Autodesk Robot Structural Analysis

[#1]

Hi. I am trying to design a shoring system consisting of diaphragm walls with counterfort walls as stiffeners for a case at hand. I get instability problems and if i don't press escape I receive a dialog saying that the matrix is not positive definitive - critical load may have been exceeded. Could that be due to the location and direction of elastic supports. Or is it because I should be using a different solver. Any ideas or advice.

[#2]

This warning suggests that the load level is excessive (structure becomes unstable under applied load).

[#3]

Hi,

When getting this message I used to check the full note of Analysis->Calcultion report->full note and make sure that all the load cases are convergent. By doing this, despite the matrix message, could we assume that the calculations, forces, displacements etc are correct? Iguess so. Please confirm.

[#4]

No, as the analysis may converge for the different state of equilibrium of the structure. You need to determine where you are with the current load level first.

[#5]

Sorry, could you explain yourself a little bit more. How can we do this you are explaining?

Thanks

[#6]

Try to run linear and  non-linear buckling analysis (with no P-Delta) for the case or combination which reports this issue and check the value the critical coefficient. Try to reduce the load and check if the original load converges with no warnings displayed and then investigate the deformation of the model and compare it with the one you have for the original load.