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30 JULY 2021
REBAR
REINFORCEMENT STEEL
REINFORCEMENT BAR

COMMON ACRONYMS
Rebar

SOURCES OF INFORMATION/ COMMON STANDARDS OF PRACTICE
  1. American Concrete Institute: "ACI 318-14 Building Code Requirements for Structural Concrete and Commentary", ISBN 978-0-87031-930-3 (2014)
  2. ASTM A496: Specification for Deformed Steel Wire for Concrete Reinforcement
  3. ASTM A615/A615M: Deformed and plain carbon-steel bars for concrete reinforcement
  4. ASTM A775/A775M: Specification for Epoxy-Coated Reinforcing Steel Bars
  5. BS EN 10080: Steel for the reinforcement of concrete. Weldable reinforcing steel. General. (2005)
  6. DIN 488-1: Reinforcing steels - Part 1: Grades, properties, marking (2009)
  7. DIN 488-2: Reinforcing steels - Part 2: Reinforcing steel bars (2009)

DEFINITION
Reinforcement Steel is commonly made of carbon steel, (tempered steel) in the shape of hot-rolled round bars, either plain or deformed patterns. It is used as a tension device in reinforced concrete structures and reinforced masonry structures to strengthen and aid the structure and the structural member under tension.

Concrete compressive strength can vary from 2500 psi (17 MPa) for residential concrete to 4000 psi (28 MPa) and higher in commercial structures. Some applications use higher strengths, greater than 10,000 psi (70 MPa). Specified strengths in the range of 15,000 to 20,000 psi have also been produced for lower-floor columns in high-rise buildings.

Studies indicate that traditional concrete’s tensile strength varies between 300 and 700 psi, i.e., around 2 to 5 MPa. This means, on average, the tension averages about 10% of the compressive strength.

Reinforcing Steel used in construction has yield strengths from 40 to 100 ksi (40,000 to 100,000 psi). The yield strength of steel is not dependent on the bar diameter and substitution of different combinations of bars with the same bar area may be readily provided. This provides flexibility in the methods of obtaining the same properties in a concrete structure. The reason most deformed rebar is limited to 60,000 psi is that the concrete would have to excessively deflect and crack to develop the rebar tension.

Yield strength is measured at the point or start of plastic (permanent) deformation. At loads less than yield, steel exhibits elastic properties that enable a structure to rebound upon reloading. Tensile strength is measured at the point of fracture (it is catastrophic). Tensile strength is rarely used in the design consideration of structures made from ductile materials. This is because these materials undergo substantial deformation before their tensile strength is reached. Rather, yield strength is considered for ductile materials, while tensile strength is used for brittle materials. e.g. The Yield strength of Structural steel ASTM A36 is 250 MPa (36,259 psi), whereas the Tensile Strength is 400 MPa (58,015 psi). Yield Strength for rebar is 275 MPa min (39,885 psi) and Tensile Strength: 480 - 620 MPa (69618.1 - 89923.4 psi). In the same way the Yield strength of Kevlar is 3620 MPa, whereas the Tensile Strength is 3757 MPa.

