![A bunch of rebar](https://upload.wikimedia.org/wikipedia/commons/f/fe/A_bunch_of_rebar.jpg)
Rebar (short for reinforcing bar), known when massed as reinforcing steel or reinforcement steel, is a
steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
bar used as a
tension
Tension may refer to:
Science
* Psychological stress
* Tension (physics), a force related to the stretching of an object (the opposite of compression)
* Tension (geology), a stress which stretches rocks in two opposite directions
* Voltage or el ...
device in
reinforced concrete
Reinforced concrete (RC), also called reinforced cement concrete (RCC) and ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having hig ...
and reinforced
masonry
Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...
structures to strengthen and aid the concrete under tension. Concrete is strong under
compression
Compression may refer to:
Physical science
*Compression (physics), size reduction due to forces
*Compression member, a structural element such as a column
*Compressibility, susceptibility to compression
*Gas compression
*Compression ratio, of a c ...
, but has weak
tensile strength
Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...
. Rebar significantly increases the tensile strength of the structure. Rebar's surface features a continuous series of ribs, lugs or indentations to promote a better bond with the concrete and reduce the risk of slippage.
The most common type of rebar is
carbon steel
Carbon steel is a steel with carbon content from about 0.05 up to 2.1 percent by weight. The definition of carbon steel from the American Iron and Steel Institute (AISI) states:
* no minimum content is specified or required for chromium, cobalt ...
, typically consisting of hot-rolled round bars with deformation patterns embossed into its surface. Steel and concrete have similar
coefficients of thermal expansion, so a concrete structural member reinforced with steel will experience minimal differential
stress
Stress may refer to:
Science and medicine
* Stress (biology), an organism's response to a stressor such as an environmental condition
* Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...
as the temperature changes.
Other readily available types of rebar are manufactured of
stainless steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
, and composite bars made of
glass fiber
Glass fiber ( or glass fibre) is a material consisting of numerous extremely fine fibers of glass.
Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the inventio ...
,
carbon fiber
Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...
, or
basalt fiber
Basalt fibers are produced from basalt rocks by melting them and converting the melt into fibers.
Basalts are rocks of igneous origin. The main energy consumption for the preparation of basalt raw materials to produce of fibers is made in natural ...
. The carbon steel reinforcing bars may also be coated in an
epoxy resin
Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...
designed to resist the effects of corrosion, especially when used in saltwater environments. Bamboo has been shown to be a viable alternative to reinforcing steel in concrete construction. These alternative types tend to be more expensive or may have lesser mechanical properties and are thus more often used in specialty construction where their physical characteristics fulfil a specific performance requirement that carbon steel does not provide.
History
![Nevjansk tower acoustic room corner](https://upload.wikimedia.org/wikipedia/commons/9/9a/Nevjansk_tower_acoustic_room_corner.jpg)
Reinforcing bars in
masonry
Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...
construction have been used since
Antiquity
Antiquity or Antiquities may refer to:
Historical objects or periods Artifacts
*Antiquities, objects or artifacts surviving from ancient cultures
Eras
Any period before the European Middle Ages (5th to 15th centuries) but still within the histo ...
, with Rome using iron or wooden rods in arch construction, later iron tie rods and
anchor plate
An anchor plate, floor plate or wall washer is a large plate or washer connected to a tie rod or bolt. Anchor plates are used on exterior walls of masonry buildings, for structural reinforcement against lateral bowing. Anchor plates are made of ...
s were employed across
Medieval
In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the Post-classical, post-classical period of World history (field), global history. It began with t ...
Europe, as a device to reinforce
arches
An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it.
Arches may be synonymous with vault ...
,
vaults, and
cupolas
In architecture, a cupola () is a relatively small, most often dome-like, tall structure on top of a building. Often used to provide a lookout or to admit light and air, it usually crowns a larger roof or dome.
The word derives, via Italian, from ...
. 2,500 meters of rebar was used in the 14th Century
Château de Vincennes
The Château de Vincennes () is a former fortress and royal residence next to the town of Vincennes, on the eastern edge of Paris, alongside the Bois de Vincennes. It was largely built between 1361 and 1369, and was a preferred residence, after ...
.
During the 18th century, rebar was used to form the
carcass
Carcass or Carcase (both pronounced ) may refer to:
*Dressed carcass, the body of a livestock animal ready for butchery, after removal of skin, visceral organs, head, feet etc.
