3 — Embedments in concrete

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6.3.5.3 — They shall not impair significantly the

strength of the construction.

6.3.6 — Conduits, pipes, and sleeves shall be

permitted to be considered as replacing structurally in

compression the displaced concrete provided in

6.3.6.1 through 6.3.6.3.



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6.3.6.1 — They are not exposed to rusting or other

deterioration.

6.3.6.2 — They are of uncoated or galvanized iron

or steel not thinner than standard Schedule 40 steel

pipe.

6.3.6.3 — They have a nominal inside diameter not

over 50 mm and are spaced not less than three diameters on centers.

6.3.7 — Pipes and fittings shall be designed to resist

effects of the material, pressure, and temperature to

which they will be subjected.



R6.3.7 — The 1983 Code limited the maximum pressure in

embedded pipe to 1.4 MPa, which was considered too

restrictive. Nevertheless, the effects of such pressures and

the expansion of embedded pipe should be considered in the

design of the concrete member.



6.3.8 — No liquid, gas, or vapor, except water not

exceeding 32°C nor 0.35 MPa pressure, shall be

placed in the pipes until the concrete has attained its

design strength.

6.3.9 — In solid slabs, piping, unless it is for radiant

heating or snow melting, shall be placed between top

and bottom reinforcement.

6.3.10 — Specified concrete cover for pipes, conduits,

and fittings shall not be less than 40 mm for concrete

exposed to earth or weather, nor less than 20 mm for

concrete not exposed to weather or in contact with

ground.

6.3.11 — Reinforcement with an area not less than

0.002 times area of concrete section shall be provided

normal to piping.

6.3.12 — Piping and conduit shall be so fabricated and

installed that cutting, bending, or displacement of reinforcement from its proper location will not be required.



6.4 — Construction joints



R6.4 — Construction joints



6.4.1 — Surface of concrete construction joints shall

be cleaned and laitance removed.



For the integrity of the structure, it is important that all

construction joints be defined in construction documents

and constructed as required. Any deviations should be

approved by the licensed design professional.



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6.4.2 — Immediately before new concrete is placed,

all construction joints shall be wetted and standing

water removed.



R6.4.2 — The requirements of the 1977 Code for the use of

neat cement on vertical joints have been removed, since it is

rarely practical and can be detrimental where deep forms

and steel congestion prevent proper access. Often wet

blasting and other procedures are more appropriate.

Because the Code sets only minimum standards, the

licensed design professional may have to specify additional

procedures if conditions warrant. The degree to which

mortar batches are needed at the start of concrete placement

depend on concrete proportions, congestion of steel,

vibrator access, and other factors.



6.4.3 — Construction joints shall be so made and

located as not to impair the strength of the structure.

Provision shall be made for transfer of shear and other

forces through construction joints. See 11.6.9.



R6.4.3 — Construction joints should be located where they

will cause the least weakness in the structure. When shear

due to gravity load is not significant, as is usually the case in

the middle of the span of flexural members, a simple

vertical joint may be adequate. Lateral force design may

require special design treatment of construction joints.

Shear keys, intermittent shear keys, diagonal dowels, or the

shear transfer method of 11.6 may be used whenever a force

transfer is required.



6.4.4 — Construction joints in floors shall be located

within the middle third of spans of slabs, beams, and

girders.

6.4.5 — Construction joints in girders shall be offset a

minimum distance of two times the width of intersecting

beams.

6.4.6 — Beams, girders, or slabs supported by

columns or walls shall not be cast or erected until

concrete in the vertical support members is no longer

plastic.



R6.4.6 — Delay in placing concrete in members supported

by columns and walls is necessary to prevent cracking at the

interface of the slab and supporting member caused by

bleeding and settlement of plastic concrete in the supporting

member.



6.4.7 — Beams, girders, haunches, drop panels, shear

caps, and capitals shall be placed monolithically as

part of a slab system, unless otherwise shown in

contract documents.



R6.4.7 — Separate placement of slabs and beams,

haunches, and similar elements is permitted when shown on

the contract documents and where provision has been made

to transfer forces as required in 6.4.3.



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CHAPTER 7 — DETAILS OF REINFORCEMENT

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7.1 — Standard hooks



R7.1 — Standard hooks



The term “standard hook” as used in this Code shall

mean one of the following:



Recommended methods and standards for preparing design

drawings, typical details, and drawings for the fabrication

and placing of reinforcing steel in reinforced concrete

structures are given in the ACI Detailing Manual, reported

by ACI Committee 315.7.1



7.1.1 — 180-degree bend plus 4db extension, but not

less than 65 mm at free end of bar.

7.1.2 — 90-degree bend plus 12db extension at free

end of bar.



All provisions in the Code relating to bar, wire, or strand

diameter (and area) are based on the nominal dimensions of

the reinforcement as given in the appropriate ASTM specification. Nominal dimensions are equivalent to those of a

circular area having the same weight per meter as the

ASTM designated bar, wire, or strand sizes. Cross-sectional

area of reinforcement is based on nominal dimensions.



