Eucalyptus is a major fast-grown species in South China, which has the potential for producing structural wood products such as cross-laminated timber (CLT). Aspect ratio (board width vs. board thickness) of eucalyptus lumbers is small due to the small diameter of fast-grown eucalyptus wood. To evaluate its rolling shear modulus and strength for potential CLT applications, three-layer hybrid CLT shear block specimens with different aspect ratios (2,4,6), were tested by planar shear test method. Digital image correlation (DIC) was employed to measure the rolling shear strain distribution and development during the planar shear tests. The mean values of rolling shear modulus and strength of eucalyptus lamination were 260.3% and 88.2% higher than those of SPF(Spruce-pine-fir) lamination with the same aspect ratio of 4, respectively. The rolling shear properties of eucalyptus laminations increased as the aspect ratio increased. Aspect ratio had a significant influence on rolling shear modulus compared to rolling shear strength. The high shear strain regions were primarily found around the gaps between segments of cross layer. The quantity of high shear strain regions increased as the aspect ratio of lamination decreased. Other high shear strain regions also occurred around the pith and along the glue line. The sudden failure of specimen occurred in the high strain region. In conclusion, the rolling shear strength and modulus of fast-grown eucalyptus laminations exceed the respective characteristic values for softwoods in the current standard by roughly factors of 3 and 8, indicating great potential for fast-grown eucalyptus wood cross-layers in CLT.

The acoustic emission (AE) technique can perform non-destructive monitoring of the internal damage development of bamboo and wood materials. In this experiment, the mechanical properties of different bamboo and wood (bamboo scrimber, bamboo plywood and SPF (Spruce-pine-fir) dimension lumber) during four-point loading tests were compared. The AE activities caused by loadings were investigated through the single parameter analysis and K-means cluster analysis. Results showed that the bending strength of bamboo scrimber was 3.6 times that of bamboo plywood and 2.7 times that of SPF dimension lumber, respectively. Due to the high strength and toughness of bamboo, the AE signals of the two bamboo products were more abundant than those of SPF dimension lumber. However, the AE evolution trend of the three materials was similar, which all experienced three stages, including gentle period, steady period and steep period, and the area of rupture precursor characteristics could be recognized before the specimen destroyed. Due to the bottom layer was first tensile failure, the main structure of bamboo plywood was destroyed after the stress redistribution. The rupture precursor characteristics could be observed before each peak. Findings put in evidence a good correlation between AE clusters of two bamboo products, while the amplitude and energy of wood signals were lower than those of bamboo. The amplitude and energy from the propagation and aggregation of cracks were greater than those related to micro-cracks initiation.

Cross-laminated timber (CLT) is a popular engineering wood product in recent years. It has some characteristics of configuration and mechanical properties, which makes it an excellent building material for floor, roof and other places. In Europe and North America, lots of middle and high-rise buildings have adopted CLT as their main structural component. CLT has recently been used to construct public buildings in China. As a building material, the lower rolling shear properties of CLT has always been a concern. To overcome this shortcoming of CLT, the structural composite lumber and bamboo have been employed to develop hybrid CLT. This chapter also presents the latest development and advances of CLT in China.