A rebar, or reinforcing bar, is a common steel bar, and is commonly used in reinforced concrete and reinforced masonry structures. It is usually formed from carbon steel, and is given ridges for better mechanical anchoring into the concrete. It can also be described as reinforcement or reinforcing steel. In Australia it is colloquially known as reo.
The resulting reinforced concrete or other material is an example of a composite material.
Concrete is a material that is very strong in compression, but relatively weak in tension. To compensate for this imbalance in concrete's behaviour, rebar is cast into it to carry the tensile loads.
Masonry structures and the mortar holding them together have similar properties to concrete and also have a limited ability to carry tensile loads. Some standard masonry units like blocks and bricks are made with strategically placed voids to accommodate rebar, which is then secured in place with grout. This combination is known as reinforced masonry.
While any material with sufficient tensile strength could conceivably be used to reinforce concrete, steel and concrete have similar coefficients of thermal expansion: a concrete structural member reinforced with steel will experience minimal stress as a result of differential expansions of the two interconnected materials caused by temperature changes.
Steel has an expansion coefficient nearly equal to that of modern concrete. If this weren't so, it would cause problems through additional longitudinal and perpendicular stresses at temperatures different of 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 precedes 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 rusting. Normally the concrete cover is able to provide a pH value higher than 12 avoiding the corrosion reaction. Too little concrete cover can compromise this guard through carbonation from the surface. 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, and ultimately, structural failure. This is a particular problem where the concrete is exposed to salt water, as in bridges built in areas where salt is applied to roadways in winter, or in marine applications. Epoxy-coated, galvanized or stainless steel rebar may be employed in these situations at greater initial expense, but significantly lower expense over the service life of the project. Especially Epoxy-coated have to be installed with great care, because even little cracks and failures in the coating can lead to intensified local chemical reactions not visible at the surface.
Fibre-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 commercially available rebar are made from unidirectional glass fibre reinforced thermo set resins.
Rebar Sizes :
U.S. Imperial Rebar sizes :
Imperial bar designations represent the bar diameter in fractions of 1⁄8 inch, such that #8 = 8⁄8 inch = 1 inch diameter. Area = (bar size/9)2 such that area of #8 = (8/9)2 = 0.79 in2. This applies to #8 bars and smaller. Larger bars have a slightly larger diameter than the one computed using the 1⁄8 inch conversion.
Imperial Bar Size
"Soft" Metric Size
Weight(lb/ft)
Weight(kg/m)
Nominal Diameter(in)
Nominal Diameter(mm)
Nominal Area
(in2)
Nominal Area (mm2)
# 3
# 10
0.376
0.561
0.375 = 3/8
9.525
0.11
71
# 4
# 13
0.668
0.996
0.500 = 4/8
12.7
0.2
129
# 5
# 16
1.043
1.556
0.625 = 5/8
15.875
0.31
200
# 6
# 19
1.502
2.24
0.750 = 6/8
19.05
0.44
284
# 7
# 22
2.044
3.049
0.875 = 7/8
22.225
0.6
387
# 8
# 25
2.67
3.982
1.000 = 8/8
25.4
0.79
509
# 9
# 29
3.4
5.071
1.128
28.65
1
645
# 10
# 32
4.303
6.418
1.27
32.26
1.27
819
# 11
# 36
5.313
7.924
1.41
35.81
1.56
1006
# 14
# 43
7.65
11.41
1.693
43
2.25
1452
# 18
# 57
13.6
20.284
2.257
57.33
4
2581
European Metric Rebar sizes :
Metric bar designations represent the nominal bar diameter in millimetres. Bars in Europe will be specified to comply with the standard EN 10080 (awaiting introduction as of early 2007), although various national standards still remain in force (e.g. BS 4449 in the United Kingdom).
Metric
Bar
Size mm
Mass (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
European Metric Rebar Sizes :
Rebar is available in different grades and specifications that vary in yield strength, ultimate tensile strength, chemical composition, 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 rebar has minimum yield strength of 60 ksi. Rebar is typically manufactured in grades 40, 60, and 75.