*Carrion, the decaying dead body of an animal or human being
*The str ...
of the
Leaning Tower of Nevyansk
The Leaning Tower of Nevyansk (russian: Невья́нская ба́шня) is a tower in the town of Nevyansk in Sverdlovsk Oblast, Russia, built in the 18th century. Its construction was funded by Peter the Great's associate Akinfiy D ...
in Russia, built on the orders of the industrialist
Akinfiy Demidov
Akinfiy Nikitich Demidov (russian: Акинфий Никитич Демидов) (1678 Tula - 5 August 1745 Yatskoye Ustye, Menzelinsky Uyezd, Orenburg Governorate) was a Russian industrialist of the Demidov family.
Life
He was the eldest so ...
. The
cast iron
Cast iron is a class of iron–carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its color when fractured: white cast iron has carbide impuriti ...
used for the rebar was of high quality, and there is no
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
on the bars to this day. The carcass of the tower was connected to its cast iron
tented roof
A tented roof (also known as a pavilion roof) is a type of polygonal hipped roof with steeply pitched slopes rising to a peak. W. Dean EastmanHometown Handbook: Architecture./ref> Tented roofs, a hallmark of medieval religious architecture, wer ...
, crowned with one of the first known
lightning rod
A lightning rod or lightning conductor (British English) is a metal rod mounted on a structure and intended to protect the structure from a lightning strike. If lightning hits the structure, it will preferentially strike the rod and be conducte ...
s.
However, it was not until the mid-19th century that rebar displayed its greatest strengths with the embedding of steel bars into concrete, thus producing modern
reinforced concrete
Reinforced concrete (RC), also called reinforced cement concrete (RCC) and ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having hig ...
. Several people in Europe and North America developed reinforced concrete in the 1850s. These include
Joseph-Louis Lambot
Joseph-Louis Lambot (born 22 May 1814 in Montfort sur Argens; died 2 August 1887 in Brignoles), is the inventor of ferro-cement, which led to the development of what is now known as reinforced concrete. He studied in Paris, where his uncle Baron L ...
of France, who built reinforced concrete boats in Paris (1854) and
Thaddeus Hyatt
Thaddeus Hyatt (July 21, 1816 – July 25, 1901) was an American abolitionist and inventor. In his opposition to slavery, Hyatt organized the efforts of abolitionists in Kansas to have the territory admitted to the Union as a free-state and camp ...
of the United States, who produced and tested reinforced concrete beams.
Joseph Monier
Joseph Monier (; 8 November 1823, Saint-Quentin-la-Poterie, France – 13 March 1906, Paris) was a French gardener and one of the principal inventors of reinforced concrete.
Overview
As a gardener, Monier was not satisfied with the material ...
of France is one of the most notable figures for the invention and popularization of reinforced concrete. As a French gardener, Monier patented reinforced concrete flower pots in 1867, before proceeding to build reinforced concrete water tanks and bridges.
Ernest L. Ransome
Ernest Leslie Ransome (1844–1917) was an English-born engineer, architect, and early innovator in reinforced concrete building techniques. Ransome devised the most sophisticated concrete structures in the United States at the time.
Ernest was ...
, an English engineer and architect who worked in the United States, made a significant contribution to the development of reinforcing bars in concrete construction. He invented twisted iron rebar, which he initially thought of while designing self-supporting sidewalks for the
Masonic Hall
A Masonic Temple or Masonic Hall is, within Freemasonry, the room or edifice where a Masonic Lodge meets. Masonic Temple may also refer to an abstract spiritual goal and the conceptual ritualistic space of a meeting.
Development and history
In ...
in Stockton, California. His twisted rebar was, however, not initially appreciated and even ridiculed at the Technical Society of California, where members stated that the twisting would weaken the iron. In 1889, Ransome worked on the West Coast mainly designing bridges. One of these, the
Alvord Lake Bridge
The Alvord Lake Bridge was the first reinforced concrete bridge built in America. It was built in 1889 by Ernest L. Ransome, an innovator in reinforced concrete design, mixing equipment, and construction systems. The bridge was constructed as a si ...
in San Francisco's Golden Gate Park, was the first reinforced concrete bridge built in the United States. He used twisted rebar in this structure.
At the same time Ransome was inventing twisted steel rebar,
C.A.P. Turner was designing his "mushroom system" of reinforced concrete floor slabs with smooth round rods and
Julius Kahn Julius Kahn may refer to:
*Julius Kahn (inventor) (1874–1942), engineer of reinforced concrete
*Julius Kahn (congressman)
Julius Kahn (February 28, 1861 – December 18, 1924) was a United States Congressman who was succeeded by his wife ...
was experimenting with an innovative rolled diamond-shaped rebar with flat-plate flanges angled upwards at 45° (patented in 1902). Kahn predicted concrete beams with this reinforcing system would bend like a
Warren truss
Warren Errol Truss, (born 8 October 1948) is a former Australian politician who served as the 16th Deputy Prime Minister of Australia and Minister for Infrastructure and Regional Development in the Abbott Government and the Turnbull Governm ...
