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Commissioned Reports - Grading

Commissioned reports related to Scanning


Date: 2008
Title: Grading of timber for engineered wood products
Authors: Report commissioned from WoodWisdom.net
Full Report: PDF

Summary
The objective is to improve the competitiveness of timber as a structural material and to increase its market share in construction. This will be achieved by improving the cost effectiveness of wood processing and raising the credibility of timber as a professional structural material by means of better practises of strength grading as part of the sawmilling process.
 
The aim of the UK component of the research work is to investigate possible alternative methods that can be used to compliment rate of growth as a visual guide for the determination of suitable density criteria, and to relate these possible complimentary criteria to structural strength and density. If it can be shown that by the use of complimentary features timbers that would fail the rate of growth criteria and be down graded can meet the strength, stiffness and density criteria of the higher strength class then these complimentary criteria could be used as a possible basis for selection. The UK work will concentrate on Douglas fir where rate of growth can down grade to a lower strength class otherwise excellent quality timber.

Visual features that can be used as complimentary criteria are the relative amounts of late wood in the growth rings or proportion of late wood to early wood, as the majority of the wood substance resides within the latewood. The relative proportions can be plotted against measured strength and density to determine overall success. The project aims are to:

  • Improve timbers reputation as a reliable material having predictable characteristics and ensuring safety of timber structures by improving the reliability of strength graded timber.
  • Develop intelligent grading – the development of procedures and practices in the supply chain for structural timber and engineered wood products, so that the above objective can be fulfilled within the economic constraints of a business.
  • Take full advantage of the strength potential of wood as accurately as possible by using state of the art technology in strength grading and development of new methods as well as renewing the strength profiles given in EN338.
  • Provide information needed for new generation of standards and for using CE marking as positive brand indication for timber.
  • Enable the use of structural UK Douglas fir that is down graded on rate of growth but has significant structural value.

Date: 2005
Title: Higher machine settings for UK Scots pine falling boards (225804)
Authors: Report commissioned from BRE
Full Report: PDF

Summary
In a recent study by BRE (The quality of Scots pine from the Grampian and Cairngorm regions of Scotland), it was identified that the inherent qualities of the material being processed shows great potential for penetrating higher value markets.  At the present time, the highest machine strength grading settings for UK grown Scots pine is C24.  To enable Scots pine to penetrate a higher value structural market, it is recommended that a series of new machine grade settings are produced (C27 - C30).  This would allow a proportion of the existing material produced to enter either glulam production or possibly trussed rafter production.  This would maintain market position against the European supply and also allow greater competition higher value markets. The main objective of the project is to demonstrate the potential for the higher strength classes and demonstrate that the UK resource has the ability to meet more these classes.

Currently both BS 5268: Part 2 and EN 338 machine grading settings only exist for Scots pine up to the Strength class of C24.  However the European Whitewood (EW) and European Redwood (ER, Scots pine) species combination can be graded to the C40 strength class. This therefore suggests that the best value is not being made of the UK resource and it should be possible to derive settings for the higher strength class for UK material.  This would improve the market potential of Scotpine derived from Scotland and England.

Within the UK C24, is considered a high strength class, but the reality within Europe is that C24 is the basic grade. In fact the Baltic States can prove that the innate strength of their EW/ER species combination is of the order of C24. Therefore, machine settings below this innate strength do not make best use of the material. This will lead to more EW/ER being available to the European market and current information suggests that it will retail for around the same price of UK strength graded C16 Sitka spruce. In addition, C24 is considered to be the basic strength class for glulam manufacture, a potential value added market for the higher strength classes. Therefore from the perspective of the Cairngorm resource and the UK supply in general the higher strength classes are needed not only to allow entry into higher value markets, but also to remain competitive with current market trends.

This project investigates the potential to grade Scots pine to higher strength classes, based on the UK supply as a whole, and demonstrate how the Northern Scotland supply would compare to the national supply.  BRE has produced higher settings of several species before but these were experimental EN338 settings that were never adopted and since that time changes have resulted relating to European standards and the model used to derive the EN338 settings has changed. Therefore, to maintain compatibility with current EN338 settings in prEN 14081 part 4 a fresh look at the data will be required.


