Which one of the following statements related to a design of laced columns as per IS 800:2007 is not correct ?
- AThe slenderness ratio for lacing bars should not exceed 145.
- BIn bolted/riveted construction, the minimum width of lacing bars shall be four times the nominal diameter of the bolt/rivet.Correct
- CLacing bars should be inclined at 40° to 70° to the axis of built up member.
- DThe effective slenderness ratio of laced columns shall be taken as 1·05 times the actual maximum slenderness ratio, in order to account for shear deformation effects.
Solution
Concept
Detailing rules for lacing (IS 800 clause 7.6)
Step-by-step solution
1. Slenderness ratio of lacing bars ≤ 145 (a). 2. In bolted/riveted work the width of lacing bars should be at least 3 times the nominal bolt/rivet diameter, not 4 times. 3. Lacing inclination 40° to 70° with the axis (c). 4. Effective slenderness ratio = 1.05 × actual (d).
Explanation
IS 800 requires the width of lacing bars in bolted construction to be at least three times the nominal diameter of the bolt. The statement with four times is the incorrect one.
Why the other options are wrong
Statements (a), (c) and (d) agree with IS 800 clause 7.6.
Shortcut
Lacing: ≤ 145 slenderness, 40°–70°, 3d width, 1.05 factor.
Common mistake
Remembering four times instead of three times the bolt diameter.
Correct answer: B) In bolted/riveted construction, the minimum width of lacing bars shall be four times the nominal diameter of the bolt/rivet.