Laced built-up columns – transverse shear to be resisted by lacing bars (IS practice) According to Indian Standard working-stress design practice, lacing bars in a built-up column are designed to resist transverse shear equal to what percentage of the member’s axial load?

Introduction / Context:
Laced built-up columns use lacing systems to tie individual components so they act as a single unit. The lacing not only keeps components in position but also resists a share of transverse shear induced by load eccentricities, initial imperfections, and secondary effects.

Given Data / Assumptions:

• Working-stress design style (traditional IS practice).
• Lacing bars are arranged in a single lacing system (typical exam assumption).
• We seek the code-recommended percentage of axial load to be taken as transverse shear for lacing design.

Concept / Approach:
Codes provide a simplified shear allowance that lacing must carry to ensure integrity against secondary shear effects. Traditional IS provisions take this nominal shear as a fixed small percentage of the member axial force, commonly 2.5% for single lacing (with slightly different values sometimes adopted for double lacing or battened systems).

Step-by-Step Solution:

Verification / Alternative check:
Classic Indian steel design texts and older IS 800 guidance list 2.5% as the nominal shear for single lacing systems, corroborating the value.

Why Other Options Are Wrong:
1.0% and 2.0% may underdesign; 3.0% or 4.0% are conservative beyond typical code guidance for single lacing, potentially uneconomical without justification.

Common Pitfalls:
Forgetting to check slenderness of lacing bars; omitting additional checks for double lacing or batten plates where recommended shear allowances differ; ignoring out-of-plane buckling of laced members.

Final Answer:
2.5% of the axial load