Alaska's bridges see extra scrutiny after Minnesota collapse

Juneau's bridges in relatively good shape, chief engineer says

Posted: Wednesday, August 08, 2007

Alaska has six steel-deck truss bridges like the one that collapsed in Minnesota last week, but state highway officials aren't worried about any of those. And it also has dozens of bridges with the same "structurally deficient" label as the Minnesota bridge, including the Mendenhall River bridge in Juneau.

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Department of Transportation Chief Bridge Engineer Richard Pratt isn't worried about those either.

"If there's any question about a bridge, we close it down," he said. "The safety of the public always comes first."

Juneau's most prominent bridge, the Douglas Bridge, is also in good shape, Pratt said. Its three components are each rated a seven on a scale of zero to nine, with nine being the highest, Pratt said.

"It's in pretty good shape overall," he said.

It was last inspected in 2005, with another inspection scheduled for this summer, he said.

The National Transportation Safety Board is now investigating the deadly collapse of the Minneapolis bridge, part of an interstate highway crossing the Mississippi River.

Steel deck truss bridges

Spans in Alaska

Kuskulana River between Chitna and McCarthy

Robertson River on the Alaska Highway

Susitna River on the Denali Highway

Nenana River at Moody on the Parks Highway

Icy Bay Big River Center Crossing

Icy Bay Big River West Crossing

After the incident, state bridge officials stepped up some inspections and began waiting for word out of Minnesota about why its bridge unexpectedly collapsed. They also had to describe how bridges are inspected and explain previously arcane terminology such as "structurally deficient."

After a television report on Alaska's bridges, Pratt said he got a call from a member of the public who demanded, "I want to see a list of which bridges are safe to drive on."

Pratt said that while the state has numerous bridges listed as structurally deficient, 124 by last count, they're all safe to cross. That terminology is given to a bridge that may need some repairs and makes it eligible for federal funding. It may be years away from having serious problems, however.

Different bridge elements get rated on a scale of zero to nine, with a one being probably already collapsed and a nine being brand new. To be eligible for funding, at least one element of a bridge must rate a four or below.

"It's not meant to say at all that the bridge is unsafe," Pratt said.

In the case of the Mendenhall River bridge on Glacier Highway, the substructure rated a four due to spalling of the concrete, Pratt said.

Spalling is something that happens to concrete in harsh climates where water enters tiny cracks, freezes and thaws and eventually pits and breaks out parts of the concrete. In the case of the Mendenhall River bridge, the rebar reinforcing-steel has been exposed in places, he said. That will shorten the life of the bridge, but does not pose an immediate safety issue.

"It's not something that has me concerned at this time," he said.

The deck and the superstructure rated a five and a six, he said.

Two of the state's steel-deck truss bridges were in poor shape, but they were on little-traveled logging roads that cross the Big River north of Yakutat.

"The other four were all in really good shape," said Pratt.

One of those bridges crosses the Kuskulana River between McCarthy and Chitna and was built in 1911 to access the rich Kennecott copper mine. Despite its age, it is still fully functional, Pratt said.

Others get more traffic, such as those on the Alaska Highway and the Parks Highway, but remain in good shape as well. Every component is either a five, six or seven.

• Contact Pat Forgey at 523-2250 or patrick.forgey@juneauempire.com.



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