X: Strong axis
Y: Weak axis
Z: Primary axis
Variable 
Description 
a 
Rotation angle for principal axes of angle section 
A 
Crosssectional area 
Af 
Area of compression flange. 
As 
Shear area for tubular member  pipe 
Asx 
X shear area of prismatic member 
Asy 
Y shear area of prismatic member 
b 
Width of member (b ≤ d) 
b0 
Distance from neutral axis to edge of web: 
be 
Effective width of structural tubing member 
bf 
Width of flange. 
Cb 
Bending coefficient dependent upon moment gradient (section F). 
Cc 
Column slenderness ratio separating elastic and inelastic buckling (section E). 
Cmx, Cmx 
Coefficient applied to bending term in interaction equation (section H). 
d 
Depth of member (d ≥ b) 
E 
Modulus of elasticity 
E0 
Distance of the shear center from center line of web for channel: E0 = e0 + tw/2 
Fa 
Maximum allowable compressive stress 
Fb 
Maximum allowable bending stress 
Fbx 
Maximum allowable strong axis bending stress 
Fby 
Maximum allowable weak axis bending stress 
Fex, Fey 
Euler stress for a prismatic member divided by factor of safety. 
Ft 
Maximum allowable tensile stress 
Fy 
Yield stress 
Fn 
Maximum allowable shear stress 
fa 
Computed axial stress (either tension or compression, both taken as positive) 
fb 
Computed bending stress (taken as a positive quantity) 
fbx 
Computed strong axis bending stress 
fby 
Computed weak axis bending stress 
fnx 
Computed shear stress in X direction 
fny 
Computed shear stress in Y direction 
h 
Clear distance between flanges in Ishaped members: h = d 2tf 
Ix, Iy 
Moments of inertia about principal axes 
Iu, Iv 
Moments of inertia about principal axes of angle section member 
K 
Effective length factor for prismatic member 
L 
Distance between cross sections braced against twist or lateral displacement of the compression flange. 
Lb 
Laterally unsupported length of the compression flange. 
Lc 
Maximum unbraced length of the compression flange. 
Lx Ly 
L in X and Y directions 
M1, M2 
Smaller and larger moment at end of unbraced length, respectively. 
P 
Axial force load 
r 
Governing radius of gyration 
rT 
Radius of gyration of a section comprising the compression flange plus 1/3 of the compression web area, taken about an axis in the plane of the web 
rx, ry 
Radius of gyration about principal axes. 
t 
Thickness 
tf 
Thickness of flange 
U, V 
Principal axes of angle section member 
u, v 
Distances from principal axes 
x, y 
Offsets of centroid of angle section 
Allowable Stresses:
X is the strong axis, and Y is the weak axis for all Ishaped and members and channels. Tees can have either axis as their strong axis.
1. Strong Axis Bending Stress
 
2. Weak Axis Bending Stress
 
3. Tensile Stress
 
4. Compressive Stress
Section E2
where KL/r is the largest of KLx/rx and KLy/ry, which are equal for pipes and squares, and .
 
5. Combined Stress
Chapter H
