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Analysis and Design of Two Structures in one STAAD
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nivassrii
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PostPosted: Wed Sep 10, 2014 8:44 am    Post subject: Analysis and Design of Two Structures in one STAAD Reply with quote

Hi,

Can somebody guide me on how to analyze and design two or more structures with their respective (specific to each structure) load combinations and design parameters in one STAAD file.


Thanks in Advance
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htulpule
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PostPosted: Thu Sep 18, 2014 4:56 pm    Post subject: Reply with quote

why would somebody want to do it? just for kicks?

screwed up earthquake analysis is obviously the downside

and no upside that i can see

Himanshu
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vegad
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PostPosted: Tue Sep 30, 2014 1:10 am    Post subject: Reply with quote

Dear Member,

Each mathematical model represents one structure. So either you need to identify the file with 2 structures as one structure and accept the results as if it is one structure.

But why would we do that?

Suppose if you are a university admissions guy, can you accept academic results of 2 poor guys and 1 intelligent guy combined together for the admission of each?

You will have to ask for a combined admission application form. . .and why would you do that?

Possibly you can rely on the local analysis results for loads independent of global behavior. Post this to leading software programmers, it may lead to something new. But before that you should be sure what you are up to.

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rahul.leslie
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PostPosted: Wed Oct 22, 2014 4:40 pm    Post subject: Reply with quote

Connect the two structures by member at the support points, and inactivate that member. I know there are cases when one has to model it that way. Itís not for kicks.
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nimish.khanolkar
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PostPosted: Thu Oct 23, 2014 1:40 pm    Post subject: Reply with quote

This problem is related to 2 different issues -

1) The issue of having two different structures in 1 staad file. This is a staad problem, wherein you get a disjoint structures warning. Other softwares are perfectly capable of handling disjoint structures as there is nothing fundamentally wrong in applying stiffness method to two disjoint structures in one go.
The cross coefficients would be zero, but the matrix would be non-singular and invertible leading to a unique solution.
To take care of this issue in staad, do as per earlier reply, of connecting the supports via a null member.

2) The other problem is of each structure in one file, havings its own seismic force, diaphragms, and loadcombinations. Seismic force can be managed via separate diaphragms for each structure and applying a mass-force in Z or X direction.
Why would you want independant load combinations for each structure? I don't think any software assigns load combinations to elements. They are there for the full file.
So you can define two subsets based on your need. Refer set 1 for first structure. Set 2 for second.
Do not cross-refer.
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nivassrii
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PostPosted: Tue Oct 06, 2015 7:18 am    Post subject: Reply with quote

My friend,

This forum in most cases is for professionals meaning that if somebody is asking some question there must some particular reason or requirement or necessity or he/she might have come across such sort of modelling or requirement. If you are not aware of it, it is not a mistake to accept that you are not aware or better don't reply at all but calling with words like 'just for kicks' seems awkward.

There are many positive replies below.

htulpule wrote:
why would somebody want to do it? just for kicks?

screwed up earthquake analysis is obviously the downside

and no upside that i can see

Himanshu


Thank you very much 'rahul.leslie' and 'nimish.khanolkar' for your positive replies.
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Abishek_Siingh
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PostPosted: Tue Oct 06, 2015 10:05 am    Post subject: Reply with quote

Hmmmm. My limited intellect is not able to comprehend a situation where such a step would need to be taken, that is, to model two buildings in one file.

What are the situations? Can someone highlight?

Mr. Leslie, I would love to read your views on this.

And I would also want to know how inactivating a beam, would ensure that two buildings have independent dynamic analyses?

I wonder what would the staad input file/editor look like!

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Thank you,
Abishek Siingh

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MallikarjunG
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PostPosted: Wed Oct 07, 2015 3:56 am    Post subject: Reply with quote

Dear nivassrii,
I suggest to use ETABS for such problems i.e., to analyse 2/more building/structures in one model. It can handle multiple structures in one model. But Etabs can handle buildings only.
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vijayarathnam
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PostPosted: Thu Oct 08, 2015 3:50 am    Post subject: Reply with quote

Dear all
This situation of modelling two structures in one file generally comes when we provide crumple joints, wherein the two parts of the same building behaves like two independent structures, connected  firmly at the Foundation level.They are separated only above Foundation level. It has got some advantages too.However, the theoretical limitations could be  explained by some scholars.

Vijayarathnam
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PREETI_SARKAR
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Joined: 10 Mar 2011
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PostPosted: Mon Dec 21, 2015 2:58 am    Post subject: Reply with quote

When you create 2 different structures in one model, during a dynamic analysis, it will be difficult to understand which period is for which structure. For the coefficient method for IS1893, you need to know the fundamental period for calculating the lateral forces. If each structure has a different period, calculating the seismic forces for each structure using the same period for all of them will be wrong.

I think this will be the case with any software.
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