Thumb rules for designing a Column layout | Civil Engineering



Guidelines to be followed for making a column layout

In this article, we will go through the essential thumb rules to be followed for giving a column layout. Of-course columns have to be designed in accordance to the total forces acting on the structure, but apart from that, it is essential for every Civil engineer and Architect to remember a few thumb rules so that they are prevented from making mistakes.

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Three thumb rules to be followed are as follows:

  1. Size of the Columns
  2. Distance between Columns
  3. Alignment of columns

Minimum Size of RCC columns

The size of the columns depends on the total load on the columns. There are axial loads and lateral loads. Large beam spans induce bending moment not only in the beams, but also in columns which are pulled by the stresses in the beams. It is important to use advanced structural design software like ETabs or Staad pro. I highly recommend every structural designer learn these software. The thumb rules are for general designing in very small projects.

For this general thumb rule, we will assume a structure of G+1 floors high, using standard 6″ walls.

Minimum size of an RCC column should not be less than 9” x 12” (225mm x 300mm) with 4 bars of 12 MM Fe415 Steel.

These days the minimum I use in my projects is 9″ x 12″ (225 mm x 300mm) with 6 bars of 12 MM Fe500 steel. You can never go wrong with strong columns. I also recommend use of M20 grade concrete for the structure (ratio 1 part Cement : 1.5 parts Sand : 3 parts Aggregate with 0.5 parts water by volume). I recommend use of 8 MM stirrups at a distance of 150 MM center to center throughout the length of column.

This setup of 9″ x 12″ RCC columns is safe for G+1 Floors. There are a lot of other considerations, but this is just a thumb rule.

Span (distance) between two columns

For the above column setup, a span of up to 5 meters is quite safe. One can use beams of size 9″ X 12″ (225 MM x 300MM) with a slab thickness of 5″ (125 MM) cast in M20 concrete for spans up to 5m. There are other considerations like secondary and tertiary spans, point loads and wall loads which have to be considered. It is complicated, but thumb rules can work if the structure is simple. It is always recommended to use structural design software like ETabs or Staad pro for design.

In a beam of up to 5 meters length, secondary spans of up to 4 meters, wall loads of up to 8 kN per running meter, I can use steel as below.

  • Top Steel – 2 bars of 12 MM
  • Crank bars – 2 bars of 12 MM, cranked at an angle of 45° at a distance of L/4 at both ends of a simply supported beam
  • Bottom Steel – 3 bars of 12 MM.

This configuration can change depending on a lot of factors.

Alignment of Columns

Placing of columns depend completely on the plan. A planner has a very important job. A grid column placement is always preferred in order to reduce point loads and unnecessary complications while construction. This reduces the cost of construction as well as time required for construction. Beams which have continuity with other simply supported beams have reduced bending moments, and thus require less steel and concrete depth to be safe.

Columns have to be connected with each other for smooth transfer of loads. An experienced planner will keep such things in mind when planning the structure.

In the next article, I will explain these three thumb rules with the help of an example “Column Layout for a Residence“.

Recommended Reading:

Introduction to design of RCC Structures

Building Design Guide which includes design of:

  1. RCC columns
  2. RCC beams
  3. Foundations
  4. Staircase

102 thoughts on “Thumb rules for designing a Column layout | Civil Engineering”

  1. sir, I have a work of common hall size20*15 with a gallery of 4*15. GF. +FF. Construction. In hall of 20*15 format there r 6 column of9″*9″ with 4-bar of 12 mm.size steel.In this we calculate 1600kg.steel for construction with footing, column,grond beam, Columbup to FF. slab. ,slab, lintel, weather she’d etc. Calculate. But after tendering party give design at time of ground beam. And total steel used by us is2915kg. I gave him in return to pay extra for steel. There is a dispute matter but I want to know I calculate steel is right. 1600kg for GF & FF.

  2. My plot size is 50feet X 65feet,
    I want to built a cold storage Ground + 1 floor.
    RCC columns till plienth level are spaced at 13 feet on two sides & 25 feet at remaining two sides (periphery).
    There are also two columns at center line of 50ft side.
    Total 16 nos. columns.
    !st floor will have equally distributed load of 400 tons ( pulses bags) on 3250 sqft area.
    My question is what should be the size of ” I” beams & internal beams. Require drawing if possible

  3. Hi, I am going to construct G+1 house in my land of 15×40 size. My constructor proposing 10 columns . 5 columns in one side and 5 columns in other side and he mentioned in between there is no columns is required because min distance between 2 columns is 15 ft. Can you give your suggestion. Is it safe if we don’t put any columns in between the 15 ft distance.

  4. Hi.we are constructing for 1st floor have roof area near about 2800sq ft. And have total pillar 16(4pillars are 12*9 and 12pillars are 9*9) is it sufficient and one more thing Tata steel we are using but for roof how many mm of steel should use and for beam also kindly tell me pls

    • It is a very large structure. I request you to get detailed drawings from a qualified structural designer. You will get foundation designs, plinth beam designs, column designs, slab designs, staircase design. Please consult a qualified designer instead of risking it on your own.

