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90-403: Steel provides several advantages over other building materials, such as wood : Some common types of steel buildings are "straight-walled" and "arch," or Nissen or Quonset hut . Further, the structural type may be classed as clear span or multiple span. A clear span building does not have structural supports (e.g. columns) in the interior occupied space. Straight-walled and arch type refer to

180-428: A construction material , for making tools and weapons , furniture and paper . More recently it emerged as a feedstock for the production of purified cellulose and its derivatives, such as cellophane and cellulose acetate . As of 2020, the growing stock of forests worldwide was about 557 billion cubic meters. As an abundant, carbon-neutral renewable resource, woody materials have been of intense interest as

270-418: A closed forest, and in the manufacture of articles where strength is an important consideration such "second-growth" hardwood material is preferred. This is particularly the case in the choice of hickory for handles and spokes . Here not only strength, but toughness and resilience are important. The results of a series of tests on hickory by the U.S. Forest Service show that: Cellulose Cellulose

360-454: A crystalline to amorphous transition when heated beyond 60–70 °C in water (as in cooking), cellulose requires a temperature of 320 °C and pressure of 25 MPa to become amorphous in water. Several types of cellulose are known. These forms are distinguished according to the location of hydrogen bonds between and within strands. Natural cellulose is cellulose I, with structures I α and I β . Cellulose produced by bacteria and algae

450-401: A heavy piece of pine is compared with a lightweight piece it will be seen at once that the heavier one contains a larger proportion of latewood than the other, and is therefore showing more clearly demarcated growth rings. In white pines there is not much contrast between the different parts of the ring, and as a result the wood is very uniform in texture and is easy to work. In hard pines , on

540-405: A large log the sapwood, because of the time in the life of the tree when it was grown, may be inferior in hardness , strength , and toughness to equally sound heartwood from the same log. In a smaller tree, the reverse may be true. In species which show a distinct difference between heartwood and sapwood the natural color of heartwood is usually darker than that of the sapwood, and very frequently

630-467: A liquid called bio-oil is obtained at 500 °C. Semi-crystalline cellulose polymers react at pyrolysis temperatures (350–600 °C) in a few seconds; this transformation has been shown to occur via a solid-to-liquid-to-vapor transition, with the liquid (called intermediate liquid cellulose or molten cellulose ) existing for only a fraction of a second. Glycosidic bond cleavage produces short cellulose chains of two-to-seven monomers comprising

720-400: A log is on the outside, it is more or less knotty near the middle. Consequently, the sapwood of an old tree, and particularly of a forest-grown tree, will be freer from knots than the inner heartwood. Since in most uses of wood, knots are defects that weaken the timber and interfere with its ease of working and other properties, it follows that a given piece of sapwood, because of its position in

810-409: A polysaccharide matrix . The high tensile strength of plant stems and of the tree wood also arises from the arrangement of cellulose fibers intimately distributed into the lignin matrix. The mechanical role of cellulose fibers in the wood matrix responsible for its strong structural resistance, can somewhat be compared to that of the reinforcement bars in concrete , lignin playing here the role of

900-481: A pretty definite relation between the rate of growth of timber and its properties. This may be briefly summed up in the general statement that the more rapid the growth or the wider the rings of growth, the heavier, harder, stronger, and stiffer the wood. This, it must be remembered, applies only to ring-porous woods such as oak, ash, hickory, and others of the same group, and is, of course, subject to some exceptions and limitations. In ring-porous woods of good growth, it

990-419: A proper solvent , e.g. in an ionic liquid . Most mammals have limited ability to digest dietary fibre such as cellulose. Some ruminants like cows and sheep contain certain symbiotic anaerobic bacteria (such as Cellulomonas and Ruminococcus spp. ) in the flora of the rumen , and these bacteria produce enzymes called cellulases that hydrolyze cellulose. The breakdown products are then used by

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1080-636: A source of renewable energy. In 2008, approximately 3.97 billion cubic meters of wood were harvested. Dominant uses were for furniture and building construction. Wood is scientifically studied and researched through the discipline of wood science , which was initiated since the beginning of the 20th century. A 2011 discovery in the Canadian province of New Brunswick yielded the earliest known plants to have grown wood, approximately 395 to 400 million years ago . Wood can be dated by carbon dating and in some species by dendrochronology to determine when

