Load Application

[Anonymous]

Hello everyone,

I need to run a linear static analysis. I have a steel frame, which is supported by 4 supports like a table, and on top of the frame there is a wooden plate (8 mm thick). I have to check if the frame and the support can withstand a load of 10 tons. The frame is quite large (7.5 m x 2.5 m). Please refer the Images.My question is, if I choose the top of the plate to apply the load, the load will be concentrated in the middle of the plate, resulting in a large deformation in the middle, but this is not really the case, there must be lots of heavy stuffs placed on the top of the plate distrributed all aover the plate. Is there any option so that I can distribute the load all over the plate or it by default concentrate the load at the center or is ther any other solution.

Thank you

Anurag

[John_Holtz · Accepted solution]

Hi @Anonymous 

Why do you say that applying a load to the top of the plate concentrates it in the middle of the plate? Have you run the analysis?

Inventor Nastran does not work that way. The load (whether a force or a pressure) is distributed over the selected geometry. If you apply a force to a face, it behaves like a pressure (=force/area of face). If you apply a force to an edge, it behaves like a distributed load (=force/length of edge).

You may be confusing the arrow (glyph) that is shown to indicate "where" the load is applied. Those arrows are just a symbol, but an arrow by itself does not indicate the extent of where the load is applied. You can change the number of arrows shown by changing the "Density" on the load dialog. That only changes the number of symbols, not where the load is applied.

[delaroca]

@John_Holtz  I have a question regarding that.
Let's say I have a hydraulic press and I want to compress a cylinder (no buckling).
If I only model the cylinder and apply the force on top (with the base fixed), it behaves as a distributed load and it forms a "parabolic" deformation on the top face.
This seems weird to me because (in the case of the press) it's not like there's a water column on top of the object, deforming and applying the same load as the object deforms.
If the middle starts to deform, it would lose contact with the press. So the press would apply a higher load on the edges, deforming them more, keeping things more as a plane than a paraboloid.
I'm not sure if this is true, but it makes sense to me.

So, how would I define a force as a "rigid plane" to compress the cylinder?
My solution would be to model another object with rigid properties (~infinite young's modulus, ~infinite yield strength) to act as the press and apply the load on top of it. But it's kinda clumsy, would there be a better solution? 

I'm yet to do some tests to see what works best.

[John_Holtz]

Hi @delaroca 

I believe your description is something like this, where the cylinder could be either a hollow tube or a solid cylinder. (The setup is the same, so that detail does not matter.)

This is a contact problem: the area of contact between the press and the cylinder changes depending on the load, so you are correct that you would need to model the press. A better load would be to apply an enforced motion because that is more statically stable, and one result of the analysis is what force is required to move the specified distance. But in theory you can also apply a force load.

Due to symmetry, I would model the 1/4 section shown by the dashed outline.