Built-up Columns MCQ with answer and solution

Concept

IS 800 gives a minimum thickness for flat lacing bars so that they do not buckle locally.

Formula

t ≥ L_e/40 (single lacing); t ≥ L_e/60 (double lacing)

Step-by-step solution

1. IS 800: for single lacing, thickness of flat lacing bar ≥ 1/40 of its effective length. 2. For double lacing, thickness ≥ 1/60 of its effective length. 3. Only option C matches (1/60 for double lacing).

Explanation

A lacing bar acts like a small strut, so it must not be too thin. Single lacing needs t ≥ L_e/40. Double lacing is stiffer, so t ≥ L_e/60 is enough.

Why the other options are wrong

A: single lacing needs 1/40, not 1/70. B: 1/40 is the value for single lacing, not double. D: single lacing needs 1/40, not 1/50.

Shortcut

Single = 40, Double = 60.

Common mistake

Swapping the values for single and double lacing.