The bridge’s main span has over a 35-to-1 span to depth ratio. Its superstructure is an asymmetric V-shaped steel box section with orthotropic stiffeners and open and closed diaphragms. Its thin profile – only two feet deep at the thickest point of the superstructure – maximizes views from the buildings to the waterfront and vice versa.
Steven Holl Architects’ design of the recent expansion of the Kennedy Center for the Performing Arts, dubbed the REACH, provides much needed educational, rehearsal and event space. The new 310-foot-long steel pedestrian bridge reflected the architect’s intent to also provide a direct connection between the Kennedy Center expansion and the riverfront, nearby memorials and pedestrian and bike paths.
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The bridge’s main span has over a 35-to-1 span to depth ratio. Its superstructure is an asymmetric V-shaped steel box section with orthotropic stiffeners and open and closed diaphragms. Its thin profile – only two feet deep at the thickest point of the superstructure – maximizes views from the buildings to the waterfront and vice versa.
The main span at Rock Creek Parkway is over 93 feet, which includes a 22.5-foot cantilever towards the REACH terraces. Though it complements the pavilions that are the centerpieces of the REACH, the bridge does not bear on or transmit any load to the buildings. After skewing in plan at the river’s edge, the bridge’s four additional spans slope down parallel to the Potomac River, with the longest sloping span at over 63 feet. The bridge is supported on five architecturally exposed concrete piers and an abutment located at the base of its ramp.
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The piers, typically oriented perpendicular to the span of the bridge, are supported on concrete-filled steel mini-caissons and concrete caps. Rather than the bridge bearing directly on the piers, the bridge rests on a steel knife plate assembly.
The piers, typically oriented perpendicular to the span of the bridge, are supported on concrete-filled steel mini-caissons and concrete caps. Rather than the bridge bearing directly on the piers, the bridge rests on a steel knife plate assembly.
Silman’s understanding of potential pedestrian-induced vibrations – as well as movements and accelerations caused by wind events – was extremely important, especially given the bridge’s asymmetrical section and extreme lightness. Silman worked with wind engineer RWDI in the early phases of design to develop several strategies to mitigate pedestrian-induced and vortex shedding vibrations. The final bridge design uses five tuned mass dampers (TMDs) within the closed asymmetrical V section: one at the main span cantilever near the buildings, two at the main span over the parkway, and another two at the uppermost ramp span.
Despite the overall bridge assembly occurring over several days, the design and construction team managed to only close Rock Creek Parkway for three days. The final assembly of the main span, cantilever and knuckle was completed on the ground adjacent to the parkway several days prior to the erection. Lifting lugs and load distribution supports were attached to the upper deck following Silman’s review of the temporary effects and the bridge was erected in four lifts.
