Big displacements

[sribeiro]

Dear STKO team,

In the pushover analysis I'm trying to carry out, I'm getting displacements of the structure that are too big.
In this analysis, I want to know the displacement for the maximum peak and for 80% of the post-peak reaction.

The structure is a RC bridge with simply supported beams, with bearings between the pillars and the deck.

I've already applied some suggestions given here on the forum but so far I haven't managed to get the desired result.

I'm leaving the model here in the hope that you can help me with this problem.

Thank you in advance

Best,
S

[STKO Team]

The steel strain the the 2 central piers are very high.
Try to go into the Hysteretic material and use an almost-zero value for the last stress point (1.0e-3 for example) at a strain of 0.1.

In this way, I obtain a load drop at 1 mt top disp.

And, if you want to view the stress in the piers, which have section aggregator, you need a custom result in the MPCO Recorder like:
section.section.fiber.strain
section.section.fiber.stress

[sribeiro]

The steel strain the the 2 central piers are very high.
Try to go into the Hysteretic material and use an almost-zero value for the last stress point (1.0e-3 for example) at a strain of 0.1.

In this way, I obtain a load drop at 1 mt top disp.

And, if you want to view the stress in the piers, which have section aggregator, you need a custom result in the MPCO Recorder like:
section.section.fiber.strain
section.section.fiber.stress

Many thanks for your reply!
I've tested it and the curve stops finally.

However, I was "playing" with the structure, making it more fragil by reducing the bearing properties. And I got the same pushover values for the bearing intact, with bearing values at 50%, 25% and 5%. I was expecting bigger differences between those scenarios and I got the same results.

Do you know by any chance what could be wrong?

[sribeiro]

I just noticed that in the model I have the Uy direction "not activated". But I changed it and did the analysis again, and still same situation, no big differences between the bearing at 100% capacity or 5%.

[kesavapraba]

Hi, I would suggest you to check the isolators material properties also. You can check the deformed shaped of the structure at both the capacity levels that you mentioned. In this way you can track down the origin of the issues.

[sribeiro]

Hi, I would suggest you to check the isolators material properties also. You can check the deformed shaped of the structure at both the capacity levels that you mentioned. In this way you can track down the origin of the issues.

Hello,
thanks for your advice!
However, after doing it, I concluded that I didn't manage a way to make the bearings do their job, somehow. Because I have columns movement, deck movement but the bearing stays vertical and follows their movement. At least, that's my Interpretation of it..

Does anybody know how to fix it?

[kesavapraba]

Ok, I appreciate your effort on understanding the defomed shaped and debugging the issue. Now, we have to look at the bearings' material model and the interaction assignment for them. Can you please share the revised model?

[sribeiro]

Ok, I appreciate your effort on understanding the defomed shaped and debugging the issue. Now, we have to look at the bearings' material model and the interaction assignment for them. Can you please share the revised model?

Sure, please find the model attached.
Yesterday I was also trying to use a different bearing input (with ElastomericX element) but couldn't make it work.

[kesavapraba]

Hi, I found following issues in your model.

1] For the isolater "isolator TL TR" : zero length materials are assgined along dir1, dir3, dir5, which means that the remaining DOFs 2, 4, and 6 must be assigned with EDOF constraints. However, the EDOF definition for the interaction considers only 4 and 6 DOF, missing 2 DOF. Please add a separate EDOF constraint to it (apart from inside isolators) and don't forget to add it to the mp constraints list in analysis section.

2] Referring to the webinar that you mentioned (link below): You mixed up with the material assignment, for example, the material definition for Y-dir rotation is assgined to DOF-1 (X-dir translation), which is actually a translation DOF! So, please pay attention to the proper zero length material assignment.

I've included an updated model here. Please review it and experiment to customize it according to your needs.

https://www.youtube.com/live/rp4N2icP1y ... j-qIT6xgKU

[sribeiro]

Thank your for your help!

I see now some changes on the analysis when I do modifications on the bearing's properties.