What Shear Means
Shear is a type of force applied to a stationary object or structure. The force is laterally applied in different directions. If you imagine two cars pulling on the same object in different directions, each counteracting the other and moving in the opposite direction, that is shear force. Shear forces come from moving objects, or the weight of different members in a structure. Usually in shear walls, the force comes from weight pulling in different directions.
A shear wall is one built to withstand this force. Shear walls withstand the force applied from overhead walls and the counteracting force of the foundation or walls below, pulling against this force. The two forces act in a similar fashion to the force of two machines pulling in opposite directions. Engineers utilize this concept to build stronger buildings that withstand both forces. The principle is applied not only in homes but also bridges, skyscrapers and even one-story buildings where the roof or other elements like wind apply different forces in the same plane.
Examples and Types
The standard shear wall is comprised of two main elements: the stud framing made of vertically aligned 2 x 4 boards nailed to horizontally-aligned baseboards and a sheeting material nailed onto the frame across its length. The material is typically plywood, but there are other types of walls made with metal sheeting and wood, or metal sheeting and metal framing. Metal framed walls with plywood are another example. The plywood or metal sheeting provides stability to counteract the opposing forces on either side of the wall.
How They Are Built
One typical example of this type of wall is made with common 2 x 4 studs installed upright between 2 x 4 baseboards on a sill or base plate, a long solid unit under the framed wall. End studs between windows and doorways provide additional support while plywood panels provide lateral support on areas with no windows or doors. A top plate provides additional support. A hold-down secures the framing to a foundation or flooring joists while horizontal blocking, or horizontal 2 x 4 boards, are positioned halfway up the wall. The floor is then built on top of this wall with diagonal blocking between the vertical studs.