Like all other objects, a bridge expands when it gets warmer and contracts when it gets colder. If it were completely fixed, the tensions in the beams would become too great. To allow it to move with changes in temperature, the bridge is given a fixed support at one end and a movable support at the other.

If it is a railway bridge, the length changes of the tracks must also be compensated for. This is done with so-called dilatation joints.

This movable support was used until 1996 at one end of the Duvnäs Bridge.

The Duvnäs Bridge has spans of 40 metres. When the temperature increases from -20°C in winter to +20°C in summer, the spans expand by about 25 millimetres

Caption: Duvnäs Bridge over the Dalälven River (between Borlänge and Mora).