Section J10.1/Flange Local Bending
AISC 360-22 Section J10.1 covers the flange local bending limit state at concentrated forces applied to I-shaped member flanges, commonly checked at beam-to-column moment connections.
When a concentrated tensile force is applied to a member flange through a plate welded across the flange width (such as a beam flange connecting to a column flange), the nominal strength for the flange local bending limit state is Rn = 6.25 x Fyf x tf squared, where Fyf is the yield stress of the loaded flange and tf is the flange thickness. The resistance factor phi is 0.90 for LRFD and the safety factor omega is 1.67 for ASD. If the concentrated force is applied at a distance from the member end that is less than 10 times the flange thickness (10 x tf), the nominal strength Rn must be reduced by 50%. This limit state is checked when the flange of the loaded member (typically a column) may bend locally under the concentrated force delivered by a beam flange or connection plate.
Why this section exists
At beam-to-column moment connections, the beam flanges deliver concentrated tension and compression forces to the column flange. If the column flange is too thin, it will bend locally under these forces, forming a yield-line pattern that compromises the connection stiffness and strength. Flange local bending is one of several concentrated force limit states that must be checked at connections, alongside web local yielding and web crippling. When the column flange is inadequate, continuity plates (stiffeners) welded between the column flanges at the beam flange levels are used to stiffen the connection.
What plan reviewers look for
Plan reviewers check connection design calculations at moment connections to verify that flange local bending has been evaluated. They look for the column flange thickness relative to the beam flange force. For connections near the top of a column, they verify the 50% strength reduction is applied when the beam flange is within 10 x tf of the column end. They check for continuity plates where the column flange capacity is exceeded. They verify the continuity plate thickness and welding are specified on the connection details per Section J2 welding requirements.