1.1 Literature Review
1.1.1 Timber in Construction History
Wood has been used by humans for constructional purposes since the ancient times (Wood as Construction Material n.d.). It has been proven that man used various natural materials with the aim of being protected from predators and severe weather conditions. Man used dugouts or caves for living and protection. Such natural materials as reed, wood, mud, stone and snow were used to build a shelter. It is believed that the first primitive structure was invented when man pulled down a tree branch with full foliage (Guilhemjouan 2013). Thus, wood is a versatile material that has comparatively low embodied energy and serves to sequester carbon (Proefrock 2011). Being widely available throughout the world, wood possesses properties of an endless supply of timber (Steer 1995).
The history of timer use in construction is ancient and dates back to about 100 BC. Timber was commonly used by the ancient Romans and Egyptians in the roof constructions. This period is well-known for the development of the tenon and mortise joints in the timber framing. For thousand years, in Europe, the use of timber frames increased in areas with the vast timber resources. Primitive construction techniques were employed for transporting wood. Timbers were tied together using primitive ropes made of animal materials. The advanced joinery techniques were developed to build more permanent and decent houses using timber frames. Stone foundations provided a superior support for houses and prevented rapid deterioration of the structural posts. Timber frames were permanently fastened using joinery techniques. In Europe, modern timber framing was developed in the 9th and 10th centuries and was characterized by exceptional building skills (BRTW 2011). Later, timber framing techniques were applied across Africa, Asia, as well as North and South Americas. In the UK, there are still some churches, which date back from 11th-12th century, and timber frame tithe barns, which are over 1000 years. A lot of the UK ancient market towns were built of timber (History of Timber Frame and Oak Construction 2013).
Wood is cut longitudinally in a tangential or radial plate. Radial sections are formed at right angles to annual rings and along rays or the radius of the log (Fig. 1). The logs are cut in quarters to form planes of the quarter sawed lumber. The rings are parallel bands that are closely spaced, and the rays have the appearance of the scattered blotches. The radial section runs in a pith-to-bar direction (Wiedenhoeft 2013, p. 13). Tangential sections are tangential to annual rings and perpendicular to the rays and the face of a log (Fig. 2). Annual rings appear as wavy and irregular patterns. Both sections are considered to be longitudinal ones because they extend along the grain (Wiedenhoeft 2013, 13). Figure 3 shows all the planes of wood.
Timber is divided into two categories: hardwood and softwood.
Hardwood includes numerous tree and shrub species that may have heavy and dense wood (Hardwoods. Trees & Shrubs With Dense, Hard Wood 2010). Trees are evergreen in the subtropics and tropics, but deciduous (broad leafed) trees are common in the regions with the temperate climate. Hardwoods can be subdivided further into very heavy, heavy, medium heavy, and ironwoods (woods that sink in water). Hardwoods are mainly angiosperms (flowering shrubs and trees). Their wood has water conducting cells that are referred to as vessel elements and tracheids. Moreover, the fiber cells are thick-walled and tightly packed.
Conifers, such as firs, pines, redwoods, and spruces, are softwoods. They have tracheids and lack fiber cells. Wood hardness depends on cell wall lignin, cell density, and the proportion of pores in the cell wall. Cherry species, walnut, hickory, maple, and oak belong to the popular hardwood species (Armstrong 2010). In the United Kingdom, hardwood trees are characterized by wood durability and hardness. They comprise robinia, walnut, beech, oak, elm, ash, and sweet chestnut. They are widely used for millwork, moldings, furniture, cabinets, etc. Hardwood species are greater in number than softwood ones. In addition, they are more expensive than softwoods. Such species are denser and have greater volume and calories than softwoods. They are highly preferred in projects where beautiful graining and strength are of a greater prerequisite. Quercus pedunculata is a common oak in Britain and the lowlands of Scotland.Quercus sessiliflora is less common; though, it is frequent in Northern England and Wales. Oak wood is the most durable and strongest amongst the timber trees in the United Kingdom of Great Britain and Northern Ireland. However, it is not favored for planting, due to slow growth. Oak trees grow in the national forests protected by the governments of the United Kingdom and Northern Ireland. Oak is widely used in building machines, furniture, ships, and houses. Thus, oak is the most preferred hardwood tree for planting.
Timber is wood derived from gymnosperm tree species. Unlike hardwood, softwood is not porous and is less dense. Softwood trees are evergreen trees and mainly comprise conifers, such as cedar, pine, Douglas fir, etc. The wood is easily cut and has a wide range of uses, for instance, furniture, chipboard, building frames, windows, doors, staircases, and paper (Hardwoods and Softwoods 2013). Coniferous forests also referred to as boreal or taiga forests are found in the Southern hemisphere. They are also common in Asia, North America, and Europe. 80% of the timber used in the world is softwood. According to the British Forestry Commission, there is a sufficient supply of softwood for both current and future use. This is largely attributed to extensive planting of conifers from 1960 to 1990. Thus, the supply of timber is at its peak when the trees attain their maturity. This is well-described in the Great Britain’s National Forest Inventory reports. The two reports reveal that the forest conifers range from 21 to 60 years old. Besides, they will be viable for commercial harvesting in the subsequent 25 years.
