Step 1 of this procedure defines the maximum expected moment, , at the plastic hinge location, which is at the last bolt away from the face of the column in the flange plate. Step 2 establishes the maximum bolt diameter that can meet this balanced criterion. Beginning with AISC 358-22, the approach used is the same as that used in the procedure for the double-tee connection found in Chapter 13. The approach that was previously used for bolted flange plate connections was developed from AISC Specification Chapter F and considers only the tension flange of the beam when determining whether gross yielding or net-section fracture will control. The current approach considers the entire cross section of the beam, which is less conservative and is substantiated by a study by Swanson (2016). Additional details are available in the Commentary to Section 13.5.
The shear strength of the flange bolts is the smallest strength permitted based on bolt shear with threads excluded from the shear plane, bolt bearing on the flange plate, and bolt bearing on the beam flange. Step 3 provides this evaluation. Step 4 is an approximate evaluation of the number of bolts needed to develop the BFP moment connection. The moment for the bolts is larger than because the centroid of the bolt group is at a different location than the primary hinge location. However, this moment cannot be accurately determined until the geometry of the flange plate and bolt spacing are established. The 1.25 factor is used as an empirical increase in this moment to provide this initial estimate for the number of bolts required. The bolts are tightened to meet slip-critical criteria, but the connection is not slip critical. The bolts are designed as bearing bolts.