Forest building materials. Raw materials for the manufacture of building materials Forest building materials

K category: Construction materials

Forest building materials

Wood is one of the oldest building materials. Not only various structural elements of buildings and structures are made from it, but also entire wooden buildings are erected. Wood is a raw material for the manufacture of finishing materials, fibrolite, fibreboard and chipboard, for the production of furniture and parquet. The widespread use of wood is facilitated by such positive properties as high strength with low weight, low thermal conductivity and ease of machining. The disadvantages of wood include: heterogeneity of the structure, which causes different indicators of strength and thermal conductivity along and across the fibers, susceptibility to rotting, combustibility and easy flammability, high hygroscopicity, the presence of various defects (knots, cracks, oblique, curvature of the trunk, graininess, etc.).

Our country has huge reserves of timber. The total area of forests in the USSR is about 700 million hectares and is equal to approximately one third of the entire forest area of the world. The annual increase in timber in the USSR is about 1 billion m3. The main part - about 76% of the forest area - is occupied by conifers valuable for construction, including (%): larch 40.2, pine 16.1, spruce 10.6, cedar 5, fir 3.4. However, despite the huge reserves of wood, care must be taken with this building material. Restorative afforestation is obligatory in used logging sites. More rational use of not only timber resources, but also wood waste (sawdust, shavings, chips, slabs), low-quality wood and softwood in the production of fiberboard, particle board and fiberboard.

Given the high physical and mechanical properties and a relatively small bulk density, coniferous wood is often used for construction purposes: pine, spruce, larch, cedar, and less often hard hardwood: oak, beech, hornbeam, maple, ash, birch. For temporary structures and auxiliary structures (formwork, sheds, lathing), soft hardwood is used: aspen, alder, poplar, linden.

Forest building materials used in construction are divided into round timber and lumber.

Round timber are segments of tree trunks (different species) cleared of bark and branches and, depending on the diameter at the upper end, are divided into logs, bollards and poles.

The logs have a diameter at the upper end of at least 14 cm and a length of 4-6.5 m. Depending on the presence of wood defects, the logs used in construction are divided into three categories according to their quality. To I and II categories include logs without defects, rot and wormholes: to III - logs with many defects other than rot.

The pedestal is a part of a tree trunk with a diameter at the upper end of 8-13 cm and a length of 3-9 m.

The poles have a diameter at the upper end of 3-7 cm and a length of 3-9 m.

Round timber is stored in piles by species, grade and length.

Sawn timber is obtained by longitudinal sawing of logs. According to the nature of processing, lumber is divided into edged and unedged. According to the cross-sectional shape, lumber is divided (Fig. 1) into planks, plates, wane bars, clean-edged bars, slabs, wane boards, clean-edged boards.

Depending on the quality of wood and the presence of defects, lumber is divided into five grades: selected, I, II, III and IV. Depending on the ratio of width to thickness, lumber is divided into boards, bars and bars.

Rice. 1. Types of lumber 1 - log (sawlog); g - lying down; 3 - lying, edged on both sides; 4- plate; 5 - obeolny bar; 6 - timber; 7 - slab; 8 - board with obul; 9 - edged milking; a - edge, b - layer; c - rib

Boards are made with a thickness of 13 to 100 mm and a width of 80 to 250 mm, but the ratio of width to thickness is always more than 2.

Bars are lumber up to 100 mm thick with a width to thickness ratio of less than 2. More often bars have a square section.
The bars have a thickness and width of more than 100 mm.

Ways to improve the durability of timber. To increase the durability, timber is dried, treated with antiseptics, and to protect it from moisture and fire, their surfaces are coated with special protective compounds.

Drying wood can be natural and artificial. During natural drying, lumber is stacked in stacks with gaskets and protected by canopies. Artificial drying of wood is carried out in drying chambers with hot air, gas, steam or high-frequency current, as well as by immersing lumber in heated petrolatum. When drying wood, its quality improves, the fungus infection and insect pests are destroyed. Moisture content of dried wood is 6-8%.

Antiseptic - impregnation of wood with solutions of sodium fluoride and fluorosilicone, ammonium, creosote or anthracene oil in order to protect it from decay. To protect wood from insect damage, coal oil with solvents, shale oil, chlorophyll in the form of dusts, suspensions, emulsions and in a gaseous state are used. To protect wood from moisture, ignition, its surfaces are coated with oil and synthetic paints and flame retardants. Fire retardants are prepared on the basis of liquid glass. At elevated temperatures, these compounds fuse and form a vitreous layer that prevents the access of oxygen. To increase fire resistance, wood is also impregnated with chemical compounds - flame retardants, for example, solutions of ammonium phosphate, borax, boric acid.

