Combining Welds and Bolts in a built-up beam

[mfritze]

Hello,

For various dimensional reasons I need to create a built-up beam. I have a W16x36 --below it is a W18x40 and the loads are applied to the lower flange of the W18 beam. I have calculated the required fillet weld to handle the transverse shear as calculated from SCM eq 1-1 (pg.1-7 SCM14). I can weld around the flange of the smaller beam to the larger beam. However, I would be concerned about the flanges flexing under loading and causing rotation at the weld root. Therefore I am proposing using the weld to handle the transverse shear and bolts spaced every 14 inches to handle the direct shear and prevent flexing of the flanges about their weld roots.

Bolts alone are not a good options as they have to be SC due to reversing load conditions. I would need a large amount of bolts.

I attached a graphic. What are your thoughts? Is this a sound approach?

Thanks

 

[MotorCity]

If you have frequent load reversals, a bolted connection will have a better fatigue life than the equivalent welded connection. Generally, it is not recommended to mix bolts and welds in the same connection. Even in standard holes, there may be a certain amount of slip required to engage the bolts, albeit a small amount of slip. Welds, unlike bolts, do not slip so the welds would take all of the force up to the point of fracture of the weld or base metal.

 

[mfritze]

I understand motorcity. I thought in this case the bolts will be loaded in tension (ie the lower beam is hanging and transferring 'shear' load to upper beam via bolt tension). The welds will be handling transverse shear and axial load transfer.

 

[MotorCity]

Do you need the beams to act compositely to take advantage of the flexural strength of both sections? I would size the weld to resist the horizontal shear and the hanging load of the lower beam

 

[mike20793]

You could check deflection of the flange if you are worried about it. How much load are you trying to resolve? Is it a new beam to an existing beam or two new beams? Is the loading only at one end, ie does the bottom beam need to be full length?

 

[dik]

I normally use bolts or welds if present, but, not both. Welded connections are much stiffer and tend to take most of the loading.

Dik

 

[KootK]

What are your thoughts? Is this a sound approach?

My thought is that your proposal is a brilliant solution to an issue that has always concerned me. Moreover, since your bolts are not actually going to be carrying any shear, I see no requirement for slip critical.

It appears that only your upper beam will make it to the support. That being the case, you'll need concentrated hanger capacity near the end of the beam in addition to uniform hanger capacity along the length of the beam. Based on all the stiffener voodoo that you're showing in your sketch, I'm guessing that you've already got that covered and I'm preaching to the choir.

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.

 

[KootK]

Another approach, in a similar vein, would be to intermittently stiffen both beams and count on only the welds near to the stiffeners to deal with the direct shear.

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.

 

[JAE]

If this is a moving/repetitive loading - I'd worry that the welds would begin to unzip - even if you used stiffeners.

You can't really use the bolts in slotted holes (in an attempt to not take shear and also further separate the bolts and welds into two different connections, but I'm not sure how practical this would be as you'd need pretensiioned bolts in this tension connection - so no easy slip behavior.



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[KootK]

One nice feature of WT reinforcement is that this issue is self solving.

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.

 

[Settingsun]

Can the bolts be welds instead?

 

[dik]

and maybe use a few only for fit up?

Dik