topic Re: Base isolation system in Robot Structural Analysis Forum

Base isolation system

Anonymous — Sun, 13 Aug 2017 16:43:30 GMT

Hello,

i tried to introduce a base isolation system on a underground +30 f (between the infrastructure and the superstructure) i introduced a new material elastomer and made a column with 50 by 50 section, i elevated the hole superstructure (separated infrastructure from superstructure by 50 cm) and introduced the new column, i obtained displacement way too big, not even close to the original displacements like 2 m from 16 cm (they should be lower than before). I think my mode of introduction of the base isolation system is wrong or the elastomer properties I introduced are wrong, i introduced a new material as other but i could not find it so i reintroduced it as concrete with elastomer properties.

i hope you can tell me if there is in robot database a rubber like material already defined or maybe you have the full properties of an elastomer like material.

also if my method of introduction of base isolation method is wrong .

Thank you

Re: Base isolation system

Rafacascudo — Sun, 13 Aug 2017 17:54:39 GMT

Can you provide a sketch ?

Re: Base isolation system

Anonymous — Sun, 13 Aug 2017 18:24:58 GMT

Re: Base isolation system

Rafacascudo — Sun, 13 Aug 2017 23:07:56 GMT

I meant , a sketch of the real structure

Re: Base isolation system

Anonymous — Mon, 14 Aug 2017 03:04:58 GMT

here it is

https://ufile.io/lhao0

Re: Base isolation system

Rafacascudo — Mon, 14 Aug 2017 11:34:22 GMT

I meant real life strucuture. But anyway. I normally use this approach here

https://forums.autodesk.com/t5/robot-structural-analysis-forum/girder-to-column-connection-with-bearings-in-bridge/m-p/7244432#M55699

when I have elastomeric bearings

Re: Base isolation system

Anonymous — Tue, 15 Aug 2017 15:48:57 GMT

can you make a simple 2d or 3d structure how it should be i do not really understand the thing with rigid link

this is my test

https://ufile.io/c9u14

Re: Base isolation system

Rafacascudo — Tue, 15 Aug 2017 22:09:56 GMT

You probably don´t need to use rigid links , but that´s why I asked for real life sketch of your structure.

But in the 1st model you sent , turn the "elastomer" bars into very rigid bars with the elastic release on the upper node side of the bar. Something like this

Re: Base isolation system

Anonymous — Sat, 19 Aug 2017 10:55:04 GMT

thank you but i still have some problems

i know that the period of vibration should increase and also the total displacement of the building should also increase but the results i obtained with the introduced elastomer are huge I i jump the period from 5.41 sec to 30 sec and deformations from 20 cm to 2 m(more or less)

and i also tried all kind of combination with elastic releases and the stiff material....

Re: Base isolation system

Rafacascudo — Sat, 19 Aug 2017 18:41:25 GMT

hard to say anything without the model

Re: Base isolation system

Anonymous — Sat, 19 Aug 2017 18:46:19 GMT

i did uploaded my model (2-nd-3rd post) ... and there is no real structure is just an empirical structure

Re: Base isolation system

Rafacascudo — Mon, 21 Aug 2017 00:43:59 GMT

It´s a large building model(elastom file) with elastomer bar ,50cm long with a material with E=4.5 MPa . And these jelly bars are supposed to support the whole building. I never saw a 30 stories building supported this way. But there´s no quakes here in Brazil , so I have never done a single seismic analysis in my life , and then , of course I can be very wrong.

The two 1st modes with large periods are in main directions X and Y and are sure related to those extremelly soft supports.

Probably official support or others users with more practice with seimic analysis can give a better opinion .

Sorry

Re: Base isolation system

Anonymous — Mon, 21 Aug 2017 03:59:04 GMT

i already modified the model as you told me ( base 2x2 m ) and elastic releases i also added an extra column in the middle of the walls

anyway when i run the analysis i have some isolated nodes. Can these nodes show me bigger displacement then the structure?

Re: Base isolation system

Artur.Kosakowski — Mon, 21 Aug 2017 06:39:37 GMT

Hi @Anonymous

anyway when i run the analysis i have some isolated nodes. Can these nodes show me bigger displacement then the structure?

No, as they are detached from the structure there will 'not' move however you should check if there is any load or support defined in them. If yes, then it means that they should be connected with the model and you need to correct this situation. Otherwise you can either ignore them or delete them.