Multiple towers

[medtayeb]

Dear sir,

Dynamic model of  multiple towers   on a common base :

Is  there a possibility to do with robot and if so what is the difference with a normal case.

Many thanks.

Tayeb.

[Artur.Kosakowski]

What is exactly the dynamic analysis you mean - modal?

[medtayeb]

Hi,Artur

Yes Modal.

Many thanks.

Tayeb.

[Artur.Kosakowski · Accepted solution]

Yes, that is possible. There is no difference comparing to running this type of analysis for e.g. a single tower but you should display the shapes of modes to find out which of the model they 'belong' to.

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.

[medtayeb]

Hi,Arthur

After modal analysis of all can we do a seismic analysis by modal superposition to get the results (forces, reactions, displacement ...)

Many thanks.

Tayeb.

[Artur.Kosakowski · Accepted solution]

Yes you can run seismic (response spectrum) analysis for such model in Robot and get values of forces and displacements.

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.

[medtayeb]

Hi,

Therefore in this case where the interests of search modes of vibration for each towers.

Many thanks.

Tayeb.

[Anonymous]

Hi Artur, 

Can we model multi tower with difference stories height level for each tower, example tower A have stories is 3m, tower B have stories height is 4.5m ?

[Tuctas]

Modal and Responce Spectrum Analysis in such cases won't give useful results. You must run seperate analysis for each tower (with common base) in order to obtain reliable results for each tower or else to assign zero mass in the rest of the towers except the one that is examined. In order to obtain reliable results for the common base, it is preferable to make an Equivalent Lateral Force Analysis. 

[Artur.Kosakowski]

Hi @Anonymous

Following @Tuctas comments - as you cannot 'correctly' define stories for each of the towers the results for stories will not be 'correct' either however all others should IMHO be fine. Make sure you have reached 90% of participating masses.

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.

[Tuctas]

Hi Artur,

Modal analysis of the whole multiple tower will result in mode shapes that combine separated structures. In fact, two (or more) towers are oscillating separately (just placed on a common base) against a seismic excitation, they don't affect each other (if they are not connected at all), so mode shapes obtained from the whole multiple tower won’t be representative for the oscillation of each tower separately.      

[Anonymous]

Hi Tuctas, 

In modal analysis theory, the mode shape will depend on distributed of mass & stiffness of each part of model, so if we have multi tower and podium base, both of them should be consider in one model to distributed their mass & stiffness correctly, if we divide two model separately, mass & stiffess for full building haven't correct, so the mode shape also haven't present response of structure exactly. 

[Anonymous]

hi Artur, IMHO mean ?? Colud you let me know more.

[Tuctas]

Hi CSTeam-ICE,

If you make a total modal analysis for the whole system (consisting of some independed oscillators) then the results will have nothing to do with what you need (and what you need is the results for each oscillator-individual tower).

Keep in mind that what it's needed for the modal responce of a structure is the mass and stiffness of the upper structure, not of its base (that could be either a foundation or a basement+foundation). This is not a problem that concerns only Robot, it is general.