Visual grading of large structural coniferous sawn timber according to Spanish standard UNE 56544

Visual grades of large section structural sawn timber from Spanish coniferous species are studied in-depth in this study. Timber pieces had a cross section from 150 by 200 mm to 200 by 250 mm and were visually graded according to the visual Spanish standard in force, UNE 56544 (2003). The efficacy of this test was analyzed. The results according to this visual standard give very low output with an excessive percentage of rejected pieces. Furthermore, the visual grading standard does not make it possible to clearly separate the mechanical properties of the different visual grades and rejected pieces. Due to this, modifications are proposed to the specifications with the aim of reducing the percentage of rejections and to stimulate discussion in the Spanish standardization committee about the creation of a special group of visual grades for timber pieces with thicknesses larger than 70 mm. The physical and mechanical properties (density, bending strength, and stiffness) of 395 sawn pieces of radiata pine (Pinus radiata D. Don), Scotch pine (Pinus sylvestris L.) and laricio pine (Pinus nigra Arn. ssp. salzmannii) from Spain were estimated using the EN 408 (2003) test standard. Statistical analyses of those properties demonstrate that special treatment for visually graded large sections is justified. Investigations of visual standards from other countries corroborate this conclusion. A new visual grade is suggested, MEG (Large Structural Timber), and its mechanical properties and visual specifications are defined.