Browsing by Author "Pagel, Calvin"
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- ItemInvestigation into material resistance factors and properties of young, engineered Eucalyptus grandis timber(Stellenbosch : Stellenbosch University, 2019-04) Pagel, Calvin; Lenner, Roman; Wessels, C. B.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Only 1 % of South Africa’s total land area is used for forestry with 51 % of that being used for Pinus and 40 % for Eucalyptus species. A country wide shortage of adequate structural timber has been forecast for the near future where SA pine is the predominant structural timber species. Recent research has looked into Eucalyptus grandis to be used as a structural timber resource due to its fast growth rate and large plantation area. This hardwood has not traditionally been used structurally due to the physical defects commonly present in sawn, dried Eucalyptus grandis timber. The development of engineered timber products has been investigated as one way to mitigate some of these defects. Young Eucalyptus grandis which has been finger-jointed in the green state was recently introduced into the South African market. Tests completed by Crafford (2013) on the material showed promising mechanical strength results with low variability when compared to similar SA pine. This lead to the consideration of determining a specific material resistance reduction factor for use with the young Eucalyptus grandis as the current factor prescribed in the code is deemed to be overly conservative as it was calibrated for softwood timber. The finger-jointed timber had still experienced many physical defects, such as twist and checking. Face lamination of the material was thus proposed with the aim of reducing defects and to further decrease the mechanical strength variation. In this study two sets of samples were tested, a group of 100 standard green finger-jointed Eucalyptus grandis and a set of 100 finger-jointed and face laminated samples. This allowed for comparisons to be made to determine if the face lamination is a worthwhile inclusion and to produce material strength results to be used for partial factor determination. The face lamination was completed using a one-component polyurethane adhesive with timber in the wet, unseasoned state. Both sets were dried to equilibrium moisture content to assess physical defects, which are usually aggravated during drying. Four point bending tests were completed to determine the flexural characteristics, modulus of elasticity (MOE) and modulus of rupture (MOR), of the samples. Only flexural strength tests were completed due to the limited material available and as they are the indicator properties listed by the JCSS along with being the most important properties for roof truss design which is the predominant end use of structural timber in South Africa. Both sets performed well in terms of warp deformation with no cases above rejection limits for bow and cup. A total of 1 % of laminates had excessive twist compared to the 9 % of the standard boards. The standard set had significantly more check (20 %) and split (15 %) defect rejections compared to the 4 % for check a 0 % for split achieved by the laminated set. Structural grade S7 requirements were achieved for MOE and MOR of both sets. Only a small difference in coefficient of variation (COV) of approximately 1 % was recorded between the sets but a 12 % lower COV was achieved for the MOR of the sets compared to equivalent SA pine. The material resistance reduction factor calculated for MOR was found to be governing, with essentially equivalent factors for the laminates and standard boards of 0.776 and 0.769 respectively. It is thus proposed that a reduction factor of 0.77 be implemented in the code for the Eucalyptus grandis to be used instead of the current 0.68 which was originally devised for softwood timber. Although the lamination process did not reduce the variation in strength results to a significant extent, significantly lower defects were recorded for the laminated set. This would result in a higher yield of material with a better visual appeal which could allow for it to be a more valuable product. For both sets, the 0.09 gain in reduction factor may not seem to be a large advantage, but when coupled with the higher structural grade being achieved and the shorter rotation age than SA pine, the young, finger-jointed and face laminated Eucalyptus grandis is a promising option for structural timber use in a country as timber scarce as South Africa.