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Posted: Tue Sep 21, 2004 5:21 am Post subject: Response acceleration coefficient in proposed code
I congratulate Dr. S.K Jain,Alpa Seth & Pankaj Joshi for initiating e-conference on Proposed Revisions to IS: 1893 & IS: 13920.
I am referring to old and proposed revision of clause 6.4.2.In the last Para of old code says that with T<0.1 sec the value of Ah will not be taken less than Z/2 whatever be the value of I/R.Proposed revision strikes out this para and instead modifies response acceleration coefficient.Code also disallows the use of rising part of spectra (T= 0 to 0.1 sec). It is also written in spectra that straight portion of curve to be used for first mode and rising part to be used for higher modes.
When we calculate seismic force for any building structure we generally follow the equation of Ah stated in 6.4.2 based on time period calculated spa per 7.6.2.So, I don't understand the aim behind writing 'To be used for higher modes' against rising part of spectra. In which condition we can use RA coefficient taken from rising part of curve? I can speculate that this can be used when seismic force calculated based on mode superposition method. Is it correct that I am thinking? Please let us have your comments.
Thanks & Regards,
Paresh Patel Jacobs Babtie India Ahmedabad
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