Clasificación estructural de la madera de "Pinus radiata" D. Don procedente de Cataluña mediante métodos no destructivos y su aplicabilidad en la diagnosis estructural

The aim of this research work is the determination of the mechanical properties of timber of Pinus radiata D. Don from Catalonia, by means of non destructive methods, with the secondary aim to complete the national data base of this species. Moreover, the prediction capacity of non destructive techniques for the estimation of mechanical properties of timber is analyzed in order to its application to the assessment of existing structures and, also, in the structural grading of new timber. The studied sample was constituted by 150 sawn timber pieces of 80x120x2400 mm dimensions of radiata pine (Pinus radiata D. Don) from Catalonia. Firstly, the pieces were visually graded according to the spanish standard UNE 56544:2011, recording all analyzed parameters that were used for the assignment of visual grades. Then, some non destructive tests were carried out; probing, screw withdrawal, ultrasound waves, stress waves, longitudinal and bending dynamic analysis of vibrations, and drill core specimens, with the same objective, for the determination of physical and mechanical properties in order to stress grading of timber pieces. Finally, mechanical tests (destructive tests) were carried out (UNE-EN 408:2011) obtaining the actual mechanical and physical values for each piece: local and global modulus of elasticity in bending, bending strength and density. These values were used to assignment of mechanical properties for the visual grade of the timber and the determination of the aptitude for the prediction of mechanical properties by means of non destructive testing. The visual grading according to the UNE 56544 standard (MEG grade), for a strength class equal or less to C18, gives a reject percentage of 47 % and a 73 % for a strength class superior to C18, being the twist, in both cases, the main reason for these high reject percentage. The studied sample belongs to large cross-section timber pieces but the width of the cross-section was selected close to the border value of the standard, 70 mm. In order to contrast the results of both grading criteria (small and large cross-section) the pieces were also graded as they were small cross-section timber pieces, obtaining outputs of 3 % for ME-1, 42 % for ME-2 and a reject percentage of 55 %. The reject percentage was higher than the percentage obtained for a strength class equal or less than C18 and less than the reject percentage for a strength class superior to C18. The presence of ME-1 grade is only a 3 % which means that it is not worthy to differentiate between two grades (ME-1 and ME-2). The use of non destructive techniques together with the drill cores technique presented good results for prediction. This aptitude together with its portability and easy use allow to consider as very adequate techniques for the estimation of strength properties of sawn timber in existing structures and in new timber. Some of the best results for prediction were the following: Determination coefficients R2 = 0,88 for the density by means of the core drilling specimens. Determination coefficients R2 = 0,86 for the modulus of elasticity by means of bending dynamic vibration analysis and 0,82 obtained by means of ultrasounds. Determination coefficients R2 = 0,54 for the modulus of rupture by means of bending dynamic vibration analysis, as in previous case and 0,46 obtained by means of ultrasounds. These results show a promising future for the non destructive tools in the estimation of mechanical properties of structural sawn timber both in existing structures and in new timber structures, mainly combined with visual grading.