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Matter of joints: a careful approach to the properties of wood

To ensure the efficiency and durability of a wooden structure, it is imperative not only to take advantage of the positive properties of the material, but also to protect against those properties that could be considered negative.

The equipment and machinery you use to work with wood are also important, so we recommend that you always refer to professionals.

The positive properties of wood.

The most recognised characteristics of wood include its compressive and especially tensile strength (considering the direction of the grain), and elasticity.

Anomalies and defects.

Analysing the properties of wood, however, becomes complex, particularly when dealing with tensile strength, due to the natural anomalies and defects such as knots, ringshake, deviated grain and shrinkage cracks. In fact, we should remember that wood is an organic material and therefore perishable, as well as being subject to its anisotropy.

Previous and current joints.

Joints used to be made with expedients such as slots, wedges and pegs, but wood-only joints present continuous challenges, mainly due to the passage of time and use. The planar processing, for example, prefers polyhedral geometries, generating areas of stress concentration and structural weakening.

To overcome these challenges, it is fundamental to operate during processing by “smoothing the joints”.

The use of CAD technology and numerically controlled working centres allows joints to be virtually designed, avoiding stress concentrations.

Constraints and connections.

In the context of wooden structures, it is almost impossible to achieve an interlocking constraint. The assumption of a hinge type constraint requires considerations of possible rotations, compatible with the actual rotation possibilities of the connection.

The ‘infinitely rigid’ connections can be approached with the use of wood glues. Changes in humidity can cause stresses in the joint, while the overlapping of wooden elements with different grain directions can generate stresses and cracks.

Carpentry knots.

Also known as connections between wooden components, knots transmit stresses through surface contact and work in compression, shear and tension.

The evaluation of the reduction in strength due to fibre permeation requires attention, especially when using trusses with beveled edges (“Uso Fiume”).

Meeting the challenges in structural timber connections requires a careful approach and the use of innovative technologies, as optimising joints helps to create functional and durable structures.

[This is the second part of the article you can find here.]

If you need advice on how our working centres can help in your projects, our technicians and sales staff are at your disposal. Contact us!