GROWTH AREAS IN EUROPE WITH REGARD TO DIFFERENT WOOD SPECIES AND GRADING PRINCIPLES

摘要

Common aim of the European joint-project "Gradewood - Grading of timber for engineered wood products" is to improve applicability of machine strength grading. Using efficient grading machines leads to higher reliability of timber used for civil engineering while making an optimal use of the available raw material. The spreading of new grading technologies across Europe is retarded due to current standards used for the evaluation of new grading systems placed on the market. One major problem are the requirements for allowing single machines to grade timber from new source countries. This causes a lot of expensive testing for machine manufacturers as large amounts of tested timber pieces are required for every single country. Whether the same settings for different countries in Europe can be used is checked by analyzing old data and by testing timber from areas where data is missing. In a first step Already existing strength data available at six European research institutes was analyzed [1]. Several thousand datasets were evaluated separately for different species and load modes. Available laboratory data was used in 14 different linear regression models using the strength as a target value, in order to simulate machine strength grading. Results in different strength classes were simulated by analysing the test data separately for different bandwidths. The assignment to the different bandwidths was based on the calculated model values. Even though all characteristic values were considered in the analysis of the existing data, the main attention was given to the strength values. Confidence limits were derived. It was assumed that if the characteristic strength values for single countries reach values which lie between the upper and the lower confidence limit, the timber can be graded with the same model and the samesettings. For the different species and loading modes the analysis of existing data showed the following results. For bending of spruce, the use of the same model using common settings for timber from Central and Northern Europe is not possible. The situation for spruce loaded in tension is different. Several models can be used for timber from Northern Europe and Central Europe at the same time. Results for bending of pine showed more variability. Settings need to be derived separately for different countries in order to have good and safe grading results. Due to the lack of test results for bending of pine, no hard conclusion could be drawn. The goal of the article is to judge the first results of more than 5000 additional tests of timber from different parts of Europe. The question is whether the models derived on a Central and North European datasets can be used for timber from Eastern Europe. Which results can be reached in the different bandwidths compared to the already available strength values and what is the effect on the yield. Different models are considered. Different research institutes have performed bending and tension tests on 5066 specimens (Table 1).