Evaluation of the Number of Load Cycles to Determine Some Wood Stiffness Properties

Abstract

For fiber accommodation in tests to obtain wood strength and stiffness properties, some standards codes provide two or more load cycles, such as the Brazilian Standard ABNT NBR 7190, which establishes a number of three cycles (two previous and the final load cycle). However, reducing the number of load cycles provides savings in energy and manpower in the operation and maintenance of the testing machines, which motivates the development of research on this topic. This study aimed to investigate, according to Brazilian Standard Code and analysis of variance (ANOVA), the influence of the number of load cycles (1, 2, 3) to determine the modulus of elasticity in compression (Ec0) and tension (Et0) in parallel direction to the grain, in normal compression (Ec90) and in static bending (Em) for the native Brazilian species Cambará Rosa, Cupiúba, Envira, Angico and Champagne woods, allowing, with the use of wood evenly distributed on strength classes, the results to be extended to other wood species. Results of the Tukey test show that only the first load cycle presented different stiffness values, with the second and third load cycles giving equivalent results of modulus of elasticity. This implies that the third load cycle can be disregarded, and stiffness properties can be obtained after only with the second load cycle.