One of the oldest building materials is wood. In construction, coniferous wood (pine, spruce, fir, larch, cedar) and deciduous (oak, beech, birch, aspen, alder) species are used. Of the conifers, pine is the most common in construction. Its wood is strong, light, soft, lends itself well to all types of mechanical processing and is used for the manufacture of load-bearing structures of buildings, scaffolding, fences, joinery, plywood, etc. Of the hardwoods, oak is considered the most valuable. It has a strong, dense, hard and flexible wood; it is used for the manufacture of parts (for example, elements of structural joints), joinery, parquet, decorative plywood, furniture, etc. In addition, wood waste (chips, sawdust, trimmings) is widely used for the production of cellulose, paper, fibreboard and chipboard, fiberboard , xylolite.
Timber is measured in cubic meters.

The range of wood building materials and products includes logs, beams, boards of various shapes and sizes. Logs (roundwood) have dimensions of 2 ... 9 m in length with a gradation of 0.5 m, and 16 cm or more in diameter. Round wood is divided into sawn wood, intended for sawing, and construction, used in a round form. Upon delivery - acceptance of the logs must be stacked in piles sorted by species, length and grades. Upon acceptance, each log is measured (rounded up to 0.5 m in length) and no more than 10% of samples are taken. The thickness is measured in the upper cut without bark along the average diameter. Round wood with a diameter of less than 16 cm is called a bollard and poles, and more than 16 cm - logs.

Longitudinal sawing of logs produces boards, bars and beams. Lumber with a section thickness of up to 45 mm is called boards, over 45 mm - bars and beams. The standard established for sawn timber are dimensions along the length of 1 ... 6.5 m with a gradation of 0.25 m. Boards are made with a width of 80 ... 250 mm, beams - 130 ... 250 mm. According to the form of edge processing, unedged boards with a raw edge, edged and tongue-and-groove boards are distinguished, having an edge in the form of a comb on one side, and on the other - in the form of a groove. Plywood is obtained by gluing racing layers of wood, the so-called veneers, with a thickness of 3 ... 18 mm. In addition to ordinary plywood, facing plywood is produced with external veneers from oak, beech, walnut and other valuable species.

For the installation of floors on reinforced concrete floors, the manufacture of door panels and partitions, wood-fiber and chipboards are used. Fibreboards are made from wood and vegetable fibres. To improve the quality of the boards, water-resistant and antiseptic substances are added to the fibrous mass during the manufacturing process. Hardboards are impregnated with synthetic waterproof resins or drying oils and heat treated to produce ultra-hard boards. Chipboards are faced with PVC tiles, which give the surface of products a finish of various colors, patterns and textures, covered with polymer films, textured paper, wood veneers or painted with enamels. The plates are fastened with nails, screws or glued with mastics, stored in closed warehouses, without exposing them to sharp fluctuations in temperature and humidity.

One of the oldest building materials is wood. In construction, coniferous (pine, spruce, fir, larch, cedar) and deciduous (oak, beech, birch, aspen, alder) species are used. Of the conifers, pine is the most common in construction. Its wood is strong, light, soft, lends itself well to all types of mechanical processing and is used for the manufacture of load-bearing structures of buildings, scaffolding, fences, joinery, plywood, etc. Of the hardwoods, oak is considered the most valuable. It has a strong, dense, hard and flexible wood; it is used for the manufacture of parts (for example, elements of structural joints), joinery, parquet, decorative plywood, furniture, etc. In addition, wood waste (chips, sawdust, trimmings) is widely used for the production of cellulose, paper, fibreboard and chipboard, fiberboard , xylolite.

Timber is measured in cubic meters.

The range of wood building materials and products includes logs, beams, boards of various shapes and sizes. Logs (roundwood) have dimensions of 2 ... 9 m in length with a gradation of 0.5 m, and 16 cm or more in diameter. Roundwood is divided into sawmill, intended for sawing, and construction, used in a round form. Upon delivery - acceptance of the logs must be stacked in piles sorted by species, length and grades. Upon acceptance, each log is measured (rounded up to 0.5 m in length) and no more than 10% of samples are taken. The thickness is measured in the upper cut without bark along the average diameter. Round wood with a diameter of less than 16 cm is called a bollard and poles, and more than 16 cm - logs.

