With reference to lacings under compression members of steel structures, the width of the lacing flat for 20 mm of nominal diameter of rivet is
- A50 mm
- B60 mmCorrect
- C55 mm
- D65 mm
Solution
Concept
The minimum width of a lacing flat is about 3 times the nominal diameter of the rivet.
Formula
bmin ≈ 3 × d
Step-by-step solution
1. Nominal rivet diameter d = 20 mm. 2. Minimum width of lacing flat ≈ 3 × d = 3 × 20 = 60 mm. 3. The code table gives: 16 mm rivet - 50 mm, 18 mm - 55 mm, 20 mm - 60 mm, 22 mm - 65 mm. 4. Answer is (B) 60 mm.
Explanation
The lacing flat must be wide enough to give proper edge distance around the rivet hole. For this reason the width is kept about three times the rivet diameter. For a 20 mm rivet, the width is 60 mm.
Why the other options are wrong
A: 50 mm is for a 16 mm rivet. C: 55 mm is for an 18 mm rivet. D: 65 mm is for a 22 mm rivet.
Shortcut
Width of lacing flat = 3 × rivet diameter.
Common mistake
Mixing up the rows of the table and picking 65 mm, which belongs to a 22 mm rivet.
Correct answer: B) 60 mm