Timber-Like Products

There have been many intereshng approaches to overeome the shortage of high quality, large dimension hmber. Engineers have turned to trusses, I-beams, and space frames to achieve what had previously been aeeomplished by solid timber beams. Composites like glulam and the new produets diseussed below provide substitute elements that can be incorporated into the kinds of modem designs just alluded to. The thmst in the development of these new produets has been improved 

The intrinsie effieieney of peeling logs to yield veneer has suggested that the same proeess should be applieable to the manufaeture of laminated struetural members. Laminated veneer lumber (LVL) was first produeed in the early 1970s, and sinee then has been eommereially available in many eountries. It is now the most widely used struetural eomposite lumber produet in the US residential housing market. 

The thiekness of the LVL ean be from 19 to 75 mm and is available in lengths up to 25 m. Subsequently the material is eut to the required profile or dimension for beams/headers, I-joist flanges, seaffold planks, truss stoek and for joinery work where its straightness and stability are positive eharaeteristies. There is no limitation on the wood speeies for LVL. Any speeies used for plywood ean be used for LVL. Low-grade or previously under utilized speeies ean be used. 

Sehaffer et al (1972, 1977) examined the prospeets for thiek peeling southern pine, press drying, applying adhesive and then relying on the residual heat within the veneers to eure the laminated members. A phenol-resoreinol adhesive, whieh eures at moderate temperatures, was eonsidered rather than a eonventional plywood 

Technically, there is no length limit for parallel strand lumber since a continuous pressing operation is used. However, considering handling restrictions, PSL billets are usually cut to 20 m lengths, by up to 280 x 480 mm in section. The billets are recut to desired dimensions for use as beams, headers, columns, and studs. 

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Steel rods or plates should be protected against corrosion, especially when used with acidic timbers like oak. Stainless steel or hot dip zinc coated steel are frequently used. Stainless steel may give poor adhesion and, therefore, it is normally surface coated for improved roughness and adhesion. If hot dip zinc coated steel rods or bars are used, the application of a priming product to improve adhesion is normally required. Threaded rods or ribbed bars and textured plates may be used instead, and in this case the mechanical anchorage will also contribute to the bonding strength. Surface preparation is particularly critical in uncoated steel and it should... 

Severe local arsenic pollution can occur adjacent to industrial enterprises producing the various arsenicals used in timber preservation and as agricultural pesticides. Concern expressed by environmental groups has led to a reduction in the use of arsenicals in agriculture over the last decade, and this trend is likely to continue. Waste disposal is the main problem in industrial arsenic production and this problem has been responsible for closing several plants in Western Europe. 

Products most likely to be subject to significant inhomogeneity include natural materials such as timber (treated or untreated) and some painted or printed surfaces. Knots in wood and particularly dense areas of color can cause relatively intense, localized sources of emissions. Potential uncertainty due to inhomogeneity is best addressed by using larger samples or by carrying out multiple emission tests on smaller pieces of the same sample. 

The major releases of terrestrial carbon result from the oxidation of vegetation and soils associated with the expansion of cultivated land. The harvest of forests for fuelwood and timber is less important because the release of carbon to the atmosphere from the oxidation of wood products is likely to be balanced by the storage of carbon in regrowing forests. The balance will occur only as long as the forests harvested are allowed to regrow, however. If wood harvest leads to permanent deforestation, the process will release carbon to the atmosphere. 

Nowadays, our wood and furniture can be sourced from all over the world. Softwoods such as pine may come from the forests of northern Europe or Russia tropical hardwoods like teak and mahogany from Africa, Brazil, or Asia. Unfortunately, much of the global timber industry is currently unsustainable. Virgin forests are being clearcut, and plantations are much less valuable for wildlife than the forests they are replacing. Using wood carefully, without waste, is a way of treating this natural product with the respect it deserves. 

Wood and biomass are raw materials (Figure 9.4.1) for traditional building products like sawn timber, prefabricated timber elements and systems as well as wood-based materials in the form of boards (e.g. particle- and fibreboards), but also as construction elements from glued products like laminated beams, plywood, oriented structural boards or laminated veneer lumber. ... 

Other binders Adhesives based on tannins, occurring naturally in some timbers, are likely to be more widely used in future as price and availability of oil-based products becomes less favourable. Usually, small amounts of urea, phenol or isocyanate are incorporated with the tannin to improve use and performance. 

Subalpine larch is a non-timber species and its wood has essentially no commercial value. As no timber harvesting has been done, even in the best-developed stands, nor does any seem likely on the upper subalpine sites in the future, and considering cultivation difficulties, there has not been any need for seedling production for the species. On an experimental basis, seedlings have been successfully grown and outplanted (Amo et al, 1995). 

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