For the long term durability of historical wooden buildings, constructors and users who deal with this subject have to know wood properties exactly.
Wood is an organic, hygroscopic and anisotropic material. Its thermal, acoustic, electrical, mechanical, aesthetic, working, etc. properties are very suitable to use it is possible to build a comfortable house using only wooden products. With other materials, it is almost impossible. Following is some very short information about this subject.
As we know, many, materials change in size and volume as the temperature changes. They expand with increasing of the temperature. This means linear and volumetric expansion. The expansion. The expansion causes decrease in the strength of materials. Steel, which is inorganic and non-combustible and therefore has an advantage against fire, but when used in buildings, it expands and collapses as a result of increase in heat.
Wood does not practically expand against heat. On the contrary, by the effect of heat, it dries out and gains strength. The only time wood expands a little is when the humidity level is below 0%, and this is only scientifically significant. In practice, the humidity level of wood does not drop under 5% even in the driest climate.
The coefficient of thermal conductivity of the wood is very low. Aluminium transmits heat 7000 times, steal 1650 times, marble 90 times and glass 23 times faster than wood. For this reason, wood is used for making matches, handles of hardware equipment, ceilings and wall coverings.
Specific heat of wood is high. That means high amount of energy is needed to increase and decrease the temperature of one-kilogram of wood. Wood requires almost twice amount of heat energy than stones and concrete; similarly, three times of energy is needed for heating or cooling steel.
Sound isolation is based on the mass of the surface. Wood, as a light material, is not very perfect for sound isolation; But it is ideal for sound absorption. Wood prevents echo and noise by absorbing sound. For this reason it is extensively used in concert halls.
Sound velocity is faster in woods than gases and liquids, and it is close to that of metals. Sound energy loss as a result of friction is also significantly low in woods due to its lightness and structure. Because of such properties, wood is extensively used in musical instruments.
Resistance to electrical current of a completely dry wood is equal to that of fhenol formaldehit. An oven dried wood is a very good electrical insulator. To some extent air dried wood is the same. Unfortunately electrical resistance of wood is lowered by increasing the moisture content. The resistance of wood saturated with water. Static electricity that is dangerous for human health is not observed in wood unlike metal, plastic and other materials. For this reason wood is preferred as a healthy material.
Although wood is a light material, its strength is quite high. For instance, while the tensile strength of wood with 0,6/cm3 specific gravity is 100 N/mm2, the tensile strength of steel with 7,89/cm3 specific gravity is 500 N/mm2. Dividing tensile strengh by specific gravity gives the breaking length and quality of material. This figure means the breaking length of the material, when hung as a result of its own weight. While the breaking length of steel is used for construction is 5.4 km, chrome mobile steel is 6.8 km, hardened bow steel is 17.5 km, breaking length of spruce wood is 19.8 km, and laminated wood made of beech is 28.3 km. For this kind of properties, wood and laminated wood is used in wide-gap constructions like health centers and sport halls.
Wood is a decorative material when considered as an aesthetic material. Each tree has its own color, design and smell the design of a tree does change according to the way it is sliced. It is possible to find different wooden materials according to color and design preference. It can be painted to darker colors of varnished, and can be given bright or mat touches.
Although wood has oxidation characteristics in some way, it is not the kind of oxidation seen in metals. Metals get rust, wood doesn’t. For such characteristics, use of wood is preferred to avoid rust when necessary.
It is easy to repair and maintain wood. While old woods can be renewed by special touches other materials are highly difficult and costly to maintain and to repair. Therefore they are usually disposed of.
There are more than 5000 kinds of woods in the world. Their specific gravity, macroscopic and microscopic structures are different. Accordingly, their physical, thermal, acoustic, electrical and mechanical properties are also different. Because of this variety, it is possible to find wood suitable for needs. For instance, for heat isolation and sound absorption woods in lightweight are used. Similarly, heavy ones are used for construction purposes.
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