Longitudinal sawing of logs produces boards, bars and beams. Lumber with a section thickness of up to 45 mm is called boards, over 45 mm - bars and beams. The standard for sawn timber is 1 ... 6.5 m in length with a gradation of 0.25 m. Boards are made with a width of 80 ... 250 mm, beams -130 ... 250 mm. According to the form of edge processing, unedged boards with a raw edge, edged and tongue-and-groove boards are distinguished, having an edge in the form of a comb on one side, and on the other - in the form of a groove. Plywood is obtained by gluing thin layers of wood, the so-called veneers, with a thickness of 3 ... 18 mm. In addition to ordinary plywood, facing plywood is produced with external veneers from oak, beech, walnut and other valuable species.

Wood is used to make window frames, window sills, door panels, frames for windows and doors, platbands, skirting boards, parquet, panels for ceilings and partitions, and even ready-made prefabricated structures - houses, warehouses, etc.

For the installation of floors on reinforced concrete floors, the manufacture of door panels and partitions, wood-fiber and chipboards are used. Fibreboards are made from wood and vegetable fibres. To improve the quality of the boards, water-resistant and anti-septic agents are added to the pulp during the manufacturing process. Hardboards are impregnated with synthetic waterproof resins or drying oils and heat treated to produce ultra-hard boards. Chipboards are faced with PVC tiles, which give the surface of products a finish of various colors, patterns and textures, covered with polymer films, textured paper, wood veneers or painted with enamels. The plates are fastened with nails, screws or glued with mastics, stored in closed warehouses, without exposing them to sharp fluctuations in temperature and humidity.

Wood is a heterogeneous material that has damage, various diseases called defects. Wood defects include knots, cracks and deformations, various deviations from the normal structure, wood damage by insects and fungi. Defects reduce the quality of wood. The influence of defects on the degree of suitability of wood for construction depends on the nature and size of the damage, as well as the purpose of the material.

In order for wood products to be durable, lumber is dried in special chambers or in open areas or treated with antiseptics (protection from decay) and flame retardants (protection from fire). Antiseptics are substances that kill fungi that cause decay. For impregnation with antiseptics, prepared wooden elements are immersed in hot and cold baths with a solution. To protect against fire, wood is treated with aqueous solutions, special coatings prepared on the basis of liquid glass.

- Forest building materials

FOREST MATERIALS

Wood is a highly porous product of living nature, characterized by a specific fibrous structure, which predetermines the originality of its physical and mechanical properties, wide and varied use in various sectors of the national economy.

Due to these properties, forest materials, as well as products and structures based on them, can work for a long time in various operating conditions.

TO positive properties wood has high mechanical strength and at the same time lightness, which makes it possible to classify it as an effective material with a fairly high coefficient of constructive quality.

Wood is able to absorb shock loads and dampen vibrations, it has high heat, sound and electrical insulating properties, chemical resistance to acids and alkalis, is easily processed with cutting tools, holds metal and other fasteners well, glues securely and, finally, has a natural decorative effect, which makes it a popular finishing material.

To negative properties wood include anisotropy, i.e., heterogeneity of structure and properties in different directions with respect to the location of wood fibers; increased hygroscopicity and water absorption, which predetermine the change in the most important physical and mechanical characteristics due to uneven swelling; warping and cracking.

Structure and composition

A growing tree consists of a root system, trunk and crown. The trunk is of industrial importance, since from 60% to 90% of wood is obtained from it. macrostructure name the structure of a tree trunk, visible to the naked eye or through a magnifying glass, microstructure- visible under a microscope. Usually, three main sections of the trunk are studied: transverse (end), radial, passing through the axis of the trunk, and tangential, passing along the chord along the trunk (Fig. LM-1a).

Rice. LM-1 Tree trunk structure:

a) the main sections of the trunk: 1 - transverse (end); 2 - radial; 3 - tangential; b) the structure of a tree trunk in a cross section: 1 - bark; 2 - cambium; 3 - bast; 4 - sapwood; 5 - core; 6 - core rays.

macrostructure

When considering sections of a tree trunk with the naked eye or through a magnifying glass, the following main parts of it can be distinguished: core, bark, cambium and wood (Fig. LM-2).

Core consists of cells with thin walls, loosely connected to each other. The core, together with the wood tissue of the first year of tree development, forms a core tube. This part of the tree trunk rots easily and has little strength.

Bark consists of skin or rind, cork and bast. Peel or skin and cork cloth protect the tree from harmful environmental influences and mechanical damage. The bast conducts nutrients from the crown to the trunk and roots.

