Design of Columns MCQ with answer and solution

Concept

Limits of Longitudinal Reinforcement in Columns

Formula

p = (Ast / Ag) × 100 Minimum area of steel: Ast(min) = 0.008 \* Ag Maximum area of steel: Ast(max) = 0.06 \* Ag (or 0.04 \* Ag when lapped) Where Ast is the area of longitudinal reinforcement and Ag is the gross cross-sectional area of the column.

Step-by-step solution

1. Calculate the minimum steel percentage: p\_min = (0.008 × Ag / Ag) × 100 = 0.8% 2. Calculate the maximum steel percentage: p\_max = (0.06 × Ag / Ag) × 100 = 6% 3. Combine the limits to get the required range: 0.8% to 6%

Explanation

According to IS 456:2000, the minimum percentage of longitudinal steel in a column is 0.8% to ensure strength against unexpected loads and creep, while the maximum percentage is 6% to prevent steel congestion and allow concrete to be poured and compacted properly.

Shortcut

Remember the rule 0.8% to 6%: minimum steel is 0.8% (just under 1%) to prevent sudden failure, and maximum steel is 6% (or 4% when lapped) to avoid steel congestion during concrete pouring. A simple mnemonic is "0.8 to 6, column is fixed".

Common mistake

Students often confuse the maximum limit of longitudinal reinforcement in columns, selecting 0.8% to 4% (Option B) because 4% is the maximum limit allowed when bars are lapped, whereas the overall code limit specified in IS 456:2000 is 0.8% to 6% (Option C).