Weld Moduli 3

[LeonhardEuler]

A C shaped weld has a different section modulus for the “top” and the “bottom”. Is this based on the part of the weld that is tension meaning that if the member were bending in such a way as to pull the top of the weld off the parent metal the “top” section modulus would be used and vice versa if the “legs” were in tension being pulled off the parent metal

 

[JAE]

The "C" shape of the weld has a neutral axis that is not centered on the overall shape depth.

Therefore, the stress on top will generally be different than the stress on the bottom (depending on the combination of axial and bending on the section).

St = I/yt and Sb = I/yb. yt is not equal to yb - so St is not equal to Sb.

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[Celt83]

all non-symmetric shapes having different section properties about the axis of non-symmetry. In the "C" case the horizontal weld line "stiffens" the the top of the shape moving the neutral axis closer to that side. When looking at the bending stresses(tension or compression)about the x-axis = Mx/S,top or bottom the tip of the side legs will have the highest stress (furthest from the neutral axis) and will vary such that the "C" above the neutral axis will be entirely in compression or tension depending on the direction of the moment.

Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[JStephen]

The question that seems to be implied up there is that for the side where the pieces are being pushed together, do you still need to size the weld for the force? And I have assumed "yes".

 

[Celt83]

Assuming Linear Elastic Behavior:

Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[LeonhardEuler]

What I’m hearing is of the bottom of the weld is in compression it still needs to be checked with M/Sbottom, but perhaps there are different allowable for compressive strength of weld than for tensile, or there would not be a point in ever checking Stop

 

[Agent666]

If bottom is in tension or compression you check that location with S_bottom.

One reason you might check S_top is if you used a different weld size/strength along the 'top' or if you are simply interested in the stresses at that particular location. Your equations however are only valid for one weld size throughout.

 

[LeonhardEuler]

Got ya! For a C shaped weld with the same effective throat throughout use the smallest of Stop and Sbottom, which should always be Sbottom

 

[LeonhardEuler]

Are there not different allowables for a weld in compression than a weld in tension? For tension we use 0.6*70/F.S. I assume the equation is same for a weld in compression

 

[Agent666]

Yes weld strength is not related to the load direction.

 

[JAE]

Your weld is always in shear. There is no tension or compression here.

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[LeonhardEuler]

Thanks everyone for the wisdom!