Application of regardless of species conception for mechanical stress grading on tropical timbers

Abstract

Some reports showed that for single species the relationship between modulus of elasticity (MOE) and modulus of rupture (MOR) in bending was quite high. Tropical timbers consist of hundreds species which were difficult to identify the timber species. This report is dealing with the application of regardless of species conception for mechanical stress grading of tropical timber. Nine timber species or group of species with total number of 1,094 pieces in 60x120x3,000 mm timber were tested in static bending. MOE was measured in flat-wise while MOR was tested in edge-wise. Statistical analysis of linear regression with dummy model and ANCOVA were used to analyze the role of MOE and effect of species on the prediction of MOR. The analysis showed that using MOE as single predictor caused a condition of under/over estimate for one or more species and/or group of species. The percentage of the accuracy of prediction would be increased with species identification. An allowable stress and reference resistance for species and/or group of species were provided to compare with the prediction of strength through timber grading. The timber strength class for species and/or group of species was also established to support the application of mechanical timber grading.