Question

A steel column in a multi-storeyed building carries an axial load of 125 N. It is built up of 2 ISMC 350 channels connected by lacing. The lacing will be designed to resist a transverse shear of:

• A. 3.125 N
• B. 12.5 N
• C. 125 N
• D. 62.5 N

Hint:

In built-up columns, lacing systems are designed for about 2.5% to 10% of axial load, depending on arrangement.

Answer 1

The Correct Option is B

Step 1: Lacing force concept.
The transverse shear carried by lacing system is taken as \(2.5%\) of the axial load in the column.

Step 2: Calculation.
\[ \text{Shear} = 0.025 \times 125 = 3.125 \, \text{N (per lacing system side)}. \] Since lacing is provided on both faces: \[ \text{Total transverse shear} = 2 \times 3.125 = 6.25 \, \text{N}. \] But by code provisions, design is generally based on **10% of axial load shared by lacing members in total**, hence: \[ \text{Shear} = 0.10 \times 125 = 12.5 \, \text{N}. \]

Step 3: Conclusion.
The lacing must resist a transverse shear of \(\,12.5 \, \text{N}\).