Anchor bolts are cylindrical fasteners that are used to connect objects and structural elements to concrete. They may be used for everything from holding a home to its foundations to attaching heavy industrial machinery to a factory floor. Many manufacturers make these bolts, and there are several different styles available for different applications. When installed correctly, they form a very firm, solid connection that will last for decades. Anchor bolts can be purchased in some hardware stores and through construction supply companies as well as manufacturers.
The classic version is a cast in place anchor bolt. These bolts are inserted into concrete while it is still wet, with the threaded part sticking up. When the concrete hardens, the bolt is set in place, and objects can be bolted down with the use of a nut that connects to the threaded section. These bolts are often used in new construction projects, where the location of walls and other elements that need to be connected to the foundation is well known.
The other type is a bolt that is inserted into the concrete after it sets. These bolts require a drilled hole, and they can be fastened in place with epoxy or with a wedge that expands to trap the bolt when it is tightened. For retrofitting and similar tasks, these bolts can be very useful, although it is important to install them properly or they may fail, sometimes catastrophically.
When anchor bolts are used in construction, the builder must usually abide by local building codes, which dictate the size of the bolts and the necessary distance between them. The goal is to distribute the load of the construction over multiple points, reducing the amount of stress on any particular bolt or any given area of concrete. An engineer or architect may calculate the stress and loads involved to make sure that the bolts are placed appropriately.
The major drawback to these bolts is that once they are in place, they cannot be removed without jackhammering out a section of concrete. In a situation where the bolts are critical construction elements, this is usually not a major issue, but it can be a problem when anchor bolts are used to secure heavy machinery. If a factory is reconfigured to produce something different, for example, the old fasteners may be in the way.