Common specifications of Rebar Grades are :
ASTM A615 Deformed and plain carbon-steel bars for concrete reinforcement.
ASTM A706 bars are more suitable for seismic applications, bar bending and welding.
ASTM A706 Low-alloy steel deformed and plain bars for concrete reinforcement.
ASTM A955 Deformed and plain stainless-steel bars for concrete reinforcement.
ASTM A996 Rail-steel and axle-steel deformed bars for concrete reinforcement.
Historically in Europe, rebar is composed of mild steel material with yield strength of approximately 250 N/mm². Modern rebar is composed of high-yield steel, with a yield strength more typically 500 N/mm². Rebar can be supplied with various grades of ductility, with the more ductile steel capable of absorbing considerably greater energy when deformed - this can be of use in design to resist the forces from earthquakes.
Reinforcing Bar Identification :
There are a number of important ways to identify reinforcing bar from the production mill to the fabrication shop to the job site. This documentation and marking system helps provide a wealth of useful information about the manufacturing and composition of each bar of reinforcing steel.
Each individual reinforcing bar is manufactured with a series of individual markings :
The top letter or symbol identifies the producing mill and deformation pattern.
The next marking is the bar size.
The third marking symbol designates the manufacturing material — usually either "S" for carbon-steel (ASTM A615) or "W" for low-alloy steel (ASTM A706).
Finally, there will be a grade marking (4 or 5, for 420 or 520) or by the addition of one line (420) or two lines (520) that must be at least five deformations long.
Placing Rebar :
Rebar cages are fabricated either on or off the project site commonly with the help of hydraulic benders and shears. The rebar are placed by rod busters or concrete reinforcing ironworkers with bar supports separating the rebar from the concrete forms to establish concrete cover and ensure that proper embedment is achieved. The rebar in the cages are connected by welding or tying wires. For epoxy coated or galvanized rebar only the latter is possible.
Welding of Rebar :
Most grades of steel used in rebar are suitable for welding, which can be used to bind several pieces of rebar together. However, welding can reduce the fatigue life of the rebar, and as a result rebar cages are normally tied together with wire. Grade ASTM A 706 is suitable for welding without damaging the properties of the steel. Besides fatigue concerns welding rebar has become less common in developed countries due to the high labour costs of certified welders. Steel for pre stressed concrete may absolutely not be welded.
In the US, most rebar is not suitable for welding. ASTM a 616 & ASTM a 617 reinforcing are re-rolled rail steel & re-rolled rail axle steel with uncontrolled chemistry, phosphorous & carbon content. These are not suitable for welding. To weld rebar you must obtain a mill statement that the reinforcing is suitable for welding.
Rebar Couplers :
When welding or wire-tying rebar is impractical or uneconomical a mechanical connection or rebar coupler can be used to connect two or more bars together. These couplers are popular in precast concrete construction at the joints between members and to reduce rebar congestion in highly reinforced areas.
A full mechanical connection is achieved when the bars connected develop in tension or compression a minimum of 125% of the yield strength of the bar.
Types of Rebar Couplers :
Suitable for the majority of rebar joining applications
Fast and simple to install
Connects rebar of the same diameter
For use where the continuation bar cannot be rotated
Connects rebar of different diameters
Types of Rebar Couplers :
No bar end preparation required
Installation requires no specialist equipment
No bar rotation required
Suitable for use on imperial, plain round or deformed bar
Ideal for remedial applications where replacement of damaged or corroded bar is necessary
Connects rebar of the same diameter
For use in phased construction
Connects rebar of different diameters
Provides dead end embedment for bars in concrete
Types of Rebar Couplers :
Quick and easy to install
For use on large scale, high coupler volume projects
Used where the continuation bar can be rotated
Used where it is difficult but not impossible to rotate the continuation bar
