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Tube Col to Tube Bm Moment Connection

Tube Col to Tube Bm Moment Connection

Tube Col to Tube Bm Moment Connection

Say you have an HSS 8x8 column and you want to frame a horizontal beam (another tube section) into the side of it.  We also want the beam to extend past the column and cantilever out a bit.

At first I thought I'd just use a bit smaller sized beam - say an HSS6x6 and just fillet weld around the ends on the faces of the HSS8x8 - but I got to worrying about distortion in the face of the column when moment is applied at the connection from gravity loads on the beams.  I have the AISC Hollow Structural Sections - Connection Manual - but it only has HSS to WF connections - not tube to tube (which is kinda strange).

I know that using a single vertical plate shear connection on the face of tube columns has been found to be OK (i.e. no serious distortions.  Would this moment connection idea be OK as well? - as long as the beam wasn't too much smaller than the column width?  What do you think?

RE: Tube Col to Tube Bm Moment Connection

I get from your post that the column is continuous past the beams and the beam is discontinuous. therefore you want to weld a tube to the face of the column on opposite sides. one for a "backspan" and one for the cant. correct? that is why you want i size smaller tube to get an easier weld.

if that is the case why not just run the beam cont. over the colummn?

to answer you question though... i would think you would be ok if the forces are reasonable then the tube top and beam flange would act as a horiz beam to carry the flange forces to the webs of the columns.

at cases were the forces are very high. i have seen a detail were a plate was cut with a hole in it and sliped over the tube column to connect the top and btm flange directly. it was also welded all around the column. the plate would also serve to stiffen the tube

hope this helps

RE: Tube Col to Tube Bm Moment Connection

yes, the column continues on up - to support a fancy roof truss.  So I can't run the "beam" tube over the top of the column.

What you indicated - that the flange forces in the beam would have to somehow translate into forces in the side "webs" of the columns - is true - and its what I'm worried about. That there would be stress concentrations at the corners of the beam-to-column weld - or that the column face, to which the beam is welded, would distort in that small gap betweent he beam and the sidewall of the column.

Right now we are thinking about running the beam through a square hole cut in the column and then welding it closed on each face...the column takes some, but not a lot of load (fancy trusses are arched roof trusses spanning only about 15-20 feet.

RE: Tube Col to Tube Bm Moment Connection


your detail would obviously work. it sounds like an erection problem to me. could they make each of these assemblies in a shop? or are you planning on field welding this?

what about using your idea but putting a "telescoping? tube that is slightly smaller then your beam that does what you describe thru the column. you could then feld weld a normal all around fillet weld for the field erected peices. the tube inside would stiffen the tube walls and still allow someting easilly erected

or run the beam over the top and put a "jump" column above the beam and brace it. i assume you have thought of that though and it is not possible to brace the column baced on you answer. just keeps occuting to me as the cheapest idea.

RE: Tube Col to Tube Bm Moment Connection

or what about the other way put a slightly larger tube thru the column in the shop and slide the final beam thru the hole in the field and field weld it.

good luck

RE: Tube Col to Tube Bm Moment Connection

Thanks for the ideas.

RE: Tube Col to Tube Bm Moment Connection

I would think that your connection would fall under the design of a branch member in a truss with flexure.  You should be able check this using the formula's in section's 8 and 9 of the HSS Connections Manual or in the LRFD 3rd edition.  To me, it would look better and be easier to deal with if the connection does not require a bunch of coping to make work.

RE: Tube Col to Tube Bm Moment Connection

The detail on page 4-135 of the ASD Manual (or something similar) is what I would use.  I would make the "beam" tube the same width as the "column" tube, and make sure the two vertical welds can take the moment.  Or make the column wall thick enough to take the local bending.


RE: Tube Col to Tube Bm Moment Connection

I would follow the procedure in AWS D1.1 Structural Welding Code Chapter on Tubular Structures.

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