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?
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A6 mm
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B8 mm
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C10 mm
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D12 mm
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E16 mm
Answer
Correct Answer: 12 mm
Explanation
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:
Identify the code-based minimum diameter requirement.12 mm is the conventional minimum for column longitudinal bars.Select 12 mm from the options provided.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