1170-465: A source of weakness. In diffuse-porous woods the pores are evenly sized so that the water conducting capability is scattered throughout the growth ring instead of being collected in a band or row. Examples of this kind of wood are alder , basswood , birch , buckeye, maple, willow , and the Populus species such as aspen, cottonwood and poplar. Some species, such as walnut and cherry , are on

1260-564: A tree is first formed as sapwood. The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests. Sometimes trees (of species that do form heartwood) grown in the open may become of considerable size, 30 cm (12 in) or more in diameter, before any heartwood begins to form, for example, in second growth hickory , or open-grown pines . No definite relation exists between

1350-423: A type of imperfection known as a knot. The dead branch may not be attached to the trunk wood except at its base and can drop out after the tree has been sawn into boards. Knots affect the technical properties of the wood, usually reducing tension strength, but may be exploited for visual effect. In a longitudinally sawn plank, a knot will appear as a roughly circular "solid" (usually darker) piece of wood around which

1440-744: A variety of uses. Nitrocellulose was initially used as an explosive and was an early film forming material. When plasticized with camphor , nitrocellulose gives celluloid . Cellulose Ether derivatives include: The sodium carboxymethyl cellulose can be cross-linked to give the croscarmellose sodium (E468) for use as a disintegrant in pharmaceutical formulations. Furthermore, by the covalent attachment of thiol groups to cellulose ethers such as sodium carboxymethyl cellulose, ethyl cellulose or hydroxyethyl cellulose mucoadhesive and permeation enhancing properties can be introduced. Thiolated cellulose derivatives (see thiomers ) exhibit also high binding properties for metal ions. Cellulose for industrial use

1530-685: A wide variety of products. While the first application of regenerated cellulose was as a clothing textile , this class of materials is also used in the production of disposable medical devices as well as fabrication of artificial membranes . The hydroxyl groups (−OH) of cellulose can be partially or fully reacted with various reagents to afford derivatives with useful properties like mainly cellulose esters and cellulose ethers (−OR). In principle, although not always in current industrial practice, cellulosic polymers are renewable resources. Ester derivatives include: Cellulose acetate and cellulose triacetate are film- and fiber-forming materials that find

1620-492: A wooden object was created. People have used wood for thousands of years for many purposes, including as a fuel or as a construction material for making houses , tools , weapons , furniture , packaging , artworks , and paper . Known constructions using wood date back ten thousand years. Buildings like the longhouses in Neolithic Europe were made primarily of wood. Recent use of wood has been enhanced by

1710-464: Is chiral and is biodegradable . It was shown to melt at 467 °C in pulse tests made by Dauenhauer et al. (2016). It can be broken down chemically into its glucose units by treating it with concentrated mineral acids at high temperature. Cellulose is derived from D -glucose units, which condense through β(1→4)- glycosidic bonds . This linkage motif contrasts with that for α(1→4)-glycosidic bonds present in starch and glycogen . Cellulose

1800-698: Is (C 6 H 10 O 5 ) n where n is the degree of polymerization and represents the number of glucose groups. Plant-derived cellulose is usually found in a mixture with hemicellulose , lignin , pectin and other substances, while bacterial cellulose is quite pure, has a much higher water content and higher tensile strength due to higher chain lengths. Cellulose consists of fibrils with crystalline and amorphous regions. These cellulose fibrils may be individualized by mechanical treatment of cellulose pulp, often assisted by chemical oxidation or enzymatic treatment, yielding semi-flexible cellulose nanofibrils generally 200 nm to 1 μm in length depending on

1890-546: Is a lightweight steel building system utilized in over 30 countries. It is notable for its ease of assembly, requiring no cranes or specialized equipment. Flospans can be moved and reused without material loss and demonstrate resilience against severe weather conditions. Uniports, originating in the UK in 1965 after being pioneered by Alfred Booth & Co in 1948, have been widely deployed worldwide, including in Arctic Canada,

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1980-555: Is a non-digestible constituent of insoluble dietary fiber , acting as a hydrophilic bulking agent for feces and potentially aiding in defecation . Cellulose was discovered in 1838 by the French chemist Anselme Payen , who isolated it from plant matter and determined its chemical formula. Cellulose was used to produce the first successful thermoplastic polymer , celluloid , by Hyatt Manufacturing Company in 1870. Production of rayon ("artificial silk ") from cellulose began in

