What is a Reinforcing Bar?

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  • Written By: T. L. Childree
  • Edited By: R. Halprin
  • Last Modified Date: 25 November 2019
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    Conjecture Corporation
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A reinforcing bar is a carbon steel bar typically used to increase the tensile strength of masonry and concrete structures. Carbon steel is ideal for use within concrete structures due to the similar thermal expansion characteristics of the two materials. A reinforcing bar typically has numerous surface ridges to help anchor it to concrete. These bars are generally arranged into a grid or cage shape before being cast into the concrete. Reinforcing bars are usually welded, tied, or coupled together prior to installation.

Although concrete has excellent compression strength, it generally has very little tensile strength. A reinforcing bar is usually needed to increase the overall strength of this material. Masonry materials such as bricks and blocks also suffer from limited tensile strength; reinforcing bars are often cast into them as well. Many masonry materials are equipped with strategic voids for placement of reinforcing bars during construction. Once the bars are in place, the voids are filled with mortar to further strengthen the structure.


Carbon steel is typically used to reinforce concrete and masonry because of its high tensile strength and similar thermal expansion characteristics. Any strong material could be used to reinforce concrete, but differing thermal expansion characteristics in the two materials would likely cause the concrete to crack or break. To further prevent this from occurring, reinforcing bars typically have numerous ridges along their surface to prevent them from slipping out of the concrete under tremendous stresses. The ends of a reinforcing bar are also hooked into the concrete to further prevent it from being pulled out.

In most cases, a reinforcing bar is constructed of unfinished steel and is subject to corrosion. In normal applications, the concrete covering the bar is sufficient to protect it from decay. In marine applications, galvanized or stainless steel reinforcing bars are often used for added corrosion protection. These corrosion-resistant reinforcing bars are also utilized for bridge construction in locations where corrosive deicing materials are used on roadways. Special fiber-reinforced polymer bars have been introduced in recent years for use in highly corrosive environments.

Reinforcing bars are usually fabricated into some type of grid or cage shape before they are cast into a concrete structure. The bars are typically welded or tied together and their ends bent into a hook shape. Bars constructed of galvanized steel or fiber-reinforced polymer cannot be welded and must be tied together using some type of corrosion-proof wire. Reinforcing bar couplers are often used to join the bars together in precast concrete products. After the bars have been arranged and secured together, supports keep the fabricated structure in place while the concrete is poured.


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