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Rebar





 

Rebar, a portmanteau for reinforcing bar or reinforcement bar, is common steel bar, an essential component of reinforced concrete and reinforced masonry structures. It is usually formed from carbon steel, and is given ridges for better frictional adhesion to the concrete. It can also be described as reinforcement or reinforcing steel. In Australia it is colloquially known as reo.

Additional recommended knowledge

Contents

Use in concrete and masonry

Concrete is a material that is very strong in compression, but virtually without strength in tension. To compensate for this imbalance in concrete's behavior, 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.

Physical characteristics

Steel has an expansion coefficient nearly equal to that of modern concrete. If this weren't so, it would be useless for reinforcing concrete.[1] Although rebar has ridges that bind it mechanically to the concrete with friction, 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, 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 steel, making it susceptible to rusting. As rust takes up greater volume than the iron or 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 rebar 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. Fiber-reinforced polymer rebar is now also being used in high-corrosion environments.

Welding

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 A706 is suitable for welding without damaging the properties of the steel.

Safety

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

Rebar sizes and grades

U.S. Imperial sizes

Imperial bar designations represent the bar diameter in fractions of ⅛ inch, such that #8 = 88 inch = 1 inch diameter. This convention applies to #8 and smaller bars only.

Imperial

Bar Size

"Soft"

Metric Size

Weight

(lbft)

Weight

(kg/m)

Nominal Diameter

(in)

Nominal Diameter

(mm)

Nominal Area

(in²)

Nominal Area

(mm²)

#3 #10 0.376 0.561 0.375 9.525 0.11 71
#4 #13 0.668 0.996 0.500 12.7 0.20 129
#5 #16 1.043 1.556 0.625 15.875 0.31 200
#6 #19 1.502 2.24 0.750 19.05 0.44 284
#7 #22 2.044 3.049 0.875 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 57.33 4.00 2581

Canadian metric sizes

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

Metric

Bar Size

Mass

(kg/m)

Nominal Diameter

(mm)

Cross-Sectional

Area (mm²)

#10 M 0.785 11.3 100
#15 M 1.570 16.0 200
#20 M 2.355 19.5 300
#25 M 3.925 25.2 500
#30 M 5.495 29.9 700
#35 M 7.850 35.7 1000
#45 M 11.775 43.7 1500
#55 M 19.625 56.4 2500

European metric 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

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 1.58 16 201
20,0 2.47 20 314
25,0 3.85 25 491
28,0 4.83 28 616
32,0 6.31 32 804
40,0 9.86 40 1257
50,0 15.4 50 1963

Grades

Historically in Europe, rebar comprised mild steel material with a yield strength of approximately 250 N/mm². Modern rebar comprises 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 against earthquakes for example.

Rebar designation

For clarity, reinforcement is usually tabulated in a Reinforcement Schedule on construction drawings. This eliminates ambiguity in the various notations used in different parts of the world. The following list provides examples of the different notations used in the architecutral, engineering, and construction industry.

United States

Designation Explanation
#4 @ 12 OC, T&B, EW Number 4 rebars spaced 12 inches on centre (centre-to-centre 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 centre. Each set consists of two ties, which is usually illustrated.

See also

References

  1. ^ GFRP Bar Transverse Coefficient of Thermal Expansion Effects on Concrete Cover
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Rebar". A list of authors is available in Wikipedia.
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