1.1.2 Timber in Construction Benefits
Timber is ranked as the world’s most eco-friendly building solution. It is not toxic and does not allow any chemical vapor to leak in the building. Furthermore, it ages naturally and is not disintegrated into toxic products, which may impact the environment rather negatively. It is worth noting that timber is renewable as it is continually grown in the plantations and forests (Gilbert 2009).
Relatively little energy is utilized in the conversion of wood into building timber. Energy in timber is the lowest in all building materials. Wood serves as a good reservoir of atmospheric carbon that contributes to the global warming. It is also a good insulator as it helps reduce the use of energy in heating buildings. Energy costs are reduced in winter, and the buildings are cooled in summer. Energy needs are decreased when timber is used in the construction of floors, doors, and windows. Timber is rather available and has made an essential impact on the local economies. A wooden structure does not require much time for construction and yields a fast financial return. Moreover, the construction of a timber building is not subject to the weather conditions. There is a high thermal value/wall width as compared to other construction forms. The construction is lighter, and thus, this reduces the cost of the foundation.
1.1.3 Timber Properties
The properties of timber vary depending on the direction. The strength is high when it is parallel to the grain, but it is low when it is perpendicular to the grain. The tensional strength is 40 times higher when the wood is parallel to the grain as compared to when it is perpendicular to it. Thus, it is easier to split wood along its grains/fibers than perpendicular to the grain. Timber is hygroscopic, and its moisture content may vary depending on the climate conditions. If the moisture content is lower than 30%, the shrinkage of the timber is perpendicular to the grain, but the shrinkage experienced along the grain is negligible. The cross-section planes can experience the 7% shrinkage. The moisture content of the timber should be maintained at equilibrium, which is supposed to be similar to that of the product. The shrinkage deformations may lead to tension on planes perpendicular to the grain, and this is considered a major failure. Owing to the varied shrinkage in the tangential and radial directions, there are splits when large planes of the timber are dried rapidly. Kiln drying minimizes the incidence of splits.
1.1.4 Timber Decay
The cause of wood decay may be dry and wet conditions, moisture, heat, absence of ventilation, or sap in wood.
Rot is considered the most common wood decay. It is largely caused by microbes or chemical processes that are responsible for putrefaction and decomposition (Fig. 5). The following process is accompanied by the evolution of gases, such as carbon dioxide and hydrogen sulphide. The two types of rots (wet rot and dry rot) are distinguished.
It is a chemical decay that leads to decomposition of the timber tissues. Usually, wet rot is caused by the alternate wet and dry conditions (Fig. 6). The timber used for the exterior works (e.g. windows, doors, etc.) is highly susceptible to wet rot. The affected timber is degraded to grayish brown powder. This process may be prevented by using the seasoned timber, which is covered with paint or tar for both ground and exterior works.
It is mainly attributed to fungi. The most common fungal species, which is believed to cause dry rot, is Merulium lechrymans (Fig. 7). The impact of dry rot on wood results in powder. Dry rot initially sets in the sap wood. The fungi break down the wood, and thus, it becomes brittle. The fibers have reduced cohesion before the ultimate degradation into powder. Fungi grow and proliferate when there is no ventilation. The poorly seasoned sap wood is highly susceptible to dry rot stored in the warm damp conditions. The favorable conditions for dry rot include: the presence of sap, warmth, dampness, the stagnated air, and absence of sunlight. Dry rot may be prevented when the seasoned timber that is devoid of sap is used. In addition, timber should be kept dry in the places where there is adequate ventilation.
Wood is often attacked by insects including beetles, marine borers, and white ants.
Among the commonly tested properties of timber are compressive strength, specific gravity, tensile strength, hrinkage, and moisture content.
- The test specimen should have the size of 50 mm × 50 mm × 25 mm.
- Take mass M1 of the test specimen.
- Oven-drying of the specimen until it reaches a constant weight at a temperature 103 ± 2 °C and take M2 of the test specimen.
Moisture content mo = M1 - M2 × 100
- The specimen selected for the test sould be 50 mm × 50 mm × 150 mm.
- By using the immersion method, V2 of the specimen should be taken.
- The end of the specimen should be dipped into hot paraffin and left to air-dry until the specimen has a moisture content ranging from 12% to 15%.
- The immersion method is used to take V2 of the specimen.
