www.sefindia.org

[paresh.patel at babtie...]

Dear All,

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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