2070-437: Is a season check in the knot, as is often the case, it will offer little resistance to this tensile stress. Small knots may be located along the neutral plane of a beam and increase the strength by preventing longitudinal shearing . Knots in a board or plank are least injurious when they extend through it at right angles to its broadest surface. Knots which occur near the ends of a beam do not weaken it. Sound knots which occur in

2160-546: Is a straight chain polymer. Unlike starch, no coiling or branching occurs and the molecule adopts an extended and rather stiff rod-like conformation, aided by the equatorial conformation of the glucose residues. The multiple hydroxyl groups on the glucose from one chain form hydrogen bonds with oxygen atoms on the same or on a neighbour chain, holding the chains firmly together side-by-side and forming microfibrils with high tensile strength . This confers tensile strength in cell walls where cellulose microfibrils are meshed into

2250-456: Is also greatly increased in strength thereby. Since the latewood of a growth ring is usually darker in color than the earlywood, this fact may be used in visually judging the density, and therefore the hardness and strength of the material. This is particularly the case with coniferous woods. In ring-porous woods the vessels of the early wood often appear on a finished surface as darker than the denser latewood, though on cross sections of heartwood

2340-431: Is an organic compound with the formula ( C 6 H 10 O 5 ) n , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D -glucose units. Cellulose is an important structural component of the primary cell wall of green plants , many forms of algae and the oomycetes . Some species of bacteria secrete it to form biofilms . Cellulose

2430-428: Is an important consideration. The weakening effect is much more serious when timber is subjected to forces perpendicular to the grain and/or tension than when under load along the grain and/or compression . The extent to which knots affect the strength of a beam depends upon their position, size, number, and condition. A knot on the upper side is compressed, while one on the lower side is subjected to tension. If there

2520-422: Is dark colored and firm, and consists mostly of thick-walled fibers which form one-half or more of the wood. In inferior oak, this latewood is much reduced both in quantity and quality. Such variation is very largely the result of rate of growth. Wide-ringed wood is often called "second-growth", because the growth of the young timber in open stands after the old trees have been removed is more rapid than in trees in

2610-560: Is difficult to control completely, especially when using mass-produced kiln-dried timber stocks. Heartwood (or duramen ) is wood that as a result of a naturally occurring chemical transformation has become more resistant to decay. Heartwood formation is a genetically programmed process that occurs spontaneously. Some uncertainty exists as to whether the wood dies during heartwood formation, as it can still chemically react to decay organisms, but only once. The term heartwood derives solely from its position and not from any vital importance to

2700-473: Is enriched in I α while cellulose of higher plants consists mainly of I β . Cellulose in regenerated cellulose fibers is cellulose II. The conversion of cellulose I to cellulose II is irreversible, suggesting that cellulose I is metastable and cellulose II is stable. With various chemical treatments it is possible to produce the structures cellulose III and cellulose IV. Many properties of cellulose depend on its chain length or degree of polymerization ,

2790-399: Is in the walls, not the cavities. Hence the greater the proportion of latewood, the greater the density and strength. In choosing a piece of pine where strength or stiffness is the important consideration, the principal thing to observe is the comparative amounts of earlywood and latewood. The width of ring is not nearly so important as the proportion and nature of the latewood in the ring. If

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2880-486: Is known as secondary growth ; it is the result of cell division in the vascular cambium , a lateral meristem, and subsequent expansion of the new cells. These cells then go on to form thickened secondary cell walls, composed mainly of cellulose , hemicellulose and lignin . Where the differences between the seasons are distinct, e.g. New Zealand , growth can occur in a discrete annual or seasonal pattern, leading to growth rings ; these can usually be most clearly seen on

2970-431: Is laid down on the outside of the wood previously formed, it follows that unless a tree materially increases its production of wood from year to year, the rings must necessarily become thinner as the trunk gets wider. As a tree reaches maturity its crown becomes more open and the annual wood production is lessened, thereby reducing still more the width of the growth rings. In the case of forest-grown trees so much depends upon

