Platform on concrete and steel in construction
In the steel and infrastructure construction sectors, fasteners are becoming increasingly specialized. Modern steel structures, bridge renovations, and dynamically loaded connections increasingly require additional specifications regarding fit, preload, tolerances, and documentation. Stafa supports companies on a daily basis with high-quality HV solutions for structural applications. The product range spans from standard HV systems compliant with EN 14399 to high-quality, project-specific solutions in accordance with DASt 021. Together with product specialist Thomas van Leeuwen, we’ll take a closer look at the product range.
We’ll start with the HR system in accordance with EN 14399-3. “This is used primarily in internationally oriented projects or projects that include specific engineering requirements,” says Van Leeuwen. “In addition, many Friedberg HV systems are used in accordance with EN 14399-4. These systems are designed for prestressed connections that require a controlled prestressing force. The standard range for these typically goes up to and including M36. For many projects, this remains the most commonly used HV system.”
When it comes to renovation projects, Van Leeuwen has noticed a growing demand for Friedberg injection systems based on EN 14399-4. “In this process, a standard high-strength bolt is fitted with an injection hole, after which a two-component resin is applied to completely fill any gaps between the bolt and the drilled hole,” he explains. “These systems use special tongue-and-groove rings so that the resin can spread in a controlled manner around the joint.”
Friedberg HV fitting bolts, which comply with EN 14399-8, are, in turn, being used more and more frequently in connections that require a very precise fit between the bolt and the hole.
“In addition, complex steel, infrastructure, and wind turbine projects are regularly carried out in accordance with DASt021,” says Van Leeuwen. “While standard EN 14399-4 systems typically go up to M36, DASt021 solutions go a step further: from M39 through M72. These larger fasteners are manufactured for applications that place high demands on fit, preload, and documentation.”
Van Leeuwen notes that additional ROK tests are typically required for Rijkswaterstaat projects. “Hardness plays an important role here. While the EN 14399 standard for strength class 10.9 allows for higher hardness values (min. 320 HV, max. 380 HV), Rijkswaterstaat’s ROK guidelines for hot-dip galvanized prestressing connections stipulate a maximum hardness of 370 HV to limit the risk of hydrogen embrittlement. For decades, Friedberg has consistently manufactured products below this limit and is therefore widely used in Dutch infrastructure projects where additional ROK testing is required. Friedberg stands for high-quality German craftsmanship, precise tolerances, and reliable performance in critical structural applications.”
Although EN 14399-4 remains the most widely used high-strength bolting system in the steel and infrastructure construction sectors, Stafa has observed that projects are increasingly requiring supplementary or project-specific solutions. “Depending on the application, HR systems, injection systems, HV studs, or DASt021 solutions can play an important role here,” Van Leeuwen summarizes. “Especially with these types of projects, it’s ultimately not just about supplying fasteners, but above all about reliability, documentation, and a supplier who understands the demands of modern steel and infrastructure projects today.”
Stafa Group is the largest independent independent distributor of fasteners and related services in the Netherlands and also a major and reputable player in Europe. A family business since 1977, Stafa Group has a proven track record of supplying high-quality fasteners and industrial components. Our more than 120 employees are committed to [...]
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