7 — Concrete protection for reinforcement

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Beams, columns:

Primary reinforcement, ties, stirrups,

spirals ...............................................................40

Shells, folded plate members:

No. 19 bar and larger ...................................... 20

No. 16 bar, MW200 or MD200 wire, and smaller.. 13



Alternative methods of protecting the reinforcement from

weather may be provided if they are equivalent to the

additional concrete cover required by the Code. When

approved by the building official under the provisions of 1.4,

reinforcement with alternative protection from the weather

may have concrete cover not less than the cover required for

reinforcement not exposed to weather.



7.7.2 — Cast-in-place concrete (prestressed)



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Unless a greater concrete cover is required by 7.7.6 or

7.7.8, specified cover for prestressed and nonprestressed reinforcement, ducts, and end fittings shall

not be less than the following:



The development length given in Chapter 12 is now a function

of the bar cover. As a result, it may be desirable to use larger

than minimum cover in some cases.



Concrete

cover, mm

(a) Concrete cast against and

permanently exposed to earth...............................75

(b) Concrete exposed to earth or weather:

Wall panels, slabs, joists .....................................25

Other members ...................................................40

(c) Concrete not exposed to weather or in contact

with ground:

Slabs, walls, joists .............................................. 20

Beams, columns:

Primary reinforcement ......................................40

Ties, stirrups, spirals ........................................25

Shells, folded plate members:

No. 16 bar, MW200 or MD200 wire, and smaller.. 10

Other reinforcement ......... db but not less than 20

7.7.3 — Precast concrete (manufactured under

plant control conditions)



R7.7.3 — Precast concrete (manufactured under plant

control conditions)



Unless a greater cover is required by 7.7.6 or 7.7.8,

specified cover for prestressed and nonprestressed

reinforcement, ducts, and end fittings shall not be less

than the following:



The lesser cover thicknesses for precast construction reflect

the greater convenience of control for proportioning, placing,

and curing inherent in precasting. The term “manufactured

under plant control conditions” does not specifically imply

that precast members should be manufactured in a plant.

Structural elements precast at the job site will also qualify

under this section if the control of form dimensions, placing

of reinforcement, quality control of concrete, and curing

procedure are equal to that normally expected in a plant.



Concrete

cover, mm

(a) Concrete exposed to earth or weather:

Wall panels:

No. 43 and No. 57 bars, prestressing

tendons larger than 40 mm diameter ...............40

No. 36 bar and smaller, prestressing

tendons 40 mm diameter and smaller,

MW200 and MD200 wire and smaller ............. 20

Other members:

No. 43 and No. 57 bars, prestressing

tendons larger than 40 mm diameter ...............50

No. 19 through No. 36 bars, prestressing

tendons larger than 16 mm diameter

through 40 mm diameter ..................................40



Concrete cover to pretensioned strand as described in this

section is intended to provide minimum protection against

weather and other effects. Such cover may not be sufficient to

transfer or develop the stress in the strand, and it may be

necessary to increase the cover accordingly.



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No. 16 bar and smaller, prestressing tendons

16 mm diameter and smaller, MW200

and MD200 wire, and smaller .......................... 30

(b) Concrete not exposed to weather

or in contact with ground:

Slabs, walls, joists:

No. 43 and No. 57 bars, prestressing

tendons larger than 40 mm diameter ............... 30

Prestressing tendons 40 mm diameter

and smaller ...................................................... 20

No. 36 bar and smaller, MW200 or MD200 wire,

and smaller ...................................................... 16

Beams, columns:

Primary reinforcement ................. db but not less

than 16 and need not

exceed 40

Ties, stirrups, spirals ........................................ 10

Shells, folded plate members:

Prestressing tendons ....................................... 20

No. 19 bar and larger ...................................... 16

No. 16 bar and smaller, MW200 or

MD200 wire, and smaller ................................. 10



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7.7.4 — Bundled bars

For bundled bars, minimum specified concrete cover

shall not be less than the equivalent diameter of the

bundle, but need not be greater than 50 mm; except

for concrete cast against and permanently exposed to

earth, where specified concrete cover shall not be less

than 75 mm.



Fig. R7.7.5—Concrete cover requirements for headed shear

stud reinforcement.

7.7.5 — Headed shear stud reinforcement



R.7.7.5 — Headed shear stud reinforcement



For headed shear stud reinforcement, specified

concrete cover for the heads or base rails shall not be

less than that required for the reinforcement in the type

of member in which the headed shear stud reinforcement is placed.



The shanks, the heads, and the base rails need to be

protected by the specified concrete cover. For efficiency in

controlling inclined shear cracks, the overall height of the

headed stud assembly should be as large as permissible

(R11.11.5). The maximum overall height of the headed

study assembly is equal to the thickness of the member less

the sum of the specified concrete covers required for the

heads and base rails as shown in Fig. R7.7.5.