3060-665: Is mainly obtained from wood pulp and from cotton . Energy crops: The major combustible component of non-food energy crops is cellulose, with lignin second. Non-food energy crops produce more usable energy than edible energy crops (which have a large starch component), but still compete with food crops for agricultural land and water resources. Typical non-food energy crops include industrial hemp , switchgrass , Miscanthus , Salix ( willow ), and Populus ( poplar ) species. A strain of Clostridium bacteria found in zebra dung, can convert nearly any form of cellulose into butanol fuel . Another possible application

3150-470: Is more complex. The water conducting capability is mostly taken care of by vessels : in some cases (oak, chestnut, ash) these are quite large and distinct, in others ( buckeye , poplar , willow ) too small to be seen without a hand lens. In discussing such woods it is customary to divide them into two large classes, ring-porous and diffuse-porous . In ring-porous species, such as ash, black locust, catalpa , chestnut, elm , hickory, mulberry , and oak,

3240-405: Is produced using the same family of proteins, although the gene is called BcsA for "bacterial cellulose synthase" or CelA for "cellulose" in many instances. In fact, plants acquired CesA from the endosymbiosis event that produced the chloroplast . All cellulose synthases known belongs to glucosyltransferase family 2 (GT2). Cellulose synthesis requires chain initiation and elongation, and

3330-448: Is short for "cellulose synthase") genes, in an unknown stoichiometry . Separate sets of CesA genes are involved in primary and secondary cell wall biosynthesis. There are known to be about seven subfamilies in the plant CesA superfamily, some of which include the more cryptic, tentatively-named Csl (cellulose synthase-like) enzymes. These cellulose syntheses use UDP-glucose to form the β(1→4)-linked cellulose. Bacterial cellulose

3420-596: Is sometimes defined as only the secondary xylem in the stems of trees, or more broadly to include the same type of tissue elsewhere, such as in the roots of trees or shrubs. In a living tree, it performs a mechanical-support function, enabling woody plants to grow large or to stand up by themselves. It also conveys water and nutrients among the leaves , other growing tissues, and the roots. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, woodchips , or fibers . Wood has been used for thousands of years for fuel , as

3510-434: Is synthesized at the plasma membrane by rosette terminal complexes (RTCs). The RTCs are hexameric protein structures, approximately 25 nm in diameter, that contain the cellulose synthase enzymes that synthesise the individual cellulose chains. Each RTC floats in the cell's plasma membrane and "spins" a microfibril into the cell wall . RTCs contain at least three different cellulose synthases , encoded by CesA ( Ces

3600-435: Is the most abundant organic polymer on Earth. The cellulose content of cotton fibre is 90%, that of wood is 40–50%, and that of dried hemp is approximately 57%. Cellulose is mainly used to produce paperboard and paper . Smaller quantities are converted into a wide variety of derivative products such as cellophane and rayon . Conversion of cellulose from energy crops into biofuels such as cellulosic ethanol

3690-431: Is the rule. Some others never form heartwood. Heartwood is often visually distinct from the living sapwood and can be distinguished in a cross-section where the boundary will tend to follow the growth rings. For example, it is sometimes much darker. Other processes such as decay or insect invasion can also discolor wood, even in woody plants that do not form heartwood, which may lead to confusion. Sapwood (or alburnum )

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3780-413: Is the younger, outermost wood; in the growing tree it is living wood, and its principal functions are to conduct water from the roots to the leaves and to store up and give back according to the season the reserves prepared in the leaves. By the time they become competent to conduct water, all xylem tracheids and vessels have lost their cytoplasm and the cells are therefore functionally dead. All wood in

3870-400: Is then known as the latewood or summerwood. There are major differences, depending on the kind of wood. If a tree grows all its life in the open and the conditions of soil and site remain unchanged, it will make its most rapid growth in youth, and gradually decline. The annual rings of growth are for many years quite wide, but later they become narrower and narrower. Since each succeeding ring

3960-426: Is under development as a renewable fuel source. Cellulose for industrial use is mainly obtained from wood pulp and cotton . Cellulose is also greatly affected by direct interaction with several organic liquids. Some animals, particularly ruminants and termites , can digest cellulose with the help of symbiotic micro-organisms that live in their guts, such as Trichonympha . In human nutrition , cellulose

4050-461: Is usually the latewood in which the thick-walled, strength-giving fibers are most abundant. As the breadth of ring diminishes, this latewood is reduced so that very slow growth produces comparatively light, porous wood composed of thin-walled vessels and wood parenchyma. In good oak, these large vessels of the earlywood occupy from six to ten percent of the volume of the log, while in inferior material they may make up 25% or more. The latewood of good oak

