Volume 42, Issue 4 - April 2007
The Tie That Binds: Structural Glazing Sets Design Standards
by Peter Poirier
Architectural specifications today call for metal framing to virtually disappear, providing clean and minimal sight lines. LEED certification calls for the utilization of natural light and outdoor views, with minimal reliance on heating and cooling systems. Architects are designing structures with increasingly larger and more dramatic window units. Building codes are requiring protection against man-made and natural disasters. Creating such structures had once seemed a tremendous challenge, but is now an everyday occurrence, made possible through the use of high-performance, structural silicone glazing systems.
Ensuring the effectiveness of these demanding requirements depends on having a structural glazing system designed and tested as a complete and unified assembly. All of the components used in the system must be compatible. Some glazing gaskets and spacers, for example, may be chemically incompatible and cause a loss of silicone adhesion to the glass and metal surfaces; staining could also occur. The system’s adhesion, weatherability and durability over the long-term depend on all products being compatible throughout their productive life.
The Nelson-Atkins Museum of Art [expansion project] in Kansas City, Mo., added 165,000 square feet of space to the museum, increasing its size by some 70 percent at a cost of $200 million. The project, however, was not typical; in fact, the international architectural community called it “the most difficult and complex project in the world today.”
The design encompassed five glass structure “lenses,” which look like monolithic, glassy sculptures or blocks of ice lying on the landscaped lawns. Some of the glass is square cut and some is the shape of a trapezoid as the buildings follow the contour of the landscape. This glass, though, is also used structurally, as it carries its own weight and transfers the forces that are imposed on it. It is not framed, and, to add to the complexity, the architects wanted all joints to disappear, again pushing the limits of anything ever done before.
To complicate matters further, Kansas City is in a part of the country known for tornadoes and seismic conditions. As a result, the project required an expansion joint system that could respond to extreme conditions of up to +/- 5 inches of movement in each direction.
Thermal movement is also a daily consideration. To ensure performance, the museum underwent a series of 39 tests for some of the most extreme conditions. Though wind-tunnel studies established expected wind loads, testing was still done for up to 60 percent more.
Making it all Work
the author: Peter Poirier is the technical director – glazing for Tremco Glazing Solutions Group in Beachwood, Ohio. Mr. Poirier’s opinions are solely his own and not necessarily those of this magazine.