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How should one define min stiffness requirement of tall buil
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bijay sarkar
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Joined: 14 Dec 2009
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PostPosted: Fri Nov 23, 2012 6:40 pm    Post subject: Reply with quote

Many of the constructed tall buildings are designed for a side sway of about 1500 mm and the whole building is like a pendulum under design wind load.  Acceleration of such oscillation disturbs the human comfort level and at some value of this oscillation, human can't stand & surrounding objects may fall down. In stiffness requirement of such buildings, acceleration at which human comfort is ensured, may be a design criteria.

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bijay sarkar
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thirumalaichettiar
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PostPosted: Sat Nov 24, 2012 1:20 am    Post subject: Reply with quote

Dear Er.Bijay sarkar,

Can you post the reference from where you get the information that the constructed tall buildings are designed for a side sway of about 1500 mm?

T.RangaRajan.
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bijay sarkar
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PostPosted: Sat Nov 24, 2012 6:05 am    Post subject: Reply with quote

Dear Sir,

If you search in Google with the string "Side Sway in Burz Khalifa", you will get several sites informing that the Burz Khalifa sways by 1500 mm. Some of the sites are informing that it is about 5.5' i.e. 1670mm.

Again to substantiate above, we are informed that Height of Burz Khalifa is 828 metre. Code restricts the side sway by H/500. If I now calculate the permissible sway of the building, it comes to 828/500 = 1656 mm. Thus, side sway of about 1500 mm has been furnished.

However, whatever be the actual side sway, there must be some exorbitant sway in such tall buildings. And such sway must have some acceleration component with it. People working or living at that height can bear with a certain limit of acceleration, exceeding which people can not bear with it. The same feelings what we feel in vehicles of our daily journeys on road.

While defining the stiffness requirement of tall buildings, should we not consider such acceleration of human comfort ?


with regards,

bijay sarkar
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thirumalaichettiar
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PostPosted: Sat Nov 24, 2012 6:32 am    Post subject: Reply with quote

Dear Er.Bijay sarkar,

http://www.sefindia.org/forum/viewtopic.php?p=52773&highlight=#52773
In the above link Dr.Suresh Kumar has quoted as

With regard to wind, tuned mass damper as well as sloshing water damper are few of the passive choices and they are very efficient in dissipating energy and control motions.

May be this type of device of others may help to reduce the acceleration and need to check the literature.

T.RangaRajan.
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gautam chattopadhyay
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PostPosted: Sun Nov 25, 2012 4:35 am    Post subject: How should one define min stiffness requirement of tall buil Reply with quote

The stipulate of H/500 dates back to the era when high rise buildings were being categorised as buildings having height beyond 150 m to 300 m. Burj Khalifa is the newest addition to the structural engineering scenario which demands a newer stipulate to restrict side sway at top of the structure. Mr. Sarkar's comment has brought forth a long discussed point, are the structural engineers not serving the civilisation properly or enjoying an indifferent isolation with discoveries in structural analysis and design, materials of various parentage? Yes, time has come to restructure our code provisions based on the endurance limit of human being. Our code provisions should now onwards take clue from human physiology also, else we shall construct some inhabitable wonders which will satisfy the engineer's ego but not the mankind. Finally such honourable wonders will become ridiculous trashes.  

On Sat, Nov 24, 2012 at 11:35 AM, bijay sarkar <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear Sir,

If you search in Google with the string "Side Sway in Burz Khalifa", you will get several sites informing that the Burz Khalifa sways by 1500 mm. Some of the sites are informing that it is about 5.5' i.e. 1670mm.

Again to substantiate above, we are informed that Height of Burz Khalifa is 828 metre. Code restricts the side sway by H/500. If I now calculate the permissible sway of the building, it comes to 828/500 = 1656 mm. Thus, side sway of about 1500 mm has been furnished.

However, whatever be the actual side sway, there must be some exorbitant sway in such tall buildings. And such sway must have some acceleration component with it. People working or living at that height can bear with a certain limit of acceleration, exceeding which people can not bear with it. The same feelings what we feel in vehicles of our daily journeys on road.

While defining the stiffness requirement of tall buildings, should we not consider such acceleration of human comfort ?


with regards,

bijay sarkar
     



     


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gautam chattopadhyay
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PostPosted: Tue Nov 27, 2012 2:55 am    Post subject: How should one define min stiffness requirement of tall buil Reply with quote

Earlier I wrote a multi storeyed building is a MDOF system that can never be simplified as a SDOF one, hence it cannot be said stiffness of a multistoreyed building as a whole. However a multistoreyed building (MSB) may be idealised as a series of springs comprising of columns and shear walls in each floor and we can then apply electrical analogy of resistances. The equivalent resistance in electricity of a system having resistors connected in parallel performs analogous to a structural system having springs connected in series. However this holds good only when the system is subjected to axial thrust. Thus equivalent stiffness of a MSB may be assumed to be reciprocal of summation of the reciprocals of storey stiffnesses. This may yield first fundamental frequency of a MSB very approximately and the result may be used as a first hand estimate to judge structural behaviour of the building towards earthquake forces but the final design must be done on the basis of MDOF analysis either by shear model or a full frame model.

On Fri, Nov 23, 2012 at 10:50 AM, mailingprabu <forum@sefindia.org (forum@sefindia.org)> wrote:
[quote]                   --auto removed--

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