Introduction of Combined Footing
Combined footings are developed when two or more columns are close to one another & their foundations overlap each other. The function of a footing or a foundation is to convey the load form the structure to the underlying soil. The selection of ideal footing style is according to the depth of bearing strata, the soil condition & therefore the superstructure form.
What Is Combined Footing?
When two or more columns are situated in a linear manner & are carried on one spread footing, it’s generally referred to as a combined footing.
Isolated footings for every column are typically affordable. When individual footing has got to accommodate in two or over two columns is referred to as combined footing.
To attain homogeneous pressure dissemination, the Centre of Gravity of footing area must coincide with the Centre of Gravity of combined weights of the two column. A Combined footing supports two or more columns within a row.
Combined footings may be rectangular in structure (if both of them hold up identical loads), or maybe trapezoidal in structure (if there are space limitations & they generally carry unequal loads). Generally, they’re made of concrete.
Combined footings are provided when it’s absolutely essential, as
- When two columns are close, causing overlap of adjacent isolated footings.
- Where soil bearing capacity is low, resulting in overlap of adjoining isolated footings.
- Where Proximity of building line, is situated adjoining to a building column.
Types of Combined Footing
- Rectangular Combined Footing.
- Trapezoidal Combined Footing.
- Strap Combined Footing.
- Raft Combined Footing.
1. Rectangular Combined Footing
Of late, rectangular combined footing is generally employed in construction. The combined footing is typically a rectangular structure & so it’s named rectangular combined footing.
This sort of combined footing generally holds up two or more columns. The combined footings are utilized when there’s a necessity for an identical dissemination of load to the sub-soil.
2. Trapezoidal Combined Footing
Combined footing for 2 columns is necessary when ponderously loaded column is close to the property line or when one column holds up ponderous load with respect to others.
This style of combined footing is employed after convey of dissimilar loads from the super-structure to the sub-soil. Trapezoidal combined footing is taken into account when a column closes the property line & footing isn’t scattered to the front of the property line.
They can’t make an identical rectangular footing because of some heterogenous load from the structure. This form of footing doesn’t have any specific structure.
3. Strap Combined Footing
A strap footing may be a combination of spread footings of two columns joined by a strap beam. When the external column is around the property line, strap footing is employed.
The connecting beam between two spread footing doesn’t convey any load. The strap footing is employed to convey load from the ponderously loaded column to the inner column.
4. Raft Combined Footing
Raft footing may be a kind of combined footing that canopies the complete area below a structure & holds up all walls & columns. When the soil conditions under the foundation haven’t enough brawn at the load of the superstructure, then raft footing is applied.
It supplies an ideal grip on the structure of the soil & resists the tendency of overturning the building. It is supplied when an oversized number of floors are exited.
There are two sorts of raft footing-square & rectangular shape. The square mat footing is developed to supply stability to the building.
When a column is just too close to the building or structure where raft footing is needed. When two columns are so near one another or they overlap one another, then raft footing is vital to supply.
The raft footing is built where there the strip footing or spread footing isn’t enough that’s coming from the superstructure. To disseminate a consistent load from the superstructure to the subsoil raft footing is manufactured.
Advantage of Combined Footing
The advantage of Combined Footing is given subsequently:-
- The advantage of combined is that if there’s a need of two or more columns constructed in an exceedingly bijou area then we are able to employ combined footing there.
- Where the soil capacity of the development area is incompetent, to disseminate the load evenly to the sub-soil combined footing is developed.
- The most ordinary advantage of combined footing is when a column closes the delimitation & footing isn’t scattered at the front of the boundary line then combined footing aids to develop the column & aids to take care of the centre of gravity of the column.
- This variety of combined footing is more lucrative than another footing.
- Combined footing is supplied to homogeneously disseminate the load to the super-structure to the sub-soil.
- Because there’s a standard footing used for 2 or more columns, construction cost of the structure is diminished.
- The combined footing are frequently utilized in the difficult construction sites.
Disadvantage of Combined Footing
The disadvantage of Combined Footing is given subsequently:-
- The most ordinary disadvantage of combined footing is that, often ground-water level rises which results in loss of soil contact with the foundation.
- If the foundation raft soupiness is great, the substance may arise because of the warmth difference.
- The footing area is diminished because an ordinary footing is employed for several columns.
- In combined footing, it’s strenuous to take care of the centre of gravity of the columns.
- Another typical disadvantage of combined footing is that its structure must be varied to the place.
- Sometimes it’s ought to be made rectangular, otherwise trapezoidal.
Application of Combined Footing
The Application of Combined Footing is as given subsequently:-
- When a combined footing is taken into account when a column closes the property line & footing isn’t scattered at the front of the property line, then combined footing help to develop the column.
- The Dimensions of 1 side of the footing are evaluated to some lower value in order that column footings could also be combined.
- If the load-bearing ability of soil is minimum, & therefore the area requirement is more under the individual footing.
- If two or more columns are constructed in a very bijou area then we will use combined footing.
- Combined footing is supplied to criss-cross a perimeter or grade beam.
- This variety of footing is applied when the proximity of building a line is adjoined to a building column.
- The combined footing is provided when a homogeneous load dissemination is needed from the structure to the sub-soil.
- It is applied to evaluate the shearing force & bending moment at the salient point & thus the SFD & BMD are drawn.
- It is applied to create a more affordable structure. Because there’s an ordinary footing used for 2 or more columns, hence, the construction cost is diminished.