, and also thought of this rebar as shear reinforcement. Kahn's reinforcing system was built in concrete beams, joists, and columns. The system was both praised and criticized by Kahn's engineering contemporaries: Turner voiced strong objections to this system as it could cause catastrophic failure to concrete structures. He rejected the idea that Kahn's reinforcing system in concrete beams would act as a Warren truss and also noted that this system would not provide the adequate amount of shear stress reinforcement at the ends of the simply supported beams, the place where the shear stress is greatest. Furthermore, Turner warned that Kahn's system could result in a brittle failure as it did not have longitudinal reinforcement in the beams at the columns. This type of failure manifested in the partial collapse of the Bixby Hotel in Long Beach, California and total collapse of the Eastman Kodak Building in Rochester, New York, both during construction in 1906. It was, however, concluded that both failures were the consequences of poor quality labor. With the increase in demand of construction standardization, innovative reinforcing systems such as Kahn's were pushed to the side in favor of the concrete reinforcing systems seen today.
Requirements for deformations on steel bar reinforcement were not standardized in U.S. construction until about 1950. Modern requirements for deformations were established in "''Tentative Specifications for the Deformations of Deformed Steel Bars for Concrete Reinforcement''", ASTM A305-47T. Subsequently, changes were made that increased rib height and reduced rib spacing for certain bar sizes, and the qualification of “tentative” was removed when the updated standard ASTM A305-49 was issued in 1949. The requirements for deformations found in current specifications for steel bar reinforcing, such as ASTM A615 and ASTM A706, among others, are the same as those specified in ASTM A305-49.
Use in concrete and masonry
Concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
is a material that is very strong in
compression
Compression may refer to:
Physical science
*Compression (physics), size reduction due to forces
*Compression member, a structural element such as a column
*Compressibility, susceptibility to compression
*Gas compression
*Compression ratio, of a c ...
, but relatively weak in
tension
Tension may refer to:
Science
* Psychological stress
* Tension (physics), a force related to the stretching of an object (the opposite of compression)
* Tension (geology), a stress which stretches rocks in two opposite directions
* Voltage or el ...
. To compensate for this imbalance in concrete's behavior, rebar is cast into it to carry the tensile
load
Load or LOAD may refer to:
Aeronautics and transportation
*Load factor (aeronautics), the ratio of the lift of an aircraft to its weight
*Passenger load factor, the ratio of revenue passenger miles to available seat miles of a particular transpo ...
s. Most steel reinforcement is divided into primary and secondary reinforcement:
*''Primary reinforcement'' refers to the steel which is employed to guarantee the resistance needed by the structure as a whole to support the design loads.
*''Secondary reinforcement'', also known as distribution or thermal reinforcement, is employed for durability and aesthetic reasons, by providing enough localized resistance to limit cracking and resist stresses caused by effects such as temperature changes and shrinkage.
Secondary applications include rebar embedded in masonry walls, which includes both bars placed horizontally in a
mortar joint (every fourth or fifth course of block) or vertically (in the horizontal voids of cement blocks and cored bricks, which is then fixed in place with
grout
Grout is a dense fluid which hardens to fill gaps or used as reinforcement in existing structures. Grout is generally a mixture of water, cement and sand, and is employed in pressure grouting, embedding rebar in masonry walls, connecting secti ...
. Masonry structures held together with grout have similar properties to concrete - high compressive resistance but a limited ability to carry tensile loads. When rebar is added they are known as "reinforced masonry".
A similar approach (of embedding rebar vertically in designed voids in engineered blocks) is also used in dry-laid landscape walls, at least pinning the lowest course in place into the earth, also employed securing the lowest course and/or deadmen in walls made of engineered concrete or wooden landscape ties.
In unusual cases steel reinforcement may be embedded and partially exposed, as in the steel tie bars that constrain and reinforce the masonry Nevyansk Tower or ancient structures in Rome and the Vatican.
Physical characteristics
Steel
Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...
has a
thermal expansion coefficient
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.
