Beam Thru Beam Moment Connection Between Beams of Different Depths

[ZSCH]

I'm trying to design a beam-thru-beam connection for a cantilevered canopy beam on the front of a building. I'm trying to frame a W4x13 (cantilever beam) and W10 into opposite sides of a W16x31 beam.

I've seen some similar connection detail approaches in a previous thread on here (

https://www.eng-tips.com/viewthread.cfm?qid=270239#post)

but my scenario is a little different with the beam locations relative to each other (due to where the architect wants the canopy and where the 2nd floor level is).

Is there any issue with me using end plates on each of the beams and doing a field bolted connection through the W16 and adding stiffener plates to the web of the W10 to match the flange of the W4 as shown in the attached sketch? In this case, I'm transferring tension forces frot the top flange of the W4 to the added web stiffener vs compression as shown in the above mentioned previous post.

 

[r13]

The tension from the W4 is transmitted to the end plate and the bolts only (similar to hanger support). Make sure the web of the W16 is capable of resisting the tension. The stiffener on W10 is doing very little, if anything.

 

[rb1957]

yes, just as you've continued the W4 cap into the W10 beam (with that plate), I'd add a fitting to the LH to give the load in the upper bolt in the W10 somewhere to go; fttg would be cantilevered on W4 upper flange, and extend LH backing plate to full depth of W10.

another day in paradise, or is paradise one day closer ?

 

[hokie66]

ZSCH,

Your detail is exactly as I would do it. It doesn't take much to resist the moment of a little bitty W4. Your connection may be overkill, but no matter.

r13,

The web of the W16 does not have to resist the force. The end plate on the W10 does that.

rb1957,

The upper bolt in the W10 may be superfluous, but just consider it a bolt in single shear.

 

[human909]

The above suggestions are a good start. You should aim to have the two end plates matching. Having different sized end plates and different bolting means that you are engaging the W16 in a manner that is undesirable. If you match the end plates and the bolting appropriately then you should put minimal force on the W16 except for shear. (Assuming enough stiffness and minimal rotation of the W4 and W10.)

Actually scratch that. I agree with hokie, given the main moment is coming from the smaller beam then what you have done should be sufficent. Though given you now effectively have a moment connection between the web of W16 and W10 you will need to consider the torsion on W16 if there is much deflection in W10.


I did something similar earlier this year where I had a reasonably significant load (20m truss gantry) coming into and landing on a seat eccentric to the supporting beam. The smaller beam is a back span picking up other minor members to resist the significant torsion that would have otherwise been exerted on the 460UB (454mm deep beam) I used gussets liberally and ran a bit of FEA on it for good measure. (The sandwich of plates you can see above the seat is a elastomeric expansion bearing.)

 

[r13]

This is how I see it. Instead of web, I shall have said "the end plate and web assembly".

 

[hokie66]

But r13, the OP also has stiffeners to take the force opposite the top flange. With only a W4, it might work without the stiffeners, but I agree with his approach.

 

[r13]

Yeah, I agree it might be fine. Just pay attention to the stiffness of the plates, individually, or combined. I don't really think the stiffener plate is required though.

 

[skeletron]

Check the W16 web for the compression force as shown by @r13. Then decide if the stiffeners need to stiffen up the web. As lots are suggesting: probably not. It's a big part of the detail cost (about 48" of fillet welding + 2 plates for fit-up).

 

[Blackstar123]

No one has pointed this out yet, but to make the moment connection more effective you should keep the bolts within the width of the flange.

 

[ZSCH]

Thanks for the tips and yes hokie66 that was my thought process as well. I know the top bolts in the end plate of the W10 are not doing anything with the moment transfer, but I thought they could even be used as erection bolts to get the W10 in place before the W4s are installed. Stiffener plate on the W10 for such a small W4 is probably overkill, but it makes me feel better to keep them on there.

Blackstar123, I agree I should shift the bolts more towards the center. Thx.

 

[rb1957]

"I know the top bolts in the end plate of the W10 are not doing anything with the moment transfer" … only because you, the intelligent designer of this, have made it so.

The upper bolt on the W10 can be effective if you give a loadpath … a fttg on the left to transfer moment into the W4.

That said, I guess it doesn't Need to be effective given the joint is limited by the W4, and you can use this bolt as an erection aid.

another day in paradise, or is paradise one day closer ?