Connection of Built-up Steel Beam to HSS Col

[SPruitt]

I am contracted to design a connection for a W14x283 beam to an HSS10x10x3/8 with a reaction of 135 kips factored load (AISC 360-10). There is not enough depth in the W14 to make an adequate connection for this amount of load so I had planned to add on to the bottom of the member with a T-section to allow for additional bolts and to lengthen the weld of the shear tab to the column. If I don't strip the flanges on the beam, I will end up with two shear tabs (one for the beam web and one on the tee). Would I be correct in assuming the center of the connection will be somewhere between the shear tabs? Is it worth the effort to look into this type of connection or would it be better to strip the flanges to use a continuous shear tab? I appreciate your input.

 

[TehMightyEngineer]

Can you make a stiffened seat connection work? I feel that would accomplish your goals in a simpler fashion.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

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[SPruitt]

@TehMightyEngineer I have tried looking at a stiffened seated connection, but have ended up with excessive punching shear in the column. I will see if using an angle seat with a stiffener will work for this connection. Thank you.

 

[KootK]

I like the stiffened seat too. If there's space, suspend the seat from plates welded to the side faces of the HSS. That should resolve any wall punching issues.

Any chance your loads here are specified as a percentage of shear capacity or uniformly loaded flexural capacity? If so, you might be able to whine your way into more manageable loads.

For your original proposal, I'd probably strip the flanges just to satisfy my gut intuition. That said, stripping the flanges costs money and I could see why you'd want to avoid it. Conceptually, I don't see a problem with two separate tabs each designed for their seperate load carrying contribution.

On 10" column you might also be able to:

- Use a double angle connection such that you've got your bolts in double shear.
- Weld a reinforcing plate to the web of the beam to improve bolt capacity there.

A drawback of this is that some field welding would be required on at least one of the double angles.

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.

 

[SPruitt]

@KootK I appreciate your input, but I have too many limiting factors for each of these approaches:
- connections on all sides of the column so I would not be able to add anything to the side faces to stiffen them
- 135 kips load was all I could get them to come down from the original 150 kips.
- when using double angles, the limiting factor was the weld to the column and the only way to increase that is to increase the length of the weld since the thickness of the column limits the weld size.

I will see about the stiffened seat so I can avoid stripping the flanges (tf = 2.07 inches - Yikes!)

 

[MGaMart]

Seems to me that you could accommodate a connection without the use of the T-section reinforcement. Would a double angle (knife) connection (bolted to the web of the W14 and welded to the HSS column) not work? Double angles puts your bolts in double shear, better utilising the capacity of the bolt, the angles help distribute the load away from the center of the HSS chord wall where punching shear becomes a concern, and there should be more than enough weld length to accommodate your reaction load. As aside, I would refrain from adding the T-section when a plate would suffice in providing more bolting space. T-sections should be used when you're trying to increase the flexural capacity of the beam itself (which in this case doesn't seem relevant). Adding the T-section in this case would only complicate the connection detail (as well as increase the fabrication time). If you use the double angle connection method, just be sure to cope one of the flanges so the beam can be easily erected (usually the bottom flange so they can drop the beam into place).

 

[KootK]

- connections on all sides of the column so I would not be able to add anything to the side faces to stiffen them

What kind of connections do you have on the other sides? If it's shear tabs again, you could install the side plates and just attach the shear tabs to the sides of those.

- when using double angles, the limiting factor was the weld to the column and the only way to increase that is to increase the length of the weld since the thickness of the column limits the weld size.

- Flare bevel weld a 3/4" plate to the face of the column. Make the plate and the weld as long as they need to be, longer than the depth of the beam.

- Attach the double angle connection to the 3/4" plate using whatever weld size is required to get the job done.

I'm trying to help, not be argumentative. Do let me know if it feels like the latter rather than the former.

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.

 

[SPruitt]

It seems like I can get a double angle connection to work as long as I strip the flanges on the beam (and use a different design software program). Thank you for all the input.

 

[KootK]

What if you coped the outstanding legs of the angles such that you could run the remaining angle leg past the beam flanges without stripping them? That takes you a little off reservation with regard matching the AISC manual connections of course. But, then, if you've got no tolerance for risk, you're in the wrong business anyhow.

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.

 

[MGaMart]

SPruitt, keep in mind that in order to develop the weld to the capacity of the HSS, an effective weld throat of approximately 1.1 times the HSS wall thickness must be used (for fillet welds). This means you can increase the fillet weld size of your double angle connection up to a maximum of approximately 9/16" before you yield the 3/8"THK HSS. Your angle thickness would need to exceed your weld size in order to accommodate the weld.

 

[SAIL3]

I believe KootK has provided a few viable options....I would prefer the seat option with side plates attached to the side of the col....the location of the seat/side pls could be lowered to avoid any members coming into the side of the col and the seat itself could be built-up to the level of the bm.....
the original concept of using a shear tab on the face of a HSS to support a 135kip load is a questionable concept in my opinion....