For over 30 years, Rothoblaas, an Italian multinational company based in the heart of the Alps, has been the reference point for carpenters all over the world. This is achieved through the continuous improvement of its products, in a continuous search for the best for its customers: whether it concerns solutions for fastening timber, soundproofing, durability, vapour control or airtightness, Rothoblaas is a guarantee of high product quality and excellent service.
One of the most successful products in the Rothoblaas universe are the VGZ connectors, full-thread screws that offer the possibility of making concealed connections between timber elements.
VGZ screws: total reliability for your timber structures
VGZ is a screw for structural timber with CE marking according to ETA-11/0030 certificate. It is characterized by very high mechanical performances thanks to the steel class.
The design of the screw: it is characterized by a full thread shank and a cylindrical head with a very small diameter. These two characteristics make the connector work well at axial stresses (traction and compression) and secondly gives the possibility to position the head a little more inside the timber during the screwing resulting almost imperceptible.
The available offer is very wide, ranging from 5×80 mm up to 5×160 mm; 7×80 mm up to 7×380 mm; 9×160 up to 9×520 mm and 11 x 250 mm up to 11×600 mm.
Types of application
The possibility of using the screw for axial actions and the great tensile strength of the steel material that composes it, make VGZ able to fulfil different types of structural applications, both structural reinforcement and real fastening of timber elements.
1) REINFORCEMENT AGAINST STRESSES ORTHOGONAL TO THE TIMBER FIBRE
The timber material is characterized by a poor resistance to compression and traction in the direction orthogonal to the grain.
A) TENSION ORTHOGONAL TO THE GRAIN
This situation occurs when the timber element is stressed by an action orthogonal to its grain to the point of triggering longitudinal cracks.
The best known cases are those of the beam cut at the head.
In this case the VGZ screw is positioned orthogonally in order to contrast the internal actions of the timber, slowing down or completely blocking the propagation of the cracks.
Similarly, a beam subjected to an orthogonal load hanging from it is another frequently observed case.
Also in this case the screw VGZ is used to reinforce the beam against the possible crack. In both cases, the connector can be applied since the construction phase to prevent the problem, or after a possible occurrence of cracks to reinforce the element.
B) COMPRESSION ORTHOGONAL TO THE GRAIN
This situation occurs where the timber element is subjected to stresses perpendicular to the grain: this occurs mainly at the support of the timber beams and panels.
Consolidation in this case consists in positioning the full thread VGZ screws orthogonally to the grain to reinforce the timber section. Generally it is recommended to place a steel plate on the support (column, wall, etc..) to create a rigid plane that enables a uniform transmission of loads on the screws.
The orthogonal compression mechanism can also be a consequence of the actual crushing of a beam or floor due to the convergence of two columns or walls.
2) REINFORCEMENT FOR LONGITUDINAL SHEAR
The longitudinal shear occurs with the sliding of two parts of the wood section towards each other, especially when the beam is subject to bending: this is a particularly fragile behaviour.
In this case, the reinforcement is made by means of VGZ screws that are positioned to counteract the reciprocal movement between the two parts. Generally, the reinforcing screw is positioned at an angle of 45° to the grain, which is the most common application, or at right angles to the grain.
3) REINFORCEMENT OF THE SECTION OF A BEAM
The reinforcement of the section can be required for different problems of a strictly mechanical nature: rehabilitation of an existing beam, reinforcement of an undersized beam, reinforcement of a beam for change of use. In this case the VGZ screws are positioned at an angle of 45°, parallel or crossed.
4) SHEAR FASTENING
Generally, the intention is to exploit the screws’ ability to react to axial stresses well by positioning them at an angle of 45° to the grain, crossed or parallel to each other.
A. shear fastening of a timber beam
The VGZ screws are positioned inclined and crossed so that the vertical load can be considered divided into tensile stress for one screw and compression for the other.
This configuration makes it possible to take full advantage of the screw thread and therefore of its axial strength.
B. shear fastening of solid timber panels – CLT
The operating principle of the crossed screws system remains exactly the same as explained in the previous case of fastening the timber beam with crossed screws.
The only difference is that this is a joint between solid timber panels.
JIG VGZ 45 TEMPLATE: the universal template for every 45° screw connection
The JIG VGZ 45 template is the VGZ screw positioning tool designed by Rothoblaas for the 45° inclined configuration. Easy to use, lightweight and small in size, JIG VGZ 45 is suitable for the installer to carry around.
Various connections typical of timber construction can be easily made without wasting time on laborious measurements, thanks to the engraved markings on the JIG VGZ 45. The correct screw size can be determined intuitively.
The template is made of 3 mm thick stainless steel, which guarantees excellent durability and can be used to make 45° timber-to-timber joints of beams and floors on solid timber, CLT and LVL. With the development of the JIG VGZ 45 template, Rothoblaas intended to give more importance to the screw angle positioning, reducing possible application errors, especially for the less experienced installer.
The JIG VGZ 45 template can be used in the previously mentioned applications:
- longitudinal shear reinforcement;
- shear fastening of a timber beam;
- shear fastening of solid timber panels – CLT;
- any other application where the VGZ screw is inclined at 45°.
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