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Large shear with continuous 2 span - am I analyzing this right?

Large shear with continuous 2 span - am I analyzing this right?

Large shear with continuous 2 span - am I analyzing this right?

(OP)
I have a 29' column primarily supporting lateral load at the upper 25'. 1.5' from the base of the column will have steel members and steel plate framing into 3 sides of the column (with welds all around). I'm analyzing this as a continuous two span (beam) and it's coming up with huge shears at the base connection due to the short 1.5' span. I pinned all three supports.
Am I modeling this correctly? It is possible to look at this as just two simply supported members therefore eliminating the large shears I'm getting? Or because it is a continous member it has to be looked at as a two span continuous member?
Any input would be great.

RE: Large shear with continuous 2 span - am I analyzing this right?

If the member is continuous, it must be modeled as such to obtain an accurate result.  Otherwise, you are just kidding yourself.  

To eliminate the extra leverage though, I would consider, if possible, putting a lateral slip connection at the 1.5 foot mark and designing it as a single span member.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Large shear with continuous 2 span - am I analyzing this right?

Draw a sketch of the column and beams.

BA

RE: Large shear with continuous 2 span - am I analyzing this right?

I ran into something similar when I was looking at my basement.  I wanted to move the posts closer to the foundation walls.  When I got one of the posts about 3 ft from one of the walls, the reaction (and shear) at the wall 3' from the post just blew up.  

As Mike says, if you can provide a slip connection, do it.  You're not modeling anything wrong, it's the geometry.  If you can't do that, then consider pinning the column at that location.  A typical column splice detail from AISC would qualify as a pin.  This will provide axial continuity, but discontinuity for moment which will take care of the shear problem.

RE: Large shear with continuous 2 span - am I analyzing this right?

i think you're over compliating it ... isn't this (just) a beam on two supports, with a long overhang ?

take moments about the lower support ... Pu*1.5 = P*25 ...
Pl = P-Pu, and (naturally) there's a large moment at teh upper support.

RE: Large shear with continuous 2 span - am I analyzing this right?

rb-

No, the column has three supports.  One at the base, one at 1.5' from the base, and one at the top (29').  At least that's the way I read it.

RE: Large shear with continuous 2 span - am I analyzing this right?

That is why we need a sketch.  Words are easily misinterpreted.

BA

RE: Large shear with continuous 2 span - am I analyzing this right?

I read it the way SEIT did. It then makes sense that he gets a large force, the two supports at 1.5" act as a fixed end while the other is pinned. It is, in effect, a propped cantilever.

Michael.
Timing has a lot to do with the outcome of a rain dance.

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