Part 1: General

Part 2: Loads & Analysis

Part 3: Members

Part 4: Joints/Connections/Anchors

Part 5: Earthquake Resistance

Part 6: Materials & Durability

Part 7: Strength & Serviceability

Part 8: Reinforcement

Part 9: Construction

Part 10: Evaluation

REFERENCES & Appendices

Heads up: There are no amended sections in this chapter.
This chapter shall apply to the design of nonprestressed and prestressed 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 shall be selected to be in accordance with Chapter 20.
Materials, design, and detailing requirements for embedments in concrete shall be in accordance with 20.6.
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.
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.
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.
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 20.5.1.
Development lengths of deformed and prestressed reinforcement shall be in accordance with 25.4.
Along development and lap splice lengths of longitudinal bars with fy ≥ 80,000 psi, transverse reinforcement shall be provided such that Ktr shall not be smaller than 0.5db.
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
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, if applicable, 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.
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 fpe ≥ 225 psi, transverse ties or hoops need not satisfy the 16db spacing requirement of 25.7.2.1.
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 ties or hoops.
If mechanical couplers or extended bars for connection to a precast element are placed in the ends of columns or pedestals, the mechanical couplers or extended bars shall be enclosed by transverse reinforcement. The transverse reinforcement shall be distributed within 5 in. of the ends of the column or pedestal and shall consist of at least two No. 4 or three No. 3 ties or hoops.
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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