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 steel reinforcement, and shall govern (a) through (c):
(a) Material properties
(b) Properties to be used for design
(c) Durability requirements, including minimum specified cover requirements
Provisions of 20.6 shall apply to embedments.
Nonprestressed bars and wires shall be deformed, except plain bars or wires are permitted for use in spirals.
Yield strength of nonprestressed bars and wires shall be determined by either (a) or (b):
(a) The offset method, using an offset of 0.2 percent in accordance with ASTM A370
(b) The yield point by the halt-of-force method, provided the nonprestressed bar or wire has a sharp-kneed or well-defined yield point
Deformed bars shall conform to (a), (b), (c), (d), or (e), except bar sizes larger than No. 18 shall not be permitted:
(a) ASTM A615 — carbon steel, including requirements specified in Table 20.2.1.3(a)
(b) ASTM A706 — low-alloy steel, including requirements specified in (i), (ii), and (iii):
(i) Tensile property requirements for ASTM A706 Grade 100 reinforcement shall be as specified in Table 20.2.1.3(b), and bend test requirements for ASTM A706 Grade 100 reinforcement shall be the same as the bend test requirements for ASTM A706 Grade 80 reinforcement.
(ii) Uniform elongation requirements for all grades of ASTM A706 reinforcement shall be as specified in Table 20.2.1.3(c), and uniform elongation shall be determined as the elongation at the maximum force sustained by the reinforcing bar test piece.
(iii) For all grades of ASTM A706 reinforcement, the radius at the base of each deformation shall be at least 1.5 times the height of the deformation. This requirement applies to all deformations, including transverse lugs, longitudinal ribs, grade ribs, grade marks, and intersections between deformations. Conformance shall be assessed by measurements taken on newly-machined rolls used to manufacture reinforcing bars, instead of measurements taken on bar samples.
Table 20.2.1.3(a)—Modified tensile strength and additional tensile property requirements for ASTM A615 reinforcement
Grade 40 Grade 60 Grade 80 Grade 100
Tensile strength, minimum, psi 60,000 80,000 100,000 115,000
Ratio of actual tensile strength to actual yield strength, minimum 1.10 1.10 1.10 1.10
Table 20.2.1.3(b)—Tensile property requirements for ASTM A706 Grade 100 reinforcement
Grade 100
Tensile strength, minimum, psi 117,000
Ratio of actual tensile strength to actual yield strength, minimum 1.17
Yield strength, minimum, psi 100,000
Yield strength, maximum, psi 118,000
Fracture elongation in 8 in., minimum, % 10
Table 20.2.1.3(c)—Uniform elongation requirements for ASTM A706 reinforcement
Grade 60 Grade 80 Grade 100
Uniform elongation, minimum, percent
Bar designation No.
3, 4, 5, 6, 7, 8, 9, 10 9 7 6
11, 14, 18 6 6 6
(c) ASTM A996 — axle steel and rail steel; bars from rail steel shall be Type R
(d) ASTM A955 — stainless steel
(e) ASTM A1035 — low-carbon chromium steel
Plain bars for spiral reinforcement shall conform to ASTM A615, A706, A955, or A1035.
Welded deformed bar mats shall conform to ASTM A184. Deformed bars used in welded deformed bar mats shall conform to ASTM A615 or A706.
Headed deformed bars shall conform to ASTM A970, including Annex A1 requirements for Class HA head dimensions.
Deformed wire, plain wire, welded deformed wire reinforcement, and welded plain wire reinforcement shall conform to (a) or (b), except that yield strength shall be determined in accordance with 20.2.1.2:
(a) ASTM A1064 — carbon steel
(b) ASTM A1022 — stainless steel
Deformed wire sizes D4 through D31 shall be permitted.
Deformed wire sizes larger than D31 shall be permitted in welded wire reinforcement if treated as plain wire for calculation of development and splice lengths in accordance with 25.4.7 and 25.5.4, respectively.
Except as permitted for welded wire reinforcement used as stirrups in accordance with 25.7.1, spacing of welded intersections in welded wire reinforcement in the direction of calculated stress shall not exceed (a) or (b):
(a) 16 in. for welded deformed wire reinforcement
(b) 12 in. for welded plain wire reinforcement
For nonprestressed bars and wires, the stress below fy shall be Es times steel strain. For strains greater than that corresponding to fy, stress shall be considered independent of strain and equal to fy.
