wood properties. Pine, spruce, larch, Siberian cedar, aspen, linden, birch are considered traditional species for the construction of a bath. Each tree has its own disadvantages and its own advantages.
The assortment of the wood and building materials market today is unusually diverse. To understand it and choose exactly what you need, we bring to your attention short description properties of the most different breeds trees.
At the same time, their features, weak and strengths, the order of preference (that is, which one is considered the most suitable for the construction of baths) and so on.
All breeds are grouped into three groups:
- With a resinous smell.
- With a pleasant smell.
- With little or no odor.
Spruce ordinary. A traditional sauna tree, with an almost white heartwood, with a not very strong but pleasant resinous smell. Quite resistant to splitting and decay. Disadvantages: the presence of resin pockets. Often, spruce is sold together with fir, it is easy to distinguish them, since fir has an unpleasant odor.
Resinous pine. Pretty strong wood with a very strong resinous smell. Resistant to splitting and decay. Disadvantages: sometimes too heavily saturated with resin.
Common pine. A species with beautiful pinkish or light brown wood. Also considered traditional tree for a bath. Resistant to decay (but not to fungal infections), quite resistant to splitting, splitting. Has a strong pleasant smell. Flaws: a large number of resin pockets, increased content resins.
Twisted pine. Wood has a high resistance to splitting and decay. The color of the core is from light to red-brown. The smell of resin is strong. The grain of the wood is straight. Disadvantages: the presence of resin pockets. modern baths not only domestic, but also imported materials are used. Therefore, it does not hurt to add that growing in Canada pine yellow although it belongs to very strong tree species, it is very unstable to splitting, and it also contains too much resin. Using radiant pine you can take only young trees, they are light, have a relatively low density (and hence low heat capacity). One of the advantages of this wood is a moderate resinous smell, the disadvantages include the presence of resin pockets and the fact that the tree is not very durable. Some breeds with a resinous odor can be corroded by iron (for example, false yew tree). If at the same time the tree is prone to splitting and splitting, use it, especially for interior decoration, not worth it.
All types of pine are soft breeds, have a distinct beautiful texture, that is, a pattern formed by the layers of wood. In addition, pine belongs to the so-called heartwood species. What does this mean? That the wood inside the trunk dies off and has more dark color than the woody layer (sapwood) located around the core. The core in such a tree is its strongest part. True, in some breeds it is very difficult to distinguish it by color (spruce, aspen, linden, fir).
And one more important point: pine wood very poorly etched and stained (due to the presence of resin passages). After special treatment (resin removal) it is easily cut and can be pickled. It is necessary to process pine, as it is easily affected by fungi, loses color, turns blue.
Siberian cedar. Beautiful woody species with a reddish-pink heartwood and yellowish-pink sapwood. The texture of the wood is distinct, uniform (considered one of the best), the smell is pleasant, slightly spicy. Cedar wood is soft, light, well processed, and very resistant to decay.
Fir. Most often, great fir can be found on sale, however, under this name, several breeds similar in properties are sold. Fir belongs to the species with a very beautiful texture. Its wood does not contain resin passages. In addition, fir is the softest of conifers. The color of the core is almost white, turning into a slightly reddish brown. Fir is not a very durable species. Some of its species have bad smell. You can get rid of it by keeping the wood.
Linden. Heavy wood with fine even texture, straight grains. The color of the wood varies from creamy white to creamy brown. Resistant to splitting. Annual rings on a cut of a linden are almost imperceptible. Its wood is soft, dries out a little, and is easy to process. Linden has such valuable property like viscosity. From linden it is good not only to build a bath, but also to cut out various bath utensils - ladles, scoops, etc. It has a very faint but pleasant smell.
Poplar. It has a good fibrous texture without resin pockets. Very resistant to splitting (can be used for shelves, benches, etc.). Poplar wood is light, homogeneous. Fresh - quite soft, after drying it becomes hard. When drying, it does not warp, does not crack. There are many varieties of poplar. Black poplar (black poplar), white (silver) and pyramidal (Italian) poplar, as well as Canadian poplar, are common in our country. All of them have similar properties.
Aspen. Widespread breed. AT recent times is increasingly used for interior decoration of baths and saunas. The wood is light, soft, easily impregnated and processed. The color is white, with a slight greenish tint. Resistant to splitting. The texture pattern is barely noticeable. One of the advantages of aspen is its low heat capacity. Among the shortcomings, it should be noted low resistance to fungal diseases. Therefore, aspen wood needs special treatment. Aspen practically does not rot in water (it is not without reason that well log cabins and light boats are made from it). Even in modern elite baths, along with exotic African tree abah are increasingly using aspen. In addition, excellent durable buckets and buckets are obtained from it.
Alder. The most common are white alder, black alder and Siberian alder. It grows in most of European Russia, in Western Siberia. The wood is white, but this applies only to freshly cut alder. In the air, it quickly turns red, acquiring a dark or light red hue, sometimes red-brown. Annual rings are almost invisible. Alder belongs to soft, light breeds, it is easy to cut, paint, polish, pickle. It does not rot in water for a very long time.
