Article 4.31 describes various types of glass available for use in windows. Thickness. Figure 11.33 can be used as a guide to estimate thickness of plate, float, or sheet glass for a given glass area, or the maximum area for a given thickness to withstand a specified wind pressure. Based on minimum thickness permitted by Federal Specification DD-G-451c, the wind-load chart provides a safety factor of 2.5. It is intended for rectangular lights with four edges glazed in a stiff, weathertight rabbet.
For example, determine the thickness of a 108 120-in (90-ft2) light of polished plate glass to withstand a 20-lb/ ft2 wind load. Since the 20-lb/ ft2 and 90-ft2 ordinates intersect below the 3â„8-in glass thickness line, the thickness to use is 3â„8 in. The correction factors in Table 11.14 also allow Fig. 11.33 to be used to determine the thickness for certain types of fabricated glass products. The table, however, makes no allowance for the weakening effect of such items as holes, notches, grooves, scratches, abrasion, and welding splatter.
The appropriate thickness for the fabricated glass product is obtained by multiplying the wind load, lb / ft2, by the factor given in Table 11.14. The intersection of the vertical line drawn from the adjusted load and the horizontal line drawn from the glass area indicates the minimum recommended glass thickness. (See also Art. 11.48.3.) Glass producers should be consulted for more accurate thickness recommendations.
Table 11.15 gives the overall thermal conductance, or U factor, and weight of glass for several thicknesses. Table 11.16 presents typical sound-reduction factors for glass, and for comparison, for other materials. As a sound barrier, glass, inch for inch, is about equal to concrete and better than most brick, tile, or plaster.
Double glazing (Fig. 11.34) is particularly effective where high resistance to sound transmission is required. Unequal glass thicknesses minimize resonance in this type of glazing, and a nonreflective mounting reduces sound transmission. For optimum performance, sound-isolation glazing should be carefully detailed and constructed, and should be mounted in airtight, heavy walls with acoustically treated surfaces.
