This is a factory-fabricated, insulating-glass unit composed of two panes of glass separated by a dehydrated airspace. This type of sash is also manufactured with FIGURE 11.35 Glazing details. TABLE 11.17 Commonly Used Glazing Compounds Compound Type of material Final form Type of glazing Vegetable oil base (skin-forming type) Gun, knife Hard Channel bedding, face Vegetable oil-rubber or nondrying oil blends (polybutene) etc. Gun, knife Hard, plastic Face, channel, bedding Nondrying oil types Gun, knife, tacky tape Plastic Channel, bedding Butyl rubber or polyisobutylene Tacky tape Plastic, rubber Bedding, channel Polysulfide rubber Gun Plastic, rubber Bedding, channel Neoprene (polychloroprene) Gun, preformed gasket Rubber Channel Vinyl chloride and copolymers Preformed gasket Hard, plastic three panes of glass and two airspaces, providing additional insulation against heat flow or sound transmission. (See Fig. 11.35e.) Heat loss and heat gain can be substantially reduced by this insulated glass, permitting larger window areas and added indoor comfort. Heat-absorbing glass often is used for the outside pane and a clear plate or float glass for the inside. However, there are many combinations of glass available, including several patterned styles. Thickness of glass and airspace between can be varied within prescribed limitations. In the selection of a window for double or triple glazing, ac- commodation of the overall glass thickness in the sash is an important

Bracing may be temporary or permanent. Permanent bracing, required as an integral part of the completed structure, is shown on the architectural or engineering plans and usually is also referred to in the job specifications. Temporary construction bracing is required to stabilize or hold in place permanent structural elements during erection until other permanent members that will serve the purpose are fastened in place. This bracing is the responsibility of the erector, who normally furnishes and erects it. Protective corners and other protective devices should be installed to prevent members from damaged by the bracing. In wood truss construction, temporary bracing can be used to plumb trusses during erection and hold them in place until other secondary framing and roof sheathing are installed. The major portion of temporary bracing for trusses is left in place, because it is designed to brace the complete structure against lateral forces. Failures during erection occur occasionally and regardless of construction material used. The blame can usually be placed on insufficient or improperly located temporary erection guys or braces, overloading with construction materials, or an externally applied force sufficient to render temporary erection bracing ineffective. (See Handling, Installing and Bracing Metal Plate Connected Wood Trusses, Truss Plate Institute, Madison, Wis., for guidance in erection of lightweight metal plate connected, wood trusses.) Structural members of wood must be stiff, as well as strong. They must also be properly guyed or laterally braced, both during erection and permanently in the completed structure. Large rectangular cross sections of glued-laminated timber have relatively high lateral strength and resistance to torsional stresses during erection. However, the erector must never assume that a wood arch, beam, or column cannot buckle during handling or erection. Specifications often require that: 1. Temporary bracing shall be provided to hold members in position until the structure

(  )/ F**  1 (10.27) b t b where t
tensile stress due to axial tension acting alone b
bending stress due to bending moment alone
Ft design value for tension multiplied by applicable adjustment factors F*
b design value for bending multiplied by applicable adjustment factors except CL F**
b design value for bending multiplied by applicable adjustment factors except CV Adjustment factors are discussed in Art. 10.5. The load duration factor CD associated with the load of shortest duration in a combination of loads with differing duration may be used to calculate F and F*. t b All applicable load combinations should be evaluated to determine the critical load combination. 10.10.2 Bending and Axial Compression Members subjected to a combination of bending and axial compression (beamcolumns) should be proportioned to satisfy the interaction equation, Eq. 10.28. 2 c b1 b2      1 (10.28) F [1  ( /F )] F [1  ( /F )  ( /F )2]F c ccE1 b1 c cE2 b1 bE b2 where c
compressive stress due to axial compression acting alone