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. hello, I would like to know is it acceptable practice to place an isolated footing in fill area ,I have 1.4 m fill over the existing ground level,or i have to embed it below the ground level

    • Hello Zahir,
      You shouldn’t place your isolated footing in fill area. You should cent percent prefer embedding your footing below the ground level to maintain the integrity and stability of the structure. If don’t do they, the structure is bound to develop foundation problems in futures. The most common one in this case would be sinking foundation.

      Be very careful while designing foundations. Remember that is the core of the structure. Let me tell you, foundation problems are disastrous and are very expensive to repair.
      Have you hear of the saying,”Precaution is better than cure”. Follow it. That is what we engineers should be doing.

      All the best!

      Also check out my articles on Sinking foundation. They will give you an idea about what kind of problems they create.
      Sinking Foundation – I
      Sinking Foundation – II

      • hello ma’am,
        all the information on the site and your explanation to all the difficulty for various questions have provided me more knowledge than any other source, thanks a lot for all the valuable information.

        • Hello Swapnil,
          We are glad to know that our articles have been helpful. We look forward to hearing from you often.

          Cheers 🙂

  2. hi, i’am second year civil engg student and i want to know what are the foundation details that are to be taken into account while selecting the type of foundation to be decided for a skyscraper

  3. HAI THIS IS VERY NICE SITE FOR CIVIL ENGINEERS
    I AM NEW FOR THIS WHICH IS BEST SOFTWARE TO DESIGN FOOTING DESIGN

    • Staad Pro is being used for structural design purpose. But of course you need to be thorough with your structural design knowledge to use this software.

  4. Dear Ben

    I want plan to start my G+2 home. please tell me about details please. building size 42’x20′

    1. column size
    2. no of rod
    3. rod size
    4. no of column (15 ok)

    please reply me…..

  5. hi
    can you help me with our thesis?
    i’m 4th yr civil eng’g student
    our thesis title is “proposed design of special foundation considering the effect of mine blasting-induced ground vibration”
    we focus only on residential house foundation.
    what is the initial step we should do?
    how to design foundation considering blast loading?

    thank you for the response and this would be a helpful for our research.

  6. Hi Benzu,

    Thanks so much for your site!

    I need to build inexpensive support pillars for the landing gear of a Boeing 727-200 airliner which serves as my home (web site references below). I’d prefer a method which is both cheap and relatively easy to dismantle, but fully reliable and very long lived. My sense is that each of the two main landing gear need to support a maximum of about 380 K Newtons, and the nose gear a maximum of about 133 K Newtons. My subsurface soil is moderately firm clay, but my terrain slops significantly.

    At this time I’m focused on the left main landing gear task. It’s support pillar needs to be very roughly 2 Meters high and very roughly 3 Meters in diameter. The pillar tops must be concave (bowl shaped) so that the landing gear tires can roll a bit during an earthquake, to insure that no stress can develop, but return to the center once earth motion ceases (an anchor chain will become taut if the travel nears the pillar perimeter).

    Air is maintained in the landing gear struts so that they absorb shock such as from an earthquake. The inflation height of the struts is easily adjusted so as to level the aircraft, even if the support pillar’s height changes a bit over time.

    For the left main gear pillar, I’m currently considering a conventional circular concrete pad onto which an unconventional pillar is assembled as follows: Ordinary 10 cm diameter ABS sewer pipe would be stacked vertically one next to another, in an array which forms a 3 Meter diameter pillar shape, and held together with outer circular perimeter steel bands or similar. At least four steel rods would be inserted through the sewer pipes, each from the top of one side of the pillar to the bottom of the opposite side of the pillar, as diagonal members so as to prevent tilting of the pillar. The tops of the pipes would be cut so as to form the bowl shaped concave top. Each pipe would be filled with concrete and one centered reinforcing bar, or perhaps simply filled with gravel (or a combination, such as concrete fill for the center most pipes, where the tires normally rest, but gravel for the outer pipes).

    A steel or similar culvert pipe to house the array of vertical sewer pipes is a conceptually easier option, and I continue to consider that. However, 3 meter diameter culvert is expensive and somewhat awkward to transport.

    A conventional solid concrete pillar strikes me as likely quite expensive, and perhaps more difficult to assemble (due in significant part to the large reinforcing bar structure presumably required). It would also be far more difficult to disassemble. And my sense is that it would be far stronger than is necessary.