Birch. Birch wood is characterized by medium strength, elasticity, it is not among the very light species. The color is white, uniform, with a slight yellowish tinge (sometimes reddish). It is very easy to process, paint, has high acoustic properties. This is good for making musical instruments, but not very suitable for baths, where they are more valued. soundproofing properties. In the construction of baths and saunas, it is used quite rarely. Among the advantages of birch is its strong bactericidal properties.
Larch. It has a very strong, durable wood. Gives a little shrinkage. The heartwood is usually yellow-red or red, with a rough pattern, the sapwood is yellowish-white. Very resistant to decay. After staying in the water for a sufficiently long time, it becomes hard as a stone. It has a mild, very pleasant smell (seasoned wood sometimes has no smell at all). One of the disadvantages is that it is processed with great difficulty, as it refers to hard rocks.
Somehow it so happened that in the minds of modern Russian people the concept of quality and durability is associated primarily with stone or marble. For some reason, everyone forgets that from time immemorial in Russia the most best material wood was used to build houses. Yes, on the one hand, in our country this direction is developing rather poorly, but, on the other hand, we have first-class craftsmen who completely devote themselves to wooden architecture, doing their work with high quality.
Your implementation experience traditional technologies wooden housing construction in modern construction Nikolai Belousov, one of the most successful architects, winner of many awards in the field of wooden architecture, head of the Oblo workshop (Moscow) will share with us.
Why did you decide to get into wood building?
I am very lazy and non-confrontational in life. I don't like to explain something to someone, I like to invent and bring my ideas to life the way I want. 11 years ago I decided: everything that I draw, I will do it myself, with my own hands. I bought a machine and tractor station 130 kilometers from Kostroma and organized my own workshop. Wonderful craftsmen were found right there, young people appeared. To date, I have five sharpened large complex teams. 4 of them grew up from boys who just came after the army and did not know how to do anything. With chainsaws, we only clean up everything rough, and then adzes, axes are used, everything is done by hand.
And we also learned how to freeze the forest. In winter, a special tractor forms stacks that are covered with snow. Then all this is filled with water from the pond using a gasoline pump. At the end, everything is sprinkled with a layer of sawdust and covered with special banners. In August, we remove sawdust and break frozen logs with a caterpillar tractor. Imagine, in the wild August heat, we play snowballs at the plant, opening another stack. We freeze 50-70 cubic meters of wood.
Do you work with any other materials besides wood?
I only work with round tree or with a gun carriage chopped by hand. This technology and this material science allows me, as an architect, to realize the most unexpected and seemingly polar issues of shaping. To work with a tree, you need to understand and feel it, you need to know how to approach it. For 11 years, I did not know the tree anymore, I began to understand it better, but more questions appeared. This is paradoxical and living material.
To date, there are criteria for the classification of residential buildings, which have been developed by a special building commission of the European Union. There are more than 400 of these criteria, they are connected, among other things, with the well-being of a person in a particular house. A sociological and statistical study was conducted, according to the results of which it turned out that a tree in all respects has a unit, that is, people feel most comfortable in a wooden house. A brick house has an index of 0.7, a concrete one - 0.08, and a house made of sandwich panels has a thousandths.
Why manual felling and not glued beams?
I live in the world of my complexes and ideas. I believe that when we take a log, spread it on boards, then dry it, process it, plan it, glue it, process it again and get the same profiled beam, we spend an inadequate amount of money, effort and glue in order to get final product, which just won't crack. But a solid log keeps in itself that fantastic plasticity of the surface of the material, which is recorded by nature. When you have all the walls and structure of your house made of solid wood, you can read the history of each log from it. Convexity, knots, waviness - this is what painting and architecture are, the main trump card of this material.
How do you feel about cutting down trees? Do you think this affects sustainability?
If we cut down a tree with a diameter of 50-60 centimeters (and I work mainly with ripe thick wood), then after one human life exactly the same tree will grow in the same place. If we take, for example, clay, which we use in smaller quantities, then it practically does not renew itself, because millions of years must pass for the clay to form in the same place.
Do you have customers who come to you with their sketches or do you only deal with author's exclusive projects?
I love only those houses that I designed myself. They are all copyrighted, all mine. Everyone comes to me, first of all, for architecture. Therefore, I am in the state of a celestial, however, I have to bear this burden. I have 5-6 clients a year.
I bring doctors of sciences from the forestry academy, who recommend me all kinds of impregnations so that the wood does not turn blue, gels for the ends. Especially from Moscow, all this is busy with KAMAZ trucks. I cannot fail to justify the hopes of people who believed in a dream drawn by me, and then received a blue frame. And for a tree there are a lot of technological negative factors.
How do you ensure fire safety in your homes?
