Define term transfer of stress to footing.
Transfer of Stress to Footing:
The column transfers the load to the top of the footing by bearing. The magnitude of the pressure allowed under direct compression on an unreinforced, loaded area of the same size is limited to 0.45fck When the supporting area is larger than the loading area on all sides, the stress may be increased by a factor √(A1/A2) where A1, is the area of footing and A2 area of column. However, this factor should not be greater than 2. If the strength of footing is less than that of column, this also should be considered. If the allowable stress is exceeded, steel reinforcement is extended into the footing to transfer the stress. Dowel bars can also be provided to transfer the stresses and they should extend into the column to a distance equal to the development length of column base. For M20 grade concrete and Fe 415, the depth required for anchorage is 37.6 Φ (here Φ is the diameter of the bar. Usually it is rounded off to 40Φ.
The external longitudinal bars or dowels should be at least 0.5 percent of the cross-sectional area of the supported columns. A minimum of 4 bars are to be provided and the diameter of the bars should not exceed the diameter of the column bars by 3 mm.