In a built-up compression member with single flat lacing, what is the minimum thickness t of a lacing bar relative to the length between inner end rivets?

Introduction / Context:
Lacing bars connect components of built-up columns, transmitting shear and restraining local buckling. Minimum thickness ensures that the lacing itself does not buckle or deform excessively under diagonal compression/tension.

Given Data / Assumptions:

• Single flat lacing configuration.
• Length is the distance between inner end rivets.

Concept / Approach:
Code provisions (IS:800 classic) prescribe thickness relative to length so that the lacing bar has sufficient stiffness. For single flat lacing: t_min ≈ length/40.

Step-by-Step Solution:
Identify lacing type: single flat.Apply codal limit: t ≥ length/40.

Verification / Alternative check:
Handbooks tabulate 1/40 for single flat and different limits for double lacing or angles, confirming the figure.

Why Other Options Are Wrong:

• 1/30: heavier than necessary.
• 1/50 and 1/60: too thin, prone to instability.
• None: not applicable because a codal limit exists.

Common Pitfalls:
Using clear rather than center-to-center length; not accounting for corrosion allowance in aggressive environments.

Final Answer:
t ≥ (1/40) × length