RCC Beams
RCC beams are cast in cement concrete reinforced with steel bars. Beams take up compressive and add rigidity to the structure.
Beams generally carry vertical gravitational forces but can also be used to carry horizontal loads (i.e., loads due to an earthquake or wind). The loads carried by a beam are transferred to columns, walls, or girders, which then transfer the force to adjacent structural compression members. In Light frame construction the joists rest on the beam.
Doubly Reinforced Beam
In this article, we are going to discuss types of beam construction and RCC design of Doubly reinforced beam…
RCC beam construction is of two types:
- Singly reinforced beam
- Doubly reinforced beam
Singly reinforced beam
A singly reinforced beam is a beam provided with longitudinal reinforcement in the tension zone only.
Doubly reinforced beam
- Beams reinforced with steel in compression and tension zones are called doubly reinforced beams. This type of beam will be found necessary when due to head room consideration or architectural consideration the depth of the beam is restricted.
- The beam with its limited depth, if reinforced on the tension side only, may not have enough moment of resistance, to resist the bending moment.
- By increasing the quantity of steel in the tension zone, the moment of resistance cannot be increased indefinitely. Usually, the moment of resistance can be increased by not more than 25% over the balanced moment of resistance, by making the beam over-reinforced on the tension side.
- Hence, inorder to further increase the moment of resistance of a beam section of unlimited dimensions, a doubly reinforced beam is provided.
Besides, this doubly reinforced beam is also used in the following circumstances:
- The external live loads may alternate i.e. may occur on either face of the member.
For example:
- A pile may be lifted in such a manner that the tension and compression zones may alternate.
- The loading may be eccentric and the eccentricity of the load may change from one side of the axis to another side.
- The member may be subjected to a shock or impact or accidental lateral thrust.
Design procedure for doubly reinforced beam
Step 1
Determine the limiting moment of resistance for the given c/s(Mulim) using the equation for singly reinforced beam
Mulim = 0.87.fy.Ast1.d [1 – 0.42Xumax]
Or
Balanced section
Ast1 = (0.36.fck.b.Xumax)/(0.87fy)
Step 2
If factored moment Mu > Mulim, then doubly reinforced beam is required to be designed for additional moment.
Mu – Mulim = fsc.Asc (d – d’) [fsc value from page no. 70]
Step 3
Additional area of tension steel Ast2
Ast2 =Asc.fsc/0.87fy
Step 4
Total tension steel Ast, Ast = Ast1 + Ast2
#1 by seetharaman on July 4, 2010 - 12:02 am
If the stress in steel in the compression zone is less than yield value, SP 16 gives a table relating strain and stresses. Is there an expression relating that strain and the corresponding stresses? Surely the values have been obtained from the accompanying graph in SP 16. From an examination point of view, how to get that table by calculation?
#2 by G.JAGAN on July 6, 2010 - 8:47 pm
its good
#3 by Bhabani sankar nahak on October 3, 2010 - 6:38 am
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#4 by Ashok on October 12, 2010 - 1:12 pm
Is this design based on ACI 318-05 code?
#5 by BenzuJK on October 13, 2010 - 11:29 am
Hello,
I am not very familiar with ACI 318-05 code. This design theory is based on Indian Standard code (IS-456-2000). But the IS code has been updated as per the standards that are recommended in the ACI 318-05 code.
#6 by suresh pujari on November 18, 2011 - 2:45 am
i agree with this answer
#7 by ravindra kumar goyal on October 27, 2010 - 6:56 am
this is the best website for all civil engineers
#8 by ravisankar on December 2, 2010 - 5:41 am
dear sir/madam,
can u pls send me ” what are the tips and conditions (limitations) used in the designs of rcc structural elements like beams, columns, slabs, footings etc”. And also the procedure steps as per codal of IS: 456-2000.
#9 by Sudhir on December 12, 2010 - 3:58 am
It is very usefull to the learned students and teaches too.pl.updadate time to time and give more examples for practice.
#10 by Anandan.S on December 16, 2010 - 3:09 am
Hi everybody this site is very useful for all civil engineers
#11 by Rahul Rajbhar on December 27, 2010 - 8:29 pm
i am setisfied this theory because my institute`s teacher also use this theory to explain the all related problems
#12 by Anil kumar gupta on January 6, 2011 - 4:09 am
dear sir/madam,
can u pls send me ” what are the tips and conditions (limitations) used in the designs of rcc structural elements like beams, columns, slabs, footings and also give the step by step designing procedure of these elemant with an suitable example as per IS:456-2000”.
