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This chapter shall apply to the design of nonprestressed, prestressed, and composite columns, including reinforced concrete pedestals.
Design of plain concrete pedestals shall be in accordance with Chapter 14.
Design properties for concrete shall be selected to be in accordance with Chapter 19.
Design properties for steel reinforcement and structural steel used in composite columns shall be selected to be in accordance with Chapter 20.
Materials, design, and detailing requirements for embedments in concrete shall be in accordance with 20.7.
If a structural steel shape, pipe, or tubing is used as longitudinal reinforcement, the column shall be designed as a composite column.
For cast-in-place construction, beam-column and slab-column joints shall satisfy Chapter 15.
For precast construction, connections shall satisfy the force transfer requirements of 16.2.
Connections of columns to foundations shall satisfy 16.3.
For columns with a square, octagonal, or other shaped cross section, it shall be permitted to base gross area considered, required reinforcement, and design strength on a circular section with a diameter equal to the least lateral dimension of the actual shape.
For columns with cross sections larger than required by considerations of loading, it shall be permitted to base gross area considered, required reinforcement, and design strength on a reduced effective area, not less than one-half the total area. This provision shall not apply to columns in special moment frames or columns not part of the seismic-force-resisting system required to be designed in accordance with Chapter 18.
For columns built monolithically with a concrete wall, the outer limits of the effective cross section of the column shall not be taken greater than 1.5 in. outside the transverse reinforcement.
For columns with two or more interlocking spirals, outer limits of the effective cross section shall be taken at a distance outside the spirals equal to the minimum required concrete cover.
If a reduced effective area is considered according to 10.3.1.1 through 10.3.1.4, structural analysis and design of other parts of the structure that interact with the column shall be based on the actual cross section.
For composite columns with a concrete core encased by structural steel, the thickness of the steel encasement shall be at least (a) or (b):

(a) for each face of width b

(b) for circular sections of diameter h

Required strength shall be calculated in accordance with the factored load combinations in Chapter 5.
Required strength shall be calculated in accordance with the analysis procedures in Chapter 6.
Pu and Mu occurring simultaneously for each applicable factored load combination shall be considered.
For each applicable factored load combination, design strength at all sections shall satisfy ϕSnU, including (a) through (d). Interaction between load effects shall be considered:

(a) ϕPnPu

(b) ϕMnMu

(c) ϕVnVu

(d) ϕTnTu

ϕ shall be determined in accordance with 21.2.
Pn and Mn shall be calculated in accordance with 22.4.
For composite columns, forces shall be transferred between the steel section and concrete by direct bearing, shear connectors, or bond in accordance to the axial strength assigned to each component.
Vn shall be calculated in accordance with 22.5.
If Tu ≥ ϕTth, where Tth is given in 22.7, torsion shall be considered in accordance with Chapter 9.
For nonprestressed columns and for prestressed columns with average fpe < 225 psi, area of longitudinal reinforcement shall be at least 0.01Ag but shall not exceed 0.08Ag.
For composite columns with a structural steel core, area of longitudinal bars located within the transverse reinforcement shall be at least 0.01(Ag — Asx), but shall not exceed 0.08(Ag — Asx).
A minimum area of shear reinforcement, Av,min, shall be provided in all regions where Vu > 0.5ϕVc.
If shear reinforcement is required, Av,min shall be the greater of (a) and (b):

(a)

(b)

Concrete cover for reinforcement shall be in accordance with 20.6.1.
Development lengths of deformed and prestressed reinforcement shall be in accordance with 25.4.
Bundled bars shall be in accordance with 25.6.
Minimum spacing s shall be in accordance with 25.2.
For nonprestressed columns and for prestressed columns with average fpe < 225 psi, the minimum number of longitudinal bars shall be (a), (b), or (c):

(a) Three within triangular ties

(b) Four within rectangular or circular ties

(c) Six enclosed by spirals or for columns of special moment frames enclosed by circular hoops

For composite columns with structural steel cores, a longitudinal bar shall be located at every corner of a rectangular cross section, with other longitudinal bars spaced not farther apart than one-half the least side dimension of the composite column.
The slope of the inclined portion of an offset bent longitudinal bar relative to the longitudinal axis of the column shall not exceed 1 in 6. Portions of bar above and below an offset shall be parallel to axis of column.
If the column face is offset 3 in. or more, longitudinal bars shall not be offset bent and separate dowels, lap spliced with the longitudinal bars adjacent to the offset column faces, shall be provided.
Lap splices, mechanical splices, butt-welded splices, and end-bearing splices shall be permitted.
Splices shall satisfy requirements for all factored load combinations.
Splices of deformed reinforcement shall be in accordance with 25.5 and shall satisfy the requirements of 10.7.5.2 for lap splices or 10.7.5.3 for end-bearing splices.
If the bar force due to factored loads is compressive, compression lap splices shall be permitted. It shall be permitted to decrease the compression lap splice length in accordance with (a) or (b), but the lap splice length shall be at least 12 in.