Date: 2001
Title: Grading guide
Authors: Report commissioned from BRE
Full Report: Available from www.brebookshop.com
Report Cover: PDF

Summary
A guidance document was produced (later published as, Guide to machine strength grading of timber - Digest 476). The aim of the work was to put into the public domain a document in a format that was easily understood by those working and interested in the process of machine strength grading of timber. The format was to allow access to the understanding of machine strength grading as both a concept and commercial practice. Not only was there a needs to put this information in to the public domain but to clarify the process so that confusion and misunderstandings, that were present at the time, could be corrected and those interested would have a common knowledge as to the process.

The pre-publication draft was circulated to individuals who were in the commercial timber grading industry but who operated the process as a black box activity to establish if the correct level of understanding had been achieved. Responses from the industry were incorporated in to the final document.

This document created the current interest and level of understanding within the UK timber grading industry - allowing them to take ownership of a commercial industrial process they operated.


Date: 2000
Title: Data acquisition & improved machine grading British Grown timber (GD7630)
Authors: Report commissioned from BRE
Full Report: Available from www.brebookshop.com
Report Cover: PDF

Summary
The aim of this work was to gather together advances that had been made in timber grading particularly of UK grown species but not exclusively and make them available in a single document to get them in to the public domain. Item included were:

  • Sweet chestnut for structural use
  • Strength class improvements to large section Douglas fir
  • Addition of the TR 20 grade for truss rafter timbers
  • The improved mean density values for amendment of density values in BS5268 Appendix A.

Much of this work was important to put to UK industry, though most were specialised areas. The work on sweet chestnut had developed from the stresses BRE and the industry developed for Oak which had been included in BS 5268. Sweet chestnut was seen as a species that could contribute significantly to temperate structural hardwood; the grade stresses for sweet chestnut have also been included in BS 5268.

The work on large section Douglas fir came as direct request from industry to help UK material find a route in to railway use, as Rail-track were specifying Douglas fir at the C24 strength class regardless of end use, all this material was of imported North American origin. The work carried out demonstrated that large section material graded to the SS visual grade could make the C24 grade, regardless of the strength class attribution in BS 5268. By so doing the work allowed several sawmills milling UK grown Douglas fir to sell in to a market previously barred to them. The BRE work still forms the basis of the UKTGC guidance of large section Douglas fir and it is noted in BS5268.

The introduction of the TR20 grade filled a gap that had been created when the UK had changed from the old BS strength classes to the proposed European strength classes. Previously the truss rafter industry had used M75 and M50 grades for truss rafter production. On adoption of the new European strength classes these grades were lost. The TR26 grade was quickly introduced with the intention that one of the other strength classes would be used by manufactures to replace the M50 grade. However, no directly comparable grade was available as so the TR20 grade was generated and introduced in to BS 5268.

The improvement to the mean density of UK grown Sitka spruce came as a request from UK industry to seek improvement to the mean value for density quoted in Appendix A of BS 5268. Main details are reported under project review “Review of the density attributed to British grown Sitka spruce”. The outcome was an increase in the value for density from 400 kg/m3 to 450kg/m3.

The results of all this work were drawn together into a BRE digest (Advances in timber grading – Digest 445).


Date: 2000
Title: Evaluation of the Dynagradser Stress Grading Machine- Partner (PII CV4212) (CV4955)
Authors: Report commissioned from BRE
Full Report: PDF

Summary
This project arose out of the TIMGRAD project looking at new technologies for grading machines. The project clearly showed that X-ray grading machines gave the best results of the new technologies. However, SP the Swedish partner pre-empted  the final reporting process and allowed commercialisation of the stress-wave technology they had been developing by a private company. The UK industry thought this machine was worthy of investigation before other technologies as a commercial machine was on the market. BRE in partnership with the Forestry Commission and UKTGC was awarded a PiI project to investigate the process and the potential for use on UK grown Sitka spruce. At this time the machine had been approved in Europe for European whitewood.

