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Response Reduction Factor 3 or 5

 
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kakulakrishnakish
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Joined: 04 Aug 2009
Posts: 7

PostPosted: Sun Mar 13, 2011 8:30 am    Post subject: Response Reduction Factor 3 or 5 Reply with quote

Dear SEFIANS,


I have to design a building (G+5 Floors) located in Zone-III.
I want to consider Response Reduction factor (RRF) as 3 instead of 5 (As per IS-13920 / IS 1893) as I would like to detail it as OMRF instead of SMRF.
The reasons for taking RRF as 3 are:
1)  In normal conditions, most of our buildings are at the mercy of the labourers or labour contractor and his Site supervisor, who are just ignorant of our IS Codal provisions. If I start giving different spacings of shear reinforcement in beams, it is difficult to execute correctly at site. Hence If I detail the beams in the normal way (as per SP-34) I can effectively control and ensure the correct execution.
2)  The steel quantity consumed will be less in case RRF is taken as 5, but it has be provided judiously at the locations as specified in the code. Instead of taking the advantage of Reduced Steel consumption, I prefer to go by normal detailing (SP-34) and ensure the correct execution.

My question to all members is:

Whether it is reasonable to violate the IS 1893 or IS 13920 in considering RRF as 3 in place of 5,  since the structure is located in Zone-III
(or)
Shall I have to follow the IS 13920 and consider RRF as 5 with confined steel and follow the size of members keeping the aspect ratio as laid in code.


Thanking you in advance

K.Krishna Kishore
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Arvind Kumar Jaiswal
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Joined: 14 Feb 2011
Posts: 47

PostPosted: Sun Mar 13, 2011 1:49 pm    Post subject: Reply with quote

Dear Friend,

IS 1893 2002 does not give you freedom to construct OMRF (Ordinary Moment Resistant Frame) for Zone-III, whereas you may choose to do so for Zone -II. This means that you have to follow IS: 13920 ; 2002 for Zones III, IV and V and you are not given a choice.

This is to avoid the sudden collapse during an earthquake and to allow the formation of hinges at the desired places only, by keeping strong column and weak beam concept. I would go one step further with a statement further added that we should talk about strongest earth, stronger foundation, strong column, weak beam and weakest brace..!!

If you are able to achieve then the structure you design will be certainly be earthquake resistant..!
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sukanta.adhikari
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Joined: 26 Jan 2003
Posts: 711

PostPosted: Sun Mar 13, 2011 5:58 pm    Post subject: Re: Response Reduction Factor 3 or 5 Reply with quote

I am finding this as a common practice in our country.Even reputed consultancy of our countries are neglecting this issue.In zone III ductile detailing is ignored.But this is not a correct practice.The basic aim of Earthquake resistant structure is to design a structure which will behave in a ductile manner,ie,a structure will undergo lot of deformation before failure,thereby giving appropriate warning before failure.
As per IS 13920 it is mandatory to do a ductile detailing in zone III and above and should not be voilated.

Regards,
S.Adhikari




kakulakrishnakish wrote:
Dear SEFIANS,

I have to design a building (G+5 Floors) located in Zone-III.
I want to consider Response Reduction factor (RRF) as 3 instead of 5 (As per IS-13920 / IS 1893) as I would like to detail it as OMRF instead of SMRF.
The reasons for taking RRF as 3 are:
1)  In normal conditions, most of our buildings are at the mercy of the labourers or labour contractor and his Site supervisor, who are just ignorant of our IS Codal provisions. If I start giving different spacings of shear reinforcement in beams, it is difficult to execute correctly at site. Hence If I detail the beams in the normal way (as per SP-34) I can effectively control and ensure the correct execution.
2)  The steel quantity consumed will be less in case RRF is taken as 5, but it has be provided judiously at the locations as specified in the code. Instead of taking the advantage of Reduced Steel consumption, I prefer to go by normal detailing (SP-34) and ensure the correct execution.

My question to all members is:

Whether it is reasonable to violate the IS 1893 or IS 13920 in considering RRF as 3 in place of 5,  since the structure is located in Zone-III
(or)
Shall I have to follow the IS 13920 and consider RRF as 5 with confined steel and follow the size of members keeping the aspect ratio as laid in code.


Thanking you in advance

K.Krishna Kishore
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View user's profile Send private message
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