If HSS Column is welded to baseplate, then how does one knows is that a moment (fixed) connection or pinned connection?

[Chirag Hingad]

If HSS Column is welded to baseplate, then how does one knows is that a moment (fixed) connection or pinned connection?

 

[BridgeSmith]

It's neither. It's partially fixed. Depending on the bending stiffness of the column, and the rigidity of the base plate, the base plate connection to the foundation, and the foundation itself, it may be almost rigid or almost pinned.

The simple approach that eliminates the need to quantify the degree of fixity, is to design the base plate and its connection to the foundation assuming it is fully fixed, and design the columns, beams, and other components of the frame assuming a pinned connection. IF you need some fixity in order to make the frame design out, then you'll have to quantify the partial fixity provided.

 

[SteelTubes]

There are two articles on Steel Tube Institute's website that talk about HSS Column to baseplate connections, one with a design example. Though I don't think they directly address your specific question, you might find them helpful.

Axially Loaded HSS Column to Base Plate Connections | Steel Tube Institute

In this article, Kim Olson, PE – HSS Consulting Engineer at the Steel Tube Institute, discusses axial compression loading and axial tensile loading for HSS column to base plate connection.

steeltubeinstitute.org

HSS Base Plate Design for Axial Compression and Bending Moment | Steel Tube Institute

All steel columns need a base plate to transfer the axial and/or flexural forces from the building above into the supporting foundation.

steeltubeinstitute.org