Rigid or Pinned Column Base Connection 2

[cap4000]

I have a shear wall with concrete columns in the foundation walls and steel columns above. The question I have is at the steel column base plate where it meets the the top of the concrete column. Is that transition between the 4 anchor bolts considered a fixed end or pinned condition for the design of the 10 foot high concrete column ??

 

[JAE]

Usually it would be considered pinned unless you specifically design the bolts, the baseplate, and the column for fixity.

 

[cap4000]

JAE

Thanks for the quick response. Do the 4 anchor bolts I have qualify for a certain percentage of fixity??

 

[JAE]

I don't think you can figure on a rotational spring at the base of the column simply because you don't have any moment-rotation information for your particular case, and I don't think the effort at engineering such a connection (partial fixity) is worth it.

I would either assume it totally pinned or totally fixed and go from there. For the upper steel column design, the pinned condition will give you (usually) a more conservative design. For the anchors, a fixed condition assumption would give you a more conservative bolt design.

Hope that answers your question.

 

[UcfSE]

JAE is right. I would also note that if you do design it as pinned then you should be sure you have a brace some where so that you don't end up with a hinge in the middle of your column. I prefer pinned personally if it fits the needs. The connection is cheaper.

 

[cap4000]

UcfSE

Assume a pinned connection.
What "hinge" are you talking about in a 10 foot high reinforced concrete column poured with a 12 inch concrete foundation wall??

 

[UcfSE]

You would only have a pin if you a pin at the top of your steel column, a pinned connection at the steel to concrete and then a pin at the bottom of your concrete. That would give you a hinge in your column and make it unstable, obviously. I've noticed some unstable designs by others where I work and only thought to through that caveat just in case, particularly since we didn't have all the other info you have. It's no biggie, but since I've seen someone do things like that in person I thought to let you know about it.