Shear Flow 15

[Stillerz]

I am sure most here are familiar with the concept of shear flow as it related to horizontal shear stresses in beams.
When designing a I-Shaped plate girder, most references, if not all, will design the weld between the flange and web using the shear formula VQ/I to determine the force on the welds.
My question is, isn't there bending stress on the weld as well in the form of MC/I?
If one had a simply support girder with a uniformly distributed load, the shear at the center of the beam would be = zero and the moment at a maximum. This would imply that no weld would be needed at the center, yet this is the section where having the entire cross-section engaged in bending is most critical.
What am I missing here?

 

[miecz]

BA-

You're right, for the case that you describe, the beams would behave the same.

 

[KootK]

BA: I agree with your comparison using the cantilevered beam example. It is a perfect example for this particular discussion.

The cantilevered, partially welded system is the closest thing to a practical situation in which the end moments would be applied as I have suggested above (applied linear varying stress instead of a force couple). This is why, in this scenario only, the non-composite beam segment is as effective (I, Mr) as a composite beam.

Miecz: if you modeled the beam using force couples to simulate the moments at the beam ends, your FEM model is likely giving you answers that are not consistent with the assumptions of our discussion. The only way to model the situation purely is to apply the end moments as linearly varying stresses.

 

[beton1]

Merry Christmas and Happy Shear Flow!

 

[cntw1953]

The beam assembly with double cantilever ends analogy concludes this discussion perfectly. Thanks to all involved. Merry X'mas & Happy New Year.