Steel Column Bases – Minimum plan dimension relative to column size The minimum length of the side or diameter of a column base shall not be less than (d is the minimum diameter/side of the column):

Introduction / Context:
Base plates spread column loads to concrete foundations, limiting bearing pressure and providing room for anchorages and edge distances. Codes set minimum plate dimensions in relation to column size to ensure adequate edge cover and fabrication tolerances. This item recalls the commonly used minimum expression for plan dimension.

Given Data / Assumptions:

• Steel column with minimum across-flat/diameter dimension d.
• Base plate bearing on concrete with grout layer.
• Need minimum plan dimension to accommodate load diffusion and detailing.

Concept / Approach:

The formula 1.6 (d + 75) mm embeds a basic margin (75 mm) around the column and a scale factor (1.6) to ensure practical edge distances, anchor position, and bearing area. It functions as a baseline before detailed bearing and bending checks determine the final size.

Step-by-Step Solution:

Verification / Alternative check:

Trial sizing by bearing pressure and cantilever strip method typically confirms this minimum is a realistic starting point for most columns.

Why Other Options Are Wrong:

d + 75 is too small for anchors/edge cover; 1.2 (d − 75) is dimensionally suspect and may be unsafe; 1.5 (d + 75) is slightly smaller than recommended minimum for general practice.

Common Pitfalls:

Ignoring grout holes/anchor bolt edge distances or not checking for biaxial load cases after preliminary sizing.

Final Answer:

1.6 (d + 75) mm