Tutorial on the Basics of Bolted Joints

What is a Joint Diagram?

To help visualise the loading within bolted connections, joint diagrams have been developed. A joint diagram is a means of displaying the load deflection characteristics of the bolt and the material that it clamps. Joint diagrams can be used to assist in visualising how a bolted joint sustains an external force and why the bolt does not sustain the whole of this force.

Joint Diagram 1

The diagram shown above presents the way that the basic joint diagram is constructed. As a nut is rotated on a bolt's screw thread against a joint, the bolt is extended. Because internal forces within the bolt resists this extension, a tension force or bolt preload is generated. The reaction to this force is a clamp force that is the cause of the joint being compressed. The force-extension diagram presented above shows the bolt extension and the joint compression. The slope of the lines represents the stiffness of each part. The clamped joint usually being stiffer than the bolt.

Joint Diagram 2

The basic joint diagram is formed by moving the compression line of the joint to the right. A triangle is formed because the clamped force tending to compress the joint is equal to the bolt preload. Positive extension is to the right such as that sustained by the bolt, negative extension (compression) is to the left and is sustained by the joint material. Go to the Previous Page
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