In September, Williams Crossing welcomed its first public users across the Arkansas River. As part of the City of Tulsa’s vision for the improved Zink Dam area, schlaich bergermann partner (sbp) was asked to design a new pedestrian bridge that would provide a safe and modern crossing between the east and west sides of the river and replace an existing bridge that was deemed structurally unsound and in need of major repair. The result is the 1,440-ft-long Williams Crossing.
This new symbol for Tulsa provides a connection to Gathering Place, an immense park designed by Michael Van Valkenburgh Associates (MVVA), as well as links to the River Parks and Midland Valley Trails. Williams Crossing is designed for both pedestrian and cyclist access and offers opportunities to stop and enjoy the dramatic river views with seating and lookout areas along the curved 18-ft-wide bridge deck. sbp and MVVA collaborated closely on the design of Williams Crossing to integrate the bridge into the park landscape for a seamless user experience and create a bridge that is an elegant and unique structure for the community of Tulsa.
The bridge was designed in homage to Robert Maillart’s 1933 Schwandbach Bridge near Bern, Switzerland, which is a curved, deck-stiffened reinforced concrete arch bridge. Over the years, sbp has continued to refine Maillart’s elegant deck-stiffened arch concept, first with the 2003 concrete Auerbachstrasse Bridge in Stuttgart, Germany and again with the 2013 hybrid concrete and steel half-arch Footbridge Josenbrücke in Schwäbisch Gmünd, Germany. The extreme slenderness of Williams Crossing’s deck-stiffened steel arches takes this typology a step further.
The deck-stiffened, plate-arch structure is the first of its kind in the U.S., and the bridge is also the first multi-span, plate-arch bridge built in the country.
Lightweight design principles were applied to the bridge’s superstructure to increase the efficiency of the bridge. The semi-integral bridge, which is supported by eleven 120-foot-long arch spans and one 120-foot approach span, was designed with extremely slender arches built from 3-1/4-inch plate of weathering steel. The thickness of the vertical spandrel plates varies throughout the bridge to provide sufficient stability for live loads and at the same time allow enough flexibility to minimize restraining forces during temperature changes. The composite deck consists of an 18-inches-thick reinforced concrete deck and 8-foot wide steel plate with stiffeners that were stiff enough to support the concrete weight during construction.
Optimized and structurally expressed steel nodes allow for the transfer of loads from the superstructure to the substructure where the arch spans meet. The original concept for the nodes considered cast steel fabrication, but due to cost and lead time advantages, milled nodes from forged steel blocks were utilized instead.
To improve the natural hydrology of the river, the total footprint of the piers was reduced (compared to the existing bridge) and the vertical deck clearance was increased to improve resiliency during more frequent 500-year flood events.