analyze as thin shell, plate or membrane

huangyhg

analyze as thin shell, plate or membrane
i have a 0.06 inch thick plate 44 inch x 24 inch. it is supported at perimeter with hss 2x2. i have to check how much udl this plate can take. i am using older version of sap. shall i assign it as thin shell, plate or membrane or shall i analyze it manually as a thin strip (beam)
it is too thin to act in bending, so you only have tension to depend on.  i suppose you would call it a membrane.  will be like a 2 way catenary.  you also have to check the perimeter   
roark would have the solution as well.
as a membrane, i'd avoid any linear fem, due to large displacements.  alternatively, model the flat panel as a spherical surface. it's easy to see deformed shape for the included circle (the circle tangent to the side) ... tricky to picture the shape near the corners (outside of the circle) ... but you can fudge something.
alternatively, as you say, you can analyze the central strips ... i expect this'll be conservative since there is some support at the sides that you're aren't accounting for.
best is a non-linear fem ... all depends on how accurate you want to be.
the plate is too thin to act as anything other than a membrane and it's capacity will be governed by deflection and capacity of the hss perimeter tubing.
dik
good point ... how is the perimeter tuding connected to "the rest of the world" ... discretely (at the corners?), or continuously (unlikely?)?
if discretely, they'll behave as beams loaded obliquely by the membrane loading ( or in two directions (from the applied pressure) and from the membrane tension (the in-plane component).
rb1957
i do not know so let's take worse case and assume connection to perimeter hss random.
sorry, but you got to know ... you're looking at the problem, what's stopping it from flying off into space ?
if the problem is (how do we say) alittle less real ... i'd assume it's supported on the corners, that'd be more conservative than say at 8 points on the perimeter (say the 1/3 and 2/3 points on each side).
rb1957
i have looked at the as-built dwg. looks like it is welded at four corners only.
is this the connection between the sheet and the perimeter tubes, or the tubes and "the rest of the world" ?
the sheet should be welded all around to the hss... if not, then if it is welded only at the corners, then this can also be modelled.  you have to analyze it by fe methods.  also what is keeping the thin sheet from lifting along the 44" length?  the hss tubing should be supported either continuously along opposite sides or possibly at the corners and mid span of the long dimension.
what sort of loading?  a few psi?
dik
rb1957
i have a 0.06 inch thick plate 44 inch x 24 inch. it is supported at perimeter with hss 2x2.there are four wheel at four corners welded to u/s hss