Rebar - Wikipedia, the f ree ency clopedia

1/8en.wikipedia.org/wiki/Rebar

A tied rebar beam cage. This will be

embedded inside cast concrete to

increase the tensile strength of the

concrete.

Corroded concrete and rebar at bridge

of Queen Elizabeth Way crossing

Welland River in Niagara Falls,

Ontario.

RebarFrom Wikipedia, the free encyclopedia

A rebar (short for reinforcing bar), also known as reinforcing steel,reinforcement steel, rerod, a deformed bar, reo, or reo bar, is acommon steel bar, and is commonly used as a tensioning device inreinforced concrete and reinforced masonry structures holding theconcrete in compression. It is usually formed from carbon steel, and isgiven ridges for better mechanical anchoring into the

concrete.[citation needed]

Contents

1 History2 Use in concrete and masonry

3 Physical characteristics

4 Sizes and grades

4.1 U.S. sizes

4.2 Canadian sizes4.3 European sizes

4.4 Grades

5 Placing rebar

5.1 Welding

5.2 Mechanical connections5.3 Safety

6 Designations

7 Recycling

8 See also9 References

10 External links

History

Rebars were known in construction well before the era of the modern reinforced concrete. Some 150 years beforeits invention rebars were used to form the carcass of the Leaning Tower of Nevyansk in Russia, built on the ordersof the industrialist Akinfiy Demidov. The purpose of such construction is one of the many mysteries of the tower.The cast iron used for rebars was of very high quality, and there is no corrosion on them up to this day. The carcassof the tower was connected to its cast iron tented roof, crowned with the first lightning rod in the Western world.This lightning rod was grounded through the carcass, though it is not clear whether the effect was intentional.Theoffice of the first Russian oligarch (http://www.itogi.ru/archive/2002/42/102260.html) (Russian)

Use in concrete and masonry

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Rebars inside the Leaning Tower

of Nevyansk.

Concrete is a material that is very strong in compression, but relatively weak in tension. To compensate for thisimbalance in concrete's behavior, rebar is cast into it to carry the tensile loads. For this purpose, the steelreinforcement of a concrete structure is, conceptually, divided in two types of reinforcement: primary reinforcementand secondary reinforcement. Primary reinforcement refers to the reinforcement steel which is employed specificallyto guarantee the necessary resistance needed by the structure to support the design loads. Secondaryreinforcement, also known as distribution reinforcement, is employed for durability and aesthetic reasons, byproviding enough localized resistance to limit cracking and resist stresses caused by effects such as temperaturechanges and shrinkage. It is also employed to confer resistance to concentrated loads by providing enough localizedresistance and stiffness for a load to spread through a wider area.

Masonry structures and the mortar holding them together have similarproperties to concrete and also have a limited ability to carry tensile loads.Some standard masonry units like blocks and bricks are made withstrategically placed voids to accommodate rebar, which is then secured inplace with grout. This combination is known as reinforced masonry.

While any material with sufficient tensile strength could conceivably be usedto reinforce concrete, steel and concrete have similar coefficients of thermalexpansion: a concrete structural member reinforced with steel will experienceminimal stress as a result of differential expansions of the two interconnectedmaterials caused by temperature changes.

Physical characteristics

Steel has an expansion coefficient nearly equal to that of modern concrete. If this were not so, it would causeproblems through additional longitudinal and perpendicular stresses at temperatures different than the temperatureof the setting."GFRP Bar Transverse Coefficient of Thermal Expansion Effects on Concrete Cover"(http://www.writing.eng.vt.edu/urs/wallenfelsz.pdf) (PDF). http://www.writing.eng.vt.edu/urs/wallenfelsz.pdf.Retrieved 2012-08-24. Although rebar has ribs that bind it mechanically to the concrete, it can still be pulled out ofthe concrete under high stresses, an occurrence that often precedes a larger-scale collapse of the structure. Toprevent such a failure, rebar is either deeply embedded into adjacent structural members (40-60 times thediameter), or bent and hooked at the ends to lock it around the concrete and other rebar. This first approachincreases the friction locking the bar into place, while the second makes use of the high compressive strength ofconcrete.

