For a reinforced concrete square column with 16 mm diameter longitudinal bars, what is the minimum diameter required for the lateral ties as per common code limits (not less than one-quarter of the largest longitudinal bar and an absolute minimum)?

Introduction / Context:
Lateral ties (transverse reinforcement) in reinforced concrete columns confine the core concrete and prevent buckling of longitudinal bars. Codes specify minimum diameters based on the size of longitudinal reinforcement and absolute minima for durability and constructability.

Given Data / Assumptions:

• Square column; longitudinal bars are 16 mm diameter.
• Standard code-based rule: tie diameter ≥ 1/4 of the largest longitudinal bar diameter and also ≥ an absolute minimum value.
• Typical practice based on IS-style provisions.

Concept / Approach:
For 16 mm bars, one-quarter is 16/4 = 4 mm. However, most codes specify an absolute minimum (for example, 6 mm) to ensure adequate stiffness and robustness of ties in handling and placement. Therefore, the controlling requirement is the absolute minimum, not the fractional rule in this case.

Step-by-Step Solution:
1) Compute 1/4 of 16 mm: 4 mm.2) Compare to absolute minimum permitted for ties: commonly 6 mm.3) Adopt the larger value: 6 mm.

Verification / Alternative check:
Design examples for small to medium columns routinely adopt 6 mm or 8 mm ties, with 6 mm being the minimum where permitted and 8 mm often used for better rigidity or larger bar cages.

Why Other Options Are Wrong:

• 4 or 5 mm: Below common absolute minimum; too slender for site handling.
• 8 or 10 mm: Acceptable but not the minimum required; increases steel without necessity for the given bar size.

Common Pitfalls:
Using only the quarter-bar rule and overlooking the absolute minimum diameter requirement in the code.

Final Answer:
6 mm