Under the bast layer of a growing tree there is a thin annular layer of living cells. - cambium. Every year, during the vegetative period, the cambium deposits cells of the bast towards the bark and inside the trunk, in a much larger volume - wood cells. Cell division of the cambial layer begins in spring and ends in autumn, so the wood of the trunk (part of the trunk from the bast to the core) in cross section consists of a number of concentric, so-called, annual rings around the core. Each growth ring consists of two layers: (spring) wood, formed in spring or early summer, and late (summer) wood, which forms towards the end of summer. Early wood is light and consists of large, but thin-walled cells; late wood is darker in color, less porous and has greater strength, as it consists of small-cavity cells with thick walls.

In the process of tree growth, the walls of the wood cells of the inner part of the trunk adjacent to the core gradually change their composition and are impregnated with resin in coniferous species, and tannins in deciduous species. The movement of moisture in the wood of this part of the trunk stops and it becomes more transparent, harder and less capable of decay. This part of the trunk, consisting of dead cells, is called the core in some species, in others it is called ripe wood. The part of the younger wood of the trunk closer to the bark, in which living cells are still changing, ensuring the movement of nutrients from the roots to the crown, is called sapwood. This part of the wood has a high moisture content, rots relatively easily, is of low strength, has greater shrinkage and a tendency to warp.

Rocks in which the core differs from the sapwood in a darker color and less moisture are called sound(pine, larch, oak, cedar, etc.). Species in which the central part of the trunk differs from the sapwood only by less moisture are called ripe woody(spruce, fir, beech, linden, etc.). Tree species in which no significant difference can be seen between the central and outer parts of the trunk wood are called bleached rocks(birch, maple, alder, aspen, etc.).

In wood of all species are located core rays, which serve to move moisture and nutrients in the transverse direction and create a supply of these substances for the winter. In conifers, they are usually very narrow and visible only under a microscope. The wood easily splits along the core rays, but it cracks along them when it dries.

The cost of building materials, products and structures is 50-70% of the cost of construction. Therefore, it is so important to know how to minimize the cost of them. This can be done through the use of modern resource- and energy-saving technologies, local raw materials, and industrial waste. At the same time, materials, products and structures are required to ensure the required quality.

Construction Materials - natural and artificial materials and products used in the construction and repair of buildings and structures. There are building materials for general and special purposes.

The following are chosen as classification features: the production purpose of building materials, the type of feedstock, the main quality indicator, for example, their mass, strength, and others. At present, the classification also takes into account the functional purpose, for example, heat-insulating materials, acoustic materials, and others, in addition to dividing into groups based on the basis of raw materials - ceramic, polymer, metal, etc. One part of the materials combined into groups refers to natural , and the other part of them - to artificial ones.

Each group of materials or their individual representatives in the industry corresponds to certain industries, for example, the cement industry, the glass industry, etc., and the planned development of these industries ensures the fulfillment of plans for the construction of facilities.

Natural, or natural, building materials and products are obtained directly from the bowels of the earth or by processing forest areas into a "business forest". These materials are given a certain shape and rational dimensions, but do not change their internal structure, composition, for example, chemical. More often than others from natural forest (wood) and stone materials and products are used. In addition to them, in finished form or with simple processing, you can get bitumen and asphalt, ozokerite, casein, kir, some products of plant origin, such as straw, reeds, bonfire, peat, husks, etc., or animals, such as wool, collagen, Bonn blood, etc. All these natural products are also used in construction in relatively small quantities, although forest and natural stone materials and products remain the main ones.

Artificial building materials and products are produced mainly from natural raw materials, less often from by-products of industry, agriculture or artificially obtained raw materials. The produced building materials differ from the original natural raw materials both in structure and in chemical composition, which is associated with the radical processing of raw materials in the factory with the involvement of special equipment and energy costs for this purpose. Factory processing involves organic (wood, oil, gas, etc.) and inorganic (minerals, stone, ores, slag, etc.) raw materials, which makes it possible to obtain a diverse range of materials used in construction. Between individual types of materials there are great differences in composition, internal structure and quality, but they are also interconnected as elements of a single material system.

Wood is one of the oldest building materials. Not only various structural elements of buildings and structures are made from it, but also entire wooden buildings are erected. Wood is a raw material for the manufacture of finishing materials, fibrolite, fiberboard and chipboard, for the production of furniture and parquet. Such positive properties as high strength with a small volumetric weight, low thermal conductivity and ease of machining contribute to the widespread use of wood. The disadvantages of wood include: heterogeneity of the structure, which causes different indicators of strength and thermal conductivity along and across the fibers, susceptibility to decay, combustibility and easy flammability, high hygroscopicity, the presence of various defects (knots, cracks, oblique, curvature of the trunk, etc.).