Common rebar is made of unfinished tempered steel, making it susceptible to rusting. Normally the concrete coveris able to provide a pH value higher than 12 avoiding the corrosion reaction. Too little concrete cover cancompromise this guard through carbonation from the surface. Too much concrete cover can cause bigger crackwidths which also compromises the local guard. As rust takes up greater volume than the steel from which it wasformed, it causes severe internal pressure on the surrounding concrete, leading to cracking, spalling, and ultimately,structural failure. This phenomenon is known as oxide jacking. This is a particular problem where the concrete isexposed to salt water, as in bridges built in areas where salt is applied to roadways in winter, or in marineapplications. Uncoated, corrosion-resistant low carbon/chromium (microcomposite), epoxy-coated, galvanized orstainless steel rebars may be employed in these situations at greater initial expense, but significantly lower expenseover the service life of the project. Care should be taken during the transport, fabrication, handling, installation, andconcrete placement process when working with epoxy-coated rebar, because damage will reduce the long-termcorrosion performance of these bars. Users must take appropriate steps to inspect bars after placement and repair

any defects found in the epoxy coating [1]. Even damaged bars have shown better performance than uncoated

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reinforcing bars, though issues from debonding of the epoxy coating from the bars and corrosion under the epoxy

film have been reported [2]. These bars are used in over 70,000 bridge decks in the USA.ame="Epoxy InterestGroup">Epoxy Interest Group. [www.epoxyinterestgroup.org "Epoxy Interest Group of CRSI"] (in English).Epoxy Interest Group of CRSI. www.epoxyinterestgroup.org. Retrieved 24 August 2012.

Fiber-reinforced polymer rebar is now also being used in high-corrosion environments. It is available in many forms,from spirals for reinforcing columns, to the common rod, to meshes and many other forms. Most commerciallyavailable rebars are made from unidirectional glass fibre reinforced thermoset resins.

Sizes and grades

U.S. sizes

Imperial bar designations represent the bar diameter in fractions of ⅛ inch, such that #8 = 8⁄8 inch = 1 inchdiameter. Area = (bar size/9)2 such that area of #8 = (8/9)2 = 0.79 in 2 . This applies to #8 bars and smaller.Larger bars are sized to correspond to square bars that were formerly used. The diameter of the #9 bar is set sothat the area is 1.000 inch2, corresponding to a 1 inch square bar. The remaining bars, #10, #11, #14, and #18,correspond to 1⅛ inch, 1¼, 1½, and 2 inch square bars, respectively.Wang, Chu-Kia; Salmon, Charles; Pincheira,Jose (2007). Reinforced Concrete Design. Hoboken, NJ: John Wiley & Sons. p. 20. ISBN 978-0-471-26286-2. The tower and sign industry commonly use #14J and #18J (for "Jumbo") bars as anchor rods for largestructures. The bars are fabricated from slightly oversized blanks such that standard 1.75" (#14J) and 2.25" (#18J)threads can be rolled at the ends to accept anchor nuts.

Imperial

Bar Size

"Soft"

MetricSize

Weight per unit

length

(lb⁄ft)

Mass per unit

length

(kg/m)

Nominal

Diameter

(in)

Nominal

Diameter

(mm)

Nominal

Area

(in²)

Nominal

Area

(mm²)

