The Monaco Street bridge over Cherry Creek has been cut in half.
One side of the bridge is under heavy construction. Workers in helmets and protective gear walk by, and the sound of welding sneaks in between car horns. The other side is filled with traffic and the occasional pedestrian jumping as a car zooms by the tiny sidewalk.
The $12.7 million replacement project began in October to address steel fatigue, water degradation and overall aging. The Monaco Street bridge was built 60 years ago with steel girders that aren’t so easy to maintain or repair now.
“ [Steel fatigue] is a small stress that's repeated over and over and over again can cause cracking. When that crack propagates, it can happen very suddenly,” said Patrick Bergman, senior engineer with DOTI’s bridge group. The issue, he said, is with the “detailing” of the bridge’s steel components — the way they are designed and connected.
“Steel, if it's not detailed properly or it’s a detail that was popular in the 1960s that has been improved upon since then, is difficult to retrofit. It's difficult to do anything about it in place,” Bergman said.
The project, which also includes an expanded sidewalk, is slated to wrap up next summer.
It’s one of the local Department of Transportation and Infrastructure's biggest bridge replacement projects, but hardly the last one.
In June, the department released a report that identified six bridges in need of repair or replacement. Three of them — the 6th Avenue and Lincoln Street bridges over Cherry Creek, and the Smith Road bridge over Quebec Street — will require full bridge replacements.
The Quebec Street over Airlawn Road bridge also needs to be removed, and the 6th and 8th avenue viaducts are slated for modifications.
Each one was built over 50 years ago.
The city report found about 14 percent of the city’s vehicular bridges are “structurally deficient,” a rate higher than the national average of 9 percent. Close to 80 of the 642 bridges in the city require some form of modification, monitoring or replacement.
“Structurally deficient” means that one of the bridge’s main components — deck, superstructure, substructure or culvert — was rated in poor condition. This assessment is performed by city engineers following guidelines set by the Federal Highway Administration (FHWA) and the National Bridge Inspection Standards (NBIS).
Bergman clarified that a “structurally deficient” rating does not mean the bridges are about to fall down or are “unsafe to operate.” Rather, it’s a call for closer monitoring and assessment to determine which bridges might need rehabilitation or replacement. Some bridges could even be “load posted,” with the city placing weight limits for vehicles on the structure.
A number of factors can contribute to bridge degradation and poor condition: age of the bridge, exposure to natural elements like flooding and traffic patterns. There are also considerations about when the bridge was built and what materials were used at the time.
“The term ‘structurally deficient’ was defined to encompass more than just the structural condition of a bridge, and so it is possible that you can have a bridge in good condition, but it was designed to an older code,” Bergman said. “So it wasn’t designed for the vehicles that it’s seeing nowadays.”
Identifying these projects is just the first step. Paying for them is a different story.
While DOTI currently receives $7 million each year from Capital Improvement Funding for bridge work, city officials say they would need another $22 million per year for bridge work. The city funded the Monaco Street bridge work with the Elevate Denver bond package, which voters approved in 2017.
Now, the proposed Vibrant Denver bond includes nearly $170 million for four of DOTI’s priority projects — the 6th and 8th avenue viaducts and the Cherry Creek bridges. The Quebec Street bridge was included in an initial project list, but was cut out of the final proposal.
Replacement of the Smith Road bridge over Quebec Street was not included.
Voters will choose whether to approve that money — and hundreds of millions for other projects — in November.
