10.7.4.1 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.
10.7.4.2 If the column face is offset 75 mm or more, longi- tudinal bars shall not be offset bent and separate dowels,
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lap spliced with the longitudinal bars adjacent to the offset column faces, shall be provided.
10.7.5 Splices of longitudinal reinforcement 10.7.5.1 General
10.7.5.1.1 Lap splices, mechanical splices, butt-welded splices, and end-bearing splices shall be permitted.
10.7.5.1.2 Splices shall satisfy requirements for all factored load combinations.
10.7.5.1.3 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.
10.7.5.2 Lap splices
R10.7.5 Splices of longitudinal reinforcement R10.7.5.1 General
R10.7.5.1.2 Frequently, the basic gravity load combina- tion will govern the design of the column itself, but a load combination including wind or earthquake effects may induce greater tension in some column bars. Each bar splice should be designed for the maximum calculated bar tensile force.
R10.7.5.1.3 For the purpose of calculating ℓd for tension lap splices in columns with offset bars, Fig. R10.7.5.1.3 illustrates the clear spacing to be used.
R10.7.5.2 Lap splices—In columns subject to moment and axial force, tensile stresses may occur on one face of the column for moderate and large eccentricities as shown in Fig. R10.7.5.2. If such stresses occur, 10.7.5.2.2 requires tension splices to be used.
The splice requirements have been formulated on the basis that a compression lap splice has a tensile strength of at least 0.25fy. Therefore, even if columns bars are designed for compression according to 10.7.5.2.1, some tensile strength is inherently provided.
Fig. R10.7.5.1.3—Offset column bars.
10.7.5.2.1 If the bar force due to factored loads is compres- sive, 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 300 mm.
(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.
10.7.5.2.2 If the bar force due to factored loads is tensile, tension lap splices shall be in accordance with Table 10.7.5.2.2.
R10.7.5.2.1 Reduced lap lengths are permitted if the splice is enclosed throughout its length by sufficient ties.
The tie leg areas perpendicular to each direction are calcu- lated separately. An example is provided in Fig. R10.7.5.2.1, where four legs are effective in one direction and two legs in the other direction.
Compression lap lengths may also be reduced if the lap splice is enclosed throughout its length by spirals due to increased splitting resistance.
Fig. R10.7.5.2—Lap splice requirements for columns.
Fig. R10.7.5.2.1—Example of application of 10.7.5.2.1(a).
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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 ℓd Class A
Other Class B
> 0.5fy All cases Class B
10.7.5.3 End-bearing splices
10.7.5.3.1 If the bar force due to factored loads is compres- sive, 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.
10.7.5.3.2 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.
10.7.6 Transverse reinforcement 10.7.6.1 General
10.7.6.1.1 Transverse reinforcement shall satisfy the most restrictive requirements for reinforcement spacing.
10.7.6.1.2 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.
10.7.6.1.3 For prestressed columns with average fpe ≥ 1.6 MPa, transverse ties or hoops need not satisfy the 16db
spacing requirement of 25.7.2.1.
10.7.6.1.4 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. 10 and need not be larger than No. 16. 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.
10.7.6.1.5 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 struc-
R10.7.5.3 End-bearing splices
R10.7.5.3.1 Details for end-bearing splices are provided in 25.5.6.
R10.7.5.3.2 The 50 percent limit on transfer of compres- sive load by end-bearing on ends of structural steel cores is intended to provide some level of tensile strength at such splices, up to 50 percent, because the remainder of the total compressive load in the steel core is to be transmitted by splice plates, welds, or other mechanisms. This provision is intended to ensure that splices in composite columns meet essentially the same tensile strength requirements as conventionally reinforced concrete columns.
R10.7.6 Transverse reinforcement R10.7.6.1 General
R10.7.6.1.4 Research (Tikka and Mirza 2006) has shown that the required amount of tie reinforcement around the structural steel core is sufficient for the longitudinal bars to be included in the flexural stiffness of the composite column as permitted by 6.2.5.2 and 6.6.4.4.5.
R10.7.6.1.5 All longitudinal bars in compression should be enclosed within transverse reinforcement. Where longitu- dinal bars are arranged in a circular pattern, only one circular tie per specified spacing is required. This requirement can
tural analyses demonstrate adequate strength and feasibility of construction.
10.7.6.1.6 If anchor bolts are placed in the top of a column or pedestal, the bolts shall be enclosed by transverse rein- forcement that also surrounds at least four longitudinal bars within the column or pedestal. The transverse reinforcement shall be distributed within 125 mm of the top of the column or pedestal and shall consist of at least two No. 13 or three No. 10 bars.
10.7.6.2 Lateral support of longitudinal bars using ties or hoops
10.7.6.2.1 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.
10.7.6.2.2 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 75 mm below the lowest horizontal reinforcement in the shallowest beam or bracket.
10.7.6.3 Lateral support of longitudinal bars using spirals 10.7.6.3.1 In any story, the bottom of the spiral shall be located at the top of footing or slab.
10.7.6.3.2 In any story, the top of the spiral shall be located in accordance with Table 10.7.6.3.2.
be satisfied by a continuous circular tie (helix), with the maximum pitch being equal to the required tie spacing.
It is prudent to provide a set of ties at each end of lap spliced bars, above and below end-bearing splices, and at minimum spacings immediately below sloping regions of offset bent bars.
Precast columns with cover less than 40 mm, prestressed columns without longitudinal bars, columns of concrete with small size coarse aggregate, wall-like columns, and other unusual columns may require special designs for transverse reinforcement.
R10.7.6.1.6 Confinement improves load transfer from the anchor bolts to the column or pier where concrete cracks in the vicinity of the bolts. Such cracking can occur due to unanticipated forces caused by temperature, restrained shrinkage, and similar effects.
R10.7.6.2 Lateral support of longitudinal bars using ties or hoops
R10.7.6.2.2 For rectangular columns, beams or brackets framing into all four sides at the same elevation are consid- ered to provide restraint over a joint depth equal to that of the shallowest beam or bracket. For columns with other shapes, four beams framing into the column from two orthogonal directions are considered to provide equivalent restraint.
R10.7.6.3 Lateral support of longitudinal bars using spirals
R10.7.6.3.2 Refer to R10.7.6.2.2.
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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 diam- eter or width of capital is twice that of the column.
10.7.6.4 Lateral support of offset bent longitudinal bars 10.7.6.4.1 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.
10.7.6.4.2 If transverse reinforcement is provided to resist forces that result from offset bends, ties, hoops, or spirals shall be placed not more than 150 mm from points of bend.
10.7.6.5 Shear
10.7.6.5.1 If required, shear reinforcement shall be provided using ties, hoops, or spirals.
10.7.6.5.2 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, mm Nonprestressed
column Prestressed column 0.33
≤ f b dc w′ Lesser of: d/2 3h/4 600
0.33
> f b dc w′ Lesser of: d/4 3h/8 300
CHAPTER 11—WALLS 11.1—Scope
11.1.1 This chapter shall apply to the design of nonpre- stressed and prestressed walls including (a) through (c):
(a) Cast-in-place (b) Precast in-plant
(c) Precast on-site including tilt-up
11.1.2 Design of special structural walls shall be in accor- dance with Chapter 18.
11.1.3 Design of plain concrete walls shall be in accor- dance with Chapter 14.
11.1.4 Design of cantilever retaining walls shall be in accordance with 22.2 through 22.4, with minimum hori- zontal reinforcement in accordance with 11.6.
11.1.5 Design of walls as grade beams shall be in accor-