Actual length of a steel column with cap and base Between which two faces is the physical (actual) length measured?

Introduction:
Columns are often provided with a base plate at the bottom and a cap plate (or beam seat) at the top. The physical or actual length is the clear dimension that the steel member occupies between its supporting and supported plates. This question checks that you select the correct reference faces.

Given Data / Assumptions:

• Steel column with a base plate at bottom and a cap plate at top.
• We are asked for actual (physical) length, not effective length for buckling.
• Plates are horizontal and well-seated.

Concept / Approach:
Actual length is the physical distance occupied by the member. For a column with cap and base, the relevant faces are the top (upper surface) of the base plate and the underside (bottom surface) of the cap plate because those bound the steel shaft length that will be fabricated and erected.

Step-by-Step Solution:
1) Identify the lower reference surface: top of the base plate.2) Identify the upper reference surface: underside of the cap plate.3) Measure the clear distance between these two faces.4) This is the actual length used for detailing and shop drawings.

Verification / Alternative check:
Effective length for buckling depends on boundary conditions and is different (K * L). The question asks purely for physical length, which is clear between plate contact faces.

Why Other Options Are Wrong:
Options including the bottom of the base or top of the cap extend beyond the column shaft into plate thicknesses, which is not the member's actual length.

Common Pitfalls:
Mixing up actual and effective length; measuring to the wrong plate faces.

Final Answer:
top of the base and underside of the cap