Types of Footing in Building Construction

Types of Footing in Building Construction Footing:  The  function  of a footing  or a foundation  is to transmit  the  load form  the structure  to the  underlying  soil.

The  choice  of suitable  type of  footing  depends on the  depth  at which  the  bearing  strata lies,  the  soil  condition  and  the type  of superstructure.

Types of footing

Following  are the  different  types  of footing  used  for concrete  structure

1.  Isolated  footing

2.  Combined  footings

3.  Strap footing

4.  Mat or raft  foundation

5.  Pile  foundation

Isolated  footings  are provided  under  each column  and may  be square,  rectangular,  or circular  in  plan.  Footing  may  be flat  or tapered.

Combined  footings  are provided  to support  two or more  column  loads.  These  may  be continuous  with  rectangular  or trapezoidal  in  plan  as shown.  Combined  footings  become necessary  under  the following  circumstances:

·         when  the isolated  footings  overlap.

·         when  the exterior  column  is  close  to the  property  line  with  the  result  symmetrical  isolated  footing  can not  be provided.

Strap footing  is  one of the  types  of combined  types  of combined.  It consists  of an isolated footing  of  two columns  connected  by a beam  called  strap beam.  The strap  beam does not  remain  in contact  with  the soil  and thus  does not  transfer  any  load to the  soil.  This  is provided  when  one of the  columns  is  on the property  line.

The  mat  foundation  is  provided  when  the soil  is  having  very  low  bearing  capacity  and or when columns  loads  are heavy,  the  required  footing  area becomes  very  large  and uneconomical.