Design of Free Flange Moment Connection

The Free Flange connection is a new public-domain beam-to-column moment connection developed at The University of Michigan. This connection is designed to alleviate excessive local deformation and shear force overload of beam flanges in pre-Northridge fully-restrained steel moment connections. These design goals were achieved by cutting the web of the beam back and away from the column, thus creating portions of the beam flanges that are not constrained by the web. Such free portions of beam flanges significantly reduce connection deformation constraints; allow the flange steel to yield freely; and help to redirect most of the shear force back into the web connection. Seven full size Free Flange connection specimens were tested to validate the design concept, check the design procedure, and prequalify the connection for use in practice. The connection was prequalified for the tested beam and column sizes, with all specimens exceeding 0.04 radian total rotations before failure, and behaving in a ductile manner. The original Free Flange connection design procedure was modified based on the observed specimen behavior. The new design procedure is presented and compared to the Free Flange connection design procedure in the FEMA 350Design Guidelines.