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Area bridges deemed safe

DOT: Poor ratings due to decking, not structural concerns

Posted: Wednesday, August 08, 2007

Four small bridges critical to transportation on the Kenai Peninsula are among more than 100 across Alaska considered in some way structurally deficient.

A span over the South Fork of the Anchor River at Mile 161 of the Sterling Highway, and bridges crossing Deep Creek, the Ninilchik River and Kasilof River between Miles 109 and 136 have decks considered in "poor condition," said Rich Pratt, chief bridge engineer with the Department of Transportation's Division of Design and Engineering Services in Juneau.

The collapse of a bridge in Minneapolis during rush hour Aug. 1 has raised interest in other states about the shape their structures are in.

None of the bridges on the peninsula is about to collapse not even close. But they are in need of repairs to their decks, Pratt said.

State inspectors use a system that assigns numerical values (9 to 0) to various parts of the bridges. Those numbers translate as: 9) Excellent Condition, 8) Very Good, 7) Good, 6) Satisfactory, 5) Fair, 4) Poor, 3) Serious, 2) Critical, 1) (in danger of) Imminent Failure, and 0) Failed.

Bridges warranting a 0 or a 1 are immediately closed. Those with ratings of 2 or 3 likely would get load limits, Pratt said.

Bridges are inspected at least once every two years, Pratt said, and all four of the Sterling Highway bridges above were inspected in 2005 and have been or will be inspected this year. Based on the 2005 ratings, DOT has designed a project to rehabilitate the decking on all but the South Fork Bridge in the summer of 2008.

Old decking will be junked and new concrete laid. Pratt said he believes the project also will involve repainting steel girders.

The South Fork Bridge, meanwhile, is in a section of the highway (Miles 157-169) between Anchor Point and Baycrest Hill near Homer that is due to be rebuilt. The bridge will be handled within that project and either rehabilitated or rebuilt at that time, Pratt said.

The deck of the Deep Creek Bridge was rated a 4, while its superstructure got a 6. So did its substructure.

The Ninilchik Bridge got respective ratings of 4, 5 and 7, while the bridge over the Kasilof got a 4, 7 and 7.

Thus, the most critical parts of these structures are considered fair to good and hence, safe.

The bridge at the South Fork of the Anchor River, meanwhile, got a deck rating of 4. Its superstructure was also rated a 5, and its substructure a 4.

The numerical designations are financially important because any rating at 4 or below makes the project eligible for federal highway dollars. That is the case with the three scheduled for redecking next summer, Pratt said.

Two-person teams that include a professional design engineer and another engineer or technician typically make visual inspections of the bridges along a route. Specific observations are written up and recommendations are made for repairs where necessary, Pratt said.

Hal Spence can be reached at hspence@ptialaska.net



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