3 Definition of Sub-Structure The supporting part of a structure; the foundation.(i.e.: footing / piling, pile cap, column stump )Sub-structure will include ground beams,ground floor column and ground floor slab.
4 Foundation An essential part of any building Spread out concentrated structural loads from walls and columns onto the generally softer material that form the surface of the earth’s crust.Structure who support the weight of the upper structure and applied loads.Designed to transmit building load to the supportive soils or rock.Foundation failure :- collapse or excessive settlement of a building supporting structure resulting from soil movement.Types of foundation include footings, piles and piers.
6 Foundation Causes of settlement are; Design and selection of foundation depends on:Total load of buildingNature and bearing capacity of soilCauses of settlement are;Deformation of soils causing by an imposed loadVolume changes of soil cause by seasonal conditions.Mass movements of ground in an unstable areas.
7 Foundation Shallow Foundations 1. Spread Foundations / Footings Foundations can be considered under two groups:Shallow FoundationsDeep FoundationsShallow Foundations1. Spread Foundations / Footings- Isolated Foundations, Strip Foundations and Combine Both2. Raft FoundationDeep Foundations- Pile, Pier and Caissons
8 Foundation Shallow Foundations Shallow foundations are those founded nearto the finished ground surface; generallywhere the founding depth (Df) is less thanthe width of the footing and less than 3m
9 Foundation Deep Foundations Deep foundations are those founding too deeply below the finished ground surfacefor their base bearing capacity to beaffected by surface conditions, this isusually at depths >3 m below finished groundlevel
13 Foundations – Strip Foundation Strip foundations are used to support a line of loads, either due to a load-bearing wall, or if a line of columns need supporting where column positions are so close that individual pad foundations would be inappropriate.
15 Foundations – Pad @ Isolated Foundation Pad foundations are used to support an individual point load such as that due to a structural column. They may be circular, square or rectangular. They usually consist of a block or slab of uniform thickness, but they may be stepped or hunched if they are required to spread the load from a heavy column. Pad foundations are usually shallow, but deep pad foundations can also be used.
17 Foundations – Raft Foundation Raft foundations are used to spread the load from a structure over a large area, normally the entire area of the structure. They are used when column loads or other structural loads are close together and individual pad foundations would interact.
19 Foundations – Pile Foundation Structures place on top of the piles.Piles + Pile Cap = Pile foundationFunction : Distributes load to the individual piles.Pile Cap will connect the pile together and distributes the superstructure loads to the layer beneath.
21 Pile Foundation Pile foundations are the part of a structure used to carry and transferthe load of the structure to the bearingground located at some depth belowground surfaceThe main components of the foundation are the pile cap and the piles
22 Pile FoundationPiles are long and slender members which transfer the load to deepersoil or rock of high bearing capacity avoiding shallow soil of low bearing capacityThe main types of materials used for piles are Wood, steel and concrete
23 Pile Foundation Functions of Piles - to transmit a foundation load to a solid ground- to resist vertical, lateral and uplift loadPilesPile CapColumn Stump
24 Pile FoundationClassifications of piles with respect to type of material1. Timber 2. Concrete 3. Steel 4. Composite piles
25 Pile FoundationClassifications of Piles – Timber Piles
26 Pile FoundationClassifications of Piles – Concrete Piles
27 Pile FoundationClassifications of Piles – Steel Piles
28 Design of reinforced concrete pad foundations The size of pad is determined from unfactored column load and the permissible bearing pressureTable : Permissible soil bearing pressure (kN/m2)Permissible pressure, not ultimate pressure…..used in conjuction with unfactored loadsSoil typeskN/m2Medium dense sand and gravel mix300Loose sand and gravel mix150Loose sand75Stiff clay200Firm clay100Soft clay<75
29 Design of reinforced concrete pad foundations Size column : 300 x 300 mm Axial load, N ; dead load = 900 kN live load = 400 kN soil bearing pressure = 200 kN/m2 Determine the dimension for a suitable square pad foundation. Assume self weight of pad footing is 120 kN Solution ; Total unfactored load = =1420 kN Required pad area = 1420 / 200 = 7.1 m2 Square pad footing, B = H = √7.1 = 2.66 m Depth of pad ≈ 2.66 / 6 = 0.44 say 0.45 m :- Use pad footing 2.66 m square and 0.45 m deep. Sketch isometric drawing of pad footing including the column and typical steel reinforcement arrangement in a footing and column
30 Design of reinforced concrete pad foundations Exercise A 325 mm square concrete column support the following characteristic loads : Dead load = 758 kN Imposed load = 630 kN Determine the dimension for a suitable square pad foundation if it bears on stiff to firm clay with a permissible bearing pressure of 150 kN/m2