Durability of Cold-Bent Insulating-Glass Units
ABSTRACT: Architectural influences upon the commercial building industry have resulted in the design and development of high-performing complex curtain walls that may include bent or warped glass. Glass on modern day curtain-wall projects is mostly insulating glass (IG). When an IG is bent out of plane, a shearing action occurs to both the primary and secondary seals. The testing described in this paper was done to determine the effect on the durability of the IG as measured by argon retention, frost point change, and visual changes after aging in a displaced condition. Full-size IG units, 5 x 10 ft2 x 1 in. (1.52 x 3.05 m2 x 25.4 mm), were fabricated, bent out of plane at 2-12 in. (50-300 mm) in 2-in. (50-mm) increments, and placed under a 100-psf (4788-Pa) wind load. One unit was displaced 15 in. (380 mm) where breakage occurred. An assessment was made based on the data as to what would be a reasonable amount of bending to avoid excessive glass stress and to avoid breakage. This full-size unit was then modeled and measured to predict and validate the stresses and strains on the primary and secondary seals. Upon completion of the bending tests and the review of modeling, small IG units 14 x 20 in.2 (350 x 500 mm2)
were tested according to the protocol specified in ASTM E2188-10 and E2190-10 with an equivalent amount of edge-seal displacement in X, Y, and Z directions. Argon-retention and frost-point measurements were taken before and after the durability testing and results reported. During the durability testing, the glass of several of the units broke in thermal cycling because of high local stresses in the glass. However, the units that did survive the aging protocol passed both frost-point and argon-retention tests, while maintaining their appearance. Additionally, the methodology developed in this research provides a strong foundation for future testing in the area of cold-bent glass durability.
KEYWORDS: insulating-glass durability, ASTM E2190, ASTM E2188, bent glass, cold-bent glass, structural silicone, architectural design feature, PIB durability, argon retention, warped glass, doubly curved glass