Construction crews this summer made significant progress on a multi-million dollar project that marries safety with art and may one day redefine the landscape along Lake Michigan.
On Chicago’s wish list for at least a decade, the Navy Pier Flyover is an elevated pathway along the 18.5 mi. (29.8 km) Lakefront Trail designed to provide a safer route for pedestrians and bikers who now share it with vehicles in places Sen. Dick Durbin, D-Ill., described as “You take your life in your hands.”
“When Mayor Emmanuel did his ground breaking speech, the one thing they touched on was that this is going to take a dangerous area on the Lakefront Trail where cars, bikes and people co-exist and it will separate them,” said Dan Anderson, a senior construction engineer of T.Y. Lin International, which is consulting with the city of Chicago on the project.
“The Lakefront trail kind of goes down on lower Lake Shore Drive and through some very busy intersections. This is basically a grade separation to get bikes and pedestrian off the road.”
The project is scheduled to be completed in three phases. Crews began work on the $22.5 million first phase last spring and expect to finish it in late 2015. Each phase is expected to take about two years, with completion of the $60 million project set for 2018. Contractor F.H. Paschen/S.N. Neilsen was the low bidder for phase one. The latter two phases have not yet been bid.
The largest challenge of building the structure is the fabrication aspect and the fit up of the pieces while they are being erected, Anderson said.
“The main scope is construction of the pedestrian structure. Steel columns, steel spine and a concrete deck. It’s a freestanding structure and part of it is actually built onto the side of Lake Shore Drive. It’s not a huge amount of concrete, only 900 cubic yards. The structural steel is more significant, estimated at about, just the pipe alone, 370,000 pounds. The rest is another 500,000 pounds. It is a significant part of what makes this a complex structure.
“The geometry of the entire steel spine — the pipe carrying the structure — is on average 2 and a half feet diameter with 1 and a half inch pipe walls. It’s got horizontal and vertical curves. The steel spine pipe is bent to follow the profile of the bridge. That design is pretty much for the aesthetics. It’s got the center big pipe running through the middle and ribs attached to side of pipe, almost like little wings, and then the deck is poured on top of those ribs.”
The flyover, so named for its location near the Navy Pier and its ability to carry users uninterrupted over congested streets, as well as the Chicago River and DuSable Park, runs from one ramp at ground level to a second over Upper Lake Shore Drive at about 20 ft. (6.1 m).
There are about 25 construction workers on the job daily, but while construction is occurring near heavily congested areas, there has been little interruption in traffic for city commuters.
“The road closures aren’t significant,” he said. “We did have one lane of upper Lake Shore Drive closed while we attached a portion of the new structure to the side of the upper Lake Shore Drive bridge. But it’s not going to significantly impact traffic other than some temporary closures, which we try to restrict to nighttime when we set the steel over the road.”
Other than the challenge of building the spine, the other significant challenge is that the design is architectural. It is meant to be a future icon of the city scape.
“There are a lot of stainless steel elements to it,” Anderson said. “There is a lot of custom LED lighting. Just the architectural aspect… It’s really supposed to be something to look at down at the Lakefront. I think it’s definitely something everybody will see who comes to this area. It’s right adjacent to Navy Pier, where a lot of people come through on a day-to-day basis. Not only will users of the Lakefront Trail see the architectural elements, but also people passing under.”
Those elements are so important, the city built full scale mock-ups for three sections of the flyover to ensure all the various pieces worked as they’d anticipated.
“That was so the Department of Transportation could look at it and say this is what it’s supposed to look like on the plans, but here is what is actually going to look like, to make sure all the details work together,” Anderson said. “The mock-ups were small sections of the superstructure so you can see the spine … a 10-foot-long section of what the bridge is actually going to look like. So if there are any real difficulties in construction of the mock-up, as well as aesthetically, we can address those situations before we start production of the actual bridge. These are freestanding models. The actual size, built out of the actual construction materials. The reason certain agencies do it this way is they want to make sure before they start fabrication and construction of the actual bridge that this is the way they want it to be because it is so architectural, because there are so many disciplines working together.”
The project is funded by the U.S. Department of Transportation using Congestion Mitigation Air Quality Improvement (CMAQ) monies, with additional funding from the State of Illinois.
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