A footing made for two adjacent columns is called combined footing. When both columns of a combined footing carry equal load, rectangular combined footing is adopted. When the columns of a combined footing carry different levels of loads trapezoidal combined footing is adopted.'
A footing made for more than 2 columns is called continuous footing. Mat or raft foundation saves a building from differential settlement. The foundation cast using steel H-sections is called grillage footing.
Grillage footing used to carry heavy concentrated load.
