Arrangement of Bolted Connections

Bolts are very strong in tension and shearing. Additionally, they are easy to use. Because of these properties, nowadays connections of steel members are made using bolted connections. In this article I will answer the question like, What are the different types of bolted connections? I will provide explanation in simple language so that the people with limited knowledge can also get benefit from this article. Engineering students and those who want to learn structural engineering will get benefit from this article.

Connections of steel members can be created by using either of the bolted, riveted and welded connections. I will discuss about design of welded connections later in some other articles. Because of necessity for heating arrangement the riveted connections are not in practice nowadays. Instead bolted connections are being used widely. However, design principle is almost same for the both riveted and bolted connections.

Example of bolted connections

Types of bolted connections: From arrangement point of view the bolted connections can be categorised basically in to two major groups, i.e., Support Connections and Member Connections. Support connections can be a connection at footings (foundation) or wall or any supporting members like steel columns,etc.

Following two figures show examples of support connections.

Support Connection example-1

Support Connection example-2

Member connections are created basically between two or more members. Any connection made using two or more members is a member connection.

Member Connection example-1

Member Connection example-2

From structural point of view also the the bolted connections can be categorised basically into two major groups, i.e., Moment and Non-moment connections. Moment connections utilise bolts in both actions, i.e. shearing only or tension and shearing. Non-moment connections utilise bolts basically in pure shearing or pure tension.

In all bolted connections the bolts are arranged such a way that they are utilised basically only in  shearing or in tension or in combined actions. As the name suggests the moment connections carry moments whereas the non-moment connections don't.

Moment Connection-example-1

Moment Connection example-2 Shear-Tension Connection

Pure Tension Connection

Pure Shear Connection

In the moment connection example-1 above, the bolts are basically utilised in shearing only. Bolts in bottom flange of the "I"section are in shearing due to flexural tension whereas, the bolts in top flange are in shearing due to flexural compression. Similarly the bottom row bolts in web are under shearing due to flexural tension and the top bolts are under shearing due to flexural compression. The moment connection example-2 utilises top bolts in both actions i.e. tension and shearing. In the example shearing of bolts occurs due to the vertical force and tension develops due to the moment caused by the vertical force.

Other two figures showing examples of pure tension and pure shearing connections show examples of non-moment connections.

Bolts in shearing are sheared in the common plane of two connecting plates. Shearing of the bolts is possible only if the plates are capable of carrying bearing stresses that develop on left side of the bolts in top plate and on right side of the bolts in bottom plate. In the following figure only bearing of bottom plate is shown, however similar bearing on top plate shall also be considered. Similarly, the plates must not fail in tearing as well.

Shearing of bolts and bearing of bottom plate

Bearing stress in bottom plate

Following example shows the basic case of plate tearing:

Plate tearing an example

In addition to such tearing the plates must also be safe against other failure modes such as different possible types of block shearing, etc.

I will discuss, in next article, on how the bearing, tearing, shearing and tensile capacities of the bolts are calculated. In the next article I will also discuss about bolt capacities against some of the combined actions and other practical approaches.  

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