Given the high physical and mechanical properties and a relatively small bulk density, coniferous wood is more often used for construction purposes: pine, spruce, larch, cedar, and less often hard hardwood: oak, beech, hornbeam, maple, ash, birch. For temporary structures and auxiliary structures (formwork, sheds, lathing) use soft hardwood: aspen, alder, poplar, linden,

Forest building materials used in construction are divided into round timber and lumber (Fig. 2.15).

Round timber are segments of tree trunks (different species) cleared of bark and branches and, depending on the diameter at the upper end, are divided into logs, podtovarnik and poles.

logs have a diameter at the upper end of at least 14 cm and a length of 4-6.5 m. Depending on the presence of wood defects, the logs used in construction are divided into three categories according to their quality - The 1st and 2nd categories include logs without defects, rot and wormholes, to the 3rd - logs with many defects, except for rot.

podtovarnik is a part of a tree trunk with a diameter in vert-

khnem butt 8-13 cm and a length of 3-9 m.

Rice. 2.15. Types of lumber:

1 - log (sawlog); 2 - bed; 3 - bed, edged on both sides; 4 - plate; 5 - wane timber; 6 ~ timber; 7 - slab; 8 - board with wane; 9 - edged board; a - edge: 6 - layer; in - rib.

poles have a diameter at the top end of 3-7 cm and a length of 3-9 m. Round timber is stored in piles according to species, grade and length

lumber obtained by longitudinal sawing of logs. According to the nature of processing, sawn timber is edged and not edged. According to the cross-sectional shape, sawn timber is divided into logs, plates, wane bars, clean-edged bars, slabs, wane boards, clean-edged boards. Depending on the quality of wood and the presence of defects, lumber is divided into five grades: selected, 1, 2, 3 and 4 Depending on the ratio of width to thickness, lumber is divided into boards, bars and beams.

Boards are made with a thickness of 13 to 100 mm and a width of 80 to 250 mm, but always the ratio of width to thickness is less than 2.

bars are lumber with a thickness of up to 100 mm with a ratio of width to thickness of less than 2. More often, the bars have a square section.

bars have a thickness and width of more than 100 mm.

Ways to increase the durability of timber. To increase the durability, timber is subjected to drying, treatment with antiseptics, and to protect against moisture and fire, their surfaces are covered special protective compounds.

Drying wood can be natural and artificial. During natural drying, lumber is stacked in stacks with gaskets and protected by canopies. Artificial drying of wood is carried out in drying chambers with hot air, gas, steam or high-frequency current, as well as by immersing lumber in heated petrolatum. When drying wood, its quality improves, fungal infection and insect pests are destroyed. The moisture content of dried wood is 6-8%.

Amtiseptization - impregnation of wood with solutions of sodium fluoride and chromium fluoride, ammonium, creosote or anthracene oil in order to protect it from decay,

To protect wood from insect damage use coal oil with solvents, shale oil, chlorophos in the form of dusts, suspensions, emulsions and in a gaseous state

To protect wood from moisture, fire its surfaces are coated with oil and synthetic paint fire retardants. Fire retardants are prepared on the basis of liquid glass. At elevated temperatures, these compounds fuse and form a vitreous layer that prevents oxygen from entering. To increase fire resistance, wood is also impregnated with chemical compounds - flame retardants, for example, solutions of ammonium phosphate, borax, boric acid.

Natural stone materials and products based on them.

The main properties of natural stone materials are: bulk density, density, porosity, compressive strength, frost resistance and softening coefficient. The quality of stone materials is evaluated by the magnitude of these properties and their grades are determined.

By volumetric weight stone materials are divided into heavy - with a density of more than 1800 kg / m 3 and light - less than 1800 kg / m 3

By tensile strength in compression, grades are established: for heavy stone materials - 100, 125. 150, 200, 300. 400, 500, 600. 800 and 1000; for light - 4. 7, 10, 15, 25, 35. 50, 75, 100, 125, 150 and 200 The figure indicates the strength of the material in N / m 2

According to the degree of frost resistance grades from 10 to 200 are established. The frost resistance figure indicates the number of freeze-thaw cycles in which strength is maintained.

According to the softening coefficient, stone materials are divided into four groups with K = 0.6; 0.75; 0.9 and 1.

Depending on the purpose, additional requirements are imposed on stone materials: resistance to abrasion, wear, color, texture, etc. Natural stones, ordinary and small blocks, are made from limestone, volcanic tuffs and other rocks with a bulk density of 2200 kg / m 3, limit compressive strength of at least 2.5 MPa, frost resistance of at least 15 and a softening factor of 0.6 or more -

Depending on the manufacturing method, processing accuracy and shape, natural stones are divided into sawn and clean, semi-clean and rough tesky, coarse-cut. flagstone and broken rubble stone.

