The slotted web (SW) connection is a welded steel beam-to-steel column connection developed through private funding by Seismic Structural Design Associates Inc. (SSDA). In the SW moment connection, slots in the beam web are made parallel and adjacent to the beam flanges. These slots, which start at the end of the beam and are typically one-third to one-half the nominal beam depth in length, are terminated at a round stress relief hole. The beam web is welded to the column flange and also to the shear plate to give the web both shear and moment capacity.
Analytical studies by Yu (1959) and finite element analyses (FEA) by Abel and Popov (1968) have shown that the shear distribution at the support of cantilever beams differs drastically from that predicted by classical Bernoulli-Euler beam theory that led to the popular design concept wherein “the flanges carry the moment and the web carries the shear.” It was shown that in the case of a rigid support (beam web and flanges welded to a rigid column flange), the entire shear is resisted by the flanges. For typical “flange-welded, web-bolted” connections such as the so-called pre-Northridge connection, however, about 50% of the shear is resisted by the beam flanges. It is this 50% shear component in combination with the tension component that causes severe stress and strain gradients across and through the beam flanges of these connections.
By separating the beam flanges from the web in the region of the connection to the column, essentially all the beam shear is resisted by the beam web and, if the beam web is welded to the column, the web also resists a moment equal to the plastic moment capacity of the web, which is typically 30% of the beam plastic moment. Moreover, the elimination of the beam flange shear results in stress and strain gradients across and through the flanges to be nearly uniform.
Cyclic qualifying tests on the SW connection have been made using the singlecantilever type and bare steel specimens; see test results in Table C-14.1. This pseudo-static test with the loading protocol developed by the FEMA/SAC program (FEMA, 2000b) has been adopted in AISC Seismic Provisions Section K2 (AISC, 2022a). These tests, along with the FEA of the SW connection, show that the yielding region is concentrated in the separated portion of the beam flanges and in the beam web at the end of the shear plate. Peak strengths of the test specimens are usually achieved at an interstory drift angle of approximately 0.03 and 0.04 rad. Reduction in strength, if any, is gradual and due to the out-of-plane buckling of both the beam flanges and web. Buckling of the flanges and web occurs concurrently but independently, which eliminates the lateral torsional mode of buckling. Review of the SSDA test data indicates that the SW connection, when designed and constructed in accordance with the limits and procedures presented herein, have developed interstory drift
| Test No. | Beam Column | Interstory Drift (%) |
|---|---|---|
| 17 | W33×141 | 4.2 |
| 18 | W14×283 | 5.1 |
| 19 | W27×94 | 4.3 |
| 20 | W14×176 | 5.0 |
| 21 | W36×300 | 4.5 |
| 22 | W14×500 | 4.4 |
| 23 | W24×94 | 4.1 |
| 24 | W30×135 | 4.1 |
| 25 | W36×170 | 4.0 |
| 26 | W30×235 | 4.0 |
| 1a | W36×256 W27×307 | 4.9 |
| 2a | W36×393 | 5.1 |
| 3a | W14×550 (Gr. 65) | 6.0 |
angles of a least 0.04 rad under cyclic loading on a consistent basis. Ultimate failure typically occurs at drift angles of 0.05 to 0.07 rad by low cycle fatigue fracture of the flange near the end of the slot or partial fracture of the beam web/shear plate weld- ment to the column flange (Richard, et al., 2001; Partridge, et al., 2002).