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defining stiffness of a tall building

 
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pcragtah
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Joined: 22 Jul 2010
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PostPosted: Fri Nov 23, 2012 2:48 am    Post subject: defining stiffness of a tall building Reply with quote

In my opinion, stiffness of a medium tall building (say 100m) can be related to ratio of sum stiffness of all vertical members to (mass per unit area) on each floor. The variation of the ratio along height can be adopted on a suitable proportion.
However, for a taller building (250 -300m), the structure may well be thought of as a open web structure for  stiffness  purposes and stiffness of the structure can again be based on ratio of stiffness of  the overall structure to mass per unit area on a typical floor.

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gautam chattopadhyay
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Joined: 17 Feb 2009
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PostPosted: Sat Nov 24, 2012 12:21 pm    Post subject: defining stiffness of a tall building Reply with quote

how can there be a unique stiffness in a multiple element, multistoreyed  structure? are we assuming a tall building which is essentially a multistoreyed structure, a SDOF one? A multistoreyed structure can be idealised only as a MDOF structure, A shear model is itself a simplified one else a framed model which will be difficult to analyse but, close to reality should be applied. In shear model it is very easy to construct the stiffness and the mass matrices but in a frame model consistent mass matrix cannot be constructed as easily as in shear model. From my experience I have seen shear model provides really a good estimate of natural frequencies (even mode by mode) which is within 10% of the framed model. Books of Mario Paz, Clough and Penezian and Newman may please be referred to in this context.

On Fri, Nov 23, 2012 at 10:48 AM, pcragtah <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           In my opinion, stiffness of a medium tall building (say 100m) can be related to ratio of sum stiffness of all vertical members to (mass per unit area) on each floor. The variation of the ratio along height can be adopted on a suitable proportion.
However, for a taller building (250 -300m), the structure may well be thought of as a open web structure for  stiffness  purposes and stiffness of the structure can again be based on ratio of stiffness of  the overall structure to mass per unit area on a typical floor.
     



     



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