F9Tees and double angles loaded in the plane of symmetry

This section applies to tees and double angles loaded in the plane of symmetry.

The nominal flexural strength, Mn, shall be the lowest value obtained according to the limit states of yielding (plastic moment), lateral-torsional buckling, flange local buckling, and local buckling of tee stems and double angle web legs.

F9.1 Yielding

(F9-1)

where

(a) For tee stems and web legs in tension

MP-F,Z,≤1.6M, (F9-2)

where My = yield moment about the axis of bending, kip-in. (N-mm) -FxSx (P9-3)

(b) For tee stems in compression

(F9-4)

(c) For double angles with web legs in compression

(F9-5)

F9.2 Lateral-Torsional Buckling

• (a) For stems and web legs in tension
• (1) When $L_{b} \leq L_{p}$, the limit state of lateral-torsional buckling does not apply.

(2) When $L_{p}<L_{b} \leq L_{r}$

(F9-6)

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

(F9-7)

where

• (b) For stems and web legs in compression anywhere along the unbraced length, $M_{c r}$ is given by Equation F9-10 with

(F9-12)

where

$d=$ depth of tee or width of web leg in compression, in. (mm)

• (1) For tee stems

Mn-Mor SM, = (F9-13)

• (2) For double-angle web legs, $M_{n}$ shall be determined using Equations F10-2 and F10-3 with $M_{c r}$ determined using Equation F9-10 and $M_{y}$ determined using Equation F9-3.

F9.3 Flange Local Buckling of Tees and Double-Angle Legs

• (a) For tee flanges
• (1) For sections with a compact flange in flexural compression, the limit state of flange local buckling does not apply.
• (2) For sections with a noncompact flange in flexural compression

M-M-- M.-M.-(M,-0.7F,S) 2-2-4 $1.6M, (F9-14)

• (3) For sections with a slender flange in flexural compression

(F9-15)

where

$\begin{aligned} S_{x c} & =\text { elastic section modulus referred to the compression flange, in. }^{3}\left(\mathrm{~mm}^{3}\right) \\ \lambda & =\frac{b_{f}}{2 t_{f}}\end{aligned}$

$\lambda_{p f}=\lambda_{p}$, 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

• (b) For double-angle flange legs

The nominal flexural strength, $M_{n}$, for double angles with the flange legs in compression shall be determined in accordance with Section F10.3, with $S_{c}$ referred to the compression flange.

F9.4 Local Buckling of Tee Stems and Double-Angle Web Legs in Flexural Compression

(a) For tee stems

(F9-16)

where

$\begin{aligned} S_{x} & =\text { elastic section modulus taken about the } x \text {-axis, in. }^{3}\left(\mathrm{~mm}^{3}\right) \\ F_{c r}, & \text { the critical stress, is determined as follows: }\end{aligned}$

(1) When $\frac{d}{t_{w}} \leq 0.84 \sqrt{\frac{E}{F_{y}}}$

(2) When $0.84 \sqrt{\frac{E}{F_{y}}} \leq \frac{d}{t_{w}} \leq 1.52 \sqrt{\frac{E}{F_{y}}}$

(F9-18)

(3) When $\frac{d}{t_{w}}>1.52 \sqrt{\frac{E}{F_{y}}}$

(F9-19)

(b) For double-angle web legs

The nominal flexural strength, $M_{n}$, for double angles with the web legs in compression shall be determined in accordance with Section F10.3, with $S_{c}$ taken as the elastic section modulus.