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

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What are Simply Supported Slabs?

Simply supported slabs are supported on columns or stanchions. They have support on all four sides.

Simply Supported Slab
Simply Supported Slab

Simply supported slabs are classified as One way slabs and Two way slabs.

One way slabs bend in one direction only and transfer their loads to the two support beams in opposite directions. Their main steel in on shorter span length. L/B ratio is generally less than 2.

oneway

Two way slabs bend in both directions, and transfer their loads and stresses on all four sides. L/B ratio is equal to or greater than 2.

twoway

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.

You can use a free app to design simply supported RCC Slab panel.

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
  • 3 x d
  • 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
  • 5 x d
  • 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.

Cover

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

48 thoughts on “Guide to Design of Simply Supported Slabs | Design of RCC Structures”

      • 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?.

        Thanks

    • 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.

      Cheers!

  19. 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?

  21. 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. 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. 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. 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

    • Sanjeev :
      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

      design details for 7*12plinth area 2bhk please give reply

  26. 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.

  35. Sir

    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 cjerry07@yahoo.com

    Thank you

  36. I wanted to extend my house vertically which has cement roof.my 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.

  42. Do correction….
    Slab is called one way if its length/breadth is greater than 2.
    Slab is called two way if its length/breadth is equal or less then 2.

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