- The following formula may be used to compute the volumetric shrinkage:
Volumetric shrinkage = V1 – V2
Compressive Strength Test
- The specimen should be prism shaped with a height of 30 mm and base of 20 mm.
- The specimen is gradually loaded into the compression testing machine.
- The failure load P is recorded.
Compressive strength = P N/ mm2
Where, A is the cross-section area of the test specimen.
The compressive strength perpendicular to the grains is lesser than parallel to the grain.
Tensile Strength Test
- A prepared specimen should be of the size 50 mm × 50 mm × 200 mm.
- A tensile load is applied either perpendicular or parallel to the grain.
- The maximum load P is noted at failure.
Tensile strength = P N/ mm2
Where, A is the test specimen’s cross-section area.
The tensile strength perpendicular to the grains is smaller than parallel to the grain.
1.1.5 Timber Fire Proofing
Timber can be treated in order to render its fire resistant to a considerable extent. This can be reached by covering it with a material or compound. The superficial layers and coatings of the preferred protective material should be used on the timber surface. The coatings reduce the usual temperature increase during fire incidences, thereby decreasing the rate at which the flame spreads. The flame penetration rate is also reduced when the timber surface is in contact with the fire. Such coatings may be viable only for the interior purposes as they wear out because of exposure to the weather. The fire-retardant water soluble chemicals are mainly formulations of borax, sodium silicate or ammonium sulphate mixed with other materials that have qualities that promote brushability, color, appearance, and timber adherence. Chlorinated rubber, as well as other fire-retardant chemicals, such as chlorinated paraffin or zinc borate, can be used to provide protective layers of timber.
Secondly, timber can be impregnated. The complete impregnation is done with chemicals that render the wood incapable of combustion. The partial impregnation may be sufficient, but inappropriate if the wood is supposed to undergo milling. The chemicals comprise dibasic ammonium phosphate, monobasic ammonium phosphate, sodium tetraborate (borax), zinc chloride, and boric acid. The ammonium phosphates inhibit glowing and flaming. Borax inhibits flaming, but it does not retard glowing. Boric acid inhibits glowing; however, it does not retard flaming effectively. During the Burnett’s fire-proofing process, timber is soaked into a mixture of water and zinc chloride. During the Abel’s fire-proofing process, a dilute sodium silicate solution is painted on timber followed by a cream of slaked lime, and finally, a concentrated solution of sodium silicate.
2.2.1 Steaming Timber
In order to increase timber performance in terms of improving its appearance and increasing its fire resistance, it can be steamed. Steaming is of vital importance in manipulating timber when it is necessary to acquire the desired shape. Steaming maintains timber properties (Johnson, n.d). The steaming procedure starts when a frame of wood is placed in the wood vessel. The wood should remain there for several hours, then it is steamed. After steaming, the wood held in a mould until it dries. There are five major approaches of wood steaming:
1. Steam bending
It takes approximately an hour.
2. Laminated wood bending (Fig. 8)
3. Kerf’s cut bending (Fig. 9)
The method of kerf-cutting is executed through cutting slots along the stick to be bent and compressing together allowing the wood to bend. The slots are usually cut to the insides where the wood is supposed to be bent (Hoadley 2000).
4. Small piece microwave steaming (Fig. 9)
The method of microwave steaming presupposes the use of small sticks in the bending process. The sticks, which should be bent, are wrapped either with a wet paper or a towel; then they are microwaved. As a rule, the time of this method is limited to several seconds. However, the microwaving period depends on such characteristics of wood as moisture and thickness.
5. Cold bending (Fig. 10) and dry bending.
Cold and dry bending are not very popular methods, but they are widely used in the Far East of Asia. During the process of cold bending, cold water is applied repeatedly to the wood. The process lasts until the wood becomes soft enough to be bent (Schleining 2010). The uses of small curvature bending approaches increase the probability that bending will fail. This means that applying components with a greater radius provides a greater probability of a successful bending. There exist some minor approaches that can be used to bend and soften the wood, including wood heating while wet. The use of boiled water has been regarded as an alternative, in addition to using chemicals to bend the wood.
The choice of a bend technique influences the quality of the wood. It has been stated that hardwood types are easier to bend as compared to the softwood counterparts. Steaming is considered the most popular method of bending. The following method is widely used in the United Kingdom. The procedure of wood steaming takes usually an hour and depends on the type of wood steamed. After steaming, the wood should be placed in a mould. In spite of the fact that the method of wood steaming is considered reliable and trusted, wood sistering is another technique, which is widely used.