4140-495: The glycosidic linkage in cellulose are glycoside hydrolases including endo-acting cellulases and exo-acting glucosidases . Such enzymes are usually secreted as part of multienzyme complexes that may include dockerins and carbohydrate-binding modules . At temperatures above 350 °C, cellulose undergoes thermolysis (also called ' pyrolysis '), decomposing into solid char , vapors, aerosols , and gases such as carbon dioxide . Maximum yield of vapors which condense to

4230-401: The grain of the rest of the wood "flows" (parts and rejoins). Within a knot, the direction of the wood (grain direction) is up to 90 degrees different from the grain direction of the regular wood. In the tree a knot is either the base of a side branch or a dormant bud. A knot (when the base of a side branch) is conical in shape (hence the roughly circular cross-section) with the inner tip at

4320-412: The hardened cement paste acting as the "glue" in between the cellulose fibres. Mechanical properties of cellulose in primary plant cell wall are correlated with growth and expansion of plant cells. Live fluorescence microscopy techniques are promising in investigation of the role of cellulose in growing plant cells. Compared to starch, cellulose is also much more crystalline . Whereas starch undergoes

4410-429: The resin which increases the strength when dry. Such resin-saturated heartwood is called "fat lighter". Structures built of fat lighter are almost impervious to rot and termites , and very flammable. Tree stumps of old longleaf pines are often dug, split into small pieces and sold as kindling for fires. Stumps thus dug may actually remain a century or more since being cut. Spruce impregnated with crude resin and dried

4500-413: The 1890s and cellophane was invented in 1912. Hermann Staudinger determined the polymer structure of cellulose in 1920. The compound was first chemically synthesized (without the use of any biologically derived enzymes ) in 1992, by Kobayashi and Shoda. Cellulose has no taste, is odorless, is hydrophilic with the contact angle of 20–30 degrees, is insoluble in water and most organic solvents ,

4590-715: The African jungle, and the Kuwait desert. They are easily assembled with basic tools, suitable for unskilled labor, and can be swiftly disassembled and relocated. Uniports offer versatility, allowing for extensions and connections, along with insulation and partition options. Compact and efficient, up to 60 Mark 1 Uniports can be packed into a single 20-foot container. Building portions that are shop assembled prior to shipment to site are commonly referenced as prefabricated . The smaller steel buildings tend to be prefabricated or simple enough to be constructed by anyone. Prefabrication offers

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4680-536: The Viscose Development Company, is the most widely used method for manufacturing regenerated cellulose products. Courtaulds purchased the patents for this process in 1904, leading to significant growth of viscose fiber production. By 1931, expiration of patents for the viscose process led to its adoption worldwide. Global production of regenerated cellulose fiber peaked in 1973 at 3,856,000 tons. Regenerated cellulose can be used to manufacture

4770-433: The addition of steel and bronze into construction. The year-to-year variation in tree-ring widths and isotopic abundances gives clues to the prevailing climate at the time a tree was cut. Wood, in the strict sense, is yielded by trees , which increase in diameter by the formation, between the existing wood and the inner bark , of new woody layers which envelop the entire stem, living branches, and roots. This process

4860-418: The annual rings of growth and the amount of sapwood. Within the same species the cross-sectional area of the sapwood is very roughly proportional to the size of the crown of the tree. If the rings are narrow, more of them are required than where they are wide. As the tree gets larger, the sapwood must necessarily become thinner or increase materially in volume. Sapwood is relatively thicker in the upper portion of

4950-410: The bacteria for proliferation. The bacterial mass is later digested by the ruminant in its digestive system ( stomach and small intestine ). Horses use cellulose in their diet by fermentation in their hindgut . Some termites contain in their hindguts certain flagellate protozoa producing such enzymes, whereas others contain bacteria or may produce cellulase. The enzymes used to cleave

5040-446: The basis of commercial technologies. These dissolution processes are reversible and are used in the production of regenerated celluloses (such as viscose and cellophane ) from dissolving pulp . The most important solubilizing agent is carbon disulfide in the presence of alkali. Other agents include Schweizer's reagent , N -methylmorpholine N -oxide , and lithium chloride in dimethylacetamide . In general, these agents modify

