What does "preload" refer to in bolted connections?

In bolted connections, "preload" specifically refers to the initial tension that is applied to a bolt before any service loads are imposed on it. This preload is critical because it ensures that the bolt remains tight and secure under working conditions. By applying a predetermined tension during the installation phase, the bolt can effectively resist external forces that might attempt to pull it loose.

Correctly establishing this preload contributes to the overall stability of the bolted joint and helps to maintain the integrity of the assembly during operation. A well-preloaded joint can withstand vibrations and fluctuations in load without losing clamping force, which is fundamental in many engineering applications such as structural assemblies, mechanical systems, and automotive components.

Overall, understanding preload allows engineers and technicians to design more reliable bolted connections, ensuring safety and performance under expected operating conditions.