Rebar
Rebar surfaces feature a continuous series of ribs, lugs or indentations to promote a better bond with the concrete and reduce the risk of slippage.
The most common type of rebar is carbon steel, typically consisting of hot-rolled round bars with deformation patterns embossed into its surface.
The carbon steel reinforcing bars may also be coated in zinc or an epoxy resin designed to resist the effects of corrosion, especially when used in saltwater environments.
[3][4] These alternative types tend to be more expensive or may have lesser mechanical properties and are thus more often used in specialty construction where their physical characteristics fulfill a specific performance requirement that carbon steel does not provide.
[5] Iron tie rods and anchor plates were later employed across Medieval Europe, as a device to reinforce arches, vaults, and cupolas.
[8] 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 wrought iron[citation needed] used for the rebar was of high quality, and there is no corrosion on the bars 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.
[10] Ernest L. Ransome, an English engineer and architect who worked in the United States, made a significant contribution to the development of reinforcing bars in concrete construction.
He invented twisted iron rebar, which he initially thought of while designing self-supporting sidewalks for the Masonic Hall in Stockton, California.
Turner was designing his "mushroom system" of reinforced concrete floor slabs with smooth round rods and Julius Kahn was experimenting with an innovative rolled diamond-shaped rebar with flat-plate flanges angled upwards at 45° (patented in 1902).
He rejected the idea that Kahn's reinforcing system in concrete beams would act as a Warren truss and also noted that this system would not provide the adequate amount of shear stress reinforcement at the ends of the simply supported beams, the place where the shear stress is greatest.
Furthermore, Turner warned that Kahn's system could result in a brittle failure as it did not have longitudinal reinforcement in the beams at the columns.
Most steel reinforcement is divided into primary and secondary reinforcement: Secondary applications include rebar embedded in masonry walls, which includes both bars placed horizontally in a mortar joint (every fourth or fifth course of block) or vertically (in the horizontal voids of cement blocks and cored bricks, which is then fixed in place with grout.
Masonry structures held together with grout have similar properties to concrete – high compressive resistance but a limited ability to carry tensile loads.
A similar approach (of embedding rebar vertically in designed voids in engineered blocks) is also used in dry-laid landscape walls, at least pinning the lowest course in place into the earth, also employed securing the lowest course and/or deadmen in walls made of engineered concrete or wooden landscape ties.
This first approach increases the friction locking the bar into place, while the second makes use of the high compressive strength of concrete.
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.
[16][17] Extra care is taken during the transport, fabrication, handling, installation, and concrete placement process when working with epoxy-coated rebar, because damage will reduce the long-term corrosion resistance of these bars.
[19] These epoxy-coated bars are used in over 70,000 bridge decks in the US, but this technology was slowly being phased out in favor of stainless steel rebar as of 2005 because of its poor performance.
Most commercially available rebar is made from unidirectional fibers set in a thermoset polymer resin and is often referred to as FRP.
FRP rebar, notably glass fibre types have low electrical conductivity and are non-magnetic which is commonly used for such needs.
The prime example of this is the collapse of the Cypress Street Viaduct in Oakland, California as a result of the 1989 Loma Prieta earthquake, causing 42 fatalities.
Rebars are quenched with water at a high level pressure so that the outer surface is hardened while the inner core remains soft.
The use of a grade by itself only indicates the minimum permissible yield strength, and it must be used in the context of a material specification in order to fully describe product requirements for rebar.
Material specifications set the requirements for grades as well as additional properties such as, chemical composition, minimum elongation, physical tolerances, etc.
Fabricated rebar must exceed the grade's minimum yield strength and any other material specification requirements when inspected and tested.
The more ductile steel is capable of absorbing considerably more energy when deformed – a behavior that resists earthquake forces and is used in design.
Mechanical couplers are an effective means to reduce rebar congestion in highly reinforced areas for cast-in-place concrete construction.
[34] To prevent injury, the protruding ends of steel rebar are often bent over or covered with special steel-reinforced plastic caps.
