Thread: Verification of modal analysis Results

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Re: Verification of modal analysis Results

Originally Posted by pascal.bogdan
Main mode – The number of the main mode for determining the sign of the given combination, so that (as you can see in the attached picture) in the seismic combination on Y direction you will have some braces tensioned and the other ones working in compression.
Thanks Pascal, but i m not understand. Cuz romanich and you say two very different things, i m confused.
Main mode number is max comb. mode number or tension - compression sign? if tension, seismic x main mode=1, if compression, seismic y main mode=2, really??

please explain this either of you??

regards..

ASC

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Re: Verification of modal analysis Results

Originally Posted by troy_the.best
Thanks Pascal, but i m not understand. Cuz romanich and you say two very different things, i m confused.
Main mode number is max comb. mode number or tension - compression sign? if tension, seismic x main mode=1, if compression, seismic y main mode=2, really??

please explain this either of you??

regards..

ASC
I have attached another pictures. There you will see the seismic combination on +Y direction and how the elements are subjected to axial force. Because I set there the main mode for Y direction, the vibration mode 2, the program will be able to tell which braces are tensioned and which are compressed.
I think that if you look at the pictures I have attached you will be able to understand why is so important this option.

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Re: Verification of modal analysis Results

Originally Posted by pascal.bogdan
I have attached another pictures. There you will see the seismic combination on +Y direction and how the elements are subjected to axial force. Because I set there the main mode for Y direction, the vibration mode 2, the program will be able to tell which braces are tensioned and which are compressed.
I think that if you look at the pictures I have attached you will be able to understand why is so important this option.
Pascal thanks for working. yes i m understood now better. But which structural type use this option. or if have a braced object in model. use this option. well If we do not use, Would it have made a mistake? Can you explain a little bit or if you have the chance to suggest any resources please, because As far as I understand this option important.

((Under what circumstances use it? please any document or website suggest to me.))

best regards

ASC

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Re: Verification of modal analysis Results

Originally Posted by troy_the.best
Pascal thanks for working. yes i m understood now better. But which structural type use this option. or if have a braced object in model. use this option. well If we do not use, Would it have made a mistake? Can you explain a little bit or if you have the chance to suggest any resources please, because As far as I understand this option important.

((Under what circumstances use it? please any document or website suggest to me.))

best regards

ASC
For structural steel is very important which brace is in compression and which is in tension, because one will be checked for buckling, one not( because it is in tension). Also, the program take into account about this issue by itself when using steel design modulus so the results will be adequate.

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Re: Verification of modal analysis Results

thanks Pascal..

yes i a m understand this case clearly now. see later..

regards
ASC

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Re: Verification of modal analysis Results

Originally Posted by troy_the.best
edward,

if Vspec > Vstatic ( Vspec too large then Vstatic) then probably a mistake your model or specrtum analysis. values are usually very close. Please pay attention to this point. Have very different results, if the model is broken or not stabil. and dont reduce spec factor (if Vspec is great) absolutely. I know this very well.. please check again this point edward. usually spectrum analysis is essentialy in our solutions. equal lateral static loads for comparison. and have any period restrictions in your Code.

To use this equation. SF2= SF1 x Vstatic/Vdyanmic (have to be Vstatic>Vspec)

sorry my english.

best regards
How r you?
See Scale factor means the accelration of spectrum diagram curve
first run we apply with scale facctor = g = 9.81 m/sec
this is not possible it means just to calebrate the results
next time we we apply the exact scale factor = 9.81 x Vstatic/Vdynamic
say = 2.3 ,
this procedure is based on the ubc code
because the response spectrum curve should be acceleration of seism/9.81
hoping this clear

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Re: Verification of modal analysis Results

Originally Posted by mecheil.edward.hanna
How r you?
See Scale factor means the accelration of spectrum diagram curve
first run we apply with scale facctor = g = 9.81 m/sec
this is not possible it means just to calebrate the results
next time we we apply the exact scale factor = 9.81 x Vstatic/Vdynamic
say = 2.3 ,
this procedure is based on the ubc code
because the response spectrum curve should be acceleration of seism/9.81
hoping this clear
thanks. edward i m fine.
No problems for me. if you are sure you are doing is correct, is okay. reduction, but we do not do that.

best regards
ASC

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Re: Verification of modal analysis Results

edward,

reduction in the scale factor we can not do. if Vstatic / Vdynamic <1 is okey. but in other situation that Vstatic / Vdynamic> 1, the reduction made by the new scale factor would again be the solution. We do not look at the the equivalent loads value if spectrum of behavior loads value is enough. (Vstatic <Vdynamic then no problem. Ok process.)

falcoando_turkey
ASC

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Re: Verification of modal analysis Results

I have trouble Robot and Etabs! You can help me? I have results period so different! Can you email your model Robot and Etabs in picture to me. My email :quangntn1992@gmail.com. Thanks you

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Originally Posted by troy_the.best
My model etabs v9.7.1 and RSA2011 sp2
results are same. ıts perfect run.
no problem modal analysis. bye

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Re: Verification of modal analysis Results

Originally Posted by quangntn1992743652
I have trouble Robot and Etabs! You can help me? I have results period so different! Can you email your model Robot and Etabs in picture to me. My email :quangntn1992@gmail.com. Thanks you

- - - Updated - - -
If you want help, tell what your problem is.

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