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sukanta.adhikari General Sponsor
Joined: 26 Jan 2003 Posts: 704

Posted: Tue Sep 18, 2012 5:12 am Post subject: Deflection of RCC beams 


Dear All,
When it comes to deflection check for a reinforced concrete beam we have total deflection as sum of short term and long term(creep and shrinkage) deflection..the calculation of short term deflection makes use of effective moment of inertia of the section...
When it comes to commercial software does any of the software calculates short term and long term deflection...in my knowledge STAAD does not calculates the short term and long term deflection...what about other software.
Regards,
S Adhikari 

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Dr. N. Subramanian General Sponsor
Joined: 21 Feb 2008 Posts: 5288 Location: Gaithersburg, MD, U.S.A.

Posted: Tue Sep 18, 2012 3:53 pm Post subject: Re: Deflection of RCC beams 


Dear Er Adhikari,
Most of the software check only short term deflection. Deflection of concrete members is also a subject under constant research. The monumental work done by Branson resulted in the excellent text book published in 1977 by McGraw Hill ( Branson, D.E., Deformation of Concrete Structures, McGrawHill, New York, 1977, 546 pp.) His research is still the basis of ACI code.
Several other researchers like Prof. Gilbert of Australia, Prof. Bischoff of Canada and Prof. A. Scanlon have done recent research on deflection and based on that Canadian and Australian code formlae have changed. You may read the following references:
 Gardner N.J., Span/thickness limits for deflection control, ACI Structural Journal, Vol. 108, No.4, JulyAug. 2011, pp. 453 460.
 Gilbert, R.I., Shrinkage, cracking and deflectionthe serviceability of concrete structures, Electronic Journal of Structural Engineering, Vol. 1, No. 1, 2001, pp. 214 (http://www.ejse.org/Archives/Fulltext/200101/02/20010102.htm)
 Gilbert, R.I., and A. Kilpatrick, Improved predictions of the longterm deflections of RC flexural members, Proceedings of the FIB Symposium, Prague, 2011, pp. 187190 (http://ww2.integer.it/Web_1/database_locale/Fib%20Praga_2011/pdf/030%20596%20065%201%20Gilbert%20SE.pdf)
 Gilbert, R.I., and G. Ranzi, Time Dependent Behaviour of Concrete Structures, Taylor & Francis, London, 2010, 426 pp
 Bischoff, P.H., Reevaluation of deflection prediction for concrete beams reinforced with steel and fiber reinforced polymer bars, Journal of Structural Engineering, ASCE, May 2005, pp. 752–767, and Discussion by Gilbert, R.I., Vol. 132, No. 8, Aug. 2006, pp. 13281330.

 Bischoff, P. H. and A. Scanlon, Spandepth ratios for oneway members based on ACI 318 deflection limits, ACI Structural Journal, Vol. 106, No. 5, Sept.Oct. 2009, pp. 617626.
I feel that the serviceability limit states like deflection, cracking, vibration, etc are not given enough importance, especially in India!
Regards,
Subramanian
sukanta.adhikari wrote:  Dear All,
When it comes to deflection check for a reinforced concrete beam we have total deflection as sum of short term and long term(creep and shrinkage) deflection..the calculation of short term deflection makes use of effective moment of inertia of the section...
When it comes to commercial software does any of the software calculates short term and long term deflection...in my knowledge STAAD does not calculates the short term and long term deflection...what about other software.
Regards,
S Adhikari 


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sukanta.adhikari General Sponsor
Joined: 26 Jan 2003 Posts: 704

