Influência do tratamento preservativo em Eucalyptus urograndis na resistência de ligações pregadas

Abstract

The use of wood in civil construction has been increasing together with the increase in studies related to the improvement and development of the material, including preservative treatment. Considering that in wood structures, the connection is the most fragile point, it is necessary to deepen also in researches in this area. Thus, the present work has the objective of analyzing the influence of the preservative treatment of the wood of Eucalyptus urograndis by autoclaving with CCA in the resistance of connections with eight nails to the simple cut. Tests of moisture, apparent density, compressive strength parallel to the fibers and retratibility were carried out for each state of the wood in order to characterize them. In addition, the bond strength test was performed on natural and treated wood specimens, with a 5 cm x 5 cm main section and a 5 cm x 2.5 cm secondary section, both with a length of 25 cm. The results of the experimental resistance of the connections were also compared with the resistances calculated through the standards NBR 7190 (ABNT, 1997), EUROCODE 5 (CEN, 2004) and NDS (AWC, 2015). Comparing the compressive strength parallel to the fibers, the treated wood presented better results, on the other hand, comparing the apparent density, the natural wood presented a higher value. For shrinkability, the preservative treatment did not influence the results, since they were the same for the wood with and without treatment. Analyzing the experimental resistances, the untreated wood presented greater final resistance. However, for the displacement up to 10mm, treated wood obtained better results, since the displacements were clearly smaller for the same applied load compared to natural wood. Regarding the theoretical models of normative documents, although all the analytical results guaranteed the safety of the structure, those based on EUROCODE 5 (CEN, 2004) were the closest to the experimental values. The Brazilian model was the only one that presented higher calculated values for the treated wood, different from the maximum experimental results. Thus, it is concluded that the preservative treatment can have positive, negative or zero influence, depending on the property analyzed. Regarding the bond strength, it is concluded that the use of treated parts in wooden structures guarantees greater comfort and safety to users. Finally, the conclusion regarding the analytical results is that EUROCODE 5 (CEN, 2004) is closer to the experimental results, even though all the standards result in smaller values than those found in practice.