The Art of Reading Buildings Practice Test

Concrete handles compression well but is weak in tension and shear. To take on those loads, reinforcement is placed inside the concrete. Steel is the standard choice because it has high tensile strength and, importantly, ductility. This means steel can carry load even after cracks form and can deform without suddenly failing, which helps the structure redistribute stresses and resist bending and shear more effectively. The steel and concrete work together as a composite material—the bond between them (through rough bars or mesh) allows them to share loads, so the overall member can resist tensile and shear forces far better than plain concrete.

Other materials like plastic, aluminum, or wood don’t provide the same combination of high strength, stiffness, and durable bonding with concrete in typical structural environments, so they aren’t used for this purpose in standard reinforced concrete.