I was lucky, I have a wonderful stove-maker with whom we have been working for many years. He once changed graphite rods at Soviet nuclear power plants - he took out the old ones and inserted new ones. He was a foreman and traveled all over the country. For this person, a micron is very long distance. According to my sketches, he draws fireplaces, sauna stoves, makes passages through all the ceilings, controls the "heaters" who install the sandwich pipes of boiler rooms, makes insulation of all ventilation pipes- Pathways for the spread of fires. I'm so lucky, I have such an Alexander Ivanovich who does this work.
In your wonderful city, half of the historical center - wooden houses. They are demolished and replaced brick buildings because they don't know how to fix it. All over the world, e.g. in Finland, Austria, France, as well as in Nizhny Novgorod, and in Kostroma there are wooden houses, tightly pressed against each other. If they are properly exploited and the fires are extinguished in time, then nothing will happen. On the contrary, a person feels much more comfortable in a wooden house than in any stone one. Wherein brick house now it is also very difficult to build, because according to the existing energy efficiency standards, it must be made of very thick walls.
What is your most favorite project?
My favourite wooden house, which I made in 11 years - one-story small house area 14.4 square meters. It has all the attributes of a residential building: a shower, a toilet, a place to sleep and work. It even has small fireplace and a balcony. This house was recognized as the smallest residential building in Russia. This is my favorite and most difficult project. While designing it, I felt like a German. By the way, a civilized and creative person lives and works in this house.
Tell us about your famous project "Roof of the World", which won the " Golden Section»for his contribution to the development of wooden architecture. Why does it have such an unusual name?
The idea of this design is that we covered the log house with one plane, allowing us to draw it the way we need. The frame always gravitates towards a rectangle, but here we have received new qualities of shaping. This approach allowed us to make a large ventilated attic that everyone would forget about. The function of this building is a bath. She, as a subject of architecture, has received many awards.
It is called "the roof of the world" because it really soars and ascends. Being inside this object, you do not feel the roof above you, you feel closer to the sun. The whole style of the house is so thought out and drawn that you are always in a state of soaring (in the sense of detachment from reality).
In general, we love and appreciate the bathhouse for the moments that we have to experience there. At first they soar terribly in this terrible heat, beat us with brooms, then pour them over ice water, in which there is nothing particularly pleasant. But that aftertaste, which we then experience, in my opinion, is the most valuable.
Currently in Russia, urban architecture uses brick as the main material for the construction of buildings. Is it possible to fit a tree into a modern urban space?
It is possible, if only they change state standards, because today according to domestic fire safety requirements wood cannot be used in an urban environment. Even as a finish.
For example, in Austria there is a law according to which nurseries, kindergartens, schools, vocational institutions, buildings for the disabled and pensioners, buildings for leisure centers and municipalities can only be made of wood by law. It has been established that academic performance is better in wooden schools, there is less aggression.
Is it possible to say that a wooden house is the prerogative of wealthy people?
At correct use of this material, a good wooden house is quite competitive with any other house.
How to care for a wooden house so that it stands for centuries?
There are wooden architectural monuments that have come down to us, which are more than 450 years old. However, they were never processed. In Norway, a Christmas tree was found, which is 800 years old, there are live olives, which are more than 2 thousand years old. In Galicia there is the oldest forest in Europe, in which ordinary spruces have been standing for more than 400 years. It’s just that most people don’t know this, so they don’t believe that wood is a durable material.
What are the tasks set by the creators of wooden housing construction?
I'm looking to bring in a new architecture. Our task as manufacturers is to treat the technology of wooden housing construction reverently and seriously. In general, the study of wood is very fascinating process. If a person wants to build a wooden house for himself, I advise him to read a few articles about the history of wooden housing construction, you can learn a lot from them.
WOOD, secondary xylem perennials; in growing trees and shrubs, it makes up the bulk of trunks, branches, roots and performs conductive, storage and mechanical functions in them. A distinction is made between coniferous (pine, spruce, etc.) and deciduous (oak, birch, etc.) species.
Structure. Wood is studied on three sections of the trunk: transverse and two longitudinal - radial and tangential (Fig. 1). In wood, sapwood (a peripheral light zone) and a core (central zone) are distinguished, which have a darker color in the so-called heartwood or differ little in color from sapwood in non-core wood. Among non-core species (spruce, fir, beech, etc.), ripe wood species are distinguished, in which the central zone of wood in a freshly cut state is less moist than the peripheral one, and sapwood (birch, maple) - with uniform moisture along the trunk cross section. Annual layers (annual growth of wood) on cross section have the form of concentric circles, on the radial and tangential - respectively, straight and curved stripes; in many species in each layer, less dense light (so-called early) and denser dark (late) wood are noticeable. In ring-vascular hardwoods (for example, oak, ash), large vessels are located only in early wood, while in scattered-vascular (birch, aspen) large and small vessels are evenly distributed over the annual layer. In some hardwoods, light radial stripes (rays) are visible on the transverse section, shiny dark or light transverse stripes on the radial, and fusiform narrow strips on the tangential. In some coniferous species (pine, cedar, etc.), in the late zone of the annual layers, light spots are visible on the cross section - resin passages.
