Design Criteria for Stiffened Seated Connections to Column Webs

In multistory braced frames, simple, or Type PR connections of beams to columns are often made using beam seats. These may be made with heavy angles or, if loads are large, a stiffened seat may be used. The stiffened seat is usually made by welding two plates in the form of a tee, as shown in Figure 1. A seated connection has an advantage over a framed connection in that it can permit larger fabrication and erection tolerances, requires only two bolts, and provides a stable erection platform for the beam before any bolts are installed. When attached to a column flange, the capacity of the seat is calculated by checking the fillet welds in combined shear and tension. There are tables in Volume II of the AISC Manual (AISC, 1995) that already have these values worked out for various seat and stiffener sizes. Because of the column flange stiffness, the seat will rotate very little under load, usually less than the end of the beam which rests on it.