Wood sistering is a traditional method when both sides of the wood are steamed. One side is referred to as a sister. The major advantage of using sistering is that the size of wood or its length does not matter.I It is a reliable method in repairing frames. Despite numerous advantages, the method of sistering has several major disadvantages:
a) The screws, which should be used during the process of sistering, may be the cause of the frame strength loss through the holes created during the process.
b) Steam bending is more time consuming than any other method of bending the wood. The equipment that used in steaming includes a wallpaper steamer, basic steamer, or kettle. This method is effective but is hazardous at the same time, especially for the users or the practitioners.
c) The thick heat resistant gloves should be worn prior to the exercise as precautionary procedures. The procedure is determined by the type of wood bent, as well as its thickness and the dryness. Small sticks are easily bent and straightened over the heated soapstone.
In general, the steaming procedure is considered to be effective; there are some problems irrelevant to other procedures, like glulam or glue laminated timber products. Theprobems lead to wood overheating, which may result in wood brattling. However, it is not easy to maintain the heat at the required temperatures, to ensure that the inside of the wood is softer than the outside for a successful bend. Choosing the wood is another issue as the wood must be absolutely parallel with the growth of a tree (How to Make Wood Bend n.d). If the wood does not meet these requirements, it may break. It is necessary to be very careful while using the steaming method; therefore, it requires long periods of steaming to make the wood pliable enough to bend as per the requirements (Johnson n.d). The inadequate steaming process results in a permanent damage of the wood and its breakage.
In case the wood is too dry, it is almost impossible to bend it. Moreover, certain wood types can bend up to a certain curve or angle. Forcing a different type of the wood may cause its break and permanent damage. In theses cases, it is advisable to wet wood before the bending procedure (Bingelis 2013). The wood may break if it is not adequately heated or if it is not straight enough (Wood Bending and Forming 2005). Thus, the wood must be chosen wisely, if the procedure is to yield the anticipated results.
2.2.2 The Steaming Procedure
This bending type is to apply heat and moisture to the material using the steaming method (Kumamoto 2004). The pipe, which transports the steam, is usually glued from each side creating a single hole, which allows the steam to escape. The absence of holes results in the pipe burst. Two additional holes are made at approximately five inches apart, and a stainless steel bolt is pushed through the steam pipe. This preparation allows the wood to be on a suspended position during the procedure and not be in contact with the pipe (How to Make Wood Bend n.d). This enables the steam to penetrate wood from all the sides making it possible to steam adequately.Wood may be steamed at a high or low temperature and pressure conditions. The process of high pressure finishes in a short time and forces the wood easy to bend. For the low-pressure method, a low pressure steamer is used (Fig. 11). The following method is the same as a method of cooking using a steamer (Kumamoto 2004). This device has a very high safety and is simple and easy in use.
2.2.3 Glulmam or Laminated Wood Bending
Nowadays, glulam is used in the varied types of construction, including leisure buildings, schools etc. More recently, glulam has been begun to be used in the construction of play grounds, churches, multi-storey car parks, bridge building, electricity masts, and many other projects. Glue laminated timber is commonly referred to as Glulam. It is widely used in the projects of the commercial and domestic construction (Fig. 12). The use of Glulam increases the design values and ensures improved product functioning (Timber Structures 2009). Moreover, its perfect performance improves its market competitiveness. The product is considered to be of high quality, visible beauty, and hidden strength. It can be used for the utilitarian and decoration purposes. Glulam is often used in the simple beam constructions to soaring arches. The composition of glulam consists of wood laminations (lams). Lams are selected according to the characteristics of their performance and are bound together with the help of the moisture tolerant adhesives. Glulam is available from depths up to 100 feet. Being abundantly strong and stiff, glulam offers a variety of advantages to the builders.
The connections on glulam are usually made with the help of steel dowels and bolts, which are supported by the steel plates. Steel plates make it strong enough to hold massive weight. One more advantage is that the material provides the best surface quality, enabling a wide range of application options. Glulam can be used in the straight and curved components, giving the material a unique favorable characteristic. It can be used in such construction areas as curved portals, tied rafters, curved beams, tied arches, and glulam trusses. Nowadays, glulam is the advanced version of the traditional techniques developed during the 20th century. However, the process of glulam was first applied at the end of the 19th century, in Switzerland. Its original name was Hetzersystem. During the Second World War, there was an increased use of glued laminated timber, which was caused by the need in the construction of military buildings, military aircraft hangers, and warehouses. The process is a major concern for those who seek constructing wood connections. During that period, the resin glues were developed and made the industry flourish due to the knowledge based on the products. The machinery used to produce glulam products is also capable of producing structural member layers (Blaustein 2008). In order to get the perfect connection between the timbers, it is necessary to consider the way how to accomplish a smooth and desirable connection. It is worth knowing that laminated beams were used in the middle of the first products of the engineered wood. They were shaped from boards, plank spiked or dowelled together and could be found in early bridges, ships, and other building constructions (Blaustein 2008).