The wood structure of a felled tree observed using optical and electron microscopes includes plant cells with dead protoplast (the so-called mesostructure). Cell walls (microstructure) consist mainly of cellulose microfibrils (nanostructure). In the thin primary and thick three-layer secondary membrane of the cell wall, the microfibrils have different orientations; in the most powerful inner layer of the secondary membrane, microfibrils are located at a small angle of inclination (5-15°) to the long axis of the cell. This preferential orientation of microfibrils is one of the main causes of wood anisotropy. From the side of the cell cavity, the wall is covered with a thin warty layer. Cell walls have simple or bordered pores. Between the microfibrils there is lignin, which causes lignification of cell walls, as well as hemicelluloses and water.
Coniferous wood mainly consists of elongated prosenchymal cells - tracheids (Fig. 2). Large-cavity tracheids located in the early zone of the annual layer perform mainly a conducting function, late thick-walled tracheids perform a mechanical function, and parenchymal cells that form rays and participate in the structure of vertical resin ducts perform a storage function. Horizontal passages in some beams intersect with vertical ones, forming a single resin-bearing system. In hardwoods (Fig. 3), the conducting function is performed by vessels, vascular and fibrous tracheids; mechanical - libriform fibers and / or fibrous tracheids; storage - parenchymal cells in the form of horizontal single-row and multi-row rays, as well as vertical axial parenchyma.
Composition and properties. The chemical composition of wood of all species is almost the same (49-50% carbon, 43-44% oxygen, 6% hydrogen and 0.1-0.3% nitrogen). In wood, these elements form organic substances: cellulose (31-50%), lignin (20-30%) and hemicelluloses (19-35%), including pentosans (5-29%) and hexosans (6-13%). Conifers contain slightly more cellulose, hardwoods - much more pentosans. The composition of wood also includes extractive substances (tannins, resins, gums, essential oils and etc.). Mineral substances during the combustion of wood form ash (0.1-1%). The mass heat of combustion of wood does not depend on the species and is 19.6-21.4 MJ / kg; volumetric heat of combustion (MJ / m 3) depends on the density of the wood.
physical properties. The appearance of wood is characterized by color, luster and texture, which serve to identify tree species, and also determine the value of wood as decorative material. The variety of colors of wood of different species depends on the composition and content of extractive substances. The color changes when wood is exposed to air, light, temperature, chemical agents, as well as as a result of steaming, prolonged exposure to water, and fungal infections. The brilliance of wood is determined mainly by the presence of rays on the longitudinal sections. The texture of wood (a pattern formed as a result of cutting anatomical elements) depends not only on the type of wood, but also on the direction of the cut of the trunk. The texture of some hardwoods is especially spectacular due to cut vessels (for example, oak, ash), rays (beech, maple) and structural defects (Karelian birch).
The moisture content of wood (W) is defined as the ratio of the mass of water contained in it to the mass of absolutely dry wood. Bound water is contained in cell walls, free water is contained in cell cavities and intercellular spaces. Humidity of freshly cut kernels coniferous trees is 35-37%, sapwood - 2-3 times more; in hardwoods, this difference is negligible. Humidity is unevenly distributed along the height of the trunk; it is also subject to seasonal and daily fluctuations. The properties of wood change dramatically when the humidity is below the saturation limit of cell walls Wbp, equal to an average of 30% (determined when moistened in water). Wood has the ability to absorb moisture from the air (in the form of bound water), while the maximum moisture content of wood reaches the limit of hygroscopicity equal to W bp at room temperature. When soaked, wood absorbs water both in free and bound form, while the highest humidity is 100-270%. According to the degree of moisture, wood is divided into: wet, long time in water (humidity more than 100%); freshly cut, retaining the moisture content of a growing tree (50-100%); air-dried wood, or air-dried, seasoned outdoors(15-20%); chamber drying, or room dry, dried in a chamber or aged in a heated room (8-12%); absolutely dry, dried at a temperature of about 103 ° C (0%). When kept in air at a constant temperature and relative humidity, the wood acquires an appropriate and identical equilibrium moisture content for all species; during conditioning (air temperature 20 ° C and humidity 65%), the moisture content of wood is called normalized and is 12%. A decrease in the content of bound water leads to shrinkage of wood. With the complete removal of bound water, the linear dimensions of wood are reduced (by 8-10% in the tangential direction, 3-7% in the radial direction, 0.1-0.3% along the fibers) and volume (by 11 -17%). An increase in the content of bound water (when the wood is kept in moist air or water) causes the wood to swell. Due to differences in shrinkage and swelling in different directions, warping of wood occurs. Uneven removal of bound water from wood due to constrained shrinkage and inhomogeneous residual deformations causes stresses that lead to cracking of the material during the drying process or a change in the given shape of parts during the mechanical processing of dried wood. Cracking of wood (for example, large beams and logs) also occurs due to stresses due to the difference in tangential and radial shrinkage.
