Guide to Design of Simply Supported Slabs | Design of RCC Structures

What are Simply Supported Slabs?

Before we discuss the technical design rules of Simply Supported slabs, lets just go through its definition and learn why they are named so…

As the name suggests, simply supported slabs are supported on columns or stanchions…

Simply Supported Slab

Simply Supported Slab

Simply supported slabs don’t give adequate provision to resist torsion at corner to prevent corner from lifting.

The maximum bending moment will be given if the slabs are restrained. But atleast 50% of the tension reinforcement provided at the mid span should extend to the support. The remaining 50% should extend to within 0.1Lx or Ly at the support as appropriate.

RCC Slab Design depends on the on the dimensions of the slab after which the slab is termed as a one-way slab or a two-way slab…

In the design of RCC structures, Column Design and Beam Design are to be done before we start with RCC Slab Design…

Basic Rules followed in the design of simply supported Slab

Thickness of slab

l/d ratio should be less than the following:

  • Simply supported slab
  • Continuous slab, l/d = 26
  • Cantilever slab, l/d = 7

In any case of the above, the thickness should not be less than 100mm

Effective span

  • Distance between centre to centre of support
  • Clear span plus effective depth

Minimum main reinforcement

  • 0.15% gross c/s of slab – for MS bars
  • 0.12% gross c/s of slab – for HYSD bars

Spacing of main bars

The spacing or c/c distance of main bars shall not exceed following:

  • Calculated value
  • 3d
  • 300mm

Distribution or Temperature reinforcement

This reinforcement runs perpendicular to the main reinforcement in order to distribute the load and to resist the temperature and shrinkage stresses.

It should be atleast equal to;

  • 0.15% gross c/s of slab – for MS bars
  • 0.12% gross c/s of slab – for HYSD bars

Spacing of distribution bars

The spacing or c/c distance of distribution bars shall not exceed the following

  • Calculated area
  • 5d
  • 450mm

Diameter of bars

The diameter of the bars varies from 8mm to 14mm and should not exceed 1/8th of the overall depth of the slab.

For distribution steel, the diameter varies from 6mm to 8mm.


The bottom cover for reinforcement shall not be less than 15mm or less than the diameter of such bar.

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  1. #1 by venkadeshwaran on September 7, 2010 - 8:12 am


  2. #2 by yogesh joshi on January 3, 2011 - 3:00 am


  3. #3 by kishan on January 18, 2011 - 9:00 am

    i shall be thankful to provide guide lines.

  4. #4 by kishan on January 18, 2011 - 9:03 am

    I needed the knowledge of rcc design.

  5. #5 by kishan on January 18, 2011 - 9:07 am

    RCC Design required for project in PHED.

    • #6 by BenzuJK on February 3, 2011 - 10:23 am

      I would be really glad if I could be of some help to you. Send me your details regarding your PHD Project… We shall discuss the project in detail and do the best we can.

      • #7 by Prasanna Kumar on February 1, 2012 - 9:46 pm

        Hi Benzu,
        I have a structural details of the house i am going to construct. I found the structure is heavy.
        Is it possible to suggest whether the structural details are fine for the proposed building?.


  6. #8 by ANIRUDH SHIRKE on January 31, 2011 - 12:20 am


  7. #9 by bral on February 28, 2011 - 3:32 pm

    thanks for guideline.

  8. #10 by VAMSI KRISHNA on March 23, 2011 - 1:20 pm

    I am very much thankful for these guidelines.

  9. #11 by VAMSI KRISHNA on March 23, 2011 - 1:21 pm

    Very nice guidelines.

  10. #12 by Asante John Amoah on March 28, 2011 - 10:23 am

    i need a help about a surveyors role in dumping site of refuse

    • #13 by BenzuJK on March 29, 2011 - 1:52 pm

      I can guess a surveyor can be used in finding and utilizing optimum locations for dumping refuse in a such a way that the space can be reused for dumping in a few months after all the refuse has decomposed, and also ensure water table and surrounding environment remains safe from pollution.