Posted: Tue Sep 18, 2012 5:29 pm Post subject: Re: Deflection of RCC beams 


Respected NS,
I agree with you that serviceability limit state is not given much importance here.
But even short term deflection is not calculated by many softwares..
Regards,
S Adhikari
Dr. N. Subramanian wrote:  Dear Er Adhikari,
Most of the software check only short term deflection. Deflection of concrete members is also a subject under constant research. The monumental work done by Branson resulted in the excellent text book published in 1977 by McGraw Hill ( Branson, D.E., Deformation of Concrete Structures, McGrawHill, New York, 1977, 546 pp.) His research is still the basis of ACI code.
Several other researchers like Prof. Gilbert of Australia, Prof. Bischoff of Canada and Prof. A. Scanlon have done recent research on deflection and based on that Canadian and Australian code formlae have changed. You may read the following references:
 Gardner N.J., Span/thickness limits for deflection control, ACI Structural Journal, Vol. 108, No.4, JulyAug. 2011, pp. 453 460.
 Gilbert, R.I., Shrinkage, cracking and deflectionthe serviceability of concrete structures, Electronic Journal of Structural Engineering, Vol. 1, No. 1, 2001, pp. 214 (http://www.ejse.org/Archives/Fulltext/200101/02/20010102.htm)
 Gilbert, R.I., and A. Kilpatrick, Improved predictions of the longterm deflections of RC flexural members, Proceedings of the FIB Symposium, Prague, 2011, pp. 187190 (http://ww2.integer.it/Web_1/database_locale/Fib%20Praga_2011/pdf/030%20596%20065%201%20Gilbert%20SE.pdf)
 Gilbert, R.I., and G. Ranzi, Time Dependent Behaviour of Concrete Structures, Taylor & Francis, London, 2010, 426 pp
 Bischoff, P.H., Reevaluation of deflection prediction for concrete beams reinforced with steel and fiber reinforced polymer bars, Journal of Structural Engineering, ASCE, May 2005, pp. 752–767, and Discussion by Gilbert, R.I., Vol. 132, No. 8, Aug. 2006, pp. 13281330.

 Bischoff, P. H. and A. Scanlon, Spandepth ratios for oneway members based on ACI 318 deflection limits, ACI Structural Journal, Vol. 106, No. 5, Sept.Oct. 2009, pp. 617626.
I feel that the serviceability limit states like deflection, cracking, vibration, etc are not given enough importance, especially in India!
Regards,
Subramanian
sukanta.adhikari wrote:  Dear All,
When it comes to deflection check for a reinforced concrete beam we have total deflection as sum of short term and long term(creep and shrinkage) deflection..the calculation of short term deflection makes use of effective moment of inertia of the section...
When it comes to commercial software does any of the software calculates short term and long term deflection...in my knowledge STAAD does not calculates the short term and long term deflection...what about other software.
Regards,
S Adhikari 



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Dr. N. Subramanian General Sponsor
Joined: 21 Feb 2008 Posts: 5288 Location: Gaithersburg, MD, U.S.A.

