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Thread: Dynamic Loads and Mass Participation

  1. #11
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    Default Re: Dynamic Loads and Mass Participation

    As for reason that you must or not must to define mass oscilating in Z direction , i think that is other issue.
    I tell my opinion for this issue:

    When you have defined load participating factors to mases in etabs by default you have on "Include lateral Mass Only" , this mean that u have says to program that mass can oscilate in X and in Y only. If you have make this into robot also yo must have same modal response and values also.
    But in this case you can't generate spectrum case in Z if you want. In this case if u want to use spectrum case or dynamic analysis in Z direction ( we know codes recomend it for defined reason and type of structure, ex EC - for structures with span >9m, and other reasons ;; you must define mass oscilating in z also.
    But spectrum datas are difFerent from X,Y and Z.


    regards
    Z.G.

  2. #12
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    Talking Re: Dynamic Loads and Mass Participation

    Quote Originally Posted by length zero View Post
    I' v never seen that robot has give me this kind of error ( zero drifts ),
    Finally they are an good control of seismic lateral response of structure, ( in this case FEM Model).
    As we know drifts are nothing more than relative story displacements and if this values of displacements are to small, you must chek your model, maybe modal mass is less than 90 %, base shear force is to small, ....
    This can happpen if you have very stiff structure, and story displacements are to small.
    Also controll the values of free vibration periods and comparasion with aproximately hand calculated is an good parameter to check your model.
    The rigid diphragm is the problem
    rigid diaphragm is the bug in the program that creates this type of wrong analysis
    Thanks "Lenght Zero" for your helping
    mecheil

  3. #13
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    Default Re: Dynamic Loads and Mass Participation

    Quote Originally Posted by length zero View Post
    As for reason that you must or not must to define mass oscilating in Z direction , i think that is other issue.
    I tell my opinion for this issue:

    When you have defined load participating factors to mases in etabs by default you have on "Include lateral Mass Only" , this mean that u have says to program that mass can oscilate in X and in Y only. If you have make this into robot also yo must have same modal response and values also.
    But in this case you can't generate spectrum case in Z if you want. In this case if u want to use spectrum case or dynamic analysis in Z direction ( we know codes recomend it for defined reason and type of structure, ex EC - for structures with span >9m, and other reasons ;; you must define mass oscilating in z also.
    But spectrum datas are difFerent from X,Y and Z.


    regards
    Z.G.


    Hi Z.G.

    first . thanks for advice. then actually responce spectrum analysis in Turkey not use Z direction and not add masses this directions. You are right. Thanks your opinion. its right.

    falconado_turkey

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