The purpose of present study was to create a theoretical model that allowed with security and reliability to obtain, values of strength and stiffness to which the structural element will be submitted throughout its useful life. The effect was studied for strength and stiffness properties, and the modulus of elasticity (EM) and bending strength (fM) were evaluated according to the increasing number of cycles of the fatigue test for the five classes of hardwoods, recommended by NBR 7190 (1997). These results allowed to construct a fatigue curve, relating the two variables as a function of the number of cycles (Nc) - construction of the curves EM x Nc and fM x Nc. The fatigue effect was present and pronounced in all strength classes. A reduction in strength and stiffness properties was observed with increasing loading Nc applied at all frequencies. From the multivariate regression models and the respective determination coefficients, a generic model was obtained for the set involving the five wood species, emphasizing the insertion of the apparent density as an independent variable, which allowed a greater generalization of the use of the adjustments in the estimation of properties.

Johnny Soares de Carvalho: Civil Engineer and Master's Degree in Structural Engineering from USP and Doctoral Degree in Structural Engineering from UFSCar. André Luis Christoforo: Civil Engineer (UNIFRAN), Master, Doctoral and Postdoctor Degree from USP and professor at UFSCar. Francisco Antonio Rocco: Civil Engineer and Full Professor at USP.