FAQs For Infrastructure Construction Bolts

Galvanized, A325, A490 and F1852 Tension Control Bolts For Construction

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Top Questions And Answers For TC Bolts

Where are tension control bolts used?

Tension control bolts are used in structural joints and other high strength applications. They have become a modern alternative to industrial rivets and conventional hex bolts because they are efficient to install at high speeds and are self-calibrating. They maintain critical connections in a wide range of high-demand applications.

What is bolt tension?

Bolt tension is one way of referring to the stretching or elongation of a bolt’s threads, which occurs as the bolt or nut is torqued. Bolt tension facilitates the clamping that fastens the connection in place and establishes a joint. It is important to correctly identify the proper amount of torque needed to achieve the right amount of bolt tension.

What is a TC gun?

A TC gun is also called a shear wrench. This is an electric tool that's integral to the correct installation of tension control bolts. A TC gun will torque the bolt’s spline and the nut at the same time but in opposite directions. The spline of the bolt will then shear off when the assembly is tightened to the correct tension.

What are tension control bolts made from?

Tension control bolts are manufactured from many of the same industrial-grade materials that are used to make standard bolts. Carbon steel, alloy steel, and weathering steel are among the most common types of materials as defined in A325 and A490 specifications. TC bolts are also sometimes mechanically galvanized when added resistance is needed but they may also be kept plain.

How does a tension control bolt work?

Tension control bolts work because of their self-calibrating capability. Their unique form and installation method contributes to optimal tensioning. They are installed using a TC gun or a shear wrench, which will simultaneously torque the nut and the spline of the bolt. Once the spline shears off of the bolt, the correct tension is reached.

How are tension control bolts measured?

The primary measurements of tension control bolts are their length and their diameter. The diameter measurement is taken across the thickness of the bolt’s shaft, which is the unthreaded portion. The length measurement is the length of the threaded portion that excludes the spline or twist-off, as this part will be sheared away once the bolt is installed.

How are tension control bolts installed?

Tension control bolts are installed through the use of a TC gun or shear wrench, which is a special tool designed specifically for the purpose. The wrench has an inner and outer socket, which grip the nut and spine of the bolt and rotates them simultaneously but in opposite directions. This action causes the spline to be sheared off once the correct tension is reached.

Do tension control bolts need washers?

Tension control bolts require the addition of washers as part of the total assembly. Manufacturers will almost always supply TC bolts that are assembled with a nut and a washer that are suitably sized for the bolt. These parts are required during the installation process. The washer is essential in distributing force as the assembly is tightened in place.

Do tension control bolts need to tensioned before installation?

When following installation best practices, tension control bolts should always be tensioned on installation. Delayed tensioning can lead to a number of problems that will compromise the bolt’s performance and security of the connection. These issues are mostly due to a loss of lubrication, which causes many other issues.

Do tension control bolts need to be lubricated?

Tension control bolts do not need additional lubrication. TC bolts manufacturers lubricate these bolts during the manufacturing process. This step is vital to ensuring the self-calibrating capability of TC bolts, which then amounts to efficient and secure installation. If any loss of lubrication occurs, only a manufacturer can properly reapply lubricant to these types of fasteners.