    I remain fully open to any ideas however – any concept which addresses the need most efficiently will ultimately win my heart. I’m an electrical circuit design engineer, not a civil nor structural engineer. So this is generally outside of my skills. In general, I prefer thoughtful exploratory approaches which yield improved efficiency over an unimaginative default to conventional design. However, if a conventional design simply proves to be the best option, then it would win my heart.

    I’d appreciate any thoughts or references you have, including the basics for the construction of the circular base pad.

    Thanks so much and regards, Bruce

    Hillsboro, OR 97123-9074

    http://www.AirplaneHome.com (http://www.AirplaneHome.com/Images/22Sep2011ImagesCatalog.htm)
    http://www.HikokiIe.com

  7. Hello I’m trying to build a ground plus two shopping center on a 400 meters squared piece of land. I need a building plan, how much material i need? etc..,

    If you can assist I’m willing to pay for your services

    Thank you

  8. Hello Sir
    I want to know the comparison between normal single/double slope truss of IS members and tubular/pipe sections for a span of 11 m and whose two ends supports on two column. Also give related books/journal/links information.

  9. how would you calculate storey shear and storey moment in kanis method of frame analysis(side sway type).I know its formula but my values are not satisfactory with my study material.Can you help me?

  10. Dear madam,
    in my three storied ratidential building(low land)-550 sq. ft area in one floor, 11 nos column all are 4-16dia bar(250X250mm), footing size 1.5mX1.5m with 12dia bar-200 spacing 1200 height, plinth & roof beams all are 250X2500 mm with 4-16dia bar.Is it safe? Please advise.

  11. Hi Benzukj,

    When a foundation slab has a strip footing for exterior load bearing walls, can it be near or above a spread footings for columns. In other words can the spread footings for the columns be place deeper so it doesn’t interfere with the strip footings in the slab on grade foundation?

  12. hi im john
    if you have a beam span of 8.50 to 10.0 mtrs. in a 15 storey building, what is the ideal section of the column on the ground floor?

    what is the ideal column size at 4th floor to support with a beam span of about 8.50 to 10m.?

    what should be the column size on ground floor if it has 8m span?

    what should be the size of a column at 4th floor if it has an 8 m. span?

  13. Dear Benzu
    I want to know about following foundation Procedure.
    01.Machine Foundation
    a. Wt 123TN b. Suppliers Recommended foundation size 12m x 5m. Also Supply Moment x,y & z axis.
    c. 750rm.
    02. Foundation design of Fuel storage Tank 25m dia 18m Ht , Fuel Capacity 8000kl.

    Thanks with best Regards

  14. I find your column very useful.. my query is that I am a layman as far as the civil structures are concerned..

    We have a G+2 story structure and wanna construct one more floor. Floor size is 400 Inch X 400 Inch and it has a total of 13 columns of x section of 522 sq cms each (ie 9 inch X 9 inch)

    Is it advisable to go ahead with 3rd floor with existing structural strength ?

  15. Dear sir,
    I am planning to construct a G+1,where ground floor is 26’*22′ and first floor is 26’*36′ for that i have selected 15 pillers made of 16 mm rod square 04 nos and connecting beams of 12 mm rod square 04 nos.The ground condition is neither hard or loose.(medium).My selection is ok or not.can you please advise.

    Regards

  16. the idea behind to tie the column bars to its foundation reinforcement is to assure that the skeletal framework of a building will be acting as one, because reinforcement are assembled separately according to their usage it is ,by principle important/neccesary that this reinforcement should be secured properly to act effectively and actually serve its purpose nevertheless tieng this rebars is to avoid them from slipping from each other when subjected to excessive force/load

  17. why it is not necessary to do rubble soling beneath the footing if the same footing rest on the hard rock. and why some consultants suggest to do double layer of rubble soling beneath the footing?

  18. hello madame,

    is it too much for a 12m x 7m 3 story residential bldg to have 0.30m x 0.30 columns spaced @ 5m, 5m and 2m on the buidings longest side?

  19. how can v calculate the cement concrete of a fotting when its base is 8’*8′ and its 6” in the base and then upward sloop and 4” each bside the coloum at the top

  20. Hi..
    This is sharat
    Im a civil Engineer,
    SBC is calculated based on SPT test
    But is it the only criteria to decide SBC..
    If not so please explain in detail how to calculate SBC.
    Depending on type of soil how do to decide SBC??
    Pls reply me….

