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  1. #1
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    Determination of the fundamental period of vibration (T1) of a building

    Is there any mathematical formula for the approximate calculation of the fundamental period of vibration of a building?

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    Ct=0.085 for moment resistant space steel frames,
    Ct=0.075 for moment resistant space concrete frames and for eccentrically braced steel frames and
    Ct=0.050 for all other structures.
    H is the height of the building, in m, from the foundation or from the top of a rigid basement (EN 1998-1 section 4.3.3.2.2).

    We can use this approximation for buildings with heights up to 40m provided that they follow the regularity criteria that are described in table 4.1 (EN1998-1 section 4.2.3.1).
    Last edited by alberto; 04-11-2011 at 10:35.

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    An empirical type we use (for concrete structures) is T=n/10 where n=number of stories (typical storey~3m).

    So for a 10 storey building T=1 sec.
    Via, Veritas, Vita

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    There are also a couple of approximation formulae in EC1 (Wind).

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    In paulay-priestley's book there are some formulas e.g. for frame buildings T=0.061*(h^ 0.75).
    Last edited by rigid_joint; 29-09-2012 at 17:07.

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    An estimation of the fundamental period can also be made by the following expression: T1=2*(d)^0.5.
    d is the lateral displacement of the top of the building in meters due to the gravity loads applied horizontally.

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    How does this formula come from?

    It seems like a performance based design equation but in that case formula is a little bit different.

    (I think T=δ/ks where δ=displacement target for mass center, not displacement at the top.)

    T1=2*(d)^0.5
    There is a unit problem with that formula except there is a unit decision in advanced.
    Last edited by rigid_joint; 07-10-2012 at 15:34.
    houston, we've got a problem

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    I really don't know what is the theory behind this expression...
    I will search through the internet and my notes... Probably I will find something!

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    I asked it just because I think that I have never seen it before.
    houston, we've got a problem

  10. #10
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    There is a unit problem with that formula except there is a unit decision in advanced
    The unit of the result is in seconds.
    This expression works the same way as the formula described by Eurocodes.

    I asked it just because I think that I have never seen it before.
    No problem at all!

 

 

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