Temperature is a monotonic function of the average molecular kinetic ...
nearly equal to that of modern
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
. If this were not so, it would cause problems through additional longitudinal and perpendicular stresses at temperatures different from the temperature of the setting. Although rebar has ribs that bind it mechanically to the concrete, it can still be pulled out of the concrete under high stresses, an occurrence that often accompanies a larger-scale collapse of the structure. To prevent such a failure, rebar is either deeply embedded into adjacent structural members (40–60 times the diameter), or bent and hooked at the ends to lock it around the concrete and other rebar. This first approach increases the friction locking the bar into place, while the second makes use of the high compressive strength of concrete.
Common rebar is made of unfinished
tempered steel, making it susceptible to
rust
Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH ...
ing. Normally the concrete cover is able to provide a
pH value higher than 12 avoiding the
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
reaction. Too little concrete cover can compromise this guard through
carbonation
Carbonation is the chemical reaction of carbon dioxide to give carbonates, bicarbonates, and carbonic acid. In chemistry, the term is sometimes used in place of carboxylation, which refers to the formation of carboxylic acids.
In inorganic ch ...
from the surface, and
salt penetration. Too much concrete cover can cause bigger crack widths which also compromises the local guard. As rust takes up greater volume than the steel from which it was formed, it causes severe internal pressure on the surrounding concrete, leading to cracking,
spalling
Spall are fragments of a material that are broken off a larger solid body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball ...
, and, ultimately,
structural failure
Structural integrity and failure is an aspect of engineering that deals with the ability of a structure to support a designed structural load (weight, force, etc.) without breaking and includes the study of past structural failures in order to ...
. This phenomenon is known as
oxide jacking. This is a particular problem where the concrete is exposed to salt water, as in bridges where salt is applied to roadways in winter, or in marine applications. Uncoated, corrosion-resistant low
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent
In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
/
chromium
Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.
Chromium metal is valued for its high corrosion resistance and hardne ...
(microcomposite),
silicon bronze
Bronze is an alloy consisting primarily of copper, commonly with about 12–12.5% tin and often with the addition of other metals (including aluminium, manganese, nickel, or zinc) and sometimes non-metals, such as phosphorus, or metalloids such ...
,
epoxy
Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...
-coated,
galvanized
Galvanization or galvanizing ( also spelled galvanisation or galvanising) is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are submerged ...
, or
stainless steel
Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...
rebars may be employed in these situations at greater initial expense, but significantly lower expense over the service life of the project. Extra care is taken during the transport, fabrication, handling, installation, and concrete placement process when working with
epoxy-coated rebar, because damage will reduce the long-term corrosion resistance of these bars. Even damaged epoxy-coated bars have shown better performance than uncoated reinforcing bars, though issues from debonding of the epoxy coating from the bars and corrosion under the epoxy film have been reported. These epoxy-coated bars are used in over 70,000 bridge decks in the US, but this technology was slowly being phased out in favor of stainless steel rebar as of 2005 because of its poor performance.
Requirements for deformations are found in US-standard product specifications for steel bar reinforcing, such as ASTM A615 and ASTM A706, and dictate lug spacing and height.
Fibre-reinforced plastic
Fibre-reinforced plastic (FRP; also called fibre-reinforced polymer, or in American English ''fiber'') is a composite material made of a polymer matrix reinforced with fibres. The fibres are usually glass (in fibreglass), carbon (in carbon-fib ...
rebar is also used in high-corrosion environments. It is available in many forms, such as spirals for reinforcing columns, common rods, and meshes. Most commercially available rebar is made from unidirectional fibers set in a thermoset polymer resin, and is often referred to as FRP.
Some special construction such as research and manufacturing facilities with very sensitive electronics may require the use of reinforcement that is non-conductive to electricity, and medical imaging equipment rooms may require non-magnetic properties to avoid interference. FRP rebar, notably glass fibre types have low electrical conductivity and are non-magnetic which is commonly used for such needs. Stainless steel rebar with low
magnetic permeability
In electromagnetism, permeability is the measure of magnetization that a material obtains in response to an applied magnetic field. Permeability is typically represented by the (italicized) Greek letter ''μ''. The term was coined by William ...
is available and is sometimes used to avoid magnetic interference issues.
Reinforcing steel can also be displaced by impacts such as
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
s, resulting in structural failure. The prime example of this is the collapse of the
Cypress Street Viaduct
The Cypress Street Viaduct, often referred to as the Cypress Structure or the Cypress Freeway, was a 1.6-mile-long (2.5 km), raised two-deck, multi-lane (four lanes per tier) freeway constructed of reinforced concrete that was originally pa ...
in Oakland, California as a result of the
1989 Loma Prieta earthquake
The 1989 Loma Prieta earthquake occurred on California's Central Coast on October 17 at local time. The shock was centered in The Forest of Nisene Marks State Park in Santa Cruz County, approximately northeast of Santa Cruz on a section of t ...
