IHF Bolting Systems
Technology
IHF Bolting Systems
Bolted joints in metal construction with high-strength fasteners of strength class 10.9/10 are marked with "HV". The "H" stands for high-strength and the "V" for prestressed. A classic HV fitting consists of the following elements:
- an HV hexagon bolt (acc. to DIN EN 14399-4 / DASt 021)
- one HV hexagon nut (acc. to DIN EN 14399-4 / DASt 021)
- two HV washers (acc. to DIN EN 14399-6 / DASt 021)
HV sets are used, among other things, in structural steel engineering, hall and bridge construction as well as in the erection of wind turbines and masts for cable cars, where load-safety-relevant pretensioning must be ensured.
The IHF assemblies: only two main components
The innovative IHF Bolting System reduces the wire to the two core elements: The IHF Stretch Bolt / IHF Stud Bolt and the IHF Round Nut. The washers are integrated into the bolt head and the nut. This reduces the number of parting lines. Likewise, a possible source of error due to incorrect installation of the washers is eliminated.
IHF bolt systems in nominal sizes M20 to M100 have been granted general building authority approval by the DIBt (German Institute for Building Technology). The subject of the approval were the IHF Bolting Systems suitable for hydraulic friction- and torsion-free tightening for the production of high-strength prestressed structural steel connections in the following IHF-HV configurations
- IHF Bolt Set consisting of IHF Stretch Bolt with an IHF Round Nut
- IHF Stud Bolt Set consisting of IHF Stud Bolt and two IHF Round Nuts
- HF/ HV stud bolt set consisting of IHF Stud Bolt, one IHF Round Nut, one HV Washer according to DIN EN 14399-6 and one HV Nut according to DIN EN 14399-4
The subject of approval was the connections made with the IHF Stud Bolt System for both static, quasi-static and fatigue loading. The IHF Bolting Systems are pretensioned by hydraulic friction- and torsion-free tightening with the aid of the ITH bolt tensioning cylinder. After pressure relief of the bolt tensioning cylinder, the connection is appropriately pretensioned. For the production of the individual parts of the IHF Bolting Systems, the regulation of DIN EN 14399-1 for system HV applies. Prerequisite for the approval were extensive scientific tests on different bolted joints. The tests were carried out at renowned German institutions.
Comparison HV / IHF system
The configuration possibilities
Cost reduction with the IHF Bolting System
In conventional HV connections, the control assembly preload is usually applied by means of torque using rotary bolting methods. In this case, the control preload forces applied to the individual bolts are subject to very strong fluctuations due to the very different friction values.
For this reason, the control assembly preload may be below the value of the minimum assembly preload. Under dynamic load, a larger oscillation width then occurs, which can lead to the breakage of the bolt. When using the IHF Bolting System with the ITH Stretch method, a higher reproducibility of the bolt preload force is guaranteed.
This allows longer maintenance intervals and thus reduces maintenance costs. The more compact tightening tool (bolt tensioning cylinder) makes it possible to reduce the center distance from the bolt to the inner wall of the housing. This allows the flange height of the ring flanges to be reduced, which leads to a considerable reduction in costs.
Stress optimized design
All IHF Fasteners were designed using the "Finite Element Method". This reduces the maximum stresses in the bolt and nut compared to standard HV fittings. The reduced maximum stress ensures that IHF bolt fittings have a longer service life than standard HV fittings.
Corrosion protection: less restricted
Since the IHF Bolting System is completely free of torsion and friction, there is no restriction on the choice of surface coating. All joint corrosion protection finishes, such as coating by hot-dip galvanizing, Dacromet, Deltaton or others, can be used with the IHF Bolting System. Due to the friction- and torsion-free tightening, reusability of IHF Fasteners is possible.
Advantages of the IHF Bolting System at a glance
Technical advantages of the IHF Bolting System
- No bending and torsion stresses in the bolt
- Higher utilization of yield strength
- Exact application of the preload forces
- The system works frictionless
- Repeatable tightening: high reproducibility of pretensioning forces in series applications
- Simple and reliable assembly - proven to be faster than conventional torque methods
- Smaller bolt dimensions with the same preload force
- Reusability of IHF Fasteners
