NEWS! Huck BobTail Lockbolts DIBt technical approval extended by 5 years
“The approval gives BobTail® Lockbolts the verification of ‘static load-bearing capacity and fatigue strength’ in the context of Eurocode 3 for applications in construction. The extension of the approval means BobTail Lockbolts can be used in areas regulated by the building authorities as a replacement for non-preloaded structural bolting assemblies (acc. to EN 15048) or high-strength structural bolting assemblies for preloading (acc. to EN 14399). The values published can also be used in many other applications, including rail, commercial vehicles, lattice towers or wind turbines.
The updated rules for design and execution enable structural engineers to take further advantage of Lockbolt technology in steel construction: the update contains some important changes for the fatigue verifications, enabling the higher fatigue strength to be applied regardless of the diameter of the fastener.
In addition to the load-bearing capacities, which are superior to that of a threaded bolt, BobTail offers other advantages, such as the low scatter when applying the preload force, the non-detachable connection, vibration resistance and high fatigue strength. BobTail Lockbolts are also characterized by the fact that they are mechanically maintenance-free (no re-tightening required) and are easy, quick and quiet to install.” Howmet Fastening Systems.
Fatigue strength studies on the BobTail Lockbolts go back more than 10 years and continue to be carried out in the test laboratories of recognized Fraunhofer-Institute IGP, Rostock and University of Applied Sciences, Wismar, Germany. The recognized German technical approval (Z-14.4-591) for Huck BobTail® Lockbolts covering diameters M12 M36 has been extended by Germanys highest building authority DIBt (public law institution) for a further five years. In addition, the newest approval version includes some important changes for the fatigue verifications for oscillating loads under axial and eccentric loads, so the higher fatigue strength can now be applied regardless of the diameter of the fastener. This represents a major advantage compared to high strength structural bolting assemblies for preloading according to EN 14399, which are widely used in steel construction.
For construction, products that fall within the scope of a harmonized European standard (hEN), the manufacturer is obliged by the Construction Products Regulation (Regulation (EU) No. 305/2011) to create a declaration of performance and affix the CE marking. As Lockbolts are not covered by a hEN, product performance can be assessed using an ETA (European Technical Assessment), which is valid throughout the EU and recognized worldwide. While the application for a Lockbolt ETA is pending, Howmet Fastening Systems has applied at the DIBt for the extension of the general technical approval and construction technique permit Z-14.4-591 for a further five years. As part of the extension, the latest research findings were also considered and included in the new version of the approval. This essentially concerns the design rules for fatigue strength and eccentrically loaded Lockbolts, which are greatly improved.
The extension of Z-14.4-591 allows for BobTail Lockbolts to be used in areas regulated by the building authorities as a replacement for non-preloaded structural bolting assemblies acc. to EN 15048 or high-strength structural bolting assemblies for preloading acc. to EN 14399. This national technical approval / construction technique permit contains all the necessary parameters for the dimensioning and execution of BobTail Lockbolt joints in steel construction applications for category A E connections. However, the characteristic values published in Z-14.4-591 can also be used in other areas of application such as rail, commercial vehicles, lattice towers or wind turbines.
The extent to which the regulations can be applied outside of Germany or in other areas of application must be clarified on a case-by-case basis with the regulatory authority or a certifier in the country in which the construction is to be undertaken.
Proof of fatigue strength
The verification of the fatigue strength in steel construction is regulated in the EN 1993 1 9:2005 AC:2009. It was therefore the aim of the approval process to provide proof of fatigue for BobTail Lockbolts in accordance with the applicable standard. The verification of fatigue strength is becoming increasingly important nowadays against the background of lightweight construction requirements and the inflation of steel prices. BobTail Lockbolts have significantly better fatigue strength than threaded fasteners due to their special groove geometry. As a result, structures can be designed more efficiently and material costs can be saved.
Continuous development of the Lockbolt design and improvement of manufacturing processes ensure the high fatigue performance of the BobTail. Fatigue strength studies on the BobTail Lockbolt's go back more than ten years and were carried out in the test laboratories of recognized Fraunhofer Institute IGP, Rostock and University of Applied Sciences, Wismar, Germany. A total of several hundred (~300) individual tests were carried out to Din 969. All test results were evaluated by an independent expert to align the results with DIN EN 1993-1-9:2010-12 and acknowledged by the DIBt.
BobTail® Product overview and to download the BobTail data sheet click here
Designed to overcome inherent weaknesses with standard Lockbolts and engineered for high performance and reliability. Benefits of installing BobTail include:
• No-break pintail means highest corrosion resistance in its class.
• High speed, easy to install systems reduce production time.
• Wide grip ranges minimise fastener inventory.
• Improves health and safety - replaces welded joints.
• Tamperproof – once installed cannot be removed without specialist tooling.
• Quick visual inspection assures quality joint.
• Fit up ability – helical lock-groves allows for pre-assembly / project alignment before the final swaging process.
• Installation indicator on collar for visual inspection to ensure correct installation – a red collar is also available that gives a clear visual installation that the collar has been fully swaged.
• Unique, low-swage technology allows lightweight, ergonomic tooling - no torque or impact is transferred to the operator.
• Lightweight, low-noise, low-maintenance tooling, with a change of nose assembly can be used for both installing and removing fasteners.
Star Fasteners are fastener experts and the largest UK Huck fastener distributor. We work globally with a diverse range of end users and distributors from across a number of industries, offering technical application knowledge and customer support.
For more information, please email sales@starfasteners.co.uk or call us on +44(0)115 9324939.