At long last, the Hamilton Street on ramp to westbound Interstate 90 is reopening. For good, and ready for this morning’s commute.
New lane configurations are in place. The left lane of the bridge will direct traffic to both directions of travel on I-90, and the right lane will shuffle motorists onto Second Avenue.
The work to repair two aging bridge decks began in July 2018, and was initially anticipated to last through October 2018. Once crews got a look at the rebar helping to hold the bridge up, however, they realized the work would take much longer than they thought.
“We don’t know exactly what we’re going to find in the deck until we get into it,” said Robert Blegen, assistant regional administrator for construction in the eastern region of the Washington State Department of Transportation. “We did not expect the top mat of rebar in the deck to have rusted to the point where they needed to be replaced. That’s very unusual to find in a bridge deck.”
To make matters worse, the Hamilton Bridge is a box girder bridge, which means the deck is part of the structure that holds the bridge up. Remove too much of one deck, in other words, and the bridge is in danger of collapse.
The original plan was to use high-pressure water to remove concrete from the deck and rust from the rebar, and then pour concrete for a new surface. Instead, with less than 80% of the rebar intact, each section had to be carefully “hydro-demolished” and repoured.
“We can only take out a certain amount of concrete at a time without ruining the bridge,” Blegen said. “When you have to go in and replace all the rebar, that takes a lot of hand labor. And it adds a lot of delay.”
It adds cost, too. For this project, the original low bid for construction was $1.4 million. The added work brought it to $2.4 million.
Even with the added cost from the rusted rebar, Blegen said it was much cheaper than full replacement. WSDOT is focused on rehabilitating bridges from the “interstate era” of the 1950s, ’60s and ’70s. Those bridges have reached the end of their life span and fully replacing them would be expensive.
“It’s still 20 cents on the dollar type of calculation,” he said. “It’s still the right way to go and the best use of money.”
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