Graded Structural Timber

The attraetion of machine grading lies in the fact that individual pieces are tested so that the defleetion in bending (the usual method for alloeating a pieee to a grade) reflects both the natural defects (knots etc) and the intrinsie features (density, MFA etc.) of that piece. 

In the United States and Canada, MSR and MEL timber are subjeet to a visual override beeause the size of edge knots in combination with E is a better predictor of strength than is E alone. Maximum edge knots are limited to a speeified proportion of the eross-seetion, depending on grade level. Other visual restrietions, which are primarily for appearance, are plaeed on checks, shake, skip (parts of the board skipped by the planer), splits, wane, and warp. 

Another method of sorting maehine-graded timber is to use density to estimate knot size and frequency. X-ray sources in eonjunetion with a series of deteetors gather density profiles in the timber, which are sensitive to knots. This information is then used to assign the graded pieee to a not to exeeed grade eategory. 

Timbers in this section have unidentified strength 

Like the designations for visually graded material, a number of different grade designations are used in various countries. A partial list of grade names for machine-graded timber available from different countries is shown in Table 10.8. 

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Procedures to derive design properties for machine-graded structural timber... 

As already discussed wide initial spacings result in large knots, but the effect in practice depends on the grading rules that apply. The knot volumes and sizes noted by Nylinder (1958) in Sweden are small (Table 5.3) and the sawn outturn yields quality board and structural timbers. This contrasts with the faster growing, heavier... 

Table 10.6. Basic working stresses and stiffiiess for structural timber (SAA, 1988b). Each grade stress is 25% greater than that below. MOE includes an allowance for shear.

ASTM (2005f) ASTM-2915-03. Standard practice for evaluating allowable properties for grades of structural timber. American Society for Testing and Materials International, West Conshohocken, Pennsylvania... 

ECS (1995) Structural timber grading-requirements for visual strength grading standards. 

EN 518. European Committee for Standardization ECS (1995) Grading of structural timber requirements for machine strength graded timber and grading machines. European Committee for Standardization ECS (1995) Design of timber structures. Eurocode 5 1-1. European Committee for Standardization... 

Sunley JG (1968) Grade stresses for structural timbers. Forest Products Research Bulletin, No. 47. HMSO, London... 

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. 

There are three main methods to stress-grade timber for structural use visual stress grading, mechanical stress grading, and proof grading. 

AITC (1990) Standard for preservative treatment of structural glued-laminated timber. AITC 109. American Institute of Timber Construction, Englewood, Colorado AITC (2001) Standard appearance grades for structural glued-laminated timber. AITC 110. 

O Carroll C (2001) Trends in Surfacing. Wood Based Panels Intemational, 21(3) 50-1 O Dea DJ (1983) Forest industries economies of scale. Ministry of Works, Wellington, New Zealand. Central North Island Forest and Transport Planning Study, Technical Paper 6 Okuma M and Lee JJ (1985) The effective use of low grade domestic plantation timber the properties of the new structural sheet material, LVB, made from small sized veneers. Mokuzai Gakkaishi, 51(12) 1015-20... 

SAA (1986a) Timber Softwood visually stress-graded for structural purposes. AS2858. 

Removal of buildings and structures is often done by a company specializing in such activities. Demolition should be accomplished using standard construction equipment wherever possible, exercising due care not to endanger life or property. After demolition, all debris must be removed from the area, including concrete, concrete block, timber, metal scrap, and so on. All foundations must be removed to a depth below the soil horizon as specified in the reclamation plan, usually 2 to 3 feet (0.6 to 1.0 meters). After removal of structures, the surface should be graded and backfilled as specified in the reclamation plan. 

Resorcinol-formaldehyde (RF), and phenol-resorcinol-formaldehyde (PRF) eold-setting adhesives are used primarily in the manufacture of structural, exterior-grade glulam fingerjoints, and other exterior timber structures. They produee bonds not... 

Oriented Strandboard (OSB). Oriented strandboard (OSB) panels have been developed as an alternative to plywood in building construction. The emergence of OSB was driven in part by a decreased supply of large diameter logs suitable for veneer production, and by innovation and productivity changes in the North American wood products industry over the past few decades as well as the structural performance of OSB products, which are suitable for use in most plywood applications but at a much lower cost. In addition, OSB manufacture allows small, low grade timber resources to be processed into a marketable product. This effectively saves raw materials that are in short supply and promotes efficient utilization of wood (3,5,6). 

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