Mat model in STAAD

[PAstructural08]

I have modeled a mat that is 115' x 83' in STAAD. I have modeled this mat using 4 noded plates and have placed spring supports on the plates using the subgrade modulus. I am also you using 'compression only' springs in the 'Y only' direction.

After running the model I have a few load cases that have warnings saying "Tension and compression did not converge after 10 iterations."

Does anyone have any suggestions on how to fix this warning??

On another note...just out of curiosity. I changed the 'compression only' springs to tension springs. And I don not get this warning at all...why is that?? It doesn't make sense to me that tension springs would work because that would suggest to me that the mat would lift up.

Thank you.

 

[JoshPlumSE]

Could the mat be in net overturning for some of your load cases? Try reducing the overturning moment and see if it converges. Then graphically view the reactions to see how close to net overturning your model is.

 

[DTJ]

You have to use REPEAT loads for this analysis in lieu of LOAD COMBINATION. For example if you have a wind only load case then it would not converge since there is no dead load within that case to resist.