In the design of laced compression members, the transverse shear to be resisted by the lacing system is commonly assumed as what percentage of the total axial load?
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A2.5% of axial load
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B3% of axial load
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C3.5% of axial load
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D4% of axial load
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E1.5% of axial load
Answer
Correct Answer: 2.5% of axial load
Explanation
Introduction / Context:Laced columns comprise individual components connected by inclined lacing bars. Imperfections and load sharing introduce secondary shear forces that the lacing must carry to keep the components acting together. A conventional design assumption prescribes a fixed percentage of the axial load as the shear to be resisted by the lacing system in each lacing plane.
Given Data / Assumptions:
- Member: laced compression member.
- Design requirement: nominal transverse shear resisted by lacing.
- Assumption: shear expressed as a percentage of total axial load.
Concept / Approach:The lacing prevents relative displacement and buckling of individual components by carrying transverse shear and ensuring composite action. Traditional provisions assume 2.5% of the member's axial load as the design shear for the lacing plane, ensuring adequate stiffness without excessive conservatism for ordinary proportions.
Step-by-Step Solution:
Let P = axial load in the member.Design transverse shear per lacing plane V = 0.025 * P (i.e., 2.5% of P).Size lacing bars and their connections accordingly for shear and slenderness.Verification / Alternative check:
Engineering texts consistently quote 2.5% for lacing, while battened systems adopt different adjustments (e.g., effective-length increases).Why Other Options Are Wrong:
3%, 3.5%, 4%: conservative relative to the customary assumption; not the standard default value.1.5%: unconservative; may under-design lacing for necessary transverse stiffness.Common Pitfalls:
Forgetting to check lacing slenderness and connection detailing after sizing for shear.Final Answer:
2.5% of axial load