Minimum clear cover for reinforced concrete columns: What is the prescribed minimum cover requirement to main reinforcement?

Introduction / Context:
Concrete cover protects reinforcement against corrosion and fire and ensures proper bond. For columns, minimum cover is larger than for many beams or slabs due to exposure and durability considerations. This question tests recognition of the standard rule used in many Indian practice texts for columns.

Given Data / Assumptions:

• Question refers to main longitudinal bars in R.C.C. columns.
• Normal environmental exposure conditions unless specified otherwise.
• Traditional rule: use a minimum clear cover not less than 40 mm or the bar diameter, whichever is greater.

Concept / Approach:

Cover must at least equal a prescribed minimum for durability, and for large bars, ensuring the cover at least equals the bar diameter aids bond and fire resistance. Hence the conditional “greater of” formulation is applied.

Step-by-Step Solution:

Verification / Alternative check:

Durability tables in codes increase cover for severe environments; however, the baseline minimum for columns remains aligned with the “40 mm or bar diameter, whichever greater” guidance.

Why Other Options Are Wrong:

(b) and (d) reduce protection unacceptably. (c) is a beam/slab-like lower limit and may be inadequate for columns. (e) ignores bar size and environment.

Common Pitfalls:

Measuring cover to the center of bars instead of to the bar surface; not accounting for tolerance and spacer thickness; forgetting increased cover for aggressive exposure or fire ratings.

Final Answer:

Greater of 40 mm or bar diameter