foundations for a number of columns in line are so closely spaced that the distance between the pads is approximately equal to the length of the side of the pads. (It is usually more economic and faster to excavate and cast concrete in one long strip, than as a series of closely spaced isolated pads.)
They are also used on weak ground to increase the foundation bearing area, and thus reduce the bearing pressure – the weaker the ground then the wider the strip. When it is necessary to stiffen the strip to resist differential settlement, then tee or inverted tee strip footings can be adopted. Typical examples are shown in Fig. 1.6.
Fig. 1.6 Strip Footings - Typical Examples.