Built-up tension member with channels – flanges turned outward: Why are the flanges of two channels in a built-up tension member commonly turned outward?

Introduction / Context:
Built-up tension members are frequently fabricated from a pair of channels connected back-to-back. The choice of turning flanges outward or inward affects fabrication convenience, lateral stiffness, inspection access, and the amount of lacing or tie plates required. Understanding these practical reasons helps in both design and detailing reviews.

Given Data / Assumptions:

• Two channels form a built-up tension member.
• Member is connected to gusset plates and splices via bolts/rivets or welds.
• Serviceability and constructability are priorities in addition to strength.

Concept / Approach:
Turning flanges outward increases the overall lateral dimension, which improves lateral rigidity and radius of gyration about the weak axis. It provides easier access for placing transverse connections (lacing or batten plates) and for inspection/maintenance. The outward orientation can reduce the number or intensity of lacing elements because the wider stance provides better inherent stability.

Step-by-Step Solution:
Compare inward vs outward flange orientation in terms of geometry and access.Identify benefits: easier detailing, potentially reduced lacing, and enhanced lateral stiffness.Conclude that outward flanges offer multiple advantages and are widely adopted where feasible.

Verification / Alternative check:
Workshop practices and standard detailing manuals routinely depict channels placed with flanges outward for tension members, confirming this as a preferred arrangement unless architectural or connection constraints dictate otherwise.

Why Other Options Are Wrong:

• Each individual reason a–c is valid; therefore, the most complete choice is “all the above.”
• “None of the above” contradicts common detailing practice.

Common Pitfalls:

• Ignoring eccentricity and shear-lag effects; adequate stitch spacing is still required.
• Assuming lacing can be omitted entirely; minimum tying provisions must be met.

Final Answer:
all the above