Similar to Steel, Aluminum combines axial, shear, and bending to come up with multi-force allowable combinations. All equations must be checked and shown to be less than unity to guarantee that a member works. Usually a majority of equations can be proven not to govern through an engineers judgment and can be ignored (e.g. if no torsion is present in the member then it is safe to assume that the shear + torsion equation will not govern).

For Combined Compression and Bending:

Use the largest of the three equations that follow to determine if the member is okay for the Axial Compression + Bending check:

\frac {f_a}{F_a} + \frac {C_{mx}f_{bx}}{F_{bx}(1-f_a/F_{ex})} + \frac {C_{my}f_{by}}{F_{by}(1-f_a/F_{ey})} \le 1.0

If fa/Fa > 0.15:

\frac{f_a}{F_{a0}}+\frac{f_{bx}}{F_{bx}}+\frac{f_{by}}{F_{by}}\le 1.0

Or if fa/Fa < 0.15:

\frac{f_a}{F_{a}}+\frac{f_{bx}}{F_{bx}}+\frac{f_{by}}{F_{by}}\le 1.0

For Combined Tension + Bending:

\frac{f_a}{F_{T}}+\frac{f_{bx}}{F_{bx}}+\frac{f_{by}}{F_{by}}\le 1.0

For Torsion and Shear in Tubes:

\frac{h}{t} = 2.9\left(\frac{R_b}{t}\right)^{5/8}\left(\frac{L_s}{R_b}\right)^{1/4}

For Combined Shear, Compression, & Bending:

\frac{f_a}{F_a}+\frac{f_b}{F_b}+\left (\frac{f_v}{F_v} \right )^2 \leq 1.0

Simple Shear Check:

f_v < F_v


fa = Calculated Axial Stress
Fa = Allowable Axial Stress (found here?)



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