Today, construction is often referred to as concrete and the world as plastic. If you look around like that, you could even agree with it. Of course, concrete is most often combined with steel to form reinforced concrete. Still, there is one well-known and used for centuries a construction material, without which even today it is difficult to imagine the construction… wood…
Wood and a tree. Are these synonyms?
Of course not! I know that most people on the construction site use these words interchangeably, considering them to be identical, but we shouldn’t take them as an example. The difference is fundamental: a tree is a plant and wood is the material obtained after it is cut down. So the tree can be planted, and the wood processed. In construction, we use both deciduous and coniferous wood, domestic and imported. Everything depends on the needs, possibilities, but above all its properties.
Basic physical properties of wood
Physical properties, in simple terms, are all the characteristics of a material that we can examine without affecting its chemical composition and structure.
Anisotropy, or having different physical properties in different directions, is one of the characteristics of wood. It results from the arrangement of fibres that make up its structure. The opposite of anisotropy is isotropy, and an example of such a material can be concrete.
The colour of the wood depends mainly on the conditions in which the tree has previously grown and its species and variety. Wood does not have the same and uniform colour, because it depends on the structure of the tree, its rings, regularity of fibres, etc. All this creates a drawing of wood, and it can be very different, even within the same species.
The moisture content of wood means the property that parquet floorers pay special attention to. Humidity depends on the conditions in which the material is located, and its processing should be carried out at a humidity close to that in which the material will eventually work.
Weight absorbability of wood is defined as the ratio of the mass of water in the material to the mass of dry material.
Hygroscopicity is another characteristic of wood. It is the ability to absorb water vapour from the environment.
Shrinkage and swelling of wood, as well as humidity, depend mainly on the conditions in which it is located. When a wooden element dries out, we are dealing with shrinkage, i.e. a reduction in dimensions, while when the material is saturated with water we are talking about swelling, i.e. an increase in dimensions.
Basic mechanical properties of wood
The mechanical properties of wood are defined as its ability to resist external forces, both static and dynamic.
The compressive strength of wood is much higher if the force acts along its fibres.
The tensile strength of wood can be higher than the compressive strength if the material has no defects. It is assumed that the tensile strength is between 50 and 124% of the compressive strength.
The bending strength is determined by bending a material sample perpendicular to the fibres.
Wood in construction
Round wood (Roundwood) is a debarked trunk of the felled tree without tops and branches. It can be used as a raw material for processing into sawn timber or directly, e.g. into poles or stamps (rather small builds, mainly in the farming system).
Depending on the thickness (trunk diameter) and length, we distinguish:
1) Thick – it is a round log with a diameter of at least 7 cm, we distinguish by its length:
a) Long-leaved – minimum size 6,00 m. for deciduous species and 9,00 m. for coniferous;
(b) log – from 2,50 m. b) log – from 2,50 m. to 5,90 m. for deciduous species and from 2,50 m. to 8,90 m. for coniferous species;
(c) vetches less than 2,50 m in length regardless of species.
2. poles – this is wood with a diameter of 7-14 cm and a length of up to 6.00 m.
Lumber is a material obtained by sawing a circular saw. Due to the degree of processing, we distinguish:
1) Uncut sawn timber obtained by sawing two side planes and the front.
2. sawn timber obtained by sawing all four side planes and both faces.
Basic products of lumber
1. 19-45 mm thick boards
2. 50-100 mm thick logs
Edges with a cross-section from 100/100 to 180/188 mm. Used as masonry.
4. beams with a cross-section of 120/200 – 220/280
Most commonly used coniferous wood species
1) Pine – resilient, softwood, easy to process.
2. spruce – resilient, soft, difficult to process, easy to crack, has a lot of knots.
3) Larch – the most durable species of coniferous wood, rarely used in Poland.
4) Fir – soft, flexible and splitting wood with a large number of knots.
The most frequently used deciduous wood species.
Oak – hard, heavy, durable, compression resistant.
2 Beech – hard, durable, easy to process, often attacked by insects.
3) Ash – heavy, durable, elastic, durable in dry conditions, easily damaged in wet conditions.
4) Hornbeam – hard, heavy, wear-resistant, with good mechanical properties.
Wood is a material that you could write a book about, and it’s not one. In construction conditions, we can talk about it a lot, and if we consider the furniture, the small library would probably be able to gather. That’s how it is with it, a very beautiful and diverse material that is both “alive” and giving character. In this article, I just pointed out some aspects of it, as you can see, we didn’t even touch on constructional reasons. We still have to remember that many wood-based products have been made on the basis of wood, and some of them were used in construction.