  21. HI BENZ,
    IS IT THERE ANY PERCENTAGE OF REINFORCEMENT FOR A SINGLE COLUMN? AND IS IT POSSIBLE TO TIE 8 NOS OF 16MM RODS IN A 9″ X 9″ SQUARE COLUMN?

  22. i am constructing a single story building (shops) and laid foundations with 3 x 3 feet column foundations. column had 4 x #5 size dia bars, we also had plinth beam. now the owner wants me to go for double story. what minimum should i do with the foundation or with columns to go for double column, help

  23. Suresh :

    Hello sir,
    1. Can u tel me the purpose and necessary of provide tapered footing in residential building?
    2. Difference between tapered footing and block footing?

    Tapered footing and block footing are two alternatives that can be used for the same purpose.
    Tapered footing is sloped at all four sides whereas block footing is a single step footing.

    Isolated footings are of two types:
    1) Tapered footing
    2) Stepped footing
    Tapered footing which I guess you are referring to as sloped footing, is used in case of small constructions such as bungalows, duplexes or G+1 structures. The reason why it is used in smaller structures is that it is economical as compared to stepped footings.
    Stepped footings
    They are used in case of multi-storied constructions. Use of Tapered footing in multistoried buildings proves to be uneconomical.

  24. Hello sir,
    1. Can u tel me the purpose and necessary of provide tapered footing in residential building?
    2. Difference between tapered footing and block footing?

  25. dear benz,

    i am building a 3 +1/2 storeyed house om a hilly slope. The foundation mesh designed by my architect is 6′ x 6′ of 16mm rods and the columns are 9”x16”( 4 nos 16mm & 2 nos 12mm) size and beam size including slab casting is of 9”x18” ( 6 nos. 16mm ) The maximum beam length is 15’4”(c to c)’. All the beam placements are in a grid formation. Please let me know the following :

    1. what do you mean by tying the column end to the foundation grid? (My architect says the cloumn end needs to be just centered on to the grid and the footing pyramid built ( i.e there is no tying of the L-shaped column end onto the grid) How do you do the tying?

    2. Are the above column and beam dimensions and the reinforcement ok?

    3. Are these rectangular shaped columns have the same structural strength as a square shaped one of same size ( say 9” x 16” versus 12” x 12” )

    4. Does the placement direction of these rectangular columns ( i.e the facing of wider & narrower side ) need any specifications or can be faced as per the rooms partition requirements?

  26. This is about ground floor column moments. We use column height from ground level to second floor in analysis of multi-storey bldgs. This results to column moment values at ground level. Now when we design the footing, we use this same value though the footing level is way below the ground level. Should we not neglect this moment as the ground slab and soil can provide rigidity and disperse column load moment when it reaches the footing level?

  27. hello friends
    any one help me for design of pile cap. . i designed pile cap by embedded piles to pile cap and calculating the max reaction of pile per meter and hence moment with respect to ecentricity for this i designed steel . . is this procedure correct . . also in some books they will designed as slab by just considering as max BM respect to simply supported condition . . which is correct

  28. hello Benz
    i want to know the procedure of machine foundation for 11kv isolator machine and transformer. . in some textbook they simply consider 0.12percent GA. . how the ecentricity calculation for this point load and hence moment. . also for mode of vibration and frequency check. .please guide me

  29. In my house plan the contractor has drawn for the hall of 14 ft by 30 ft approx with 4 pillars at about 10 ft distance each and on other parallel side 3 pillars at 15 ft distance each and each pillar from foundation column has 6 no.s of 12 mm rods in 9″ by 12 ” column/pillar; Whether 12 mm rod vizag/TISCO make ok whether any special care to be taken in concealed beam on lintel or roof level required. How to cross check my plan if it is correct without defect………….lakshmanan

  30. Sir, i want construct a G+4th storey building, build up area is 3973 sq.feet in 23’9″x158’5″ , the soil is not hard ,from entrence in right side 4’6″ wide open duct and left side 6’9″ wide
    passage. And, i want to provide 56 nos columns accrding to room(12’0″ x 12’0″) and their corner. and want also to provide 9.84″x17.71″(16mm dia) RCC column in outer wall. am i right or wrong
    thank you !
    S.rama

    • Hello Rama,
      The structural design depends on the building plan. WE cannot make assumptions. It is all calculated and required professional knowledge. Every project is different and has to be dealt separately.

