Modal and Seismic Analysis

[Anonymous]

Hello,

I have two separated steel structures in a same model, they have one story each but different heights, the foundation is shared, I want to:

1. Run the modal analysis

2. Run the spectral analysis

3. Run the concrete spread footing design

It’s necessary run Modal Analysis to run spectral Analysis?

How can I define the stories, if the two separated structures have different heights?

I had defined story one for the small one and story two for the highest one, but I get an error message when I try to run analysis.

Thank you for your help.

[Anonymous]

Maybe I shouldn’t use stories?  

[Artur.Kosakowski]

Yes, it is necessary to run the modal analysis first.

You can either define a single story from the bottom to the top of the structure or delete them. Do you really need to explore the results for stories for the structure type as yours?

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[Anonymous]

Is it possible in Robot analyse and design two separated steel structures in a same model, with different heights and the foundation shared?

If yes can I see two different periods and masse participant different?

Thanks

[Artur.Kosakowski · Accepted solution]

Yes, it can. The modal analysis can be run for separate models. On the other hand you may find it difficult to check if the calculated modes contribute towards having 90% of participating masses for each of the structures. Personally I would:

1. Create two separate models for each of the steel structures. The foundation modeled as nodal supports.

2. Create a third model for the foundation with loads being the reactions from the above ones

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Thanks,
For the third model, is it possible translate automatically the reactions of the others two or I need input by hand?

David (Eu)

[Artur.Kosakowski]

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/Only-reaction-for-new-model-API/m-p/3659242

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Hello Sir! I've been having struggling with seismic analysis of russian code for weeks.. Still couldn't succeed. In order to transfer from using Lira 9.6 (Russian structural analysis software) to RSAP, I need to analyse same model in both Lira and RSAP. So that I can compare the result. Without seismic load, results are almost same. (of course same codes are set in job preferences and DCF). But results of shells are quite different. Results of ROBOT is higher than Results of Lira. Ecpecially on the edge of support. Second problem is: I can't find same Russian seismic code in both software. I've tried some codes. But I got completely different results. Also in Lira software when I use Load to Mass Conversion, there is only X and Y direction, not -X,+X,-Y,+Y... I hope I could explain what my problem is. I really need your help. If someone who knows and uses both Robot and Lira, please make me contact to him. I'd appreciate your help.

[Artur.Kosakowski]

I can't find same Russian seismic code in both software

The codes available in Robot are:

Also in Lira software when I use Load to Mass Conversion, there is only X and Y direction, not -X,+X,-Y,+Y.

My assumption is that you confuse definition of eccentricities with load to mass conversion. For the later you should just set the conversion direction Z- (meaning that you want to convert vertical loads acting downwards (as mass does)

and you mark all or just horizontal directions (in case you want to exclude "vertical" shapes of vibrations).

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

I really thank you for your help. Finally I found the same codes as you showed for both software. But still results of seismic analysis are completely different. Probably I'm defining my seismic load cases wrong. I tried to upload my model but because of size it can't be uploaded. So I recorded small video and uploaded in youtube. Here is link https://www.youtube.com/watch?v=klVpgICMdJI . Can you check it and reply me if you find out what I was doing wrong, please. Sorry for bothing you. But it will be very helpful if it be solved. 

Thank you!

[Artur.Kosakowski]

Please do not duplicate posts in different topics and continue this one in http://forums.autodesk.com/t5/robot-structural-analysis/having-trouble-to-get-same-seismic-result-in... only. Thank you.

[Anonymous]

I'm sorry sir. I didn't know it'd make trouble that duplicating same post in different topics. I just saw in different topic there someone possibly know the both software according to his post. So that I asked help from him too by replying. By the way could you check the video and find any solution for me? if you did, please let me know.

thank you! 

[Artur.Kosakowski · Accepted solution]

Please read the post from StefanoPasquini6790 in the other topic.