Laminated beam

Laminated beams (glulam), parallam (or LSL) and fingerjoints a flat pressed multilayer wood beam, thiek wood planks constituting the layers, used for structural exterior applications and bonded with PRF (phenol-resorcinol-formaldehyde) cold-setting resins, or MUF cold-setting resins, or even with certain types of polurethanes (although the use of these latter ones is only established in one country and can show creep and temperature-induced creep problems). The indi-... 

Laminated plates are one of the simplest and most widespread practical applications of composite laminates. Laminated beams are, of course, simpler. However, such essentially one-dimensional structural elements do not display well the unique two-dimensional capabilities and characteristics of composite laminates. 

The equilibrium equations for a beam are derived to illustrate the derivation process and to serve as a review in preparation for addressing plates. Then, the plate equilibrium equations are derived for use in Chapter 5. Next, the plate buckling equations are discussed. Finally, the plate vibration equations are addressed. In each case, the pertinent boundary conditions are displayed. Nowhere in this appendix is reference needed to laminated beams or plates. All that is derived herein is applicable to any kind of beam or plate because only fundamental equilibrium, buckling, or vibration concepts are used. 

However, the foregoing derivation is valid only for isotropic beams of rectangular cross section. For beams of nonrectangular cross section, the parabolic stress distribution is not correct. Also, for laminated beams, the parabolic distribution is most assuredly incorrect because of layer inhomogeneity. In fact, for laminated beams, we must expect different shapes of stress distribution in each layer as seen in Figure 6-19 for wide beams (there interpreted as cylindrical bending of a long strip, i.e., a special plate). 

The book opens with a paper on the structure and composition of wood to define the material under discussion and then considers molds, permeability, wood preservation, thermal deterioration and fire retard-ance, dimensional stability, adhesion, reconstituted wood boards such as fiberboard and particleboard, plywood, laminated beams, wood finishes, wood-polymer composites, and wood softening and forming. A final paper treats the common theme of wastewater management. Only one of the papers presented at the meeting is not included in this volume, and its subject of conventional wood preservation methods is adequately treated in detail elsewhere (e.g., Nicholas, D. D., Ed Wood Deterioration and Its Prevention by Preservative Treatments, 2 vols., Syracuse University Press, 1973). 

The types of adhesives suitable for laminating beams are restricted by the conditions of application and by their end-use requirements. A wider choice of adhesives for plywood depends on whether softwoods or hardwoods are used, whether they are required for internal or external exposures, or whether they are to be used for ornamental or structural purposes. Thus phenol-formaldehyde types would be used for marine or exterior construction uses urea-formaldehyde types would be advantageous for cold pressing, or melamine-urea adhesives might be preferred for hardwood plywood, or lumber-core panels used in furniture production. 

From about 1930 to the present, casein glues have been used successfully for bonding high-strength softwood lumber into glued laminated beams and arches for interior or covered exterior service. Even earlier, until perhaps 1900, casein... 

In many cases of interest, the vibrating system comprises a number of elements, each of which may have its own loss factor T i and its own contribution Wi to the system vibratory energy. These elements might be, for example, the several layers of a laminated beam or plate. 

In this paper the influence of the level of thermal residual stresses on the development of transverse cracking in cross-ply carbon-polyetherimide laminated beams subjected to bending has been considered. Different levels of ply-to-ply residual stresses were obtained by producing cross-ply ([90/0]s) laminates having different lay-ups in the 0° layer. Two methods were used to analyse the bend tests. The first considered the stress at the formation of the first transverse crack, the second the energy released at the formation of this crack. 

Architecture. By curving the timber during manufacture, a variety of architectural effects can be obtained from glulam that are impossible or difficult with other materials. The degree of curvature is determined by the thickness of the laminations. Beams with curvature are generally made with 19 mm (nominal 1 in.) timber, while 13 mm (1/2-in.) or thinner material may be required for very sharp curves. 

A second type of urethane adhesive is currently being introduced to the U.S. construction industry. The adhesive was originally developed in Japan. The system is two component. The isocyanate component is a modified polymeric MDI. The cross-linkable component contains water with water-soluble or water-emulsifiable resins. The adhesive produces strong, water-resistant bonds and has shown promise as a possible lower cost substitute for resorcinol formaldehyde resins in the adhesion of laminated beams. The product is now being used in Japan to bond wood and various other porous substrates at the rate of about 10 million pounds per year. The first U.S. application of the product has been the bonding of wood doors. The opportunities for products of this type should be excellent in view of the ever-increasing governmental pressures on solvents. 

Glued Laminated Beam (Glulam)- A structural beam composed of wood laminations or lams. The lams are pressure bonded with adhesives to attain a typical thickness of 1 V2. (It looks like 5 or more 2 X 4 s are glued together). 

Resorcinol-based adhesives are used extensively to bond structural grade, exterior laminated beams for building construction (see Chap. 29 on Resorcinol Adhesives). The coldsetting adhesives which dominate this field are based on phenol-resorcinol-formaldehyde (PRF) resins. The adhesive itself is composed of the PRF resin and a hardener that includes formaldehyde, often in the form of paraformaldehyde mixed with inert fillers. The performance of the resin is resorcinol dependent. The cost of the resin is also resorcinol dependent as this is a very expensive chemical produced industrially in only three locations in the world. The research work on these resins from their inception has then been based on the optimization of their bonding performance coupled with the decrease in the relative percentages of resorcinol used. It has the been a long and successful work of empirical research and development which still continues. 

R. Hernandez, J. F. Davalos, S. S. Sonti, Y. Kim, and R. C. Moody, Strength and Stiffness of Reinforced Yellow-Poplar Glued-Laminated Beams, FPL-RP-554, USDA, Forest Service, Forest Products Laboratory, Madison, WI 1997, 28 pp. 

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. ... 

Li, G., Pourmohamadian, N., Cygan, A., Peck, J., Hehns, J.E., and Pang, S.S. (2003) Fast repair of laminated beams using UV curing composites. Composite Structures, 60, 73-81. 

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