C+S November 2020 Vol. 6 Issue 11(web)

ule. The thermal breaks eliminated the need for the usual edge forms that create the joint where the deck joins the balcony slab, saving time and materials to prep the balcony slab after pouring the main deck and letting it set up enough to strip the form, which is the typical sequence.” Eric Feile of Pierce Engineers, a con- sulting structural engineering firm based in Milwau- kee, said, “There’s

Underside of slabs reveal The Spark’s post-tension concrete construction supporting 10 ft (3 m) cantilevered balconies.

Structural thermal breaks are installed at right angles to the post-tension tendons.

always the danger of elements like structural thermal breaks being ‘value engineered’ out of the project. But we fought for them and they stayed a part of the project.” Building codes require tighter building envelopes ASHRAE building codes are requiring continuous insulation of building envelopes to conserve energy. The organization requires separate modeling of uninsulated assemblies, such as balconies, for energy efficiency. Whereas in the past “uninsulated assemblies” could be ignored if these assemblies comprised less than 2.5 percent of the total envelope surface area, the latest ASHRAE code requires remedying uninsulated assemblies with thermal-bridging resistant elements like structural thermal breaks. Further, the state of Wisconsin as of October 2017 has mandated continuous building envelope insulation. Better insulation, better design, better building Nate Lambrecht, Midwest and Western U.S. regional manager of Schöck North America, pointed out that while The Spark is among the first applications of concrete-to-concrete thermal breaks in Wisconsin, Isokorb® installations within the U.S. are becoming more common- place. With global applications exceeding 10 million, North America will surely catch up,” he said. “As municipalities and states increas- ingly adopt energy codes requiring continuous insulation, and owners look for practical solutions to limit liability and durability concerns, the inclusion of structural thermal breaks as ‘best design practice’ will become more prevalent.” “The Spark application has planted the seed for future use of structural thermal breaks,” Feile concludes.

Lopera says the thermal breaks worked well with the post-tensioned concrete structure, allowing for the 10 ft (3 m) long and 12 in. (305 mm) thick balcony slabs to freely cantilever, for a more elegant build- ing. “Structural thermal breaks gave me more freedom as a designer,” he adds. Early planning led to success The architect, structural engineer, contractor and structural thermal break supplier conducted early planning and design meetings to deter- mine the best way to install and integrate the structural thermal breaks with the post-tensioning layout. Eric Lewis, project manager with J.H. Findorff & Son Inc. Construc- tion, of Madison and Milwaukee, said, “This was a first-time experi- ence with Schöck's structural thermal break technology. But the mod- ules became easy to install after the pre-planning and design meetings with Schöck as well as their site visits and instructions and guidance to our crews at first install.” Lewis added that the structural thermal breaks “allowed us to pour the deck and the balcony in the same day, improving the overall sched- Stainless steel tension and shear rebar of Isokorb® structural thermal break ties into carbon steel rebar of interior and exterior slabs prior to casting.

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november 2020

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