Limiting values of structural deformation and foundation movement
(1) The components of foundation movement, which should be considered include settlement, relative (or differential) settlement, rotation, tilt, relative deflection, relative rotation, horizontal displacement and vibration amplitude. Definitions of some terms for foundation movement and deformation are given in figure H.1.
(2) The maximum acceptable relative rotations for open framed structures, infilled frames and load bearing or continuous brick walls are unlikely to be the same but are likely to range from about 1/2000 to about 1/300, to prevent the occurrence of a serviceability limit state in the structure. A maximum relative rotation of 1/500 is acceptable for many structures. The relative rotation likely to cause an ultimate limit state is about 1/150.
(3) The ratios given in (2) apply to a sagging mode, as illustrated in figure H.1. For a hogging mode (edge settling more than part between), the value should be halved.
(4) For normal structures with isolated foundations, total settlements up to 50 mm are often acceptable. Larger settlements may be acceptable provided the relative rotations remain within acceptable limits and provided the total settlements do not cause problems with the services entering the structure, or cause tilting etc.
(5) These guidelines concerning limiting settlements apply to normal, routine structures. They should not be applied to buildings or structures, which are out of the ordinary or for which the loading intensity is markedly non-uniform.
a) definitions of settlement p, differential settlement δp, rotation θ and angular strain α
b) definitions of relative deflection ∆ and deflection ratio ∆/L
c) definitions of tilt ω and relative rotation (angular distortion) β