, causing 42 fatalities. The shaking of the earthquake caused rebars to burst from the concrete and
buckle
The buckle or clasp is a device used for fastening two loose ends, with one end attached to it and the other held by a catch in a secure but adjustable manner. Often taken for granted, the invention of the buckle was indispensable in securing tw ...
. Updated building designs, including more circumferential rebar, can address this type of failure.
Sizes and grades
US sizes
US/Imperial bar sizes give the diameter in units of for bar sizes #2 through #8, so that #8 = inch = diameter.
There are no fractional bar sizes in this system. The "#" symbol indicates the
number sign
The symbol is known variously in English-speaking regions as the number sign, hash, or pound sign. The symbol has historically been used for a wide range of purposes including the designation of an ordinal number and as a Typographic ligature, ...
, and thus "#6" is read as "number six". The use of the "#" sign is customary for US sizes, however "No." is sometimes used instead. Within the trades rebar is known by a shorthand utilizing the bar diameter as descriptor, such as "four-bar" for bar that is four-eighths (or one-half) of an inch.
The cross-sectional area of a bar, as given by ''πr''², works out to (bar size/9.027)², which is approximated as (bar size/9)² square inches. For example, the area of #8 bar is (8/9)² = 0.79 square inches.
Bar sizes larger than #8 follow the -inch rule imperfectly and skip sizes #12-13, and #15-17 due to historical convention. In early concrete construction bars 1 inch and larger were only available in square sections, and when large format deformed round bars became available around 1957 the industry manufactured them to provide the cross-sectional area equivalent of standard square bar sizes that were formerly used. The diameter of the equivalent large format round shape is rounded to the nearest inch to provide the bar size. For example, #9 bar has a cross section of , and therefore a diameter of . #10, #11, #14, and #18 sizes correspond to 1 inch, 1, 1, and 2 inch square bars, respectively.
Sizes smaller than #3 are no longer recognized as standard sizes. These are most commonly manufactured as plain round undeformed rod steel, but can be made with deformations. Sizes smaller than #3 are typically referred to as "wire" products and not "bar", and specified by either their nominal diameter or wire gage number. #2 bars are often informally called "pencil rod" as they are about the same size as a pencil.
When US/Imperial sized rebar are used in projects with metric units, the equivalent metric size is typically specified as the nominal diameter rounded to the nearest millimeter. These are not considered standard metric sizes, and thus is often referred to as a
soft conversion or the "soft metric" size. The US/Imperial bar size system recognizes the use of true metric bar sizes (No. 10, 12, 16, 20, 25, 28, 32, 36, 40, 50 and 60 specifically) which indicates the nominal bar diameter in millimeters, as an "alternate size" specification. Substituting a true metric size for a US/Imperial size is called a
hard conversion, and sometimes results in the use of a physically different sized bar.
Canadian sizes
![Qew bruecke nf beton kaputt 33 von 46](https://upload.wikimedia.org/wikipedia/commons/4/43/Qew_bruecke_nf_beton_kaputt_33_von_46.jpg)
Metric bar designations represent the nominal bar diameter in millimeters, rounded to the nearest 5 mm.
European sizes
Metric bar designations represent the nominal bar diameter in millimetres. Preferred bar sizes in Europe are specified to comply with Table 6 of the standard
EN 10080, although various national standards still remain in force (e.g. BS 4449 in the United Kingdom). In Switzerland some sizes are different from European standard.
Australian sizes
Reinforcement for use in concrete construction is subject to the requirements of Australian Standards AS3600-2009 (Concrete Structures) and AS/NZS4671-2001 (Steel Reinforcing for Concrete). There are other standards that apply to testing, welding and galvanizing.
The designation of reinforcement is defined in AS/NZS4671-2001 using the following formats:
Shape/ Section
D- deformed ribbed bar, R- round / plain bar, I- deformed indented bar
Ductility Class
L- low ductility, N- normal ductility, E- seismic (Earthquake) ductility
Standard grades (MPa)
250N, 300E, 500L, 500N, 500E
:''Examples:''
:D500N12 is deformed bar, 500 MPa strength, normal ductility and 12 mm nominal diameter - also known as "N12"
Bars are typically abbreviated to simply 'N' (hot-rolled deformed bar), 'R' (hot-rolled round bar), 'RW' (cold-drawn ribbed wire) or 'W' (cold-drawn round wire), as the yield strength and ductility class can be implied from the shape. For example, all commercially available wire has a yield strength of 500 MPa and low ductility, while round bars are 250 MPa and normal ductility.
