Patch load on stiffened panel ?

[XaeroR35]

I need help analyzing a load scenario. I have a stiffened panel with fixed and pinned edges. There are fairly sturdy stiffeners equally spaced below the panel.

There is a uniform patch load (pressure) that can be applied at any point around the panel. I need to determine the resulting stress in the plate. I have tried to apply Roark’s formulas to this situation, but I don’t think they can directly apply. FEA analysis gives me much different results than using Roark’s formulas.

I am showing two scenarios in the picture below.

A: Load direction over a single stiffener.
B: Load spanning two stiffeners.

Any help would be appreciated.

 

[nvn]

XaeroR35: I suppose Roark formulas are for something completely different from this scenario. Therefore, they would not be expected to be applicable nor give the same answer. There is not always a hand-calculation formula for nontrivial plate problems (unless you want to be conservative and basically ignore plate action). Do you not trust your FEA? It seems it would probably be close to the correct answer.

 

[XaeroR35]

Yes, I trust FEA. I just need to know if there is a way to do this calculation by hand.