Published on March 6, 2014
SHALLOW FOUNDATION PREPEARED BY MOHAMMAD SHAHID B.ARCH 3RD YR
INTRODUCTION TO FOUNDATION The lowest part of a structure is generally referred to as foundation. FUNCTION OF FOUNDATION To transfer load of the superstructure to the soil on which it is resting REQUIREMENTS A properly designed foundation is one that transfers the structural load throughout the soil without overstressing of soil which can result in either excessive settlement or shear failure, both of which can damage the structure.
LOADS AND SETTLEMENT OF FOUNDATIONS Types of loads on foundations Dead, live, wind, inclined thrusts and uplift, water table and earthquake forces Types of settlements Uniform and differential - Differential settlement must be minimized, depends on site soil conditions and distribution of loads on columns supporting the building
TYPES OF FOUNDATION Foundations are classified as SHALLOW FOUNDATION AND DEEP FOUNDATION 1. Shallow foundation- It has a smaller depth limited to the depth of the footing. It spreads the load from superstructure on a larger area of soil. They are classified as a. Isolated footing b. Combined footing An isolated footing supports one wall or one column .either flat Or stepped which distribute the Load of wall to the soil. An Isolated footing supporting a Single column is commonly Used where the loads on column are Small and columns are not closely Spaced. They are of the following Footing for column Shapes. Footing for wal
SQUARE SPREAD FOOTINGS / PAD FOUNDATION support a single centrally located column use concrete mix 1:2:4 and reinforcement the reinforcement in both axes are to resist/carry tension loads.
RECTANGULAR SPREAD FOOTINGS Useful when obstructions prevent construction of a square footing with a sufficiently large base area and when large moment loads are present
CIRCULAR SPREAD FOOTINGS are round in plan view most frequently used as foundation for light standards, flagpoles and power transmission lines
SPREAD FOOTING FOUNDATION Also known as a footer or footing It’s an enlargement at the bottom of a column/ bearing wall that spreads the applied structural loads over a sufficiently large soil area. Each column & each bearing wall has its own spread footing, so each structure may include dozens of individual footings. The spread foundation consists of concrete slabs located under each structural column and a continuous slab under load-bearing walls. For the spread foundation system the structural load is literally spread out over a broad area under the building It is most common type of foundation used due to their low cost & ease of construction. SPREAD FOOTING
COMBINED FOOTINGS Combined footing supports two or more columns. Combined footing supporting two columns may be used for column on property lines.
When the bearing capacity of the soil is low , then continuous strip footings supporting more than two columns in a row are provided. Such strip footings more than two columns in both the directions are known as grid foundation. GRID FOUNDATIONS
RAFT FOUNDATION A foundation system in which essentially the entire building is placed on a large continuous footing. It is a flat concrete slab, heavily reinforced with steel, which carries the downward loads of the individual columns or walls. Raft foundations are used to spread the load from a structure over a large area, normally the entire area of the structure. It is normally consists of a concrete slab which extends over the entire loaded area. It may be stiffened by ribs or beams incorporated into the foundation. Raft foundations have the advantage of reducing differential settlements as the concrete slab resists differential movements between loading positions. They are often needed on soft or loose soils with low bearing capacity as they can spread the loads over a larger area.
PLAN VIEW ELEVATION
DEPTH AND LOCATION OF FOUNDATION Depth and location of foundation depends on 1. Zone of significant volume changes in soil. 2. Adjacent structures and property lines. 3. Ground water 4. Underground defects
Adjacent structures and property lines. Structures may be damaged by the construction of new foundations, as a result of vibrations, undermining by excavation or lowering of the water table. After new foundations have been constructed, the (new) loads they place on the soil may cause settlement of previously existing structures as a result of new stress pattern in the surrounding soil. In general, deeper the foundations and closer to the old structure, greater will be the potential for damage to old structures. Ground water Presence of water reduces soil bearing capacity, larger footing size more cost. During construction pumping is necessary – adds to the cost of construction. Part existing property line Property line
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