1.3 Composite action of reinforced concrete

Understanding the Role of Steel in Reinforced Concrete

The Basics of Concrete and Tension

• Concrete has a low tensile strength, only about 10% of its compressive strength. For design simplicity, it is assumed that concrete does not resist tensile forces; these are fully supported by reinforced steel.

Behavior Under Load

• When a reinforced concrete beam is loaded, it initially shows no deformation or stress. As loading continues, the beam bends downward, creating tension at the bottom and compression at the top.

Deformation and Cracking

• The bending causes elongation at the bottom and compression at the top due to concrete's limited deformability. This leads to cracking in the concrete while tensile forces are transferred to the steel bars.

Failure Mechanisms

• A member fails when either its compressive strength is exceeded or if there’s failure in bond integrity between steel and concrete. The composite material must maintain integrity to withstand loads effectively.

Importance of Bonding

• Adequate bonding between steel bars and concrete is crucial for composite action. Poor bonding can compromise load resistance capabilities of reinforced concrete members.

Surface Features of Steel Bars