C-F11F11 Rectangular bars and rounds

The provisions in Section F11 apply to solid bars with round and rectangular cross section. The prevalent limit state for such members is the attainment of the full plastic moment, $M_{p}$. The exception is the lateral-torsional buckling of rectangular bars where the depth is larger than the width. The requirements for design are identical to those given in Table A-F1.1 in the 1999 LRFD Specification (AISC, 2000b) and the same as those in use since the 2005 AISC Specification (AISC, 2005b). Because the shape factor, $Z / S$, for a rectangular cross section is 1.5 and for a round section is 1.7 , consideration must be given to serviceability issues such as excessive deflection or permanent deformation under service-load conditions.

Figure description:

Figure Description: Unequal-leg angle in bending

• Principal Axes: Labeled as $w$ and $z$.
• Loading: Bending moment $M_{ob}$ applied along the $w$-axis.
• Configurations:
  • (a $+\beta_w$: Moment vector $M_{ob}$ directed away from the angle cross-section.
  • (b $-\beta_w$: Moment vector $M_{ob}$ directed toward the angle cross-section.
• Shear Center: Identified at the junction of the two legs.
• Note: For equal-leg angles, the value of $\beta_w$ is zero.

Fig. C-F10.4. Unequal-leg angle in bending.

Specification for Structural Steel Buildings, August 1, 2022 AMERICAN INSTITUTE OF STEEL CONSTRUCTION

TABLE C-F10.1

βw Values for Angles

${ }^{[\mathrm{a}] \beta_{w}}=\frac{1}{l} \int z\left(w^{2}+z^{2}\right) d A-2 z_{o}$

where

$I_{w}=$ moment of inertia for the major principal axis, in. ${ }^{4}\left(\mathrm{~mm}^{4}\right)$

$\begin{aligned} I_{w} & =\text { moment of inertia of the major principal axis, in. }(\mathrm{mm}) \\ z_{0} & =\text { coordinate along the } z \text {-axis of the shear center with respect to the centroid, in. (mm) }\end{aligned}$

$\beta_{w}$ has a positive or negative value depending on the direction of bending (see Figure C-F10.4).