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Thread: Verification of modal analysis Results

  1. #31
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    Default Re: Verification of modal analysis Results

    Quote Originally Posted by pascal.bogdan View Post
    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..

    falconado_turkey
    ASC

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    Default Re: Verification of modal analysis Results

    Quote Originally Posted by troy_the.best View Post
    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..

    falconado_turkey
    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.
    Attached Images Attached Images

  3. #33
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    Default Re: Verification of modal analysis Results

    Quote Originally Posted by pascal.bogdan View Post
    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.))

    thanks in advice
    best regards

    falconado_turkey
    ASC

  4. #34
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    Default Re: Verification of modal analysis Results

    Quote Originally Posted by troy_the.best View Post
    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.))

    thanks in advice
    best regards

    falconado_turkey
    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.

  5. #35
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    Default Re: Verification of modal analysis Results

    thanks Pascal..

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

    regards
    ASC

  6. #36
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    Default Re: Verification of modal analysis Results

    Quote Originally Posted by troy_the.best View Post
    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
    falconado_turkey
    Hi Falconado,
    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

  7. #37
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    Default Re: Verification of modal analysis Results

    Quote Originally Posted by mecheil.edward.hanna View Post
    Hi Falconado,
    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.
    Thanks again for your interest.

    best regards
    falconado_turkey
    ASC

  8. #38
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    Default 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.)

    thanks in advice

    falcoando_turkey
    ASC

  9. #39
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    Default 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

    - - - Updated - - -

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

    falconado
    Last edited by Ed Jobe; 2017-02-15 at 03:08 PM.

  10. #40
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    Default Re: Verification of modal analysis Results

    Quote Originally Posted by quangntn1992743652 View Post
    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.
    C:> ED WORKING....

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