Modulus of elasticity, Es, for nonprestressed bars and wires shall be permitted to be taken as 29,000,000 psi.
Yield strength for nonprestressed bars and wires shall be based on the specified grade of reinforcement and shall not exceed the values given in 20.2.2.4 for the associated applications.
Types of nonprestressed bars and wires to be specified for particular structural applications shall be in accordance with Table 20.2.2.4(a) for deformed reinforcement and Table 20.2.2.4(b) for plain reinforcement.
Table 20.2.2.4(a)—Nonprestressed deformed reinforcement
Usage Application Maximum value of fy or fyt permitted for design calculations, psi Applicable ASTM specification
Deformed bars Deformed wires Welded wire reinforcement Welded deformed bar mats
Flexure; axial force; and shrinkage and temperature Special seismic systems Special moment frames 80,000 A706[2] Not permitted Not permitted Not permitted
Special structural walls[1] 100,000
Other 100,000[3][4] A615, A706, A955, A996, A1035 A1064, A1022 A1064, A1022 A184[5]
Lateral support of longitudinal bars; or concrete confinement Special seismic systems 100,000 A615, A706, A955, A996, A1035 A1064, A1022 A1064[6], A1022[6] Not permitted
Spirals 100,000 A615, A706, A955, A996, A1035 A1064, A1022 Not permitted Not permitted
Other 80,000 A615, A706, A955, A996 A1064, A1022 A1064, A1022 Not permitted
Shear Special seismic systems[7] Special moment frames[8] 80,000 A615, A706, A955, A996 A1064, A1022 A1064[6], A1022[6] Not permitted
Special structural walls[9] 100,000
Spirals 60,000 A615, A706, A955, A996 A1064, A1022 Not permitted Not permitted
Shear friction 60,000 A615, A706, A955, A996 A1064, A1022 A1064, A1022 Not permitted
Stirrups, ties, hoops 60,000 A615, A706, A955, A996, A1035 A1064, A1022 A1064 and A1022 welded plain wire Not permitted
80,000 Not permitted Not permitted A1064 and A1022 welded deformed wire Not permitted
Torsion Longitudinal and transverse 60,000 A615, A706, A955, A996 A1064, A1022 A1064, A1022 Not permitted
Anchor reinforcement Special seismic systems 80,000 A706[2] Not permitted Not permitted Not permitted
Other 80,000 A615, A706, A955, A996 A1064, A1022 A1064, A1022 A184[5]
Regions designed using strut-and-tie method Longitudinal ties 80,000 A615, A706, A955, A996 A1064, A1022 A1064, A1022 Not permitted
Other 60,000
[1]All components of special structural walls, including coupling beams and wall piers.
[2]ASTM A615 Grade 60 shall be permitted if requirements of 20.2.2.5(b) are satisfied.
[3]In slabs and beams not part of a special seismic system, bars that pass through or extend from special structural walls shall satisfy 20.2.2.5.
[4]Longitudinal reinforcement with fy > 80,000 psi is not permitted for intermediate moment frames and ordinary moment frames resisting earthquake demands E.
[5]Welded deformed bar mats shall be permitted to be assembled using only ASTM A615 or A706 deformed bars of Grade 60 or Grade 80.
[6]ASTM A1064 and A1022 are not permitted in special seismic systems if the weld is required to resist stresses in response to confinement, lateral support of longitudinal bars, shear, or other actions.
[7]This application also includes shear reinforcement with a maximum value of 80,000 psi fy or fyt permitted for design calculations for diaphragms and foundations for load combinations including earthquake forces if part of a building with a special seismic system.
[8]Shear reinforcement in this application includes stirrups, ties, hoops, and spirals in special moment frames.
[9]Shear reinforcement in this application includes all transverse reinforcement in special structural walls, coupling beams, and wall piers. Diagonal bars in coupling beams shall comply with ASTM A706 or Footnote [2].
