Guide to Foundation Design | Column Footings



Foundation Design

Foundation is the base of any structure. Without a solid foundation, the structure would not hold for long. We have to be very cautious with the design of foundations because our entire structure rests on the foundation. The job of a foundation is to transfer the loads of the building safely to the ground.

Laying of Column Footing Reinforcement | Foundation Design
Laying of Column Footing Reinforcement | Foundation Design

The strength of the foundation determines the life of the structure. As we discussed in the earlier article, design of foundation depends on the type of soil, type of structure and its load. Higher the load bearing capacity of the soil, the larger the load it could safely carry.

Foundations are basically divided into Shallow Foundations and Deep Foundations.

In this article, we are going discuss the step by step guide to Column Footing Design for a shallow foundation.

Reinforced Concrete Footings

Footing comprises of the lower end of a column, pillar or wall which i enlarged with projecting courses so as to distribute load.

Footings shall be designed to sustain the applied loads, moments and forces and the induced reactions and to ensure that any settlement which may occur shall be as uniform as possible and the safe bearing capacity of soil is not exceeded.

In sloped or stepped footings, the effective cross-section in compression shall be limited by the area above the neutral plane, and the angle of slope or depth and location of steps should be such that the design requirements are satisfied at every section.

Design Procedure of Column Footings | Foundation Design

Here is a step-by-step guide to Column Footing Design:

Column Footing Plan and Section | Foundation Design
Column Footing Plan and Section | Foundation Design

Step 1

Area required for footing

Square = B = (w+w1)/P0

Where,  Po = safe bearing capacity of soil

w1 = self weight of footing

w = self weight of footing

For Rectangle = b/d = B/D

A = b x d

Net upward pressure on the footing

q/p = W/A

Step 2

Bending Moment

Critical section for maximum bending moment is taken at the face of the column

For a square footing,

Mxx = q x B/8 (L – a)2

Mxx = q x L/8 (B – b)2

Myy = q x B/8 (L – a)2

Step 3

To fix the depth of the footing shall be greater of the following:

Depth from bending moment consideration

d =(M/Qb)

where, Q = moment of required factor

Depth from shear consideration

Check for one way shear

Check for two way shear or punching shear

Critical shear for one way shear is considered at a distance ‘d’ from face of the  column.

Shear force, V = qB [ ½(B – b) d]

Nominal shear stress, Tv = k . Tc

Tc = 0.16√fck

Step 4

Check for two way shear

Critical section for two way shear is considered at a distance at a distance d/2 from all the faces of the column.

SF, V = q [ B2 – (b + d)2]

SF, V = q [L x B – (a + d)(b + d)]

Nominal shear stress, Tv =  V/2((a+d)(b+d)d) ——- {for a rectangle

Tv = V/4((b+d)d)         ——- {for a square

Tv = k . Tc

k = 0.5 + β > 1                       ; [Beta β = ratio of sides of the column

Tc = 0.16√fck

Area of steel, Ast = M/((σ)stjd)

387 thoughts on “Guide to Foundation Design | Column Footings”

  1. Sir,
    As a general practice, we used to make Starter (of approx. 100mm ht.) for column formwork. But, from some expert, it is said that ht. of starter would be of 500mm ht. as per standard.
    Could you pl. explain the exact mathods.
    Thanks & Regards….

  2. Dear madam/sir

    I strat next month my house work.house area is 1300 Sqft.kindly request to yoy please send footing and column sizes and reinforcement details and distance of every columns and roof slab thickness and reinforcement details. house size is 9m*12m

    Thanks and Regards

    M.Thirumurugan.

  3. Dear sir,
    in a school building some of the footings are coming over a sloping rock.here the strata is hard but the slope may leads to slipping of footing .so wat will be the possible solution that i want to follow?

    • Hello Fazil,
      The construction can be very well executed in a rocky terrain. You should keep one thing in mind while constructing on a rocky and slopy terrain; the rock which is being used for laying the foundation is not a loose rock, this could lead to structural failure. But if the rock is hard and solid but has a slope, then you need not worry about it. It would not affect the strength of the construction. I suggest, before you plan on initiating the construction, you should go for land surveying and get the important details which will help you figure out what kind of foundation is to be laid and if the construction is feasible in such a site. If you have any further questions regarding the construction, you are most welcome…. 🙂

  4. Dear Sir,

    I would request you to advise me about the foundation plan. what type and size of foundation required to carry out the 300Ton weight?

