6  d/b  7 Hold ends in position and both edges firmly in line If a beam is subject to both flexure and compression parallel to grain, the ratio may be as much as 5:1 if one edge is held firmly in line, e.g., by rafters (or roof joists) and diagonal sheathing. If the combined loads will induce tension on the unbraced face of the member, the ratio may be 6:1. *From National Design Specification for Wood Construction, American Forest & Paper Association. direction, deflection can still occur, but in the direction of the strong dimension. Thus, the unsupported length L, width b, and depth d are key variables in formulas for lateral support and for reduction of design values for buckling. Design for lateral stability of flexural members is based on a function of Ld/b2. The beam stability factor, CL, for lumber beams of rectangular cross section having maximum depth-width ratios based on nominal dimensions, as summarized in Table 10.13, can be taken as unity. No lateral support is required when the depth does not exceed the width of a beam. In that case also, the design value for bending does not have to be adjusted for lateral stability. Similarly, if continuous support prevents lateral movement of the compression flange, and the ends at points of bearing are braced to prevent rotation, then lateral buckling cannot occur and the design of value Fb need not be

modification coefficient, R System overstrength factor, o Deflection amplification factor, Cd System limitations and building height limitations (ft) by seismic design category A and B C D E F Bearing wall systems Ordinary reinforced concrete shear walls 5 21/2 41/2 NL NL NP NP NP Detailed plain concrete shear walls 3 21/2 21/2 NL NL NP NP NP Ordinary plain concrete shear walls 2 21/2 2 NL NP NP NP NP Composite eccentrically braced frames 8 2 4 NL NL 160 160 100 Composite concentrically braced frames 5 2 41/2 NL NL 160 160 100 Ordinary composite braced frames 3 2 3 NL NL NP NP NP Composite steel plate shear walls 61/2 21/2 51/2 NL NL 160 160 100 Special composite reinforced concrete shear walls with steel elements Ordinary composite reinforced concrete shear walls with steel elements Special reinforced masonry shear walls 5 21/2 4 NL NL 160 160 100 Intermediate reinforced masonry shear walls 41/2 21/2 4 NL NL 160 160 100 Ordinary reinforced masonry shear walls 21/2 21/2 21/4 NL 160 NP NP NP Detailed plain masonry shear walls 21/2 21/2 21/4 NL 160 NP NP NP Ordinary plain masonry shear walls 11/2 21/2 11/4 NL NP NP NP NP Light frame walls with shear panels 7 21/2 41/2 NL NL 160 160 160 TABLE 5.9 Design Coefficients and Factors for Basic Seismic-Force-Resisting Systems (Continued) Basic seismic-force-resisting system

Screws. Three types of screws, all with cupped Phillips heads are used for attachment of gypsumboard. Type W, used with wood framing, should penetrate at FIGURE 11.24 Gypsumboard base ply attached to wood supports with staples. least 5/8 in into the wood. Type S, used for sheet metal, should extend at least 3/8 in beyond the inner gypsumboard surface. Type G, used for solid gypsum construction, should penetrate at least 3/8 in into supporting gypsumboard. These screws, however, should not be used to attach wallboard to 3/8-in backing board, because sufficient holding power cannot be developed. Nails or longer screws should be driven through both plies. Staples. Used for attaching base ply to wood framing in multi-ply systems (Fig. 11.24) staples should be made of flattened, galvanized, 16-ga wire. The crown should be at least 7/16 in wide. Legs should be long enough to permit penetration into supports of at least 5/8 in, and should have spreading points. When the face ply is to be laminated with adhesive to the base ply, the staples should be spaced 7 in c to c. When the face ply is to be nailed, the staples should be placed 16 in c to c. Adhesives. These may be used to attach gypsumboard to framing or furring, or to existing flat surfaces. Nails or screws may also be used to provide supplemental