Guide to Doubly Reinforced RCC Beam Design

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RCC Beams

RCC beams are cast in cement concrete reinforced with steel bars. Beams resist compression and tensile forces 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
Doubly Reinforced Beam

In this article, we are going to discuss types of beam construction and RCC design of simply supportedreinforced beam.

Simply supported 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. Compressive forces are handled by the concrete in the beam.

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, in order 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

69 thoughts on “Guide to Doubly Reinforced RCC Beam Design”

  1. 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?

    • 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. 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.

  10. 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”.

  11. 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”.

  16. 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′).

  17. 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.

  18. 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.,

  20. 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. 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

  24. Hey,

    I am planning to build my house in which ,I need a column and beam design,which can support the slab spread over about 18 feet,also I like to use only two columns which starts from 1st feet and another in 18th feet,the beams in between this columns has been killing my mind,need help.
    This house will be ground +2 floors.

    • Hello Dhanasekar,

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  28. 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.

  32. Dear sir/madam
    i have single storey house of 200 meter side walls are 9 inches thicks and inner walls are 4 inches. There are no beams and columns of iron bars with cement and artfical beams. i want to construct two more storeys on it and i want to construct beams and columns lthough for that i have to break the walls which will exceed my cost.what should i do without breaking walls i can put beams and columns or i cam construct without these kindly suggest regards

  33. hey can u tell me how design a continous beam with load calculations bcz in practical continous beams are to be designed na

    And Please also tell me to calculate breadth & depth for beam ,slab & coloumn

  34. Dear Sir/ Madam,

    With reference to the subject “RESIDUAL STRENGTH OF CORROSION DAMAGED CONCRETE STRUCTURES”
    Where can I able to get M30 grade concrete compressive strength test for corrosion damage.
    For example, an experiment which someone might have carried out for a particular type of beam section. The first set of specimens shows results for what is the strength initially (uncorroded). The second set of specimen shows what is its strength after some corrosion. The next set of specimen shows strength for totally depleted concrete cover. The final set specimens show results on section strength based on reduced bar diameter.

  36. In Doubly REF. beam, 50% of Shear stress is Taken By stirrups and bent-up…. But Now Curtail bars are provided. By decreasing the Spacing of stirrups at joint (it’s also help in horizontal forces)

  37. BenzuJK :
    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.

  38. for an example T-beam girder (in bridges) is designed by limit state method compare with working stress method is there tension reinforcement will be increase or decrease with reason please

    kind regards,
    karthik.c

  41. sir,i want to some question that when we done the select the singly reinforced beam than we make the four steel bar and on these beam provided the compression zone and the tension zone .sir please tell me that when very load come on the load than it will be felldown.

  43. Actually i want to know about 30′ ( clear span ) beam supported by 15” x 15” column having 1.2% of steel for black cotton soil
    please design this beam for a Hotel building with two way slab
    for short span 14’6” ( clear ) and 15’6” long span . I know about this type of design but this time due to confusion please guide me.

  44. 30 ft’ long balcony roof is standing on two rcc pillars on 10 ft’ from both left and right side at the corner in the left side there is brick wall of 9 inch and 4 ft wide and at right corner brick pillar of 9 inch i want to remove one rcc pillar from right side to increase the parking space no load on roof and pillars are supporting only roof some one suggest me for GADER but it will decrease the height of roof from the floor plz suggest best way to remove the pillar with minimum height decrease

  49. I want to calculate the quantity of beam,cloumn,slab,&staircase
    please sen the statement how to calculate the same & thump rule the same
    Thanking you,

    Y.F.
    DDDeshpande

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