Types of Foundations | Design of RCC Structures

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Foundations

Foundation of a structure is like the roots of a tree without which the tree cannot stand. The construction of any structure, be it a residence or a skyscraper; starts with the laying of foundations.

Before designing the foundation, the type of soil is determined. Depending on whether the soil is hard soil or soft soil, a specific type of foundation is adopted.

Shallow Foundations versus Deep Foundations
Shallow Foundations versus Deep Foundations

Foundations are made in various materials… They could be reinforced cement concrete foundations or brick foundations or stone rubble masonry foundations etc. The choice of material to be used in the construction of foundations also depends on the weight of the structure on the ground.

The bearing capacity of soil plays a major role in deciding the type of foundation. The safe bearing capacity of soil should be 180N/mm2 to 200N/mm2.

Foundations are broadly classified into shallow foundations and deep foundations. The depth of the foundation means  the difference of level  between the ground surface and the base of the foundation. If the depth of the foundation is greater than its width the foundation is classified as a deep foundation.

Shallow foundations are commonly used in smaller structures such as residences and small buildings whose floor height is limited to 10m whereas Deep Foundations are used in Skyscrapers…. Piles are the most commonly used Deep Foundations used in skyscrapers…

Types of Shallow foundations

Footings

Footings are structural members used to support columns and walls and to transmit their load to the underlying soils.

Mats or rafts

Combined footings, strap and strip footings

Column Footing

  • In this type of foundation the base of the column is sufficiently enlarged to act as the individual support. The widened base not only provides stability but is useful in distributing the load on sufficient area of the soil.
  • Column footings are usually used in the foundations of residences and buildings where the soil is hard enough has has sufficient bearing capacity.

Pressure distribution Under a Foundation

  • The law of distribution of pressure under a foundation depends on the homogeneity of the soil and flexibility of the base. If really the soil is homogeneous and the base of the foundation is flexible, the pressure distribution under the foundation will be uniform. On the contrary if the foundation base is absolutely rigid, the pressure distribution will not  be uniform but may follow such pattern.
  • In our designs it is usual to assume a flexible base and hence to regard the pressure distribution to be uniform. This can be achieved by gradually decreasing the thickness of the base towards the edges so that the base is only as much thick as it is regarded to resist the induced moments and shears.

 

General rules of Foundation Design

While designing a foundation the following points must be borne in mind.

  • When a soil is yielding soil, a certain amount of settlement must be reduced as much as possible by bringing down the pressure intensities.
  • It is necessary that a foundation shall be designed so that if at all a settlement should occur, it will be uniform. In other words, the settlement of all the footings must be more or less the same.
  • This is a very important point in reinforced concrete structures due to the rigid connection between the different components of the structure.

In our next article, we will discuss the procedure of designing an isolated foundation and also justify the foundation design rules mentioned above.

Step 1:

Calculation of loads on the footing

Step 2:

Guide to Foundation Design

77 thoughts on “Types of Foundations | Design of RCC Structures”

    • That would be complicated. Water tanks are different than regular structures, as most of the weight and bulk is concentrated at the top. 10 m3 of water would mean 10 tons of water (10000 kilograms). Add to it weight of structure, and you can easily reach and even cross 25 tons of total weight.

      You must contact a qualified engineer for this design.

      Cheers!

      • I AM A CIVIL ENGINEERING STUDENT OF THE FEDERAL POLYTECHNIC ADO-EKITI, NIGERIA. I AM PASSIONATE IN BEING YOUR FRIEND, SO THAT ANYTIME I WANT TO INQUIRE SOMETHING ABOUT CIVIL ENGINEERING, I CAN CONTACT YOU. CAN I KNOW YOU BETTER? IF POSSIBLE YOUR CELLPHONE NUMBER, AS WE CAN ALWAYS TEXT-CHAT OR YOUR E-MAIL ADDREESS.

      • Hello Friend,
        now a days i am making my own home so please can you help me to design some stuructural components..and some constuction technical things…please provide me ur email id..so that i contact u..

        Thanks
        Ganesh from india.

    • Dear Abera
      your query is not a simple one. it needs more details. apparently required structure in very heavy and it would require pretty healthy columns to support the structure. roughly each column would have to bear a load of 3 to 3.5 ton which is not a small burden. moreover, as the height required is 4 meter which is again a challenging factor is mandatory to be addressed to avoid the columns from bring slender. so it is advised to get a proper design of this facility before even thinking to construct it at site.

  13. Want to build a garage one foot from an established oak tree thirty feet tall and 3 feet around. Want to save tree. Need to go 18 to 24 inches deep for footing. Can do?

  16. Thanks for sharing this.In-situ concrete slabs are commonly used. They are a typical method of construction of RCC slabs. And ofcourse they are less expensive than the prefabricated or precast construction methods.

  18. Hi I have encountered a hard rock very large while excavating for building foundation for 3 storey RCC building. The rock has been found at 1.2 m depth. I am thinking of inserting Steel rods in hapazard manner before casting of the concrete and hooking it to the mesh. The width of the mesh is 1.8m. I have not calculated exactly but I think since the rock is stable it should do fine and I am thinking of using M30 for the PCC at foundation. Please advice.