    • Hello Hari,
      Preferably, you should go for Framed Structures and avoid Load bearing structures. Load bearing structure is safe for a two story building but framed structure would be the safest. Though there is a little difference between the construction costs but keeping in mind the long term usage, one must go for Framed Structures.
      Also, the disadvantage of going for Load bearing walls for a two story building is that the walls get thicker and the inner space decreases. Since land has become so costly, going for a framed structure would be a sensible choice.

  5. Hi Benz,
    Thanks for the clarifications on earlier comments. I have my foundation ready now. Initially I planned for the red bricks for building the walls. Now changed it to cement blocks with MSand for plastering. What are the things I need to be careful while using the cement blocks with M Sand?

    • Hello Kuttan,
      The only care you will have to take while constructing your walls with cement blocks is checking the alignment of the walls. A wall with cement blocks is more prone to collapse as compared to the red brick walls if the alignment is not proper.

  6. Hi,
    i have to construct a house which has houses on both sides. what is the design for foundation and columns with out disturbing the sides of other houses. the critical situation is that i cannot afford space between the walls.

  7. If somebody don’t tie the column reinforcement to the mesh below then what will be the possible type of failures.What should be the design load to be taken for the footing design of a single storey, two storey, and 3 storey residential building ? I hope you can answer all my questions.

    • Hello,
      Tying the mesh to the column reinforcement keeps the foundation and column tied to each other which results in its stability and strength. Structural cracks might appear if one fails to do so.
      As i have already explained earlier, four loads are to be considered in order to measure total load on the footing:
      1) Self load of the column x Number of floors
      2) Self load of beams x Number of floors
      3) Load of walls coming onto the column
      4) Total Load on slab (Dead load + Live load)

      I hope I have made it clear.
      Benzujk

  8. thanks for the post. I want to design the reinforcement for upward (negative) reaction. (As it happens in Factory shed where both positive and negative reactions should be check.)

    need a technical help.

  9. what is the main difference between one way shear and two way or punching shear,when we have such shear in buildings?

    thank u

    • Hello Khan,
      One way shear means stress coming onto the structural members in the horizontal direction from one side. It generally causes cracks in the RCC members. Two way shear is said to occur when the horizontal stresses occur from either sides of the members causing it to crack or result in crushing of the structural members if not designed properly.

      Punching shear
      It generally occurs between a column and a footing. The column tries to punch itself inside the footing because of the excessive stress on it. This could cause weak joints between columns and footings and also lead to structural failure.

  10. Dear Sir,
    in case of having 3 pillars supported to on founation in triangle posetion, can please provide me the hence of the design in this case

    Thanks
    Bassel

  11. what is the difference between one way shear and two way shear?

    is there two shear in any other RCC member apart from footing?

    thank you

    • One way and two way shear is found in beams and columns too but punching shear is only evident in between a column and a footing.

      I hope it helped.

      Benzu

  12. Sir, i constructed a single storey building, build up area is 900 sq.feet, the soil is hard and rocky, the depth of the footing is 6 feet, column footing size is 4’x4’feet, number of columns are 9, each column size is 12’x9′, rods used in column are four 16mm and two 12mm. plinth beam tie up with all eight columns one column is isolated, it is in parking area ( the rooms are 2 feet height compared to parking area ).
    i would like to know plinth beam is really required for that isolated column and how many floors can i construct on this foundation. please give your valuable opinion.

    thanking you,
    srinivas.

    • Hello Srinivas,
      Firstly, you need a plinth beam to tie the isolated column because if you dont do so, it might result into bending of column resulting in collapse.
      4’x4′ footing size is pretty small. Your column steel design is good. If the column c/c are not more than 12′ than you could go for G+3 without any hesitation.

      I hope the answer was helpful.

      Benzujk

    • Four loads are to be considered in order to measure total load on the footing:
      1) Self load of the column x Number of floors
      2) Self load of beams x Number of floors
      3) Load of walls coming onto the column
      4) Total Load on slab (Dead load + Live load)

      Benzujk

  13. I am designing 3 storeyed building using staad pro, and sap software, I have probelem in defining load combinations. Can anyone one help me out..