Posted: Tue Sep 18, 2012 5:40 pm Post subject: Re: Deflection of RCC beams 


Dear Er Adhikari,
As you are aware if the L/d ratio is within the code permissible limits (Canadian and ACI codes have better equations), there is no need to check short term deflection.
Having said that, I want to emphasize that in long Cantilever beams, say > 3 m, it is better to check long term deflection as due to creep of sustained loading the long term deflection may be 2 to 3 times the short term deflection.
Regards,
NS
sukanta.adhikari wrote:  Respected NS,
I agree with you that serviceability limit state is not given much importance here.
But even short term deflection is not calculated by many softwares..
Regards,
S Adhikari
Dr. N. Subramanian wrote:  Dear Er Adhikari,
Most of the software check only short term deflection. Deflection of concrete members is also a subject under constant research. The monumental work done by Branson resulted in the excellent text book published in 1977 by McGraw Hill ( Branson, D.E., Deformation of Concrete Structures, McGrawHill, New York, 1977, 546 pp.) His research is still the basis of ACI code.
Several other researchers like Prof. Gilbert of Australia, Prof. Bischoff of Canada and Prof. A. Scanlon have done recent research on deflection and based on that Canadian and Australian code formlae have changed. You may read the following references:
 Gardner N.J., Span/thickness limits for deflection control, ACI Structural Journal, Vol. 108, No.4, JulyAug. 2011, pp. 453 460.
 Gilbert, R.I., Shrinkage, cracking and deflectionthe serviceability of concrete structures, Electronic Journal of Structural Engineering, Vol. 1, No. 1, 2001, pp. 214 (http://www.ejse.org/Archives/Fulltext/200101/02/20010102.htm)
 Gilbert, R.I., and A. Kilpatrick, Improved predictions of the longterm deflections of RC flexural members, Proceedings of the FIB Symposium, Prague, 2011, pp. 187190 (http://ww2.integer.it/Web_1/database_locale/Fib%20Praga_2011/pdf/030%20596%20065%201%20Gilbert%20SE.pdf)
 Gilbert, R.I., and G. Ranzi, Time Dependent Behaviour of Concrete Structures, Taylor & Francis, London, 2010, 426 pp
 Bischoff, P.H., Reevaluation of deflection prediction for concrete beams reinforced with steel and fiber reinforced polymer bars, Journal of Structural Engineering, ASCE, May 2005, pp. 752–767, and Discussion by Gilbert, R.I., Vol. 132, No. 8, Aug. 2006, pp. 13281330.

 Bischoff, P. H. and A. Scanlon, Spandepth ratios for oneway members based on ACI 318 deflection limits, ACI Structural Journal, Vol. 106, No. 5, Sept.Oct. 2009, pp. 617626.
I feel that the serviceability limit states like deflection, cracking, vibration, etc are not given enough importance, especially in India!
Regards,
Subramanian
sukanta.adhikari wrote:  Dear All,
When it comes to deflection check for a reinforced concrete beam we have total deflection as sum of short term and long term(creep and shrinkage) deflection..the calculation of short term deflection makes use of effective moment of inertia of the section...
When it comes to commercial software does any of the software calculates short term and long term deflection...in my knowledge STAAD does not calculates the short term and long term deflection...what about other software.
Regards,
S Adhikari 




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es_jayakumar General Sponsor
Joined: 24 Nov 2011 Posts: 1164 Location: Cochin

Posted: Thu Jun 20, 2013 2:35 pm Post subject: 


Sir,
The attached drawing is that of a portion of a multistoreyed building RCC frame, in plan. The internal transverse beam is just below 10m in length and two secondary beams frame into it as a grid. The size of the beam is 450mmx650mm. What method should be adopted to check deflection of this beam ? The deflection value obtained from STAAD is within 40mm (L/250). Is it necessary to calculate long term deflection also, in this case ?
Regards,
E S Jayakumar 

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Dr. N. Subramanian General Sponsor
Joined: 21 Feb 2008 Posts: 5288 Location: Gaithersburg, MD, U.S.A.

Posted: Thu Jun 20, 2013 2:56 pm Post subject: 


es_jayakumar wrote:  Sir,
The attached drawing is that of a portion of a multistoreyed building RCC frame, in plan. The internal transverse beam is just below 10m in length and two secondary beams frame into it as a grid. The size of the beam is 450mmx650mm. What method should be adopted to check deflection of this beam ? The deflection value obtained from STAAD is within 40mm (L/250). Is it necessary to calculate long term deflection also, in this case ?
Regards,
E S Jayakumar 
Dear Er Jayakumar,
In this case it can be analyzed fir deflection purposes as a simply supported beam with a Point load at mid span and udl. Since it is not a cantilever beam, the creep effects will be less. Of course the long term deflection will be greater than short term defln. I think, you need not check for long term defln.
Best wishes,
NS 

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mohanarbat26 SEFI Member
Joined: 01 Mar 2014 Posts: 1

Posted: Fri Feb 10, 2017 10:31 am Post subject: Short and Long Term Deflection Limit for cantilever beam 


