Rebar Detailing, Estimating Drawings

A rebar or reinforcing bar refers to a common steel bar, which is commonly used in reinforced concrete and reinforced masonry structures. Rebar are generally formed from carbon steel and for better anchoring into the concrete, these rebar are given ridges. Though concrete is very strong in compression, it is weak in tension. By casting rebar into the concrete, this imbalance between compression and tension is nullified.  

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 co-efficient 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 ridges 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, 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.

U.S. Imperial 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. Bars higher in number have a slightly larger diameter than the one computed using the 1⁄8 inch formula.  

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

GRADES

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 instance grade 60 rebar has a minimum yield strength of 60 ksi. Rebar is typically manufactured in grades of 40, 60, and 75.

Common specifications are:

:: ASTM A 615 Deformed and plain carbon-steel bars for concrete reinforcement.
:: ASTM A 706 Low-alloy steel deformed and plain bars for concrete reinforcement.
:: ASTM A 955 Deformed and plain stainless-steel bars for concrete reinforcement.
:: ASTM A 996 Rail-steel and axle-steel deformed bars for concrete reinforcement.


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 to resist the forces from earthquakes for example.

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