An experimental study of flexural behavior of glulam beams made out of thermally treated fast-growing poplar laminae.

In this study, to improve the structural applications of glued laminated timber (glulam) in high RH environment according to its relatively lower MOE, fast-growing poplar laminae with a thickness of 35 mm were thermally treated at 20 o C for 3.5 h. The effects of thermal treatment and RH in the surrounding environment on laminae strength class was conducted. Afterward, 12 full-scale same-grade composition glulam beams made out of untreated and thermally treated poplar laminae were prepared. The four-point bending tests were conducted to reveal the effects of laminae thermal treatment and RH in the surrounding environment on flexural properties of glulam beams with a span-depth ratio of 18. The results showed that the strength class of fast-growing poplar laminae was negatively related to RH in the surrounding condition, and thermal treatment can contribute to the increase in strength class. In 90% RH, strength class increased from untreated laminae M E 7 to the heat-treated M E 10, according to China standard. The relationship between bending properties of glulam beams and RH in the surrounding environment was negatively correlated, as well as thermal treatment, whereas MOE was improved significantly after thermally pretreated, especially in high RH. In 90% RH, MOE of glulam beams made of thermally pretreated laminae was 29.57% higher than the untreated beams with an MOR reduction of 8.82%. The results of characteristic load-deformation curves, characteristic load-strain curves, average extreme fiber strain, and the failure mode can support each other in this study. Industrial thermal treatment technology to laminae improved the MOE of glulam beams significantly in high RH with a reduction in MOR, and glulam beam made out of thermally treated fast-growing poplar laminae can be used in  construction, but need checking in MOR or be used for a limited range of structural elements.