The machine was identified to have characteristics that at the time but it outside the then current machine grading standard (BS EN519) particularly with the effect of not being able to identify the position and size of defects. Though the manufactures claimed this was possible no definitive proof was ever but forward. The machine was demonstrated to perform poorly with UK grown Sitka spruce and the co-efficient of determination (R2) between machine indicating parameter and measured strength was lower than that required in BS EN 519, however, this requirement was removed when the global cost analysis method of machine performance was introduce. The aim of the global cost analysis is to ensure the machine grades safe even when there is a poor correlation between machine indicating parameter and strength, usually at the cost of yield. The machine also had issues relating to the moisture content of the timber.

The final outcome decided upon by the UKTGC was to allow the machine to grade European whitewood for the UK market but indicate to the manufacture that to seek approval to grade UK grown Sitka spruce would not be viewed positively. In consequence the manufacturer never sought approval to grade UK Sitka spruce for the UK market.



Date: 2000
Title: Work on British grown pine Tiling battens (201921)
Authors: Report commissioned from BRE
Full Report: Awaiting electronic version

Summary
This project was to investigate the classification of British grown Scots pine tiling battens in relation to the Type A and Type B classification in BS5534: Part 1 - 1997. It followed on from work carried out at BRE on behalf of John Brash on European redwood / whitewood and work sponsored by the Forestry Commission and the UKFPA on UK grown Sitka spruce. The evaluation of the test material indicated that the 5th percentile value for strength of the test material was in excess of the target value as determined by BS 5534.  The results of all the work carried out on tiling batten were used to amend BS 5534 in the 2003 edition. The Type A and B battens were replaced with redefined strength categories that showed an improvement for UK grown Scots pine and Sitka spruce and a reduction for European redwood and whitewood.


Date: 2000
Title: The use of Control planks to determine the within and between variability of UK based strength grading machines: Part 1 Characterisation of the Control planks.
Authors: Detailed below
Full report: PDF

Summary
This project was set up to address the concerns of the UK timber grading Industry with regard to the degree of possible within and between machine variability. This was a collaborative project between the Forestry Commission, the United Kingdom Forest products Association (UKFPA), TimberSolve and BRE. The project consists of 2 parts; the first part, to which this report relates, is on the characterisation of the control planks that are to be used to determine the within and between machine variability. The second, which is the collection of data to determine the current amount of variability within and between strength grading machines is subject of a further report by TimberSolve.



Date: 2000
Title: Comparison of results for the current method of determining Modules of Elasticity and the proposed "Global-E" method on Sitka spruce
Author: Report commissioned from BRE
Full report: PDF

Summary
This report sets out the comparative testing that was carried out on Sitka spruce to determine the test values for a selected population of timber when tested to determine the MoE for E-Cen (current method), E-true (former BS method) and the proposed Global-E method. The initial part of the testing to compare E-Cen values with Global-E was carried out to meet a deadline for voting on the proposal in January 2000. The Etrue analysis was carried out after the results of the initial work were made public.


Date: 1999
Title: Grading research at BRE, Current advancements
Author: Report commissioned from BRE
Full report: Awaiting electronic version



Date: 1998
Title: The relationship between growth characteristics of sawn timber, logs and machine stress grading
Authors: Report commissioned from BRE
Full Report: PDF

Summary
This report presents the progress towards establishing a statistical model to quantify the log and batten growth features of Sitka spruce that influences timber strength.

Successful marketing of UK grown spruce relies in part on strength criteria measured non-destructively by machine stress grade stiffness. This can be influenced by tree breeding, therefore it is important to identify and establish the relative importance of each growth characteristic. This will assist forest management to maximise yields of structural timber or allow logs to be graded and directed for conversion into relevant markets.

After extensive measuring, recording and analysis of raw data, a new robust data base is established which describes the growth features of 60 logs and their sawn yield of battens. Two models have been established using two different modelling techniques to investigate the influence growth factors have on machine grade stiffness.