www.sefindia.org

STRUCTURAL ENGINEERING FORUM OF INDIA [SEFI]

 Forum SubscriptionsSubscriptions DigestDigest Preferences   FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups  RegisterRegister FAQSecurity Tips FAQDonate
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log in to websiteLog in to websiteLog in to websiteLog in to forum 
Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.

ACI 318-63 Coefficient Method of Slab Design

 
Post new topicReply to topic Thank Post    www.sefindia.org Forum Index -> SEFI General Discussion
View previous topic :: View next topic  
Author Message
engr.alishan
SEFI Member
SEFI Member


Joined: 30 Dec 2013
Posts: 1
Location: Paksitan

PostPosted: Tue Mar 31, 2020 6:08 pm    Post subject: ACI 318-63 Coefficient Method of Slab Design Reply with quote

I have a query regarding manual slab design, whether the co-efficient method of slab design given in ACI 318-63 considers role of supporting beam stiffness? I have gone through the code and could not find that the moment co-efficients are co-related with supporting beam stiffness. But whenever the beam stiffness will be varied, there would certainly be variation of moments in slab determined by aforesaid method in ACI 318-63.

Exceptionally, I have seen somewhere on a webpage that for applicability of co-efficient method of slab design given in ACI 318-63, the slab has to be supported by walls or STIFF BEAMS? The question is again that HOW MUCH STIFF BEAMS??
Back to top
View user's profile Send private message
es_jayakumar
General Sponsor
General Sponsor


Joined: 24 Nov 2011
Posts: 1339
Location: Cochin

PostPosted: Wed Apr 01, 2020 9:37 am    Post subject: Reply with quote

Er. Alishan,
The criteria to ensure stiffness of beams supporting two-way slabs, so that the slab can be designed using the coefficients for slabs on rigid supports, are discussed in the book "Design of Reinforced Concrete Structures" by N.Subramanian (10.4.2) [ Oxford University Press]. The book explains the criteria as per the Swedish Code, as well as the Canadian Code.

E S Jayakumar
Back to top
View user's profile Send private message
es_jayakumar
General Sponsor
General Sponsor


Joined: 24 Nov 2011
Posts: 1339
Location: Cochin

PostPosted: Sat Apr 04, 2020 5:11 am    Post subject: Reply with quote

In continuation to the subject under discussion, I attach an excerpt taken from an Indian book (1984), that has become out of print now. Hope, you will find it useful.

E S Jayakumar



Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.
1.pdf
 Description:

Download
 Filename:  1.pdf
 Filesize:  515.64 KB
 Downloaded:  208 Time(s)

Back to top
View user's profile Send private message
thirumalaichettiar
Silver Sponsor
Silver Sponsor


Joined: 26 Jan 2003
Posts: 3544

PostPosted: Tue Apr 07, 2020 3:46 am    Post subject: Reply with quote

Dear Er.alishan,
Please find the attached pdf in which good explanation for your query is vividly explained.
This page is from my HANDBOOK prepared for my office design purpose.

T.RangaRajan



Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.
REQUIRED STIFFNESS OF BEAM FOR SLAB DESIGN.pdf
 Description:

Download
 Filename:  REQUIRED STIFFNESS OF BEAM FOR SLAB DESIGN.pdf
 Filesize:  355.37 KB
 Downloaded:  173 Time(s)

Back to top
View user's profile Send private message
Dr. N. Subramanian
General Sponsor
General Sponsor


Joined: 21 Feb 2008
Posts: 5384
Location: Gaithersburg, MD, U.S.A.

PostPosted: Tue Apr 07, 2020 5:18 pm    Post subject: Reply with quote

Dear Er Jayakumar

Thank you for pointing out that the situation is explained in Section 10.4.2 of my RC Design book. Not sure whether Er. Alishan of Pakisthan can get a copy of my book-He can order it through Amazan or directly from OUP web site.

Anyway I thank Er Rangarajan (welcome back Sir) for providing his notes which is similar to what is available in my book on this question.

Er. Alishan: Why are you referring a very old version of ACI 318:63? The current version is ACI 318:2019!

Warm regards
Subramanian
es_jayakumar wrote:
Er. Alishan,
The criteria to ensure stiffness of beams supporting two-way slabs, so that the slab can be designed using the coefficients for slabs on rigid supports, are discussed in the book "Design of Reinforced Concrete Structures" by N.Subramanian (10.4.2) [ Oxford University Press]. The book explains the criteria as per the Swedish Code, as well as the Canadian Code.

