Full-Scale Testing

The full-scale test units consisted of a 10-ft-high by 5-ft-wide (3.05 x 1.52 m2) IGU framed by vertical and horizontal extruded aluminum profiles. Three identi­cal test units were fabricated and each one was anchored at all four corners to its own wood test frame. Each individual wood frame was rigidly connected and sealed to a strong wall integrated with an air compressor capable of producing both negative and positive pressures. During testing the anchor at the same top corner of each test frame was removed to apply the out-of-plane displacement.

A preliminary finite-element model of a full-scale test unit was created to determine the limit of out-of-plane deflections that can be applied in actual con­struction practice. In the model beam, elements represented the framing mem­bers and plate elements simulated a single glass layer. Two adjacent edges of the glass were restrained in the out-of-plane direction, whereas the other two edges were allowed to freely translate. An incremental displacement was applied to the free corner of the model to determine at what displacement the maximum long-term stress in the glass (factored to account for the stiffness two layers of glass in the actual unit) would exceed limits specified in ASTM E1300-07 [8] and Glass Association of North America (GANA) Glazing Manual [9]. The finite – element analysis indicated that 12 in. (300 mm) was the maximum amount one corner of the full-size unit could be pulled out of plane before exceeding the long-term allowable stresses in the glass. A more-refined model was developed later in the project to accurately predict edge-seal strains.

The three test assemblies (a test assembly is the full-scale test unit, wood frame, and associated measurement devices) were each subjected to unique test procedures and data-acquisition methods to evaluate the various behaviors of the IGU under applied cold-bending, and also to validate computer finite ele­ment models. The first test assembly was set up as a baseline test to evaluate the structural capacity of the test unit in cold-bending. Measurements were taken at incremental out-of-plane displacement up to the maximum of 12 in. (300 mm). The second test assembly provided information about the edge-seal deforma­tions between the outer and inner glass layers at the same increments used in

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the first test assembly. The third test assembly was designed to validate the results of the first and second test assembly through comparisons between their strain data, and also to determine if the unit under maximum bending was ca­pable of withstanding repeated applications of static pressure.

All three test assemblies were also designed with measurement devices to correlate their cold-bending and compare strains at specific locations on the glass. However, only test assemblies one and three were subjected to a baseline test performed in accordance with ASTM E330-02 [10] Procedure A. Test assem­bly 2 required access to the displaced corner for measurements and thus could not be sealed to the test wall for pressurization. During the pressure test, the air compressor applied a pressure of 100 lbf/ft2 (4788 Pa) to the glass surface through the sealed pressure chamber. Engineering judgment and prior job ex­perience were used to identify 100 lbf/ft2 as a typical maximum wind pressure that a high-rise building might experience in a 50-year-return period. The struc­tural silicone used as the secondary seal for the IGU and also to attach the insulating glass to the metal frames was sized and designed around the above – mentioned wind load so that the structural silicone would maintain its industry standard 20 psi (138 kPa) design stress. Because of the limited sample size and inherent imperfections in glass, this test provided a necessary baseline perform­ance criterion that units had to pass to be accepted as fit for cold-bending. This test also provided additional information about the deformation states of the cold-bent surfaces under pressure.