5.2. Single-plate Connections

5.2.1. In the design procedure for single-plate connections in the AISC Steel Construction Manual, the plate thickness is limited relative to the bolt diameter and the fillet weld size is required to be 5/8 of the plate thickness. What does this accomplis

It ensures the plate will be the critical element of the connection and that the connection will possess sufficient rotation capacity to accommodate the simple beam end rotation as required by Section B3.6a of the AISC Specification. Bolt bearing will occur before bolt shear and plate yielding will occur before weld rupture; thereby, a ductile limit-state will control the strength of the connection.

5.2.2. Are through-plates always required for singleplate connections to HSS columns?

No. Sherman and Ales (1991) demonstrated that local yielding of the support was not a concern due to the self-limiting nature of simple-shear connection end rotation and that the compressive strength of the HSS column was unaffected by the associated local deformations. However, this same research indicated that punching shear may be of concern for relatively thin supporting material thicknesses. Punching shear can be prevented by selecting an HSS with a wall thickness t w that meets the following criteria:

tw is greater than or equal to (Fy pl)(t pl) / Fuw where Fy pl = the yield strength of the single plate tpl = the thickness of the single plate Fuw = the tensile strength of the HSS wall

Note that this equation differs slightly from that given in Sherman and Ales (1991). Here, the expression is derived at the design strength level (omega factors included) whereas it was previously derived at the nominal strength level (no omega factors). If the actual maximum stress is known, it can be substituted for Fy pl in the above equation for a less conservative result.

The above minimum thicknesses would also be applicable to a welded plate tension connection (uniform stress distribution assumed). However, for cantilevered bracket connections, which do not have self-limiting rotations, yielding must also be checked. Sherman, D.R. and Ales, J.M. (1991), “The Design of Shear Tabs with Tubular Columns,” Proceedings of the 1991 AISC National Steel Construction Conference, AISC, Chicago, IL.