I4Shear

I4.1 Encased Composite Members

The design shear strength, $\phi_{v} V_{n}$, and allowable shear strength, $V_{n} / \Omega_{v}$, of encased composite members shall be determined based on one of the following:

• (a) The available shear strength of the structural steel section alone as specified in Chapter G
• (b) The available shear strength of the reinforced concrete portion (concrete plus transverse reinforcement) alone as defined by ACI 318 with

$\phi_{v}=0.75$ (LRFD) $\quad \Omega_{v}=2.00$ (ASD)

• (c) The nominal shear strength of the structural steel section, as defined in Chapter G, plus the nominal strength of the transverse reinforcement, as defined by ACI 318, with a combined resistance or safety factor of

$\phi_{v}=0.75$ (LRFD) $\quad \Omega_{v}=2.00$ (ASD)

I4.2 Filled Composite Members

The design shear strength, $\phi_{v} V_{n}$, and allowable shear strength, $V_{n} / \Omega_{v}$, of filled composite members shall be determined as follows:

$\phi_{v}=0.90$ (LRFD) $\quad \Omega_{v}=1.67$ (ASD)

The nominal shear strength, $V_{n}$, shall include the contributions of the structural steel section and concrete infill as follows:

(14-1)

where

• $A_{v}=$ shear area of the steel portion of a composite member. The shear area for a round section is equal to $2 A_{s} / \pi$, and for a rectangular section is equal to the sum of the area of webs in the direction of in-plane shear, in. ${ }^{2}\left(\mathrm{~mm}^{2}\right)$

$A_{c}=\operatorname{area}$ of concrete infill, in. ${ }^{2}\left(\mathrm{~mm}^{2}\right)$

• $K_{c}=1$ for members with shear span-to-depth, $\left(M_{u} / V_{u}\right) / d$, greater than or equal to 0.7 , where $M_{u}$ and $V_{u}$ are equal to the maximum required flexural and shear strengths, respectively, along the member length, and $d$ is equal to the member depth in the direction of bending
• = 10 for members with rectangular compact composite cross sections and $\left(M_{u} / V_{u}\right) / d$ less than 0.5
• = 9 for members with round compact composite cross sections and $\left(M_{u} / V_{u}\right) / d$ less than 0.5
• = 1 for members having other than compact composite cross sections, for all values of $\left(M_{u} / V_{u}\right) / d$

Linear interpolation between these $K_{c}$ values shall be used for members with compact composite cross sections and with $\left(M_{u} / V_{u}\right) / d$ between 0.5 and 0.7 .

User Note: For most members, $K_{c}$ will be equal to 1.0. Low shear span-to-depth ratios may occur in connection design (panel zones) or other special situations, for which higher values of $K_{c}(>1.0)$ are more appropriate.

I4.3 Composite Beams with Formed Steel Deck

The available shear strength of composite beams with steel headed stud or steel channel anchors shall be determined based upon the properties of the steel section alone in accordance with Chapter G.

I4.4 Composite Plate Shear Walls

The design in-plane shear strength, $\phi_{v} V_{n}$, and allowable shear strength, $V_{n} / \Omega_{v}$, of composite plate shear walls shall be determined as follows:

$\phi_{v}=0.90$ (LRFD) $\quad \Omega_{v}=1.67$ (ASD)

The nominal shear strength, $V_{n}$, shall account for the contributions of the structural steel section and concrete infill as follows:

(I4-2)

where

$A_{s w}=\text { area of steel plates in the direction of in-plane shear, in. }^{2}\left(\mathrm{~mm}^{2}\right)$

(I4-3)

$\begin{aligned} G_{s} & =\text { shear modulus of steel } \\ & =11,200 \mathrm{ksi}(77200 \mathrm{MPa}) \\ K_{s c} & =\frac{0.7\left(E_{c} A_{c}\right)\left(E_{s} A_{s w}\right)}{4 E_{s} A_{s w}+E_{c} A_{c}}\end{aligned}$