Void-Enabled Stage
The REACH at JFK Performing Arts Center
Washington, DC
“Cobiax void forms were used extensively throughout the REACH to help achieve the Kennedy Center’s and the Architect’s vision. The use of void forms with and without post tension provided the design team with the flexibility to achieve the form and function of the interior spaces, creating long-span, column-free spaces, all while supporting landscape and plaza loading.”
At first glance, the three pavilions of the REACH—the Welcome, Skylight, and River Pavilions—appear to be three independent structures planted within a terraced landscape covering about 5 acres. However, upon further inspection, the terrace is a green roof above two levels of interconnected corridors, performance spaces, practice halls, and a parking structure below.
The green roof is supported by a post-tensioned slab incorporating Cobiax void formers to minimize the dead load. Void formers greatly reduce the nonstructural concrete from the middle of the slab, effectively decreasing the dead load and maximizing the overall slab span. During the construction phase, some of the voids had to be eliminated to ensure enough anchorage capacity for formwork loads without impacting the original design parameters for span and deflection. The post-tensioning was also reviewed to ensure adequacy for construction loads.
Throughout, the REACH complex features a variety of exposed concrete finishes and structural and architectural components. The base of the structure is supported by a 2 ft (0.6 m) thick mat on existing caissons and new H-piles, whereas the level above comprises solid slabs (both one-way and two-way), two-way voided slabs, and two-way posttensioned voided slabs. The green roof structure primarily contains one-way post-tensioned voided slabs except for the roof structure over Studio K, which is a post-tensioned one-way slab with a sawtooth soffit.
Project Voided Slab Achievements:
Enabled a flexible column layout
Load reduction: 37 to 104 psf in voided areas
Created large open spans with flat soffits
Combined voided slab and post-tensioned solutions
Noteworthy Article
In the March 2021 issue of Concrete International, author Yvonne Nelson highlights the benefits of voided slabs in combination with post-tensioning in structures, with this project as a prime example. It’s worth noting that post-tensioning on this project worked hand-in-hand with a voided slab system, provided by CobiaxUSA, creating even greater efficiencies as a result.
