While an extremely effective type of fastener, most people will never use tension control bolts unless they are working in the steel construction industry. These highly specialized bolts are seen as the ideal option for steel construction due to their ease of use, high strength and ability to hold materials in place effectively and in a structurally safe way free from failure.
The use of tension control bolts is recommended by the American Institute of Steel Construction. They are also an approved fastener recommended by the Research Council on Structural Connections for high-strength structural bolting. These bolts are tested and rated, so it’s important to choose the correct size to meet the needs of the project.
How They Work
As with all fasteners, tension control bolts come in a wide range of different diameters, each designed to have different tensile strength requirements. These include stress, tensile and proof load minimum and maximum amounts.
The bolt itself is actually sold as an assembly with a nut, bolt, and washer as well as a built-in spline. The spline is the tension control feature as it will snap at a particular tension level that prevents the need to test each bolt with a meter.
The bolts are installed with a specialized wrench, known as a shear wrench, that is an electric tool for quick and easy installation. The wrench has an outer and an inner socket that fits over the domed shape of the head to hold the outer edge of the nut as well as the inner spline on the top of the bolt head.
The outer socket turns counterclockwise while the inner turns clockwise. At the point where the predetermined tension level occurs between the two, the spline snaps preventing further tightening and giving the correct and accurate tension on every bolt installed.