7.14 : Reinforcements in Concrete

Reinforced concrete is a composite material used extensively in construction, combining the compressive strength of concrete with the tensile strength of steel. This synergy is essential as concrete, while excellent at resisting compression, is weak under tension. Steel bars, or rebars, are embedded in the concrete to handle these tensile forces. The choice of steel is strategic; it shares a similar coefficient of thermal expansion with concrete, which ensures uniformity in response to temperature changes.

The steel used in reinforced concrete is typically produced through a hot-rolling process. These rebars are circular in cross-section, available in standard diameters and lengths, and have surface ribs that enhance their bonding with the concrete. They are categorized into different grades, which correspond to the steel's yield strength.

The design of a reinforced concrete structure includes calculating the optimal cross-sectional area of steel needed. This can vary, involving either more bars of smaller diameter or fewer bars of larger diameter, depending on the structural requirements. The arrangement of these reinforcements is determined by factors such as the dimensions of the concrete member, the required concrete cover, and the necessary spacing between the bars to allow for the passage of concrete aggregates.

In addition to the main reinforcement, other forms include stirrups and spiral reinforcements, which help maintain the integrity of the structure. Innovations like fiber-reinforced concrete, which incorporates fibers, and ferrocement, which uses mesh, also represent advances in reinforcement techniques, offering enhanced durability and strength.