membrane stress 3

I am looking for software that considers membranes (for example aluminum 48"x .02"x 120&quot with concentrated loads. Presently using RISA-3D but can not sucessfully convert plates into membranes. Roark is no help with membranes and concentrated loads

 

[hadi_imported]

You may try AFEMS from FEM Engineering. They have it under CATIA.

http://www.femengineering.com

 

[SWang]

One simple way is to use Flat Plate Yield Line method for rectangle plates. This method applies virtual-work solution to solve the rotation and subsequently the moment at the edge.

 

SWang.....thank you for your reply. Can you provide a reference text for the Flat Plate Yield Line method.
wlw32

 

[Gourile]

wlw32
This method is widely used by metalurgical engineers, and less by structural engineers. See for example, Reinforced Concrete Design by Wang & Salmon, under a chapter dedicated to yield line theory for reinforced concrete slabs. The analysis is based on statics equilibrium (or as Swang stayted by means of virtual work) of the membrane after yielding occurs on certain lines that turns the problem to an statically determinate structure. The method can be applied for any membrane slab of any kind of material. You might be interested if you know that Rusians applied this method by doing tests on ice slabs

 

[Scranton]

I am looking into the same situation - concentrated loads on membranes (stainless steel, 1000mm x 2000mm x 1.5mm).

I'm looking for approximate solutions at this stadge, so does Wang & Salmon's text provide some approx. formulae for different cases of conc. loading?

Or would one have no choice but to consult FEA for this?

 

[Scranton]

Forgot to mention that I'm considering either simply-supported or clamed edges for the membrane.

Thanks.

 

[emil]

This is not so simple problem. RISA3D cannot be used in this case. For simple geometry, such as rectangle there are closed form solutions. Or, you can try some general purpose FE package. You have to use geometrical non-linearity to get reliable results. Linear static is not appropriate. Also, Yield-Line is not appropriate. Let me know if you need any extra help.

 

[Scranton]

Hi emil,

The thing is that like wlw32 I'm looking at concentrated loads or loads applied in small circular/rectangular regions on the middle of the steel membrane.

These loads produce large deflections. So far I've been at a loss in trying to track down theoretical sources that can provide some sort of approximate formulae (upto 10% error is OK) for this case study.

FEA is a last resort really (I have very limited access to a decent package at the moment), so any extra help in finding mechanical solutions would be much appreciated.

 

[prex]

You may give a try at the site below, under Plates->Membranes->Circular...
Only circular membranes at the moment: hope this is OK for your needs.
Please note that the solution for membranes is strongly non linear: no superposition applicable!
Scranton: clamped membranes, if you mean by that with no edge rotation, makes no sense for membranes. If you mean held end (no radial displacement at support) then it's OK.
prex
motori@xcalcsREMOVE.com

http://www.xcalcs.com

Online tools for structural design

 

[emil]

I did two similar project like this before. It was a lift shaft covered by thin metal sheet. The load was a pressure on a small area, simulating a worker with tools. I performed a non-liner static finite element analysis, which worked very well. You may contact me directly on emil@inducta.com.au, if you need any more details.

 

[abhio]

There are commercial FEA softwares that combine plate bending and "shell" type membrane stiffness, for example the plate/shell element NKTP 20 in NISA.