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Simple beam with gravity load; displacement does not change when in tension

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Simple beam with gravity load; displacement does not change when in tension

I have a simple beam, fully constrained at both ends, with a gravity load applied (gravity applied in Z). When I change on constraint at on end of the beam to be free in Y, add a force at the end of the beam in Y, and measure displacement, the displacement is the same. If I double the load, the displacement is stil the same.

 

The displament of the beam should decrease with the added tension. Is there something I'm issing or is simulate not working properly?

 

I have attached the file.

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Re: Simple beam with gravity load; displacement does not change when in tension

This sounds like a large-displacement problem.

If I'm understanding correctly, your assumption is that applying tension to a beam should decrease its bending displacement - like a length of string with a weight hung in the middle.

I don't believe that this would be the case in regular, linear FEA because the assumption is that the beam is straight at the point of analysis. In this case, the tension does not have a vertical component, and so does not contribute to supporting the load on the beam.

If you run it as a Large Displacement Analysis (LDA), I think it should work as you expect, because it should re-calculate the stiffness matrix using the deformed shape of the beam. In this case the tension will have a vertical component, and will therefore reduce the bending displacement.

I don't know whether you can run LDA using beam (1D) elements.

2 REPLIES 2

Re: Simple beam with gravity load; displacement does not change when in tension

This sounds like a large-displacement problem.

If I'm understanding correctly, your assumption is that applying tension to a beam should decrease its bending displacement - like a length of string with a weight hung in the middle.

I don't believe that this would be the case in regular, linear FEA because the assumption is that the beam is straight at the point of analysis. In this case, the tension does not have a vertical component, and so does not contribute to supporting the load on the beam.

If you run it as a Large Displacement Analysis (LDA), I think it should work as you expect, because it should re-calculate the stiffness matrix using the deformed shape of the beam. In this case the tension will have a vertical component, and will therefore reduce the bending displacement.

I don't know whether you can run LDA using beam (1D) elements.

Re: Simple beam with gravity load; displacement does not change when in tension

Jonathan,

Yes, your response makes perfect sense. I ran a non-linear analysis with LDA and the results were as I expected; more horizontal tension, less vertical deflection.

Thanks much!

Chris