In applications such as bridges and tunnels, for the holding of large tanks and machines, and in many large buildings to connect the foundations to the walls for improved earthquake resistance, anchor bolts are able to provide a stable connection. Anchor bolts are also called cast-in place bolts. The heavy duty bolt is set into wet concrete headfirst and once the concrete has hardened, the threaded end of the bolt is attached to a component which anchors the bolt to its intended external load. Anchor bolts are commonly used because they provide a strong fastening with minimal room for error. Setting a bolt into wet concrete can be tricky, but once it has hardened, the bolt is very secure and able to hold a large amount of tension.
There are several different types of anchor bolts which will be chosen determined by the intended applications. Bent rods, hook bolts or J bolts, sleeve bolts and swaged bolts are some of the most common types of anchor bolts. Another widely used type is wedge anchors. These use a wedge shape bolt end, combined with a fastening sleeve to ensure a secure connection within the concrete setting. These need to be deeply embedded into the concrete so that the bolt cannot be pulled out under extreme force. For shallow installation, machine screw anchor bolts should be used. In terms of determining the most suitable type of bolt for an application, there are a number of factors to consider in terms of the demands placed on the bolts with corrosion, strength capacity and physical environment. Steel and carbon are commonly used to construct bolts as they are durable materials with strong physical properties. Stainless steel bolts are resistant to corrosion and are able to maintain their shape and strength even in high temperatures and extreme environments. Industrial bolts are also commonly galvanized, as this further increases the strength of a material. In terms of construction, the diameter of a bolt will increase with the need for greater strength and resistance. Anchor bolts are able to be used with high demand and high stress applications as they can withstand the tension produced by the holding system.