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IS 800-2007 for tall buildings
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krane
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PostPosted: Sat Dec 01, 2012 10:20 am    Post subject: IS 800-2007 for tall buildings Reply with quote

Dear Yogesh Sir, Thank you very much for your detailed reply. I would like to add few more points here...1. Capacity based design may result in more than 20%, because here the capacity is based on elastic or plastic limit. We have designed one power plant bldg. wherein connection % was close to 50%. 2. As you mentioned we need to closely study AISC code in order to use IS code, but IS code is actually based on Euro 3. Please clarify. 3. If we refer AISC code, it is very clear in defining high seismic and low seismic categories and have linked response reduction factor for the same. However, IS code is not at all clear on this. I heard that few people from IITs are thinking of bringing SP series handbook soon on this. However it may be too late, because by the time SP comes out, so many buildings would have been already build with lot of unclarity which might be unsafe or very uneconomical. 4. Tall buildings is the current trend in India. Practicing engineers needs absolute clarity while designing. In such scenario its very difficult for practicing structural engineers to take appropriate decision on this. Please share your views. Regards, K Rane Sent from BlackBerry® on Airtel
From: "Yogesh.Pisal" <forum@sefindia.org>
Date: Sat, 01 Dec 2012 09:58:38 +0530
To: <econf34289@sefindia.org>
ReplyTo: econf34289@sefindia.org
Subject: [E-CONF] Re: IS 800-2007 for tall buildings

     Dear Er Krane,  We have implemented IS800: 2007 in our design for industrial structures. I think there should not be any harm in implementing the same for the Tall buildings also.   One really need to closely study AISC to interprete IS800 2007 correctly. Following are some of the points.   1. Vertical bracing configuration: Indian code has very limited / generalized provisions - One has to closely interact with AISC before finalizating the design. Further, we need to go for X-bracing or double storey X-bracing or Zipper columns.   2. Utilization ratio - If we will be keeping margin in our design of members then it will result into the higher consumption of material into the connection. Main reason - Our conenctions are based on capacity instead of actual forces.   3. Design of base plates specially for braced frames: Its always debatable to design the base plate for capacity. But, one need to finalize the philosophy very carefully. e.g. Mainly in the braced frame we should design the base plates for the braced bays for the capacity.   4. Optimization - It is expected by most of engineers that IS800 2007 will result into the lower consumption of steel. But, it is incorrect to conclude the same. Further, consumption of material in connection can be as high as 18 to 20% instead of 10 to 12% as per previsous code. Hence, it is really difficult to have overall economy, but definitely we will be having more safely.  Further, I personally feel that - In no case we should not use IS800 1984.  Regards, Yogesh Pisal
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Yogesh.Pisal
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PostPosted: Sat Dec 01, 2012 1:09 pm    Post subject: Reply with quote

Dear K Rane Sir,

You are right, IS800:2007 is based on BS5950. But, when it comes to Chapter 12 : I feel AISC 341 is more relevant.

Already there is a manual on IS 800:2007 by INSDAG costing around Rs 5000. It is very good reference manual, but nothing has been specified about the implementation of Chapter 12.

I too feel the urgent need of Explaination manual / commentary specially on Chapter 12. In our case, we are quite lucky because our client was flexible enough to give liberty to follow provisions of AISC 341 wherever there is doubt about Chapter 12 provisions.

Regards,
Yogesh Pisal
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Dr. N. Subramanian
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PostPosted: Sat Dec 01, 2012 6:38 pm    Post subject: Re: IS 800-2007 for tall buildings Reply with quote

Dear Er Rane,

You are right.BIS takes lot of time to publish the codes. by the time the SP is published, lot of constructions would have completed. But as steel is used in our country mainly in industrial sheds, the dead weight will not be high and they may not be governed by EQ forces! High rise buildings or other heavy buildings of course will be affected.

Note that IS 800 has only one chapter on earthquake resistant design, whereas AISC has a separate code complete with commentary. Hence the provisions are exhaustive. I hastened to add that in other situations, IS 800 is adequate, though a few explanations and commentary is necessary- especially in deflection provisions.

Buildings designed with old versions of IS 800 may be adequate in most of the cases. But will not provide consistent FOS in al, loading cases.

