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Moment connections between beams of different depths 1

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Ipetu

Ipetu

Structural
Jun 5, 2007
54
A W8x18 beam and a W14x22 beam frame into the opposite sides of a W10x16 bream in a moment connection. The challenge in this type of configuration is that the W8 is 2" shallower than the W10 and the W14 is 4" deeper than the W10. Any ideas on making this work are appreciated.

For the W8x18 to W10x16 connection factored forces to be resisted are 33 ft-kips moment and 21 kips shear. For the W14x22 to W10x16 connection the factored forces to be resisted are 33 ft-kips moment and 31 kips shear.
 
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If I'm the designer, I change the sizes to make them more logical, unusual connections cost more than the extra poundage.

If I'm the detailer, I note that the beams are only adding vertical load to the W10. I would weld a 6" tee under the W8 and run plates top and bottom to take the moment and a normal web connection to handle the vertical, the W14 having a bolt row below the bottom of the W8.

Michael.
Timing has a lot to do with the outcome of a rain dance.
 
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I'd look into change the beam sizes...sounds like it is too late.
I never could stand jobs where designers use the exact damn beam size the software spit out with no due regard to actually framing the building.
 
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i'd use a machined brkt to pick up the outside of the lower flange of the W8 and the inside of the lower flange on the W10 (which crosses at about 90deg ?). then another brkt to pick-up the outside of the W10 and connect with the W14 lower flange.

i'm sort of supposing that the upper surfaes align.

then again you're probably muttering "bloody aero ... machined bloody brkt ... geezz !"
 
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Aerospace guy-
I agree with your sentiment about the machined bracket and the bloody aerospace guy.
We dont generally machine structural steel connections [afro2]
 
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a "machining" could be a solid block, welded all round ... not elegant but quick and simple
 
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What stops that bottom flange from buckling?

Also how does the force transfer to the bottom flange?

Have you considered the torsion that is induced in the cross beam?
 
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Flange buckling? The flange is stiffened by the beam web.

Torsion? The net force is zero. Equal and opposite flange forces.

Why does the force need to be in the bottom flange of the W14? The moment force is based on the W8 and is basically resisted by the same size cross section on the back side. The moment capacity of the W14 is not needed.


I thought of another option on the detail. The W8 could have an endplate connection continuing below the bottom flange. The 4 bolt connection can be shared through the girder web. The bottom flange could be fillet welded to the end plate. This would eliminate one of the field CJP welds.

 
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Can the W8 be attached to the W10 (if cantilever not too big) and the W14 connect via bolts?
 
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@connectegr

I'll preface this by saying that I don't do a lot of structural steel framing. Is it common to bolt 3 members together with one set of bolts like your R2 drawing? It seems like alignment might be difficult. Although in this case the W8 is probably light enough to manhandle into place.
 
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The structural steel preference is shop welding and field bolting. Bolted connections with shared bolts is typical in structural steel. For erection safety, we try to have at least one row of un-shared bolts, especially in large connections. Quite often axial load is passed through the shared bolt connection, at column web connections.

Often we will provide horizontal short slots in the outstanding legs of connection angles. This is so the GOL (gage of angle) can be standardized and does not have to change for every beam web thickness. But this does not apply to endplate connections.

 
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Ipetu
Structurally I think your detail is OK. It is not necessary to remove the bottom flange of the W8 to add the extension. Then the extension can be fillet welded to the W8 flange. Also the extension does not need to be tapered, the "web" portion should be checked for bending and the welds designed for eccentricity. It could be a WT piece cut from the remainder of the other WT. It might be a little more expensive, with the added material for height and the 4 CJP field welds.

 
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connectegr

I thought the OSHA requirements were for all connections where bolts were shared (columns or girders). The beams must be held in their final position by either a seat or you must stagger the bolts. Resting the beam on the bottom flange would not count unless the web of the connecting beam was detailed to rest on the bottom flange (no space between the bottom flange and the web once the final connection is made).
 
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I have not seen an OSHA requirement for beam to girder connections. The primary intent is not as an erection aid, but rather as a safety issue. If during erection a beam to column web connection falls during alignment of shared holes, the beam will fall to the floor below (pretty dangerous). But if a beam to girder connection, with share connection to the web, falls the beam web falls to the girder flange.

Also the erection conditions vary for these connections. Often an iron worker supports himself on a free standing column while aligning the connections of both beams into the column web. But once the girders are erected the iron worker can sit on the girder while aligning beams into the web. This is all amazing stuff to watch. Especially the Indians in New York working at amazing heights.

I have had erectors ask for additional erection assistance, such as staggered connections or erection seats.

 
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