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Monday, 8 January 2018

FOOTING

Footing is designed to sustain the applied load, moment and forces and the induced reactions and to insure that any settlement which may occur is as nearly uniform as possible. The term footing is commonly used in conjunction with shallow foundation. A footing is a foundation unit constructed in brick work, masonry or concrete under the base of a wall or column for the purpose of distributing the load over a larger area.
·        Types of footing chosen for a particular structure are affected by the following.

Ø The bearing capacity of underground soil.
Ø The magnitude of the column load.
Ø The position of water table.
Ø The depth of foundation of adjacent building.

·        Types of footing:
·        Isolated footing.
·        Stepped footing.
·        Combined footing.       

·        ISOLATED FOOTING:
An isolated footing is used to support the load on a single column. It is usually either square or rectangular in plan. It represents the simplest, most economical type and most widely used footing. Whenever possible, square footings are provided so as to reduce the bending moments and shearing forces at their critical sections. Isolated footings are used in case of light column loads, when columns are not closely spaced, and in case of good homogeneous soil. Under the effect of upward soil pressure, the footing bends in a dish shaped form. An isolated footing must, therefore, be provided by two sets of reinforcement bars placed on top of the other near the bottom of the footing. In case of property line restrictions, footings may be designed for eccentric loading or combined footing is used as an alternative to isolated footing.
·        COMBINE FOOTING:-
It is used when two column are so closed to each other that there individual footing overlap.  Combined footing is trapezoidal or rectangular in a plan. Trapezoidal footing is provided when the load on one of column is larger than the other column.
·       Foundation details:-
Ø Foundation base lean concrete shall be of mix 1:3:10.
Ø Concrete mix for raft and footing is M30.
Ø All reinforcement shall be in form of high strength cold rolled deformed steel bars of grade fe-500 conformed to IS: 1768-1985.
Ø Standard ‘L’ hooks shall be provided at the ends of all bars.

Ø Clear cover at top and bottom is 50mm.

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