History and Reasons for Research

Over the past decade, the practice of architecture has witnessed the widespread introduction and adoption of new modeling software programs that facilitate the rapid conceptualization of highly complex, curvilinear building geometries. Based on non-uniform rational B-spline geometry that was developed in the automotive, nautical, and aerospace industries, these types of programs have become very popular among designers. Often resulting in surfaces that are dou­bly curved, these building designs inevitably proceed through some process of “post-rationalization" in which the architect’s aesthetic design intent must be reconciled with the realities of construction limitations (budgets), material be­havioral properties, and laws of physics.

One approach often considered in this process of post-rationalization is known as “cold-bending." Cold-bending refers to a practice of fabricating unit­ized curtain-wall panels in a standard process (without any curvature induced) and then bending the panels into a cold-bent condition as they are installed on the face of the building. The theoretical appeal of this approach is primarily twofold: (1) aesthetically, it has the potential to allow designers to realize a con­tinuously smooth, industrial-design-quality reflective surface (as opposed to a faceted surface); and (2) it can prove to be a cost-effective strategy for cladding a building surface of double curvature (relative to the other options available).

Currently, however, architects are often hesitant to pursue this approach. Naturally, there are limits to the amount of bending that can be induced in the panels, but unfortunately there is currently little information available that clarifies these limitations. Manufacturers, fabricators, installers, and designers (and their insurers) are all left to establish their own comfort levels with respect to cold-bending practices in an ad hoc and extremely conservative manner because so little is known about the structural and other performance-related qualities of the glass, the sealants, and the other components of the panels when exposed to long – and short-term bending forces, in combination with the complications of weathering.

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Therefore, the goal of this research is to begin to establish some empirical data with respect to cold-bending. Because this study is necessarily constrained to a single specific set of conditions (particular panel size and aspect ratio, par­ticular panel components by particular manufacturers, etc.) and because the study was primarily focused on the behavior of the polyisobutylene (PIB) pri­mary seal, much more research will be required to develop a more comprehen­sive understanding of the behavior of cold-bent curtain-wall panels. Nevertheless, this research has yielded some valuable insights.