Slenderness limit (compression members): What is the maximum permissible slenderness ratio for compression members that carry dead load and imposed (superimposed) load according to standard steel design practice?

Introduction / Context:
Slenderness ratio limits are prescribed to ensure compression members have adequate stiffness against buckling and to limit serviceability issues. For columns carrying sustained gravity loads (dead plus imposed), the most widely cited limit in traditional Indian practice is 180, frequently examined in design quizzes.

Given Data / Assumptions:

• Member is a compression element of a building frame.
• Loads include dead load plus superimposed (imposed) load.
• Slenderness ratio is defined as effective length divided by least radius of gyration.

Concept / Approach:
To prevent excessive elastic buckling and secondary effects, codes cap the slenderness ratio for different functions: bracing, compression with stress reversal, tension members, and compression under permanent loads. For gravity-carrying columns, the limit often adopted in problems is 180.

Step-by-Step Solution:
Identify the functional class: compression member carrying dead and imposed load.Recall the conventional limit: slenderness ratio ≤ 180.Select the correct option accordingly.

Verification / Alternative check:
Design handbooks tabulate different limits (e.g., 180, 250, 350) for different roles. The 180 value aligns with members in sustained compression rather than bracing or tension-only components.

Why Other Options Are Wrong:

• 250, 350: used for bracing or members not primarily in sustained compressive stress.
• 80 or 75: too restrictive for ordinary columns; usually for special stiff elements or serviceability-critical parts.

Common Pitfalls:

• Using the wrong effective length because of misidentified end restraints, which changes the computed slenderness.
• Forgetting to use the least radius of gyration (weak axis) in the ratio.

Final Answer:
180