Lacing bars for compression members – basic detailing rules Which of the following statements about lacing of built-up compression members are correct?
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ASlenderness ratio of lacing bars should not exceed 145
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BMinimum width of a lacing flat with 16 mm rivets is about 50 mm
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CMinimum thickness of a flat lacing bar is about one-fortieth of its length between inner end rivets
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DInclination of the lacing to the member axis should be between 40° and 70°
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EAll the above
Answer
Correct Answer: All the above
Explanation
Introduction / Context:Lacing transforms individual components into one built-up compression member that acts integrally. Codes provide detailing rules to ensure sufficient stiffness and strength against shear and buckling.
Given Data / Assumptions:
- Traditional IS working-stress design guidance is referenced.
- Member is a built-up column with lacing flats or angles.
- We compare typical limits for width, thickness, slenderness, and inclination.
Concept / Approach:Limits on slenderness (for lacing stability), minimum width and thickness (for connection and durability), and inclination (for efficient shear path) are prescribed to keep the lacing system effective without being overly flexible.
Step-by-Step Solution:
Check slenderness → typical limit around 145 for lacing bars.Check minimum width → commonly about 50 mm for 16 mm rivets to give edge distance and hole clearance.Check minimum thickness → about L/40 between inner rivets gives sufficient stiffness.Check inclination → 40° to 70° range provides a good diagonal bracing action.Verification / Alternative check:Compare with classic Indian steel design texts; the numerical limits are consistent with standard practice problems.
Why Other Options Are Wrong:Each individual statement aligns with standard rules; therefore the comprehensive choice “All the above” is the correct answer.
Common Pitfalls:Using too slender lacing that buckles; inadequate width leading to poor edge distances; inclination too shallow or too steep causing inefficiency.
Final Answer:All the above