What is the difference between preloaded and non-preloaded bolting assemblies?

Apart from dimensional differences ( bigger head of the bolts and bigger nuts on preloaded assemblies), the main difference is in the way how these goods are installed.

Non-preloaded bolting assemblies are generally tightened to at least snug-tight. The connected components are drawn together to achieve firm contact without any specific preload.

The “snug-tight” is generally referenced as tightening the assembly by one man using a normal-sized spanner without an extension arm until the wrench starts hammering.

See more: Tightening of non-preloaded bolts

Preloaded bolting assemblies are tightened to at least a minimum specified force (preload). The tightening is carried out according to specified installation method (with DTI washers , using part-turn, torque figures or tension controlled). This type of product is generally used for critical, slip-resistant, seismic connections, fatigue resistance, execution purposes or as a quality measure (for example: for durability).

Preloaded bolting assemblies can be used as non-preloaded bolting assemblies, where non-preloaded shall not be preloaded unless specified by the construction engineer.

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