Laced compression members: recommended inclination of lacing bars with the member axis Choose the suitable range for the angle that lacing bars make with the longitudinal axis.
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A20° to 50°
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B30° to 60°
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C40° to 70°
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D50° to 80°
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E15° to 30°
Answer
Correct Answer: 30° to 60°
Explanation
Introduction:Lacing systems connect components of a built-up compression member so that they act together. The angle of lacing bars ensures efficient shear transfer and stability while keeping bar forces reasonable.
Given Data / Assumptions:
- Built-up steel compression member with double lacing.
- Lacing bars primarily resist shear and provide lateral restraint.
Concept / Approach:
Design recommendations limit the inclination so that the axial and transverse components of bar forces are balanced. A commonly adopted range is 30° to 60° with the member axis.
Step-by-Step Solution:
1) Select a bar angle that avoids very flat lacing (inefficient) and very steep lacing (large forces).2) The practical window 30°–60° satisfies both strength and detailing needs.3) Choose the option exactly matching this window.Verification / Alternative check:
Check slenderness of lacing and node strength; connection design must also satisfy shear flow.
Why Other Options Are Wrong:
20°–50° admits too-flat lacing at the lower end; 40°–70° and 50°–80° skew the range upward; 15°–30° is excessively flat.
Common Pitfalls:
Ignoring out-of-plane buckling of lacing, inadequate end tie plates, and mismatched single vs double lacing assumptions.
Final Answer:
30° to 60°