Q. Explain about Differential settlement?

Structural stability is not very much affected by uniform settlement of a structural system. Major amount of damages will be taking place to the structure due to differential settlement. Hence, the maximum differential settlement is the determining factor for the design of foundation. Even slight amount of differential movement can cause substantial damage between two adjoining columns of a structure.

Figure shows the settlement of a number of columns. Some columns have settled more and some have settled less. Maximum differential settlement is 6. The critical settlement is that settlement which causes the maximum amount of distortion to a part of the building only. The ratio of 6/L is called the angular distortion.

Hence the settlement is to be computed at various points in a structure such as comer, centre, heaviest column location, lightest column location. If the angular distortion is less than 11300, structural damage or damage to the interior wall finish will not occur. The permitted angular distortion in framed structure (without interior brick wall) is 11150. Hence in a brickwall a differential settlement of 1 cm can be permitted for a span of 3 m. Differential settlement will occur either due to a) differences in loading or b) differences in soil conditions.