For the attached configuration, I am looking at 2 options to support a girder at a WF beam location. Vertical cover plates will be added between the flanges to make a more torsionally resistant box section. The question I have is, does the magnitude of the torsion vary depending on if a top mount hanger is used vs. a bearing seat bracket welded to the web? In the attached drawing, the distance from the centroid of the beam to the centroid of girder bearing is the same leading me to believe the magnitude of torsion is equal. However, I "think" there may be more torsion when the load is hung from the top flange. Can't quantify this in my head though if there is in fact a difference.
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WF Torsion Question 1
- Thread starter BadgerPE
- Start date
Whether or not you have real torsion on the supporting beam depends on the stiffness of the connection. So the connection which takes the force into the web is much better, provided the connection to the supported member is capable of taking the bending.
msquared48
Structural
Depending on the shear load of the LVL to the W shape, I would notch the top of the beam and weld a "U" shaped bracket with an extended bearing seat and side plates to the bottom of the wide flange beam, inserting the remaining portion of the LVL into this bracket and butting the end to the flanges of the W shape. This should reduce the torsional effect on the wide flange. I would also add a additional plate connectors from the top flange of the beam to the LVL to further mitigate some of the induced torsion.
Mike McCann, PE, SE (WA)
Mike McCann, PE, SE (WA)
In the un-deformed state, I agree, the torsion would be equal. Like you, however, I have a visceral preference for the second option. For me, I think that's because that detail looks more convincing for turning torsion in the wide flange into bending in the girder (related to hokie's comments). I would keep two additional things in mind with this:
1) Welding side plates onto your wide flange beam to make an HSS will cost a bundle. You're much better off detailing the torsion away as other here have suggested.
2) Remember that, whatever you do to improve the torsional capacity of your wide flange, the solution will only be as good as the connections at the ends of your beam. Standard beam connections are generally not appropriate for torsion.
In the past, I've used top flange hangers as you have in combination with a strap tying the bottom flange of the steel beam to the side of the girder. Again, this just turns wide flange torsion into girder bending. Of course, if your application is exposed, that's not likely to fly and you should consider something sexier like Mike's proposal.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
1) Welding side plates onto your wide flange beam to make an HSS will cost a bundle. You're much better off detailing the torsion away as other here have suggested.
2) Remember that, whatever you do to improve the torsional capacity of your wide flange, the solution will only be as good as the connections at the ends of your beam. Standard beam connections are generally not appropriate for torsion.
In the past, I've used top flange hangers as you have in combination with a strap tying the bottom flange of the steel beam to the side of the girder. Again, this just turns wide flange torsion into girder bending. Of course, if your application is exposed, that's not likely to fly and you should consider something sexier like Mike's proposal.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
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msquared48
Structural
Let's not get torqued here, guys.
Mike McCann, PE, SE (WA)
Mike McCann, PE, SE (WA)
If your attachment can induce torsion, be aware that normal (end) connections will likely not suffice. You have talked about (what sounds like) modifying an existing beam along the length. It is likely that simple shear connections are present at the ends, and you typically need some type of flange restrained connection (i.e. moment) to transfer a significant amount of torque.
FootNMouth
Structural
Can you not add a kicker to the opposite side of the wide flange? This is typically how we take out torsion in spandrels due to eccentric cladding loads.
slickdeals
Structural
I think he's suggesting that the torsional span is cut down.
There's some good information here, which formed the basis of AISC Design Guide 22
There's some good information here, which formed the basis of AISC Design Guide 22
Yes slick, I see that, but that requires another beam to which the "kicker" can be attached. There is no evidence of another beam in the present case.
The simplest way to remove torsion in this case is to rotationally fix the WF to the end of the LVL girder, or effectively ensure the LVL spans to the center of the WF.
BA
The simplest way to remove torsion in this case is to rotationally fix the WF to the end of the LVL girder, or effectively ensure the LVL spans to the center of the WF.
BA
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