Evaluation of the load carrying capacity of large cross section coniferous timber in standing structures

A total of 85 large section timber pieces (Pinus sylvestris L. and Pinus pinaster Alt.) found in a number of old buildings were visually analyzed and graded pursuant to Spanish standard UNE 56544 and German standard 4074. The object was to formulate a non-destructive method to reliably and effectively determine the mechanical properties of existing timber structures with large cross sections. A new system is proposed based on the chief visual grading parameters and consisting in a single grade; the percentage of rejections with this system is low. In this regard, a specific strength class is established for large cross section members in existing coniferous wood structures, namely F14/E9/D380 (MOR of 14 N/mm2, MOE of 9 kN/mm2 and characteristic density of 380 kg/m3). The use of ultrasonic velocity is proposed to define the next higher strength class - F16/E10/D380, to which timber with velocities of 4,900 m/s or over would be assigned.