Univiti breaks down: EN 15048 & EN 14399, your guide to structural bolting standards

Structural bolts in metal fabrication

Implementing some key European standards has further emphasized the importance of structural bolts in metal fabrication. These standards, specifically EN 14399 and EN 15048, define structural bolts' characteristics and ensure compliance with essential safety requirements through CE marking. They categorize structural bolts based on the type of fastening to be achieved:

• - EN 15048 specifies non-preloaded assemblies (SB - Structural Bolts).
  - EN 14399 specifies preloaded assemblies.
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The choice of bolts depends on the assembly type (preloaded vs. non-preloaded). In the following paragraphs, we'll explore the distinctions between these two types and their reference specifications.

EN 14399 preloaded assemblies

EN 14399 preloaded assemblies consist of a bolt, nut, and washer, products which form preloaded assemblies using HV, HR, and HRC systems. In detail, EN 14399 preloaded assemblies constitute controlled tightening and are primarily used in applications where the structure or joint being created is subjected to tensile forces. As a controlled tightening assembly, the preload is applied using a torque wrench to ensure control over the tightening torque.

The acronyms HV, HR, and HRC indicate different failure modes under stress, although the three systems are equivalent. For instance, the HV system utilizes a shorter nut that will be the first to fail under stress. Instead, in the HR system, the nut is taller and paired with an extended bolt thread; under stress, the bolt will be the first to yield.

EN 15048 non-preloaded assemblies (SB - Structural Bolts)

EN 15048 elements consist primarily of a bolt and a nut, products which together form non-preloaded assemblies, known as SB (Structural Bolts).

Unlike preloaded assemblies, these EN 15048 non-preloaded assemblies do not require controlled tightening and can be tightened manually.
UNI EN 15048 elements are mainly manufactured from high-strength steels, typically grade 8.8, which is the structural grade for fasteners according to the standard. They are available in two versions: partially threaded and fully threaded. Additionally, certain types of non-preloaded assemblies are also produced in stainless steel and are available upon request from Univiti.

UNI EN 15048 structural bolts: kits and products

All structural bolts are supplied in sealed packaging by the manufacturer. EN 14399 and EN 15048 standards do not allow for open packaging, and therefore the customer must purchase the assembly in the quantities specified on the package. Both standards provide precise rules for packaging:

• - Single packages containing nut + bolt + bolt for SB systems and nut + washers for HV, HR, and HRC systems, all from a single batch of each piece.
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• - Separate packages containing nuts, bolts, and washers, all from a single batch on which the manufacturer must indicate the tightening characteristics.
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In order to better understand the expected performance of the product, the package label must also show the recommended values for setting the torque wrench for assembly.

Fastener certification: decoding the CE mark

The UNI EN 15048 standard mandates that all individual components of the assembly (bolt, nut, and washer upon request) must bear the CE marking, including the mark of the manufacturer of the assembly and the special SB (Structural Bolting) mark.

As for SB (EN 15048) assemblies, they must adhere to the following key characteristics:

- Standard diameters from M12 to M36.
- Non-increased head radius.
- Partial or full threading along the entire bolt length.

The CE marking applies to the product itself, which in this case is the bolt-nut assembly. Washers, as they are not necessarily part of the assembly batch, do not bear the marking. To identify the genuine CE marking on labels, it should include various information such as:

• - Identification number of the CE marking certification body.
  - Name or trademark of the assembly manufacturer.
  - CE conformity certificate number.
  - Reference to the EN 15048 standard.
  - Product designation according to the different parts of EN 15048.
  - Declaration of any dangerous substances.
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CE marking must be affixed to construction products for which the manufacturer has provided a Declaration of Performance (DoP). This document describes information about the product's essential characteristics and compliance with relevant standards.

For the latest information on Univiti's extensive structural fasteners catalog, visit their online stand on Expometals.net. The company offers a wide catalog of standardized screws and bolts, alongside a production service for screws, bolts, nuts, and small metal parts according to customer specifications.
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