footings.pptx
- 2. Introduction Foundations ( sub structure) is the lower portion the building , usually located below ground level, which transmits the load of the super structure to the sub soil a foundation is therefore that part of the structure which is in direct contact with the ground to which the loads aretransmitted. The soil which is located immediately below the base of the foundation is called the sub-soil or foundation soil, while the lowermost portions of the foundation which is in direct contact with the sub soil is called the footing.
- 3. Functions of foundations The basic function of a foundation is to transmit the dead loads, super – imposed loads (or live loads) and wind loads from a building to the soil on which the building rests. Foundation serves the following purposes: 1. Reduction of load intensity Foundations distribute the loads of the super structure, to a larger area so that the intensity of the load at its base does not exceed the safe bearing capacity of the soil. 2. Even distribution of load Foundations distribute the non – uniform loads of the super structure evenly to the sub-soil 3. Provision of level surface Foundation provide leveled and hard surface over which the super-structure can be built.
- 4. 4. Lateral stability It anchors the super structure to the ground, thus imparting lateral stability to the superstructure. 5. Safety against under mining It provides the structural safety against undermining due to burrowing animals and flood water. 6. Protection against soil movements Special foundations measures prevents or minimizes the distress (or cracks) in the superstructure, due to expansion of the sub soil because of moisture movement in same problematic soils. Functions of foundations
- 5. Foundation loads Dead Load this is the load of the material used for the various components of a building such as walls, floors, roofs, etc. all permanent loads are thus included in dead load. Live Load this is the movable load on the floor and hence its variable. Its also sometimes known as the super imposed load. It includes the load of persons standing on a floor, weight of the material stored on a floor, weight f snow on a roof, etc. Wind Load In case of tall buildings, the effect due to wind should be considered. Structural Member Forces Uplift Earthquake Horizontal and vertical forces caused by the motion of the ground relative to the building.
- 7. Definition – Footings are structural members used to support columns and walls and to transmit and distribute their loads to the soil in such a way that the load bearing capacity of the soil is not exceeded, excessive settlement, differential settlement,or rotation are prevented and adequate safety against overturning or sliding is maintained. Footing
- 8. Wall footings are used to support structural walls that carry loads for other floors or to support nonstructural walls. Wall footings
- 9. Isolated or single footings are used to support single columns. This is one of the most economical types of footings and is used when columns are spaced at relatively long distances. Isolated or single footings
- 10. Combined footings usually support two columns, or three columns not in a row. Combined footings are used when tow columns are so close that single footings cannot be used or when one column is located at or near a property line. Combined footings
- 11. Cantilever or strap footings consist of two single footings connected with a beam or a strap and support two single columns. This type replaces a combined footing and is more economical. Cantilever or strap footings
- 12. Continuous footings support a row of three or more columns. They have limited width and continue under all columns. Continuous footings
- 13. Rafted or mat foundation consists of one footing usually placed under the entire building area. They are used, when soil bearing capacity is low, column loads are heavy single footings cannot be used, piles are not used and differential settlement must be reduced. Rafted or mat foundation