The term ‘shear’ is used in construction in several different ways. Shear can be used when referring to a lateral load or force that is applied during high wind events or earthquakes, but it is also more generally used to describe stress on a wall system that occurs due to an applied load.
A structural wall member can fail due to the force of a shear load. Unlike tension, compression or bending, when a member fails due to shear forces, it is torn in two because the two sides of the member are being pulled in different directions. A good example of shear forces occur during hurricanes. Here winds pull the members up and sideways so the walls are forced in two different directions at the same time and this can lead to failure.
Wood structural panels are utilized in order to prevent shear forces from damaging homes. The ability of a wall system to resist shear forces relies entirely on the way in which it was constructed. This means that a ‘shear’ wall has been constructed with the intention of resisting shear forces.
The ability of a wall system to resist shear forces is also determined by the strength of the sheathing and installation. Here fastener schedule (nailing pattern) plays a critical role in securing the structural sheathing to the framing members to create the shear wall. If taller sheathing panels such as TallWall or Windstorm are not used, then blocking at the edges of the panels must be installed so all edges fall on framing members.
Engineers and designers determine how lateral and uplift loads will be distributed throughout the home. They then strategically place shear walls to resist those loads. OSB-sheathed walls have a better capacity to resist a larger amount of shear force and taller structural wall sheathing has the ability to resist these combined forces while reducing labor and material costs.
When a designer asks for walls to be ‘sheared off’ what they mean is that the sheathing needs to be applied to studs with a nailing pattern that will be able to resist high winds and earthquakes.
If you have any doubts about the need for shear walls or how they must be constructed, talk to your design professional or local building department for an explanation relating to your specific application. Shear walls are a critical component of the structure and for the well-being and safety of occupants.