    • Hello Ahmad,
      Thank you for the comment. I am glad the articles were helpful. Do keep visiting because we will be putting up more informative and live examples of construction for better understanding.

      Cheers 🙂

  25. How to design Eccentric footing…?
    The column is @ the edge of the property line.. so the footing cant be extended in neighbour site.. how to design the eccentric footing.

  27. hi,
    I`m from Korea, and I need some information of other country`s foundation work. Plz help me.
    In our country, we use PHC(pretensioned spun high strength concrete pile) for most building foundation construction. And there are many method of foundation work such as RCD(Insitu method), PHC pile, Steel pipe …
    I wonder how do you usually do on your work?

  28. A total area of 870 Sqft is to be designed for 2 storey while one room size is 15′-0”x11′-0” will it be ok to give columns at 11′-0” interval each with 6 no. 4 bars in each column of 1′-0”x1′-0”

  29. Hi
    A total area of 870 Sqft is to be designed for 2 storey while one room size is 15′-0”x11′-0” will it be ok to give columns at 11′-0” interval each with 6 no. 4 bars in each column of 1′-0”x1′-0”

  30. Hi,
    I plan to construct a small house ground floor and first floor. length of 30 feet and width of 20 feet. this dimension is wall to wall only can you advise the foundation details, the soil is clay.
    regards,
    jalal

  31. My name is Santosh Kumar.I have some problem with my project. I studying in B.E(civil) in India.
    My Professor is given me one project of “RUBBER MASONRY FOUNDATION “. I search about that topic in internet ,but i did not find any information.
    Please help me to make this project.
    thank you.

  32. I am plannintg to construct a 4 storey RCC residential building of approx 2000sq. ft. per floor. The type of soil (according to soil test report) is Medium/Type II; design safe bearing capacity is 233.09 KN. For the foundation, is RCC Independent Column footing good .

  33. Respected Sir/ madam,

    i am a civil engineer, i need to design a supporting insert plate, can suggest a good website or books for me.

    Thanking you,

    Regards
    Mukesh Shakti

    • Hello Manish,
      You do not require a machine for RCC construction. It is a framed construction. You only need a machine if you are going for prefabricated or precast construction.

  39. Hi, I’m planning on building a G+1 villa house by the sea. The structural eng decided to go with shallow strip raft foundation which would lead to partial load bearing walls.The strip raft foundation has columns which are of lesser thickness & depth, and use minimal steel than what you have in regular RCC column footings but then it goes through the entire set of house walls and is 3-4′ wide and 1′ thick with steel bars.

    Is this the cheaper than going for individual RCC footings ?? if so then by how much in % terms??

  41. hello madam, sir
    3 tons singal gardar crane .gardar span 40 feet, hoist hight 20 feet please suggestion beem size and beem fondection detals with civel drawing
    sunil yeoe
    simra bara
    nepal

  42. Respected Madam
    i am building my small villa next to sea during foundation of my house wht things i should tell the contractor to remind him.plz give me guidelines for RCC foundation help will be highly appreciated

  48. Hai mam, i am karthickeyan. I finished my civilengineering at 2012 and right now working in Chennai.
    “Sharing the knowledge is greater.”
    i need your help mam. could you send the step wise topics on building construction. So that it may useful get the knowledge and doubt about it.

  51. Hi my are saibu ahmed a student from kawara state polytechnic civil engineering department, I have a story building project which have construct the foundation and grand floor now my client want to change the design, he want building to have catilever both side. Please enlighten me on what to do.

  52. Hi my are saibu ahmed a student from kawara state polytechnic civil engineering department, I have two story building project which have construct the foundation and grand floor now my client want to change the design, he want building to have catilever both side. Please enlighten me on what to do.

  53. Thanks it looks every thing is important . i am interested to learn every thing step by step design with real examples or case studies with simple building to multystory building eventhough i am geotechnical engineering.

  54. Dear Benzu,

    Can you tell me if the number of rods in the columns reduce for higher floors? I find in construction of a seven storied building, the number of rods inside a column were 11 for the ground floor whereas it has reduced to 10 for the first floor. Will it continue to be reduced for 2nd , 3rd floors and so on?

    Can the full length of the column (10′) for a particular floor be constructed at a go or it is better to construct a 10′ column in two stages, i.e 5′ each?

    • Hello Tameem,
      It completely depends on the building plan. If the building plan is the same throughout, then the number of columns should not change from floor to floor. The dimensions of the column might change but not the number.

      Also, you can seek expert advise on the your project at minimal costs.

      Seek expert advise – By Civil Projects Online

  55. Hello,, I would like to know abt the load combination and factor of safety,, do we have to multiply 1.5 after adding all loads like dl+ll+wl etc etc??????

  56. Thanx for the piece, its really informative, plx will you continue deeply to advanced foundation, its meaning, types and factors to be considered on design? Thank u so much.

  57. Hi,

    I would like to know, if there is any system that can prove the maximum bearing capacity after construction of the base? For example, pile can be tested by compression test.

    Please answer…

    Thanks

    Adil

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