New Zealand
Reinforcement for use in concrete construction is subject to the requirements of AS/NZS4671-2001 (Steel Reinforcing for Concrete). There are other standards that apply to testing, welding and galvanizing.
Reinforcement steel bar Grade 300 & 500 Class E''
India
Rebars are available in the following grades as per IS:1786-2008 FE 415/FE 415D/FE 415S/FE 500/FE 500D/FE 500S/FE 550, FE550D, FE 600. Rebars are quenched with water at a high level pressure so that the outer surface is hardened while the inner core remains soft. Rebars are ribbed so that the concrete can have a better grip. Coastal regions use galvanized rebars to prolong their life. BIS rebar sizes are 10, 12, 16, 20, 25, 28, 32, 36, 40 and 50 millimeters.
Jumbo and threaded bar sizes
Very large format rebar sizes are widely available and produced by specialty manufacturers. The tower and sign industries commonly use "jumbo" bars as anchor rods for large structures which are fabricated from slightly oversized blanks such that threads can be cut at the ends to accept standard anchor nuts. Fully threaded rebar is also produced with very coarse threads which satisfy rebar deformation standards and allow for custom nuts and couplers to be used. Note that these customary sizes while in common use, do not have consensus standards associated with them, and actual properties may vary by manufacturer.
Grades
Rebar is available in grades and specifications that vary in
yield strength
In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and wi ...
,
ultimate tensile strength
Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...
,
chemical composition
A chemical composition specifies the identity, arrangement, and ratio of the elements making up a compound.
Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for ...
, and percentage of
elongation.
The use of a grade by itself only indicates the minimum permissible yield strength, and it must be used in the context of a material specification in order to fully describe product requirements for rebar. Material specifications set the requirements for grades as well as additional properties such as, chemical composition, minimum elongation, physical tolerances, etc. Fabricated rebar must exceed the grade's minimum yield strength and any other material specification requirements when inspected and tested.
In US use, the grade designation is equal to the
minimum yield strength of the bar in
ksi
Olajide Olayinka Williams "JJ" Olatunji (born 19 June 1993), known professionally as KSI, is an English YouTuber and rapper. He is a co-founder and member of the British YouTube group known as the Sidemen. He is the CEO of Misfits Boxing and ...
(1000 psi) for example grade 60 rebar has a minimum yield strength of 60 ksi. Rebar is most commonly manufactured in grades 40, 60, and 75 with higher strength readily available in grades 80, 100, 120 and 150. Grade 60 (420 MPa) is the most widely used rebar grade in modern US construction. Historic grades include 30, 33, 35, 36, 50 and 55 which are not in common use today.
Some grades are only manufactured for specific bar sizes, for example under ASTM A615, Grade 40 (280 MPa) is only furnished for US bar sizes #3 through #6 (soft metric No.10 through 19). Sometimes limitations on available material grades for specific bar sizes is related to the manufacturing process used, as well as the availability of controlled quality raw materials used.
Some material specifications cover multiple grades, and in such cases it is necessary to indicate both the material specification and grade. Rebar grades are customarily noted on engineering documents, even when there are no other grade options within the material specification, in order to eliminate confusion and avoid potential quality issues such as might occur if a material substitution is made. Note that "Gr." is the common engineering abbreviation for "grade", with variations on letter capitalization and the use of a period.
In certain cases, such as earthquake engineering and blast resistant design where post-yield behavior is expected, it is important to be able to predict and control properties such as the maximum yield strength and minimum ratio of tensile strength to yield strength. ASTM A706 Gr. 60 is an example of a controlled property range material specification which has a minimum yield strength of 60 ksi (420 MPa), maximum yield strength of 78 ksi (540 MPa), minimum tensile strength of 80 ksi (550 MPa) and not less than 1.25 times the actual yield strength, and minimum elongation requirements that vary by bar size.
In countries that use the metric system, the grade designation is typically the yield strength in
megapascal
The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI), and is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is defined as ...
s MPa, for example ''grade 400'' (similar to US grade 60, however metric grade 420 is actually the exact substitution for the US grade).
Common US specifications, published by ACI and ASTM, are:
*
American Concrete Institute
The American Concrete Institute (ACI, formerly National Association of Cement Users or NACU) is a non-profit technical society and standards developing organization. ACI was founded in January 1905 during a convention in Indianapolis. The Institu ...
