Singly reinforced beam behavior: If, in a singly reinforced RCC beam, the permissible stress in concrete is reached earlier than the permissible stress in steel, the section is called a(n)…

Introduction / Context:Classifying a singly reinforced beam as under-reinforced, balanced, or over-reinforced is essential to predict failure mode and ductility. The sequence in which concrete and steel reach their permissible or ultimate stresses dictates this classification.

Given Data / Assumptions:

• Singly reinforced rectangular section.
• Comparison is based on permissible (working) stresses or limit state strains.

Concept / Approach:

• Under-reinforced: steel reaches its limit first → tension steel yields before concrete crushes → ductile behavior.
• Balanced: steel and concrete reach limits simultaneously.
• Over-reinforced: concrete reaches its limit first → crushing in compression zone governs → brittle behavior.

Step-by-Step Reasoning:Given that concrete reaches permissible stress earlier than steel, the compression zone limits govern.Hence the section has more tensile reinforcement relative to balanced, i.e., it is over-reinforced.

Verification / Alternative check:Over-reinforced sections are generally avoided in modern limit-state design because they lack ductility and warning before failure.

Why Other Options Are Wrong:Under-reinforced: Opposite condition (steel would govern).Economic / critical: Not standard classifications for this context.Balanced: Implies simultaneous attainment, not earlier concrete control.

Common Pitfalls:

• Assuming more steel always improves safety; it can reduce ductility.

Final Answer:over reinforced section