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Force Distribution in the UFM

Force Distribution in the UFM

Force Distribution in the UFM

(OP)
With Reference to attached sketches:
When using the UFM (Uniform Force Method) for bracing connections, the beam to column connection is normally designed to resist the gusset to col. horizontal force Hc.
Here is the question: In sketch (b) the bracing terminates above the base of the column. At that point, the horizontal
loads are transferred to the column. Column shear and bending are utilized to transfer the horizontal loads down
to the base / foundation.
In this case, it appears the beam to column connection is not required to resist Hc, since Hc "goes" into the column,
and the load path does not require it to act axially through the beam.
Just wondering if anyone is in agreement with this. I don't know if having Hc act through the beam to column
connection is "embedded" into the UFM theory such that the beam to column connection must always resist the Hc force
regardless of over-all structure load path.

RE: Force Distribution in the UFM

I disagree. For case B, 100% of the horizontal component needs to be transferred into the beam/foundation.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Force Distribution in the UFM

(OP)
Yes, 100% of the brace horizontal component will be transferred to the foundation.
The question has to do with which components of the brace-beam-column connection must resist Hc.
Here, I'm using UFM terminology for Hc, Hb, Vc, Vb.

Assuming the left and right columns have the same stiffness, each column will resist (in shear and bending)
1/2 of the brace force horiz. component.
If Hc is the brace gusset to column force, assuming Hc is not greater than 1/2 of the brace horiz. force,
then Hc (at the brace-beam-col. connection), should be resisted by the col. and would not need to transfer
through the beam-col. connection.
Hb, is the brace to beam gusset force. That would transfer through the beam to the right side beam-col. connection.
Its a bit difficult to describe in type-written words.

RE: Force Distribution in the UFM

Ah, I think that I get it now. I apologize for my initial response. In retrospect, it must have sounded a bit condescending. I've taken a swing at the statics below.

My conclusion is that you should design the connection using UFM just as you would if the bracing continued to the foundation below with one exception, you'll need to balance out the horizontal loads transferred between the beams and columns as I've shown below.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Force Distribution in the UFM

(OP)
KootK,
I like you're sketch, that's a good way of looking at it. I was taking a slightly different approach,
but I think we are in agreement on the general concept.
Thank you for your response and feedback.

RE: Force Distribution in the UFM

You're very welcome. My thinking was that, in the specific case of Hb = Hc = Ph/2, my sketch would yield no axial force transfer at the left end. If you could then tweak your connection geometry such that you had only uniform gusset edge forces (UFM) while still satisfying Hc = Hb = Ph/2, you'd be all set. Of course, there's no eliminating the axial load delivered to the beam at the right end.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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