Wall footings are pad or spread and strip Footings. The basic purpose of this foundation is to spread the load over a larger area so that the soil is able to withstand the stress, and the safe bearing pressure is not exceeded. In such types of foundations, if the resultant of the load deviates from the centre line by more than 116 of its least dimension at the base of the footing, it should be suitably reinforced.
Construction of Wall Footings:
In the case of brick walls, the width of section is increased by 114 brick (5 cm) offset on either side. The base rests on a plain concrete footing which projects 10 to 15 cm beyond the last brick offset as shown in Figure 1.
Fig.1: Masonry Wall Footing
The width at the base shall not be less than the width of the supported wall plus 30 cm. The depth of each course can be one brick or multiples of brick thicknesses. In the case of stone masonry walls, the offsets could be 15 cm with the heights of the course as 30 cm. The depth of the concrete which is generally of 1:4:8 (1 Cement : 4 Fine aggregate : 8 Coarse aggregate) or 1 : 5 : 10 ( 1 Cement : 5 Fine aggregate : 10 Coarse aggregate) mix should not be less than 15 cm. The angular spread of load from the wall should not be more than 1 vertical to 112 horizontal in masonry and 1 vertical to 1 horizontal for cement concrete.
If the load on the wall is heavy or the soil is of low bearing capacity, reinforced concrete strip footing can be provided (Figure 2). The thickness of the strip can be reduced towards the edge to effect economy.
Fig.2: RCC Wall Footing
No comments:
Post a Comment