DIN EN 14081-1:2011-05

There are basically two methods of strength grading: visual grading and machine grading. Machine grading is in common use in a number of countries. Two basic systems are used, referred to as "output controlled" and "machine controlled". Both systems require a visual override inspection to cater for strength-reducing characteristics that are not automatically sensed by the machine. The output-controlled system is suitable for use where the grading machines are situated in sawmills grading limited sizes, species and grades in repeated production runs of around one working shift or more. This enables the system to be controlled by testing timber specimens from the daily output. These tests together with statistical procedures are used to monitor and adjust the machine settings to maintain the required strength properties for each strength class. With this system it is permissible for machine approval requirements to be less demanding and for machines of the same type to have non-identical performance. The machine controlled system was developed in Europe. Because of the large number of sizes, species and grades used it was not possible to carry out quality-control tests on timber specimens drawn from production. Therefore, strict assessment and control of the machines is essential. Furthermore, considerable research effort is necessary to derive the machines settings, which remain constant for all machines of the same type. There are many different visual strength grading rules for timber in use in Europe. These have come into existence to allow for different species or groups of species, geographic origin, different dimensional requirements, varying requirements for different uses, quality of material available, historic influences or traditions. Because of the diversity of existing visual grading rules in use in different countries, it is currently impossible to lay down a single set of acceptable rules for all Member States. The requirements given in this European Standard on visual strength grading rules therefore give basic principles, which should be followed when drawing up requirements for limits for some of the characteristics. This European Standard specifies the requirements for visual and machine graded structural timber with rectangular cross-sections shaped by sawing, planing or other methods, and having deviations from the target sizes corresponding to EN 336. This European Standard covers structural rectangular timber, either untreated or treated against biological attack. This European Standard does not cover timber treated by fire retardant products. This European Standard identifies the characteristics for which limits shall be given in visual grading rules. Finger jointed timber is not covered in this European Standard. The European Standard EN 14081-1:2005-11 was consolidated, with Amendment A1 of February 2011, and contains the following amendments: a) normative references updated; b) the term "package" incorporated in clause 3; c) subclauses 7.1, 7.2 and 7.3 in clause 7 revised; d) clause ZA.3 in Annex ZA revised and updated examples for CE marking incorporated. The European Standard (EN 14081-1:2005+A1:2011) has been prepared by the European Committee for Standardization (CEN) of Technical Committee CEN/TC 124 "Timber structures", the secretariat of which is held by AFNOR (France), with the collaboration of German experts. The responsible Working Committee is NABau Spiegelausschuss (Mirror Committee of NABau) NA 005-04-01 AA "Holzbau (SpA CEN/TC 124, CEN/TC 250/SC 5)" ("Timber structures (Mirror Committee of CEN/TC 124, CEN/TC 250/SC 5)").