The leaves of the 91-year-old Wells Street Bridge, a bascule bridge in downtown Chicago, were recently replaced during two nine-day closures. Chicago Department of Transportation
Chicago transportation agencies coordinated to reconstruct a historic multimodal bridge without significantly disrupting transit service.
May 28, 2013—Reconstructing a 91-year-old movable bridge that carries train and vehicular traffic as well as bicyclists and pedestrians in downtown Chicago while minimizing disruption to commuter traffic was sure to be no mean feat. But thanks to close collaboration, the owners, engineers, and builders were able to limit much of the work to just two nine-day construction periods.
The Wells Street Bridge is a dual-leaf, bilevel bascule bridge that traverses the main branch of the Chicago River. It carries Chicago Transit Authority (CTA) trains on its upper level and vehicles, bicyclists, and pedestrians on its lower deck. The bridge carries 12,000 vehicles a day, but perhaps more importantly it is a critical path for the CTA, which transports more than 70,000 passengers across the structure daily. “It’s one of only two bridges in the city that has elevated CTA transit traffic,” says Johnny Morcos, P.E., M.ASCE, a project manager for the Chicago Department of Transportation (CDOT). “The only other bridge that has CTA trains on top of it is Lake Street, and that bridge was rehabilitated when the trains were shut down for a couple of years.”
The Wells Street Bridge has been repaired as needed through the years, but a recent inspection revealed that it was beyond repairs and in need of a complete overhaul. Shutting down the bridge and disrupting train service for months was not an option, so the CDOT coordinated with the CTA to replace the bridge’s movable leaves during two nine-day closures that coincided with scheduled track maintenance to the north and south of the bridge. Two closures were necessary because one leaf had to be maintained and operable at all times to make way for the recreational boat traffic that travels the river. “The biggest concern was, how are you going to accommodate those 70,000 users of the train,” Morcos says. “You can detour roadway traffic, you can detour pedestrians, but there’s no alternate route for those trains. That’s why it was limited to just these nine-day closures.”
Oxygen-fed lance rods were used to cut the gusset plates and
remove the existing leaves. Chicago Department of Transportation
The CDOT put the project out for bid and awarded the construction contract to a joint venture of two Chicago-based firms, Walsh Construction and II in One Contractors. Collins Engineers, also based in Chicago, is the engineer for the general contractor, while AECOM, an international engineering firm headquartered in Los Angeles, served as the designer of record, and Parsons Brinckerhoff, headquartered in New York City, served as the resident engineer. It was up to the contractor and its team to determine the best method for replacing the bridge’s leaves during the established timeframes. “The only requirement that we had was that they could make only two chord connections at once,” Morcos says. “We didn’t want them to try to assemble all four chords at the same time.”
Designed to replicate the existing bridge trusses, the new trusses were constructed off-site prior to the bridge closings. The first closing took place in early March during which the south leaf was replaced; the second took place from April 26 to May 5 during which the north leaf was replaced. A new preassembled truss was floated up the river on a barge before the start of each closure. Then at the beginning of the work period, oxygen-fed lance rods were used to flame-cut the gusset plates of the existing truss, which was then removed. Shoring towers supported the new truss as 250-ton hydraulic jacks positioned at each of the truss’s four corners aligned the truss with the existing chords. Crews had just 1/16 in. of tolerance in which to align each of the 4,000 bolts that were necessary to attach the new trusses to the existing chords, Morcos says.
The new leaves were successfully replaced during the two closure windows and after each closure CTA train service was promptly restored. It is estimated that by coordinating their projects the CDOT and the CTA saved $500,000, according to a City of Chicago press release. Although the trains are back in operation, the bridge remains closed to vehicles, pedestrians, and bicyclists while work on the lower deck and mechanical system continues. The entire project is expected to be complete by December 1. Morcos says the bridge reconstruction exemplifies the goals of Chicago Mayor Rahm Emanuel’s Building a New Chicago program—a three-year, $7-billion coordinated effort among municipal agencies to improve the city’s infrastructure while preserving its history and limiting negative impacts on residents.