Desempenho estrutural de placas de Cross Laminated Timber submetidas à flexão

Abstract

The growing demand for sustainable materials makes wood to have great potential for its use in construction. Cross Laminated Timber (CLT) is an engineered wood product consisting of wood boards arranged in orthogonally cross-linked layers and is mainly used as a plate or sheet structure. In Brazil, CLT panels are produced industrially using reforestation wood of Pinus taeda species. As the physical and mechanical wood properties depend on several natural factors, knowing the structural performance of CLT boards produced with nationally grown wood is important. This study analyzes the structural performance of CLT plates by experimental tests and numerical simulations. The main experimental tests were conducted with 21 plates composed of five layers of boards, totaling 16 cm in thickness, and submitted to fourpoint bending, according to BS EN 16351:2015. Pinus taeda samples were extracted from tested plates that were later analyzed by simple bending, according to NBR 7190:1997, and by perpendicular compression and parallel compression to the grain, according to BS EN 408:2010 to explore the properties of the raw material. Numerical analysis of static and vibration mode performance ware carried out by RF-LAMINATE and RF-DYNAM Pro modules of the commercial software RFEM 5, using composite plate elements and determining mesh discretization by the Grid Convergence Index method. Such simulations considered Mindlin and Kirchhoff plate theory, as well as normative resistance classes according to NBR 7190:1997 and BS EN 338:2016. Physical and mechanical properties were obtained from experimental tests, such as specific gravity, moisture, bending strength and stiffness, as well as shear strength and stiffness of CLT plates. The CLT´s bending strength was associated with the tensile strength of finger joints on the lower layers, while ruptures due to shear stress occurred due to the deficiency of strength capacity of rolling shear in the transverse layers of the CLT. When plate theories and different normative characterization were evaluated in numerical simulation, results of strength and stiffness with relevant variations were found, some of which are not admissible. The difference between adhesive weights from 220 to 250 g/m 2 was statistically evaluated and no significant difference was observed regarding the stiffness and strength of the samples. It was also possible to estimate acceptable loads as a function of the length of CLT plates, being analytically and numerically, verified that the natural vibration is one of the critical factors that limits CLT design length. Finally, this research is a result of the partnership between university and industry, which allowed conducting experimental tests of structural size for characterization of CLT plates and predicting their static structural behavior and vibration modes through analytical and numerical simulations, expanding the technical knowledge on CLT industrially produced with raw material planted in the national territory.

Caracterização físico-mecânica da madeira de tuturubá (Pouteria oblanceolata Pires)

“…Para a resistência à compressão paralela às fibras foi encontrado valor médio de 60,03 MPa. Considerando a classificação das rupturas da madeira em ensaios de resistência à compressão paralela às fibras, presente no estudo de VILELA [21], foram identificados os seguintes tipos de ruptura: divisão em cunha (Figura 2a), cisalhamento (Figura 2b), esmagamento superficial (Figura 2c) e esmagamento (Figura 2d).…”

“…Os CPs utilizados para a determinação da resistência à flexão exibiram modo de fratura frágil (Figura 9), apresentando os tipos de rupturas de lascamento por tração, tração em fibras inclinadas e tração simples [21]. Segundo VILELA [21], a ruptura por tração simples raramente ocorre no ensaio de flexão, no entanto, o mesmo autor ressalta a possibilidade de ocorrência em madeiras de alta densidade, tais como a espécie tuturubá. Já a ruptura do tipo lascamento por tração ocorre em amostras com baixo teor de umidade.…”