Valid Pin Boundary Condition?

[duckhawk]

For a square moment frame, do you think this is a valid pin boundary condition at the base?

Where does the moment go?

 

[phamENG]

Maybe? Depends on the moment. And what deformation is expected at ultimate load and whether or not the connection will survive that deformation. Only true pin is, well, a pin.

Not sure what you mean by where the moment goes?

 

[Luceid]

Will it provide moment resistance? To some extent...yes as almost always. The moment would be resolved as base plate bearing on the concrete and tension in the bolts. But depending on the elongation and movement, this becomes more and more like a pin. Engineering judgement as always

 

[canwesteng]

It is certainly conventionally treated as a pin condition. Provided there is a sufficiently stiff load path above the base plate, you are ok to call it as a pin.

 

[rb1957]

"where does the moment go ?" ... in a pinned base, there is no moment ... though this will support "some" moment.

I guess the failure scenario would see the connection lose moment capability before it fails completely ... so pinned might represent the final state.

You could analyze as pinned, fixed, and/or partially fixed ... depending on how much time you thought this detail was worth.

 

[JoshPlumSE]

Yes, this is generally considered a "pinned" connection.

However, if there were a small amount of moment, then you could justify it with a hand calc. I had a case where I had a very small equipment support column with a base plate like this. No seismic load. Minimal wind and gravity loads.

I ran a calculation demonstrating that the wind load could be handled by the moment resistance at the base. IMO, the column was perfectly safe. But, the lead engineer objected and we moved the anchor bolts out to a more traditional moment resisting location. I didn't have a problem with changing it for him because he was the project lead and he had ultimate responsibility for my work.