Flat Plate Bending Weld Stress

[ENG2194]

Hello, I have scenario where a flat plate is welded inside a ridged cylinder with top and bottom fillet welds all the way around and pressure on top. Im trying to figure out how to calculate the bending stress in the fillet welds. I was thinking I could approximate it like the following beam example where "b" is the circumference of the ID of the ridged cylinder. However, even with this approximation I'm struggling to figure out what to use for "M". For clamped flat plate stress calculations the radial bending is calculated in terms of lbf-in/in then divided by plate thickness squared to get in terms of stress. Not sure what bending moment could be approximated as in terms of lbf-in to be able to fit in the beam weld stress equation below.

 

[JStephen]

To fit that specific model, you could use b as the full circumference and M as full circumference x moment/in. Or use b as 1" and M as moment/inch, should be the same.
If it's a code-related question, refer to the code in question for weld requirements.
That model assumes rigid support and flexible beam. If you consider the rotation of the cylinder wall, you would get lower weld stresses. So if you come up with unreasonable weld sizes, it can be refined.

 

[Snickster]

Could you provide a sketch. I think you are saying you have a flat plate installed in a pipe in the center and from one end to the other, such that it splits the top and bottom evenly into two compartments. The upper compartment is pressurized so that it causes bending of the plate and bending and shear in the welds. Is this correct?

 

[ENG2194]

Could you provide a sketch. I think you are saying you have a flat plate installed in a pipe in the center and from one end to the other, such that it splits the top and bottom evenly into two compartments. The upper compartment is pressurized so that it causes bending of the plate and bending and shear in the welds. Is this correct?

Yes that is correct. Im also curious about having only an upper fillet weld. With just an upper fillet weld would "d" just become "h"?

 

[Geoff13]

Not sure I understand the "ridged cylinder". Sketch?

If there's just an upper fillet isn't that a pinned rather than moment connection?

Is the pressure high enough to fall within ASME Section VIII Division 1 and thus you should follow the details and rules in UG-34?

 

[Snickster]

It has been a while since I did weld design but this is how I see it.

With weld on top and bottom I would look it as the plate being a fixed beam with shear V and moment M in the equations shown above determined by the fixed beam formula.

With weld only at top I would consider only shear exists in the weld as determined by a simply supported beam model as the single welds at ends will act as a pinned connection that cannot support a moment as indicated by Geoff. So shear V will only exist and stress will exist only per equation a.