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Wood is the product found in trees. The tough, fibrous tissue makes up the hard part of most trees. There are two categories of wood, hard wood and soft wood. Both of these categories of wood have been used over thousands of years for various reasons. The types of uses include its use as fuel, for construction and various other purposes. In the plant, the woody portion acts as support for the heavy plant. This enables a plant (woody plant) to grow to great heights without falling (Haygreen & Bowyer, 1996).
Wood has been used for various reasons and its uses have changed with time. In the past, it was used for making houses, tools and weapons but now, it is being used to make products such as paper, packaging and furniture. Its use for construction still stands. The only difference is that different technologies are being used to make work easier and the structures more efficient. This paper will look at the technical description of wood and its properties. The reasons why it was selected, its economic viability and manufacturability will also be addressed. The manufacturing process will also be discussed in the paper and alternatives suggested.
Technical description of the material
Wood is the hard portion of the woody plants and makes up the portion that is useful for construction and the manufacturing of various products. Wood is an organic material in the trees and is made up of cellulose fibers. These cellulose fibers are held together in a tough matrix by some substance secreted by the plant. This substance is known as lignin. The matrix that results from this process is so tough that is resists compression. Wood is also the portion of the plant that facilitates the transportation of water and nutrients to other parts of the plant for growth.
Properties of wood
Wood’s mechanical properties are displayed in its ability to withstand the force applied to it. These forces may be any form of external energy that may try to deform it or make any changes to it. The mechanical properties are what determine the uses of that particular piece of wood. The properties of any particular type of wood may be determined by either employing experimental designs or putting that piece of wood into work in order to test the wood for its usability.
Since the properties of different types of wood vary a lot, various tests need to be performed and the confounding variables be eliminated if possible in order to obtain accurate information on a particular type of wood. There should also be the use of standard methods for the testing procedures in order to provide the comparison of the different types or sizes of the wood. This will therefore, call for the use of standard values.
One property of wood that needs to be studied is its strength and stiffness. The strength and stiffness of wood vary due to the structure of the wood. When measurements on these properties are being made, the best thing to do is to find the laws that govern the variations and find the mean values. Another property of wood is its tensile strength. Tensile strength is the ability of wood to resist tension on both ends of its body. The wood’s abilities would be facilitated by its cohesive properties (Bailey, 2008).
Compressive or crushing strength is another property of wood. This properties show the resistance of the wood to crushing when weight is placed on it. This strength varies with the position of the weight with reference to the direction of the grain. Compression across the grain gives the wood more resistance to the weight but when compression is made along the grain, the probability of the wood crushing is increased.
Another property of wood is its shearing strength. This is the ability of the wood to resist shearing. Shearing is whereby one portion of the wood tends to slide on another when force is exerted on it. Transverse strength of wood shows its resistance to bending. Toughness of wood may be characterized by its ability to resist the ease of splitting or not being easily rapture when considerable load is applied on it. The toughness of the wood is tested by using the twisting test. This would show the abilities of the wood to resist twisting.
The use of wood for construction is very common. Many single-family houses around the globe use wood for construction. In places where access to wood and timber is guaranteed, construction with wood is said to be the cheapest way of constructing houses. One of the cheapest forms of constructions using wood includes the traditional houses that are normally thatched. The use of wood makes this construction cheap. The traditional houses are common in rural area in African countries.
In the United States, Canada and Japan, the use of wood for construction is common. Most houses are made out of plywood or gypsum boards that form the frames of the structure. However, the foundations of these buildings are normally made of concrete or stones. This means that wood makes up the majority of the raw material used to make the buildings. This makes construction of houses relatively cheaper than construction using bricks or stones. In Russia, for example, wood is used to construct low-income housing. The government prefers to use wood for this construction because it is cheap and easy to construct (Arnold, 1995).
Many constructions in the United States of America are made out of wood frame and this makes for about 90% of all constructions. Timber has also been used to create cost-effective seismic-strengthening techniques. This technique has been applied in the U.S. and Canada. This method is very simple and can be made by a homeowner without the necessity of having high carpentry skills. This method is also very cost-effective since it does not cost as much as it would if other building materials were to be used.
The manufacturability of wood/timber gives it the added advantage to other materials used for construction. The first thing is that timber-frames made of wood are rapidly erected. It takes a relatively short time to erect wooden frames and this makes construction a time saver. Use of wood makes it much easy to do mass production of housing units. It also makes prefabrication and modular construction easy.
