Types of Foundations | Design of RCC Structures





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



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  1. #1 by devendra singh on December 2, 2012 - 11:16 am

    which method is better in rcc
    working stress or ultimate load or limit state method
    nd how we used means we take anyone

  2. #2 by parwez on November 16, 2012 - 5:14 am

    you have done fantastic job……….

  3. #3 by karthickeyan on November 4, 2012 - 4:53 am

    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.

  4. #4 by sami on November 1, 2012 - 2:09 am

    can you give example and explain how to design raft foundation for buildings

  5. #5 by Amit Parikh on October 16, 2012 - 2:38 am

    I want to know priliminary information about foundation. Their types and where and why each type is suitable?

  6. #6 by aswathy on October 2, 2012 - 4:57 am

    hello madam
    i am a civil engineering student i have doubts on different type of supports what is the differnce between pinned support and fixed support

  7. #7 by Shahab on October 1, 2012 - 2:35 am

    i want vocational trainning . where it will best for me .student of btech 3rd year civil branch

  8. #8 by Khalil on September 28, 2012 - 11:56 pm

    Thanks so much for this information and site, this is really important for civil engineer student i will follow it

  9. #9 by Muzammil Madre on September 3, 2012 - 7:08 am

    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

  10. #10 by sunil yeole on August 31, 2012 - 8:26 am

    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

  11. #11 by SUJIT GHOSH on August 8, 2012 - 2:06 am

    how shall I calculate Reinforcement detail e.g. shape of bending, cutting length while considering a footing with trapizidal section?????

  12. #12 by charles on August 2, 2012 - 1:43 am

    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??

  13. #13 by Mohammed on July 5, 2012 - 1:25 am

    Thanks a lot mam for this site.It is very help ful for civil engineering students.

  14. #14 by dhaval on May 24, 2012 - 10:10 pm

    Hello madam,i am a civil engineer and i have some douts about structures. So please give me some suggestion.how we design a bridge foundation?

  15. #15 by Manish kumar on May 3, 2012 - 11:56 pm

    really nice website dud…
    i want to know about the latest machine required in r.c.c.
    plz tell me….

    • #16 by BenzuJK on May 15, 2012 - 10:00 am

      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.

  16. #17 by Rahul on April 20, 2012 - 4:59 am

    I want to know that,
    How we decide foundation for various structure’s…
    Can you give me infomation about significance of several foundation…….

  17. #18 by manish on April 14, 2012 - 5:06 pm

    it is proving out to be very helpful with my projects

  18. #19 by mukesh shakti on March 22, 2012 - 12:04 am

    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

  19. #20 by Satya Pratim kakoty on March 18, 2012 - 9:14 pm

    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 .

  20. #21 by Santosh Kumar on March 9, 2012 - 4:59 am

    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.

  21. #22 by Jalal on January 28, 2012 - 10:13 pm

    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

  22. #23 by Faisal Hayat on January 11, 2012 - 10:24 am

    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”

  23. #25 by Faisal Hayat on January 11, 2012 - 10:23 am

    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”

  24. #26 by Ho sun Song on December 27, 2011 - 12:05 am

    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?

  25. #27 by bharath on December 14, 2011 - 8:13 am

    Dear sir.. we r doing our 4th b.tech. we need to do a project report.. we are intrested in buildings and design.. so please guide us.. in what way we have to go ahead

  26. #28 by Mohiddin N O on December 8, 2011 - 8:11 am

    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. #29 by ramesh singh on December 7, 2011 - 8:31 am

    what is the pipe foundation where it is used

    • #30 by BenzuJK on December 14, 2011 - 7:50 am

      Check this out:
      Metal Pipe Foundations

  28. #31 by shahzad khan on November 28, 2011 - 2:43 am

    out standing website ………

  29. #32 by sudha on November 25, 2011 - 8:56 pm

    thanks for this useful site

  30. #33 by nazir sangrasi on October 31, 2011 - 12:13 am

    it z really a great effort

    • #34 by BenzuJK on November 6, 2011 - 3:34 am

      Thank you Nazir. We are glad our articles have been helpful to you ! Do keep visiting.
      Cheers 🙂

  31. #35 by Munesh on October 4, 2011 - 11:57 pm

    Good to get updated on subject.

