Balanced reinforced concrete section: What do we call the cross-section of an R.C.C. beam in which the extreme concrete in compression and the tension steel simultaneously reach their respective permissible stresses at the same load level?

Introduction / Context:
Design philosophies distinguish between under-reinforced, balanced, and over-reinforced sections. Understanding “balanced section” helps clarify ductility and failure mode expectations for safe design.

Given Data / Assumptions:

• R.C.C. beam under bending.
• Concrete in compression and steel in tension have specified permissible stresses (working-stress) or design limits (limit-state).

Concept / Approach:
In a balanced section, the chosen reinforcement ratio is such that, at the limiting state, concrete in compression and steel in tension both reach their allowable/limit stresses simultaneously. This condition defines the balanced steel percentage and neutral axis depth for that material set and stress limits.

Step-by-Step Solution:
Define balanced: concrete and steel reach permissible stresses together.Contrast with under-reinforced: steel yields first (ductile).Contrast with over-reinforced: concrete crushes first (brittle).Hence, the named condition is “balanced section.”

Verification / Alternative check:
Textbook stress–strain diagrams and rectangular stress block analyses confirm the balanced condition at a specific reinforcement ratio for a given concrete and steel grade.

Why Other Options Are Wrong:

• Economic section: refers to minimal cost/weight for required capacity, not necessarily balanced.
• Critical section: generic phrase; not the definition of balanced condition.
• All of the above: only one is the precise definition.

Common Pitfalls:
Assuming balanced sections are always desirable; in modern limit-state design, under-reinforced (ductile) behavior is generally preferred.

Final Answer:
Balanced section