Dr. N. Subramanian wrote:  es_jayakumar wrote:  Sir,
The attached drawing is that of a portion of a multistoreyed building RCC frame, in plan. The internal transverse beam is just below 10m in length and two secondary beams frame into it as a grid. The size of the beam is 450mmx650mm. What method should be adopted to check deflection of this beam ? The deflection value obtained from STAAD is within 40mm (L/250). Is it necessary to calculate long term deflection also, in this case ?
Regards,
E S Jayakumar 
Dear Er Jayakumar,
In this case it can be analyzed fir deflection purposes as a simply supported beam with a Point load at mid span and udl. Since it is not a cantilever beam, the creep effects will be less. Of course the long term deflection will be greater than short term defln. I think, you need not check for long term defln.
Best wishes,
NS 


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saikiran gone General Sponsor
Joined: 22 Apr 2016 Posts: 214

Posted: Tue Feb 14, 2017 7:27 am Post subject: Re: Deflection of RCC beams 


sukanta.adhikari wrote:  Respected NS,
I agree with you that serviceability limit state is not given much importance here.
But even short term deflection is not calculated by many softwares..
Regards,
S Adhikari
Dr. N. Subramanian wrote:  Dear Er Adhikari,
Most of the software check only short term deflection. Deflection of concrete members is also a subject under constant research. The monumental work done by Branson resulted in the excellent text book published in 1977 by McGraw Hill ( Branson, D.E., Deformation of Concrete Structures, McGrawHill, New York, 1977, 546 pp.) His research is still the basis of ACI code.
Several other researchers like Prof. Gilbert of Australia, Prof. Bischoff of Canada and Prof. A. Scanlon have done recent research on deflection and based on that Canadian and Australian code formlae have changed. You may read the following references:
 Gardner N.J., Span/thickness limits for deflection control, ACI Structural Journal, Vol. 108, No.4, JulyAug. 2011, pp. 453 460.
 Gilbert, R.I., Shrinkage, cracking and deflectionthe serviceability of concrete structures, Electronic Journal of Structural Engineering, Vol. 1, No. 1, 2001, pp. 214 (http://www.ejse.org/Archives/Fulltext/200101/02/20010102.htm)
 Gilbert, R.I., and A. Kilpatrick, Improved predictions of the longterm deflections of RC flexural members, Proceedings of the FIB Symposium, Prague, 2011, pp. 187190 (http://ww2.integer.it/Web_1/database_locale/Fib%20Praga_2011/pdf/030%20596%20065%201%20Gilbert%20SE.pdf)
 Gilbert, R.I., and G. Ranzi, Time Dependent Behaviour of Concrete Structures, Taylor & Francis, London, 2010, 426 pp
 Bischoff, P.H., Reevaluation of deflection prediction for concrete beams reinforced with steel and fiber reinforced polymer bars, Journal of Structural Engineering, ASCE, May 2005, pp. 752–767, and Discussion by Gilbert, R.I., Vol. 132, No. 8, Aug. 2006, pp. 13281330.

 Bischoff, P. H. and A. Scanlon, Spandepth ratios for oneway members based on ACI 318 deflection limits, ACI Structural Journal, Vol. 106, No. 5, Sept.Oct. 2009, pp. 617626.
I feel that the serviceability limit states like deflection, cracking, vibration, etc are not given enough importance, especially in India!
Regards,
Subramanian
sukanta.adhikari wrote:  Dear All,
When it comes to deflection check for a reinforced concrete beam we have total deflection as sum of short term and long term(creep and shrinkage) deflection..the calculation of short term deflection makes use of effective moment of inertia of the section...
When it comes to commercial software does any of the software calculates short term and long term deflection...in my knowledge STAAD does not calculates the short term and long term deflection...what about other software.
Regards,
S Adhikari 


Hi Adhikari sir,
Staad software will calculate the deflection (Only short term/first order). Later designer turn to check the deflected values are within the limmit or not.
With Best,
Saikiran Gone. 

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