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Tall Building Design :: Tension Column

 
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bijay sarkar
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Joined: 14 Dec 2009
Posts: 314

PostPosted: Mon Dec 03, 2012 3:04 pm    Post subject: Tall Building Design :: Tension Column Reply with quote

Dear All,

IS 456 : 2000 is silent regarding design parameters of columns under tension along with biaxial moments. SP-16 has provided some interaction graphs, but has specifically mentioned that the graphs have not considered crack control.

In tall buildings, tension columns are inevitable. On previous occasion also, this question was raised in Sefi, but there was no reply. When thinking about tall buildings in India, discussion on this subject may also be covered.

with regards,

bijay sarkar
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gautam chattopadhyay
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Joined: 17 Feb 2009
Posts: 128

PostPosted: Tue Dec 04, 2012 5:05 am    Post subject: Tall Building Design :: Tension Column Reply with quote

Mr. Sarkar, I fully subscribe to your thought that SP 16 while processing interaction charts for columns under axial tension and bi axial bending has not considered the parameters of crack. SP 16 has provided charts for Limit state of collapse and not at SLS. Well, when a section is subjected to axial tension and bi axial moment there must develop a zone which will remain under compression. It should be noted that concrete in tension is primarily cracked and there is no SLS design in this regard. In Reynold's handbook (10th edition alongwith Steedman) some working stress design (modular ratio method) is mentioned but crack control criterion is avoided there also. It is probably because we do not consider concrete to be effective in tension. Hence concrete under tension and moment should be considered to be cracked at first place.

On Mon, Dec 3, 2012 at 8:34 PM, bijay sarkar <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear All,

IS 456 : 2000 is silent regarding design parameters of columns under tension along with biaxial moments. SP-16 has provided some interaction graphs, but has specifically mentioned that the graphs have not considered crack control.

In tall buildings, tension columns are inevitable. On previous occasion also, this question was raised in Sefi, but there was no reply. When thinking about tall buildings in India, discussion on this subject may please be made.

with regards,

bijay sarkar
     



     


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bijay sarkar
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Joined: 14 Dec 2009
Posts: 314

PostPosted: Tue Dec 04, 2012 9:32 am    Post subject: Reply with quote

Dear Sir,

If direct tension is higher than bending compression, there may be no compression on the section.

Again, considering that crack control is neglected and we read the moment capacities from the given charts of SP-16.  Now we require the interaction equation to be used for biaxial check. The Power, Alpha_n to be used in the interaction equation as given in SP-16 is based on Pu & Puz which are compressive loads. Is it that the same Alpha_n shall be used for Tension columns also ?

What is presently being done ? Provided by softwares ?

with regards,

bijay sarkar
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