Rubble stone mined mainly from sedimentary rocks (dense limestone, dolomite, sandstone) and less often from igneous rocks. The tensile strength of rubble stone is not less than 10 MPa, the softening coefficient is not less than 0.75, the mass of individual stones is from 15 to 40 kg. Waste in the manufacture of rubble stone and torn rubble stone are processed into crushed stone,

Large blocks of natural stone. Large limestone blocks with a tensile strength of 2.5-10 MPa and a bulk density of 1500-1800 kg/m 3 are most widely used. Block sizes and nomenclature are established by GOST 15884-70. Blocks are produced for two-, three- and four-row cutting for the walls of residential and public buildings and multi-row for industrial construction.

Cladding slabs made of natural stone are made according to GOST 9480-77 with abrasive (polished, polished, polished, sawn) and rock (embossed, thermal jet, dotted, grooved) texture of the front surfaces. Facing plates are made of granite, syenite, diorite, gabbro, labrodite, quartzite, limestone, tuff, sandstone, marble. In addition to facing plates, profile parts are made from natural stone: skirting boards, fillets, capitals, steps, window sills, etc.

natural sands used in construction in its natural state, and also as a filler for mortars and concretes. Sands are divided into heavy sands with a bulk density of more than 1200 kg / m 3 and light (porous) - less than 1200 kg / m 3.

Heavy natural sand (GOST 8736-77) is a product of the natural destruction of rocks and, according to its grain composition, is divided into coarse sand with a grain size of 2.5-5 mm, medium - 2.5-2 mm, fine - 2-1.5 mm and very small - 1.5-1 mm.

Natural porous sands (GOST 22263-76) are obtained by crushing and screening pumice, volcanic slag, tuff, porous limestone and shell rock.

Gravel is a product of the natural destruction of rocks and is a mixture of rounded stone grains ranging in size from 5 to 70 mm.

State educational institution
higher professional education
"St. Petersburg State
University of Engineering and Economics"

ESSAY

By discipline:

"Construction Materials"

"Forest Materials"

Completed by: Bozhko A.V.
3rd year student
Lecturer: Konovalov V.F.
Position: Cand. tech. Sciences, Assoc.
Grade:______________Date_____ ___________
Signature:______________________ ___________

Saint Petersburg
2012

Wood is one of the oldest building materials. Not only various structural elements are made from it

Wood is a raw material for the manufacture of finishing materials, fibrolite, fibreboard and chipboard, for the production of furniture and parquet. The widespread use of wood is facilitated by such positive properties as high strength with a small volume mass, low thermal conductivity and ease of machining. The disadvantages of wood include: heterogeneity of the structure, which causes different indicators of strength and thermal conductivity along and across the fibers, susceptibility to rotting, combustibility and easy flammability, high hygroscopicity, the presence of various defects (knots, cracks, oblique, curvature of the trunk, graininess, etc.).

In modern industrial construction, timber materials occupy a significant place among other building materials. They are used for the manufacture of load-bearing and enclosing wooden structures of buildings and structures, joinery, formwork, scaffolding, sleepers, etc. In addition, wood waste (chips, sawdust, branches, slabs, slats) is widely used for the production of wood concrete, fibrolite, xylolite, wood-cement, wood-fiber and particle boards. The widespread use of forest materials in construction is mainly due to the presence of a number of positive properties. They have high strength, low average density, ease of processing, high frost resistance and resistance to salt solutions, alkalis, organic acids.
Wood consists of living and dead cells that have different shapes, sizes and perform different functions. Wood contains conductive, mechanical and storage cells. Conductive cells serve to transfer nutrients from roots to branches and leaves. These are the so-called vessels (in hardwoods) and tracheids (in conifers). Mechanical cells are elongated, have thick walls and narrow internal cavities. In hardwood wood, the functions of mechanical cells are performed by the so-called libriform (spindle-shaped cells), and in coniferous wood, late wood tracheids. Storage cells serve to store nutrients and transfer them to living cells in a horizontal direction. They are found mainly in the medullary rays. Each living wood cell has a cell membrane and protoplasm, cell sap and nucleus inside it.
The chemical composition of wood of all species contains on average 49.5% carbon, 6.3% hydrogen, 44.1% oxygen, 0.1% nitrogen. The cell membranes account for about 95% of the mass.
The main components of the shells are cellulose (43...56%) and lignin (19...30%). The rest of the shells are occupied by hemicelluloses, pectin substances, mineral salts, fats, essential oils, alkaloids, glycosides, etc.
The following main parts (macrostructure) of the trunk are distinguished: bark, bast, cambium, sapwood, core, core, core rays and annual layers.
The bark consists of outer (crust) and inner (bast) layers. It protects the tree from temperature and mechanical influences. Under the bast is a thin layer of cambium, consisting of living cells. The thick layer of wood following the cambium consists of a series of thin concentric layers, the inner part of which is called the core, and the peripheral part is called sapwood. There are species, such as birch, maple, alder, etc., in which the core is absent. Such breeds are called sapwood. According to these features, all tree species are classified into heartwood (having a core and sapwood), sapwood (devoid of a core, having only sapwood) and sapwood (having a not pronounced core - ripe wood and sapwood).
All tree species are classified into coniferous and deciduous. The most widespread in construction are conifers. These include pine, spruce, fir, larch and cedar. In recent years, in connection with a significant increase in the volume of capital construction, deciduous species, such as oak, beech, birch, aspen, linden, hornbeam, alder, elm, etc., have become increasingly used in industry.