The glulam production machinery can produce wide and long products, which can be handled. A larger and stronger structural member is produced through laminating several small pieces of timber. They are usually applied as arching shapes, vertical columns, as well as curved and horizontal beams (Aghayere & Vigil 2007). Several pieces of timber that are glued to form a single structure unit make the horizontal columns. The use of large timber has caused environmental worries as the efficient use of available wood has been emphasized. Moreover, the laminating process, which aims at producing bigger products, has enabled the usage of almost all timber available for construction (Timber Structures 2009). The majority of glulam products is made of less attractive timber, making other products much stronger. The products from glulam have much better characteristics than other products that are made of solid timber:
1. The glulam products are not often defected.
2. The products of glulam are more environmentally friendly than the concrete or steel products (Ahmad et al. 2012).
Thus, the procedure of making glulam is easier and safer than the steaming method. It requires thin pieces of wood. Sometimes pieces are glued together and used. When the form or mould is ready, the glue is spread on the pieces, which are stacked together (Hermawati Massijayaand, & Nugroho 2010). After the glue dries, the edges are trimmed. Glulam is made of both hard and soft wood species (Hermawati et al. 2010). Some of the most common species used in this mode of bending wood include the Dauglas FirLarch, the Alaskan Yellow Cedar, and the Southern Pine. It is a resistant, lightweight, insulating, fire resistant, and strong material, which leads to large degree of factory machining, accurate detailing, and a quick installation.
2.2.4 Glulam Product Classification
Glulam products are categorized in accordance with their strength, and their stress class system consists of the soft glulam combinations of wood. Glulam owns four main grades of appearance as included in ANSI A190.1. The horizontal glulam remains the only categorized product. The laminatedtimber with laminated sections is a feature of homogeneous types that are in the same grade in their amount (Hermawati et al. 2010). The mix of lamination, which includes different types of laminations in both inner and outer sections, is featured in the combined type. The most ordinary choice for home building is the grade of the framing appearance. It is worth stressing that this mode is only recommended for the hidden areas usage. The Glulam industrial grade appearance form is used on areas where aesthetics is not a priority. The industrial grade appearance is better done compared to the framing grade. It is commonly used in areas that are invisible to the public. Thus, this mode demonstrates a wood disadvantage as there are knots and voids on the surface . The most preferred is architectural grade when glulam is applied as the demonstrative element in the framework (Forest Products Laboratory 2007). This product represents a fully completed glulam product because the wood incompleteness and voids are examined or filled so as to make the exhibition of an architectural framework with a good structure. The version of top quality is used onlyin the special situations. It happens mostly in places where there are a lot of people (Laminated Timber Architecture n.d). It is easy to make the top quality glulam because of the smooth surface (Structural Glued Laminated Timber n.d).
Glulam products, which are pressurized, may be widely used in a variety of areas. Among the advantages of glulam pressurized products are highly durablility of material and ideal properties of covering. Also, the product satisfies all needs of customer distinctive construction, as well as ensures a stuff that is easily deployed and fixed (Laminated Timber Architecture n.d). Moreover, the completed product is lighter than other products.
The completed glulam product is almost one sixth lighter than concrete blocks of the same size. With such a weight advantage, the completed product provides cheap transportation and handling costs. The material is built in the large sections and long lengths, as well. Its main advantage on the market is its resistance to the fire. The lloingfeature makes it attractive (Timber Structures 2009). Bridge constructions use different kinds of durable, like Alaska Yellow Cedar, as it has the possibility to provide enough strength to hold the colossal weight (Laminated Timber Architecture n.d). Additionally, glulam and steel balks were put in exact fire circumstances. It turned out that glulam product would survive the situation in better condition than steel would do. This advantage decreases the risk of fast fire spreading, thus being very advantageous. However, glulam products require handling with care. Fabric sling should be used during product lifting. If a person uses chains to lift the products, it will damage the completely smooth surface. The accomplished product should be vertically stored and covered with plastic covering to protect it from external obstacles. Only if the product is not intended to be used in the exposed places, it should remain protected till the installation. Therefore, wood has the ability to consume blow and hit forces provided by traffic, which makes it preferable for the de-icing agents included in the road constructions where it opposes chemical effects.
2.2.5 Glulam Manufacturing
The highly trained craftsmen with the necessary tools and equipment to conduct the procedure are involved in the process of glulam manufacturing. When the process starts, the surfaces are being glued. Firstly, they must be cleaned to ensure that they are dirt-free, dust to reach for maximum effect of the laminating material, and make it outstanding. It is encouraged that the frameworks are glued during 48 hours after the cleaning process to prevent from having more dust set on the rest of the surfaces. In addition, for timber’s surface to be used must be flat and roughness possibility should not exceed 0.015 inches in height or depth. Moisture is checked, as well. During the gluing process, BS EN 386 needs the moisture capacity to be not over 3 to 15%. However, it should not be more than 15% or go below 3%. Such a moisture volume is required during the bending process. Additionally, the moisture capacity of other lumber pieces used in the process should not have more than 6% difference; it means that all active parts should have a moisture capacity of 6% with one another. At the moment of gluing, the joints are brought into tight contact by applying pressure. A contact should be maintained during the gluing process (Tannet et al. 2010). Also, a conditioning time is a must because some adhesives do not achieve extreme strength during the gluing or curing time. When the glue used in the process is pressed from the edges while pressure is being applied, it notifies that glue still remains wet (Stalnaker & Harris 1997).
