Design of Beams MCQ with answer and solution

Concept

Purpose of shear reinforcement in RCC

Formula

NONE

Step-by-step solution

1. Shear forces in reinforced concrete beams induce principal tensile stresses along inclined planes near supports. 2. Concrete has low tensile strength and can fail abruptly due to these principal tensile stresses, known as diagonal tension. 3. Shear reinforcement (stirrups or bent-up bars) is specifically provided to carry these diagonal tension forces and prevent brittle failure. Answer: A

Explanation

When an RCC beam is subjected to shear forces, inclined tensile stresses develop near the supports, causing diagonal cracking. Since concrete is weak in tension, special shear reinforcement such as stirrups or bent-up bars must be provided. This steel reinforcement directly crosses potential diagonal cracks to safely carry the diagonal tension.

Why the other options are wrong

B) Concrete adequately resists diagonal compression without requiring steel reinforcement. C) Horizontal shear causes principal stresses that result in diagonal tension failure. D) Vertical shear creates diagonal tension cracks, which shear reinforcement directly resists.

Shortcut

Concrete is weak in tension, so shear reinforcement resists diagonal tension.

Common mistake

Assuming shear reinforcement directly resists direct shear stress rather than the induced principal diagonal tension.