      But I don’t know very much about the subject.


  11. #14 by Rob on May 10, 2011 - 7:10 am

    Thanks for the detailed information — much appreciated!

  12. #15 by Valerie on May 11, 2011 - 3:41 am

    I’ve just discovered this site — so many interesting posts! I’m off to explore some more…

  13. #16 by Ravi on August 17, 2011 - 3:57 am

    can i cast rcc slab on 9″ thk brick wall for room size 12′ x 12′

  14. #17 by dhrudat on August 27, 2011 - 11:58 pm

    hi.i m student of structure engineering if anybody knows about fiber reinforced concrete then please reply me.

  15. #18 by sree on August 31, 2011 - 12:51 am

    I am very much thankful for these guidelines.

  16. #19 by sree on August 31, 2011 - 12:51 am

    I am very much thankful to you for these guidelines.

  17. #20 by omojola benjamin ademola on October 12, 2011 - 12:10 pm

    this is the most complete page for design i therefore recomend it engineer and builder in the house to it for their design

  18. #21 by Dilip W Jadhao on October 25, 2011 - 8:59 pm

    The guideline that you are given which help me lot while designing of slab and other structure.So thanks for such nice guideline

  19. #22 by surender mohan verma on December 6, 2011 - 9:26 pm

    I gave my plot to a builder.aftermaking ground floor a full parkng area. After finding that the colums supportd by tie beams are not placed at the required positions unknowingly, He is suggesting and intends to cast upper floor/first floor by flat beams included in the lentile.Is he doing a right thing? Is it safe as compared to the regular practice(i.e a lentile on columns and tie beams) request advise?

  20. #24 by PRASHANT on January 15, 2012 - 10:15 pm

    thankful for these guidelines.

  21. #25 by kais marmarchi on February 1, 2012 - 6:41 pm

    1. moment in simply supported one-way slab is max at the middle and zero at the supports. my question is why half of the bottom bars are bent up at the supports?
    2. my other question if the slab sits on masonry block wall and a second masonry wall sits on top of the slab coninside with the wall below, will it considered as restrained and required negative bars?

  22. #26 by Rama on February 19, 2012 - 11:38 pm

    Can an RCC slab be extended to some length after the rest of the slab and beams of the apartment has been already casted? if so, how will the joinery be? considering that there wont be any extension of the reinforcement of the existing slab…

  23. #27 by Ajay.N on March 11, 2012 - 1:33 am

    Hi,actually i am preparing report on analysis & design of multistory building with software package. For validation purpose doing manual calculations. I am struck up with load distribution. Please help me out.