5130-740: The benefits of being less costly than traditional methods and is more environmentally friendly (since no waste is produced on-site). The larger steel buildings require skilled construction workers, such as ironworkers , to ensure proper and safe assembly. There are five main types of structural components that make up a steel frame - tension members, compression members, bending members, combined force members and their connections. Tension members are usually found as web and chord members in trusses and open web steel joists. Ideally tension members carry tensile forces, or pulling forces, only and its end connections are assumed to be pinned. Pin connections prevent any moment(rotation) or shear forces from being applied to

5220-450: The biomass of land plants . In contrast to cellulose, hemicelluloses are derived from several sugars in addition to glucose , especially xylose but also including mannose , galactose , rhamnose , and arabinose . Hemicelluloses consist of shorter chains – between 500 and 3000 sugar units. Furthermore, hemicelluloses are branched, whereas cellulose is unbranched. Cellulose is soluble in several kinds of media, several of which are

5310-449: The border between the two classes, forming an intermediate group. In temperate softwoods, there often is a marked difference between latewood and earlywood. The latewood will be denser than that formed early in the season. When examined under a microscope, the cells of dense latewood are seen to be very thick-walled and with very small cell cavities, while those formed first in the season have thin walls and large cell cavities. The strength

5400-458: The cell walls are composed of micro-fibrils of cellulose (40–50%) and hemicellulose (15–25%) impregnated with lignin (15–30%). In coniferous or softwood species the wood cells are mostly of one kind, tracheids , and as a result the material is much more uniform in structure than that of most hardwoods . There are no vessels ("pores") in coniferous wood such as one sees so prominently in oak and ash, for example. The structure of hardwoods

5490-446: The cellulose was historically termed "tunicine" (tunicin)). Cellulolysis is the process of breaking down cellulose into smaller polysaccharides called cellodextrins or completely into glucose units; this is a hydrolysis reaction. Because cellulose molecules bind strongly to each other, cellulolysis is relatively difficult compared to the breakdown of other polysaccharides . However, this process can be significantly intensified in

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5580-557: The cellulose, rendering it soluble. The agents are then removed concomitant with the formation of fibers. Cellulose is also soluble in many kinds of ionic liquids . The history of regenerated cellulose is often cited as beginning with George Audemars, who first manufactured regenerated nitrocellulose fibers in 1855. Although these fibers were soft and strong -resembling silk- they had the drawback of being highly flammable. Hilaire de Chardonnet perfected production of nitrocellulose fibers, but manufacturing of these fibers by his process

5670-435: The central portion one-fourth the height of the beam from either edge are not serious defects. Knots do not necessarily influence the stiffness of structural timber; this will depend on the size and location. Stiffness and elastic strength are more dependent upon the sound wood than upon localized defects. The breaking strength is very susceptible to defects. Sound knots do not weaken wood when subject to compression parallel to

5760-445: The competition of the trees in their struggle for light and nourishment that periods of rapid and slow growth may alternate. Some trees, such as southern oaks , maintain the same width of ring for hundreds of years. On the whole, as a tree gets larger in diameter the width of the growth rings decreases. As a tree grows, lower branches often die, and their bases may become overgrown and enclosed by subsequent layers of trunk wood, forming

5850-433: The contrast is conspicuous (see section of yew log above). This is produced by deposits in the heartwood of chemical substances, so that a dramatic color variation does not imply a significant difference in the mechanical properties of heartwood and sapwood, although there may be a marked biochemical difference between the two. Some experiments on very resinous longleaf pine specimens indicate an increase in strength, due to

5940-415: The end of a log, but are also visible on the other surfaces. If the distinctiveness between seasons is annual (as is the case in equatorial regions, e.g. Singapore ), these growth rings are referred to as annual rings. Where there is little seasonal difference growth rings are likely to be indistinct or absent. If the bark of the tree has been removed in a particular area, the rings will likely be deformed as

6030-451: The entire building together. They join these members together and must ensure that they function together as one unit. Wood Wood is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants . It is an organic material  – a natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin that resists compression. Wood