2. Properties of wood

The main properties of wood are classified into physical and mechanical. The physical properties of wood are characterized by color, luster, texture, density, hygroscopicity, etc. The mechanical properties of wood are characterized by strength and deformation characteristics in its various stressed states (strength in compression, tension, bending, chipping, modulus of elasticity and shear, creep, shrinkage, etc. .).
Physical properties of wood. Consider those physical properties of wood that are of the greatest importance for the construction industry.
The moisture content of wood has a significant effect on its properties. Wood contains free (in cell cavities) and bound (in cell membranes) moisture.
Complete (with the removal of all cohesive moisture) shrinkage in the tangential direction for wood of various species is b ... 10%, and in the radial direction 3 ... 5%, along the fibers 0.1 ... 0.3%, full volumetric shrinkage approximately 12 ... 15%. Due to the difference in the values of radial and tangential shrinkage during drying (or moistening), warping of the wood is observed.
The bulk density, or average density, of wood depends on its moisture content and pore volume. The density of woody matter (specific gravity) is the same for all species (since their chemical composition is the same) and is approximately equal to 1.5. The density of wood due to the presence of cavities in it is less than the density of the wood substance and varies significantly depending on the species, growth conditions, the position of the wood sample in the trunk, etc.
Mechanical properties of wood. When using wood as a structural material and creating composite materials, it becomes necessary to take into account the ability of wood to resist the action of forces, i.e. its mechanical properties. The mechanical properties of wood include its strength and deformability, as well as some of its operational properties associated with mechanical influences.

The strength of wood characterizes its ability to resist destruction under the influence of mechanical loads. An indicator of this mechanical property is the tensile strength - the maximum amount of stress that a material can withstand without destruction. The tensile strength is determined by testing wood samples for compression, tension, bending, shear and (very rarely) torsion. Wood belongs to anisotropic materials, therefore, the determination of strength indicators is carried out in different structural directions - along and across the fibers (in the radial and tangential directions).

The deformability of wood is its ability to change its size and shape under the influence of forces. An indicator of the deformability of wood is the moduli of elasticity, coefficients of transverse deformability, shear moduli, long-term moduli of elasticity, creep, shrinkage, etc.
When calculating the elements of wooden structures, it is necessary to know the mechanical properties of wood and the analytical definition of its stressed and deformed states. Many specific problems are solved by methods of the theory of elasticity and resistance of the material.
Among the operational and technological properties that manifest themselves under the influence of forces include: hardness, impact strength, wear resistance, the ability to hold fasteners, etc. According to its mechanical properties, wood belongs to anisotropic materials. It has a significant difference in terms of strength and deformation properties in different structural directions. Wood has the greatest strength and rigidity along the fibers, the smallest - in the transverse direction.
Indicators of the mechanical properties of wood depend on its moisture content. When wood is moistened to the saturation limit of cell walls, the indicators of all mechanical properties sharply decrease. With a further increase in the moisture content of wood (over 30%), the indicators of mechanical properties practically do not change.
Some indicative indicators of the physical and mechanical properties of wood are given in table. 7.1 ....7.5.
When calculating structures made of wood, working in compression, bending, tension, or under conditions of a complex stress state, the numerical values of the indicators of the mechanical properties of wood are taken from the reference literature, taking into account the transition coefficients to the design resistances of wood, depending on the species.

