A unique “guitar key” shaped ellipse made practical by a voided slab.
PROJECT VOIDED SLAB ACHIEVEMENTS:
Enabled a 1,500 sf curvilinear retail space with a 50’ column-free span.
Worked hand-in-hand with post-tensioning to achieve structural requirements.
Reduced weight while maintaining strength required by code.
The unique design of the building brought forth many challenges. With limited structural walls to support the concrete roof slab, the utilization of voided slab technology supplied by CobiaxUSA was used in conjunction with a post-tensioning system to achieve structural requirements and aesthetic design.
To meet the final design of the curvilinear form allowing for only three elements of exposed architectural concrete, the remainder balanced with walls of solid glass, Becker Structural Engineers, Inc. (BSE), was challenged with limited structural wall to support the roof slab expected to span distances of up to 50 feet. An evolution of design concepts addressed the unique geometry by providing post-tensioned reinforced beam sections within the depth of the flat plate and an innovative solution that would reduce overall slab weight called voided slab technology.
The particular technology utilized by BSE was supplied by CobiaxUSA, and was the first use of this product in New England. CobiaxUSA voided slab technology involves a series of plastic void formers manufactured from 100% recycled plastic, that are encased in the concrete slab and displace an equivalent volume of concrete. The achieved reduction of concrete weight in the slab maintained the strength capacity necessary for code. To improve deflection above the glass curtain wall below and eliminate the need for unsightly deflection joints, BSE proposed post-tensioning within banded sections. This technology counteracted downward deflections by stressing the bands to balance for most of the concrete dead load prior to the shored concrete placement.
This is one of a growing list of projects in the United States using post-tensioning systems in conjunction with a CobiaxUSA voided slab system.
Canal 5 Studio
Becker Structural Engineers (BSE), a Thornton-Thomasetti Company