#3 #10 0.376 0.561 0.375 = ⅜ 9.525 0.11 71

#4 #13 0.668 0.996 0.500 = ½ 12.7 0.20 129

#5 #16 1.043 1.556 0.625 = ⅝ 15.875 0.31 200

#6 #19 1.502 2.24 0.750 = ¾ 19.05 0.44 284

#7 #22 2.044 3.049 0.875 = ⅞ 22.225 0.60 387

#8 #25 2.670 3.982 1.000 25.4 0.79 509

#9 #29 3.400 5.071 1.128 28.65 1.00 645

#10 #32 4.303 6.418 1.270 32.26 1.27 819

#11 #36 5.313 7.924 1.410 35.81 1.56 1006

#14 #43 7.650 11.41 1.693 43 2.25 1452

#18 #57 13.60 20.284 2.257 57.3 4.00 2581

#18J 14.60 21.775 2.337 59.4 4.29 2678

Canadian sizes

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Metric bar designations represent the nominal bar diameter in millimeters, rounded to the nearest 5 mm.

Metric

Bar Size

Mass per unit length

(kg/m)

Nominal Diameter

(mm)

Cross-Sectional

Area (mm²)

10M 0.785 11.3 100

15M 1.570 16.0 200

20M 2.355 19.5 300

25M 3.925 25.2 500

30M 5.495 29.9 700

35M 7.850 35.7 1000

45M 11.775 43.7 1500

55M 19.625 56.4 2500

European sizes

Metric bar designations represent the nominal bar diameter in millimetres. Bars in Europe will be specified tocomply with the standard EN 10080 (awaiting introduction as of early 2007), although various national standardsstill remain in force (e.g. BS 4449 in the United Kingdom).

Metric

Bar Size

Mass per unit length

(kg/m)

Nominal Diameter

(mm)

Cross-Sectional

Area (mm²)

6,0 0.222 6 28.3

8,0 0.395 8 50.3

10,0 0.617 10 78.5

12,0 0.888 12 113

14,0 1.21 14 154

16,0 1.579 16 201

20,0 2.467 20 314

25,0 3.855 25 491

28,0 4.83 28 616

32,0 6.316 32 804

40,0 9.868 40 1257

50,0 15.413 50 1963

Grades

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Rebar is available in different grades and specifications that vary in yield strength, ultimate tensile strength, chemicalcomposition, and percentage of elongation.

The grade designation is equal to the minimum yield strength of the bar in ksi (1000 psi) for example grade 60 rebarhas a minimum yield strength of 60 ksi. Rebar is typically manufactured in grades 40, 60, and 75.

Common ASTM specification are:American Concrete Institute: "Building Code Requirements for StructuralConcrete (ACI 318-08) and Commentary," ISBN 978-0-87031-264-9

ASTM A82: Specification for Plain Steel Wire for Concrete Reinforcement

ASTM A184/A184M: Specification for Fabricated Deformed Steel Bar Mats for Concrete ReinforcementASTM A185: Specification for Welded Plain Steel Wire Fabric for Concrete Reinforcement

ASTM A496: Specification for Deformed Steel Wire for Concrete Reinforcement

ASTM A497: Specification for Welded Deformed Steel Wire Fabric for Concrete Reinforcement

ASTM A615/A615M: Deformed and plain carbon-steel bars for concrete reinforcementASTM A616/A616M: Specification for Rail-Steel Deformed and Plain Bars for Concrete Reinforcement

ASTM A617/A617M: Specification for Axle-Steel Deformed and Plain Bars for Concrete Reinforcement

ASTM A706/A706M: Low-alloy steel deformed and plain bars for concrete reinforcementASTM A767/A767M: Specification for Zinc-Coated(Galvanized) Steel Bars for Concrete Reinforcement

ASTM A775/A775M: Specification for Epoxy-Coated Reinforcing Steel Bars

ASTM A934/A934M: Specification for Epoxy-Coated Prefabricated Steel Reinforcing Bars

ASTM A955: Deformed and plain stainless-steel bars for concrete reinforcementASTM A996: Rail-steel and axle-steel deformed bars for concrete reinforcement

ASTM A1035: Standard Specification for Deformed and Plain, Low-carbon, Chromium, Steel Bars for

Concrete Reinforcement

ASTM marking designations are:

'S' billet A615

'I' rail A616 (superseded by A996 "ASTM A616 / A616M - 96a Standard Specification for Rail Steel

Deformed and Plain Bars for Concrete Reinforcement (Withdrawn 1999)"

(http://www.astm.org/Standards/A616.htm) . Astm.org. http://www.astm.org/Standards/A616.htm.Retrieved 2012-08-24.)

