An investigation of selected mechanical and physical properties of young, unseasoned and finger-jointed Eucalyptus grandis timber

[摘要] ENGLISH ABSTRACT: South Africa is a timber scarce country that will most probably experience a shortage of structuraltimber in the near future. In this study the concept of using young finger‐jointed Eucalyptus grandistimber was evaluated for possible application in roof truss structures while the timber is still in thegreen, unseasoned state. 220 finger‐jointed boards of cross‐sectional dimension 48 x 73 mm and 36 x111 mm timber, cut from 5‐18 year old Eucalyptus grandis trees were obtained from Limpopo province,South Africa. The boards were manufactured using a polyurethane (PU) adhesive at moisture contentlevels above fibre saturation point and no drying was performed. The objectives of this study were todetermine various mechanical and physical properties of this finger‐jointed product. More specifically(1) to determine the strength and stiffness potential of the product in the wet and the dry condition, (2)to evaluate physical properties such as density, warp, checking and splitting, (3) to evaluate potentialindicator properties to be used as structural grading parameters, and (4) to compare the flexuralproperties to the current SA pine resource and SANS structural grade requirements.The boards were divided into two groups of the same size, which constituted the wet and the drysamples. Each sample was further separated into six different groups for testing the different strengthand stiffness properties. The dry group was stacked in a green‐house for nine weeks until equilibriummoisture content was reached. Afterwards selected physical properties such as warp, checking andsplitting were assessed. Destructive testing was conducted on the boards and the results were used todetermine various mechanical properties. Finally, each board was assessed for density and moisturecontent (MC) values.The study showed that the young finger‐jointed Eucalyptus grandis timber had very good flexuralproperties. Both mean modulus of elasticity (MOE) and modulus of rupture (MOR) 5th percentilestrength values for wet and dry boards complied with the current SANS 10163‐1 (2003) requirements forgrade S7.The values of tensile perpendicular to grain and compression perpendicular to grain strengthdid not conform to SANS requirements for grade S5. The other strength properties for the wet and drygroups complied with one of the three SANS structural grades. The 5 year old (48 x 73 mm) boards'showed significantly higher levels of twist and checking compared to 11 year old boards of the samedimension. Only 46.3% of the finger‐jointed products conformed to the density requirements in SANS1783‐2 (2004) for grade S7. There was a significant difference in density between the three age groups (5, 11 and 18 years) presented in this study. The variation in both MOE and MOR values of the fingerjointedproduct proved to be significantly lower in comparison to currently used SA pine sources.Based on the results from this study the concept of producing roof trusses from wet, unseasoned andfinger‐jointed young Eucalyptus grandis timber has potential. However, additional research on a numberof issues not covered in this study is still required for this product including full scale truss evaluations,proof grading, PU adhesive evaluation at elevated temperatures, nail plate load capacity, and thepossible need for chemical treatment of the product against Lyctus beetles.

[发布机构] Stellenbosch University