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Seeking inputs on your experience of 2016 editions of IS 1893 Pt 1 and IS 13920
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dcrai
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Joined: 26 Jan 2003
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PostPosted: Mon Mar 18, 2019 7:27 am    Post subject: Seeking inputs on your experience of 2016 editions of IS 1893 Pt 1 and IS 13920 Reply with quote

Dear Colleagues,

It has been about two years since the new editions of seismic codes IS 1893 Part 1 and IS 13920 have been published and are in use. Several new provisions have been introduced in these revisions. We have undertaken a project,  a part of which is to learn from the professionals about their experiences in implementing these provisions for seismic analysis and design of buildings. We would like to hear from you about the issues related to difficulty in understanding and implementing a particular provision. Your input sent to me at dcrai@iitk.ac.in will help us develop a comprehensive proposal for further improvement of these codes with the necessary background. Thanking you in advance and looking forward to hearing from you,

With best regards,
Durgesh Rai
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Rudra Nevatia
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PostPosted: Mon Mar 18, 2019 10:30 am    Post subject: Seeking inputs on your experience of 2016 editions of IS 1893 Pt 1 and IS 13920 Reply with quote

Thank you Sir for initiating discussion on IS:1893.

My comment relates to Clause 7.8.2 Design Eccentricity. Apparently, two methods are commonly used to account for this clause : 


1. Shifting of modal mass in RSA
2. Adding effects of eccentricity obtained from a static analysis to RSA


Can some guidelines be provided as to the preferred method ?


Regards,
Rudra Nevatia











On Mon, Mar 18, 2019 at 1:04 PM dcrai <forum@sefindia.org (forum@sefindia.org)> wrote:

Quote:
Dear Colleagues,

It has been about two years since the new editions of seismic codes IS 1893 Part 1 and IS 13920 have been published and are in use. Several new provisions have been introduced in these revisions. We have undertaken a project,  a part of which is to learn from the professionals about their experiences in implementing these provisions for seismic analysis and design of buildings. We would like to hear from you about the issues related to difficulty in understanding and implementing a particular provision. Your input sent to me at  will help us develop a comprehensive proposal for further improvement of these codes with the necessary background. Thanking you in advance and looking forward to hearing from you,

With best regards,
Durgesh Rai








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anjan_sen
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PostPosted: Mon Mar 18, 2019 3:30 pm    Post subject: Seeking inputs on your experience of 2016 editions of IS 1893 Pt 1 and IS 13920 Reply with quote

Dear Sirs,In my opinion consideration of alternative 2 might be easier and least complicated in case detailed design procedures are adopted, however in case a design software programme like say etabs is relied upon then the software would take care when proper inputs are fed.


Regards
Sen


On Mon 18 Mar, 2019, 19:55 Rudra Nevatia <forum@sefindia.org (forum@sefindia.org) wrote:

[quote]            Thank you Sir for initiating discussion on IS:1893.

My comment relates to Clause 7.8.2 Design Eccentricity. Apparently, two methods are commonly used to account for this clause : 


1. Shifting of modal mass in RSA
2. Adding effects of eccentricity obtained from a static analysis to RSA


Can some guidelines be provided as to the preferred method ?


Regards,
Rudra Nevatia











On Mon, Mar 18, 2019 at 1:04 PM dcrai forum@sefindia.org (forum@sefindia.org))> wrote:

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Nithya Chandran j
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PostPosted: Mon Mar 18, 2019 5:30 pm    Post subject: Seeking inputs on your experience of 2016 editions of IS 1893 Pt 1 and IS 13920 Reply with quote

Mam.Actually it was my project topic. Iam planning to proceed as a research topic..


On Mon, Mar 18, 2019, 10:02 PM Rudra Nevatia <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            Thank you Sir for initiating discussion on IS:1893.

My comment relates to Clause 7.8.2 Design Eccentricity. Apparently, two methods are commonly used to account for this clause : 


1. Shifting of modal mass in RSA
2. Adding effects of eccentricity obtained from a static analysis to RSA


Can some guidelines be provided as to the preferred method ?


Regards,
Rudra Nevatia











On Mon, Mar 18, 2019 at 1:04 PM dcrai forum@sefindia.org (forum@sefindia.org))> wrote:

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Nithya Chandran j
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PostPosted: Mon Mar 18, 2019 5:30 pm    Post subject: Seeking inputs on your experience of 2016 editions of IS 1893 Pt 1 and IS 13920 Reply with quote

I need a deep study...Can you help me regarding this?

