Bending Moment Applied to Fillet Welds
Bending Moment Applied to Fillet Welds
(OP)
Attached is a sketch that shows a small W-section connected to a larger W-section by fillet welds at the flange tips. The smaller beam is relatively short and transfers a tension load to the larger beam. The welds are the only connections between the beams (i.e. no bolts, end plates, etc.). The flange thickness of the two beams is the same.
I've always avoided using details like this as I feel the fillet welds would not be able to transfer the bending moment at the welds. (The bending capacity across fillet weld throats being very small.)
The only time I could see a detail like this working is if one of the flanges was much thicker than the other and the thinner flange allowed the thicker flange to rotate a small amount (similar to a deep girder and slender columns). In this case the load would predominately be transferred in shear.
Is there any other way of looking at this detail that would give it a higher capacity than I've assumed?
I've always avoided using details like this as I feel the fillet welds would not be able to transfer the bending moment at the welds. (The bending capacity across fillet weld throats being very small.)
The only time I could see a detail like this working is if one of the flanges was much thicker than the other and the thinner flange allowed the thicker flange to rotate a small amount (similar to a deep girder and slender columns). In this case the load would predominately be transferred in shear.
Is there any other way of looking at this detail that would give it a higher capacity than I've assumed?





RE: Bending Moment Applied to Fillet Welds
B.E.
RE: Bending Moment Applied to Fillet Welds
RE: Bending Moment Applied to Fillet Welds
this thread has a very similar question, you might want to browse it through for ideas...
RE: Bending Moment Applied to Fillet Welds
The problem with that detail is that the load causes the flanges to bend as if cantilevers from the webs and semi-fixed and loaded out at the flange tips. There is a prying action at the root of the weld, and it puts the weld roots in tension across the axis of the weld. The very worst possible condition at a location of poor weld quality; lack of fusion, poor/no penetration, they faying surface is a crack starter lined up across the stress field. Maybe put a few bolts through the flanges at high load points, just to clamp the flanges together.
RE: Bending Moment Applied to Fillet Welds
RE: Bending Moment Applied to Fillet Welds
After the above is assumed, this is what I think you can do to figure out the flange bending effect:
1) To check the flange in bending, assume simply supported at the welds.
2) To check the additional stresses in the welds due to the flange bending, assume the flange is fixed at both ends and transfer that end-moment into your weld (using throat thickness for section).
And of course superimpose all other stresses you would normally calculate (shear stress across weld due to section bending.... etc).
RE: Bending Moment Applied to Fillet Welds
RE: Bending Moment Applied to Fillet Welds
RE: Bending Moment Applied to Fillet Welds
RE: Bending Moment Applied to Fillet Welds
Do you see the difference? That the weld has not failed in practice may simply be that it has never been loaded yet to a fatal condition. And, in truth, it may never be loaded that way.
But we can't show that. We can't reliably calculate that.
RE: Bending Moment Applied to Fillet Welds
RE: Bending Moment Applied to Fillet Welds
RE: Bending Moment Applied to Fillet Welds
RE: Bending Moment Applied to Fillet Welds
RE: Bending Moment Applied to Fillet Welds
RE: Bending Moment Applied to Fillet Welds