Wednesday, October 17, 2012

SHALLOW FOUNDATION - Spread Footings: Single footing, Stepped footing, Sloped footing, Wall footing, Grillage foundation.

Spread footings are those which spread the super-imposed load of wall or column over a larger area. Spread footings support either a colunm or wall. Spread footings may be of the following kinds:

(i)   Single footing [ Fig. 2.2(a)] for a column
(ii)  Stepped footing [ Fig. 2.2(b)] for a column
(iii) Sloped footing [ Fig. 2.2(c)] for a column
(iv)  Wall footing without step [ Fig. 2.3(a)]
(v)   Stepped footing for wall [ Fig. 2.3(b)]
(vi)  Grillage foundation [ Fig. 2.4]


Fig. 2.2 (a) shows a single footing for a column, in which 
the loaded area (b x b) of the column has been spread to the size 
B x B through a single spread. The base is generally made of concrete. 
Fig. 2.2 (b) shows the stepped footing for a heavily loaded column, 
which requires greater spread. The base of the column is made of 
concrete. Fig. 2.2 (c) shows the case in which the concrete base does 
not have uniform thickness, but is made sloped, with greater thickness 
at its junction with the column and smaler thickness at the ends.


Fig. 2.3 (a) shows the spread footing for a wall, consisting 
of concrete base without any steps. Usually, masonry walls have 
stepped footings as shown in Fig. 2.3 (b), with a concrete base.

Fig. 2.4  shows a steel grillge foundation for a steel stanchion carrying heavy load. It is a special type of isolated footing generally provided for heavily loaded steel stanchions and used in these locations where bearing capacity of soil is poor. The depth of such a foundation is limited to 1 to 1.5 m. The load of the stanchion is distributed or spread to a very large area by means of two or mor tiers or rolled steel joints, each layer being laid at right angle to the layer bellow it. Both the tiers of the joists are then embeden in cement concrete to keep the joists in position and to prevent their corrosion.
The detailed method of construction has benn explained in 3.6 Grillage foundation is also constructed of timber beams and planks (Fig. 3.12 and 3.13)

1 comment:

  1. Where's the link to steel grillage foundation details? I'd like to know the thickness of the I section