The Interstate 70 viaduct in Denver — one of the most heavily traveled spans in the state and rated as “structurally deficient” — will get a $20 million overhaul starting in January.
The elevated highway received a 44 “sufficiency rating,” according to the Federal Highway Administration standard. Anything below a 50 on the 1-to-100 scale is structurally deficient, which means a significant load-carrying element is in poor condition because of deterioration or damage, but doesn’t mean a bridge is about to collapse.
The project will remove half the bridge’s 62 expansion joints between Brighton Road and Colorado Boulevard, a stretch traveled by an average of 140,000 cars a day, said Mark Leonard, a Colorado Department of Transportation bridge engineer.
The highway will be closed at night for the work, which will take several months, Leonard said.
The joints, which are allowing water and a de-icing chemical to seep into the bridge deck and deteriorate the concrete, are the main contributor to the span’s low score, Leonard said.
“If it wasn’t for the expansion joints, this bridge would probably be in a lot better condition,” Leon ard said. “We like to think at least half of the problem will go away with this.”
The project should raise the span’s rating into the 70s, Leonard said.
CDOT is accepting bids from contractors for the project, Leonard said. The work is slated to begin after the National Western Stock Show, which is next to the highway.
The bridge, completed in the mid-1960s, is a “cast-in-place concrete” design.
A design standard among bridges constructed at the time was the inclusion of expansion joints, which allow for flexibility when a bridge expands and contracts in hot and cold temperatures, Leonard said.
“That’s great for someplace like Arizona,” Leonard said. “Here in the northern states, more than 40 years of snowmelt and de-icer have rusted the rebar on the bridge deck and cracked concrete.”
Since the joints are key to the design of the bridge, CDOT engineers had to find a way to maintain the span’s structural integrity during the construction, Leonard said.
CDOT developed a technique to buttress the expansion joints with panels and successfully tested it on four joints earlier this year, Leon ard said.
“Basically, it will be like removing every other joint, and the remaining ones will be repaired to allow twice as much movement,” Leonard said.
The completed project should extend the life of the span 10 to 20 years before replacing the bridge is necessary, CDOT spokeswoman Stacey Stegman said.
A total of $800 million would be needed to rebuild the viaduct, according to an annual inspection of CDOT-owned bridges across the state.
CDOT has completed $60 million in “band-aid” projects to maintain the highway until the funds to build a new bridge that meets current design standards are available, Stegman said.
CDOT has been studying the area around the bridge and should have a final recommendation in 2008.
Some possibilities include rebuilding and widening the bridge to accommodate more traffic or realigning the highway farther north, Stegman said.
“There is a greater need beyond just replacing the bridge,” Stegman said. “Unfortunately, it’s going to take a major shift in transportation funding, and the future looks pretty bleak — $800 million right now is almost our entire budget for one bridge.”
Cassie Hewlings: 303-954-1638 or chewlings@denverpost.com