According to the manufacturing instructions, the adhesive material should be used in the binding and applied respectively. Although laminating seems as an easy work of gluing pieces together, some danger may occur if a person is not very careful. The process should be conducted only by the skilled and professional craftsmen to avoid the replacements, which are not cheap. Replacement cost is important as it can lead to a financial disaster of the company (De Luca & Marano 2011). Thus, extreme precautions should be made, additionally certain qualification acquired before the producing process start. Nevertheless, the craftsmen are not able to be structural engineers, but they are required to have a minimum qualification in the area that consists of basic understanding in engineering as it is a must. Such requirements would provide that the person could practice manufacturing standards of the highest level (Janowiak et al. 1997). The glulam development depends on the proper timber usage, in addition to appropriate pressure and application exertion of the certain glue amount where these practices should be followed accordingly to the already achieved classification and grading rules (Structural Glued Laminated Timber n.d.).
After the laminated timber has been removed from the clamping system, the product should be polished in order to clean glue beads that pressed out during pressure exertion. This provides the smooth product realization. At the next stage, additional finishing is involved, which ensures the look of the finished product. A product look enhancement is provided at this stage, but the timber strength is not affected in any way. Making holes and cuts is provided at the final step as per the customer’s request. A sealer also can be applied as per the expected product function. The completed glulam has a fire resisting ability even after long exposure to the fire wood resists catching it. Even if it still catches the fire, it burns slowly because of the binding ability and additives included during manufacturing (Timber Structures 2009). The formed insulation layers on the surface prevent the fast fire spread. In times of fire, the glue-laminated timber slowly starts to lose its strength, but due to large product extension, it takes much longer to lose all of its power comparing with steel. It is considered to be the main advantage of the laminated timber over its counterparts (De Luca & Marano 2011).
The steaming process of wood bending does not give the ability of fire resistance making glulam an opposing choice in today’s market, even much better than steel. Frankly speaking, there is no completely fireproof construction. The only difference in the construction materials is that some can catch the fire quickly, when others just deform, for example, metals (Glulam: Engineered Strength. Unsurpassed Versatility. Dependable Quality 2007). In addition, concrete may break or split off during the fire. Glulam materials remain in this trend providing a product that makes it longer to catch fire decreasing the fire spread rate making it willing compared to solid lumber. Solid wood catches fire extremely fast and falls to ashes at a higher rate. The next advantage with glue laminating wood is that it becomes more universal (Timber Structures 2009). This means that wood can be manipulated to form different shapes at various sizes needed. A person can form versatile shapes with glulam products ranging from the curved bends to straight beams. This unique framework adaptability of glulam makes wood to increase its qualities to different applications as requested by the designers (Rice et al. 2006).
2.2.6 Comparing Glulam Strength to Steamed Frames
Timer is considered to be an ideal choice for being the raw material in glulam products, due to the variety of properties it has. It also has the ability to form many shapes, allowing to produce a fine and attractive product (Wood Bending and Forming 2005). For many years, The types of products, which are used in glulam products, usually depended on trial, empirical or error experimentations according to purposes and hazards. Two major components are essential for the glulam process: timber and adhesives. The components, which are required for the steam procedure, are timber and bending equipments. In spite of different components, both procedures require hard work, as well as a reliable approach, a customizable beam and a frame (Tannet et al. 2010). The difference is evident when comparing their products in terms of span and strength. The glulam option is easier to accomplish as there are not so many requirements as for the steam procedure. Moreover, there is a great risk, which is in the wood bending as it is prone to breakage errors (Glulam: Engineered Strength. Unsurpassed Versatility. Dependable Quality 2007). The glulam option makes use of adhesive, and the procedure itself requires some pressure to be used in binding the wood and some bolts to hold the bonded wood together. The steaming option requires a source of steam and an equipment to help in the bending process. There is no doubt that the glulam option is capableof producing much stronger structural product when compared to steaming. One of the key concerns and differences between these options is safety. On the contrary to steaming, the glulam method does not require much safety concern. An individual could be burnt when setting up the procedure with the hot water. However, the method of steaming has a longer history. Another difference is the option popularity, which is brought about by the time needed to complete a process. One of the disadvantages of steaming method is that it requires a very long time and has a higher failure risk.
