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JMSSNL at ltecd.ltindi... Guest
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Posted: Wed Oct 15, 2003 10:37 am Post subject: Response reduction factor R |
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Dear All,
While as I agree with Prof. Chandrasekaran's point of allowing larger 'R' value for steel structures, I will like to draw attention to mismatch between IS:800 and IS:1893 in R values.
1. Ordinary moment frames (OMF) per IS:1893 (Table 7 item (1) i) is 3.0. Please read with foot note 20 which states frames detailed per IS:456 or IS:800 , there by meaning this is applicable for steel frames also.
'R' value for similar frame is provided as 4.0 in Table 12.1 Sr no. 2 a) in IS:800 draft.
While as it is understandable that for steel frame 4.0 is more logical value ,per reason cited by Prof. Chandrasekaran below, the appropriate place to define it is IS:1893 using which an engineer determines seismic forces.
Since, IS:1893 is already published , it makes sense to eliminate table 12.1 from IS:800 draft
Thanks,
Jignesh
Quote: | Quote: | Quote: | for_prof_arc@hotmail.com 10/06/03 06:45PM >>>
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| ************************************************* SEFI e-Conference on draft revision of IS:800, October 06 to 18, 2003 *************************************************
Dear Prof. Kalyanraman,
First of all, I would like to congratulate you for opening discussions on draft code IS:800 via web. I do hope such procedure would be followed for other draft codes also which are of interest to members of this forum. Such efforts are all the more necessary as BIS does not respond to requests for drafts meant for wide circulation even to persons like me who were associated with BIS for a very long time.
I feel that IS:800 should have explicit provisions for earthquake effects as IS:1893 is primarily meant for RCC structures. In particular, the punitive clauses of IS:1893 should not be applied to steel structures. The empirical formulae for fundamental period [which is used for defining minimum base shear] is NOT applicable to steel structures.The modelling of steel structures could be far more accurate than RCC structure as the properties of section [EA,EI,GJ]can be accurately determined. Further, it is likely that steel structures would be "an engineered construction" and therefore let the forces as obtained from analysis be taken for design without imposing arbitrary penalties.
There is also a case for larger reduction factors for steel structures as compared to concrete construction !! The reduction factor of 5 is mostly unachievable in RCC whereas it could be achieved in steel. Hence to have overall effective seismic factor [a combination of Z,I,R,T] of the same order, R for steel structure could be larger, say, 5 & 6 instead of 4 & 5.
Some attention may also be given in composite construction in which the vertical elements are mainly steel or steel encased with concrete.
Sincerely, A R Chandrasekaran
******************************************* The views, opinions, analyses and assessments contained herein do not necessarily reflect the views of SEFI. Also SEFI does not guarantee the accuracy of the data included in the proceedings of this e-conference and accepts no responsibility for any consequences of their use. ******************************************* ========powered by Reach1to1 Office Everywhere (http://www.reach1to1.com)======
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