BS EN 16737:2016 pdf download – Structural timber — Visual strength grading of tropical hardwood
5.3 Density If, in the judgment of the grader and taking account of the moisture content, a piece of timber is of unusually low density for the species and provenance, this may be given as a reason for rejecting the piece. In case of uncertainty, the density and moisture content of a piece of the timber shall be measured and the density value adjusted to 12 % moisture content. The adjusted density shall be considered unusually low if it is more than 20 % below the mean value for the intended EN 338 strength class, as assigned in EN 1912. For unassigned species and provenance combinations, the adjusted density shall be considered unusually low if it is more than 20 % below the lowest published value in EN 350-2 for the species, which are reproduced in Annex A. NOTE The density of tropical hardwood cannot reliably be derived from estimates of the rate of growth. This criterion shall not be used when determining the characteristic values in accordance with EN 384.
5.4 Fissures Measurement of fissures shall be taken at the time of grading. Fissures shall be measured in accordance with EN 1310. The depth of a fissure may be taken as the maximum depth to which a 0.2 mm feeler gauge can be inserted and expressed as the reduction of width or thickness caused by the crack taking into account its orientation. The length and depth of fissure is linked with moisture content and therefore the limits given below are only applicable at the time of grading.
5.5 Wane Wane shall be measured in accordance with method b for wane in EN 1310:1997, 4.8. The amount of wane shall be expressed as a decimal fraction of the face or edge on which it appears. When wane occurs on both arises of a face or edge, the amount of wane shall be the cumulative sum for that face or edge at any single cross-section. The limitation on wane shall apply at the cross-section with the greatest reduction in the basic dimensions of a face or edge.
5.6.1 Bow and spring Bow and spring shall be measured in accordance with the method for bow and spring in EN 1310. The amount of bow and spring shall be expressed in mm per 2m length.
5.6.2 Twist Twist shall be measured in accordance with the method for twist in EN 1310. The amount of twist shall be expressed in mm per 25 mm width per 2 m length.
5.7 Biological characteristics
5.7.1 Fungal biodegradation Biodegradation due to fungal stains shall be assessed separately from biodegradation due to wood destroying fungi (rot).
5.7.2 Insect attack Degradation by insects shall be assessed by evidence of damage. If the damage is caused by an insect that might still be active, it shall be assumed that the infestation is active.
5.7.3 Marine borers The extent of damage by marine borers shall be assessed by comparison with the limitations given for other defects such as knots. If there is any doubt as to the extent of damage, this may be given as a reason for rejecting the piece.
5.8 Other defects and characteristics Any piece which contains other defects such as brittleheart, compression failure, mechanical damage or other characteristics that might cause a decrease in strength properties to an amount which threatens its serviceability, shall be excluded from the grade. Any piece which contains such defects shall be accepted to the grade only if the reduction in strength caused by these defects is obviously less than that caused by the defects admitted by the grade, as long as these defects are of a type which does not progress after conversion. If there is any doubt as to the extent of the damage attributable to the defect, this may be given as a reason for rejecting the piece.