CIVIL ENGINEERING FORMULAS

TIMBER ENGINEERING FORMULAS 165

For shear, the adjusted design value FVis computed from

(6.21)

whereFVis the design value for shear and CHis the shear stress factor 1—
pemitted for FVparallel to the grain for sawn lumber members.
For compression perpendicular to the grain, the adjusted design value is
obtained from

(6.22)

where is the design value for compression perpendicular to the grain and
is the bearing area factor.
For compression parallel to the grain, the adjusted design value is given
by

(6.23)

whereFcis the design value for compression parallel to grain and Cpis the col-
umn stability factor.
For end grain in bearing parallel to the grain, the adjusteddesign value, is
computed from

(6.24)

whereFgis the design value for end grain in bearing parallel to the grain.
The adjusted design value for modulus of elasticity, isobtained from

(6.25)

where Edesign value for modulus of elasticity

CTbuckling stiffness factor—applicable only to sawn-lumber truss

compression chords 24 in (50.8101.6 mm) or smaller, when

subject to combined bending and axial compression and plywood

sheathing in (9.5 mm) or more thick is nailed to the narrow face

Cother appropriate adjustment factors

Size and Volume Factors

For visually graded dimension lumber, design values Fb,Ft, and Fcfor all
species and species combinations, except southern pine, should be multiplied
by the appropriate size factor Cf,given in reference data to account for the
effects of member size. This factor and the factors used to develop size-specific

(^3) 
8

EECMCTC

E

FgFgCDCt

Fg

FcFcCDCMCtCFCp

Fc

Fc Cb

FcFcCMCtCb

Fc

FVFVCDCMCtCH