CLASSIFICATION
Various types of materials used to manufacture rebars are as follows;
  1. Tempered steel rebar: It is most commonly used variety of rebar, also known as carbon steel rebar or black bar. It is inexpensive but corrodes more easily than other types of rebar.
  2. Basalt rebar: Basalt is an inert volcanic rock, and basalt rebars offer several advantages over standard steel rebars. Basalt rebar is 2-3 times stronger than steel rebar and is about ¼ the weight for a similar diameter product. In addition, basalt rebar is non-conductive electrically or thermally, is non-hygroscopic, and is resistant to corrosion.
  3. Epoxy coated rebar: It mainly black rebar with an epoxy coat. It has the same textile strength as the black rebar, but is 70 to 1,700 times more resistant to corrosion. Utmost care is required in handling the epoxy coated rebar to avoid scrathes.
  4. Galvanised rebar: Galvanized rebar (zinc coated) is only 40 times more resistant to corrosion than black rebar, but it is more difficult to damage the coating of galvanized rebar. In that respect, it is about 40% more expensive than epoxy-coated rebar.
  5. Glass-Fiber-Reinforced-Polymer rebar (GFRP): GFRP is a composite fiberglass resin wrapped with a fiberglass roving – an interlaced series of glass fibers – to form a reinforcement bar for construction. It will not corrode. Field bends are not permitted when using GFRP. It might cost 10 times as much as epoxy coated rebar, but in length it might be only 2 times more expensive than the epoxy coated rebar. GFRP rebar achieves yield tensile strength about 13% higher than that the steel rebar, while yield strain of GFRP is higher than steel about 58%.
  6. Stainless Steel rebar: Stainless steel rebar is the most expensive, about eight times the price of epoxy-coated rebar. It 1,500 times more resistant to corrosion than black bar. It is also more resistant to damage than any of the other corrosive-resistant or corrosive-proof types or rebar and it can be bent in the field.
  7. Threaded rebar: Also known as jumbo rebars or starter bars, contain single or double threaded ends on the black bar to enable the use of standard UNC fasteners to be used for securing items in place, similar to an anchor bolt. It used to tie reinforced masonry or concrete walls to concrete slabs or footings.
  8. Welded Wire Fabric (WWF): It is not identified as a rebar but serves the same purpose. It is a product manufactured with fusion welded low carbon steel wire or stainless steel wire joined into a square grid pattern or mesh in common sizes that is used for the reinforcement of concrete slabs. It serves to enhance the tensile strength of concrete slabs in the same manner as other types of rebar.
  9. Expanded Metal: Similar to WWF in usage, the mesh is made from a single steel sheet that is expertly cut and expanded, and is detailed in diamond-shaped lines. It is commonly used when extremely thick plaster is needed to support the concrete, as in sidewalks or walking surfaces, but not for heavy vehicle traffic or heavy weights.
  10. European rebar: Made of a carbon, manganese, silicon, etc. alloy, principally of manganese, European rebar is the least resistant type of rebar with respect to bending. While easy to work with, it is generally not recommended for use in areas that experience earthquakes nor for projects that require substantial structural integrity from its rebar.
Carbon Steel rebars are manufactured for construction with the following common grades;
  1. ASTM Grade 40 rebar has a minimum yield strength of 40 KSI (40,000 psi or 280 Mpa), and a minimum tensile strength of 60 KSI (60,000 psi or 420 Mpa)
  2. ASTM Grade 60 rebar has a minimum yield strength of 60 KSI (60,000 psi or 420 Mpa), and a minimum tensile strength of 90 KSI (90,000 psi or 620 Mpa).
  3. ASTM Grade 75 rebar has a minimum yield strength of 75 KSI (75,000 psi or 520 Mpa), and a minimum tensile strength of 100 KSI (100,000 psi or 690 Mpa).
  4. ASTM Grade 80 rebar has a minimum yield strength of 80 KSI (80,000 psi or 550 Mpa), and a minimum tensile strength of 105 KSI (105,000 psi or 725 Mpa).
  5. ASTM Grade 100 rebar has a minimum yield strength of 100 KSI (100,000 psi or 690 MPA), and a minimum tensile strength of 115 KSI (115,000 psi or 790 Mpa).
    6. Commonly the ratio (Tensile Strength/ Yield Strength) = 1.189 to 1.287
Reinforcing Bars are commonly manufactured in the following sizes and weights;
Size Imperial
Size Metric
Weight (lb/ ft)
Weight (kg/ m)
Nominal Dia (inch)
Nominal Dia (mm)
Nominal Area (inch2)
Nominal Area (mm2)
Size (Imperial)
#3
Size (Metric)
#10
Weight (imp)
0.376 lb/ ft
Weight (met)
0.561 kg/ m
Nominal Dia (imp)
0.375 (3/8) inch
Nominal Dia (met)
9.525 mm
Nominal Area (imp)
0.110 in2
Nominal Area (met)
71 mm2
Size (Imperial)
#4
Size (Metric)
#13
Weight (imp)
0.668 lb/ ft
Weight (met)
0.996 kg/ m
Nominal Dia (imp)
0.50 (1/2) inch
Nominal Dia (met)
12.70 mm
Nominal Area (imp)
0.20 in2
Nominal Area (met)
129 mm2
Size (Imperial)
#5
Size (Metric)
#16
Weight (imp)
1.043 lb/ ft
Weight (met)
1.556 kg/ m
Nominal Dia (imp)
0.625 (5/8) inch
Nominal Dia (met)
15.875 mm
Nominal Area (imp)
0.310 in2
Nominal Area (met)
200 mm2
Size (Imperial)
#6
Size (Metric)
#19
Weight (imp)
1.502 lb/ ft
Weight (met)
2.240 kg/ m
Nominal Dia (imp)
0.750 (3/4) inch
Nominal Dia (met)
19.050 mm
Nominal Area (imp)
0.440 in2
Nominal Area (met)
284 mm2
Size (Imperial)
#7
Size (Metric)
#22
Weight (imp)
2.044 lb/ ft
Weight (met)
3.049 kg/ m
Nominal Dia (imp)
0.875 (7/8) inch
Nominal Dia (met)
22.225 mm
Nominal Area (imp)
0.60 in2
Nominal Area (met)
387 mm2
Size (Imperial)
#8
Size (Metric)
#25
Weight (imp)
2.670 lb/ ft
Weight (met)
3.982 kg/ m
Nominal Dia (imp)
1.000 (8/8) inch
Nominal Dia (met)
25.400 mm
Nominal Area (imp)
0.790 in2
Nominal Area (met)
509 mm2
Size (Imperial)
#9
Size (Metric)
#29
Weight (imp)
3.400 lb/ ft
Weight (met)
5.071 kg/ m
Nominal Dia (imp)
1.128 inch
Nominal Dia (met)
28.650 mm
Nominal Area (imp)
1.00 in2
Nominal Area (met)
645 mm2
Size (Imperial)
#10
Size (Metric)
#32
Weight (imp)
4.303 lb/ ft
Weight (met)
6.418 kg/ m
Nominal Dia (imp)
1.270 inch
Nominal Dia (met)
32.260 mm
Nominal Area (imp)
1.270 in2
Nominal Area (met)
819 mm2
Size (Imperial)
#11
Size (Metric)
#36
Weight (imp)
5.313 lb/ ft
Weight (met)
7.924 kg/ m
Nominal Dia (imp)
1.41 inch
Nominal Dia (met)
35.810 mm
Nominal Area (imp)
1.560 in2
Nominal Area (met)
1006 mm2
Size (Imperial)
#14
Size (Metric)
#43
Weight (imp)
7.650 lb/ ft
Weight (met)
11.410 kg/ m
Nominal Dia (imp)
1.693 inch
Nominal Dia (met)
43.00 mm
Nominal Area (imp)
2.250 in2
Nominal Area (met)
1452 mm2
Size (Imperial)
#18
Size (Metric)
#57
Weight (imp)
13.600 lb/ ft
Weight (met)
20.284 kg/ m
Nominal Dia (imp)
2.257 inch
Nominal Dia (met)
57.330 mm
Nominal Area (imp)
4.000 in2
Nominal Area (met)
2581 mm2
Size (Imperial)
#20
Size (Metric)
#64
Weight (imp)
16.63 lb/ ft
Weight (met)
24.82 kg/ m
Nominal Dia (imp)
2.50 inch
Nominal Dia (met)
63.50 mm
Nominal Area (imp)
4.91 in2
Nominal Area (met)
3166.92 mm2

