Defining stories for warehouse halls

[Anonymous]

Hello everyone,

I made a model of a warehouse which contains concrete columns connected with a prestressed I beam at tops (see attachment). Analysis is made for Modal case and two seismic cases (equivalent lateral forces method). I defined a single story and base of structure. Once I defined a story at top of roof and once at top of columns (in this case i manually assigned elements of roof to the story1). What I expected of results was same mode frequencies and same base shear forces, but larger moment reactions for seismics under columns in first case (because of larger resultant distance). Base shear and frequencies was the same but moment reactions wasn't what i expected (see attachments).

Which is a proper way to define stories for single story structures like warehouses (reguarding seismics) and why?

PS. in both cases I had a warning that I shoud use DSC algorithm in case of dynamic and non-linear analysis of structure containing released directions. May I ignore this warning and with what consequences?

[Artur.Kosakowski]

Hi @Anonymous

The generated forces are applied to the nodes being in the plane of the story (top)level. Try to define two stories, the first from the bottoms of the columns to their tops and the second from this level to the top of the roof.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Hi @Artur.Kosakowski,

should I worry about warnings: 1. The element is defined on a story different from the assigned one

2. the element is defined outside of stories

3. the element exceeds geometric limits of a story

4. The element is not assigned to any story ? (screenshots attached)

They appear wether I select whole model and set story assignment to automatically or I manually define each element.

Thank you for your time and advices in advance

[Artur.Kosakowski]

Hi @Anonymous

Could you attach the model?

[Anonymous]

Here it is

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

You need to divide the columns at the level of the top of the 1st story and then create superbars if you want to design them in the RSA steel design module.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Thank you @Artur.Kosakowski for fast replies.

And what would be consequences of ignoring DSC algorithm warning ?

[Artur.Kosakowski]

Hi @Anonymous

Small chance of getting incorrect results.

[Anonymous]

Hi @Artur.Kosakowski.

How should I define buckling length coefficients in member type definition after dividing columns?

Originally, when columns were single member from base to top, i defined them like cantilevers like this

[Anonymous]

For example, if I divide columns in middle should every half-column have buckling length coefficient 4 instead of 2 ?

[Artur.Kosakowski]

Hi @Anonymous

No, you should create a superbar with both parts and assign the same parameters as for not divided column.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

Dear @Artur.Kosakowski,

I searched forum and help but I can not find the way how to create the Superbar of concrete members. Colud you give me some tips?

[Artur.Kosakowski]

Hi @Anonymous

You cannot define superbars for RC Columns. Mind that Robot cannot design an RC column with load applied along their height. 

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

[Anonymous]

So, which values of buckling length coef. should I assign to divided parts of these columns? 

[Artur.Kosakowski]

Hi @Anonymous

You should not divide the columns when you want to design them in the RC Design module. This means that you should either use the response spectra analysis instead of the static seismic approach.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.