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IS:875-Part-3 Wind Code - Dynamic Analysis

 
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Rudra Nevatia
...
...


Joined: 26 Jan 2003
Posts: 207
Location: Mumbai

PostPosted: Thu Dec 23, 2004 8:16 am    Post subject: IS:875-Part-3 Wind Code - Dynamic Analysis Reply with quote

Dear Sirish,

My understanding of the subject differs from that
implied by the equation given in Cl. 7.2.1. Rather
than calculating vortex shedding frequency, one has to
calculate the critical velocity Vcr corresponding to
the first and in rare cases to the second mode of
vibration of the building. If the critical velocity
turns out to be less than design wind velocity,
cross-wind vibrations are possible. Again, wheather
resonance will occur at Vcr depends on Scruton number.

I think this is a very important topic and should be
discussed threadbare.

For those on the list not familiar with Indian codes,
may I point out that IS:875 being discussed here is
very similar to CP3.

Regards,
Rudra Nevatia

--- sirish@lntecc.com wrote:

Quote:
Dear Mr. Rudra,

The hitch that we are facing is, how to calculate
the frequncy of vortex shedding with the available
information in code.  We have very raw parameters
that the building is in Banglore (or some other
city).  We have 100% control on the structural
behavior of the building, like its natural
frequencies, mode shapes etc etc.,  

Whether the shedding frequency (Cl 7.2.1 p.4Cool can
be helpful?? Can we conclude that the structure is
safe, if the building natural frequency is greater
than the shedding frequency??

We have done the wind load calculations both in
static and dynamic cases also with in-house
developed specialized software.  We like to ensure
that the building will perform well under wind, if
the building is shifted from Banglore (Vb=33m/s) to
Chennai (Vb=50m/s).

Regards,
Sirish

-----Original Message-----
Message From  rudra_nevatia@yahoo.com
[mailto:rudra_nevatia@yahoo.com]
Sent: Thursday, December 23, 2004 3:17 PM
To: Sirish Bellana
Subject: IS:875-Part-3 Wind Code -
Dynamic Analysis


Dear Sirish,

Susceptibility of buildings to dynamic loads arises
on
account of cross wind vibrations caused by vortex
shedding and along wind vibrations caused by gust.

Cross wind vibrations will dominate if the frequency
of  vortex shedding given in Cl. 7.2.1 is close to
the
natural frequency of the building.

Along wind load due to gust is calculated by Cl. 8.3
as Fz and should be compared with the static wind
force given by Section 6.

Hope that helps.

Regards,
Rudra Nevatia














          
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