Design of Connections for Steel Frame

[Colin Dale]

I am working on a project involving a mostly open building with a truss supported by a wooden beam, which in turn transfers load to wooden columns which run down to concrete foundations.

Some of the posts are being removed and a portion of the wooden beam is being replaced by a steel beam, and the wooden posts removed will be replaced by steel columns. I am planning to weld the columns to an anchor plate on the concrete foundation, which in turn is anchored to the concrete post with anchor bolts.

I am wondering how to model this. I have a STAAD Pro model created with fixed supports at the anchor plates. I am wondering if it is a more sound decision to model the top corners as fixed or pinned connections. This will determine what kind of connection to design at the tops of the frame. Many of the places I have looked seem to imply a pinned connection at the bases and a fixed connection at the top corners of the frame, but I feel to resist wind (and due to the fact that the truss is somewhat unreliable), the bases should provide a fixed connection.

I have attached a couple working pages of plans. Any advice would be greatly appreciated. My email is [email protected].

Thank you.

5375P881-881.pdf

 

[Lomarandil]

You will get some degree of fixity (maybe better termed moment resistance) at an anchor bolt/base plate connection, but not nearly as much as a properly designed beam-column moment connection could give. I guess my approach would depend on how heavily the lateral load is influencing the system.