MYTHS TO DISPEL : Wood posts are stronger than concrete posts

MYTHS TO DISPEL : Wood posts are stronger than concrete posts

Wood posts have always played a key role in agricultural installations. In fact you’ll find wood posts installed everywhere throughout the five continents.

The reason for their success is easy to guess, mainly due to the abundance of trees worldwide.

But they also have another advantage which is their durability, as long as they are pre-treated against attacks of fungi, insects and humidity, which can greatly reduce their sturdiness over time.

Moreover, it’s common knowledge that the materials used to support the installations must have characteristics that can withstand various types of stress, from the use of agricultural machinery to increasingly violent weather events.

Having said that, let’s take a look at the specific characteristics of wood so we can better classify its performance.

Durability: Its ability to withstand the forces of external, mechanical or atmospheric stressors.
The radial cross-section of the trunk, the side exposing the grain along the widest surface of the board, is the most durable part. In contrast, the side perpendicular to the grain is the weakest part.

Density: Expresses the mass/volume ratio of each wood species. This characteristic is also sometimes expressed as compactness, and it is a very important parameter when choosing a type of wood that must be subjected to significant structural loads. Usually it should not be less than 600 kg/m3.

Hardness: This is the resistance of a material to penetration by an external body. In the case of wood it translates into the ability to be cut and machined.
Very hard woods are more resistant to compression than soft woods.

Rigidity: Expresses wood’s flexibility.
One might think that a soft wood is easier to bend than a hard one. However, the most important parameter is the distribution of the fibres: the more straight and parallel they are, the greater its ability to be bent.

There are also some environmental factors that considerably influence the physical properties of wood, in particular humidity and susceptibility to fungi and insects.

After analysing these characteristics, the wood is compared to other materials in an attempt to create a sort of classification.

Indeed, we often hear it said that wood posts are more durable than concrete by virtue of the fact that they are better able to withstand the impacts of machines and to more effectively resist weather events.

Is that the case?

The truth is that it’s not possible to make a precise comparison between the two products, simply because they are made with completely different materials in terms of composition, shape and durability.

Speaking of composition, therefore, we should test different wood species to determine which are the most and least durable.

Looking at the shape, wood posts with diameters of 8-10-12 cm are often compared to concrete posts with a square cross-section of 7-8-9 cm per side, a comparison that makes no sense because the geometric shapes combined with the composition of the material greatly influence the durability of the final products.

When it comes to durability, the decisive factor for wood posts is the pre-treatment against weathering, humidity and insects, which pre-stressed reinforced concrete posts do not need.

We should then give each element a score that allows us to establish a final ranking of the best woods to be used in agriculture, so that they can be compared with the characteristics of pre-stressed reinforced concrete posts.

As far as the latter are concerned, the strength values will surely depend on the section of the post, the reinforcement used and the quality of the concrete.

But it is certain that pre-stressed reinforced concrete posts possess the most important quality, namely the ability to maintain their technical/mechanical characteristics over time, guaranteeing that their original resistance and durability will remain unaltered throughout their entire lifetime.

The same cannot be said about wood, which suffers a progressive and inexorable decay of its mechanical and physical characteristics, making it completely unusable and in need of replacement within a few years, with a consequent increase in costs.

Moreover, despite their reputation for being resistant to stress, wood posts are also subject to breakage or damage caused, for example, by machines working in the vineyard.

In the following pictures you can see the damage caused by a grape harvester and a mulcher.

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This evidence proves that wood posts are not at all more resistant than reinforced concrete posts.

In fact, as has been clearly demonstrated there are many variables at play, and many of them favour the concrete post: in the end the choice of materials, cross-section, type of treatments applied (to wood) and the use of operating machines will determine the installation’s efficiency and durability.

 

Valente is always available to provide the advice and information needed for a correct assessment of the installation materials, helping you make the best possible choice!