7.1.3 — For stirrup and tie hooks



R7.1.3 — Standard stirrup and tie hooks are limited to

No. 25 bars and smaller, and the 90-degree hook with 6db

extension is further limited to No. 16 bars and smaller, in

both cases as the result of research showing that larger bar

sizes with 90-degree hooks and 6db extensions tend to pop

out under high load.



(a) No. 16 bar and smaller, 90-degree bend plus 6db

extension at free end of bar; or

(b) No. 19, No. 22, and No. 25 bar, 90-degree bend

plus 12db extension at free end of bar; or

(c) No. 25 bar and smaller, 135-degree bend plus

6db extension at free end of bar.

7.1.4 — Seismic hooks as defined in 2.2.



7.2 — Minimum bend diameters



R7.2 — Minimum bend diameters



7.2.1 — Diameter of bend measured on the inside of

the bar, other than for stirrups and ties in sizes No. 10

through No. 16, shall not be less than the values in

Table 7.2.



Standard bends in reinforcing bars are described in terms

of the inside diameter of bend because this is easier to

measure than the radius of bend. The primary factors

affecting the minimum bend diameter are feasibility of

bending without breakage and avoidance of crushing the

concrete inside the bend.



7.2.2 — Inside diameter of bend for stirrups and ties

shall not be less than 4db for No. 16 bar and smaller.

For bars larger than No. 16, diameter of bend shall be

in accordance with Table 7.2.



R7.2.2 — The minimum 4db bend for the bar sizes

commonly used for stirrups and ties is based on accepted

industry practice in the United States. Use of a stirrup bar

size not greater than No. 16 for either the 90-degree or

135-degree standard stirrup hook will permit multiple

bending on standard stirrup bending equipment.



7.2.3 — Inside diameter of bend in welded wire

reinforcement for stirrups and ties shall not be less

than 4db for deformed wire larger than MD40 and 2db

for all other wires. Bends with inside diameter of less

than 8db shall not be less than 4db from nearest

welded intersection.



R7.2.3 — Welded wire reinforcement can be used for stirrups

and ties. The wire at welded intersections does not have the

same uniform ductility and bendability as in areas that were

not heated. These effects of the welding temperature are

usually dissipated in a distance of approximately four wire

diameters. Minimum bend diameters permitted are in most

cases the same as those required in the ASTM bend tests for

wire material (ASTM A1064M).



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TABLE 7.2 — MINIMUM DIAMETERS OF BEND

Bar size



Minimum diameter



No. 10 through No. 25



6db



No. 29, No. 32, and No. 36



8db



No. 43 and No. 57



10db



7.3 — Bending



R7.3 — Bending



7.3.1 — All reinforcement shall be bent cold, unless

otherwise permitted by the licensed design professional.



R7.3.1 — For unusual bends with inside diameters less than

ASTM bend test requirements, special fabrication may be

required.



7.3.2 — Reinforcement partially embedded in

concrete shall not be field bent, except as shown in the

contract documents or permitted by the licensed

design professional.



R7.3.2 — Construction conditions may make it necessary to

bend bars that have been embedded in concrete. Such field

bending should not be done without authorization of the

licensed design professional. Contract documents should

specify whether the bars will be permitted to be bent cold or

if heating should be used. Bends should be gradual and

should be straightened as required.



7



Tests7.2,7.3 have shown that A615M Grade 280 and Grade 420

reinforcing bars can be cold bent and straightened up to

90 degrees at or near the minimum diameter specified in

7.2. If cracking or breakage is encountered, heating to a

maximum temperature of 820°C may avoid this condition

for the remainder of the bars. Bars that fracture during bending

or straightening can be spliced outside the bend region.

Heating should be performed in a manner that will avoid

damage to the concrete. If the bend area is within approximately 150 mm of the concrete, some protective insulation

may need to be applied. Heating of the bar should be

controlled by temperature-indicating crayons or other suitable

means. The heated bars should not be artificially cooled (with

water or forced air) until after cooling to at least 320°C.



7.4 — Surface conditions of reinforcement



R7.4 — Surface conditions of reinforcement



7.4.1—At the time concrete is placed, reinforcement

shall be free from mud, oil, or other nonmetallic coatings

that decrease bond. Epoxy-coating of reinforcement in

accordance with standards referenced in 3.5.3.8 and

3.5.3.9 shall be permitted.



Specific limits on rust are based on tests,7.4 plus a review

of earlier tests and recommendations. Reference 7.4

provides guidance with regard to the effects of rust and

mill scale on bond characteristics of deformed reinforcing

bars. Research has shown that a normal amount of rust

increases bond. Normal rough handling generally removes

rust that is loose enough to injure the bond between the

concrete and reinforcement.



7.4.2 — Except for prestressing steel, steel reinforcement with rust, mill scale, or a combination of both

shall be considered satisfactory, provided the minimum

dimensions (including height of deformations) and

weight of a hand-wire-brushed test specimen comply

with applicable ASTM specifications referenced in 3.5.



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