3. Wood-based building materials

The main wood building materials include round timber, sawn timber, glued products and structures, chipboard, wood-cement and wood-fiber boards, wood concrete, fibrolite, xylolite, etc.
Round timber - pieces of a tree trunk of different breeds and sizes, cleared of bark and branches. In general, round timber is used in construction as wall material, supports and poles for overhead communication lines and power lines and flooring in the construction of bridges, roads, for fencing territories, etc.
Made from round materials that have retained the natural structure of wood, sawn timber, split timber (barrel staves), sliced and peeled veneer, and others belong to the processed group.
Lumber - products obtained by cutting logs, having standard dimensions and quality, used in its entirety or for the production of blanks, parts and wood products. In lumber, the longitudinal and wide sides are called layers, the longitudinal narrow ones are called edges, and those perpendicular to them are called ends. The lines of intersection of the layers and edges of sawn products are called ribs. The part of the surface of the log remaining on the lumber is called the wane.
By species of wood, sawn timber is divided into two main groups: coniferous and deciduous. According to the dimensions of the cross section, they are divided into bars, bars and boards (7.1).
Bars - lumber with a thickness and width of 100 m or more. According to the number of sawn layers, two-, three- and four-edged bars are distinguished. Bars - lumber with a thickness of up to 100 mm and a width of no more than double the thickness. Boards - lumber up to 100 mm thick and more than double thickness wide.
Lumber can be edged (7.1, c - e) and unedged (7.1, a, b, e). For edged lumber, the faces and edges are propylene along the entire length; unedged faces are propylene, and the edges are not propylene or partially propylene, and the size of the uncut part exceeds the allowable dimensions for edged
lumber. During the production of sawn timber, an associated sawn product is formed in the form of an obapol. Obapol - sawn products obtained from the side of the log and having one sawn and the other unsawn or partially sawn surface.
From lumber, various products and structures are made for the needs of the construction industry, which are described below.
Sleepers - products obtained by longitudinal sawing of logs with a cross section close to bars, 1.35 ... 2.7 m long. Sleepers are used in railway construction.
A checker made of wood is a four- or six-sided shape. Height of checkers for floors 60...80 mm; for road bridge coverings 100...120 mm, width 50...100 mm. The moisture content of the wood for checkers should be no more than 25%. Checkers are made from softwood and hard hardwood, with the exception of fir, birch, beech and oak. Take into account the checker in square meters of their end surface.
Semi-finished products, blanks and products. Semi-finished products and blanks are boards or bars cut to the specified dimensions, with appropriate allowances for machining and shrinkage. These include tongue-and-groove floor boards, skirting boards, fillets for sealing the space between the floor and walls, platbands for sheathing window and door frames.
Construction details are elements of prefabricated houses, various joinery products made at specialized factories. The most progressive are glued wooden structures.
Glued wooden structures - products obtained by gluing boards (bars) and plywood. The technology for manufacturing glued structures consists of the following main operations: drying, selecting and sorting lumber, treating surfaces for gluing, applying glue, pressing, keeping in presses under pressure, treating the surfaces of finished elements and sending them to the finished product warehouse.
Lumber intended for the manufacture of glued structures is dried to a moisture content of 10 ... 15%, sorted by quality, cut to length with cutting out defective areas and prepared for gluing into a “toothed spike”. The size of the glued thread of the boards is usually equal to the length of the structure or its element. After gluing, the elements are chipped on a four-sided planer.
Pressing of glued wooden structures is usually carried out in special horizontal and vertical clamp presses, as well as in pneumatic and hydraulic presses. When pressing the package, two main requirements must be observed:
1) careful calibration of the boards (their warping and different thicknesses are unacceptable); 2) uniform application of glue on the surfaces to be glued, with strict observance of the adhesive viscosity and the processing and pressing time established by the instructions.
After curing until the glue is cured, the structures are fed to the finishing post, where they are cleaned of glue streaks and coated with paints and varnishes, sometimes to increase bio- and fire resistance (these operations can be performed on lumber before they are glued) - with antiseptics and flame retardants. These structures are increasingly used in the national economy due to their low density, high strength and durability in operation in various conditions, including aggressive environments, the possibility of manufacturing any size and shape.
In construction, glued structures of two fundamentally different types are used: load-bearing and enclosing. The load-bearing structures are multi-layer, i.e. glued from layers of wood. Sometimes multilayer wooden structures are reinforced by gluing metal or plastic reinforcement. Such structures are called reinforced. There are combined structures consisting of layers of solid wood glued to plywood. Most often, these are I-beam or box-section structures, upper and lower
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