Presentation on theme: "FOUNDATION The foundation of a structure is the lowest part of the sub-structure interfering with the soil and the structure. It consists of some structural."— Presentation transcript:
1 FOUNDATIONThe foundation of a structure is the lowest part of the sub-structure interfering with the soil and the structure. It consists of some structural element (pad or base) the soil underneath.
2 FOUNDATION ENGINEERING Foundation engineering is the branch of civil engineering which deals with the following two types of problemsEvaluation of the ability of soil or bearing capacity of soil.Decision of the proper type of footing, size of footing and at what depth it should be placed.
3 PURPOSE OF FOUNDATIONThe purpose of foundation is to transfer the load of the structure to the underlying soil without causing the danger of failure in shear and excessive settlement.
4 CLASIFICATION OF FOOTING Shallow foundationDepth/Width < 1Deep foundationDepth/Width >4Shallow foundations spread the load laterallyDeep foundations distribute the load vertically rather than horizontally.
5 TYPES OF FOUNDATION STRIP FOOTING It is simply the enlargement of the bottom of the wall that will sufficiently distribute the load to the foundation soil.When length to the width ratio of bearing area is greater than or equal to 10, this type of footing is called “strip footing”.L/B > 10
6 STRIP FOOTINGThis type of footing displays essentially one dimensional action, cantilevering out on each side of the wall.
7 TYPES OF FOUNDATION SPRAED OR ISOLATED OR INDIVIDUAL FOOTNGS Spread footings are square or rectangular pads that distribute the column load to an area around a column i.e.; these support only one column. These are most commonly used type of shallow footings because they are usually more economical. A spread supports one column or one wall.
8 SPRAED OR ISOLATED OR INDIVIDUAL FOOTNGS These may beIsolated or Individual footingStepped FootingsTappered FootingsIt is used to support the load of a single column. These are provided where loads are relatively light and columns are far spaced.
9 COMBINED FOOTINGSA combined footing is a long footing supporting two or more columns in one row. Such a footing is often used when one column is closed to the property line, also when the loads are heavy and the isolated footing overlaps.
10 COMBINED FOOTINGSThe shape of the footing is normally rectangular but trapezoidal footings are also used if loads from two columns are different or if one column lies on the property line for the even distribution of stress.If combined footings are designed on the basis that line of action of the resultant must coincide with the centroid of the footing. By the provision of combined footing the risk of differential settlement is reduced.
11 STRAP FOOTING (Concreted or cantilever footing) If two isolated footings are connected by a beam then this whole assembly is called ‘strap footing’.When footings are at different level, they can also be joined by a strap.A strap footing is used to connect an eccentrically loaded column footing to an interior column.
12 RAFT OR MASS OR MAT FOOTING A mat footing is a large footing usually supporting several columns in two or more rows. If there are a number of columns, and footings for most of the columns overlap in both the directions, then we provide a single footing for all the columns. This type of footing is called a ‘mat footing’.
13 RAFT OR MASS OR MAT FOOTING If the sum of the areas of individual footings is greater than the half of the total area of the building, it is economical to provide a raft footing.
14 FLOATING FOUNDATIONSWhere the basement is constructed, then the weight of the overburden soil is reduced, the balance is obtained by floating foundation.
15 GRILLAGE FOOTINGIt consists of a single or double tier of steel beams. The top tier is laid at right angle to the bottom tier. The beams are encased by concrete. It is suitable for single column load.
16 PILESIf bearing capacity of the upper soil layer is insufficient for a spread foundation but firmer strata is available at greater depth then the piles are used to transfer the load to the deeper layer.