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<!--BeginDoc 62506134--> <PRE> <p align="center"><span class="htmla_titolo">WOOD ENGINEERING</span></p><p /><p><img height="222" hspace="20" src="/files/01705200511.53.16-legno.bmp" width="279" align="right" vspace="5" border="0" /><em><strong>This Section summarizes information on wood as an engineering material. We present properties of wood and wood-based products of particular concern to the architect and engineer, including discussion of designing with wood and wood-based products along with some pertinent uses.</strong></em></p><p align="left">Throughout history, the unique characteristics and comparative abundance of wood have made it a natural material for homes and other structures, furniture, tools, vehicles, and decorative objects. Today, for the same reasons, <strong>wood is prized for a multitude of uses</strong>. <br />Historically, some species filled many purposes, while other less available or less desirable species served only one or two needs. For example, because white oak is tough, strong, and durable, it was highly prized for shipbuilding, bridges, cooperage, barn timbers, farm implements, railroad crossties, fence posts, and flooring. Woods such as black walnut and cherry were used primarily for furniture and cabinets. Hickory was manufactured into tough, hard, and resilient striking-tool handles, and black locust was prized for barn timbers. What the early builder or craftsman learned by trial and error became the basis for deciding which species were appropriate for a given use in terms of their characteristics. <br />It was commonly accepted that wood from trees grown in certain locations under certain conditions was stronger, more durable, more easily worked with tools, or finer grained than wood from trees in other locations.<br /><strong>Modern research</strong> on wood has substantiated that location and growth conditions do significantly affect wood properties. </p></PRE> <!--EndDoc 19639601--> <BR>
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<p /><p /><p /><p align="center"><span class="htmla_titolo">CHOOSING GOOD APPLICATIONS</span></p><p>The image of crumbling particle-board (PB) furniture protruding from urban dumpsters is the Achilles heel of the wood panel industry. An entire sector is tarnished by the bottom-line mentality of some furniture producers and consumers. By choosing an inferior veneer/facing applied to the lowest density particle board, both the consumer and the manufacturer pocket a few dollars in savings. Unfortunately, the environment has to bear the costs in wasted resources and landfill run-offs.</p><p><img height="65" src="http://www.valuecreatedreview.com/images/panPB.gif" width="120" align="top" /> <img height="65" src="http://www.valuecreatedreview.com/images/panPBedged.jpg" width="120" align="top" /></p><p><small><font size="2"><strong>(1)</strong> PB = poor application <strong>(2)</strong> PB = good application</font></small></p><p>Superior panels to PB exist for most furniture applications - medium density fibreboard (MDF), plywood and (most recently) agriboard (AB). As PB is less expensive to produce, those savings could be used to produce a superior panel with increased quality/density and substantial face veneers. Then it would have a life expectancy close to its competitors.</p><p>PB, MDF and AB can all claim a major environmental advantage - they are made mainly of waste or recycled wood fibre. Some would argue that plywood, with its requirement for large pristine logs, is the least eco-friendly panel, but even that position can be questioned. Plywood is less susceptible to degrade because of high moisture resistance and boasts the highest strength-to-weight ratio of any panel. The most important consideration in eco-design is to minimize the quantity of material needed for the task. The following chart shows the relationship between weight (density) and bending strength for common furniture panels.</p>
Wood panels: poor and good applications
Superior panels to PB exist for most furniture applications - medium density fibreboard (MDF), plywood and (most recently) agriboard (AB).
<p><span class="htmla_titolo">Wood-based Composites and Panel Products</span></p><p>Because wood properties vary among species, between trees of the same species, and betweenpieces from the same tree, solid wood cannot matchreconstituted wood in the range of properties that can becontrolled in processing. When processing variables areproperly selected, the end result can sometimes surpassnature’s best effort. With solid wood, changes in propertiesare studied at the cellular level. With reconstituted woodmaterials, changes in properties are studied at the fiber,particle, flake, or veneer level. Properties of such materialscan be changed by combining, reorganizing, or stratifying these elements</p><p>The basic element for composite wood products may be thefiber, as it is in paper, but it can also be larger wood particlescomposed of many fibers and varying in size and geometry.These characteristics, along with control of their variations,provide the chief means by which materials can be fabricatedwith predetermined properties.</p><p>In any discussion of the strength properties of wood-basedpanels and other adhesive-bonded wood composites, the firstconsideration is the constituents from which these productsare made (O’Halloran and Youngquist 1984; Youngquist1987, 1988). The elements can be made in a great varietyof sizes and shapes and can be used alone or in combination. The choice is almost unlimited.</p><p>Currently, the term <span class="htmla_titoletto">composite</span> is being used to describe anywood material adhesive-bonded together. This product mixranges from fiberboard to laminated beams and components. </p><p>Composites are used for a number of struc-tural and nonstructural applications in product lines rangingfrom panels for interior covering purposes to panels for exte-rior uses and in furniture and support structures in manydifferent types of buildings.</p>
Wood-based Composites and Panel Products
John A. Youngquist
