The Al-Fer Self-Levelling Connector consists of a single metal piece obtained from a Ø 16mm bar suitably machined with thread for wood in the part will be secured on the beam.The bar remains smooth in the portion corresponding to the floor board to obtain the maximum diameter of the connector (ø16mm), while the upper part is made up of double head with Shear (Snap-Off) Self-Levelling System.

The lower part, threaded with a continuous screw, was made with a constant diameter outer spiral while the central worm is conical with a reverse fit. In this way the fixed tip is more resistant to hooking near the neutral axis of the wooden beam.

Ideally, it can be divided into three parts:

The Al-fer Self-Levelling Connector head is composed of two hexagonal elements (17 mm) held together by a slender connection. During the screwing phase, the bushing is gripped on both heads until the washer is completely penetrated into the wood. At the end of the insertion, the upper head will be sheared (Snaped-Off) in automatic from the botton head, thus obtaining a flat extrados for the laying of the upper planking.

The central body has a circular cross-section with a constant diameter of 16 mm. It has the role of absorbing the greater shear and momentum forces induced by external stresses on the mixed system. As the thickness of the new upper beam increases, the connector will be subject to an increasing free length of inflection, therefore the central body is equipped with an important area resistant to bending shear (200 mm ²).

The thread is created with the external spiral with a constant diameter of 16 mm, while the central worm is conical with reverse fit. In other words, the central core of the thread has a circular section with a diameter of 11.5 mm near the central body of the connector and gradually widens to a diameter of 12 mm at the tip. This way the fixed tip is more resistant to mechanical coupling in both wood and concrete.

This particular “taper” of the thread together with the appropriate calibration of the pre-drilled hole give the connector a considerable resistance to extraction, in fact 2500 kg are needed to extract a standard connector in a third category wood (C18) fixed perpendicular to the fibre. In wood, a pre-drill with a tip diameter of 11.5 mm is made, thus obtaining a compression of the wood fibres along the circumference of the maximum section of the thread, at the tip, which is 12 mm. Similar to a “pressure cap”, the particular thread gives the connector a mechanism for diffusing cone forces, as shown in the images above.

During the screwing phase, the wood is compressed first along the external spiral of the thread and then also along the internal part of the thread thanks to the greater section of the stem compared to the pre-drilled hole. After the connector is inserted, the stop and thread therefore generate a constraint, a sort of “vertical pre-compression” between the floor board and the wooden beam. Once the maturation of the jet is obtained and the connector is put into operation, this vertical force will act as a friction force that will further reduce the horizontal flows to which the connector is called to resist.

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