Thin Plate Model in STAAD
Thin Plate Model in STAAD
(OP)
I'm trying to check the behavior of a perforated plate. It's 10 ft. by 10 ft. by 1/8 inch thick. I put a 20 psf wind load on it. I ran it on STAAD with each side simply supported in all three directions. I thought it would deflect a few inches and put a lateral load (in the plane of the plate) at the supports, like a catenary.
The analysis results showed 23 inches of deflection and no lateral forces at the supports. (Side note; when you animate it it's like a trampoline!) Is there a way to get STAAD to analyze this more realistically? I know I might have to add some stiffening members, but I'd feel better about it if my first try would come out more as I expect.
The analysis results showed 23 inches of deflection and no lateral forces at the supports. (Side note; when you animate it it's like a trampoline!) Is there a way to get STAAD to analyze this more realistically? I know I might have to add some stiffening members, but I'd feel better about it if my first try would come out more as I expect.






RE: Thin Plate Model in STAAD
I did a quick Roark analysis on a 1/8" thick solid plate (I did neglect diaphragm action) and came up with 22.6" of deflection for the geometry and loading you indicated. I don't know if the deflection makes you feel any better or not as a starting point.
If i get some more time tonight I'll take a another look at it.
Patrick
RE: Thin Plate Model in STAAD
If you want to get membrane tensions to resist the load, this would require a true 2nd order analysis of the plates. I do not know if STAAD has that capability or not.
To validate this line of thinking you might try the following:
Apply 10% of the applied load and record the deflected shape. Change the geometry of the model so that the starting shape is approximately equal to this 10% deflected shape.
Then apply the remaining 90% of the load and see what you get for the deflected shape. The structure should be a lot stiffer and the axial stiffness of the plates should start resisting a good amount of the total applied load.
RE: Thin Plate Model in STAAD
RE: Thin Plate Model in STAAD
RE: Thin Plate Model in STAAD
Like Josh said, this requires a 2nd order analysis. In effect it's a non-linear analysis because the materials behavior changes as the deflection changes.
I don't think that STAAD can do this.
SAP2000 may be able to if you specify a non-linear analysis. I haven't tried it. You may have to use a staged construction analysis to work your way to the final deflected shape per Josh's recommendation. The good thing is that's very simple in SAP.
Josh, can RISA do this (in a single analysis, not a two stage one as you described)?
RE: Thin Plate Model in STAAD
You could contact SAP or GTStrudl to see if they added it without my knowing. If not, then it probably gets more expensive than is worthwhile unless your business plan depends heavily on these types of projects.
RE: Thin Plate Model in STAAD
...our shell element includes two stiffness matrices, one for membrane and one for plate action and they are not coupled. Hence, you can't get any membrane action while loading the shell in out of plane direction.
One modeling approach could be creating a dense grid of cables and between them inserting shells with only membrane stiffness. So the shells do load transfer between cables through their membrane action while cables do catenary action.
RE: Thin Plate Model in STAAD
I was just a little surprised that STAAD didn't consider this in the first place. When a plate is deflecting to the magnitude I got, it seemed that some of the load has to go into tension.
RE: Thin Plate Model in STAAD
Maine EIT, Civil/Structural.