Table 20.2.2.4(b)—Nonprestressed plain spiral reinforcement
Usage Application Maximum value of fy or fyt permitted for design calculations, psi Applicable ASTM specification
Plain bars Plain wires
Lateral support of longitudinal bars; or concrete confinement Spirals in special seismic systems 100,000 A615, A706, A955, A1035 A1064, A1022
Spirals 100,000 A615, A706, A955, A1035 A1064, A1022
Shear Spirals 60,000 A615, A706, A955, A1035 A1064, A1022
Torsion in nonprestressed beams Spirals 60,000 A615, A706, A955, A1035 A1064, A1022
Deformed nonprestressed longitudinal reinforcement resisting earthquake-induced moment, axial force, or both, in special seismic systems and anchor reinforcement in Seismic Design Categories (SDC) C, D, E, and F shall be in accordance with (a) or (b):
(a) ASTM A706, Grade 60, 80, or 100 for special structural walls and Grade 60 and 80 for special moment frames.
(b) ASTM A615 Grade 60 if (i) through (iv) are satisfied. ASTM A615 Grade 80 and Grade 100 are not permitted in special seismic systems.
(i) Actual yield strength based on mill tests does not exceed fy by more than 18,000 psi
(ii) Ratio of the actual tensile strength to the actual yield strength is at least 1.25
(iii) Minimum fracture elongation in 8 in. shall be at least 14 percent for bar sizes No. 3 through No. 6, at least 12 percent for bar sizes No. 7 through No. 11, and at least 10 percent for bar sizes No. 14 and No. 18.
(iv) Minimum uniform elongation shall be at least 9 percent for bar sizes No. 3 through No. 10, and at least 6 percent for bar sizes No. 11, No. 14, and No. 18.
Except as required in 20.3.1.3 for special moment frames and special structural walls, prestressing reinforcement shall conform to (a), (b), (c), or (d):
(a) ASTM A416 — strand
(b) ASTM A421 — wire
(c) ASTM A421 — low-relaxation wire including Supplementary Requirement S1, "Low-Relaxation Wire and Relaxation Testing"
(d) ASTM A722 — high-strength bar
Prestressing strands, wires, and bars not listed in ASTM A416, A421, or A722 are permitted provided they conform to minimum requirements of these specifications and are shown by test or analysis not to impair the performance of the member.
Prestressing reinforcement resisting earthquake-induced moment, axial force, or both, in special moment frames, special structural walls, and all components of special structural walls including coupling beams and wall piers, cast using precast concrete shall comply with ASTM A416 or ASTM A722.
Modulus of elasticity, Ep, for prestressing reinforcement shall be determined from tests or as reported by the manufacturer.
Tensile strength, fpu, shall be based on the specified grade or type of prestressing reinforcement and shall not exceed the values given in Table 20.3.2.2.
Table 20.3.2.2—Prestressing strands, wires, and bars
Type Maximum value of fpu permitted for design calculations, psi Applicable ASTM Specification
Strand (stress-relieved and low-relaxation) 270,000 A416
Wire (stress-relieved and low-relaxation) 250,000 A421
A421, including Supplementary Requirement S1 "Low-Relaxation Wire and Relaxation Testing"
High-strength bar 150,000 A722
As an alternative to a more accurate calculation of fps based on strain compatibility, values of fps calculated in accordance with Eq. (20.3.2.3.1) shall be permitted for members with bonded prestressed reinforcement if all prestressed reinforcement is in the tension zone and fse ≥ 0.5fpu.
(20.3.2.3.1)
where γp is in accordance with Table 20.3.2.3.1.
If compression reinforcement is considered for the calculation of fps by Eq. (20.3.2.3.1), (a) and (b) shall be satisfied.
(a) If d' exceeds 0.15dp, the compression reinforcement shall be neglected in Eq. (20.3.2.3.1).
(b) If compression reinforcement is included in Eq. (20.3.2.3.1), the term
shall not be taken less than 0.17.
Table 20.3.2.3.1—Values of γp for use in Eq. (20.3.2.3.1)
fpy/fpu γp
≥ 0.80 0.55
≥ 0.85 0.40
≥ 0.90 0.28
For pretensioned strands, the strand design stress at sections of members located within d from the free end of strand shall not exceed that calculated in accordance with 25.4.8.3.
As an alternative to a more accurate calculation of fps, values of fps calculated in accordance with Table 20.3.2.4.1 shall be permitted for members prestressed with unbonded tendons if fse ≥ 0.5fpu.
