analysis of submerged flat plate
analysis of submerged flat plate
(OP)
I'm looking for a little help in determining the proper bending equation to use in the analysis of 1/2" plate welded out around it's perimeter to a structural frame. The frame is submerged and is used to isolate a gate on a hydroelectric dam for maintenance. I was able to analyze the structural members, but what about the plate? Fixed-fixed ends using the longest dimension for (l) is way too conservative.






RE: analysis of submerged flat plate
do you have sitffeners breaking up the plate ?
is the load carried by bearing of the plate onto the frame, or by tension in the welds (i think it's obvious which way is better) ?
is the plate welded to the frame along a single line weld, or multiple welds ? ... i picture that the frame (possibly a sq tube structure) bears against the plate so that the frame could be welded to the plate along more than one line.
RE: analysis of submerged flat plate
RE: analysis of submerged flat plate
RE: analysis of submerged flat plate
i think you're better off using the plate to distribute the pressure onto your stiffeners (1' pitch ?) ... then the stiffeners are "just" beams with a UDL (144lb/in), and maybe fixed ends ... the shear connection to the frame looks like somethig to watch (3500 lbs).
RE: analysis of submerged flat plate
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RE: analysis of submerged flat plate
RE: analysis of submerged flat plate
I agree, why would there be a hinged condition all sides? They covered everything else.
I thought there must be a fair amount of work done on this problem. I have run into this before and never felt quite comfortable with my method. My only solution was to "detatch" the plate on the long side and analyze it as a beam. Way too conservative! Thanks again.
RE: analysis of submerged flat plate
RE: analysis of submerged flat plate
Roark refernces the legendry Timoshenko, "plates and shells" if you need further info.
RE: analysis of submerged flat plate
On my earlier post I was asking for assistance with the units used in the publication referenced by miecz earlier. I downloaded the publication from the Dept. of Interior and would like to use it, but I'm not sure if I am using the correct units for UDL on a plate fixed on all sides.
I can analyze the backing stiffeners correctly, it's just the plate I'm having trouble with.
I am going to dig into "Design of Weldements" by Omar today as well.
Thanks to all.
RE: analysis of submerged flat plate
RE: analysis of submerged flat plate
The plate is fully welded out around its perimeter (to seal out the water). I only mentioned "detatching" two sides because it is the only way I know to analyze bending in the plate, but this method is far too conservative. In design I would consider the end fixture on all sides of the plate to be fixed which lends the calculation to both the Roark's formula and to the tables referenced in the Dept. of Interior bulletin.
Thanks for the help. I am not trying to frustrate anyone. I think I'm just a little lean on reference material in this situation, that's all.
RE: analysis of submerged flat plate
RE: analysis of submerged flat plate
I wouldn't rely on Roarke's tables for flat plates. See thread507-205764: Roarke's Tables for Flat Plates.
RE: analysis of submerged flat plate
RE: analysis of submerged flat plate
RE: analysis of submerged flat plate
RE: analysis of submerged flat plate
The coefficients in the tables are unitless. So, if you had a 48" x 64" plate with fixed ends all around, the maximum moment is found at x/a=0 and y/b=0.5. The coefficient for a/b=3/4 in Figure 34 is 0.0686. The moment for 12 psi is 1.90 k'/ft and the stress is 45.5 ksi. For your plate, you'd have to do some interpolation.
RE: analysis of submerged flat plate
if you want to optimise the weight of the structure, reduce the thickness of the plate, and add more stiffeners (as the stiffeners are more effective in reacting the moment from the pressure.
RE: analysis of submerged flat plate
RE: analysis of submerged flat plate
I just want to make sure I am applying the correct formulas for the analysis of a plate under a UDL with its edges supported or even fixed. I know the DL is actually decreasing with the decrease in submerged depth, which I will account for in higher sections of the panel I am designing.
Thanks.
RE: analysis of submerged flat plate
By 1.90 k'/ft, I meant 1.90 kip-ft per foot. (It could also have been 1.90 kip-inch per inch.) That is, there is 1.90 k-ft of bending moment for each foot of support length. For 1.90 k'/ft, when you calculate your section modulus, "b" is one foot. For 1.90 k-in/in, "b" would be one inch.
RE: analysis of submerged flat plate
a = length in in, or mm
resulting in moment in lbs*in or N*mm
consistent units yield intelligent results !
if you're trying to minimise weight and build costs and all those good things, sharpen your pencil and use the tapered pressure distribution.
RE: analysis of submerged flat plate
RE: analysis of submerged flat plate