: "ACI 318-14 Building Code Requirements for Structural Concrete and Commentary", (2014)
*ASTM A82: Specification for Plain Steel Wire for Concrete Reinforcement
*ASTM A184/A184M: Specification for Fabricated Deformed Steel Bar Mats for Concrete Reinforcement
*ASTM 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 reinforcement
*ASTM 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 reinforcement
*ASTM A722/A722M: Standard Specification for High-Strength Steel Bars for Prestressed Concrete
*ASTM 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 reinforcement (Supplementary Requirement S1 is used when specifying magnetic permeability testing)
*ASTM 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 ()
*'IR' Rail Meeting Supplementary Requirements S1 A616 )
*'A' Axle A617 )
*'W' Low-alloy — A706
Historically in Europe, rebar is composed of mild steel material with a yield strength of approximately 250 MPa (36 ksi). Modern rebar is composed of high-yield steel, with a yield strength more typically 500 MPa (72.5 ksi). Rebar can be supplied with various grades of
ductility
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
. The more ductile steel is capable of absorbing considerably more energy when deformed - a behavior that resists
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
forces and is used in design. These high yield strength ductile steels are usually produced using the TEMPCORE process, a method of
thermomechanical processing Thermomechanical processing is a metallurgical process that combines mechanical or plastic deformation process like compression or forging, rolling, etc. with thermal processes like heat-treatment, water quenching, heating and cooling at various ra ...
. The manufacture of reinforcing steel by re-rolling finished products (e.g. sheets or rails) is not allowed. In contrast to structural steel, rebar steel grades are not harmonized yet across Europe, each country having their own national standards. However some standardization of specification and testing methods exist under EN 10080 and EN ISO 15630:
*BS EN 10080: Steel for the reinforcement of concrete. Weldable reinforcing steel. General. (2005)
*BS 4449: Steel for the reinforcement of concrete. Weldable reinforcing steel. Bar, coil and product. Specification. (2005/2009)
*BS 4482: Steel wire for the reinforcement of concrete products. Specification (2005)
*BS 4483: Steel fabric for the reinforcement of concrete. Specification (2005)
*BS 6744: Stainless steel bars for the reinforcement of and use in concrete. Requirements and test methods. (2001/2009)
*DIN 488-1: Reinforcing steels - Part 1: Grades, properties, marking (2009)
*DIN 488-2: Reinforcing steels - Part 2: Reinforcing steel bars (2009)
*DIN 488-3: Reinforcing steels - Part 3: Reinforcing steel in coils, steel wire (2009)
*DIN 488-4: Reinforcing steels - Part 4: Welded fabric (2009)
*DIN 488-5: Reinforcing steels - Part 5: Lattice girders (2009)
*DIN 488-6: Reinforcing steel - Part 6: Assessment of conformity (2010)
*BS EN ISO 15630-1: Steel for the reinforcement and prestressing of concrete. Test methods. Reinforcing bars, wire rod and wire. (2010)
*BS EN ISO 15630-2: Steel for the reinforcement and prestressing of concrete. Test methods. Welded fabric. (2010)
Placing rebar
![Tie wire](https://upload.wikimedia.org/wikipedia/commons/c/ce/Tie_wire.jpg)
Rebar cages are fabricated either on or off the project site commonly with the help of
hydraulic
Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counter ...
benders and shears. However, for small or custom work a tool known as a Hickey, or hand rebar bender, is sufficient. The rebars are placed by
steel fixers "rodbusters" or concrete reinforcing iron workers, with bar supports and concrete or plastic
rebar spacer
A rebar spacer is a device that secures the reinforcing steel or "rebar" in reinforced concrete structures as the rebar is assembled in place before the final concrete pour. The spacers are left in place for the pour to keep the reinforcing ...
s separating the rebar from the concrete
formwork
Formwork is Molding (process), molds into which concrete or similar materials are either precast concrete, precast or cast-in-place concrete, cast-in-place. In the context of concrete construction, the falsework supports the shuttering mold ...
to establish
concrete cover Concrete cover, in reinforced concrete, is the least distance between the surface of embedded reinforcement and the outer surface of the concrete ( ACI 130). The concrete cover depth can be measured with a cover meter.
Purpose of provision of conc ...
and ensure that proper embedment is achieved. The rebars in the cages are connected by
spot welding
A spot welder
Spot welding (or resistance spot welding) is a type of electric resistance welding used to weld various sheet metal products, through a process in which contacting metal surface points are joined by the heat obtained from resistance ...
, tying steel wire, sometimes using an electric
rebar tier
Rebar (short for reinforcing bar), known when massed as reinforcing steel or reinforcement steel, is a steel bar used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension ...
, or with
mechanical connections
Mechanical rebar connections, also known as mechanical splices or mechanical coupler, are used to join lengths of rebar together to transfer forces from one steel rebar to another.
