Last Updated on September 17, 2026 by Maged kamel
Introduction to Bolted Connections.
The Brief Overview of the Post on bolted connections.
These are the items to be discussed in this Post: The first point, with God’s will, is the Bolt types; there are two types: the first type is low-carbon steel, and the second type is high-tensile steel bolts, which are the most used types of connections and can be classified into two types: ASTM A325 and A490.
The second subject is the Bolt’s structural dimensions, length, and component names.
The third subject is the related Chapter in the AISC concerning connections.
The first material we have is ASTM A-307 low-carbon steel, used in secondary structures such as handrails, light stairs, service platforms, and similar structures not subject to cyclic loads.
These structures have loads that remain constant over Time. Unfinished bolts have a lower load-carrying capacity than high-strength bolts, so they are used in secondary structures with lower loads. The second subject is high-strength bolts.
ASTM specifications classify these bolts into two categories. We have ASTM A325 & ASTM A490. The non-high-strength Bolt is ASTM A307, which we discussed earlier.
The high-strength bolts are made from medium-carbon, heat-treated steel and have a tensile strength much greater than that of ordinary bolts. These bolts are much stronger than ASTM A307 bolts.
The different components of High-strength bolts for bolted connections.
For the shape of bolts. I quote that high-strength bolts are the most common type of Bolt used in steel structures and have more than twice the tensile strength of unfinished bolts.
This is a sample of ASTM A325 from one of the suppliers; it is marked on the head with the symbol U for unfinished.
The second Bolt sample is for the ASTM A490 Bolt. Again, it is written on the head with the ASTM A490 symbol.
I quote that these ASTM A490 bolts are very commonly used in steel construction where large loads are transferred. They have higher strength than ASTM A325 bolts, so fewer may be required if Bolt strength limits connection strength.
This is the advantage of using a higher-strength Bolt, which minimizes the number of bolts required for the connection.
This section addresses the types of bolts and their components for bolted connections. This is the Bolt head with a shank, the smooth part of a fastener above the threads, followed by the threads.
This is the washer shown in the two sections that follow. The next part is the nut. Here again, we see the washer and nut on the threaded portion.
The Bolt length can be divided into two parts: the head and shank, and the threaded portion up to the washer.
This is called grip. The sketch shows the threaded part; the Bolt’s total length is the shank plus the threaded length. The washer diameter is specified as 1.65D. It is written as body diameter E, as in the cut-thread picture; the length of the round portion. H is the head height. The thread length is Lt. The transition thread length is Y, as shown here in the picture. G is the width across corners.
Classification of high-tensile bolts according to Section J3 for bolted connections.
Which Chapter deals with the design of connections in the AISC? It is Chapter J. If we need to check the welded connection, the relevant section is J2.
High-strength bolts for bolted connections.
In Chapter J, Part J3, Bolts and threaded parts, item 1, the code describes high-strength bolts and classifies them into Group A and Group B.
A325 bolts fall under Group A.
If a problem states that a Bolt is Group A, Then, it is the ASTM A325 Bolt. If he wants to include ASTM A490 bolts, then they fall within the group.
Additionally, there are two categories: whether threaded connections are included or excluded for bolted connections. We will discuss this other classification in God’s will next Time. What about snug, tight, and fit?
The snug-tight bolts for a bolted connection.
As we can see in the picture, the bolts in the base plate are in place and need to be tightened. Two angles intersect. This is a Structural part, possibly a pedestal, but it is unclear.
Then tightening is done with a spanner, which is a spud wrench, an open-ended wrench approximately 16″ long. So, the torque produced by the spud tightens the bolts.
Another method is pre-tensioning. This type of connection is called a Shear connection. I quote: The snug-tight can be specified as a Shear connection or a tension-only connection.
The snug-tight method is not permitted for connections supporting non-elastic loads, nor is it permitted for ASTM A 490 in tension.
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This is a useful source for designing various steel elements: A Beginner’s Guide to the Steel Construction Manual, 15th ed., Chapter 4 – Bolted Connections.
This is a useful source ffor designing elements A Beginner’s Guide to the Steel Construction Manual, 16th ed., Chapter 4 – Bolted Connections.
The following part on Bearing Type connections -part,,-1- discusses the types of bearing bolts.- Types of failure for the bolted joint.