Table 20.3.2.4.1—Approximate values of fps at nominal flexural strength for unbonded tendons
n/h fps
≤ 35 The least of: fse + 10,000 + fc'/(100ρp)
fse + 60,000
fpy
> 35 The least of: fse + 10,000 + fc'/(300ρp)
fse + 30,000
fpy
The tensile stress in prestressed reinforcement shall not exceed the limits in Table 20.3.2.5.1.
Table 20.3.2.5.1—Maximum permissible tensile stresses in prestressed reinforcement
Stage Location Maximum tensile stress
During stressing At jacking end Least of: 0.94fpy
0.80fpu
Maximum jacking force recommended by the supplier of anchorage device
Immediately after force transfer At post-tensioning anchorage devices and couplers 0.70fpu
Prestress losses shall be considered in the calculation of the effective tensile stress in the prestressed reinforcement, fse, and shall include (a) through (f):
(b) Elastic shortening of concrete
(c) Creep of concrete
(d) Shrinkage of concrete
(e) Relaxation of prestressed reinforcement
(f) Friction loss due to intended or unintended curvature in post-tensioning tendons
Calculated friction loss in post-tensioning tendons shall be based on experimentally determined wobble and curvature friction coefficients.
Where loss of prestress in a member is anticipated due to connection of the member to adjoining construction, such loss of prestress shall be included in design calculations.
Headed shear stud reinforcement and stud assemblies shall conform to ASTM A1044.

20.5.1.1

Diagram
Unless the general building code requires a greater concrete cover for fire protection, the minimum specified concrete cover shall be in accordance with 20.5.1.2 through 20.5.1.4.
It shall be permitted to consider concrete floor finishes as part of required cover for nonstructural purposes.
Nonprestressed cast-in-place concrete members shall have specified concrete cover for reinforcement at least that given in Table 20.5.1.3.1.
Table 20.5.1.3.1—Specified concrete cover for cast-in-place nonprestressed concrete members
Concrete exposure Member Reinforcement Specified cover, in.
Cast against and permanently in contact with ground All All 3
Exposed to weather or in contact with ground All No. 6 through No. 18 bars 2
No. 5 bar, W31 or D31 wire, and smaller 1-1/2
Not exposed to weather or in contact with ground Slabs, joists, and walls No. 14 and No. 18 bars 1-1/2
No. 11 bar and smaller 3/4
Beams, columns, pedestals, and tension ties Primary reinforcement, stirrups, ties, spirals, and hoops 1-1/2
Cast-in-place prestressed concrete members shall have specified concrete cover for reinforcement, ducts, and end fittings at least that given in Table 20.5.1.3.2.
Table 20.5.1.3.2—Specified concrete cover for cast-in-place prestressed concrete members
Concrete exposure Member Reinforcement Specified cover, in.
Cast against and permanently in contact with ground All All 3
Exposed to weather or in contact with ground Slabs, joists, and walls All 1
All other All 1-1/2
Not exposed to weather or in contact with ground Slabs, joists, and walls All 3/4
Beams, columns, and tension ties Primary reinforcement 1-1/2
Stirrups, ties, spirals, and hoops 1
Precast nonprestressed or prestressed concrete members manufactured under plant conditions shall have specified concrete cover for reinforcement, ducts, and end fittings at least that given in Table 20.5.1.3.3.
Table 20.5.1.3.3—Specified concrete cover for precast-nonprestressed or prestressed concrete members manufactured under plant conditions
Concrete exposure Member Reinforcement Specified cover, in.
Exposed to weather or in contact with ground Walls No. 14 and No. 18 bars; tendons larger than 1-1/2 in. diameter 1-1/2
No. 11 bars and smaller; W31 and D31 wire and smaller; tendons and strands 1-1/2 in. diameter and smaller 3/4
All other No. 14 and No. 18 bars; tendons larger than 1-1/2 in. diameter 2
No. 6 through No. 11 bars; tendons and strands larger than 5/8 in. diameter through 1-1/2 in. diameter 1-1/2
No. 5 bar, W31 or D31 wire, and smaller; tendons and strands 5/8 in. diameter and smaller 1-1/4
Not exposed to weather or in contact with ground Slabs, joists, and walls No. 14 and No. 18 bars; tendons larger than 1-1/2 in. diameter 1-1/4
Tendons and strands 1-1/2 in. diameter and smaller 3/4
No. 11 bar, W31 or D31 wire, and smaller 5/8
Beams, columns, pedestals, and tension ties Primary reinforcement Greater of db and 5/8 and need not exceed 1-1/2
Stirrups, ties, spirals, and hoops 3/8
Deep foundation members shall have specified concrete cover for reinforcement at least that given in Table 20.5.1.3.4.