(a) For tied columns, where ties throughout the lap splice length have an effective area not less than 0.0015hs in both directions, lap splice length shall be permitted to be multiplied by 0.83. Tie legs perpendicular to dimension h shall be considered in calculating effective area.

(b) For spiral columns, where spirals throughout the lap splice length satisfy 25.7.3, lap splice length shall be permitted to be multiplied by 0.75.

If the bar force due to factored loads is tensile, tension lap splices shall be in accordance with Table 10.7.5.2.2.

Table 10.7.5.2.2—Tension lap splice class

Tensile bar stress Splice details Splice type
≤ 0.5fy ≤ 50% bars spliced at any section and lap splices on adjacent bars staggered by at least d Class A
Other Class B
> 0.5fy All cases Class B
If the bar force due to factored loads is compressive, end-bearing splices shall be permitted provided the splices are staggered or additional bars are provided at splice locations. The continuing bars in each face of the column shall have a tensile strength at least 0.25fy times the area of the vertical reinforcement along that face.
For composite columns, ends of structural steel cores shall be accurately finished to bear at end-bearing splices, with positive provision for alignment of one core above the other in concentric contact. Bearing shall be considered effective to transfer not greater than 50 percent of the total compressive force in the steel core.
Transverse reinforcement shall satisfy the most restrictive requirements for reinforcement spacing.
Details of transverse reinforcement shall be in accordance with 25.7.2 for ties, 25.7.3 for spirals, or 25.7.4 for hoops.
For prestressed columns with average fpe225 psi, transverse ties or hoops need not satisfy the 16db spacing requirement of 25.7.2.1.
For composite columns with a structural steel core, transverse ties or hoops shall have a minimum db of 0.02 times the greater side dimension of the composite column, but shall be at least No. 3 and need not be larger than No. 5. Spacing shall satisfy 25.7.2.1, but not exceed 0.5 times the least dimension of the composite column. Deformed wire or welded wire reinforcement of equivalent area shall be permitted.
Longitudinal reinforcement shall be laterally supported using ties or hoops in accordance with 10.7.6.2 or spirals in accordance with 10.7.6.3, unless tests and structural analyses demonstrate adequate strength and feasibility of construction.
If anchor bolts are placed in the top of a column or pedestal, the bolts shall be enclosed by transverse reinforcement that also surrounds at least four longitudinal bars within the column or pedestal. The transverse reinforcement shall be distributed within 5 in. of the top of the column or pedestal and shall consist of at least two No. 4 or three No. 3 bars.
In any story, the bottom tie or hoop shall be located not more than one-half the tie or hoop spacing above the top of footing or slab.
In any story, the top tie or hoop shall be located not more than one-half the tie or hoop spacing below the lowest horizontal reinforcement in the slab, drop panel, or shear cap. If beams or brackets frame into all sides of the column, the top tie or hoop shall be located not more than 3 in. below the lowest horizontal reinforcement in the shallowest beam or bracket.
In any story, the bottom of the spiral shall be located at the top of footing or slab.
In any story, the top of the spiral shall be located in accordance with Table 10.7.6.3.2.

Table 10.7.6.3.2 —Spiral extension requirements at top of column

Framing at column end Extension requirements
Beams or brackets frame into all sides of the column Extend to the level of the lowest horizontal reinforcement in members supported above.
Beams or brackets do not frame into all sides of the column Extend to the level of the lowest horizontal reinforcement in members supported above.
Additional column ties shall extend above termination of spiral to bottom of slab, drop panel, or shear cap.
Columns with capitals Extend to the level at which the diameter or width of capital is twice that of the column.
Where longitudinal bars are offset, horizontal support shall be provided by ties, hoops, spirals, or parts of the floor construction and shall be designed to resist 1.5 times the horizontal component of the calculated force in the inclined portion of the offset bar.
If transverse reinforcement is provided to resist forces that result from offset bends, ties, hoops, or spirals shall be placed not more than 6 in. from points of bend.
If required, shear reinforcement shall be provided using ties, hoops, or spirals.
Maximum spacing of shear reinforcement shall be in accordance with Table 10.7.6.5.2.

Table 10.7.6.5.2—Maximum spacing of shear reinforcement

Vs Maximum s, in.
Nonprestressed column Prestressed column
Lesser of: d/2 3h/4
24
Lesser of: d/4 3h/8
12
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