I-79 spans during the summer of 1999.

Kirkpatrick said that PennDOT undertook the latest preventive work as part of its bridge inspection and oversight program after being alerted to the bridge problem in Wisconsin. Thirty-nine other states have bridges with the same style of welded steel plates.

The Hoan Bridge carrying Interstate 794 over the Milwaukee River began to visibly sag on Dec. 13, 2000, and was closed the same day. A subsequent investigation, which showed the brittle fracture that was the first of its type in the United States, eventually prompted PennDOT to start remedial action.

"The Hoan Bridge [was] unique in that there was no evidence of fatigue prior to the failure," an investigation by Lichtenstein Consulting Engineer concluded, basically pointing to intersecting welds whose stiffness didn't enable the rest of the steel plates to flex appropriately.

Here's a list of the local bridges with welded steel web plates that are to be modified or retrofitted:

Allegheny County

I-79 bridges -- Over Neville Island, Route 65 and the Ohio River; over Robinson Run; over Route 19; and over Route 246.

Route 28 bridges -- Over Coal Co. Road-Barge Basin, northbound and southbound (counts as two bridges).

Monongahela Bridge -- Over Monongahela River connecting Forward to Monongahela in Washington County.

Clairton-Glassport Bridge -- Over the Mon River.

Birmingham Bridge -- Over the Mon River between South Oakland and the South Side.

Tri Boro Expressway bridges -- Over McKeesport Boulevard, northbound and southbound (counts as two bridges).

Legislative Route 8015 -- Over back channel of the Ohio River.

Beaver County

Route 60 bridge -- Over Brady's Run.

Shippingport Bridge -- Over Ohio River.

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