Plan torsion is the torsional stress suffered by the supporting structure of a building when it is subjected to large horizontal forces. This effect is particularly significant in earthquakes.

The torsion in the plan appears due to the eccentricity between the center of rigidity of a floor and the center of mass of the load it supports, that is, the center of mass of that floor and upper floors.[1]​.

Seismic movements generate large lateral forces on buildings. As a reaction to this effort, the supporting structure of the building moves, vertically transmitting that displacement.[2]​ Because this movement is transmitted through the most rigid area of ​​the building (center of rigidity), while each floor will move around its center of mass, when the center of mass and the center of rigidity do not coincide, the floors will tend to rotate, producing a torsion effect in the structural elements that connect each floor.

Due to this effect, the structure can suffer multiple damages, both structural (cracks, warping) and non-structural (cracks in partition walls, broken windows), leading to the complete collapse of the building.[2]​ For this reason, the designs of earthquake-resistant buildings must be significantly symmetrical and regular,[3]​ since the asymmetry in the distribution and direction of the structural supports will tend to increase this torsion effect.