'IR' Rail Meeting Supplementary Requirements S1 A616 (superseded by A996 "ASTM A616 / A616M -

96a Standard Specification for Rail Steel Deformed and Plain Bars for Concrete Reinforcement (Withdrawn1999)" (http://www.astm.org/Standards/A616.htm) . Astm.org. http://www.astm.org/Standards/A616.htm.

Retrieved 2012-08-24.)

'A' Axle A617(superseded by A996 "ASTM A617 / A617M - 96a Standard Specification for Axle Steel

Deformed and Plain Bars for Concrete Reinforcement (Withdrawn 1999)"(http://www.astm.org/Standards/A617.htm) . Astm.org. http://www.astm.org/Standards/A617.htm.

Retrieved 2012-08-24.)

'W' Low-alloy — A706

Historically in Europe, rebar is composed of mild steel material with a yield strength of approximately 250MPa(36ksi). Modern rebar is composed of high-yield steel, with a yield strength more typically 500MPa (72.5ksi).Rebar can be supplied with various grades of ductility. The more ductile steel is capable of absorbing considerablymore energy when deformed - a behavior that resists earthquake forces and is used in design.

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Placing rebar

Rebar cages are fabricated either on or off the project site commonly with the help of hydraulic benders and shears,however for small or custom work a tool known as a Hickey - or hand rebar bender, is sufficient. The rebars areplaced by rodbusters or concrete reinforcing ironworkers with bar supports separating the rebar from the concreteforms to establish concrete cover and ensure that proper embedment is achieved. The rebars in the cages areconnected either by welding, tying steel wire, or with mechanical connections. For epoxy coated or galvanisedrebars only the latter is possible.

Welding

The American Welding Society (AWS) D 1.4 sets out the practices for welding rebar in the U.S. Without specialconsideration the only rebar that is ready to weld is W grade (Low-alloy — A706). Rebar that is not produced tothe ASTM A706 specification is generally not suitable for welding without calculating the "carbon-equivalent".Material with a carbon-equivalent of less than 0.55 can be welded. (AWS D1.4)

ASTM A 616 & ASTM A 617 reinforcing are re-rolled rail steel & re-rolled rail axle steel with uncontrolledchemistry, phosphorus & carbon content. These materials are not common.

Rebar cages are normally tied together with wire, although welding of cages has been the norm in Europe for manyyears, and is becoming more common in the US. High strength steels for prestressed concrete may absolutely notbe welded.

Mechanical connections

Also known as "mechanical couplers" or "mechanical splices", mechanical connections are used to connectreinforcing bars together. Mechanical couplers are an effective means to reduce rebar congestion in highlyreinforced areas for cast-in-place concrete construction. These couplers are also used in precast concreteconstruction at the joints between members.

The structural performance criteria for mechanical connections varies considerably between different countries,codes, and industries. As a minimum requirement, codes typically specify that the rebar to splice connection meetsor exceeds 125% of the specified tensile strength of the rebar. More stringent criteria also requires the developmentof the specified ultimate strength of the rebar. As an example, ACI 318 specifies either Type 1 (125% Fy) or Type2 (125% Fy and 100% Fu) performance criteria.ACI. "ACI 318-08 Building Code Requirements for StructuralConcrete and Commentary" (http://www.concrete.org/pubs/newpubs/318-08.htm) . ACI (American ConcreteInstitute). http://www.concrete.org/pubs/newpubs/318-08.htm.

