Question

Flexural collapse in over reinforced beams is due to

• A. Primary compression failure
• B. Secondary compression failure
• C. Primary tension failure
• D. Bond failure

Hint:

Under-reinforced beam $\rightarrow$ Tension failure (desirable) Over-reinforced beam $\rightarrow$ Compression failure (brittle failure)

Answer 1

The Correct Option is B

Concept: In an over-reinforced beam, the percentage of steel is greater than the balanced reinforcement. As loading increases,
• Concrete in compression reaches its crushing strain before the steel yields.
• Failure occurs suddenly by crushing of concrete. This mode of failure is known as secondary compression failure.

Step 1: Understand the behaviour of an over-reinforced beam. Since excessive steel is provided, \[ \rho>\rho_{bal}, \] the neutral axis shifts upward and concrete reaches its limiting strain first.

Step 2: Identify the mode of failure. The beam fails due to crushing of concrete before yielding of steel. Hence, \[ \boxed{\text{Secondary compression failure}.} \] Therefore, the correct option is \[ \boxed{(B)\;\text{Secondary compression failure}.} \]