J10Flanges and webs with concentrated forces

This section applies to single- and double-concentrated forces applied normal to the flange(s) of wide-flange sections and similar built-up shapes. A single-concentrated force is either tensile or compressive. Double-concentrated forces are one tensile and one compressive and form a couple on the same side of the loaded member.

When the required strength exceeds the available strength as determined for the limit states listed in this section, stiffeners and/or doublers shall be provided and shall be sized for the difference between the required strength and the available strength for the applicable limit state. Stiffeners shall also meet the design requirements in Section J10.8. Doublers shall also meet the design requirements in Section J10.9.

User Note: See Appendix 6, Section 6.3, for requirements for the ends of cantilever members.

Stiffeners are required at unframed ends of beams in accordance with the require- ments of Section J10.7.

User Note: Design guidance for members other than wide-flange sections and similar built-up shapes, including HSS members, can be found in the Commentary.

J10.1 Flange Local Bending

This section applies to tensile single-concentrated forces and the tensile component of double-concentrated forces.

The design strength, $\phi R_{n}$, and the allowable strength, $R_{n} / \Omega$, for the limit state of flange local bending shall be determined as

(J10-1)

$\phi=0.90$ (LRFD) $\quad \Omega=1.67$ (ASD)

where

$\begin{aligned} F_{y f} & =\text { specified minimum yield stress of the flange, ksi (MPa) } \\ t_{f} & =\text { thickness of the loaded flange, in. (mm) }\end{aligned}$

If the length of loading across the member flange is less than $0.15 b_{f}$, where $b_{f}$ is the member flange width, Equation J10-1 need not be checked.

When the concentrated force to be resisted is applied at a distance from the member end that is less than $10 t_{f}, R_{n}$ shall be reduced by $50 \%$.

When required, a pair of transverse stiffeners shall be provided.

J10.2 Web Local Yielding

This section applies to single-concentrated forces and both components of double-concentrated forces.

The available strength for the limit state of web local yielding shall be determined as follows:

$\phi=1.00$ (LRFD) $\quad \Omega=1.50$ (ASD)

The nominal strength, $R_{n}$, shall be determined as follows:

• (a) When the concentrated force to be resisted is applied at a distance from the member end that is greater than the full nominal depth of the member, d

(J10-2)

• (b) When the concentrated force to be resisted is applied at a distance from the member end that is less than or equal to the full nominal depth of the member, d

where

$\begin{aligned} F_{y w} & =\text { specified minimum yield stress of the web material, ksi (MPa) } \\ k & =\text { distance from outer face of the flange to the web toe of the fillet, in. (mm) } \\ l_{b} & =\text { length of bearing, in. (mm) } \\ t_{w} & =\text { thickness of web, in. (mm) }\end{aligned}$

When required, a pair of transverse stiffeners or a doubler plate shall be provided.

J10.3 Web Local Crippling

This section applies to compressive single-concentrated forces or the compressive component of double-concentrated forces.

The available strength for the limit state of web local crippling shall be determined as follows:

$\phi=0.75$ (LRFD) $\quad \Omega=2.00$ (ASD)

The nominal strength, $R_{n}$, shall be determined as follows:

• (a) When the concentrated compressive force to be resisted is applied at a distance from the member end that is greater than or equal to $d / 2$

(J10-4)

• (b) When the concentrated compressive force to be resisted is applied at a distance from the member end that is less than d/2

(1) For $l_{b} / d \leq 0.2$

(J10-5a)

(2) For l/d >0.2

where

• $\begin{aligned} Q_{f} & =\text { chord-stress interaction parameter }=1.0 \text { for wide-flange sections, channels, } \\ & \text { box sections, and for HSS (connecting surface) in tension } \\ & =\text { as given in Section K1.3 for all other HSS conditions }\end{aligned}$
• $d \quad$ = full nominal depth of the member, in. (mm)

When required, a transverse stiffener, a pair of transverse stiffeners, or a doubler plate extending at least three-quarters of the depth of the web shall be provided.

J10.4 Web Sidesway Buckling

This section applies only to compressive single-concentrated forces applied to members where relative lateral movement between the loaded compression flange and the tension flange is not restrained at the point of application of the concentrated force.