#13 by adil on January 25, 2011 - 6:29 am
dear sir/madam,
can u pls send me ” what are the tips and conditions (limitations) used in the designs of rcc structural elements like beams, columns, slabs, footings and also give the step by step designing procedure of these elemant with an suitable example as per IS:456-2000”.
#14 by adil on January 25, 2011 - 6:36 am
please send step by step procedure of rcc design residential building with example and also designing formula sheet.
#15 by BenzuJK on February 3, 2011 - 10:21 am
Addition of formula sheets and more numericals regarding Structural Design will be done in my succeeding articles…
#16 by Amar Pakale on January 31, 2011 - 1:59 am
please send step by step procedure of rcc design of footing ,column,beam,slab for residential building with example and also designing formula sheet.
#17 by prasad on February 8, 2011 - 1:32 am
can u help me how to draw the reinforcement details for slab(1 & two way….)
#18 by palaprasanna on February 14, 2011 - 1:44 am
please seand in civil is codes and rcc footing, column beams slab and rainforcement concret,and structural design and formula sheet
#19 by subramani on February 24, 2011 - 7:51 pm
sir,we have started a excavation of earth for new construction of house.west facing house.i need help how to design a two way slab for 3 floor residential building.site dimension(w 15′x48′).
#20 by suresh kumar on February 28, 2011 - 6:33 am
sir, i started new construction. site dimensions are 18′x36′ having east facing. i need the formula for column and beam designing. also need the formula between two column.
#21 by T.S.Janarthanan on March 1, 2011 - 11:52 pm
what is the limitation in % of steel should be use in doubly reinforced beam sections in compression zone, and max layers of steel
if any limitation pl guide the value with ref.,
#22 by Rajkumar on March 12, 2011 - 7:55 pm
Hello everybody,
Looking for a structural design of multistory building, covered area 450 sq. feet (15′ x 30′).
#23 by yogesh on March 19, 2011 - 10:35 pm
sir, i started new construction. site dimensions are 18?x36? having east facing. i need the formula for column and beam designing. also need the formula between two column.
#24 by BenzuJK on March 29, 2011 - 2:15 pm
Please consult a qualified engineer or architect for this. He or she can help you in good planning, optimum use of natural resources, proper column placement, structural design, which will ultimately save you tension and money.
You can contact Architect and Engineer Javed Kachchhi. He is a renowned specialist in the field. Check it out.
http://www.architectjaved.com
Cheers!
#25 by Brijkishore Singh Thakur on August 2, 2011 - 10:34 am
can you explain me detail step by step procedure for designing a building
#26 by BenzuJK on August 4, 2011 - 2:19 am
Check them out. These articles could be of help to you…
Design of Foundations
Design of Beams
Design of columns
Design of staircase
Design of Simply supported slab
Design of Sunken slab
Cheers
#27 by dramachandran on April 26, 2011 - 7:16 pm
very nicely dealt with re design of doubly reinforced beam…..but steel beam theory also is a mode where steel area in tension zone is equal to that in compression zone …otherwise we have take moment of the areas with respect to NA which may shift up or down depending on over or under reinforced design… am i right ..pl post reply for further knowledge..
i have more than 40 yrs service since graduation from UNIVERSITY Of MADRAS
#28 by pancham on June 11, 2011 - 2:16 am
hey i want to know about charectristic strength of hollow concrete any one know plz tell me..?
#29 by BenzuJK on June 17, 2011 - 12:00 am
Hello Pancham,
The average compressive strength of a hollow concrete block is 5N/mm2.
#30 by Jitendra kumar on June 26, 2011 - 7:42 am
hey iwant to know about max tensile load on a singly reinforced beam?
#31 by AYUSH AGARWAL on September 18, 2011 - 11:09 am
i like the concept………………….its easy to understand……….!!!!!!
#32 by abdullah on September 25, 2011 - 1:47 pm
u can find almost evey solution in it
#33 by RAJESH on November 6, 2011 - 7:34 am
please add problems of design of RC beams and slabs as per IS 456:2000. The process of design in detail with diagrams.
#34 by BenzuJK on November 12, 2011 - 9:49 am
Hello Rajesh,
We will see to it that problems for design of RCC beams are put up on site. Thank you for your feedback.
Cheers
#35 by mohamed azhar on November 21, 2011 - 3:39 am
thanks, it was nice to revisit the tecnicalities of designs of stucture after long time, being civil engineers we often tend to forget the basics due to the practice which go arround. looking forward for more.
#36 by ws on January 19, 2012 - 6:21 am
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