Mechanical couplers can be advantageous in comparison with conven ...
. For tying epoxy-coated or galvanized rebars, epoxy-coated or galvanized wire is normally used, respectively.
Stirrups
![Stirrup_sample](https://upload.wikimedia.org/wikipedia/commons/c/cf/Stirrup_sample.png)
Stirrups form the outer part of a rebar cage. Stirrups are usually rectangular in beams, and circular
in piers and are placed at regular intervals along a
column
A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member. ...
or
beam
Beam may refer to:
Streams of particles or energy
*Light beam, or beam of light, a directional projection of light energy
**Laser beam
*Particle beam, a stream of charged or neutral particles
**Charged particle beam, a spatially localized grou ...
to secure the structural rebar and prevent it from shifting out of position during concrete placement. The main usage for stirrups or ties is to increase the shear capacity of reinforced concrete component it is included in.
Welding
The American Welding Society (AWS) D 1.4 sets out the practices for welding rebar in the U.S. Without special consideration the only rebar that is ready to weld is ''W grade'' (Low-alloy — A706). Rebar that is not produced to the 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.
ASTM A 616 & ASTM A 617 (now replaced by the combined standard A996) reinforcing bars are re-rolled rail steel and re-rolled rail axle steel with uncontrolled chemistry, phosphorus and carbon content. These materials are not common.
Rebar cages are normally tied together with wire, although spot welding of cages has been the norm in Europe for many years, and is becoming more common in the United States. High strength steels for
prestressed concrete
Prestressed concrete is a form of concrete used in construction. It is substantially "prestressed" ( compressed) during production, in a manner that strengthens it against tensile forces which will exist when in service. Post-tensioned concreted i ...
cannot be welded.
Reinforcement placement in rolls
Roll reinforcement system is a remarkably fast and cost-efficient method for placing a large quantity of reinforcement over a short period of time. Roll reinforcement is usually prepared off-site and easily unrolled on site. Roll reinforcement placement has been applied successfully in slabs (decks, foundations), wind energy mast foundations, walls, ramps, etc.
Mechanical connections
Also known as "mechanical couplers" or "mechanical splices",
mechanical connections
Mechanical rebar connections, also known as mechanical splices or mechanical coupler, are used to join lengths of rebar together to transfer forces from one steel rebar to another.
Mechanical couplers can be advantageous in comparison with conven ...
are used to connect reinforcing bars together. Mechanical couplers are an effective means to reduce rebar congestion in highly reinforced areas for cast-in-place concrete construction. These couplers are also used in precast concrete construction at the joints between members.
The structural performance criteria for mechanical connections varies between countries, codes, and industries. As a minimum requirement, codes typically specify that the rebar to splice connection meets or exceeds 125% of the specified yield strength of the rebar. More stringent criteria also requires the development of the specified ultimate strength of the rebar. As an example, ACI 318 specifies either Type 1 (125% Fy) or Type 2 (125% Fy and 100% Fu) performance criteria.
![Rebars with plastic endcaps](https://upload.wikimedia.org/wikipedia/commons/6/69/Rebars_with_plastic_endcaps.jpg)
For concrete structures designed with ductility in mind, it is recommended that the mechanical connections are also capable of failing in a ductile manner, typically known in the reinforcing steel industry as achieving "bar-break". As an example, Caltrans specifies a required mode of failure (i.e., "necking of the bar").
Safety
To prevent injury, the protruding ends of steel rebar are often bent over or covered with special steel-reinforced plastic caps.
Designations
Reinforcement is usually tabulated in a "reinforcement schedule" on construction drawings. This eliminates ambiguity in the notations used around the world. The following list provides examples of the notations used in the architectural, engineering, and construction industry.
Reuse and recycling
![Metal rebar reclamation for recycling at building demolition site - 02](https://upload.wikimedia.org/wikipedia/commons/3/32/Metal_rebar_reclamation_for_recycling_at_building_demolition_site_-_02.jpg)
Rebar is frequently
recycled
Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...
, and rebar is often made entirely from recycled steel.
Nucor
Nucor Corporation is an American producer of steel and related products based in Charlotte, North Carolina. It is the largest steel producer in the United States, the largest "mini-mill" steelmaker (i.e. it uses electric arc furnaces to melt scr ...
, the largest steel producer in the United States, claims its steel bar products are made from 97% recycled steel.
References
External links
OSHA rebar impalement protection measures
{{Authority control
Building materials
Concrete
Reinforced concrete
Russian inventions
Steels
Steel objects