Conclusions

The full-scale units that were subjected to wind load of ±100lb/ft2 (4.8 kPa), while under a cold-bend did not break. The initial modeling suggesting at 8 in. (200 mm) of bending as the limitation of our design was a good engineering judgment. The successful completion of testing on assembly 3 shows that the curtain-wall system was able to survive a pressure, which was greater than what the profiles were designed for on a previous project. In fact, the immediate fail­ure of the glass during the over-deflection of 15 in. (38.1 cm) suggests that the initial calculation of long-term glass stress at 12 in. (30.48 cm.) was indeed a good estimation of allowable bending from a glass-stress standpoint.

There were no thermal failures in the control set of small IGUs tested to the ASTM E2188-10 [6] protocol. Additionally, all of the control specimens qualified under ASTM E2190-10 [7] by maintaining a low frost point and high argon retention. This is evidence of the quality of workmanship in the specimens as they were all procured at the same time using the same methodology. Therefore, the workmanship of the other specimens is not in question and the weathering data collected bears this conclusion out.

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The argon was retained in each of the small units that represented deflected large-scale units to the same degree or better than the control group. This is a very positive signal. In no case were the frost points reduced below —90°F (—68°C). Therefore the surviving units must have had the insulating-glass pri­mary and secondary seals remaining intact. Further testing would require an appropriate number of specimens for each specimen set.

The epoxy that was used in this testing was not adequate to be placed under load in the accelerated weathering environments. The adhesive loss of the epoxy was a significant disappointment because the epoxy was thought to be a very – high-performing product. When the epoxy was performing, keeping the glass strained in the Z direction, the glass failed.

The deformations in the X and Y direction of the IGUs did not affect the frost point and argon retention of the surviving units. In fact, because of the creep of the structural silicone secondary seal and the relative stiffness of the silicone protection pad, the X and Y direction displacements increased throughout the high humidity testing. This means that the displacements induced were conservative because they increased throughout the high – humidity phase of testing. This also is a very positive signal. It is very likely that a revision in the method to deflect small insulating-glass units subjected to the ASTM E2188-10 [6] protocol can be done and a full compliance with the ASTM E2190-10 [7] specification can be obtained.

This study was not intended to test the strength of the glass during the weathering cycles, but to test the effect of strains on the primary and secondary seals. The thermal breakage that occurred during the weathering cycling does not constitute a failure in the spirit of this testing, but it is a result of an under­estimation of the physical strength of the tempered glass. The measurements that were taken while the glass was intact suggest that a strained edge seal is quite resilient to moisture infiltration. Further testing may provide evidence in favor of these preliminary conclusions.