## 293 Design of Glass

The linear deflection theory, which assumes that deflections are directly proportional to applied load, is of sufficient accuracy for many engineering applications. However, for a thin glass plate simply supported on four sides, the linear theory is invalidated when the deflection is larger than three fourths of its thickness (Canadian code [4]). The typical load versus central deflection curve for a glass panel is shown in Figure 29.10, and it can be seen that the linear theory is only valid in a small loading range before deflection is significant. The use of the linear theory will result in a deviation from the real solution as shown in Figure 29.10 for deflection and Figure 29.11 for stress. In the linear theory, the location of maximum stress is predicted at the plate center. In fact, the

Center lateral deflection, mm

FIGURE 29.10 Load vs. center deflection of a 4-side simply supported glass pane of2000 mm x 1000 mm x 5.6 mm.

Center lateral deflection, mm

FIGURE 29.10 Load vs. center deflection of a 4-side simply supported glass pane of2000 mm x 1000 mm x 5.6 mm.

location of maximum stress changes with the load level and the aspect ratio of glass plate. This change is illustrated in Figure 29.11. From the figure, it can be seen that the maximum principal stresses at the corner and the center are more or less the same for aspect ratio equal to 1 and load level equal to 0.1 kPa in the glass plate under consideration. When the load level is increased to 0.76 kPa, the maximum principal stress at the corner increases more rapidly than the stress at the center. Thus, the maximum stress location is at the corner of the plate. On the other hand, the rate of increase of the maximum principal stress at the center is much faster than the rate of increase of the maximum principal stress at the corner for aspect ratio equal to 5. In this case, the maximum stress is located at the center of the plate. As mentioned above, the failure of glass depends on the stress state and surface flaws. Thus, there is a need to develop a numerical procedure to find out the stresses at various locations of the glass plate under different load levels in order to determine its load capacity in terms of probability of failure.