Construction using wood makes construction of bent areas easy. It enables pre-fitting of frames possible. Wood also makes the construction of sections of the wall that are aligned with jig. This enables faster erection of the product and allows greater accuracy and precision. The ease at which construction is made out of wood enables a wooden frame of a medium-sized building to be completed within a span of only 48 or 72 hours.
The wooden frame (timber-frame) can then be easily fitted with SIPs that make the frame ready for installation of windows, roof and other mechanical appliances. The manufacturability of wood in construction is also seen in the ease at which it can be tailored to fit the tastes of the customer. If a customer needs to see some creative carvings on the structure, then this can be easily incorporated. Such constructions can be advantageous and economical since discarded or recycled wood can be used constructively. The manufacturability of wood is also seen in the ease at which windows and doors can be placed or relocated. This can be done during construction and after (Harris, 1993).
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Wood also has some structural benefits. If well engineered, wood can be used to increase the seismic performance of the building. Wood frames provide the structure with relatively high seismic resistance. The lightness of wood, compared to its counterparts, helps reduce the force produced due by earthquakes. Since wooden houses have numerous walls that are attached using many nails, they have often performed better than brick and stone houses in resisting earthquakes. Deaths have also been minimized and injuries made less serious. Research has also proved that the non-structural portions usually enhance the seismic strength of the timber houses. Such components include the finishes such as the non-load-bearing walls, crack, stucco and spall. They work by increasing the energy of the building to resist earthquake forces.
The manufacturing process
Timber or the raw materials for construction such as plywood normally go through a manufacturing process in a mechanical wood-based industry that uses energy. The first activity in the manufacturing process is sawmilling. This is usually the least sophisticated of the methods. It involves the activities such as the handling and transporting of logs. This process also includes the drying of timber. Timber is then sorted and classified and these processes require different types of energy.
At the mill where logs are transported, they are sorted and stored in different categories including length, species and diameter. The logs are then debarked either manually or using machines. This is done to prevent the unnecessary wearing of tools such as the saws. The bark might have some stones or other hard substances embedded in it. Debarking also allows evaluation to be done effectively. The head sawyer does this.
The log is then cut along the grain to make the longest straight cut as possible in order to minimize wastage. The pattern made by the cut would depend on the nature (condition) of the log or the requirements of the market. This will determine its width and thickness. The headrig breaks down the large pieces of timber into smaller slabs and planks. The rough edges of pieces of timber are then removed using some special types of saws. They are then cut into standard lengths and any other defects removed accordingly.
The next process is the sorting and grading. The properly sawn timber is then sorted. They are sorted in terms of thickness, quality, grade and species of tree used. This may either be done manually or mechanically. The timber may then be dipped into special chemicals that would prevent it from attacks from fungi and some insects that may eat away the wood and reduce its quality. The ends of the pieces of timber (end-grain) are painted or waxed in order to seal the water within the timber to ensure slow drying. This is necessary to ensure that air-dried timber does not split or check because of the quick process of drying.
Timber that is not sold immediately may require to be air-dried or dried in the kiln. The other advantage of kiln-dried timber is that it is lighter and easily transported. This is because the water in the timber has been dried off with heat.
Another alternative other than just constructing a building using timber only is to construct what has come to be known as the half-timbered buildings. This is whereby the frames are made out of timber but the spaces in between are filled with stone, plaster or bricks. These types of buildings are also strong and durable. This is because of the added materials that increase its strength (Vince, 1994).
Wood is a very important naturally occurring material that has been used for various uses. The construction industry has used this raw material for building and construction since time immemorial. However, for wood to be in its usable form, it must pass through several processes that include sawmilling, debarking, sawing, smoothening and drying. All these processes are necessary to ensure that the quality of the product matches with what is expected in the market. Timber may be used to produce strong structures and products owing to its properties that include tensile strength, shearing strength and compressive strength.
- Arnold, C. (1995). Building Systems Development: Timber construction. New York, NY: Anchor.
- Bailey, C. (2008). Timber: Structural material behavior in fire. Manchester: University of Manchester Press.
- Harris, R. (1993). Discovering timber-framed buildings. New York, NY: Shire Publications.
- Haygreen, J., & Bowyer, L. (1996). Forest products and wood science – An introduction. Iowa: Iowa State University Press.
- Vince, J. (1994). The timbered house. Chicago: Sorbus.