    • Hello Vijay,
      The column footing size taken for a three storied building depends on the spans i.e. column to column distance. Generally the size of the column footing is taken as 4’6″x5′ for 4m c/c

  14. I want to replace 3- 6×6 bearing posts in the basement of a 3 story wood structure. They are currently sitting on 2×8 wood on an existing 1-2 inch old concrete slab floor. I want to put new footings under posts. I’m using 6000 psi concrete mix, what size footing width x length x thickness should they be, and configuration of rebar?

  15. what should be the design load to be taken for the footing design of a single storey, two storey, and 3 storey residential building ?

  16. Sir,
    I would like to know the follwing for the calculation bearing pressure below a footing, to know whether the pressure is below the safe bearing pressure of soil.
    1. The unit weight of RCC below ground level to be taken is 25 KN/m2 or (25-15) KN/m2, where 25 is the unit weight of RCC and 15 is the unit weight of soil.
    2. Whether weight of soil above footing, i.e, weight of backfilling to be taken.

    • I didn’t understand your question. From what I could understand,

      Weight of backfilling is negligible. I won’t affect the footing much… 15 kN/m2 is not much, when a typical building load per square meter can reach above 1000 kN/m2. Even for a simple 3-storeyed structure, loads on columns routinely cross 500 kN/m2

      I believe a RCC design book would help you…

      Cheers!

    • Hello Labannya,
      Supporting a RCC slab on a 5″ brick is unsafe and not practical. It has to have a Column and beam structure above which RCC slab could be casted.
      The reason is that there are heavy chances that the brick wall might slip which would lead to the collapse of the structure. I hope would find the answer helpful.

  17. dear sir,
    i want to design a pre engineering structure on top top of r c c framed design. size is 120m x 31m. please help me to find out how many columns and footing size to find out. load of pre engineering structure is 60 ton.

  18. Hi,
    We have one old building without columns slab rest on brick wall. It’s constructed before 10 years, now walls are formed cracks the building is in oil and gas plant no of times wall chipping and reconstructed for windows and Ac opening pls suggest the building is suitable for living or need to dismantled

    • Hello Ashish,
      The column between foundation and plinth beam is called a stub column. It is squarish in shape. The dimensions of the column changes above the plinth beam…

  19. sir/madam,
    hi, I wish to know if in old structure foundation bolts and concret on surface damaged so to renew the foundation for steel structure. what can be done?

  20. sir,
    i wish to know why it is that when designing footings reinforced bars as placed closed to where the pillar will stand

  21. Hello
    I am designing a G+1 Residential building that rests on a rock and the maximum column load I have got is 200KN. Since it is difficult to excavate the rock what is the possible solution and what minimum dimension of footing shall I use

  22. i need details load, vibration and wind force calculation tank foundation as folloing:

    1.0 Foundation size = 8500 mm x 3200mm and need height
    2.0 need re-bar datails fourmula
    3.0 tank weight = 13 ton

    i hope my request will receive kindly consideration by you..

    Regards
    Ram

  23. Dear sir
    I want to build up a home of two storied building , area 22?x52?. so I need the rod calculation formula and also roofing, foundation,beam, column diagram.

  24. Dear sir
    I want to build up a home of two storied building , area 30’x25′. so I need the rod calculation formula and also roofing diagram.

  25. dear sir,,
    i want to build up a flat RCC roof for roofing area of 43′.4″x31’3″. so i need the rod calculation formula and also the roofing diagram.

    • Grouting at the column base plate helps in strengthening and stiffening of the column base. This could help in avoiding flexural and structural failure.

  26. is Achorage requried for a 6feet x 6feet x 1.3feet footing. also kindly advise whether anchorage required for columns, plinth beams, and tie beams. kindly advise.

  27. Hi,

    Please explain me the design proedure of Generator building. what are the loads i have to consider.

    Thanks,
    Sateesh

    • Generator Building is a place where heavy machinery is placed. Firstly, you will have to study the kind of machinery that will be used in the Generator Building. Only then can you estimate the load on the building. Once you know the average weight of the machines and the number of machines that your design supports you can then move on with the load calculations. More than the live load of the workers or technicians, consideration of the dead load of the machinery plays a vital in the design of Generator Building.

