February 26, 2010

JAMES HAEFNER PHOTOGRAPHY

Using a cable-stayed platform allowed having just one large pylon in the structure of Detroit’s Bagley Street bridge.

FEATURE | Roadbuilding

Detroit’s Bagley Street pedestrian bridge uses unique cable-stayed design

RON STANG

correspondent

WINDSOR, Ont.

Detroit’s signature Bagley Street pedestrian bridge for years was an under-the-radar project that, when completed, took local residents and motorists by surprise.

Now it’s a stunning introduction to Detroit as motorists depart the Ambassador Bridge and proceed on to U.S. freeways.

The US$7-million bridge was part of the recent $230-million Gateway project, which aligned expressways and created more efficient ramps for travellers entering the Motor City.

In part, it is the creation of Sudbury, Ont. native and Windsor resident Cory Lavigne.

The bridge, along with several other projects, has brought Lavigne recognition as the American Institute of Architects’ (AIA) Michigan Young Architect of the Year and Detroit Young Architect of the Year.

Lavigne, a graduate of Ryerson University’s architectural science program, with a bachelor of architecture degree from Michigan’s Lawrence Technological University, has been employed at suburban Detroit firm inFORM Studio for almost 10 years.

The boutique firm has been widely recognized. Lavigne described its philosophy as taking a “holistic” approach incorporating design and project materials that “sit and fit” into a community.

As indeed, the Bagley St. Bridge does. The bridge was long ago promised to the low-income but vibrant Mexican Town community in southwest Detroit, which had been bisected by freeways during Michigan’s 1960s urban roadbuilding boom.

On one side are blocks of Mexican restaurants and Hispanic shops. On the other, only a few businesses and forlorn streets, along with iconic St. Anne church, the United States’ second- oldest Catholic parish.

JAMES HAEFNER PHOTOGRAPHY

An asymmetrical 155-foot-high pylon is part of the cable-stayed design of Detroit’s new Bagley Street bridge, which greets motorists crossing the Ambassador Bridge from Canada and entering the city. The bridge design is in part the creation of Sudbury, Ont. native and Windsor, Ont. resident Cory Lavigne.

inFORM won the work after a series of earlier designs had been proposed, many rather conventional.

The project changed due as much to property acquisition and political issues, as to purely practical ones like a desire to reduce the number of pylons among the 10 freeway lanes and ramps over which the bridge crosses.

Lavigne, the project manager and design director, along with inFORM’s Michael Guthrie and Ken VanTine, decided on a cable-stayed platform since it meant having only one pylon.

“It’s essentially a two-span bridge and it’s the first cable-stayed bridge in Michigan,” he said.

The asymmetric concrete and steel pylon is 155 feet high and located one-third way from the eastern edge of the 407-foot-long long deck. That location provided enough room at ground level to accommodate the strut holding the trapezoidal box girder. It also marks the point where the bridge walkway widens from 12 feet to 30 feet, creating an apron that integrates into the plaza of the adjacent community Mercado or marketplace, as well as the Michigan tourism department’s Welcome Center.

The tapered pylon, the work of Chicago-based structural engineering firm HNTB, also leans east, symbolically nodding to those new buildings, constructed to revitalize this neglected half of Mexican Town.

Amusingly, the pylon, constructed before the deck, for several months caused head scratching by passersby, who thought the “big spike” might have been a “mistake,” Lavigne said.

Meanwhile, the bridge’s east apron was designed as a community gathering place that allows views of Detroit landmarks like St. Anne’s, the nearby 18-storey former Michigan Central Railroad depot, and downtown Detroit’s skyscrapers.

On the bridge itself, the cables are strung along the north side.

The west span’s backstays descend into the deck at regular intervals. The east span’s cables come together in a single earth anchor wall at the point where the deck opens north into the apron. The anchor wall chamber includes the mass dampeners.

On the west side, the cables attach to a series of stay pipes, encased in concrete, that penetrate the deck to the box girder below.

Fencing is supported by a two-foot, four-inch cement barrier with nine-foot-high galvanized support posts every 12 feet. Metal fabric fencing comes from GKD. Each post is topped by a light fixture with curved panel to redirect illumination down to the deck.

The east apron incorporates several “nodes” including bicycle racks and a “leisure” section with steel chess and game boards alongside cast-in-place concrete benches.

Lavigne described the project as a “learning curve” requiring “a whole unique approach to dimensioning.” Designing construction elements, based on this “was beyond anything really that we had done up to this point.”

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