Both steaming and glulam are used in almost all constructions. They are also freely applied when designing big hall and bridges that require a large span of material, as well as when constructing ships and boats. It has been stated that the steamed frames are not widely used in large constructions. However, they are very often used in the in-building constructions, including staircase construction and in-door furniture. The main disadvantages of the steamed frames are that the are expensive and take a long period of time to deliver. On the contrary to the steamed frames, the glulam products are more demanding, but they may be are prepared in a variety of sizes, shapes, and grades. It is important to carry out appropriate tests after the manufacturing of glulam products. They are done to confirm that the products meet the required standards.
In case of glulam, at least 20% of the whole production need to be tested in order to confirm the standards. The same is with the steamed frames, which also require testing. In the steaming procedure, testing is carried out to determine the following:
1. The test must verify the whole procedure of steaming.
2. The test is conducted to make sure that the wood does not break.
3. The test checks the fact that the wood is not bent beyond the curve.
4. The test is conducted to make sure that the wood is not too dry as it may prevent from different problems.
5. The timber is also tested to ensure that the wood grain was straight enough and adequately heated during the process of steaming.
The above mentioned factors should be assessed to make sure that the wood will not brittle during the bending process. Thus, it has become evident that the steaming process requires many tests and confirmations, which should be done before the process of bending in order to prevent damage and breakage during the bending process. Steaming has a variety of disadvantages, which make it not so popular ad competitive in the market as glulam.
3.3.1 Main Introduction to the Project
The aim of the study is to compare the glulam strength with the strength of the steamed timber frames. A brief timber history in construction has been studied and analyzed. The study covers the period from the ancient times up to nowadays.
Timber is usually categorized into softwood and hardwood. It is worth noting that hardwood is more expensive than softwood, due to the superior nature of the products. However, softwood is more preferable in many areas because of the higher growth rate. Currently, it is one of the most used materials not only in the United Kingdom, but in the whole world, as well.
The main defects of wood are dry and wet rot. Different timber properties, such as specific gravity, moisture content, compressive strength, tensile strength and shrinkage are tested in order to improve the quality of wood. The timber steaming process is also described in the following study. There are several approaches: laminated wood bending, steam bending, kerfs’ cut bending, microwave steaming for smaller pieces, cold bending, and dry bending.
The procedure of laminated wood bending or glulam is described in detail. This includes the manufacturing process, as well as the production of the glue laminated timber goods. During the research, the literature review on the given topic has been conducted. Different books, articles and websites have been used in order to obtain the necessary information.
In the process of comparing the strength of two materials chosen, the strength of both horizontal and vertical beams is researched, as well. The examined beams are laminated by means of gluing together four laminated sections that are parallel to their grains. In the horizontal laminated solid beam, the strength will be compared with other beams in which two notches have been made in the sides.
Furthermore, the strength of the following beams will be compared with two other beams. The first beam will be with two cuts or notches made in the sides; it has been glued with other two-pieces of timber. The fourth beam has two cuts or notches in the sides, which are the same as the other two beams. It has been bolted with two pieces of timber to a 10 inch bolt.
A comprehensive comparison between the glue laminated timber and the steamed frame products is conducted in the following study. The main advantages include the capability of glue laminated timber products to hold massive weights and resist fthe ire. Also, the advantages that make the glue laminated timber more attractive in the market are evaluated. The key attractive properties of glulam include its ability to produce fully customizable goods and create the appealing look in the areas where there may be a large number of people. The limitations involved in the glue laminated timber products are also qualified. It is worth stressing that the differences between the horizontal and vertical lamination methods are also evaluated in the study. The individual methods are highlighted, as well. Furthermore, the deflections involve both experimental and theoretical investigations. The horizontal and vertical lamination of glulam is also discussed and compared in the following study. Deflections of all four glue laminated beams generated in the laboratory are investigated and analyzed.
The classification of the products as per the individual quality and strength is also given in the study. In fact, the classification of the horizontal frames differs from the classification of the vertical ones.
The research examines the potential risks that are involved in preparing the products, in particular while burning or breaking the wood. The standards are presented by the Control of Substances.
3.3.2 Experimental Procedures and Setting Up
We have chosen sixteen suitable timbers so as to obtain long smooth solid beams that should have no knots. It is advisable to select wood without knots as these knots may decrease the timber strength. Thus, a beam, which has knots in it, may fail under tension when a load is put at the bottom or at the top.
If a beam with knots is glued, the strength of the beam may be influenced greatly. The first section of gluing was done in accordance with the grading rules of timber, BS EN519, BS EN 518, and BS EN 5756. All edge knots were patched; all end joints were cut, laminated by machining, glued, and then dried. The glued timber was dried approximately for 24 hours. In some cases, the process of timber drying should last 48 hours.