  5. Can we design structure for g+2 with entire beam column with m20+ and 8 tmt rebars of multiple sizes 2 –16 mm
    Rest 12mm
    entire structure with rectangular dimension of 24’x48 consisting of 15 columns 3rows of columns but column and slab beam of 6inch x18 inch
    Totaling 108 cubic inch with cross sectional?
    Instead of standard 10’x10′
    (Note the columns will be multi directional that no subsequent parallel columns

  6. I have a technical question, I recently bought a land and started construction in rainy season. When we started digging the land for pillar/footwork, after 4 feet, there was water coming up from few sides of the land, we used dewatering pumps to remove water and laid mat and pillar, even after that the thin water flow from sides didn’t stop, we closed the pillar by spreading soil.

    Could you please tell me will the water beneath the land that was coming during the pillar/footwork construction effects the house.

    Thanks,
    Pavan

    • It shouldn’t be a major problem as long as the footing is designed according to the reduced bearing capacity of soil due to high water table.

  7. MY 20 by 45 ft structure have four 9″ by 12″ column and four 9″ by 9″ column having 9″ by 9″ beam and 5″ slab thickness. Column and beam will have 12 mm TMT bars and m20 grade. Building will have G+1 floors only and wall will be of AAC blocks. Total weight of First floor roof and beams is 600 Kn. So please tell me is it a good structure or need improvement.

    • The best option would be to consult a structural designer. In my professional practice, our organization has stopped using 9″ X 9″ columns and beams many years ago. Minimum recommended size should be 9″ X 12″.

  8. Hi Benzu jk, my house under construction G floor is already completed. it’s a rectangular layout with 3 room having dimension 16*15 feet. since 16 feet is too long as I assume ,and put a support column .the steel bar I used is 4 no.of 16 m and 04 no of 12 mm. size of main column is 12’*12′ and support column is 10’*10′ with 04 no. 12 mm.
    The beam size for G floor was 10′ depth with 6 no of 16 mm with one 12 mm reinforcement on both side of beam.
    but in 1st floor I am making a change , the beam depth is 13′ with 04 no of 16 mm down and 03 no of 16 mm up.
    but my concern is slab size, will be 16*14.5 sq.feet with no beam along the support column.
    SHALL I MAKE SOME CHANGE, GIVE SOME LIGHT AND PLEASE TELL ME POSSIBLE AND SAVE STOREY ,I CAN MAKE.

    • I generally try to maintain beam depth of 12″ excluding slab depth. Also, minimum slab depth standards these days is 5″. I would suggest you approach a local structural designer. it will save you money and give peace of mind.

  9. Dear Sir

    How much steel can be saved on moving to High strength steel bars i.e. from Fe 500 to Fe 550?
    Question-1. If we take an example of 20″ x 20″ column and height – 10′. How to calculate how many TMT bars are required and of what size? Also how to know which concrete grade is required M30 or M40 etc?

    Question-2. If we use Fe 550 from Fe 500, how much percentage saving is there? I mean will there be the reduction in bar size or what? Properties of Fe 550 and Fe 500 below:-

    For Fe 550:- UTS 645 N/mm2, Yield stress 575 N/mm2, %elogation 16%.
    For Fe 500:- UTS 600 N/mm2, Yield stress 525 N/mm2, %elogation 20%.
    Your help is solicited.

    Regards
    Manu

    • Generally, we preselect the grade of concrete and grade of steel to be used based on experience and need. These days, for regular buildings up to 5 floors height, we use M20 concrete and Fe500 Steel. For smaller structures, the client may insist on Fe415 steel. But in my opinion, Fe500 is economical. I have not used Fe550 in my projects, but in my opinion, concrete has a larger effect on the load carrying capacity of a column than steel grade.

      We calculate loads on each individual columns, then calculate the size and steel required. See article — http://www.civilprojectsonline.com/building-construction/calculation-of-loads-for-foundation-design-structural-design/

      In your example of 20″ X 20″ column, the minimum steel according to IS codes, is 0.8% of cross-sectional area, which is 2000 square mm, which comes to around 10 bars of 16 MM, That is the minimum steel for that size of column, cannot go below that.

      Keeping size (20″ X 20″) and steel constant (10 bars of 16 MM), and playing around with concrete grade and steel grade, we can conclude

      If you choose M20 concrete, and Fe500 steel, the load carrying capacity of that column would be 1770 kN.
      If you choose M20 concrete, and Fe415 steel, the load carrying capacity would be 1695 kN.
      If you choose M15 concrete, and Fe415 steel, the load carrying capacity would be 1360 kN.
      If you choose M15 concrete, and Fe500 steel, the load carrying capacity would be 1440 kN.
      If you choose M25 concrete, and Fe415 steel, the load carrying capacity would be 2025 kN.
      If you choose M25 concrete and Fe500 steel, the load carrying capacity would be 2100 kN.

      In the end, a qualified structural designer would be able to give you a good, economical structural design. It is always better to consult a professional for such purposes.

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