Built-up struts (compression members): which connection detailing statements are correct for ensuring composite action of the components?

Introduction / Context:
Built-up compression members (e.g., pairs of angles, channels, or tees) require adequate lacing or battening so that the components act together, sharing load and preventing local buckling.

Given Data / Assumptions:

• Member in compression composed of multiple elements.
• Connections by rivets/bolts/welds.
• Service loads within elastic range.

Concept / Approach:
Minimum connection requirements at the ends and at intervals ensure load transfer, torsional restraint, and control of relative slip. Where components are spaced apart, packing or solid washers maintain the required spacing and provide proper bearing for the fasteners.

Step-by-Step Solution:

Verification / Alternative check:
Check effective slenderness per relevant code considering lacing/battening; confirm stability against local and global buckling.

Why Other Options Are Wrong:
Each individual statement (a), (b), and (c) reflects accepted practice; selecting anything other than “All the above” would omit necessary detailing requirements.

Common Pitfalls:
Using thin packings that deform; too-wide connection spacing leading to independent buckling; inadequate end connection stiffness.

Final Answer:
All the above