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The Arkansas River flows through the western fringe of Tusla, Oklahoma, as a wide and shallow, sandbank-studded, tributary of the Mississippi River, located some 300 miles downstream. The city has longed turned its back on its most prominent waterway, though in recent years that relationship has seen a robust reappraisal, most notably with public park projects like the 66-acre Michael Van Valkenburgh Associates (MVVA)-designed Gathering Place, which wrapped up construction in 2018. Williams Crossing, a 1,440-foot-long pedestrian and cycling bridge that opened on September 3, is the latest expansion of the park, and, designed by engineering firm Schlaich Bergermann Partner (sbp), is the first steel-plate arch bridge built in the United States.

The Williams Crossing spans across the Arkansas River, and its curvature offers numerous vantage points. Photo © High Caliber Captures

The project dates back nearly a decade to the initial design and construction of the park and the newly built Zink Dam and its whitewater flume, when it was discovered that the existing bridge, a utilitarian girder assembly, was structurally unsound and in need of significant repair. This provided an opportunity to expand the scope of the project to provide increased connectivity across the river, from Gathering Place to a nature trail on the west riverbank, and to create a new city landmark. The city government provided $27 million for the infrastructural upgrade, and an additional $5 million was sourced from civic backers.

Initially, the client looked west, across the state, to Oklahoma City and its sculptural Skydance Pedestrian Bridge for inspiration, but, ultimately, the design team successfully argued that a system of structural elegance, the first of its kind in the country, would stand on its own right. The principal objectives were to build a more resilient and accessible bridge, which, at its peak, stands 40 feet above the riverbed, well over the high-water mark of a destructive 1986 flood spawned by the remnants of Hurricane Paine—an extreme weather event that saw the old bridge nearly submerged in the floodwaters. The old bridge, just eight-feet wide and a straight shot across the Arkansas River, was also not designed specifically to entice pedestrians.

The whitewater flume offers numerous recreational activities. Photo © Gathering Place

“We are choreographing an experience, that, rather than being an add on to some sort of rail or vehicular route, is an extension of the park,” says sbp project manager Stephan Hollinger. “As an 18-foot-wide public space, one can take in the view of the Arkansas River, and, if curious, figure out how the bridge’s different materials are put together.”

In coordination with the Army Corps of Engineers, the design team received approval to cordon off half of the Arkansas River at a time for the installation of a cofferdam—though a flood event in 2021 swept away the initial intervention—to allow for the drilling of 12-foot diameter foundation shafts from which the bridge’s concrete monopiles rise. The weathered steel structure was transported to Tulsa in 60-foot-long segments, half of the 120-foot spans, by truck from St. Louis. Once on site, they were craned into position and held in place by temporary shoring towers, and then welded together. Notably, the 18-inch-thick reinforced concrete deck, supported by eight-foot-wide steel plates, was built using precast elements as formwork, a move that simplified the erection sequence; and the varying thicknesses of the steel structure’s spandrel plates allow for temperature-induced expansion and contraction.

The steel trusses are light and airy, offering a unique profile and straightforward maintenance. Photo © High Caliber Captures

The bridge’s long spans and weathered steel also help to ease the long-term maintenance costs and operations of Williams Crossing. The airiness of the steel structure limits pockets of moisture from forming that could corrode the steel over time, and its patination removes the need for periodic repainting. In a clever move, the design team integrated a curved steel channel to collect the iron-heavy water runoff of the bridge, which, rather than staining the concrete piers, is then directed to vertical runs at their center, which provides the visual effect of a small layer of steel sandwiched between concrete elements.

“It’s a fun detail, that takes the disadvantage of a material and leverages it into something that accentuates the elegance of Williams Crossing’s thin lines and proportions,” notes MVVA partner Gullivar Shepard. “And, with all sorts of weathering steel details found in Gathering Place, this really has become part of the park.”

The bridge deck offers ample room for pedestrians and cyclists. Photo © The Crossing

Williams Crossing joins several collaborative projects by MVVA and sbp, like Buffalo’s Ralph Wilson Park Bridge, set for completion in October 2024, and the Port Lands Bridges in Toronto, which wrapped up construction in January 2024.