The density of the cell wall material (woody substance) does not depend on the species and is 1530 kg/m 3 . The density of wood in a dry state due to the presence of voids in it depends on the species and varies from 100 kg / m 3 ( balsa tree) up to 1300 kg/m 3 (backout). The density of wood for the most common domestic species at normalized humidity is 400-700 kg / m 3. With an increase in humidity (above W bp), the density of wood increases. Wood has the ability to pass liquids and gases under pressure (water and gas permeability). The permeability of deciduous wood is higher than that of coniferous wood, the sapwood has more permeability than the heartwood, and more along the fibers than across the fibers.
The specific heat capacity of absolutely dry wood is the same for all species - 1.55 kJ / (kg ° C); increases with increasing humidity and temperature. The thermal conductivity of wood also increases with increasing density, humidity and temperature; along the fibers it is twice as high as across the fibers. The thermal expansion of wood is small. Dry wood has a very high electrical resistance (it is a dielectric), which decreases sharply (millions of times) with an increase in humidity to W bp, and with further moisture - only hundreds or tens of times. Wood has a low electrical strength; to increase the breakdown resistance, it is impregnated with mineral oils. The dielectric constant of dry wood is 2-5 and increases with increasing humidity and temperature. Under the action of mechanical loads in dry wood, electric charges arise. The piezoelectric properties of wood are due to the presence of an oriented component - cellulose; in dry wood, they are most noticeable, decrease with increasing humidity and practically disappear at a moisture content of 6-8%. In wood, the speed of sound propagation along the fibers is 5000 m / s, across the fibers - 3-4 times less and decreases with increasing humidity and temperature of the wood. The specific acoustic resistance of wood, equal to the product of its density and the speed of sound, is about 3 10 6 Pa s/m. The decrement of sound attenuation in wood depends on the oscillation frequency, humidity, temperature and is (2-4)·10 -2 Np. Wood has a relatively low sound absorption and high resonant capacity, which led to wide application wood (especially spruce, fir) for the manufacture of soundboards of musical instruments.
The effect of electromagnetic oscillations on wood depends on their frequency: IR radiation heats the surface layers in wood (used for drying veneer and other thin assortments); visible light has a high penetrating power (for wood flaw detection); light laser radiation burns through wood (as a kind of "cutting" tool for figured cutting of wood products, engraving, etc.); UV radiation causes wood luminescence (to control the quality of wood processing). X-ray and nuclear radiation, passing through the wood, are attenuated depending on the thickness, density and moisture content of the assortment; they are also used for flaw detection of wood.
Mechanical properties. Wood is characterized by strength and deformability (the ability to change size and shape). The strength of wood samples is determined by compression, tension, bending, shear and (less commonly) torsion tests. The indicators of the mechanical properties of wood along the fibers are much higher than across the fibers. For the most common domestic species, the strength limits of wood (for samples without defects, with a moisture content of 12%) are: when compressed along the fibers 40-73 MPa; when stretched along the fibers 66-171 MPa, across the fibers in the radial direction 4-13.3 MPa, in the tangential direction - 2.8-9.2 MPa; at bending 68-148 MPa. Increasing the moisture content of wood to W p.n. reduces the compressive strength along the fibers by 2-2.5 times; an increase in the size of samples and the presence of defects in wood also reduces its strength. Under short-term and relatively small loads, wood is deformed as an elastic material; the modulus of elasticity of wood along the fibers is 12-18 GPa, across the fibers it is 15-30 times less. The rheological properties of wood (characterizing its increased ability to deform under load over time) increase with an increase in the content of bound water in it and temperature. With a decrease in humidity and temperature of the loaded wood, a significant part of the elastic deformations degenerates into "frozen" deformations, which manifest themselves in the processes of drying, pressing, and bending of wood. Frozen deformations determine the “memory” of wood for temperature and humidity effects. The strength of wood under prolonged exposure to a load can decrease by 2 times. Multiple changes in the load leads to a decrease in strength - fatigue of wood; cyclic changes in the moisture content of loaded wood cause hygrofatigue, i.e., a decrease in strength and increased deformation. When designing wooden structures design resistances are used, which are several times less than the tensile strength, which makes it possible to take into account the influence of the duration of the load, humidity, temperature, flaws and other factors. The impact strength of wood characterizes its ability to absorb work on impact without breaking; in hardwoods, this figure is 2 times higher than in conifers. The hardness of wood depends on its density, and the end hardness is greater than the side hardness.
vices. Disadvantages that change appearance wood, the integrity of tissues, the correctness of the structure, etc., reduce the quality of wood and limit the possibilities of its practical use. They occur both in a growing tree and in felled wood during its storage and processing. These include: knots; cracks (metic, frost, peeling) that occur in a growing tree and during drying; defects in the shape of the trunk - taper (an abnormal decrease in diameter along the length of the trunk), buttiness (a sharp increase in diameter in the lower part of the trunk), as well as curvature, outgrowths; defects in the structure - the slope of the fibers, serration (tortuous and disorderly arrangement of fibers), curl (local curvature of the annual layers), roll (reactive wood in conifers), false heartwood and internal sapwood in hardwoods, stepson (large knot); wounds - dryness (external necrosis of the trunk) and prorost (overgrown wound containing bark and dead wood), pitching and pocket (resin deposits), water layer (waterlogged areas of the core or ripe wood), etc. Wood defects also include: changes in natural color wood (for example, produbina and yellowness); fungal lesions in the form of blue, mold, rot; biological damage by insects and birds (for example, wormholes from larvae); mechanical damage trunks and defects in the processing of timber, foreign inclusions (stones, metal fragments, etc.), charring, warping. Some defects of wood can be considered as its advantages, for example, growths with a beautiful texture.
