Roof Trusses – Slenderness of Tie Members with Stress Reversal For a roof-truss tie member that may experience reversal of stress (tension to compression), what is the limiting slenderness ratio (effective length / least radius of gyration)?

Introduction / Context:
Slenderness ratio limits control buckling risk in compression and govern vibration and serviceability in tension members. If a nominal “tie” can be subjected to stress reversal due to wind, erection, or temperature effects, codes restrict its slenderness as if limited compression might occur.

Given Data / Assumptions:

• Member: roof-truss tie with possible tension-compression reversal.
• Definition: slenderness = effective length / least radius of gyration.
• Design intent: ensure stability under accidental or occasional compression.

Concept / Approach:

Members that can see compression must satisfy a lower upper bound on slenderness to provide robustness. Ties with potential reversal therefore adopt limits closer to those for light compression members rather than very high ratios typical of pure tension bars.

Step-by-Step Solution:

Verification / Alternative check:

Classic steel design references list 180 for tension members liable to reversal, while members always in tension may be allowed higher values (e.g., up to ~400).

Why Other Options Are Wrong:

• 200 or 240: Higher than the commonly adopted cap for reversal cases; less conservative.
• 350: Suitable for pure tension elements in some contexts, not for reversal.

Common Pitfalls:

Assuming a tie never experiences compression; neglecting erection and wind suction scenarios; using the high tension-only limits indiscriminately.

Final Answer:

180