      Civil Projects Online has made things easier for you. It has launched Architectural and Structural Design Services at minimal costs. You can also receive expert advise.

      Architectural and Structural Design Services

  31. Hi there,

    I am planing to construct my house on plot area of 20 ft x 20 ft = 400 sq ft, ground, and 400 sq ft. first floor, total Rcc area as per architact is 990 sq.ft aprox. I would like to know how much steel, cement sand and aggregates will be required so that I know the cost of material.

    Your earliest reply will be highly apriciated,

    Thanks

    Regards

    Dinesh Trivedi.

    • Hello Dinesh,
      The structural design depends on the building plan. WE cannot make assumptions. It is all calculated and required professional knowledge. Every project is different and has to be dealt separately. The quantities of sand, cement, steel and aggregates require a detailed analysis of the structural design. I hope what I am saying is making sense to you.

      Civil Projects Online has made things easier for you. It has launched Architectural and Structural Design Services at minimal costs. You can also receive expert advise.

      Architectural and Structural Design Services

  32. I have booked one flat of a residential six storey building.The size of its colums is 12/16,its foundation is 7ft deep in hard soil,it has seperated colum footings.Is the building safe? Colums are cons
    tructed with 8 tmt bars(four of 16mm ,and four of 12 mm).Please help.

  33. For seven storied residential framed structure with RCC columns 5.00 meter apart, which type of foundation would be required on moderate type of soil. If raft foundation is required, then what would be adequate depth of the raft ?

    • Hello Arun,
      You could go for an isolated footing even in case of a seven storey structure with RCC columns 5m apart. Raft foundation is used only in case of extremely weak soils. Isolated footing can be used even for a 10 storey building if the soil is moderately strong.

    • Hello Descravel,
      Isolated footings are of two types:
      1) Tapered footing
      2) Stepped footing
      Tapered footing which I guess you are referring to as sloped footing, is used in case of small constructions such as bungalows, duplexes or G+1 structures. The reason why it is used in smaller structures is that it is economical as compared to stepped footings.
      Stepped footings
      They are used in case of multi-storied constructions. Use of Tapered footing in multistoried buildings proves to be uneconomical.

  34. hai frds
    this website is very useful for engineers
    we r learn to our doubt clarifications through it.
    im a new comer from tuty in tamilnadu

  35. iam consturcting single story building at the edge of minor irrigation tank ,there is silty soil and room size is 24′-0″ x14′-0″ ,what depth ,size footing needed please reply

  36. Some references use net allowable soil pressure for the design, that is allowable bearing capacity less surcharge and the weight of the soil backfill but some does not consider deducting the weight of the soil backfill. When do we need to consider deducting the weight of the soil backfill from the allowable bearing capacity.

    Thanks!!!

    • 12mm reinforcement bar for columns can be used for three storey building. It depends on the load coming onto the columns. Making an appropriate column layout is very important. 12mm reinforcement bars can be used if the distance between columns is appropriate.
      Check out this article. It will surely be of help to you.
      Thumb rules for making a column layout

  37. I am building a 2 storey house in a land that was previously a paddy field. It was slushy / marshy land in which I filled with soil in 2001about 7-8 feet deep. Now i am planning to construct this house and do you think I need to go in for any specific deep foundations. One person suggested column foundation that goes to about 10 feet below ground. Another suggestion was well foundation. Please comment.

    Thanks,
    Kurian

    • Hello Kurian,
      Well Foundations are pretty outdated. You must preferably go for Pile foundations. Concrete Pile Foundation will be perfect in your case. Raft Foundation can also be used but since they are little more expensive option as compared to Pile Foundations, you could avoid them.
      Let us know if you have any more queries.

  38. Hello,
    What are the general specifications for length of L for short columns.Because in some drawing I dont see the length extended inside footing.Suppose columns length is 3 m high then how much should be bended (L) inside footing.

    Regards

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

  40. please tell me the critical situation of footing designs like footing between two walls in which one is already constructed and other we have to construct with L shape

  41. abbas :hello friends i find this website very interestingi ve learnt many things through it.thank you for sharing your experiences with us.i am a newcomer from senegal:

  42. dear sir,
    I would like to ask you that below o.oomtr lvl should a part of colm be considered as footing,as it is written in chinese code.

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