Discussion of Glass Performance at Various Drift Levels

The results of the cyclic racking tests carried out on four different configurations with the same boundary conditions are summarized in Table 2 and Fig. 7. The data for each configuration are the average of its two test repetitions. Drift amplitude (and drift index) corresponding to glass spalling, glass cracking, glass fallout, and glass shattering of only the middle panel (considered the test panel) are plotted in Fig. 7. The data show that FT Mono, glass in the two-side SSG configuration has an approximately 38 % higher drift capacity than AN Mono, before cracking occurs. Of course, for FT glass cracking/fallout/shattering occurs at the same drift value. The FT Mono, configuration also showed slightly higher cracking (15 %) and fallout (5 %) drift capacities than AN Lami. In contrast, the AN 1GU configuration showed larger cracking (13 %) and fallout (16 %) drift capacities than FT Mono. It is obvious that panel configuration is an important parameter in the simulated seismic response of two-side SSG curtain walls.

For a comparison of the expected performance of a given two-side SSG curtain wall on an actual building with the test results shown in Fig. 7, one should note the differences in the boundary conditions between these laboratory mockups and the actual curtain wall installation. These mockups were con­structed under controlled conditions and also had somewhat different boundary conditions than would

FIG. 7—Drift capacities of middle test panels (Fig. 2) observed during two-side structural silicone mockup tests.

curtain walls on actual buildings. Boundary conditions are influenced by a number of factors such as the type of glazing frame, end conditions, and restraints (end panel versus interior panel), and method of attachment of the glazing frame to the structural system. Thus, a quantitative comparison of the failure capacity of the lab mockups in this study to SSG curtain walls on actual buildings cannot be made. One should also note that the ASCE Standard 7-02 [11] design criteria for curtain walls, which is based on life safety, is that the drift causing glass fallout be at least 25 % larger than the building design drift multiplied by the building importance factor. Therefore, to determine the drift capacity of glass in curtain walls for life safety design, the satisfaction of ASCE criterion should be demonstrated. This can be done through mock-up testing that reflects the exact condition of the curtain wall on the real building (e. g., boundary conditions, glass panel aspect ratio, and size, among other parameters).

Previous dry-glazed racking tests on mockups constructed with the same curtain wall framing used for the dry-glazed portions of the mockups tested in this study have shown that the cracking drift capacity of dry-glazed FT Mono, is approximately 87 % higher than that of AN Mono. [12]. When compared to the 38 % difference observed between the FT and AN Mono, two side SSG mockups tested in this study, it is clear that the effect of glass type is reduced in SSG construction. It is also possible to make direct comparisons between the two-side SSG mock-ups test results in this study with the results from previous racking tests on dry-glazed mock-ups [6,12] that were constructed with the same glass configurations, the same curtain wall framing system, and anchored in a similar fashion to the racking facility. For example, Memari et al. [12] reported a cracking drift capacity of 39.1 mm (1.54 in.) for dry-glazed, 6 mm (0.24 in.) AN Mono, glass. As shown in Table 2 and Fig. 7, the SSG system with AN Mono, has a cracking drift capacity of 83 mm (3.25 in.) for the middle panel, which is approximately 112 % higher than its dry – glazed counterpart. Comparisons between the two-side SSG FT Mono., AN Lami., and AN IGU configu­rations and their dry-glazed counterparts also reveal sizable performance gains for two-side SSG systems. These comparisons confirm the widely held view that SSG systems perform favorably in earthquakes.

The test matrix employed in this study also provided some insight into how the boundary condition of adjacent panels and the weatherseal width can affect performance. Mock-up 1, which had dry-glazed exterior vertical edges at its end panels exhibited lower serviceability and ultimate drift capacities in the end panels when compared with mock-up 2, which was constructed with the same wet-glazed detail used for the other mockups in this study (Fig. 1). However, the end panel detail had only a small effect on the performance of the middle “test” panel.