Column K Factor

[kxa]

Is there a way to determine what K factor to use when a steel column base plate is bolted to a footing. The footing sizes vary from 2'x2' to 4'x4'. The columns are about 24' long and are braced about 8' from their tops(hinged conn.). At what point (ftg size)do we say that the column base is fixed?

 

[jike]

Most engineers would consider a column as pinned if it is supported by a single spread footing no matter the size.

The rotation of the base of a column is a function of three things:

the rotation of the footing due to the compressible nature of the soil.

the rotation due to the bending flexibility of the base plate.

the rotation due to the elongation of the anchor bolts.

The rotation would need to be minimized in all 3 cases, to create "fixity".

A footing would need to be stiffened by connecting it to another footing with a grade beam, foundation wall, strap, etc. to minimize rotation. The base plate would need to be stiffened with gussets, etc. to minimize rotation. The anchor bolts need to placed at the farthest reaches of the base plate to minimize rotation.

I hope this helps!