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Attention Span

Project: Animal Bridge, Jackson Park, Chicago, IL

Clients: Illinois and Chicago Departments of Transportation, Chicago Park District

Architects: Johnson Lasky Architects, Chicago, IL (Stone Restoration); CTE, Chicago, IL (Architect, Structural and Civial Engineer)

Contractors: Walsh Construction, Chicago, IL; W.R. Weis, Chicago, IL (Stone Restoration)

By Eve M. Kahn

Some 100,000 cars a day roll in six lanes over a lagoon channel beside Lake Michigan in Chicago's Jackson Park. From a car window, the crossing looks unprepossessing: four sandstone obelisks and some metal slat railings. Only pedestrians, bikers and boaters, taking slow and scenic routes through the park, realize that the masonry structure is a feat of architecture, engineering and zoology.

Chicago-based architect Peter J. Weber designed the bridge as a competition entry in 1903 on a harbor where replicas of Columbus's ships were anchored during the 1893 World's Columbian Exposition. Weber set his elliptical concrete arch on innovative steel reinforcements and posted irresistibly charming water creatures on the side walls. A dozen hippos cohabit with a dozen rhinos, as well as four water gods wearing water-lily-pad crowns and two galleon prows topped in wide-mouthed gargoyles.

"It was a very savvy competition entry," explains Bill Grosche, the stone-restoration project architect with Chicago-based Johnson Lasky Architects (JLA) for the bridge's recent $6.2 million reconstruction. "Weber made references to a much simpler granite elliptical-arch bridge that was already in progress nearby, and then embellished his in the exotic ornament that the fair had made popular."

The competition brief had called for something "substantial and durable," requiring "the minimum expenditure for maintenance, and of suitable strength to carry satisfactorily the greatest traffic that may come upon it." Weber, however, couldn't have foreseen how many commuters would barrel through Jackson Park, and how many pollutants would attack the bridge. JLA assisted Chicago-based CTE's engineering team as part of a $162 million overhaul of six miles of South Lake Shore Drive. Crews have scoured away the bridge's entrenched residues from car fumes, motor oil, coal dust, steel-plant smoke, road asphalt, de-icing salts and graffiti paint. They also rebuilt dozens of vandal-smashed carvings and patched hundreds of chips and spalled spots. Not to mention peeling, dismantling and razing the entire bridge and reconstructing it 20 feet upstream with four new traffic lanes plus bike and pedestrian trails – all without impeding vehicle or boat traffic.

The surrounding marinas and basins were dug into former marshland in the 1890s, based on plans from the Olmsted Brothers. Weber dreamed up what's now called the Animal Bridge while the Columbus ship replicas – plus some ersatz gondolas and Viking boats – were still moored nearby. The German-born architect had started his own firm after a stint working for Columbian Exposition powerhouses Charles B. Atwood and Daniel Burnham. Weber had caught the fair's infectious faith in progress and new technologies. He chose steel rebar for his Animal Bridge with eight-in.-long angled prongs, which Albert Julius Kahn had just invented for factory construction. (Weber went on to moderate professional success; his major work was the Seattle Public Library, a 1906 Neoclassical landmark that was razed in the 1950s and since replaced by Rem Koolhaas' faceted glass box.)

Weber clearly meant the Animal Bridge's galleons, hippos and water deities to harmonize with the aquatic scenery. But why landlubbing rhinos?

"We have no clue," Grosche says. "Was he thinking they were water animals? Or did he just want a head shape similar to the hippo, to alternate in the pattern? And the horns on his rhinos aren't realistic – they're caricatures, much shorter than in real life."

In 1947, as more and more cars clogged Jackson Park, the city abolished the bridge's sidewalks. A steel-pipe supplemental bridge was stretched along stilts 10 feet upstream for pedestrians and bikers. A gas pipe was snuck along the bridge's downstream flank. By the time the project team got to work in 2002, vandals had destroyed one hippo head, one galleon gargoyle's top hat and every rhino horn. Painted "no swimming" signs were staining the cutwaters. Mortar, concrete and oak pilings were failing. "The base of one obelisk had slumped, and it was held in place only by the gas pipe," Grosche recalls.

JLA orchestrated the stone overhaul during the winters of 2002 and 2003. Year-round vehicle traffic and summer boating routes were never disrupted. Each winter, contractor Walsh Construction built cofferdams and cutoff walls to dry out the bridge base; pumps removed some 2.6 million gallons of lagoon water. During the first winter, stone subcontractor W.R. Weis sawed out the granite cutwaters and three-ft.-deep sandstone blocks. Trolleys rolled the pieces along an aluminum monorail attached to the bridge's underside and then cranes hoisted them onto trailers. Meanwhile, the scaffolding was constantly monitored and adjusted to keep it from sinking into the muck. The crew labeled each block and inserted stainless-steel bolts for easy hauling around during scrutiny and cleaning at Weis's facilities.

"We analyzed every animal to see what was needed," Grosche deadpans. Weis and Midwest Pressure Washing put the stones through multiple cleansings and poulticing with PROSOCO products. Stone supplier Galloy & Van Etten, a century-old firm, searched out sources for replacement parts. The pink-gray granite's original quarry in St. Cloud, MN, was still operating. But the salmon-colored sandstone had come from a now-shuttered quarry at Kettle River, MN (the stone didn't sell well, since it's hard to cut and stains easily). Galloy & Van Etten finally tracked down some Kettle River leftovers, moldering in a Duluth, MN, quarry yard.

Paul Petreanu, a sculptor at Galloy & Van Etten, made new carvings while mimicking Weber's array of tool marks – "he specified three or four different textures, for maximum artistic effect," says Grosche. Mortar and epoxy patches also had to be textured; to control costs, artisans used an inexpensive alternative to quarrymen's tools: "We bought a variety of meat mallets at a local Target store," Grosche explains.

To support a six-lane version of Weber's arch, Walsh drove in new steel piles and poured concrete foundations, abutments and wing walls. Egyptian Concrete Co. of Salem, IL, provided precast shells in 21 sections, each five ft. wide. Wood templates, cut to each stone's outline, were used to shape elliptical plywood forms that held the arch stones in place and contained the outboard arches' poured concrete.

Refurbished cutwater stones were rolled along the monorail and then shimmed and dovetailed into place. With two tints of Jahn restoration mortars patching the sandstone, and some faint traces of stains and water absorption for patina, the six-laner already fits well into the maritime landscape.

Boston ivy is growing around the opening of a new concrete pedestrian underpass added below the bridge. Water laps against the freshly quarried St. Cloud granite. Fishermen come for the Coho salmon. Gulls perch on the obelisks, oblivious to the daily passage of 100,000 cars. TB



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