Types of bolts in steel structures

In this article we will discuss the most common types of bolts in steel structures. A bolt is a small piece of metal equipment made up of high-strength steel. The steel structure is the assembly of different members like beams, columns. These various steel members are interconnected using Bolts and Welding.

During hoisting, connectors will install a minimum of two bolts per connection. After the rest of the bolts are installed, they are tightened after the structure is plumbed. A systematic pattern must be followed when tightening bolts so that a joint is drawn together, and all fasteners are properly installed.

Parts of bolt assembly

It consists of a head and a shank. The size of the bolt is designed according to the diameter of the shank. The shank is threaded at the end to receive the nut.

• Grip is the distance from behind the bolt head to the back of the nut or washer. It is the sum of the thicknesses of all the parts being joined exclusive of washers.
• Thread length is the threaded portion of the bolt.
• Bolt length is the distance from behind the bolt head to the end of the bolt.

There are many bolt types, installation methods and joint types used in steel structure.

Recommended for you: Bolt tightening methods in steel structure.

ASTM bolt types

There are several types of bolts used in steel structure, including steel to steel connection bolts are

A307- Machine bolts, Ft=45 ksi (Low carbon steel)

• Not commonly used bolts, these bolts cannot carry the same load that high-strength bolts can
• Used for erection purpose only.

Group A-High Strength Bolts, Ft, = 90 ksi (High strength medium carbon steel)

• The most common bolts used in building construction.
• ASTM A325, A325M, F1852, A354 Grade BC, A449

Group B-High Strength Bolts, F, 113 ksi (High strength heat treated steel)

• The cost of these bolts is more than A325 bolts.
• ASTM A490, A490M, F2280, and A354 Grade BD

Ft = tensile strength from AISC Table J3.2

Note: F1852 and F2280 are Tension Control Bolts or “Twist-Off” Bolts which require a special tightening tool.

High-strength bolts obtain their strength not only through the shear and tension along the shaft, but also from the friction forces that are generated from tensioning the nut to prescribed levels.

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What are the common bolt sizes?

• High-strength bolts are available in diameter ranging from 1/2″ to 1 1/2″.
• The most common sizes of bolts are 3/4″⌀, 7/8″⌀ and 1″⌀.
• Commonly available in incremental length up to 8″. For more than 8″ length, threaded rods should be used.

It’s important to note that longer bolts may require greater torque to achieve the desired tension, which can make the installation process more difficult. Additionally, longer bolts may be more prone to bending or buckling under load, which can affect the overall performance of the structure.

Therefore, the length of high strength bolts used in a steel structure should be carefully determined based on the specific requirements of the project, and in accordance with applicable design codes and standards. Consulting with a structural engineer can provide a more accurate determination of the maximum bolt length for a specific steel structure.

Final words or conclusion

In this post we have covered common types of bolts in steel structure. Structural steel bolts are typically used in conjunction with other structural steel members, such as beams, columns, or trusses, to form a load-bearing structure.