The available strength of the web for the limit state of sidesway buckling shall be determined as follows:

$\phi=0.85$ (LRFD) $\quad \Omega=1.76$ (ASD)

The nominal strength, $R_{n}$, shall be determined as follows:

• (a) If the compression flange is restrained against rotation

(1) When $\left(h / t_{w}\right) /\left(L_{b} / b_{f}\right) \leq 2.3$

(J10-6)

• (2) When $\left(h / t_{w}\right) /\left(L_{b} / b_{f}\right)>2.3$, the limit state of web sidesway buckling does not apply.

When the required strength of the web exceeds the available strength, local lateral bracing shall be provided at the tension flange or either a pair of transverse stiffeners or a doubler plate shall be provided.

• (b) If the compression flange is not restrained against rotation
• (1) When $\left(h / t_{w}\right) /\left(L_{b} / b_{f}\right) \leq 1.7$

(J10-7)

• (2) When $\left(h / t_{w}\right) /\left(L_{b} / b_{f}\right)>1.7$, the limit state of web sidesway buckling does not apply.

When the required strength of the web exceeds the available strength, local lateral bracing shall be provided at both flanges at the point of application of the concentrated forces.

In Equations J10-6 and J10-7, the following definitions apply:

• $\begin{aligned} C_{r} & =960,000 \mathrm{ksi}\left(6.6 \times 10^{6} \mathrm{MPa}\right) \text {, when } \alpha_{s} M_{r}<M_{y} \text { at the location of the force } \\ & =480,000 \mathrm{ksi}\left(3.3 \times 10^{6} \mathrm{MPa}\right) \text {, when } \alpha_{s} M_{r} \geq M_{y} \text { at the location of the force }\end{aligned}$
• $\begin{aligned} L_{b} & =\text { largest laterally unbraced length along either flange at the point of load, } \\ & \text { in. (mm) }\end{aligned}$
• $\begin{aligned} M_{r} & =\text { required flexural strength using LRFD or ASD load combinations, kip-in. } \\ & \text { (N-mm) }\end{aligned}$
• $M_{y}=$ yield moment about the axis of bending, ksi (MPa)

$=F_{y} S_{x}$

• $b_{f}=$ width of flange, in. (mm)
• $\begin{aligned} h & =\text { clear distance between flanges less the fillet or corner radius for rolled shapes; } \\ & \text { distance between adjacent lines of fasteners or the clear distance between } \\ & \text { flanges when welds are used for built-up shapes, in. (mm) }\end{aligned}$

$\alpha_{s}=1.0$ (LRFD); 1.5 (ASD)

User Note: For determination of adequate restraint, refer to Appendix 6.

J10.5 Web Compression Buckling

This section applies to a pair of compressive single-concentrated forces or the compressive components in a pair of double-concentrated forces, applied at both flanges of a member at the same location.

The available strength for the limit state of web compression buckling shall be determined as follows:

(J10-8)

$\phi=0.90$ (LRFD) $\quad \Omega=1.67$ (ASD)

where

• $Q_{f}=1.0$ for wide-flange sections, channels, box sections, and for HSS (connecting surface) in tension
• = as given in Section K1.3 for all other HSS conditions

When the pair of concentrated compressive forces to be resisted is applied at a distance from the member end that is less than $d / 2, R_{n}$ shall be reduced by $50 \%$.

When required, a single transverse stiffener, a pair of transverse stiffeners, or a doubler plate extending the full depth of the web shall be provided.

J10.6 Web Panel-Zone Shear

This section applies to double-concentrated forces applied to one or both flanges of a member at the same location.