Plain old white glue or PVA glue was used. PVA glue was selected as it is not very hazardous and because of its strength. Usually, the wood is supposed to be flat, and roughness should not exceed 0.015 inches in height or depth at the time of gluing. When the experiment takes place, the beam should not move. To make sure that the gauges are reading exactly zero deflection, the beam should lie flat on the top of two supports.
The beam that has a length of 1600mm was put on the two supports. A spam between these two supports was 1500mm. It should be noted that the same load was used for all beams. Any load can be used, but it should cause a failure of a beam. Loads of 20N and 50N were used incrementally in order to give a total of 450N (Figure 5.7).
3.3.3 Introduction to the Experiment
The experiment was carried out at London Southbank University in E 123 Lab. The purpose of the following experiment was to examine the deflection of four various beams and then to compare their deflections. The theoretical calculations of deflections will be compared using the finite element strand 7 programs. This experiment aims at testing a timber beam in many different ways. Beams that are of the same size will be tested with the same load. Results are expected to be very close but different.
The four beams will be used in the experiment. Solid beam (Glulam beam) will be compared to a beam that has two cuts (notches) 5mm inside. Also, other beams that have notches will be analyzed. One of these beams is bolted, and the other one is glued. The comparison of glued and bolted beams has shown that the bolts decreased the thickness in spite of the fact that they could be more rigidly joined.
3.3.4 Experiment Procedure
Four glued timber beams were brought and then placed on the simple supports in order to examine their deflections. The beams had such dimensions: width - 34mm, depth - 44mm, and length -1500mm. The span dimension between two supports was 1400mm. Before the point load was placed, the deflection had been recorded starting zero. The point load weighed 18N, the middle beam deal gauge was recorded each time 10N. The increment was placed in the point load up to 130N load.
3.3.5 The Four Beams Descriptions
Each of the four beams was cut in four pieces. Each piece had the dimension 11mm. Then it was glued using PVA. Three of the beams were cut in two sides in 5mm deep. One of them was used to glue the notches made, and the second one was bolted. The third one was cut to test the deflection constructed, and the fourth one was a solid glulam beam.
During the beam construction process, the different inspections were made according to grading rules of glulam beams.
The beam was supported on either side. The dimension of these beams was the length of 1500mm and 44mm*34mm. The span dimension was 1400mm (Le+1400mm) between the two supports.
3.3.6 The First Beam (without Notches)
This type of a glued timber beam was a solid beam.
3.3.7 The Second Beam
The second beam had two cuts (notches) in the middle. The depth of notches was 5mm. The deflection of the following beam was compared with the beam that had no notches. This beam was expected to deflect more if to compare to the first one as it had been cut and, thus, had lost some of its strength.
3.3.8 The Third Beam
The third beam had two cuts (notches) in the sides. Then it was glued with two pieces of wood that had notches. The same type of glue (PVA) was used during the procedure.
The third beam was observed to have less thickness; though, it gave some strength back to the beam. The deflection of the glued beam was compared to the deflection of the bolted one.
3.3.9 The Fourth Beam
The last beam was cut on both sides. Two notches were made in the fourth beam. The depth of these notches was 5mm. The third and second beams and two pieces of wood were bolted together. The size of the bolt was 10mm X 34mm. The deflection of the fourth beam was compared with the deflection of the third (glued) beam.
3.3.10 Deflection Result of Beam 1 (without Notches)
This type of beam was solid and was not cut. It was loaded 18N and 10N increment up 138N .The experiment results showed the deflection of 8.00mm. This deflection result was compared to the beam with two notches on sides, in which the depth of notches was 5mm. Then, the obtained results were compared.
3.3.11 Beam 2 Deflection Result (with Two Notches)
The timber beam had two notches or cuts made in the sides. The depth was to 5mm inside the direction of the Y axis. The same procedure was used with the same load of 10N increments increased to a maximum 138N. The result indicated the behavior of the second beam when it was cut. When it was compared with the solid beam, it turned out that the difference in the deflection was not very high in accordance with the experiment. It is worth stressing that this may depend on the depth and the size of the notch made. The timber beam with cuts in the sides recorded the deflection of 8.93mm.
3.3.12 Deflection Result of Beam 3 (Glued Beam)
This type of a timber beam was cut and had two notches in the sides. The depth of notches was 5mm. The beams were glued with two pieces of wood. The glue used was PVA. The same procedure was used with the same load of 10N increments that increased to a maximum 138N. This type of a timber beam had the deflection of 8.49mm.
3.3.13 Beam 4 Deflection Result (Bolted Beam)
This beam was cut in two sides. The depth was 5mm. Then two pieces of wood were bolted. The same procedure was conducted with the same load of 10N increments that increased to 138N. The deflection results showed the deflection of 9.17mm.