lrb based isolation modelling unexpected displacement

04-Unexpected behaviour/errors
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ramazanoruc
Posts: 2
Joined: 18 Dec 2018, 14:19

lrb based isolation modelling unexpected displacement

Post by ramazanoruc » 18 Dec 2018, 14:35

Hello everybody,
I modeled a reinforced concrete frame system whose support system is lrb base isolation. As a result of dynamic analyze, the behavior of the superstructure was unexpected. (i mean the displacement difference between node 631 and node 031 was 20 cm.). Can someone help me to solve this problem? The file is attached as a google drive link.

https://drive.google.com/open?id=1MnXlu ... F1LxaQ9zNu

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seismosoft
Posts: 567
Joined: 06 Jul 2007, 04:55

Re: lrb based isolation modelling unexpected displacement

Post by seismosoft » 18 Dec 2018, 15:21

What do you mean unexpected? Unexpected because of the large deformations?
With such a large record (more than 0.4g) and with a base isolated structure 20cm is not a very large drift.
Note also that your gravity loads (and hence your inertia forces) seem to be relatively large, almost 6000kN in 5 columns.
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huffte
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Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: lrb based isolation modelling unexpected displacement

Post by huffte » 18 Dec 2018, 23:00

I agree with the comments from SeismoSoft, ramazanoruc. I would also add that the post-yield stiffness ratio of your isolation devices is extremely high (0.654). Typical LRB isolators have post-yield stiffness around 0.100. If you are modeling a particular LRB with high post-yield stiffness, then the effectiveness may be hindered by such. If you are modeling typical isolators, I would recommend re-checking your post-yield stiffness calculations to verify their correctness or reduce if an error is found.
Tim Huff

ramazanoruc
Posts: 2
Joined: 18 Dec 2018, 14:19

Re: lrb based isolation modelling unexpected displacement

Post by ramazanoruc » 26 Dec 2018, 07:24

Thank you for all replies. I fixed it as you said.

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