The available strength of the web panel-zone for the limit state of shear yielding shall be determined as follows:

$\phi=0.90$ (LRFD) $\quad \Omega=1.67$ (ASD)

The nominal strength, $R_{n}$, shall be determined as follows:

• (a) When the effect of inelastic panel-zone deformation on frame stability is not accounted for in the analysis
• (1) For $\alpha P_{r} \leq 0.4 P_{y}$

(J10-9)

• (2) For $\alpha P_{r}>0.4 P_{y}$

• (b) When the effect of inelastic panel-zone deformation on frame stability is accounted for in the analysis
• (1) For $\alpha P_{r} \leq 0.75 P_{y}$

(J10-11)

• (2) For $\alpha P_{r}>0.75 P_{y}$

(J10-12)

where

• $F_{y}=$ specified minimum yield stress of the column web, ksi (MPa)
• $P_{r}=$ required axial strength using LRFD or ASD load combinations, kips (N)
• $\begin{aligned} P_{y} & =\text { axial yield strength of the column, kips (N) } \\ & =F_{y} A_{g}\end{aligned}$
• $A_{g}=$ gross area of member, in. ${ }^{2}\left(\mathrm{~mm}^{2}\right)$
• $b_{c f}=$ width of column flange, in. (mm)

$d_{b}=$ depth of beam, in. (mm)

• $d_{c}=$ depth of column, in. (mm)
• $t_{c f}=$ thickness of column flange, in. (mm)
• $t_{w}=$ thickness of column web, in. (mm)
• $\alpha=1.0$ (LRFD); $=1.6$ (ASD)

When required, doubler plate(s) or a pair of diagonal stiffeners shall be provided within the boundaries of the rigid connection whose webs lie in a common plane.

See Section J10.9 for doubler plate design requirements.

J10.7 Unframed Ends of Beams and Girders

At unframed ends of beams and girders not otherwise restrained against rotation about their longitudinal axes, a pair of transverse stiffeners, extending the full depth of the web, shall be provided.

J10.8 Additional Stiffener Requirements for Concentrated Forces

Stiffeners required to resist tensile concentrated forces shall be designed in accordance with the requirements of Section J4.1 and welded to the loaded flange and the web. The welds to the flange shall be sized for the difference between the required strength and available strength. The stiffener to web welds shall be sized to transfer to the web the algebraic difference in tensile force at the ends of the stiffener.

Stiffeners required to resist compressive concentrated forces shall be designed in accordance with the requirements in Section J4.4 and shall either bear on or be welded to the loaded flange and welded to the web. The welds to the flange shall be sized for the difference between the required strength and the applicable limit state strength. The weld to the web shall be sized to transfer to the web the algebraic difference in compression force at the ends of the stiffener. For fitted bearing stiffeners, see Section J7.

Transverse full depth bearing stiffeners for compressive forces applied to a beam flange(s) shall be designed as axially compressed members (columns) in accordance with the requirements of Section E6.2 and Section J4.4. The member properties shall be determined using an effective length of 0.75h and a cross section composed of two stiffeners and a strip of the web having a width of 25tw at interior stiffeners and 12tw at the ends of members. The weld connecting full depth bearing stiffeners to the web shall be sized to transmit the difference in compressive force at each of the stiffeners to the web.

Transverse and diagonal stiffeners shall comply with the following additional requirements:

• (a) The width of each stiffener plus one-half the thickness of the column web shall not be less than one-third of the flange or moment connection plate width delivering the concentrated force.
• (b) The thickness of a stiffener shall not be less than one-half the thickness of the flange or moment connection plate delivering the concentrated load nor less than the width divided by 16.
• (c) Transverse stiffeners shall extend a minimum of one-half the depth of the member except as required in Sections J10.3, J10.5, and J10.7.

J10.9 Additional Doubler Plate Requirements for Concentrated Forces

Doubler plates required for compression strength shall be designed in accordance with the requirements of Chapter E.

Doubler plates required for tensile strength shall be designed in accordance with the requirements of Chapter D.

Doubler plates required for shear strength (see Section J10.6) shall be designed in accordance with the provisions of Chapter G.

Doubler plates shall comply with the following additional requirements:

• (a) The thickness and extent of the doubler plate shall provide the additional material necessary to equal or exceed the strength requirements.
• (b) The doubler plate shall be welded to develop the proportion of the total force transmitted to the doubler plate.

J10.10 Transverse Forces on Plate Elements

When a force is applied transverse to the plane of a plate element, the nominal strength shall consider the limit states of shear and flexure in accordance with Sections J4.2 and J4.5.

User Note: The flexural strength can be checked based on yield-line theory and the shear strength can be determined based on a punching shear model. See AISC Steel Construction Manual Part 9 for further discussion.