On Mon, Mar 18, 2019, 10:20 PM Chandra Panicker <kcpnisha@gmail.com (kcpnisha@gmail.com)> wrote:

[quote]Mam.Actually it was my project topic. Iam planning to proceed as a research topic..


On Mon, Mar 18, 2019, 10:02 PM Rudra Nevatia <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            Thank you Sir for initiating discussion on IS:1893.

My comment relates to Clause 7.8.2 Design Eccentricity. Apparently, two methods are commonly used to account for this clause : 


1. Shifting of modal mass in RSA
2. Adding effects of eccentricity obtained from a static analysis to RSA


Can some guidelines be provided as to the preferred method ?


Regards,
Rudra Nevatia











On Mon, Mar 18, 2019 at 1:04 PM dcrai forum@sefindia.org (forum@sefindia.org))> wrote:

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Rudra Nevatia
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PostPosted: Tue Mar 19, 2019 7:07 am    Post subject: Seeking inputs on your experience of 2016 editions of IS 1893 Pt 1 and IS 13920 Reply with quote

Dear Mr. Sen,

IMHO choice of the method should not be left to any software.

One of the important findings in FEMA P-2012 / September 2018 is stated below and hopefully will be incorporated in future revisions of seismic codes :

Allow only the static method of applying accidental torsion for buildings with extreme torsional irregularity. In other words, do not permit use of 5% mass offsets with modal response spectrum analysis or linear response history analysis for such buildings


Regards,
Rudra Nevatia
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sktrisal
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PostPosted: Wed Mar 20, 2019 8:30 am    Post subject: Seeking inputs on your experience of 2016 editions of IS 1893 Pt 1 and IS 13920 Reply with quote

The directions in respect of column 20 times the beam bar dia are not being followed.the dangers of non observance of this stipulation need to be highlighted.the approving offices should observe  these stipulations.Some positive steps need to be taken in this direction.
Sktrisal
9910416668


On Mon, 18 Mar 2019, 19:54 Rudra Nevatia, <forum@sefindia.org (forum@sefindia.org)> wrote:

[quote]            Thank you Sir for initiating discussion on IS:1893.

My comment relates to Clause 7.8.2 Design Eccentricity. Apparently, two methods are commonly used to account for this clause : 


1. Shifting of modal mass in RSA
2. Adding effects of eccentricity obtained from a static analysis to RSA


Can some guidelines be provided as to the preferred method ?


Regards,
Rudra Nevatia











On Mon, Mar 18, 2019 at 1:04 PM dcrai forum@sefindia.org (forum@sefindia.org))> wrote:

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anjan_sen
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PostPosted: Wed Mar 20, 2019 11:30 am    Post subject: Seeking inputs on your experience of 2016 editions of IS 1893 Pt 1 and IS 13920 Reply with quote

Dear Sir,In case detailed analysis has to take care of seismic loading then the mass and a percentage of live load need be considered as per NBC provision. This is however needed for high structures. 
For low structures, seismic effect is normally are not considerable where the codal provision of eccentricity would be appropriate.
These considerations would be safe.
Regards
Sen

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Rudra Nevatia
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PostPosted: Thu Mar 21, 2019 8:53 am    Post subject: Reply with quote

Dear Dr. Rai,

I believe, 1.5 factor on static eccentricity accounts for magnification of closely spaced lateral and torsional mode frequencies which is not captured in Equivalent Static Method or when using SRSS combination in Response Spectrum Analysis.

CQC  in RSA, on the other hand does magnify effect of closely spaced frequencies as I understand from the attached original paper by Prof. Wilson as also implied in Cl. 7.7.5.3 of IS 1893.

If so, can we say that amplification on static eccentricity need not be applied when using CQC in RSA similar to the concession given to Time History Method in Cl. 7.8.2.

Regards,
Rudra Nevatia



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dcrai
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PostPosted: Fri Mar 22, 2019 6:00 am    Post subject: Reply with quote

Thank you for bringing out a few inaccuracies prevalent in the practice and codal provisions regarding torsional response.

A 3D dynamic analysis (both RSA and THA) will account for torsional effects and no amplification is necessary. For RSA, the CQC is better choice as close modes are adequately represented due to cross-modal terms of CQC.

In dynamic analysis, physically adjusting mass to account for the torsional response inadvertently changes the dynamics of the structure with each mass shift. Therefore, the safe method is to calculate the effect of accidental eccentricity by static means (ASCE permits Equivalent Static vertical force distribution for this purpose) and then combine it with dynamic analysis results.

Regards,
Durgesh Rai
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