IS-style limits for longitudinal reinforcement in columns: As per IS practice, the percentage of longitudinal steel in an RCC column shall not be less than the minimum and not more than the maximum of what limits (as a percentage of gross cross-sectional area)?

Introduction / Context:
Columns require a minimum percentage of longitudinal steel for ductility and crack control, and a maximum percentage to ensure proper concrete placement and avoid congestion.

Given Data / Assumptions:

• IS-style working stress/limit-state detailing limits.
• Percentages are of the gross concrete cross-sectional area (Ag).

Concept / Approach:
Per standard Indian practice, the minimum longitudinal reinforcement in columns is 0.8% of Ag, and the maximum is typically limited to 6% of Ag (with higher values allowed locally only at laps). None of the given single options list the correct pair together.

Step-by-Step Solution:
Check each option against (min, max) = (0.8%, 6%).Option (a) 0.5–5% → too low.Option (b) 0.6–6% → minimum too low.Option (c) 0.7–7% → minimum too low and maximum too high.Option (d) 0.8–8% → maximum too high.Therefore, “none of these” is correct, and the correct limits are 0.8% ≤ steel ≤ 6% of Ag.

Verification / Alternative check:
Standard detailing references and code commentaries confirm the 0.8% minimum and 6% maximum for longitudinal reinforcement in columns.

Why Other Options Are Wrong:

• They do not reproduce the correct pair (0.8%, 6%).

Common Pitfalls:
Confusing tie/spiral columns or local congestion allowances; ignoring that 6% is a maximum primarily controlled by constructability.

Final Answer:
none of these