Application. wood like structural material has become widespread in construction, shipbuilding, railway transport, etc.; used in the form of timber, lumber, wood materials. Wood is used in the production of paper, cardboard, fibreboard. As a chemical raw material, wood is used to produce various organic compounds, such as cellulose, ethanol, fodder yeast, xylitol, sorbitol, charcoal, resin, methanol, acetic acid, acetone and other solvents, combustible and non-combustible gases (during wood pyrolysis). Wood retains its importance as a fuel.
Wood science is a scientific discipline that studies the structure and properties of wood and bark using the methods of biology, chemistry, physics and other sciences. To determine the quality of wood, tests are carried out, including non-destructive ones, based on the use of IR, light, UV, X-ray and nuclear radiation, sound and ultrasonic vibrations. New methods for researching wood are being developed, as well as ways to improve its properties (modification of wood by pressing, the introduction of synthetic polymers and other substances; impregnation with antiseptics and flame retardants to protect against decay and fire).
Lit .: Vanin S.I. Wood science. M.; L., 1949; Perelygin L. M. Wood science. 4th ed. M., 1971; Ugolev BN Timber science with the basics of forest commodity science. M., 2001.
Wood has a wide range of properties. They are revealed most fully when studying the physical and mechanical properties of wood.
Physical properties of wood. On the properties of wood big influence provides moisture. Water in wood is divided into three types: capillary (or free), hygroscopic and chemically bound. Capillary water fills the cell cavities, intercellular spaces and vessels in the wood. Hygroscopic water is found in cell walls. Chemically bound water is included in chemical composition wood-forming substances. The main mass of water in a growing tree is capillary and hygroscopic water or only hygroscopic water. The state of wood in which there is no capillary water and contains only hygroscopic water is called the saturation point of the fibers. In wood of different species, it is 23 ... 35%. When the wood dries, moisture gradually evaporates from the surface of the outer layers, and the moisture remaining in the wood moves from the inner layers to the outer ones.
According to the degree of humidity, wood is distinguished: wet, freshly cut (humidity 35% and above), air-dry (humidity 15 ... 20%) and room-dry (humidity 8 ... 12%).
The hygroscopicity of wood is the property of absorbing vaporous water from the air. The degree of absorption depends on the air temperature and its relative humidity.
Equilibrium is the moisture that wood has when exposed to air for a long time with constant relative humidity and temperature. The equilibrium moisture content of room-dry wood is 8 ... 12%, so parquet riveting and wood used indoors are dried to this moisture content. Wet wood releases moisture to the surrounding air, while dry wood absorbs it. Since the air humidity is not constant, the moisture content of the wood also changes - a change in the moisture content of the wood from zero to the saturation point of the fibers causes a change in the volume of the wood. The latter leads to swelling and shrinkage, warping of wood and the appearance of cracks. To reduce hygroscopicity and water absorption, the wood is coated paintwork materials or impregnated with various substances.
The density of wood depends on the volume of pores and moisture and characterizes it physical and mechanical properties(strength, thermal conductivity, water absorption). The density index is used in determining the quality factor, which is found by the ratio of compressive strength to density. In pine it is 0.6, and in oak it is 0.57. The porosity of coniferous wood ranges from 46 to 85%, hardwood - from 32 to 80%.
Shrinkage of wood is a decrease in its linear dimensions and volume during drying. Evaporation of capillary water is not accompanied by shrinkage. The latter occurs only during the evaporation of hygroscopic moisture. At the same time, the thickness of the water shells decreases, the micelles approach each other, and the dimensions of the wood decrease. Due to the heterogeneity of the structure, wood dries out or swells in different directions differently. Linear shrinkage along the fibers is 0.1...0.3%, in the radial direction - 3...6%, and in the tangential direction - 7...12%.
The property of uneven change in linear dimensions in different directions is one of the negative properties of wood as a building material. Slow drying of the wood ensures more uniform shrinkage and fewer cracks. Uneven shrinkage of wood in different directions causes different stresses, in connection with which the wood warps and becomes covered with cracks. AT round log cracks are located radially. Boards cut closer to the core of the trunk warp less than boards sawn closer to the surface of the log.