  24. #28 by Sanjeev on March 20, 2012 - 4:26 am

    i m going to construct residential building G+1RCC structure in village. Available foundation strata is soil. i considered the following sizes of RCC member & reinforcement
    1) plinth area 6m x 7 m ,01BHK at ground floor & 01 bhk at 1st floor, floor height -floor top to slab top 3.2 m
    2) Excavation depth 1.5 m
    3) size of RCC footing 1m x 1m
    4) depth of RCC footing 200mm vertical & then tappered for 250mm
    5) reinforcement for RCC footing tor steel 10mm, 9nos. of bar bothway.
    6) Reinforcement for column size 230mm x 350mm- Tor steel 12mm, 06nos of bar & stirrups 8mm@ 200mm c/c
    7) Total 09 nos of footing & column @ less than 4m c/c both way & in one line
    8) All the columns connecting by plinth beam of size 230mm x 450 mm.
    9) Reinforcement of plinth beam – Bottom bar of 12mm dia 02nos full length with 300mm bend at both end & 12mm dia 01 curtail bar end at 500mm from both the inner face of end column. Top bar 10mm dia 02 nos full length & 10mm dia bar 02 nos at mid junction of column-beam length equally divided 500mm both side (total length is 1000mm),stirrups 200mmc/c for beam of 8mm dia bar
    10)1st floor slab reinforcement 8mm dia bar 250mm c/c parallel to shorter span & 230mm c/c parellel to longer span with alternet bent-up slab thk 110mm& the same steel for sunken portion of toilet & kitchen
    11) 1st floor & roof beam design same as plinth beam reinforcement details
    12) roof slab slope in two direction towards front & rear with 500 mm projection from external face of periphery wall
    13) Roof slab reinforcement details same as 1st floor slab.
    * I wanted to know whether i can go ahead with this RCC details OR some changes needs to do. if yes then plz suggest.
    * Also i wanted to know for ground floor toilet block is it required to take internal plinth beam to construct 230mm thk. wall for toilet block or can i construct toilet block wall by doing proper soling & PCC of 150 mm thk.
    * Whether i can construct 230 mm thk wall on 1st floor flat portion of slab upto height of 3.2m( portion of slab without beam support)
    *For roof slab is it ok if i construct only periphery beam & slope at two sides from mid of the span(total span is 7.0m)

    Please do the needful

  25. #29 by Sanjeev on March 20, 2012 - 4:31 am

    i m going to use 1:1.5:3 proportion for entire concrete work for this G+1 structure.

  26. #30 by bijay kumar pradhan on March 29, 2012 - 5:42 pm

    Thanks for the web side having verious useful guidelines are thre. I am making house having 970 sq.feet aera(48*20 feet) main rooms covering 400 sq feet were built earlier without columns . while making bounderies I have given columns having 3-4 feet depth and within 12 feets with 10 mm tmt bars. all the columns are joined by foot beams. Now for making 1st floor i have utilised the idle area and making 4*4 columns using 12 mm tmt bars and extending the existing 10 mm columns by using 12 mm bars. Columns are having 4 rods. Can I go for 2nd floor with this structure. Pl. suggest and guide for construction.

  27. #31 by sareenparmod on May 14, 2012 - 11:57 pm

    Informative for students and learners. Thanks and goodluck.

  28. #32 by belinda ashon on July 26, 2012 - 9:12 am

    i will be glad if you show me a full design of a one storey residential building

  29. #33 by Manikandan on August 29, 2012 - 6:03 am

    I am studing :) civil engg:) its help full for ma studies :) thanks and best wishes for ur site

  30. #34 by kavitha on September 5, 2012 - 3:01 am

    HI…………… i m final year student.Its very useful to my design project.SO Thanku very much

  31. #35 by knbs on December 19, 2012 - 6:17 am

    good set of data THANKS

  32. #36 by Fahee Haque on February 6, 2013 - 8:08 pm

    Please send me guide lines regularly for support. Thanks

  33. #37 by Shariful Islam on February 10, 2013 - 7:35 pm

    It will be very helpful for civil Engineer, Thanks

  34. #38 by k on August 22, 2013 - 10:55 pm

    l/d ratio for Rcc girder and PSC girder

  35. #39 by Jerry on April 2, 2014 - 12:13 pm


    Can you please help me I want to buil a 2 storey house 8m x 6mor 48sqm floor area. What Iis he standard column size and the steel dia. Vertical and horizontal and also he beam size and steel bars dia.also the distance stirrups of beam and column..also the distance between he column..and the required thichness of slabs 2nd floor including the steel bars..if u can send me your response it woul be better just send [email protected]

    Thank you

  36. #40 by arjun on November 14, 2014 - 12:23 am

    I wanted to extend my house vertically which has cement problem is I want to cast rcc slab at 10 feet on my already existing walls which are 15 feets in height.I dont want to break those walls as I want to extend my house vertically. my mason idea is to cast rcc slab upto 05 inches inside existing walls. is he right technically??? or how it should be done? Pl this is very important for me and my family.

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