Last edited 14 Sep 2020

Lateral loads

Lateral loads are live loads that are applied parallel to the ground; that is, they are horizontal forces acting on a structure. They are different to gravity loads for example which are vertical, downward forces.

The most common types are:

Wind load.
Seismic load.
Water and earth pressure.

Wind load may not be a significant concern for small, massive, low-level buildings, but becomes more importance with height, the use of lighter materials and the use of shapes that may affect the flow of air, typically roof forms.

Significant seismic loads can be imposed on a structure during an earthquake. They are likely to be relatively instantaneous loads compared to wind loads. Buildings in areas of seismic activity need to be carefully designed to ensure they do not fail if an earthquake should occur.

Water pressure tends to exert a lateral load which increases linearly with depth and is proportional to the liquid density. Similarly, earth pressure (such as settlement) can be applied against below-ground structures such as basement walls, retaining walls, and so on.

Lateral loads such as wind load, water and earth pressure have the potential to become an uplift force (an upward pressure applied to a structure that has the potential to raise it relative to its surroundings). For more information, see Uplift force.

Structures should be designed carefully with likely lateral loads in mind. A structural element that is typically used to resist lateral loads is a shear wall. In simple terms, lateral forces could push over parallel structural panels of a building were it not for perpendicular shear walls keeping them upright. For more information see: Shear wall.

Similarly, bracing can be used to resist lateral loads. The beams and columns of a braced frame structure carry vertical loads, whilst the bracing carries the lateral loads. For more information, see Braced frame structure.