Swelling is the ability of wood to increase its size and volume by absorbing water that impregnates cell membranes. Wood swells as it absorbs moisture to the fiber saturation point. Swelling, like shrinkage, is not the same in different directions. The swelling of wood along the fibers is 0.1...0.8%, in the radial direction - 3...5% and in the tangential direction - 6...12%.
The thermal conductivity of wood is low, it depends on the nature of the porosity, humidity, direction of the fibers, species and density of the wood, as well as temperature. The thermal conductivity of wood along the fibers is about 1.8 times greater than across the fibers. On average, it is 0.16 ... 0.30 W / (m - ° C). With an increase in density and humidity, the amount of air in the voids decreases, and therefore the thermal conductivity of wood increases.
The electrical conductivity of wood depends on its moisture content. Electrical resistance dry wood averages 75-107 Ohm/cm, and raw wood - 10 times less. Wood is used for electrical wiring as boards, sockets, etc.
The permeability of wood depends on the type of wood, the initial moisture content, the nature of the cut (end, radial, tangential), the location of the wood in the trunk (core, sapwood), the width of the annual layers, and the age of the wood. Water permeability along the fibers is greater than through the radial and tangential surfaces. The water permeability of wood is characterized by the amount of water filtered through the surface of the sample (g / cm 2).
Resistance of wood to the action of acids, alkalis and water. Prolonged action of acids and alkalis destroys wood, and the higher the concentration, the stronger their destructive effect. Slightly alkaline solutions do not destroy wood. In an acidic environment, wood begins to break down at pH
The mechanical properties of wood as an anisotropic material are not the same in different directions. The mechanical properties of wood depend on many factors: with increasing humidity, the strength of wood decreases; high density wood has higher strength; the strength of wood is affected by the percentage of late wood, the presence of defects, rot, and aging.
Compressive strength of wood. Efforts to structural element can be applied, taking into account the structure of the wood, along or across the fibers, therefore, compression along and across the fibers is distinguished. For a compression test along the fibers, wood samples without knots are taken in the form of a rectangular prism measuring 20X20X30 mm with a wood size of at least 30 mm along the fibers and tested on a press.
The compressive strength of wood in compression along the fibers with a moisture content of 12%, depending on the type of wood, varies over a wide range - from 30 to 80 MPa. The tensile strength of wood in compression across the fibers is much less than in compression along the fibers, and is: in the radial direction for fir - 4.1 MPa, hornbeam - 25.6 MPa, and in the tangential direction for spruce - 7.1 MPa, hornbeam - 15.6 MPa.
Tensile strength of wood. Wood has a high tensile strength along the grain. For our main rocks, this value varies from 80 to 190 MPa.
The strength of wood for static bending is high, due to which it is widely used for bending elements of buildings and structures (beams, bars, rafters, trusses, etc.).
The bending strength of wood should be reduced to a moisture content of 12%. In hardwoods, the bending strength in the radial and tangential directions is almost the same, and in conifers, the strength in the tangential direction is slightly greater than in the radial direction. Static bending strength depends on the same factors as compressive strength.
The strength of wood for chipping along the fibers is low - 6.5 ... 14.5 MPa. The resistance to cutting wood across the fibers is 3-4 times higher than the resistance to chipping along the fibers, but a clean cut usually does not take place, since the fibers are crushed and bent at the same time. AT building structures wood often works on chipping along the fibers, for example in roof trusses and other structural elements. At the same time, it should be borne in mind that at present, at the leading enterprises, there is a tendency to switch to a standard wood moisture content of 12%.
In our age of progress, there are innovative building materials. But in past centuries, and now such material as wood remains popular. This material is noble and very beautiful, and correct operation and care can last for many years.
What is wood?
Wood in construction
Since ancient times, wood has been used as construction material for building walls, for a log house. Although lately they put metal-plastic windows and doors, but wooden crafts still not inferior, but even superior in their properties.
A natural wood floor will create a warm microclimate in your home. A wooden staircase will also look unsurpassed.
Wood material in the design field is used for wall cladding of houses, saunas, for the production of furniture.
Why do builders and designers leave their choice on natural material - wood?
Advantages
- - has a low weight (when compared with reinforced concrete, wood material has a weight 5 times less and 16 times less than steel);
- - high strength;
- - it is easy to mine;
- — does not require sophisticated technology in processing;
- — wooden details structures are easy to assemble, disassemble, move and remake individual wooden buildings and entire buildings
- - wood has a low coefficient of thermal conductivity, so it is valuable as effective insulation;
- - the material is characterized by durability, if, of course, the rules for the operation of the structure are observed;
- - wood can be renewed, it gives wide opportunities for the manufacture of many types of products;
- - perfectly combined with other building materials;
- - acts as a moisture-regulating and filtering component, ( wooden walls purify the air, and in both directions slowly passes it through the structures of its fibers);
- – wood is an environmentally friendly material.
