Relative and Absolute Deflections

Tekla Structural Designer calculates both relative and absolute deflections. Relative deflections measure the internal displacement occurring within the length of the member and take no account of the support settlements or rotations, whereas absolute deflections are concerned with deflection of the structure as a whole. The absolute deflections are the ones displayed in the structure deflection graphics. The difference between relative and absolute deflections is illustrated in the cantilever beam example below.

Relative deflections are given in the member analysis results graphics and are the ones used in the member design.

Steel beam deflections

Deflections of steel beams in design are calculated from first order linear results since these are SLS deflections that are compared with standard limits such as span/360. This means that the effects of any non-linearity such as a continuous beam sitting on sinking supports i.e. non-linear springs are not taken into account in design. If these springs are linear this is not an issue.