Best wishes
NS
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krane
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PostPosted: Sat Dec 01, 2012 8:24 pm    Post subject: IS 800-2007 for tall buildings Reply with quote

Dear Subramanian Sir, Although this code on board, usage of the same is limited and that too with lot relaxation due no economy. This is actually driven by customers when they see uneconomy over old code. Structual engineers have no choice left but to satisfy customers. Another reason probably government doesn't foce the design or its approval thr latest codes. I guess in US, it is more of a mandatory requirement. This situation is alarming and may lead to disaster in future. Reg,K RaneSent from BlackBerry® on Airtel
From: "Dr. N. Subramanian" <forum@sefindia.org>
Date: Fri, 30 Nov 2012 19:05:07 +0530
To: <econf34289@sefindia.org>
ReplyTo: econf34289@sefindia.org
Subject: [E-CONF] Re: IS 800-2007 for tall buildings

     Dear Er Sriprakash,  I appreciate your points. We have already discussed about this in ourvregular forum and many have written that the code is economical only in a few cases. Limit state method is supposed to provide the required level of safety in all load cases, which is doubtful while using WSD. Hence the main point here is safety and not economy, though it is also imp.  IS 800 was revised after about 25 years! It is now on bar with other international code. Of course AISC still used WSD but the formulae have been modified to give uniform results in both the cases. It uses LSD also. Thus the designer has the choice to use both.   Regards, NS         sriprakash_shastry wrote:                Dear Mr. Krane,  I dont know if someone would have implemented the new code for tall buildings and I very much doubt it. However, one thing is to be kept in mind. THe new code is no magic compared to the old code. The designer is not going to be saving 20% on structural steel tonnage just by using the new code. THe old code had a lower Yield Stress and serviceability combinations for design whereas in the new code we are using Ultimate Stress and also increasing the loading with a factor of 1.5.   So one cannot expect magic to happen. In our comparisons we have seen that the maximum savings we get are to the tune of about 8% between the 2 codes.  With regard to the use of the new code in tall buildings one has to be extremely careful. There are so many conditions and stipulations for every aspect of design. I think the engineer has to know the code thoroughly before taking the leap into using this code for tall structures.  Warm Regards, Sriprakash     
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Dr. N. Subramanian
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PostPosted: Sun Dec 02, 2012 7:30 pm    Post subject: Re: IS 800-2007 for tall buildings Reply with quote

Dear Er Rane,

I have seen Govt. Dept. documents which insist on Latest version of Indian codes.

Safety is more imp. than economy. I now remember a cartoon which appeared in an IABSE paper long ago, showing a lion being tied by a thin rope, to show that safety is imp. than economy.

Best wishes,

NS

krane wrote:
Dear Subramanian Sir, Although this code on board, usage of the same is limited and that too with lot relaxation due no economy. This is actually driven by customers when they see uneconomy over old code. Structual engineers have no choice left but to satisfy customers. Another reason probably government doesn't foce the design or its approval thr latest codes. I guess in US, it is more of a mandatory requirement. This situation is alarming and may lead to disaster in future. Reg,K RaneSent from BlackBerry® on Airtel
From: "Dr. N. Subramanian" <forum>
Date: Fri, 30 Nov 2012 19:05:07 +0530
To: <econf34289>
ReplyTo: econf34289@sefindia.org
Subject: [E-CONF] Re: IS 800-2007 for tall buildings

     Dear Er Sriprakash,  I appreciate your points. We have already discussed about this in ourvregular forum and many have written that the code is economical only in a few cases. Limit state method is supposed to provide the required level of safety in all load cases, which is doubtful while using WSD. Hence the main point here is safety and not economy, though it is also imp.  IS 800 was revised after about 25 years! It is now on bar with other international code. Of course AISC still used WSD but the formulae have been modified to give uniform results in both the cases. It uses LSD also. Thus the designer has the choice to use both.   Regards, NS         sriprakash_shastry wrote:                Dear Mr. Krane,  I dont know if someone would have implemented the new code for tall buildings and I very much doubt it. However, one thing is to be kept in mind. THe new code is no magic compared to the old code. The designer is not going to be saving 20% on structural steel tonnage just by using the new code. THe old code had a lower Yield Stress and serviceability combinations for design whereas in the new code we are using Ultimate Stress and also increasing the loading with a factor of 1.5.   So one cannot expect magic to happen. In our comparisons we have seen that the maximum savings we get are to the tune of about 8% between the 2 codes.  With regard to the use of the new code in tall buildings one has to be extremely careful. There are so many conditions and stipulations for every aspect of design. I think the engineer has to know the code thoroughly before taking the leap into using this code for tall structures.  Warm Regards, Sriprakash     
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