Glued Structural Members

There are many types of glued struetural members, with more products actively being developed. These use woody material that is reassembled with adhesives to make a wide range of stmctural produets. The grading of glued structural members 

Stmetural eomposite lumber was developed in response to inereasing demand for high quality timber at a time when it was beeoming diffieult to obtain this from the forest resouree. Stmetural eomposite lumber produets are made from smaller pieees of wood glued together into sizes eommon for solid-sawn timber. 

In early operations LVL was made in multidaylight presses using 3.2 to 2.5 mm (1/8 to 1/10 in.) veneer, which were hot pressed with phenol-formaldehyde adhesive into lengths from 2.4 to 18.3 m (8 to 60 ft) or more. 

Commonly, LVL is produced in 0.6 to 1.2 m (2-4 ft) widths in a thickness of 38 mm (1.5 in.). New plants with continuous presses form a potentially endless sheet that is cut to the desired length. Various widths of product can be manufactured or recut in the retail facility. 

Parallel strand lumber (PSL) is defined as a composite of wood strand elements with the wood elements primarily oriented along the length of the member the average length of the strands must be a minimum of 150 times that of the least dimension. 

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Because of its biological nature, which is influenced by many factors as discussed in Chapter 6, the quality of timber is enormously variable. Therefore, some sort of arrangement or classification must be undertaken prior to its use, in order to get the most out of this valuable resource. It is obvious that not all lumber can be used for the same purposes because not all of it has the same properties. It is the intension of this chapter to discuss the various classification or grading techniques that are applied to timber and glued structural members. 

Wood is essentially a good fire endurance material because it forms a carbonized layer on the surface during combustion which prevent flame development. The fire endurance is proportional to the cross section dimension of it A glued laminated wood for structural members called gluelam for building purposes make good use of this characteristics. It is difficult to make a door, especially a panel- stile constructed one which has a large thickness dimension. Such a door is usually made thin with a nice profile. Therefore fire retardant wood has been tried for such style wooden fire door. 

High hazard Full exposure to the weather, e.g. marine structures and exterior structures where the glue-line is exposed to the elements. Glued structures other than glued laminated members are not recommended for use under this exposure condition. Resorcinol-formaldyehyde (RF) Phenol-formaldehyde (PF) Phenol/resorcinol formaldehyde (PF/RF) ) ) Type WBP ) BS 1204 Part 1 (25)... 

Figure 13.32 Regulation of the catalytic activity of members of the Src family of tyrosine kinases, (a) The inactive form based on structure determinations. Helix aC is in a position and orientation where the catalytically important Glu residue is facing away from the active site. The activation segment has a conformation that through steric contacts blocks the catalytically competent positioning of helix aC. (b) A hypothetical active conformation based on comparisons with the active forms of other similar protein kinases. The linker region is released from SH3, and the activation segment changes its structure to allow helix aC to move and bring the Glu residue into the active site in contact with an important Lys residue.

It is of interest to note that all members of the endopeptidase family sequenced to date share a consensus site (-His-Glu-X-X-His-) for the binding of the zinc ion in the active site (21). Typically the metalloproteases are found with only the zinc ion bound to the consensus site however, in vitro several other divalent cations can replace the zinc ion (Co+2 often is able to restore native enzyme activity levels)(22,25). In certain cases the metal ion has also been shown to play a structural role as well as a catalytic role (24). 

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