In a city of monuments, appearance is important. So, when plans began to come together for the first major expansion of the John F. Kennedy Center for the Performing Arts in Washington, D.C., white architectural concrete was a natural choice.
Architects who dream big continually challenge those who are charged with bringing their dreams to fruition. Such was the case on this project, where the concrete contractor, The Lane Construction Corporation, began working with PERI Formwork Systems very early in the process to develop the detailed project strategy that would be required.
Coming nearly half a century after the construction of the original facility, the expansion project took advantage of the advancements in concrete construction —specifically self-consolidating concrete and 3-D modeling - which made this project buildable, but still far from easy.
Known as the REACH, the expansion consists of three new buildings strategically placed on the 4.6-acre site extending along the Potomac River south of the existing structure. The new structures feature both crisp, clean lines and sweeping curves that complement, rather than replicate, the hewn Carrara marble columns of Edward Durell Stone’s original design and provide a variety of flexible indoor and outdoor spaces.
Numerous facilities were constructed below grade to provide additional parking space, multipurpose rehearsal studios, and classrooms, but the project’s predominant features are three plaza-level structures above grade. All are white cast-in-place concrete with various architectural finishes including multiple board form patterns.
Featuring 36-foot ceilings, The Skylight Pavilion is the largest of the three structures and offers a large that will serve as a public atrium during the day, as well as a space for special events, seated dinners, and receptions. Highlighting the Pavilion is a wave-shaped wall approximately 145 feet (45m) long and 44 feet (4.8m) high, which posed the project’s largest single challenge. (A similar but smaller wave wall also posed formwork design challenges in the River Pavilion due to its proximity to Rock Creek Parkway.)
Unlike common curved concrete walls that are designed with a set radius, the wave wall’s curvature changes continuously, both vertically and horizontally. In addition to geometric considerations, using self-consolidating concrete to achieve the desired architectural finish meant forming and pouring the wall in three lifts of 16 feet or less, with the entire length of each lift being poured at one time.
Because the curvature of the wave wall varies continuously, each of the form panels PERI provided required a unique design. Starting from the architect’s original two-dimensional representation, the contractor developed a 3D virtual model of the wall. PERI engineers further manipulated the model and from that began designing the individual form panels.
Each panel consisted of a plywood face whose shape was defined by individually cut gussets, roughly 10 to 12 inches on center. The 8-foot-wide panels were assembled in PERI’s Elkridge, Maryland yard and shipped by truck to the jobsite.
PERI Formwork collaborated with the contractor as they performed numerous test placements. These efforts ultimately resulted in a design pressure for the formwork of 2,100 pounds per square foot (100 kN/m3), somewhat less than full liquid head but much greater than standard design pressure.
Accommodating the high form pressure and unique geometry required much more bracing than is typically provided for standard concrete placement. This included the unusual need to provide additional bracing along the length of the wall for lateral forces as high as 112 kips (500 kN), in addition to what were essentially bulkheads on each side of the wall forms because of the changes in curvature. Special care had to be taken with both the design and installation of this formwork due to the void slab supporting much of the bulkhead system.
To ensure adequate lateral support along the wall, PERI engineers developed a special tension-compression system (TCS) wherein the panels were connected horizontally to one another in a way that gradually transferred the load to a structural system - rather than to the adjacent panels - ultimately providing a system that prevented the panels from being crushed. The TCS works like a chain to take the loads out of the timber elements and transfer them into the stop-end system, which made it possible to use standard components even for such extremely high forces.
Numerous standard PERI systems were also used to form the more traditional portions of the project. PERI RUNDFLEX panels, which can be shipped flat and then adjusted to the necessary radius on the jobsite, were used on some of the simpler curved walls. PERI’s VARIO system, which can be configured to resist high pressures, was employed on many of the tall, flat walls. PERI’s conventional shoring system, MULTIFLEX, was used throughout the project, and the SKYDECK system was used in constructing the underground parking garage. Much of the bracing was assembled using PERI VARIOKIT components.
The concrete work on the REACH was substantially completed in June 2018. Finishing of the interior spaces is continuing, with an opening set for Sept. 7, 2019.
On the Kennedy Center expansion, the concrete is the project. It required a lot of coordination because there was so much curvature, and not something that could be easily built. We needed architectural buy-in that what we were building and what we were providing was correct. And that all had to be all done prior to PERI manufacturing a single form.
Numerous standard PERI systems as well as custom made solutions