Concentrated forces on beams
A W, S, M or HP member under a force normal to its flange: a beam or column bearing on it, a hanger below it, a reaction, or the flange forces of moment connections framing into a column. The limit states of AISC 360-22 J10, with transverse stiffeners and web doubler plates designed for what the member lacks.
Inputs of the concentrated force #
- Loaded member: the shape, its steel, and the distance from the force to the member's end (near the end J10.1, J10.2, J10.3 and J10.5 reduce the strength).
- Single force: P by load type onto the flange (compression positive, a hanger negative) and the member's moment at the force (it sets Cr of J10.4). The length of bearing lb along the member, the loaded width across the flange (J10.1 is not checked under 0.15 bf), the thickness of the flange or plate delivering the force (J10.8(b)). Your statements: an equal compressive force on the other flange at the same place (J10.5); whether the flanges are restrained against relative lateral movement at the force (else J10.4 applies), whether the loaded compression flange is restrained against rotation (Appendix 6), the largest unbraced length along either flange; an unframed end not restrained against rotation (J10.7).
- Moment connections: one or two beams, the beam end moments by load type (positive with the beam's top flange in tension), the column's axial force and story shear; the beam depth, flange thickness and width. The flange force is M/(db − tfb); for flange plates enter the beam depth plus two plate thicknesses and the plate's thickness. Whether the analysis includes inelastic panel-zone deformation (J10.6(b)): your statement.
- Stiffeners and doubler: a pair of transverse stiffeners (steel, width, thickness, corner clip, full depth or not, fitted to bear), a web doubler plate (thickness, steel).
Auto-design varies the stiffeners (none first, then the width and thickness of a pair) and, for moment connections, the doubler. The member, the forces and your statements are kept.
Checks performed #
| Check | Basis |
|---|---|
| Flange local bending (tension) | J10.1, Eq. J10-1 |
| Web local yielding | J10.2, Eqs. J10-2, J10-3 |
| Web local crippling (compression) | J10.3, Eqs. J10-4, J10-5a, J10-5b |
| Web sidesway buckling | J10.4, Eqs. J10-6, J10-7 |
| Web compression buckling (a pair of compressive forces) | J10.5, Eq. J10-8 |
| Web panel-zone shear, with a doubler | J10.6, Eqs. J10-9 to J10-12; J10.9, G2.1 |
| Full-depth stiffeners at an unframed end | J10.7 |
| Stiffeners for the difference, in tension or compression; a full-depth bearing stiffener as a column (0.75 h, 25 tw or 12 tw strip) | J10.8, J4.1, J4.4, Chapter E |
| Bearing of fitted stiffeners | J7, Eq. J7-1 |
| Stiffener width, thickness and length | J10.8(a) to (c) |
| Doubler slenderness for Cv1 = 1 | G2.1(b) |
With stiffeners, the member's own limit states at that location are shown as notes (their available strengths), and the stiffeners carry the difference between the required force and the least of them. For a pair of forces at both flanges from two beams, the smaller compression is taken as the pair; the difference goes into panel-zone shear.
Limitations #
- The welds of stiffeners and doublers are not designed.
- A doubler serves panel-zone shear only; doublers for local yielding or crippling are not designed.
- HSS members (Chapter K) and cantilever ends (Appendix 6.3) are not covered.
- The required strength of a full-depth bearing stiffener checked as a column is the difference, as J10 says for stiffeners in general (to confirm against the code text for bearing stiffeners).
- The member's own flexure and shear are designed by the beam or column types.
Verification examples #
Verification status: 22 values compared in 6 examples (4 published, 2 hand calculations from the cited equations): 22 within tolerance, 0 recorded deviations. Code basis: the provisions it uses were read in the target edition.
AISC Design Examples v16.0 J.7 (girder under a beam: web yielding, crippling, sidesway buckling) and II.B-1 (column side: flange bending, web yielding, crippling), AISC Design Guide 13 Example 6-1 (panel zone, flange bending; the guide is written to the 1999 Specification and only equations unchanged in 2022 are compared). Web compression buckling, stiffeners and the doubler are hand calculations.