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Clarification requested for Period Formula for Buildings with RC Structural Walls

 
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aditya
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Joined: 05 Apr 2008
Posts: 159

PostPosted: Sun Apr 07, 2019 4:53 pm    Post subject: Clarification requested for Period Formula for Buildings with RC Structural Walls Reply with quote

Dear Dr. Durgesh Rai Sir, Dr. Subramanian Sir and Fellow Sefians,
BIS recently issued amendment no. 1 to IS 1893 (Part 1): 2016 through which it was suggested to correct the exponent by moving from inner bracket to outer bracket so that the amended formula looks as:
Aw=sum [Aw{0.2+(Lwi/h)}2]   ------(a)
in place of the original version shown below:

Aw=sum [Aw{0.2+(Lwi/h)2}]   ------(b)

It is to be noted that this formula is also given in Eurocode 8 Part 1 as equation 4.8 in the format shown above as equation (a).

However, the original version seems to be derived from UBC 97 in which the equation is given in section 1630.2.2 in the following form:

Ac=sum [Ac{0.2+(De/hn)2}]  ------(c)
in which only the notations are different, meaning
Ac=Aw , De=Lwi, hn=h
This fact has also been highlighted by Crowley and Pinho in the article titled "Revisiting Eurocode 8 formulae for periods of vibrationand their employment in linear seismic analysis" published in the Journal EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS.

So my queries are:
1. Should we revert to the equation (b) and will BIS amend back to this formula?
2. Aw and Awi refer to the FIRST storey of the building. Does it mean GROUND floor in the Indian context? Why skip GROUND floor and calculate areas of walls in the FIRST storey?

with regards,
Aditya
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aditya
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Joined: 05 Apr 2008
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PostPosted: Mon Apr 22, 2019 4:11 pm    Post subject: Reply with quote

Dear Dr. Durgesh Rai Sir, Dr. Subramanian Sir,
Could you please throw some light on this important matter?
with best regards,
Aditya
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Dr. N. Subramanian
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PostPosted: Tue Apr 23, 2019 2:56 am    Post subject: Re: Clarification requested for Period Formula for Buildings with RC Structural Walls Reply with quote

Dear Er Aditya,


I wish to thank you for bringing out this problem due to the  amendment no. 1 to IS 1893 (Part 1): 2016.

I think someone might have compared it with Eurocode 8 Part 1 and found that Eqn.(b) has an error and issued as an amendment.

As noted by Crowley and Pinho in their article"Revisiting Eurocode 8 formulae for periods of vibration and their employment in linear seismic analysis", Journal EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, 2010; 39:223235, the formula in Eurocode is due to some printing error. Someone in BIS committee should approach BIS and ask them to withdraw this amendment.

I am also enclosing a recent paper from India on this topic.

Warm regards
Subramanian


aditya wrote:
Dear Dr. Durgesh Rai Sir, Dr. Subramanian Sir and Fellow Sefians,
BIS recently issued  amendment no. 1 to IS 1893 (Part 1): 2016 through which it was suggested to correct the exponent by moving from inner bracket to outer bracket so that the amended formula looks as:
Aw=sum [Aw{0.2+(Lwi/h)}2]   ------(a)
in place of the original version shown below:

Aw=sum [Aw{0.2+(Lwi/h)2}]   ------(b)

It is to be noted that this formula is also given in Eurocode 8 Part 1 as equation 4.8 in the format shown above as equation (a).
However, the original version seems to be derived from UBC 97 in which the equation is given in section 1630.2.2 in the following form:

Ac=sum [Ac{0.2+(De/hn)2}]  ------(c)
in which only the notations are different, meaning
Ac=Aw , De=Lwi, hn=h
This fact has also been highlighted by Crowley and Pinho in the article titled "Revisiting Eurocode 8 formulae for periods of vibrationand their employment in linear seismic analysis" published in the Journal EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS.

So my queries are:
1. Should we revert to the equation (b) and will BIS amend back to this formula?
2. Aw and Awi refer to the FIRST storey of the building. Does it mean GROUND floor in the Indian context? Why skip GROUND floor and calculate areas of walls in the FIRST storey?

with regards,
Aditya



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Pulkit & Pradeep Kumar-2017New Empirical formula for Fundamental Period of Tall Indian Buildings-16WCEE.pdf
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aditya
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PostPosted: Wed Apr 24, 2019 2:12 am    Post subject: Reply with quote

Dear Dr. N. Subramanian Sir,
Thanks a lot for your kind response on this important topic. Would you also please clarify on the meaning of "first storey" as requested in my second query, i.e., whether "first storey" is the same as "Ground Storey" in our context in the clause for time period formula?
with best regards,
Aditya
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Dr. N. Subramanian
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PostPosted: Wed Apr 24, 2019 4:09 am    Post subject: Reply with quote

aditya wrote:
Dear Dr. N. Subramanian Sir,
Thanks a lot for your kind response on this important topic. Would you also please clarify on the meaning of "first storey" as requested in my second query, i.e., whether "first storey" is the same as "Ground Storey" in our context in the clause for time period formula?
with best regards,
Aditya

Dear Er. Aditya,
  
This problem arises due to the different nomenclature used in India and USA for designating floors. In India we start with Ground Floor. But in USA, Ground floor is called the first floor.

Regards
Subramanian
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hsrai
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Joined: 26 Jan 2003
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Location: Ludhiana, Punjab, India

PostPosted: Wed Apr 24, 2019 4:47 am    Post subject: Re: Clarification requested for Period Formula for Buildings with RC Structural Walls Reply with quote

aditya wrote:
2. Aw and Awi refer to the FIRST storey of the building. Does it mean GROUND floor in the Indian context? Why skip GROUND floor and calculate areas of walls in the FIRST storey?

You can't skip ground floor.Take it as of Ground Floor.

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hsrai
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Joined: 26 Jan 2003
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Location: Ludhiana, Punjab, India

PostPosted: Wed Apr 24, 2019 4:54 am    Post subject: Re: Clarification requested for Period Formula for Buildings with RC Structural Walls Reply with quote

Dr. N. Subramanian wrote:
I think someone might have compared it with Eurocode 8 Part 1 and found that Eqn.(b) has an error and issued as an amendment.

As noted by Crowley and Pinho in their article"Revisiting Eurocode 8 formulae for periods of vibration and their employment in linear seismic analysis", Journal EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, 2010; 39:223235, the formula in Eurocode is due to some printing error.


If BIS works like this, then it is very unfortunate.

It is of equal concern that no amendment is issued with regards to that formula in EuroCode 8 part 1. Does not it indicate that all such organisations work in same fashion.

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aditya
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PostPosted: Sat Apr 27, 2019 4:36 am    Post subject: Reply with quote

Dear Dr. N. Subramanian Sir,
I wish to express my gratitude for clarifying the issue on the empirical time period formula for shear walled buildings.
I would like to request you to further clarify the following points:
1. What should be the shear wall density in a building for using this formula? For example, if a building has shear walls only along the lift well, is this formula applicable? Is the minimum shear wall density 2% of the floor area?
2. Is this formula applicable for Dual System (RC Frame+ Shear Wall) building or is it applicable for pure shear wall building (meaning lateral force is fully resisted by shear walls only)?
3. What should be the time period for a building with shear walls in which the shear walls are discontinued for upper floors after a number of storeys?

with best regards,
Aditya
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