Last Updated on June 7, 2025 by Maged kamel
Introduction to Bolted Connections.
The brief content of the post.
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 to two types ASTM A325, A490.
The second subject is the structural bolt dimension, the length, and the names of the different components of the bolt.
The third subject is the related chapter in the AISC concerning connections.
The first material we have is ASTM A-307, low-carbon steel, which is used in secondary structures such as handrails, light stairs, service platforms, and other similar structures that are not subject to cyclic loads.
These structures have loads that remain constant over time. Unfinished bolts have Lower load-carrying capacity than high-strength bolts, so bolts, due to lower capacity, are used in secondary structures, which have a lower load capacity acted upon by lighter loads. The second subject is the High-strength bolts.
These bolts can be classified into two categories according to the ASTM specifications for high-strength bolts. We have ASTM A 325& ASTM A 490. The non-high-strength bolt is ASTM A307, which we discussed earlier.
The high-strength bolts are made from medium carbon, heat-treated, which has a tensile strength much greater than those of ordinary bolts. The strength of these bolts is much greater than ASTM A307 bolts.
The different components of High-strength bolts for bolted connection.
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 as much tensile strength as unfinished bolts.
This is a sample of ASTM A325 for one of the suppliers, it is written on the head and the symbol of U for unfinished.
The second bolt sample is for the ASTM A 490 bolt. Again, it is written on the head and the symbol of ASTHMA 490.
I quote that these bolts, ASTMA490 bolts, are very commonly used in steel construction where large loads are being transferred. they have higher strength than ASTM A325 bolts, so fewer may be required if connection strength is limited by bolt 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 head of the bolt with a shank, which is the smooth part of a fastener above the threads, followed by a thread.
This is the washer shown in the two sections that follow. The next part is the nut. Here, again, is shown when we use the washer and nut in the threaded portion.
The bolt length can be divided into two parts: the first part is the head, the shank, and part of the thread till the washer.
This is called grip. The threaded part is shown in the sketch; the total length of the bolt is the shank + the threaded length. The diameter of the washer is specified as 1.65D. it is written, body diameter E as in the cut thread picture. The bolt length L. E is 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 the High-tensile bolts according to section J3 for bolted connection.
What about the chapter that deals with the design of connection 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 connection.
In chapter j- part j3, Bolts and threaded parts at item 1, the code describes the high-strength bolt and classifies the bolts into Group A and Group B.
When dealing with bolt A325 it is included in group A.
If, in a given problem, it is mentioned that the bolt is of group A. then, it is the ASTM A325 bolt. If he wishes to include bolt ASTM A490, then it falls within the group.
Additionally, there are two categories, whether threaded connections are included or excluded for bolted connections. This other classification will be discussed in God’s will next time. What about the snug, tight, and fit?
The snug-tight bolts for bolted connection.
As we can see in the picture, the bolts in the base plate are placed and need to be tightened. There is an intersection of two angles. This is a Structural part, possibly a pedestal, but it is unclear.
then tightenings by spanner, which is a spud wrench, which is an open-ended wrench approximately 16″ long. So, by torque produced by the spud, the bolts are tightened.
There is another method known as pre-tensioning. This type of connection is called a shear connection. I quote, The snug-tight can be specified as a shear connection, as well as tension-only..connections.
The snug-tight method is not permitted for connections supporting non-elastic loads, nor is it allowed with ASTM A 490 loaded in tension.
For a valuable external resource, Chapter 4 for bolted Connection-A Beginner’s Guide to the Steel Construction Manual, 14th ed.
Chapter 4 for bolted connection Beginner’s Guide to the Steel Construction Manual, 15th ed.
For the most recent Update, please go to Beginners’s guide to Steel Construction Manual 16– Chapter 4.
The following post is Bearing Type connections -part -1- discussion includes -types of bearing bolts.-Types of failure for the bolted joint.