Pine, spruce, larch, fir, cedar are used in construction from conifers. Pine and larch are more suitable for the manufacture of supporting structures, unlike spruce and fir, they are less susceptible to rotting. In the European construction industry, due to its prevalence, pine takes the first place. Hardwoods are used much less often, of which oak, ash, beech, birch, aspen are most applicable.
If you look closely at the cross section of a tree trunk (Fig. 1), you can distinguish the following main parts – the core (5), wood, cambium (2) and bark (1). The core is thin <a tube> in the very center of the trunk, it has low strength and rots easily. The wood (part of the trunk from the bast (3) to the core) in cross section is a series of concentric (annual) rings around the core.
In the process of tree growth, the walls of the wood cells adjacent to the core gradually change their composition, being impregnated with resin in conifers, and with tannins in deciduous trees. The movement of juices in this part of the trunk stops, the wood becomes harder and less prone to decay. This part of the trunk in conifers is called the core, and in others it is called ripe wood. The part of the younger wood that is closer to the bark (there are still living cells in it) is called sapwood (4). It has a high moisture content, is relatively easy to decay, has low strength, is subject to significant shrinkage and is prone to warping. Species in which the core differs from the sapwood in a darker color and less moisture are referred to as sound (pine, larch, oak, cedar, etc.), in ripe-tree species (spruce, fir, beech, linden, etc.), the central part the trunk differs from sapwood only in less moisture. In sapwood (birch, maple, alder, aspen, etc.), it is impossible to notice a significant difference between the central and outer parts of the trunk..
Such a detailed description of the macrostructure of a tree will be needed in the future in order to understand what purpose is pursued by the cylindering of heartwood logs – pine and larch. By its microstructure, wood is a natural polymer; its fiber cells are tubular and directed along the trunk. Due to this, wood has a number of advantages – high strength, elasticity, low density, and, consequently, low weight, low thermal conductivity, resistance to chemically aggressive media, natural decorative effect, ease and simplicity of processing and installation. The thermal insulation properties of wood are of particular importance: low thermal conductivity is its indisputable advantage (see table). The most important characteristic of the thermal insulation properties of a structure is the value of thermal resistance, which establishes a relationship between the physical properties of the material and the thickness of its layer. It is defined as the ratio of the thickness of the material layer to its coefficient of thermal conductivity.
The greater the thermal resistance of the material from which the house is built, the warmer it is.
The superiority of wood over brick in terms of thermal insulation properties is obvious: a brick wall 510 mm thick (two bricks) has almost the same thermal resistance as a wall made of a wooden beam 100 mm thick. However, along with advantages, wood has disadvantages: anisotropy (its properties are sharply different along and across the fibers), structural defects, hygroscopicity and, as a consequence, moisture deformation, decay and flammability.
The most significant effect on the operational properties of wooden structures is hygroscopicity, decay and flammability. To reduce their negative effect, first of all, drying, impregnation of wood with antiseptics or antipyrine is used, as well as measures to prevent moisture from structures during operation (protection from atmospheric precipitation; isolation from soil, stone, concrete; good natural ventilation, etc.). ). Currently, for antiseptic and antipyrine treatment of wood, the KSD composition is used, which replaced the previously widely used impregnating compositions MS, PP, PPL. From century to century in Russia, skillfully chopped down wooden structures, adjusting the log to the log, the butt to the top, skillfully eliminating the natural escape of the tree trunk. With the expansion of the scale of construction, a simplification of the technological process was required. The solution came in the form of a rounded log (with the same diameter along its entire structural length) and a planed log..
Mechanized cylindering technologies were used in Russia and abroad at the beginning of the century. Due to the reduction in the number of assembly operations, wooden houses have become easier and faster to build, in addition, the use of rounded logs made it possible to create a more rigid structure during assembly. Since the log is fitted to the log more tightly, the thermal insulation properties of the walls are improved, and the building itself looks more aesthetically pleasing..
For the manufacture of rounded logs and profiled beams, which replaced the usual four-edged, pine is mainly used. When rounding this classic heartwood, the looser sapwood is cut off and a harder, resin-impregnated core remains. The log only benefits from this. In fig. 2 shows the options for marking sawlogs for rounded logs and profiled beams.
Cutting the sapwood has another positive effect – a decrease in the crack width when it dries, which in turn improves the thermal insulation of the walls. Cracking of logs is fought purposefully, provoking the appearance of cracks in the vertical plane. To do this, a shallow vertical cut is made along the log..
During cylindering, as well as in the manufacture of profiled timber, a high cleanliness of the processed surface is achieved, the wood becomes extremely smooth, which allows you not to use additional materials for the interior and exterior of buildings and, therefore, avoid unnecessary costs.
Finnish firms are considered trendsetters in the production of rounded logs, profiled beams and the construction of houses from them..
The profile of rounded logs produced by leading companies is far from the traditional round profile (Fig. 3 shows the traditional profiles of rounded logs and profiled beams, and Fig. 4 shows the profiles of Honka). Modern profiles have special wedge locks, which together with the insulation placed between the logs reliably protect the house from wind and moisture.
When erecting buildings from rounded logs and profiled beams, pins, bolts, studs, brackets, as well as adjustable anchors are used (as in traditional assembly technologies) to fasten structures. The assembled house necessarily gives draft, but it is much less than that of a house made of ordinary logs. Forced screed of the structure helps to reduce the amount of settlement. Since the house is made of well-processed material, it generally does not require additional finishing, you can live in it almost immediately after its construction.
The natural texture of the wood creates a special pattern of the walls, and since wood with operating moisture is used, the house can be painted from the outside immediately. This additionally protects the wood from moisture penetration.
A wooden house made of rounded logs and profiled beams is quickly erected and environmentally friendly, it combines a relatively low cost with high performance characteristics. The natural beauty of wood and the architect’s imagination make it possible to create modern comfortable country houses and cottages from this material. All of the above has made these wooden houses very popular both abroad and in our country.