modified Riks method

[dkeatley]

For the modified Riks method, how do you know when general buckling has occurred?

 

[truckcab]

Hi,
the force shows a pronounced dip due to buckling. If you plot an F-disp curve it should be quite easy to idenify the buckling load.

 

[dkeatley]

I have two separate questions.

1. I have read that if two consecutive steps have negative eigenvalues that the first step is buckling; is there any truth to this?

2. My models are 3D what force do I plot?

 

[bassmanjax]

One of the easiest quantities to plot is the Load Proportionality Factor, LPF. You can look for 'kinks' in this curve which represent points at which the structure's stiffness has changed. These are usually buckling points. Check the deformed shape in Viewer aswell to see if the model is partially or fully collapsed.

You get the actual buckling load by multiplying the LPF by the reference load applied in the Riks step.

1. I have read that if two consecutive steps have negative eigenvalues that the first step is buckling; is there any truth to this?

Never read that anywhere, do you have a link to the source?

Negative eigenvalues in a *BUCKLE analysis usually just mean that the direction of the buckling load is opposite to the applied load. In a *STATIC analysis, they can mean that a structure has reached a buckling point.

Regards



Martin Stokes CEng MIMechE

 

[dkeatley]

http://www.google.com/search?hl=en&...he+Validity+of+the+Wagner+Hypothesis+in+Thin-

Page 57

 

[dkeatley]

I meant two consecutive increments.