Channel to top flange of Beam

[marinaman]

I have a situation where I have a wide flange beam spanning 32’.

The vertical force on the beam is very very small.

But, there is lateral force in the top flange, so to resist that, I’ve added a channel, laying flat, to resist the lateral forces. I didn’t feel good about the lateral deflection of the wide flange subject to out of plane loading.

That said, how would you guys fasten the channel to the beam top flange?

The reason I ask this is that the loads are very small......so I’m left with the question of what would be a minimum needed fastening?

I don’t want to go crazy here and place my welds way too far apart...even though my analysis numbers would say I could.

Would welding at 1/4” fillet welds, 2” per weld, spaced at 24” o.c. And staggered to each side of beam top flange, be a reasonable weld?

The beam is W18x86.....not for stress nor for deflection....but rather, for geometry.....I needed the beam depth and flange width to fit a bolt pattern that’s going to be bolted to the beam.....stresses are very low. Channel is C15 x 33.9.....reasonable channel size for the span and lateral loads. Loading is not going to govern this weld....IMO....I think minimums and engineering judgement are.

What do you guys think?

 

[JAE]

Is there cyclic loading (i.e. fatigue) issues?

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[hokie66]

Why not bolt the two members together at intervals?

 

[marinaman]

Good point hokie66. No reason not to.....just had welding on my mind.

No cyclical loading.

 

[hokie66]

When we use a channel on a wide flange for a crane runway girder, we weld, and JAE's fatigue question is relevant. But for your application, bolting is probably more logical.

 

[KootK]

A criterion for your fastener spacing might be to limit it to a spacing that provides adequate lateral torsional buckling restraint to the channel. Baring that, I'd probably be willing to spread it out to 4' oc or even 1/4 points.

What I'm about to say is so pedantic that I'd not even follow the advice myself. Particularly with welding, the connections will produce a shape that tries to behave compositely for vertical load whether you want that or not. I've some concern that, in the act of trying, some of the fasteners might fail under the associated demand.

Coming full circle, yeah I like your 24" oc. That feels like good judgement to me.

 

[Agent666]

I think if you were bolting, simply providing standard 2mm oversized holes would allow for some minor level of slip between the members to alleviate the entire thing trying to take loads as a composite member vs two stacked members. The channel still has to accommodate the vertical deflection of the girder so will pick up some minor actions from this. Just impose the girder deflection on the channel and whatever minor axes moment comes out of this check in conjunction with all the other design actions. I suspect this will be very small and can be ignored based on exercising some engineering judgement.

Codes also have rules around the spacing (max/min) of intermittent welds, so check your local steel or welding code for this. Usually at the member ends you need some minimum length of continuous welds before you break into the intermittent welds. There will also be rules around the minimum length of each weld and the spacing between the welds.

 

[WARose]

To add to what the others are saying above....you may also want to consider axial load (if there is any; that can make the required "stitch" strength a bit larger if the axial load is significant).....and also the shear from torsion. The situation you describe (i.e. with the lateral load on the top flange) sounds to me like it would produce some torsion.

Speaking of torsion, (and at the risk of getting outside your question).....make sure your end connections can transfer such forces if they do indeed make it to the ends.

 

[Agent666]

I think if the combined channel + top flange is good for the load on its own, then you are good to go and don't specifically need to think much about any torsion except for how the top flange level reactions are dealt with at the ends of the member. Of course you need to take out the top flange load at top flange level to ignore any torsional effects, usually in a crane you have some tie backs for example to the cap channel/top flange level back to adjacent structure.

 

[FLCraneBuilder]

for crane girder or runway girder
we would usually be 1/4" fillets - 3 on 15 if lightly loaded beam, 3/12 for moderate & 3/9 for heavier loaded girders
we would aloes run a long continuous weld at ends - say 16 to 30" - again - load dependent

welding way cheaper than bolting -

Capped crane girders are losing favor because of the space that exists between the beam flange and the channel web- - when wheel riders over the space & closes it up, it works the weld

side plate (1) or wing angles eliminate this

 

[KootK]

I will have to find some hard argument to convince him.

I see it now. Classic Blodgett: don't put your welds in bending.

ide plate (1) or wing angles eliminate this

I wasn't aware that things were headed in this direction. Could you describe these options in more detail or, if convenient, post detail sketches? I think that I get it but would like to be sure.