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foundation introduction.pptx

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foundation introduction.pptx

  1. 1. DATE: 12/18/2022
  3. 3. WHAT IS FOUNDATION ? • A foundation is the lowest and supporting layer of a structure. • is the lowest artificially prepared part of the structure that is in direct contact with the ground and that transmit the load of the structure to the ground • is the substructure of the building
  4. 4. WHAT IS FOUNDATION ? Super-structure Sub-structure Foundation Basement G+upper floors
  5. 5. FOUNDATION Isolated footing Combined footing Mat footing
  6. 6. FUNCTION OF FOUNDATION • to bear and support the structure • distribute the load of the building to the ground • Anchor/secure the structure against natural forces such as earthquakes, wind, rain etc • to isolate it from ground moisture • to prepare a level surface for masonry work
  7. 7. TYPES OF FOUNDATION I. Shallow foundation II. Deep foundation i. SHALLOW FOUNDATION: • Is the foundation that are provided immediately beneath the lowest part of structure near to the ground level • shallow if its depth is equal to or less than its width or if the depth is less than 3m
  8. 8. i. Shallow foundation:……………………… • These foundations are mostly placed on the first hard and firm strata available below the ground level • These type of foundations are used when surface soils are sufficiently strong and stiff to support the imposed/forced loads • Generally unsuitable in weak or highly compressible soil as poorly compacted fill, alluvial deposits etc
  9. 9. i. Shallow foundation:……………………… Various shallow foundation
  10. 10. ii. DEEP FOUNDATION: •when the depth of the foundation is more than the width of the footing •generally adopted for bridge piers etc
  12. 12. 1. Spread footings a. Single footing b. Stepped footing c. Sloped footing (RCC) d. Wall footing without step e. Stepped footing for wall f. Grillage foundation 2.Combined footings a. Rectangular combined footing b. Trapezoidal combined footing c. Combined column-wall footings 3. Strap footings 4. Mat foundation a. Solid slab system b. Beam slab system c. Cellular system TYPES OF SHALLOW FOUNDATION: pad footing/isolated footing Wall footing/ strip footing
  13. 13. 1. Spread footings •Spread footings are those which generally supports one wall or one column •Spread footings are those which spread the super- imposed load of wall or column over a larger area. •Foundations constructed by increasing the area at the base of the structure by means of offsets are called spread footing
  14. 14. 1. Spread footings……………. Types: a. Single footing b. Stepped footing c. Sloped footing d. Wall footing without step e. Stepped footing for wall f. Grillage foundation pad footing/isolated footing Wall foundation/ strip footing In above a. b. c. if columns are of brick these are known as masonry pillar footing and if the columns are of concrete than these are reinforced concrete footing)
  15. 15. 1. Spread footings……………. •Pad/isolated footing: is the one which provides footing for a single column or a wall •Strip footing: is the one which provides footing for a continuous wall •RCC footing: these may be stepped or sloped like pad footings in order to support heavy loads, reinforcement is provided at the base
  16. 16. b b B B Fig: concrete column footing/ reinforced concrete
  17. 17. a. Single footing: isolated/pad footing or RCC •shows a single footing for a column, in which the loaded area (b x b) of the column has been spread to the size B x B through a single spread • The base is generally made of concrete In brick columns: •The offset is generally 10 to 20 cm •The base should not be less than the offset(in case of cement concrete the base should be equal to offset and in lime concrete 3/2 of offset)
  18. 18. b. Stepped footing: isolated/pad footing or RCC •shows the stepped footing for a heavily loaded column, which requires greater spread or when soil bearing pressure is less •The base of the column is made of concrete •In case of brick pillar offset should not exceed 5cm •In case of masonry pillar the offset is 10 to 15cm • the height of each step 15cm to 22.5cm
  19. 19. c. Sloped footing: RCC •shows the case in which the concrete base does not have uniform thickness •but is made sloped, with greater thickness at its junction with the column and smaller thickness at the ends •Since concrete can be mould in any shape, sloped footing is possible in RCC
  20. 20. d. Wall footing without step: (strip footing) •This type comes under the wall foundation/ strip foundation and is the simplest type of footing •shows the spread footing for a wall •Consisting of concrete base without any steps t 3t
  21. 21. d. Wall footing without step: ………….(strip footing) •This footing is applicable when the wall carries light loads or when safe bearing pressure is very high •The wall directly rest on the concrete base with no offsets •The projection of the base varies from 10cm to 20 cm •as a thumb rule the width of concrete base should not be less than twice the width of the wall
  22. 22. e. Stepped footing for wall:(strip footing) •Usually masonry walls have stepped footings with a concrete base •Offsets are provided at the base of brick wall (offsets are generally one fourth of brick length) t j j 2(t+j)
  23. 23. e. Stepped footing for wall: ……….. (strip footing) •In case of brick walls the offsets does not exceed 5cm; the corresponding height each step would be 10cm •In case of stone masonry offsets are provided upto 10 cm and height of each step 15 to 20cm •When wall carries heavy load and the safe bearing pressure is not very high
  24. 24. •In the above figure : t: thickness of wall j: projection of concrete bed at the base
  25. 25. f. Grillage foundation: •Is a type of isolated footing provided for heavily loaded steel foundations especially in those locations where the bearing capacity of soil is poor •The depth of foundation is limited to 1m to 1.5m •The load of column or stanchion is distributed to a large area with the help of tiers of joists •Tiers are placed right angle to the tier at next level •Tiers are wooden or rolled steel section(I-section)
  26. 26. f. Grillage foundation
  27. 27. f. Grillage foundation:……………. •Grillage foundation avoids deep excavation and provide necessary area at the base of structure to reduce the intensity of pressure •Types of grillage foundation: Steel grillage foundation Timber grillage foundation
  28. 28. Steel grillage foundation: •These foundation are constructed of rolled steel joists(R.S.J) • joists are provided in two tiers placed at right angle to each other •At each tier the joist(steel beam) are held in position with the help of 20mm diameter spacer bars •The grillage beams/ joist(steel beam) are embedded in concrete however concrete do not take the load
  29. 29. Steel grillage foundation:
  30. 30. Suitability of steel grillage foundation: •For structures like columns, pier, foundations subjected to heavy loads •Employed to foundations of buildings as theatre and town halls Steel grillage foundation are provided for a masonry wall on a soils of low bearing capacity
  31. 31. Timber grillage foundation: •Provided for heavily loaded timber column or masonry wall •Instead of steel joists timber planks and timber beams are provided •Useful in water logged areas and when bearing power of soil is very low •In water logged areas the steel may be corrugated •Unlike steel grillage foundation , concrete is not embedded in timber beam
  32. 32. THANK YOU

Notas do Editor

  • Order of soil suitability for foundation support
    Best : Bed rock
    Very good : Sand and gravel Good : Medium to hard clay (that is kept dry)
    Poor : Silts and soft clay
    Undesirable : Organic silts and organic clay
    Unsuitable : Peat