WORLD FOR CIVIL

Size and Volume Factors

For visually graded dimension lumber, design values F_b, F_t, and F_c for all species and species combinations, except southern pine, should be multiplied by the appropriate size factor C_f, given in reference data to account for the effects of member size. This factor and the factors used to develop size-specific values for southern pine are based on the adjustment equation given in American Society for Testing and Materials (ASTM) D1990. This equation, based on in- grade test data, accounts for differences in F_b, F_t, and F_c related to width and in F_b, F_t, related to length (test span). For visually graded timbers [5*5 in (127*127 mm) or larger], when the depth d of a stringer beam, post, or timber exceeds 12 in (304.8 mm), the design value for bending should be adjusted by the size factor

C_F= (12 /d)^1/9

Design values for bending F_b for glued-laminated beams should be adjusted for the effects of volume by multiplying by

C_v=K_L[(1291.5/Ldb)]^1/x

where
L =length of beam between inflection points, ft (m)

d= depth, in (mm), of beam

b= width, in (mm), of beam

width, in (mm), of widest piece in multiple-piece layups with various widths; thus, b ? 10.75 in
(273 mm)

x= 20 for southern pine and 10 for other species

K_L =loading condition coefficient

For glulam beams, the smaller of C_v and the beam stability factor C_L should be used, not both.