The use of wood in construction requires knowledge of the mechanical properties and the particularities that wood presents in comparison with other materials used for structural purposes such as steel, concrete, brick, or stone. The introduction mentions the environmental advantages that justify the use of wood today. The orthotropy of wood is one of the differentiating characteristics that must be taken into account when studying its behaviour. The determination of the properties of wood is then addressed from a historical perspective and the differentiation is made between the properties of small clear wood (defect-free timber) and structural timber. The timber grading systems (visual and mechanical grading) and the non-destructive techniques that currently prevail are explained. Finally, the factors that influence the mechanical properties, such as duration of the load, moisture content, quality, temperature, and the effect of size are explained. The objective of this work is to provide an overview of the current knowledge on the mechanical properties of wood, based mainly on published articles and European and North American standards, including historical references to the beginnings and current trends in this field.

In this study the static (µe) and kinetic (µd) coefficients of friction were obtained for Pinus sylvestis L. sawn timber of Spanish origin. Friction between transverse surfaces sliding perpendicular to the grain (tangential direction) and radial surfaces sliding parallel to the grain was analyzed. A specifically designed device was used for tests, which makes it possible to apply contact pressure and measure displacements and applied loads simultaneously. Coefficients of friction between transverse surfaces (µe = 0,24; µd = 0,17) were about twice of the coefficients of friction between radial surfaces (µe = 0,12; µd = 0,08). Furthermore, these values are located within normal values of those commonly reported for softwood. The results are considered preliminary due to the small number of specimens.

Bending properties have been determined by mechanical testing [modulus of elasticity (MOE) and modulus of rupture (MOR)] and by means of longitudinal (L) and transverse (T) vibration nondestructive methods on 150 sawn timber pieces of Pinus radiata D. Don, with the dimensions of 80×120 mm cross-section and 2500 mm long, from Catalonia, Spain. The fundamental vibration frequency was measured by recording the sound produced by hitting the piece in L and T directions, and this signal was analyzed by fast Fourier transform sound analyzer. The dynamic MOE was obtained for both procedures and compared with static MOE and MOR. The notion of concentrated knot diameter ratio (CKDR) was introduced to improve the prediction of MOR. CKDR gives better results when this parameter is referred to the central portion of piece length. Both methods (L and T frequencies) have similar accuracy in prediction of mechanical properties, but the first one is simpler and has some practical advantages. The timber graded with this nondestructive method offers better results than the visual grading rules for the same output.