E S Jayakumar
Back to top
View user's profile Send private message
es_jayakumar
General Sponsor
General Sponsor


Joined: 24 Nov 2011
Posts: 1339
Location: Cochin

PostPosted: Thu Apr 09, 2020 6:20 am    Post subject: Reply with quote

The Codal provisions mentioned above are examined by taking a simple case and analysed using STAAD Pro.
Done inquisitively.
It appears that the Codal provisions (Swedish & Canadian) do not look very convincing to ensure the stiffness of the beam so as to enable it to carry the BM almost entirely, in this study.
Details enclosed.

E S Jayakumar



Warning: Make sure you scan the downloaded attachment with updated antivirus tools  before opening them. They may contain viruses.
Use online scanners
here and here to upload downloaded attachment to check for safety.
Beam Stiffness.rar
 Description:

Download
 Filename:  Beam Stiffness.rar
 Filesize:  43.26 KB
 Downloaded:  115 Time(s)

Back to top
View user's profile Send private message
Dr. N. Subramanian
General Sponsor
General Sponsor


Joined: 21 Feb 2008
Posts: 5384
Location: Gaithersburg, MD, U.S.A.

PostPosted: Thu Apr 09, 2020 3:34 pm    Post subject: Reply with quote

Dear Er Jayakumar


Thanks for doing some work on this and presenting your results. I appreciate it.
I have not yet seen the enclosure. But I always have this doubt. When you are analyzing using the standard program, you are assuming that that the frame is the centerline of columns and beams. But there is a small difference in the centerline of beams and slabs. How will that affect the calculation and behaviour?

We can't simply accept all computer analysis. We need to do some real experiments to find out the behaviour. Computer models should then be developed to predict the experimental behaviour. I hope the Canadian and Swedish code provisions are based on some experiments and not on some computer analysis.

Warm regards
Subramanian


es_jayakumar wrote:
The Codal provisions mentioned above are examined by taking a simple case and analysed using STAAD Pro.
Done inquisitively.
It appears that the Codal provisions (Swedish & Canadian) do not look very convincing to ensure the stiffness of the beam so as to enable it to carry the BM almost entirely, in this study.
Details enclosed.

E S Jayakumar
Back to top
View user's profile Send private message
es_jayakumar
General Sponsor
General Sponsor


Joined: 24 Nov 2011
Posts: 1339
Location: Cochin

PostPosted: Thu Apr 09, 2020 4:48 pm    Post subject: Reply with quote

Dear Sir,
Thanks for your kind words of appreciation. The plate analysis tool in STAAD Pro follows FEM. It can be fairly accurate, except for that :
1.     The analysis does not take into consideration the reinforcement provided in the slab & beam and the cracked property of sections.
2.     The Concrete is assumed to be purely elastic, which is only an approximation.
Experimental investigation will certainly give better results by overcoming the above shortcomings.  I am eager to know how the moment carried by a beam is measured experimentally.
I have a reservation on the Swedish Code method :
Db/Ds more than or equal to 2.5 for r less than or equal to 1.5 and Db/Ds more than or equal to 2.5 r for  r more than 1.5.
Suppose, r = 1.51. For a marginal increase of 0.01 for r, the limiting value for Db/Ds increases from 2.5 (for r= 1.5) to  2.5*r, ie, 2.5*1.51 = 3.78, abruptly, in this case. This sounds illogical. It would have been more logical, if the restrictions were for r less than or equal to 1.0 and r more than 1.0, for the same formulae, where, for r more than 1, the value of Db/Ds will increase smoothly beyond  r=1, without any jerk.

Kind regards,

E S Jayakumar
Back to top
View user's profile Send private message
thirumalaichettiar
Silver Sponsor
Silver Sponsor


Joined: 26 Jan 2003
Posts: 3544

PostPosted: Fri Apr 10, 2020 1:24 am    Post subject: Reply with quote

Er.es.Jeyakumar,
Yes Doctor Subramaniam is correct. Since in computer the modeling is done using c.l and while designing as per IS code the member is designed to the BM value at the face of the support. This is negligible if the width of the support is less but is very high if the support width is more.

In Etabs the value of BM is at the face of the support.

I also done like you long time back with staad.

The Swedish and Canadian formulae are a good guide for the beam sizes.

T.RangaRajan.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topicReply to topic Thank Post    www.sefindia.org Forum Index -> SEFI General Discussion All times are GMT
Page 1 of 1

 

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


© 2003, 2008 SEFINDIA, Indian Domain Registration
Publishing or acceptance of an advertisement is neither a guarantee nor endorsement of the advertiser's product or service. advertisement policy