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January 23, 2008

15 bridges in R.I. are similar to fatal Minneapolis bridge

PROVIDENCE _ State transportation officials have begun recalculating the designs of a small but vital structural part in 15 Rhode Island bridges after a federal warning that a design flaw affecting similar parts may have caused the fatal collapse of the Minneapolis Bridge across the Mississippi River last August.

Kazem Farhoumand, the acting chief engineer of the state Department of Transportation, said the bridge at the top of the list for review is the Sakonnet River Bridge, connecting Portsmouth to Tiverton, which already has a reduced weight posting because of deterioration and is to be replaced.

The other 14 Rhode Island bridges are scattered across the state, from Woonsocket to Westerly. Farhoumand said the DOT reviews will be completed within 60 days, with an outside engineering company, Commonwealth Engineering, evaluating the Sakonnet River Bridge and DOT staff engineers doing the rest.

The National Transportation Safety Board urged the review last week after investigators studying the wreckage in Minneapolis found that 16 gusset plates, at eight joints in its main span, had fractured. Gusset plates are flat, often roughly rectangular, steel plates. They are bolted or riveted to the sides of joints where a steel bridge's beams come together. They reinforce the joints, helping to resist the complex forces that alternately push and pull at them as traffic passes over the bridge and the load on it shifts.

The plates are easily visible on the joints on the Sakonnet River Bridge. Farhoumand said there are 250 such joints on that bridge alone.

Along with the plates, all but one of the Rhode Island bridges are supported by steel trusses and are considered "fracture-critical," or vulnerable to collapse if key structural elements fail.

(The exception, the C.L. Hussey Memorial Bridge in North Kingston, is a concrete arch bridge, not a truss bridge, but has parts like gusset plates, the DOT said. A truss is a structure composed of triangular units built of relatively slender straight members.)

The NTSB urged the owners of similar bridges to calculate whether the gusset plates and other structural elements were designed to be strong enough.

The Rhode Island bridges were already on a list of 37 "fracture-critical" bridges the DOT put together for inspections last year, also at the urging of federal officials, after the Minneapolis collapse, which killed 13 persons and injured 145.

List of bridge on next page.
-- Bruce Landis, Journal staff writer

Posted by Peter Phipps  at 5:30 PM | Permalink

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Bob | January 23, 2008 6:00 PM link

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