C-11.411.4 column-beam relationship limitations

See Figures 11.14 through 11.21 for depictions of the alphabetical and numerical designations. The beams and columns selected must satisfy physical geometric compatibility requirements between the beam flange and column flange to allow sufficient lateral space for depositing fillet welds {5} along the longitudinal edges of the beam flanges that connect to the top and bottom cover plates {B}. Equations 11.4-1a/11.4-1aM and 11.4-1b/11.4-1bM assist designers in selecting appropriate final beam and column size combinations prior to the SidePlate moment connection actually being designed for a specific project. Note: One of the field-bolted connection tests utilized a PJP weld for weld {5}, which allows for a tighter tolerance in the geometric compatibility checks. The test performed similar to others with fillet welds for weld {5}; thus, weld {5} may be deposited as a PJP weld or fillet weld as needed.

Unlike more conventional moment frame designs that typically rely on the deformation of the column panel zone to achieve the required rotational capacity, SidePlate moment connection technology instead stiffens and strengthens the column panel zone by providing a minimum of three panel zones (the column web plus the two full-depth side plates {A}). This configuration forces the vast majority of plastic deformation to occur through flange local buckling of the beam.

The column web must be capable of resisting the panel zone shear loads transferred from the horizontal shear plates {D} through the pair of shop fillet welds {3}. The strength of the column web is thereby calculated and compared to the ultimate strength of the welds {3} on both sides of the web. To be acceptable, the panel zone shear strength of the column must be greater than the strength of the two welds. This ensures that the limit state will be failure of the welds as opposed to failure of the column web. The two side plates {A} may be used as doubler plates to check the overall panel zone strength. The following calculation and check is built into the SidePlate moment connection design software:

(C-11.4-1)

where

$\begin{aligned} R_{n} & =\text { nominal strength of column web panel zone in accordance with AISC } \\ & \text { Specification Section J10.6(b), kips (N) }\end{aligned}$

$=0.60 F_{y} d_{c t c w}\left(1+\frac{3 b_{f c t f c}^{2}}{d_{s p} d_{c t c w}}\right)$ (from Spec. Eq. J10-11)

$R_{u}=$ ultimate strength of fillet welds {3} from horizontal shear plates {D} to column web, kips (N)

where

$\begin{aligned} b_{f c} & =\text { width of column flange, in. (mm) } \\ d_{c} & =\text { depth of column, in. (mm) } \\ d_{s p} & =\text { depth of side plate }\{A\}, \text { in. (mm) } \\ t_{c w} & =\text { thickness of column web, in. (mm) } \\ t_{f c} & =\text { thickness of column flange, in. (mm) }\end{aligned}$

In determining the SMF column-beam moment ratio to satisfy strong column/weak beam design criteria, the beam-imposed moment, $M_{p b}^{*}$, is calculated at the column centerline using statics (i.e., accounting for the increase in moment due to shear amplification from the location of the plastic hinge to the center of the column as a result of the development of the probable maximum moment of the beam, $M_{p r}$, at the plastic hinge location), and then linearly decreased to one-quarter the column depth above and below the extreme top and bottom fibers of the side plates {A}. This location is used for determination of the column strength because the column is unlikely to form a hinge within the panel zone due to the presence and strengthening effects of the two side plates {A}.

In calculating the biaxial column-beam moment ratio, it is permitted to take the actual yield strength of the column material as the specified yield strength in lieu of the specified minimum yield stress, $F_{y}$, and to consider the full composite behavior of the column for axial and flexural loading action (story drift analysis) if it is filled with concrete. The column strength formula, Equation 11.4-6, assumes equal column properties about both axes. For column sections with unequal properties about both axes, interaction equations based on rational analysis should be used. Guidance for checking columns subject to biaxial bending and axial force is provided in AISC Seismic Provisions Section E3 Commentary.

This requirement need not apply if any of the exceptions articulated in AISC Seismic Provisions Section E3.4a are satisfied. The calculation and check are included in the SidePlate connection design software.