C-9.79.7 design procedure

The design procedure for prequalified CBB connections is intended to develop the probable maximum moment capacity of the connecting beam. Test data indicate that connecting the brackets to the column and beam in accordance with the requirements herein allows the connection to resist this level of moment.

Step 2 requires the selection of a trial bracket. Tables C-9.1, C-9.1M, C-9.2, and C-9.2M can be used as a guide in selecting trial bracket-beam combinations. The tables are based on beams that satisfy the limitations of Section 9.3.1 for ASTM A992/A992M or A572/A572M Grade 50 (Grade 345) wide-flange shapes.

Step 8 defines the minimum column flange width so that yield of the gross section of the column flange precedes tensile rupture. Because the column is subjected to combined bending and axial force (which may be tension or compression) and the magnitude of these force components when acting in combination are subject to considerable uncertainty, the approach used in this step was intended to be simple and conservative.

Step 9 was updated in ANSI/AISC 358-22 to be consistent with the approach used in Chapter 6. Satisfying Equation 9.7-4 checks column flange flexural yielding and eliminates bolt prying action.

Step 10 of the procedure applies to beams with flange holes and is intended to preclude beam net section fracture. Beginning with ANSI/AISC 358-22, the approach used is the same as that used in the procedure for the double-tee connection in Chapter 13 and the bolted flange plate connection in Chapter 7. Additional details are available in the Commentary to Section 13.5.

Step 17 requires checking continuity plate requirements. Step 9 requires a column flange thickness that will adequately satisfy the column flange local bending limit state. However, the limit states of column web local yielding and web local crippling, as defined in AISC Specification Sections J10.2 and J10.3, respectively, must also be checked and may require continuity plates. When required, the plates are positioned at the same level as the beam flange as shown in Figures 9.4 and 9.5. Continuity plates may interfere with the placement and installation of the column flange bolts, and detailing of the continuity plates should consider this possible interference. It may be advantageous to choose a column section that does not require continuity plates to avoid this interference.

Step 20 of the procedure is supplemental if the column is a built-up box configuration. The procedure is based on the limit state of yielding (plastic moment) as defined in AISC Specification Section F11.1. The design assumes a simply supported condition with symmetrical point loads applied at the bolt locations.