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STRUCTURAL GLASS FACADES - USC School of Architecture

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6.2.3 Class Comparisons: Application <strong>of</strong> Evaluation Criteria to<br />

Glass and Glass Panel Types<br />

6.2.3.1 Heat-Treatment<br />

Annealed Glass<br />

<br />

Description: Glass straight from the float process is in the annealed condition. From the<br />

molten state, the glass sheet is slowly cooled in a manner to prevent any residual<br />

stresses resulting from the process.<br />

<br />

Fabrication: The lack <strong>of</strong> residual stresses in annealed glass allows the material to be<br />

easily cut and machined.<br />

<br />

Strength: The modulus <strong>of</strong> rupture (flexure) based on a 60 second load: 6,000 psi<br />

(43N/mm²). (Loughran 2003, p.110)<br />

<br />

Break Pattern: Annealed glass breaks in large sharp shards, and consequently most<br />

building codes restrict its use in public areas; near doorways and walkways.<br />

<br />

Spontaneous Breakage: Nickel-sulfide causes no problem in annealed glass, even if<br />

the contaminant is present.<br />

<br />

Safety: Annealed glass does not qualify as safety glass.<br />

<br />

Optical Distortion: Good quality annealed glass is remarkably free <strong>of</strong> optical distortion.<br />

<br />

Size Limitation: Up to 130 in width (3,302mm), with larger widths available from a<br />

limited number <strong>of</strong> manufacturers (Loughran 2003, p. 113).<br />

246

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