LRB base isolated structure problem "fbd_inv..."

[wangyanan]

Problem of LRB base isolated structure Incremental dynamic analysis
(1),fbd_inv
(2),fbd_ite
(3),(1)and(2)result in analysis interminate

[huffte]

A forum search on any of the following will get you plenty of hits to begin solving your problem:

fbd_inv
fbd_ite
convergence problem

Best of luck wangyanan.

[Fiona Dong]

Hi, huffte.I have search 'fbd_inv' on forum and the help. It means stiffiness matrix can not be inverted. My problem is that the same model can be analyzed under 0.4g while not under 0.62g. Is there something wrong with my model?

[huffte]

Hi Fiona Dong. Glad your making progress with the isolated structure analysis.

It really does simply sound as though the limiting load on the structure is somewhere between the 0.40g and 0.64g values. Do you have strain criteria that you are tracking? Can you estimate at what load level those criteria are exceeded.

Particularly, since the model runs fine at 0.40g, which is a significant loading, I tend to believe that there may be no modeling problem at all. Of course, you will have to judge that for yourself.

If you wish, I could take a look at the model. But it will be several days before I am able to do so as I am on travel several days over the next 2 weeks.

I would encourage you to run a dynamic time history analysis without the IDA to more closely examine the state of the structure at the 0.40g level. Perhaps you will find that it is well beyond yield at this loading and near collapse at something less than 0.64g.

Best of luck with your interesting work Fiona Dong.