Properties of Mixed Species/Densities Cross Laminated Timber made of Rubberwood and Coconut Wood

The utilization of rubberwood (Hevea brasiliensis) and coconut wood (Cocos nucifera L.), the essential economic crops in Thailand and tropical countries, was proposed for manufacturing mixed species/density cross-laminated timber (CLT) for building construction. Six 3-layer CLT configurations, which are composed of either medium-density (600 – 799 kg/m3 ) rubberwood (MRB) or coconut wood (MCC) or high-density (800 – 999 kg/m3 ) coconut wood (HCC) laminations, were determined considering the mechanical properties and material costs. The outer layers of the control MCC CLT were replaced with either MRB or HCC to improve its mechanical properties, while either outer or core layers of the control MRB CLT were replaced with HCC to reduce its material cost. The material properties of the three wood types and the six CLT configurations were examined. The densities of the produced CLTs were not affected by the chosen manufacturing parameters showing a strong correlation to the lamination's density. From the bonding performance perspective, the mixed-species approach significantly increased the average wood failure percentage of the control MRB CLT. However, only the control MCC CLT achieved the average wood failure percentage greater than 80%, as required in North America's CLT standard. The compressive strength properties of the CLTs in their major strength directions, σclt, were governed by the outer laminations' parallel-to-grain compressive strength. Unlike softwood CLTs, neglecting the load sharing contribution of the core layer in the σclt estimation resulted in 15% underestimation. Rolling shear strength, τrs, was determined by the core laminations regardless of the CLT layups. MRB achieved the highest τrs followed by HCC and MCC, and all values were significantly larger than the common softwood used in CLT production. The results imply that the mixed species/densities approaches can effectively improve the mechanical properties of the coconut wood CLT and reduce the material cost of rubberwood CLT without compromising structural performance

Effect of compression ratios and original wood density on pressing characteristics and physical and mechanical properties of thermally compressed coconut wood

This experimental study aims to improve the engineering properties of coconut wood by using a thermal compression method (TM). The effects of original wood density and compression ratio on the pressing characteristic as well as physical and mechanical properties of thermally densified coconut wood were evaluated. Coconut wood boards obtained from the plantation located in Nakhon Si Thammarat province, Thailand, were sorted into low-density (359±36 kg/m3) and medium-density (532±35 kg/m3) groups. They were compressed by 25%, 40%, 55%, and 70% of their original thicknesses under a clamping pressure of 19.6 MPa (pressure gauge), at a temperature of 140 °C for 15 min. The physical and mechanical properties of the densified specimens were measured and compared with the control group specimens. Low-density specimens could be compressed with a higher degree of densification without shape distortion. Thermal compression improved bending strength, modulus of elasticity, compressive strength parallel to grain, and perpendicular-to-grain shear strength up to 125%, 54%, 112%, and 129%, respectively, for low-density wood and 47%, 13%, 41%, and 58%, respectively, for medium density wood. However, the densification did not improve parallel-to-grain shear strength. When the low-density and medium-density wood were compressed to the same density, the densified specimens manufactured from the medium-density group showed more improved dimensional stability, shear strength, and bending properties than those manufactured from the low-density group, while their parallel-to-grain compressive strength properties were not significantly different. However, at the same density level, the natural wood mechanically outperformed the densified wood except for the perpendicular-to-grain shear strength, parallel-to-grain compressive strength, and bending strength perspectives. Thus, the experimental results indicate that the densified coconut wood can be used for structural applications where parallel-to-grain compressive strength or perpendicular-to-grain shear strength is critical

Effect of wall thickness and node diaphragms on the buckling behavior of bamboo culm

The buckling behavior of bamboo culm is highly affected by internodal properties, i.e. material properties and geometric parameters of the trunk. In this study, the effects of Phyllostachys Edulis bamboo culms have on buckling phenomena under bending and compressive loads are investigated. Internodal walls are assumed to be composed of orthotropic functionally graded-type materials which are controlled by the volume fraction of the vascular fiber bundle. Provided that the trunk wall thickness near the node is greater than that in the internode and that the number of fibers is mostly unchanged, the internode and node walls are defined by shell elements with the same composite layup material but different thicknesses. It is found that, with a constant internodal length the buckling behavior transitions from global to local as the tube radius increases. The global buckling load increases with approximately a fourth order polynomial in relation with the radius while the local buckling load linearly increases with the tube radius. Nodal wall thickening enhances the buckling load in both the global and local domains. There is an interactive contribution of nodal wall and diaphragm thicknesses on the buckling behavior up to a certain point where the local buckling load is independently determined by each internodal structure. The buckle can occur within thin diaphragms, which results in much lower buckling load compared with the tube without/removed the diaphragms