Under what condition are plain bars or wires permitted in reinforced concrete?

Plain bars or wires are typically permitted in reinforced concrete primarily when used in specific conditions such as in spirals. Spirals serve a unique function in concrete structures, especially in columns subjected to lateral and axial loads. The smooth surface of plain bars or wires allows for effective confinement of the concrete, enhancing ductility and reducing the risk of buckle failure.

In many structural applications, the use of deformed bars is standard because they provide better bonding with the concrete due to their surface texture. However, for certain applications like spirals, plain bars can successfully meet the design requirements when deformations are not necessary for structural integrity.

This context emphasizes the importance of understanding the specific functions of different types of reinforcement in concrete applications, allowing for appropriate material selection according to the structural needs.