  28. I need to design a storey building how the load calculations r carried out that is coming in the column can pls tell

  29. salam & hi,
    can u explain me … that the proceture to calculate total load of single story building + how to determine the area for (width of foundation , depth of foundation , thickness of block & number of off sets)…
    atiq….

    • Hi Atiq,

      Foundation design is a complex process. It depends on the total load on a particular foundation as well as the Safe Bearing Capacity of the soil.

      For example, a single storey building foundation with hard soil, where total load on footing does not exceed 300kN, a footing pit of 1M X 1M at a suitable depth upto hard strata would be sufficient. The pit would have a 6″ layer of PCC. On top of that, you would place a mesh of steel consisting of 8 rods each of 10mm diameter on both sides. Then place the column steel frame on top of it and tie the column bars to the steel mesh. Pour 6″ of concrete and let it harden. Then you can go for either tapered footing or block footing. Total thickness of block should be 15″, including the 6″ you of RCC poured earlier. So, for a single storey building whose load does not exceed 300 kN, and the soil strata is hard, the above given design should be sufficient.

      • If somebody don’t tie the column reinforcement to the mesh below then what will be the possible type of failures.

        • Never observed any such failures in structures. So, am unaware of that. Maybe Google Search might help…

          Practically speaking, column reinforcement is embedded in many feet of concrete. Ensuing footing would be weak, but I doubt if it would fail.

          Cheers!

        • Yes! you are correct! If at all the workman ship does not satisfy , like the plumb of the column/building), there are no failures observed.

        • There is no failure but the eccentricity of the column reinforcement might be disturbed, thats why its important to tie the reinforcement after alligning to the center line.

        • Hello Ajaynder,
          When the eccentricity of the column reinforcement gets disturbed, it leads to structural cracks which results into structural failure. Structural failure does not just mean that “the structure would collapse” but it also means that the structural components like beams or columns in a structure are damaged which affects their strength considerably.

          Cheers:)
          BenzuJK

        • If u do not tie your column to the bottom mesh… then there will be joint failure (probably cracks in diagonal direction will arise that is shear failure) between column and the other member.

      • Hi Benz,
        I am bit tensed aftre readiing this article. My 2 story building (1300+1200 sqft) foundation design consists a mesh of with 8mm rods and column steel frame of 12mm. Is this is sifficient for this building? there are around 17 columns in the foundation with beams connecting all the columns. Reammy appreciated your reply on this ASAP.

        Sasi

        • Hello Sasi,
          8mm rods can be used for the footing mesh. The number of steel rods change with the thickness of the mesh. So the mesh being 8mm or 10mm is not an issue. It all depends on the load coming on a particular footing. The load on every column is different depending on which we calculate the total quantity of steel required. If your engineer is qualified enough then don’t worry, he will take care of it. Your building will be safe.

        • Hello Benz,
          Thanks for the quick reply. Just one more quiry. The beam size connecting all the columns are 30cmx20cm with avg span of around 4mts. Is it sufficeint dimension? just wanted to have second opinion. Also whether we need to extend the column pillars to to the roof level? My architect says its not required. Instead we can have 15 cm concrete belt with some additional rods running through out the plinth. Please advice.

        • Hello Mr. Kuttan,
          You can always keep in touch with me through my site. You can ask any questions that have regarding the construction field. Will try me best to help you whenever possible.

          Benzu

      • Dear Sir,
        I have 4 story building the foundation slab for each column is 1m2 and deepness is 70cm2 and beams connected in foundation each column 40x40cm with 6 each of 14mm rebar . it has totally 15 columns the size of the columns are 30x40cm each column has used 8 each of 16mm rebar and the soil of the fundation is strong. now please advice can i build one other story at the top of it to became 5 story. THANKS

    • yehh…If u consider G+3 bldg. go from top to bottom. first of all distribute the load of slab to the beam as per nature of slab i.e. if one way half-half or two way in trapezoidal & triangular section then beam will be loaded as VDL transfer this load to the supporting column .
      same procedure done for 2nd & 1st & Ground floor but while go to down word direction add upper respective floor load then you’ll get the total load on column

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