ETABS UNSTABLE WHEN LOAD INCREASED

[Redtelis]

Hi,

I have applied to my model's floors a super dead load of 1.5kN/m2 as a surface load. Analysis run ok without any errors or unstable message.

When I change the superdead load of the roof floor only from 1.5 to 5.0 (rest floors 1.5 as before) then the analysis run log says that the model is unstable-ill.

Any thoughts on this? The way I am doing the change of the load s to select the floor (shell) and go to surface loads and then choose super dead case, set 5.0 and then click replace load.

Any thoughts on why the analysis run log says that the model is unstable?

 

[jayrod12]

Is it possible that the higher loads are causing P-delta instabilities that the lateral system can't resist?

 

[Agent666]

If you run the model with the standard solver selected, then it will give you additional information on the locations of any instabilities. Also using the check model function can expose any geometry or load issues to be fixed.

As a check to see if its p-delta issues like jayrod noted, try increasing the member sizes and see if the errors go away.