Table 20.5.1.3.4—Specified concrete cover for deep foundation members
Concrete exposure Deep foundation member type Reinforcement Specified cover, in.
Cast against and permanently in contact with ground, not enclosed by steel pipe, tube permanent casing, or stable rock socket Cast-in-place All 3
Enclosed by steel pipe, tube, permanent casing, or stable rock socket Cast-in-place All 1-1/2
Permanently in contact with ground Precast-nonprestressed All 1-1/2
Precast-prestressed
Exposed to seawater Precast-nonprestressed All 2-1/2
Precast-prestressed All 2
For bundled bars, specified concrete cover shall be at least the smaller of (a) and (b):
(a) The equivalent diameter of the bundle
(b) 2 in.
and for concrete cast against and permanently in contact with ground, the specified cover shall be 3 in.
For headed shear stud reinforcement, specified concrete cover for the heads and base rails shall be at least that required for the reinforcement in the member.
In corrosive environments or other severe exposure conditions, the specified concrete cover shall be increased as deemed necessary. The applicable requirements for concrete based on exposure categories in 19.3 shall be satisfied, or other protection shall be provided.
For prestressed concrete members classified as Class T or C in 24.5.2 and exposed to corrosive environments or other severe exposure categories such as those given in 19.3, the specified concrete cover for prestressed reinforcement shall be at least one and one-half times the cover in 20.5.1.3.2 for cast-in-place members and in 20.5.1.3.3 for precast members.
If the precompressed tension zone is not in tension under sustained loads, 20.5.1.4.2 need not be satisfied.
Nonprestressed coated reinforcement shall conform to Table 20.5.2.1.
Table 20.5.2.1—Nonprestressed coated reinforcement
Type of coating Applicable ASTM specifications
Bar Wire Welded wire
Zinc-coated A767 Not permitted A1060
Epoxy-coated A775 or A934 A884 A884
Zinc and epoxy dual-coated A1055 Not permitted Not permitted
Deformed bars to be zinc-coated, epoxy-coated, or zinc and epoxy dual-coated shall conform to 20.2.1.3(a), (b), or (c).
Wire and welded wire reinforcement to be epoxy-coated shall conform to 20.2.1.7(a).
Unbonded prestressing reinforcement shall be encased in sheathing, and the space between the prestressing reinforcement and the sheathing shall be completely filled with a material formulated to inhibit corrosion. Sheathing shall be watertight and continuous over the unbonded length.
The sheathing shall be connected to all stressing, intermediate, and fixed anchorages in a watertight fashion.
Unbonded single-strand tendons shall be protected to provide resistance to corrosion in accordance with ACI 423.7.
Ducts for grouted tendons shall be grout-tight and nonreactive with concrete, prestressing reinforcement, grout, and corrosion inhibitor admixtures.
Ducts shall be maintained free of water.
Ducts for grouted single-wire, single-strand, or single-bar tendons shall have an inside diameter at least 1/4 in. larger than the diameter of the prestressing reinforcement.
Ducts for grouted multiple wire, multiple strand, or multiple bar tendons shall have an inside cross-sectional area at least two times the cross-sectional area of the prestressing reinforcement.
Anchorages, couplers, and end fittings shall be protected to provide long-term resistance to corrosion.
External tendons and tendon anchorage regions shall be protected to provide resistance to corrosion.

20.6 Embedments

Diagram
Embedments shall not significantly impair the strength of the structure and shall not reduce fire protection.
Embedment materials shall not be harmful to concrete or reinforcement.
Aluminum embedments shall be coated or covered to prevent aluminum-concrete reaction and electrolytic action between aluminum and steel.
Reinforcement with an area at least 0.002 times the area of the concrete section shall be provided perpendicular to pipe embedments.
Specified concrete cover for pipe embedments with their fittings shall be at least 1-1/2 in. for concrete exposed to earth or weather, and at least 3/4 in. for concrete not exposed to weather, or not in contact with ground.
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