Rebars are marked in a number of ways. The ASTM rebar marking sequence is as follows;
  1. The first letter or symbol identifies the producing mill.
  2. The next marking is the bar size.
  3. The third marking symbol designates the type of reinforcing steel.
    1. S = ASTM A615, Carbon Steel
    2. A = ASTM A996, Axle Steel
    3. W = ASTM A706, Low Alloy Steel
    4. SS = ASTM A955, Stainless Steel
    5. CS = ASTM A1035, Low Carbon Steel
  4. The fourth marking symbol designates the grade of steel. Garde 40 has no grade markings. Grade 60, 75, 80, 100, 120 are shown. Another way of bar marking is to not show the grade but to leave spaces/ lines in ribs blank such as one line (for grade 60) or two lines (75), three lines (80, 100), or four lines (120) that must be at least five deformations long.

WHY
Since concrete is strong under compression but weak under tension, and makes it prone to cracking at around 400-500 psi in tension, rebars are placed in concrete forms before pouring concrete to increase the tensile strenth of hardened concrete structures, and is named as reinforced concrete or reinforced cement concrete (RCC). In reinforced concrete, the two materials (concrete and steel) act together in resisting forces. While the compressive strength of reinforced concrete stays the same as unreinforced concrete after placing rebars, the tensile strength of reinforced concrete is significantly increased to 3,000 to 6,000 psi range. Reinforced concrete in Footings and columns is generally in the 3,000 to 4,000 psi range and bridge superstructures are in the 4,000 to 6,000 psi range where weight is a major design factor.

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