Shear walls are interior and exterior walls that are designed to ensure the structural stability of a building. They transfer lateral loads down to the foundation, which prevents a building from toppling over. When designing shear walls, the location, climate conditions and building design determine which materials are used and where the walls are located.
Function
Shear walls are designed to resist lateral forces such as wind and transfer these forces to the component below them, which might be be other shear walls, floors, foundation walls, or slabs and footings. Shear walls prevent the roof or upper floors from swaying or moving off their supports as well. Buildings with stiff shear walls suffer less damage under extreme conditions, like in the event of an earthquake.
About Force
Shear walls resist shear lateral and uplift forces. These forces are caused by elements like wind, earthquakes and settlement, as well as the weight of the structure and its contents. These combine to create a twisting force that can tear, or shear, a building apart. Attaching a shear wall ensures the building will not be affected. Each wall must be supported perpendicularly, either with walls under or perpendicular to them, to ensure stability under forces from all sides. The shear force is transferred over the wall adjoining it, but no further. Uplift forces lift one end of a wall and push the other end down. This can result in a building toppling over. Uplift forces tend to be greater on tall narrow walls and lesser on longer walls.
Placement
Shear walls are located on each level of a structure, including crawlspaces. They're placed in equal lengths along all four exterior walls of the building to ensure an effective box structure is created. When a building's exterior walls cannot provide enough strength, or when the minimum height-to-width ratio for the building is exceeded, shear walls are added to the interior as well. Shear walls function best when they are located so that they align with foundation walls or footings vertically.
Materials
Shear walls may be made of several materials, although in any given structure these materials are not typically combined. Stucco, when properly installed and reinforced with wire mesh, resists small lateral loads. Lath and plaster construction is also used, although it is not common in new building projects. Plywood was once the material most used for constructing wood shear walls because thickness, grade and nail type and spacing could be combined in a variety of ways to achieve different strengths. With the creation of oriented strand board, it isn't used as often. OSB allows the manufacturer to produce the boards in the thickness, proportion and type of wood fiber that is needed in specific jobs or applications. Gypboard and gypsum sheeting are also listed as shear-resisting materials, but in regions where earthquakes are a risk, they're not effective because they lack the flexibility needed in these conditions. Foam core panels, or structural foam, may be used in the place of wood or metal studs between interior and exterior sheathing. Brick, clay, concrete and masonry can also be used to create a shear wall but must be assembled correctly to be effective. These materials are typically used when the forces exerted on the structure exceed what is acceptable for wood construction, or the height of the structure exceeds three stories. Steel is used when the forces on the structure are more than any other material can handle.
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