6120-403: The exact mechanisms determining the formation of earlywood and latewood. Several factors may be involved. In conifers, at least, rate of growth alone does not determine the proportion of the two portions of the ring, for in some cases the wood of slow growth is very hard and heavy, while in others the opposite is true. The quality of the site where the tree grows undoubtedly affects the character of

6210-505: The grain. In some decorative applications, wood with knots may be desirable to add visual interest. In applications where wood is painted , such as skirting boards, fascia boards, door frames and furniture, resins present in the timber may continue to 'bleed' through to the surface of a knot for months or even years after manufacture and show as a yellow or brownish stain. A knot primer paint or solution (knotting), correctly applied during preparation, may do much to reduce this problem but it

6300-412: The greater the water content, the greater its softening effect. The moisture in wood can be measured by several different moisture meters . Drying produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry spruce block 5 cm in section, which will sustain a permanent load four times as great as a green (undried) block of

6390-683: The internal construction. Clear span steel buildings utilize large overhead support beams, thus reducing the need for internal supporting columns. Clear span steel buildings tend to be less cost efficient than structures with interior columns. However, other practical considerations may influence the selection of framing style such as an occupancy where interior structural obstructions are undesirable (e.g. aircraft hangars or sport arenas). Long Bay buildings are designed for use in bay spans of over 35'. They use prefabricated metal frames combined with conventional joists to provide larger openings and clearances in buildings. The Flospan frameless building system

6480-407: The larger vessels or pores (as cross sections of vessels are called) are localized in the part of the growth ring formed in spring, thus forming a region of more or less open and porous tissue. The rest of the ring, produced in summer, is made up of smaller vessels and a much greater proportion of wood fibers. These fibers are the elements which give strength and toughness to wood, while the vessels are

6570-602: The melt. Vapor bubbling of intermediate liquid cellulose produces aerosols , which consist of short chain anhydro-oligomers derived from the melt. Continuing decomposition of molten cellulose produces volatile compounds including levoglucosan , furans , pyrans , light oxygenates, and gases via primary reactions. Within thick cellulose samples, volatile compounds such as levoglucosan undergo 'secondary reactions' to volatile products including pyrans and light oxygenates such as glycolaldehyde . Hemicelluloses are polysaccharides related to cellulose that comprises about 20% of

6660-636: The member. Compression members are also considered as columns, struts, or posts. They are vertical members or web and chord members in trusses and joists that are in compression or being squished. Bending members are also known as beams, girders, joists, spandrels, purlins, lintels, and girts. Each of these members have their own structural application, but typically bending members will carry bending moments and shear forces as primary loads and axial forces and torsion as secondary loads. Combined force members are commonly known as beam-columns and are subjected to bending and axial compression. Connections are what bring

6750-480: The moisture content of the air) retains 8–16% of the water in the cell walls, and none, or practically none, in the other forms. Even oven-dried wood retains a small percentage of moisture, but for all except chemical purposes, may be considered absolutely dry. The general effect of the water content upon the wood substance is to render it softer and more pliable. A similar effect occurs in the softening action of water on rawhide, paper, or cloth. Within certain limits,

6840-508: The number of glucose units that make up one polymer molecule. Cellulose from wood pulp has typical chain lengths between 300 and 1700 units; cotton and other plant fibers as well as bacterial cellulose have chain lengths ranging from 800 to 10,000 units. Molecules with very small chain length resulting from the breakdown of cellulose are known as cellodextrins ; in contrast to long-chain cellulose, cellodextrins are typically soluble in water and organic solvents. The chemical formula of cellulose

6930-542: The other hand, the latewood is very dense and is deep-colored, presenting a very decided contrast to the soft, straw-colored earlywood. It is not only the proportion of latewood, but also its quality, that counts. In specimens that show a very large proportion of latewood it may be noticeably more porous and weigh considerably less than the latewood in pieces that contain less latewood. One can judge comparative density, and therefore to some extent strength, by visual inspection. No satisfactory explanation can as yet be given for

7020-604: The outside shape of the building. More generally, these are both structural arch forms if they rely on a rigid frame structure. However, curved roof structures are typically associated with the arch term. Steel arch buildings may be cost efficient for specific applications. They are commonly used in the agricultural industry. Straight-walled buildings provide more usable space when compared to arch buildings. They are also easier to blend into existing architecture. Straight-walled buildings are commonly used for commercial, industrial, and many other occupancy types. Clear span refers to

