Discussion of Air Leakage Performance

Air leakage tests were performed at selected racking displacement intervals in order to serve as an indicator of serviceability damage to the weatherseals and structural seals of the test panel. Air leakage test results are summarized in Fig. 8. As shown in the figure, a constant air leakage was measured up to a drift index of about 4 % for mock-ups 1 and 2 and about 5-6 % for the other mockups. Beyond about 4-5 %, a sharp increase in air leakage was generally observed, which was coincident with serviceability failure in the sealant joints.

Observations of sealant damage during these tests suggest that the onset of damage to the weatherseal and structural seals is repeatable and perhaps predictable. However, the mode of failure (in particular, cohesive versus thin film failure), its exact location, and the length over which the failure will occur is variable and somewhat uncertain after the onset of damage. Sealant failures were observed in both the weatherseals and structural seals. During air leakage tests, if there was no observable failure in the weatherseal, air leakage tests would not easily detect failure in the structural seal behind it. A plot of sealant damage length as a function of drift index is shown in Fig. 9, and appears to correlate well with the air leakage data plotted in Fig. 8. The two figures provide a basis for developing a correlation between air leakage rate and visible damage to seals. The AN Lami. and AN IGU configuration mockups had slightly thicker weatherseals than the AN and FT Mono, configurations, and as shown in Figs. 8 and 9, this led to improved air leakage resistance and sealant damage resistance in these configurations.

FIG. 8—Air leakage rates through silicone sealant joints versus drift ratio imposed on the two-side structural silicone mockups.

FIG. 9—Length of sealant damage versus drift index imposed on the two side structural silicone mockups.


Based on the results obtained in this study and comparisons with data collected during comparable studies on dry-glazed curtain walls, several conclusions can be drawn.

• Serviceability and ultimate drift capacities of two-side SSG systems are significantly higher than their dry-glazed counterparts. The magnitude of the increase depends on the glass configuration.

• Wet-glazed end panels within a two-side mockup lead to superior serviceability and ultimate drift capacity performance for all the panels in the mockup than do dry-glazed end panels.

• Glass-to-frame contact at the corner location of horizontal framing members is the cause of glass cracking in two-side SSG systems.

• When compared to comparable dry-glazed systems, the effect of glass type on serviceability and ultimate glass panel drift capacities is not as significant in two-side SSG systems.

• Air leakage tests showed that for the curtain wall mockups tested, beyond a drift index of 4-5 %, air leakage rate increases sharply.

• Air leakage tests and sealant damage observations suggest that there is a strong correlation between air leakage rate and sealant failure length.