C7. Offsets

Most finite element software offer several options to define a beam on a fiber other than its neutral fiber.

This option is very useful, for example:

to easily create links between elements of different or variable heights (or thicknesses), but with an aligned face (see below),

to define the geometry of a variable-height deck (it is easier to introduce a fixed upper surface and to introduce a vertical distance between the upper surface and mean fiber that may vary during design),

for the application of loads on one side (for example on the upper surface of a bridge, for the creation of “load trains").

However, it is necessary to define the offset between this defining fiber and the neutral fiber, this offset being the eccentricity that can vary along the beam.

In case of doubt about the operation of this option, you can check it with another model where each beam is defined at its neutral fiber by creating the offset yourself with rigid links.

The subject of offsets is partially illustrated in the document Example of Prestressing and Offsets.

Illustration of the offset of a series of beam elements with respect to a horizontal upper surface.