Moment Frame Base Condition....to Fix or not to Fix
Moment Frame Base Condition....to Fix or not to Fix
(OP)
I was running some design on a moment frame (end fixity at beam and column connection) and realized that I was always taught to
leave one of the column connections pinned, and the other "released", or a roller if you will.
I started playing around with modeling both column bases as "pinned" and noted that the frame behavior improved significantly in terms
of story drift.
In the real world, we will bolt that column base to the beam or wall on which it stands....it is not rolling around.
what is the accurate way to model a typical, 3 member moment frame? Pinned on both column bases? Or Pinned on one, roller on the other?
leave one of the column connections pinned, and the other "released", or a roller if you will.
I started playing around with modeling both column bases as "pinned" and noted that the frame behavior improved significantly in terms
of story drift.
In the real world, we will bolt that column base to the beam or wall on which it stands....it is not rolling around.
what is the accurate way to model a typical, 3 member moment frame? Pinned on both column bases? Or Pinned on one, roller on the other?






RE: Moment Frame Base Condition....to Fix or not to Fix
RE: Moment Frame Base Condition....to Fix or not to Fix
DaveAtkins
RE: Moment Frame Base Condition....to Fix or not to Fix
RE: Moment Frame Base Condition....to Fix or not to Fix
In thinking about it though, that could be the case if there was no grade beam or wall between the columns, but only isolated spread footings.
Mike McCann, PE, SE (WA)
RE: Moment Frame Base Condition....to Fix or not to Fix
I don't agree. For a support to become a roller, the footing would have to actually slide. I don't see that happening. Pinned--yes. A roller--no.
DaveAtkins
RE: Moment Frame Base Condition....to Fix or not to Fix
But, I've never done it in practice when lateral loads are applied.
RE: Moment Frame Base Condition....to Fix or not to Fix
another day in paradise, or is paradise one day closer ?
RE: Moment Frame Base Condition....to Fix or not to Fix
I agree in most cases, but if one footing is fully laterally restrained by soil and the other is not, as with a footing on or very near a downslope, I can see the footing want to move laterally without a tension tie. Hence I would use the roller without the tension tie to be conservative.
Mike McCann, PE, SE (WA)