F5Doubly symmetric and singly symmetric I-shaped members with slender webs bent about their major axis

This section applies to doubly symmetric and singly symmetric I-shaped members with slender webs attached to the mid-width of the flanges and bent about their major axis as defined in Section B4.1 for flexure.

The nominal flexural strength, $M_{n}$, shall be the lowest value obtained according to the limit states of compression flange yielding, lateral-torsional buckling, compression flange local buckling, and tension flange yielding.

F5.1 Compression Flange Yielding

(F5-1)

F5.2 Lateral-Torsional Buckling

(F5-2)

(a) When $L_{b} \leq L_{p}$, the limit state of lateral-torsional buckling does not apply.

• (b) When $L_{p}<L_{b} \leq L_{r}$

(c) When $L_{b}>L_{r}$

Сьп²Е For SF (F5-4) L

rt

where

$L_{p}$ is defined by Equation F4-7

(F5-5)

rt = effective radius of gyration for lateral-torsional buckling as defined in Section F4, in. (mm)

$R_{p g}$, the bending strength reduction factor, is

(F5-6)

$a_{w}$ is defined by Equation F4-12, but shall not exceed 10

F5.3 Compression Flange Local Buckling

(F5-7)

• (a) For sections with compact flanges, the limit state of compression flange local buckling does not apply.
• (b) For sections with noncompact flanges

(F5-8)

(c) For sections with slender flanges

(F5-9)

where

$\begin{aligned} k_{c} & =\frac{4}{\sqrt{h / t_{w}}} \text { and shall not be taken as less than } 0.35 \text { nor greater than } 0.76 \text { for calculation purposes } \\ \lambda & =\frac{b_{f c}}{2 t_{f c}}\end{aligned}$

$\lambda_{p f}=\lambda_{p}$, the limiting width-to-thickness ratio for a compact flange as defined in Table B4.1b

$\lambda_{r f}=\lambda_{r}$, the limiting width-to-thickness ratio for a noncompact flange as defined in Table B4.1b

F5.4 Tension Flange Yielding

(a) When $S_{x t} \geq S_{x c}$, the limit state of tension flange yielding does not apply.

(b) When $S_{x t}<S_{x c}$

(F5-10)