  32. #36 by ahmad on September 14, 2011 - 3:37 am

    thank it is good wibsite for engineers

    • #37 by BenzuJK on September 15, 2011 - 5:42 am

      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 🙂

  33. #38 by Freddy Ochi N Sangma on September 12, 2011 - 11:58 pm

    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.

    • #39 by BenzuJK on December 14, 2011 - 8:00 am

      Hello Freddy,
      What you are doing is absolutely fine. Go ahead!

      Cheers 🙂

  34. #40 by Florence M. Cano on August 25, 2011 - 11:58 pm

    Exellent for civil engineering! You have such a brilliant idea. Good website to know more on subject especially for civil engineers.

  35. #41 by Anne on August 16, 2011 - 11:59 pm

    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.

  36. #42 by Kartik Sharma on August 12, 2011 - 9:29 am

    iTs SuPEr cOOL!!!!!!!!!!!!

  37. #43 by Lloyd Amarille on August 10, 2011 - 11:04 pm

    Excellent post for this could be helpful on footing details. I just wanted to know on the allowable distance on the deep of natural grid lines. Thanks!

  38. #44 by Jim on June 6, 2011 - 8:04 am

    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?

  39. #45 by benjamin brighton on June 3, 2011 - 12:58 am

    Exellent for civil engineering to be a good creative&me as member i need a lot of cooperation so as to do different researches

  40. #46 by Hazmath on May 30, 2011 - 12:50 am

    Great job as civil engineering student i got lot of befits from this site good luck!!!

  41. #47 by Nayanjyoti Hatibaruah on May 17, 2011 - 9:06 pm

    nice

  42. #48 by sheela on May 12, 2011 - 6:59 am

    great job………

  43. #49 by Priyank on April 25, 2011 - 10:00 am

    Excellent….

  44. #50 by Sunday ugochukwu daniel on April 5, 2011 - 9:06 pm

    Super civil ! Great job has been done here meant for civil engineers. Come and peruse…

  45. #51 by VAMSI KRISHNA on March 23, 2011 - 1:25 pm

    very good for civil people.

  46. #52 by Ashok kumar on March 15, 2011 - 5:43 am

    Good website to know more on subject especially for civil engineers.

  47. #53 by Abera on March 11, 2011 - 10:59 pm

    how to design a column to up 4 metre height of 10 m3 water tanker

    • #54 by BenzuJK on March 29, 2011 - 2:25 pm

      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!

      • #55 by ADEKUNLE ALEX AWOLALU on July 12, 2011 - 4:17 am

        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.

        • #56 by BenzuJK on July 13, 2011 - 4:46 am

          Hello Alex,
          You can always stay in touch through my blog. You are always welcome to ask any questions regarding Civil Engineering and Architecture and I will make sure I answer them and clear your doubts to the best of my ability.

        • #57 by ramesh on January 27, 2012 - 9:24 pm

          i need to clarify some doubts
          .. plz reply to my mail

        • #58 by ankit on April 6, 2012 - 10:34 am

          ok. i want to become in touch of u so that i can improve my career in civil engineering

        • #59 by BenzuJK on April 8, 2012 - 3:56 am

          Hello Ankit,
          You can always ask questions and contact me through the comment section on my blog.

          Cheers 🙂

      • #60 by GANESH on December 18, 2011 - 11:04 pm

        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.

    • #62 by Saqib on December 15, 2012 - 2:52 am

      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.

  48. #63 by berhanu on March 7, 2011 - 4:39 am

    how to make a design for tunnels of rail ways?

  49. #64 by dith on March 2, 2011 - 12:06 am

    how to design earth crack(foundation)?

  50. #65 by fanka kongnyuy on January 11, 2011 - 4:27 am

    why do we determine factors of safety for beams and columns

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