That something is not, we are sorry to say, big windows. When wind or earthquake forces are applied to the house, the floors and roofs want to move sideways. Getting the lateral force from the exterior walls to the roof or floor and into the shearwall is only one step in the sequence, though.
Once the forces are distributed to the shearwall, the integrity of the shearwall itself becomes an important factor. The diagram below to the left shows how a shearwall resolves the applicable lateral forces applied to it. The connections between the framing 2x4s or 2x6s and the sheathing plywood creates a wall member that works as one element think of it like a big wood block.
Without the sheathing, the wall fails to act as one member and the individual connections between framing members fail under the same lateral forces as in the diagram above to the right.
When the shearwalls of a project are inadequate or absent and cannot resolve the load of the shifting weight above due to lateral forces, it can result in something like the image below. Garage doors, as it turns out, are not recommended in lieu of shearwalls.
Wood has its limitations as far as shearwalls are concerned and there are certainly other solutions, but they come at an expense. Moment frames below, right keep the structure to orthogonal lines, opening up the majority of the wall for that nice, big window, but the steel and labor involved puts a price tag on that window in the thousands or tens of thousands of dollars. So back to wood …. There is an important relationship between the proportions of a typical wood shearwall; the taller it is, the more of a tendency it has to turn over when a lateral force is applied.
In order to be effective, tall, skinny shearwalls either need to grow in width or the connections between the sheathing and framing members need to be increased. Increasing the connections typically results in larger nails at a greater frequency attaching the sheathing to the framing. As a general rule of thumb, shearwalls should have a minimum length of five feet. Shorter than that and you should plan on sending your structural engineer a bottle of something nice.
Because the shearwall acts as one member, the single force on the wall produces a compression force at one corner of the wall and a tension force at the other. So both sides of the wall typically need to resolve a compression force as well as a tension force.
Compression forces in the shearwall assembly are resisted through columns or studs in wood framing speak ; multiple 2x4s or 2x6s typically satisfy most situations, 4x4s or 4x6s can be used for larger compression forces, and the occasional steel post is used for excessive conditions. While many shear walls are simple rectangular planes, they can be even more effective at resisting wind or earthquakes when they are built in a variety of shapes:.
The best shape to use in any particular situation—some are more effective at absorbing seismic impacts while others are better suited to high winds—will be determined by the structural engineer. When you are installing shear walls in a house, a few simple rules will assure success. In most houses in the United States, the process consists of attaching sheathing either plywood or OSB to frames.
MT Copeland offers video-based online classes that give you a foundation in construction fundamentals with real-world applications. Classes include professionally produced videos taught by practicing craftspeople, and supplementary downloads like quizzes, blueprints, and other materials to help you master the skills.
He learned to build and weld while working on the farm with his grandad, and after earning a degree in Welding and Materials Engineering, he spent the next 10 years working in the heavy construction building everything from robots to ships to offshore oil rigs before transitioning to residential construction.
After spending a couple of years working with industry leading builders in Austin, Jordan and his wife Veronica struck out on their own to form Smith House Co.
Smith House Co. Jun 30, Share: Facebook Twitter Email. In this article 1 What is a shear wall? Share: Facebook Twitter Email. Explore Classes. Up Next.
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