Determination of Small Unit Displacements
The four specimen sets that were tested in the weatherization chamber have been subjected to edge-seal deformations that correlate to maximum strains in the full-size specimen at four values of out-of-plane displacement. These groups represented 0 %, 50 %, 100 %, and 150 % of the maximum design displacement. The maximum design displacement was determined with an engineering judgment. In practical applications, this would depend on the wind pressures, the size or shape of the panels, the makeup of the IGU and many more parameters. The engineering judgment has been made considering the maximum glass stress from the FE model. Numerical tests performed on the model revealed that 8 in. (200 mm) of displacement produces maximum stresses of 4.7 ksi (32 MPa). This is still well below the long-term limit stress of the fully tempered glass but considering additional possible stresses from positive and negative wind pressures, climatic loads and other safety factors, 8 in. (200 mm) of bending has been determined to be a reasonable limit of engineering design. Therefore the maximum applied edge-seal deformations during cold-bending of the full-size unit have been recorded for 4, 8, and 12 in. (100, 200, and 300 mm) of corner displacement. The location of where the PIB is strained the most varies
Copyright by ASTM Int’l (all rights reserved); Tue May 6 12:07:08 EDT 2014
Rochester Institute Of Technology pursuant to License Agreement. No further reproductions authorized.
depending on the stiffness of the framing elements, connections between them and many other factors. From preliminary numerical modeling it has been determined that the location is about 40 in. (1.016 m) below the loaded corner. After the physical tests were performed, the numerical model needed to be revised. These revisions included applying the proper glass offsets, modeling the air pressure in the cavity, considering the pin behavior for the framing members and modeling an accurate location of the applied load. The outcome of the analysis was very sensitive to these minor model modifications but after the above modifications have been applied, the location of the maximum shear displacements of the PIB did not change significantly from the initial model and the modeled system correlated much more accurately to the test data.
To obtain edge-seal strain between the two panes of glass, three dial gauges per location of concern have been used in phase two of the full-scale test. The three dial gauges have been configured to obtain the differential movement along the short edge, the differential movement along the long edge and inplane rotation of the panes with respect to each other at each of the edge locations (Fig. 7). The recorded differential displacements between panes have been converted to the displacement at single points of interest and they have been compared with the numerical results. Because of the sensitivity of the model and some modeling inaccuracies (described above) the results of the model match very well only for selected displacement values. Readings of all six dial gauges compared with numerical results are presented in Fig. 20. Refer to Fig. 7 for dial gauges numbering. Values of edge-seal strains from various locations of the numerical model have been put side by side with the physical results in Table 3. It should be noted here that the edge-seal deformations are applied to the small test specimens on all four edges simultaneously; therefore a displacement that is perpendicular to the long edge of the small specimen will be at the same time parallel to the shorter edge. The strains applied to the small specimens are shown in the right-most column of Table 3 and are summarized in Figs. 21 and 22, 23 and 24 which graphically depict the deformations for the control, 50 % design, 100 % design, and 150 % design specimens, respectively.