The maximum pitch for tension and compression members respectively are
- A(12t or 200 mm, whichever is less) and (16t or 200 mm, whichever is less)
- B(12t or 300 mm, whichever is less) and (16t or 300 mm, whichever is less)
- C(16t or 200 mm, whichever is less) and (12t or 200 mm, whichever is less)Correct
- D(16t or 300 mm, whichever is less) and (12t or 300 mm, whichever is less)
Solution
Concept
Compression members need a closer pitch than tension members, to prevent local buckling of the plate between fasteners.
Formula
Tension: pmax = min(16t, 200 mm); Compression: pmax = min(12t, 200 mm)
Step-by-step solution
1. IS 800:2007 gives the maximum pitch of fasteners. 2. For tension members: 16t or 200 mm, whichever is less. 3. For compression members: 12t or 200 mm, whichever is less. 4. Here t is the thickness of the thinner outside plate. 5. So the order (tension, compression) is (16t or 200 mm) and (12t or 200 mm). Answer is (C).
Explanation
In compression, the plate between two bolts can buckle, so the pitch is kept smaller (12t). In tension there is no buckling, so a larger pitch (16t) is allowed. The upper limit in both cases is 200 mm.
Why the other options are wrong
A: The values are reversed (12t is for compression, not tension). B: The values are reversed and 300 mm is the wrong limit. D: The order is correct, but 300 mm is the general maximum (32t or 300 mm), not the limit for tension or compression members.
Shortcut
Compression is closer, so it gets the smaller number: C = 12t, T = 16t, both ≤ 200 mm.
Common mistake
Mixing up 12t and 16t, or using the 300 mm general limit.
Correct answer: C) (16t or 200 mm, whichever is less) and (12t or 200 mm, whichever is less)