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7.7.6 — Corrosive environments



R7.7.6 — Corrosive environments



In corrosive environments or other severe exposure

conditions, the concrete cover shall be increased as

deemed necessary and specified by the licensed

design professional. The applicable requirements for

concrete based on exposure categories and classes in

Chapter 4 shall be met, or other protection shall be

provided.



Where concrete will be exposed to external sources of chlorides in service, such as deicing salts, brackish water,

seawater, or spray from these sources, concrete should be

proportioned to satisfy the requirements for the applicable

exposure class in Chapter 4. These include minimum air

content, maximum w/cm, minimum strength for normalweight and lightweight concrete, maximum chloride ion in

concrete, and cement type. Additionally, for corrosion

protection, a specified concrete cover for reinforcement not

less than 50 mm for walls and slabs and not less than 65 mm

for other members is recommended. For precast concrete

members manufactured under plant control conditions, a

specified concrete cover not less than 40 mm for walls

and slabs and not less than 50 mm for other members is

recommended.



7.7.6.1 — For prestressed concrete members

exposed to corrosive environments or other severe

exposure categories such as those defined in Chapter 4,

and which are classified as Class T or C in 18.3.3,

specified concrete cover shall not be less than 1.5

times the cover for prestressed reinforcement required

by 7.7.2 and 7.7.3. This requirement shall be

permitted to be waived if the precompressed tensile

zone is not in tension under sustained loads.



R7.7.6.1 — Corrosive environments are defined in

Sections 4.2, R4.2.1, and R4.3.1. Additional information on

corrosion in parking structures is given in ACI 362.1R.7.12



7



7.7.7 — Future extensions

Exposed reinforcement, inserts, and plates intended

for bonding with future extensions shall be protected

from corrosion.

7.7.8 — Fire protection

If the general building code (of which this Code forms

a part) requires a thickness of cover for fire protection

greater than the concrete cover in 7.7.1 through 7.7.7,

such greater thicknesses shall be specified.



7.8 — Reinforcement details for columns



R7.8 — Reinforcement details for columns



7.8.1 — Offset bars

Offset bent longitudinal bars shall conform to the following:

7.8.1.1 — Slope of inclined portion of an offset bar

with axis of column shall not exceed 1 in 6.

7.8.1.2 — Portions of bar above and below an offset

shall be parallel to axis of column.

7.8.1.3 — Horizontal support at offset bends shall be

provided by transverse ties, spirals, or parts of the

floor construction. Horizontal support provided shall be

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designed to resist 1-1/2 times the horizontal component

of the computed force in the inclined portion of an

offset bar. Transverse ties or spirals, if used, shall be

placed not more than 150 mm from points of bend.

7.8.1.4 — Offset bars shall be bent before placement

in the forms. See 7.3.

7.8.1.5 — Where a column face is offset 75 mm or

greater, longitudinal bars shall not be offset bent.

Separate dowels, lap spliced with the longitudinal bars

adjacent to the offset column faces, shall be provided.

Lap splices shall conform to 12.17.



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7.8.2 — Steel cores



R7.8.2 — Steel cores



Load transfer in structural steel cores of composite

compression members shall be provided by the

following:



The 50 percent limit on transfer of compressive load by end

bearing on ends of structural steel cores is intended to provide

some tensile strength at such splices (up to 50 percent),

since the remainder of the total compressive stress in the

steel core are to be transmitted by dowels, splice plates,

welds, etc. This provision should ensure that splices in

composite compression members meet essentially the same

tensile strength as required for conventionally reinforced

concrete compression members.



7.8.2.1 — 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.

7.8.2.2 — At end bearing splices, bearing shall be

considered effective to transfer not more than 50 percent

of the total compressive stress in the steel core.

7.8.2.3 — Transfer of stress between column base

and footing shall be designed in accordance with 15.8.

7.8.2.4 — Base of structural steel section shall be

designed to transfer the total load from the entire

composite member to the footing; or, the base shall be

designed to transfer the load from the steel core only,

provided ample concrete section is available for

transfer of the portion of the total load carried by the

reinforced concrete section to the footing by compression in the concrete and by reinforcement.



7.9 — Connections



R7.9 — Connections



7.9.1 — At connections of principal framing elements

(such as beams and columns), enclosure shall be

provided for splices of continuing reinforcement and

for anchorage of reinforcement terminating in such

connections.



Confinement is essential at connections to ensure that the

flexural strength of the members can be developed without

deterioration of the joint under repeated loadings.7.13,7.14



7.9.2 — Enclosure at connections shall consist of

external concrete or internal closed ties, spirals, or

stirrups.



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