Column design – factor of safety parameter “m” in the safe compressive stress formula In the classic working-stress formula for safe compressive stress of a column, the factor of safety parameter m is typically taken as:

Introduction / Context:Older column design under working-stress method used empirical/analytical formulae (e.g., Rankine or secant-type relations) containing a factor of safety parameter denoted by m. This factor provides a margin between elastic instability/yield and permissible stress.

Given Data / Assumptions:

• Working-stress design approach.
• Steel columns of common structural grades.
• Parameter m appears in the safe compressive stress expression.

Concept / Approach:Design aids and classic codes often adopt m ≈ 1.68 for steel columns, balancing safety and economy in allowable compressive stress calculations across practical slenderness ranges.

Step-by-Step Solution:Identify the parameter used in the safe stress formula.Select the standard value m = 1.68 for steel columns in WSM tables.

Verification / Alternative check:Tabulated allowable compressive stresses reverse-engineer to an m around 1.68 when matched to experimental buckling data and customary safety margins.

Why Other Options Are Wrong:

• 1.50 or 1.60: used in other contexts; not the cited standard for this formula.
• 1.88: more conservative than usual practice for ordinary structural steel columns.

Common Pitfalls:Mixing limit-state safety factors with working-stress parameter m; they are not interchangeable.

Final Answer:1.68