Cross bracing is a construction technique in which braces are crossed to form an X shape to support a frame. Cross braces are often metal, but they can also be made of wood. This type of bracing is used on many different types of items including ship frames, furniture, walls and flooring. Virtually any type of frame can be strengthened with a cross brace — even building frames.
It's easy to understand the concept of cross bracing if we think of how wobbly a frame can be on its own. After all, a frame is mostly hollow space. Frames can be as simple as four strips of wood attached at each end like a picture frame, or as complex as a scaffold made from metal pipes twisting in many different directions. Scaffolds are large framed structures such as those used to raise up painters and window washers. The larger a framework is, the less sturdy it's likely to be without any supporting braces of some type added.
Metal is sturdy, yet because there are such long lengths of it in larger scaffolds, an unsteady frame that wiggles too easily can result. If another metal piece is attached between two of the frame's bars, less wiggling will occur. Yet, for the sturdiest solution, a second piece of metal attached and crossed to form an X is needed. This cross bracing effect reinforces any type of frame when the braces are added at sufficient places in the frame. Since crossed X patterns are diagonals in shape, these braces are known as a diagonal type of brace.
Anyone who has ever assembled furniture sold flat packed with diagonal braces included probably has a good idea of how strong cross bracing can make otherwise rickety structures. Backs of bookcases and entertainment units are usually cross braced to give them strength to hold heavy loads. Braces of this style on bottoms of chairs or tables keep seats and tabletops from wobbling.
In flooring installations, cross bracing is done in between floor joists to prevent them from moving around. Even large structures such as ships and buildings need the structural reinforcement achieved by this type of bracing. Ships are cross braced to help them stand up to heavy winds. Buildings are made in this way to help disaster proof them in case of earthquakes.
The cross brace technique used as a part of disaster-proofing buildings can only be done if the foundation is solid enough. Cross bracing can't take the place of a building's lack of structural integrity. If a building can be cross braced, one of the most effective methods is to create the X brace shape right from the top of the walls down to the floors.