STRUCTURAL GLASS FACADES - USC School of Architecture

Optical Distortion: The heat-treating process can result in certain distortions to the
glass, such as roller-wave (see Chapter 2).
Size Limitation: Viracon, the largest US glass fabricator, limits tempered glass sizes to
84" x 165" or 96" x 144" (2134 x 4191 or 2438 x 3658mm); see Table 2-9.
Application: Heat-strengthened glass is used where higher strength is needed to
handle thermal stresses or concentrated loads. It is twice as strong as annealed glass,
and can be used in point-fixed glass applications. It is however, only half as strong as
fully tempered glass, and a thicker glass may be required for a given application. Heatstrengthened
glass has the benefit of being free from the concern of spontaneous
breakage. It is sometimes used in point-fixed systems in combination with a tempered
ply in a laminated panel in overhead or sloped glazing applications. The heatstrengthened
pane is used as the outer ply. In the unlikely circumstance that both panes
break, the theory is that the larger shards of the heat-strengthened ply will go into
compression as the panel sags, and thus help prevent drop out of the panel.
Tempered Glass
Description: Glass is strengthened in a heat and quench process referred to as
tempering or toughening. Tempered, or fully-tempered glass is subject to the same
process as heat-strengthened glass, except that it is heated to a higher temperature.
Tempering produces a glass with maximum strength properties and a unique break
pattern.
Fabrication: All fabrication; cutting, holes, counter-sinking, sandblasting, must be
completed before heat-treating.
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