Flaws
- - heterogeneous structure. So, if the wood is sawn incorrectly, then the compressive strength can drop by almost 5 times;
- - knotty;
- - creep. With prolonged exposure to the load on the wood, it is deformed;
- - exposed to rotting and insect damage;
- - moisture absorption. With increased humidity, the strength of wood in almost all types of work with it drops sharply;
- - drying of wood. May cause severe cracking;
- - subject to combustion.
Knowing the characteristics of timber is very important in the design, construction and operation of wooden structures.
As a building material, wood is used in two forms:
- - initial (round timber, logs, etc.)
- - secondary (board, timber, plywood, veneer, etc.).
What type of wood to choose for construction?
1. Conifers- the most popular wood material. It, when compared with deciduous, is the most affordable. And, of course, it has high technical properties.
- Pine. On the scale of use is in the highest position. Why? Firstly, this material is durable, dense, resistant to cracking, drying out and decay, wear-resistant. Secondly, pine is light wood, not knotty, and this greatly facilitates the processing process. The disadvantage is such a property as "blue", the appearance of the log house is spoiled by this.
- El. Differs in flexibility therefore it is widely applied to production of bent details. Spruce, like pine, is very durable (when dry). But it is not so rich in resinous substances, so it needs to be further processed. Spruce is knotty, and this complicates the processing process, and the scope is narrowed.
Compared to pine, spruce does not lose its color palette for a long time.
- Larch. She possesses high density and strength, especially after drying, and it is also resistant to decay. Therefore, it is used for the manufacture of basic load-bearing structures. It has low degree water absorption. Also, it is practically not knotty and does not warp. Among the shortcomings can be distinguished: easy splitting and difficulty in processing.
- Fir. It has low elasticity and low strength. It pricks easily and is also processed. This breed is much more susceptible to decay than pine, because it does not have resin passages. Fir is not suitable for the manufacture of basic external structures. It has found its application in the manufacture of windows, doors, floors and other interior structures.
- Cedar. High strength material, yet flexible and soft. It is light, resistant to rotting, easy to process. External structures are made from cedar. The advantages of cedar include its antiseptic properties, so it is successfully used in eco-building.
2. Hardwood
Many hardwoods not as strong and resistant to decay (they do not have resin passages) as conifers, so they are used in construction industry not so wide.
AT construction industry The most widely used hardwoods are:
— Oak. He has very beautiful texture, so it does not require additional staining. Virtually unaffected by fungi. Oak wood is very durable, it is a very hard material. It is used in the manufacture of external structures, as well as a finishing material (windows, doors, floors).
- Nut. The material is heavy, durable and hard. It is well processed and remarkably polished. The walnut texture is very beautiful.
- Ash. Elastic and durable material, has a light color. Ash is very hard to split. Due to the increased viscosity, it is difficult to process wood manually. It does not have the same properties as oak, so it is rarely used in external structures. Most actively used as a finishing material.
- Elm. Rot resistant. The material is characterized by density, viscosity, hardness and strength. It is difficult to prick, but it is perfectly processed. By their own technical specifications inferior to many conifers, therefore it is not used for building houses. Mainly used in furniture production, shipbuilding.
Types of lumber
When building wooden structures and choosing lumber, you will come across the names of types of lumber, the meaning of which you need to know:
- ridge - a thick tree trunk, freed from the bark, or a segment of it of a sufficiently large length (but not more than 25 cm);
- garter - the same range, but with a diameter of less than 25 cm;
- pole - a thin tree trunk (less than 9 cm in diameter), peeled from the bark;
- plate - a tree trunk, sawn along the fibers;
- quarter - ½ plate, which is sawn along the fibers;
- lying down is a log in horizontal position, which is hewn on both sides;
- beam - a log that is hewn on all four sides with a section of at least 100x100 mm.
- bar - the same as a bar, but smaller in size.
- treated wood
In the construction industry, the so-called improved wood has recently become popular - wood plastics obtained after processing products of wood material.
Types of wood plastics:
- plywood;
- fiberboard (wood fiber boards);
- chipboard ( particle boards);
- OSB (oriented strand board);
- wood-laminated plastic.
When choosing timber for construction, what should be considered?
- Strength. How stronger material, the lower the destruction coefficient. Each type of wood has its own strength. It is also affected by humidity, density and its defects.
- Density. Weight, ease of processing and resistance to decay depend on it.
- wear. The harder and denser wood, topics more degree wear resistance.
- Crack resistance. It depends on the degree of drying out of the wood: during the drying process, moisture from the wood material evaporates unevenly, this leads to internal stress and the wood cracks. Low-drying species are fir, cedar, pine.
- susceptibility to decay. Under the influence of various fungi, the wood is destroyed. Think that conifers less prone to rot than hardwoods. This can be explained by the presence of resinous substances.
- Texture. It is important here how it manifests itself after coating with stain, wax or varnish. This is very important in a design decision.
- Ability to hold fasteners made of metal (nail or screw). Density and humidity are important here - the higher the density, the more difficult it will be to pull out the mount.
- The presence of knots. The more woody material has knots, the lower the strength. This will result in additional processing costs.
Innovative wood processing technologies make it possible to produce any product.
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