7110-404: The plant overgrows the scar. If there are differences within a growth ring, then the part of a growth ring nearest the center of the tree, and formed early in the growing season when growth is rapid, is usually composed of wider elements. It is usually lighter in color than that near the outer portion of the ring, and is known as earlywood or springwood. The outer portion formed later in the season

7200-605: The point in stem diameter at which the plant's vascular cambium was located when the branch formed as a bud. In grading lumber and structural timber , knots are classified according to their form, size, soundness, and the firmness with which they are held in place. This firmness is affected by, among other factors, the length of time for which the branch was dead while the attaching stem continued to grow. Knots materially affect cracking and warping, ease in working, and cleavability of timber. They are defects which weaken timber and lower its value for structural purposes where strength

7290-411: The properties of the wood. Certain rot-producing fungi impart to wood characteristic colors which thus become symptomatic of weakness. Ordinary sap-staining is due to fungal growth, but does not necessarily produce a weakening effect. Water occurs in living wood in three locations, namely: In heartwood it occurs only in the first and last forms. Wood that is thoroughly air-dried (in equilibrium with

7380-468: The reverse is commonly true. Otherwise the color of wood is no indication of strength. Abnormal discoloration of wood often denotes a diseased condition, indicating unsoundness. The black check in western hemlock is the result of insect attacks. The reddish-brown streaks so common in hickory and certain other woods are mostly the result of injury by birds. The discoloration is merely an indication of an injury, and in all probability does not of itself affect

7470-453: The same size will. The greatest strength increase due to drying is in the ultimate crushing strength, and strength at elastic limit in endwise compression; these are followed by the modulus of rupture, and stress at elastic limit in cross-bending, while the modulus of elasticity is least affected. Wood is a heterogeneous , hygroscopic , cellular and anisotropic (or more specifically, orthotropic ) material. It consists of cells, and

7560-524: The treatment intensity. Cellulose pulp may also be treated with strong acid to hydrolyze the amorphous fibril regions, thereby producing short rigid cellulose nanocrystals a few 100 nm in length. These nanocelluloses are of high technological interest due to their self-assembly into cholesteric liquid crystals , production of hydrogels or aerogels , use in nanocomposites with superior thermal and mechanical properties, and use as Pickering stabilizers for emulsions . In plants cellulose

7650-430: The tree, may well be stronger than a piece of heartwood from the same tree. Different pieces of wood cut from a large tree may differ decidedly, particularly if the tree is big and mature. In some trees, the wood laid on late in the life of a tree is softer, lighter, weaker, and more even textured than that produced earlier, but in other trees, the reverse applies. This may or may not correspond to heartwood and sapwood. In

7740-445: The tree. This is evidenced by the fact that a tree can thrive with its heart completely decayed. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut , black locust , mulberry , osage-orange , and sassafras , while in maple , ash , hickory , hackberry , beech , and pine, thick sapwood

7830-416: The trunk of a tree than near the base, because the age and the diameter of the upper sections are less. When a tree is very young it is covered with limbs almost, if not entirely, to the ground, but as it grows older some or all of them will eventually die and are either broken off or fall off. Subsequent growth of wood may completely conceal the stubs which will remain as knots. No matter how smooth and clear

7920-430: The two processes are separate. Cellulose synthase ( CesA ) initiates cellulose polymerization using a steroid primer, sitosterol -beta- glucoside , and UDP-glucose. It then utilises UDP -D-glucose precursors to elongate the growing cellulose chain. A cellulase may function to cleave the primer from the mature chain. Cellulose is also synthesised by tunicate animals, particularly in the tests of ascidians (where

8010-418: The wood formed, though it is not possible to formulate a rule governing it. In general, where strength or ease of working is essential, woods of moderate to slow growth should be chosen. In ring-porous woods, each season's growth is always well defined, because the large pores formed early in the season abut on the denser tissue of the year before. In the case of the ring-porous hardwoods, there seems to exist

8100-409: Was relatively uneconomical. In 1890, L.H. Despeissis invented the cuprammonium process – which uses a cuprammonium solution to solubilize cellulose – a method still used today for production of artificial silk . In 1891, it was discovered that treatment of cellulose with alkali and carbon disulfide generated a soluble cellulose derivative known as viscose . This process, patented by the founders of

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