Reinforcing steel

Rebar (short for reinforcing bar), collectively known as reinforcing steel and reinforcement steel, is a steel bar or mesh of steel wires used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and hold the concrete in tension. Rebar's surface is often patterned to form a better bond with the concrete.

Originally, concrete structures were unreinforced. Rebar has been used in construction since at least the 15th century; for example, 2500 m of rebars were used in the Château de Vincennes.

More recently, during the 18th century, rebar was used to form the carcass of the Leaning Tower of Nevyansk in Russia, built on the orders of the industrialist Akinfiy Demidov. The cast iron used for the rebar was of high quality, and there is no corrosion on them to this day. The carcass of the tower was connected to its cast iron tented roof, crowned with one of the first known lightning rods. More recently these techniques have been refined by embedding steel bars in the concrete, and by the introduction of deformed bars to improve bonding, thus producing modern reinforced concrete.

Concrete is a material that is very strong in compression, but relatively weak in tension. To compensate for this imbalance in concrete's behavior, rebar is cast into it to carry the tensile loads. Most steel reinforcement is divided into primary and secondary reinforcement, but there are other minor uses:

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 voids to accommodate rebar, which is then secured in place with grout. This combination is known as reinforced masonry.

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