Minimum diameter of longitudinal bars in reinforced concrete columns: As per standard practice, the longitudinal reinforcement in a column should not be less than what bar diameter?

Introduction / Context:

Minimum bar diameters ensure adequate stiffness during construction, resistance to buckling between ties, and robustness at laps/anchorage. Column longitudinal bars must satisfy code-mandated minimums to perform under axial load and bending.

Given Data / Assumptions:

• Reinforced concrete column under combined actions.
• Standard building code provisions (typical of IS/BS/ACI ranges).

Concept / Approach:

Codes specify a minimum longitudinal bar diameter to maintain constructability and mechanical performance. A widely taught minimum is 12 mm for column longitudinal bars in general building practice.

Step-by-Step Solution:

Verification / Alternative check:

Detailing manuals and exam standards consistently use 12 mm as the minimum column longitudinal bar diameter for typical RC frames.

Why Other Options Are Wrong:

• 6–10 mm: Undersized for column main bars; prone to handling/buckling issues.
• 16 mm: Acceptable but not the minimum; using larger bars is a design choice, not a requirement.

Common Pitfalls:

• Confusing minimum diameter of ties (stirrups) with longitudinal bars—ties can be smaller (e.g., 6–8 mm).

Final Answer:

12 mm