论文信息 - Madera aserrada de gran escuadría para uso estructural y sus particularidades

Madera aserrada de gran escuadría para uso estructural y sus particularidades

The size effect on mechanical properties of timber is described including the recent evolution of testing procedures and stress grading. Further, a specifi c research work on large cross section timber is explained. A total of 395 pieces of sawn timber from three species (Pinus sylvestris L., Pinus nigra subs. salzmanii (Dunal) Franco and Pinus radiata D. Don) with cross section between 150x200 y 200x250 mm, have been visually graded according to UNE 56544 standard obtaining its output and mechanical properties. The percentage of rejected pieces is too high (38 to 45%) and therefore, a modifi cation of standard specifications is proposed. The output is highly improved in the proposal of standard (rejected percentage of 11 to 17%) whereas the mechanical properties are not modified in practice.A similar procedure was applied to 85 timber pieces from old timber structures of building demolition of Pinus sylvestris L. and Pinus pinaster Ait. The percentage of rejected pieces is 52% in a visual grading according to the application of all grading parameters of the standard UNE 56544:2003. This procedure is not practical for existing structures and therefore, it is proposed the application of grading considering only the parameters of knots size and slope of grain. In that way the output is improved reducing the rejected percentage to 10%.

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