E6Special cantilever column systems (SCCS)

E6.4a Columns

Columns shall be designed using the load combinations including the overstrength seismic load. The required axial strength, $P_{r c}$, shall not exceed $15 \%$ of the available axial yield strength, $P_{y c}$, for these load combinations only.

E6.4b Stability Bracing of Columns

Bracing required in this section shall restrain lateral-torsional buckling of the cantilever column to develop flexural yielding at the column base. When columns are bent about their major axis, bracing shall be provided at the top of the column and at intermediate locations if necessary, satisfying the following requirements:

• (a) Both flanges of the column shall be laterally braced for lateral-torsional buckling or the column cross section shall be braced for lateral-torsional buckling with point torsional bracing.
• (b) Bracing shall meet the requirements of Specification Appendix 6 for lateral or point torsional bracing of beams, where $C_{d}$ is 1.0 and the required flexural strength of the member shall be determined in accordance with Equation D1-1 in Section D1.2a.1(b).
• (c) For doubly symmetric I-shaped members, the bracing shall have a maximum spacing of

where

• $F_{y c}=$ specified minimum yield stress of column, ksi (MPa)
• $L_{b c}=$ length between base and bracing point or between bracing points of a cantilever column where the bracing points are either braced against lateral displacement for both flanges or braced against twist of the cross section, in. (mm)
• $M_{1}^{\prime}=$ effective moment at the end of the unbraced length opposite from $M_{2}$ as determined from Specification Appendix 1, kip-in. (N-mm)
• $M_{2}=$ larger moment at end of unbraced length, kip-in. (N/mm) (shall be taken as positive in all cases)
• $\begin{aligned} R_{y} & =\text { ratio of expected yield stress to specified minimum yield stress of } \\ & \text { column, } F_{y}\end{aligned}$
• $r_{y}=$ radius of gyration about y-axis of column, in. (mm)
• (d) For rectangular hollow structural sections (HSS) and box sections, the bracing shall have a maximum spacing of

(E6-2)

Exceptions:

• (a) Bracing may be omitted for square or round HSS and for square box sections.
• (b) Bracing may be omitted for any column section acting as a cantilever only about its minor axis.
• (c) Bracing may be omitted for cantilever columns bent about their major axis when the column cantilever length from the base to the top does not exceed half the maximum spacing calculated in accordance with Equation E6-1 or E6-2, as applicable.

E6.5a Basic Requirements

Column members shall satisfy the requirements of Section D1.1 for highly ductile members.

E6.5b Column Flanges

Abrupt changes in column flange area are prohibited in the protected zone as designated in Section E6.5c.

E6.5c Protected Zones

The region at the base of the column subject to inelastic straining shall be designated as a protected zone and shall satisfy the requirements of Section D1.3. The length of the protected zone shall be 2 times the column depth.