For axially loaded steel columns subjected only to dead load and superimposed (sustained) service loads, what is the maximum permissible slenderness ratio?

Introduction / Context:
Slenderness ratio limits (effective length divided by radius of gyration) control susceptibility to buckling and excessive lateral deflection. Codes specify different maxima depending on the nature of loading—sustained gravity loads vs transient wind or earthquake actions—because reliability requirements differ.

Given Data / Assumptions:

• Member type: steel column.
• Loading: dead load and superimposed service loads only (no predominant wind/earthquake).
• We require the limiting slenderness ratio for such a case.

Concept / Approach:

For columns carrying sustained gravity loads, a commonly adopted maximum slenderness ratio is 180. More relaxed limits (e.g., 250) may apply when members are subjected primarily to wind/earthquake, but not for sustained compression governing service behavior.

Step-by-Step Solution:

Verification / Alternative check:

Design manuals align with this limit; larger limits are reserved for members where loads are transient and service instability is less critical.

Why Other Options Are Wrong:

• 250/350/400: Too high for columns with sustained compression; increase buckling risk.
• 120: More restrictive than required; uneconomical without specific service demands.

Common Pitfalls:

• Using wind/earthquake-only limits for gravity-dominated columns.
• Ignoring effective length (end restraint) when computing slenderness.

Final Answer:

180