For concrete structures designed with ductility in mind, it is recommended that the mechanical connections are alsocapable of failing in a ductile manner, typically known in the reinforcing steel industry as achieving "bar-break". Asan example, Caltrans specifies a required mode of failure (i.e., "necking of the bar").California Dept. ofTransportation. "METHOD OF TESTS FOR MECHANICAL AND WELDED REINFORCING STEELSPLICES" (http://www.dot.ca.gov/hq/esc/ctms/pdf/CT_670Feb2011.pdf) . Caltrans.http://www.dot.ca.gov/hq/esc/ctms/pdf/CT_670Feb2011.pdf. Retrieved Feb, 2011.

Safety

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Workers extracting rebar

from demolition rubble.

To prevent workers and / or pedestrians from accidentally impaling themselves, the protruding ends of steel rebarare often bent over or covered with special steel-reinforced plastic "plate" caps. "Mushroom" caps may provideprotection from scratches and other minor injuries, but provide little to no protection from impalement.

Designations

For clarity, reinforcement is usually tabulated in a "reinforcement schedule" on construction drawings. Thiseliminates ambiguity in the various notations used in different parts of the world. The following list providesexamples of the different notations used in the architectural, engineering, and construction industry.

New Zealand

Designation Explanation

HD-16-300,

T&B, EW

High strength (500 MPa) 16 mm diameter rebars spaced at 300 mm centers (center-to-center

distance) on both the top and bottom face and in each way as well (i.e., longitudinal and

transverse).

3-D12 Three mild strength (300 MPa) 12 mm diameter rebars

R8 Stirrups

@ 225

MAX

D grade (300 MPa) smooth bar stirrups, spaced at 225 mm centres. By default in New Zealand

practice all stirrups are normally interpreted as being full, closed, loops. This is a detailingrequirement for concrete ductility in seismic zones; If a single strand of stirrup with a hook at each

end was required, this would typically be both specified and illustrated.

United States

Designation Explanation

#4 @ 12 OC,

T&B, EW

Number 4 rebars spaced 12 inches on center (center-to-center distance) on both the top and

bottom faces and in each way as well, i.e. longitudinal and transverse.

(3) #4 Three number 4 rebars (usually used when the rebar perpendicular to the detail)

#3 ties @ 9

OC, (2) per set

Number 3 rebars used as stirrups, spaced at 9 inches on center. Each set consists of two ties,

which is usually illustrated.

#7 @ 12" EW,

EFNumber 7 rebar spaced 12 inches apart, placed in each direction (each way) and on each face.

Recycling

In China, and many other countries, after the demolition of a building, workers arecalled in to remove the rebar. They scour the site, extracting the metal using boltcutters, welding equipment, sledgehammers, and other tools. The metal is partiallystraightened, bundled and sold. In April 2012, such rebar sold for 2.4 RMB per

kilogram.[citation needed]

See also

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Carbon gridConcrete cover

Cover Meter

Welded wire mesh or weldmesh

FormworkFusion bonded epoxy coating for coated rebars

Steel fixer

Rebar spacer

References

1. ^ Recommended Field Handling of Expoy-Coated Reinforcing Bars(http://epoxyinterestgroup.org/cfcs/cmsIT/baseComponents/fileManagerProxy.cfc?method=GetFile&fileID=719D7622-90A6-58C4-4D14365D2D5B5099&fileName=Field_Handling_Card.pdf) ,Concrete Reinforcing Steel Institute

2. ^ Ramniceanu, Andrei [1] (http://virginiadot.org/vtrc/main/online_reports/pdf/08-CR5.pdf) Parameters Governingthe Corrosion Protection Efficiency of Fusion-Bonded Epoxy Coatings on Reinforcing Steel, VirginiaTransportation Research Council, January 2008

External links

OSHA Rebar Impalement Protection Measures(http://www.osha.gov/SLTC/etools/construction/falls/protruding_rebars.html)

Concrete Reinforcing Steel Institute (http://www.crsi.org)

American Concrete Institute (http://www.aci-int.org)

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