The structural grading of young South African grown <i>Pinus patula</i> sawn timber

Abstract

In this study sawn timber from 16- to 20-year-old Pinus patula trees were obtained from a wide variety of sites along the Mpumalanga escarpment in South Africa. The objectives of this study were to assess the efficiency of the current visual and mechanical grading rules on this timber and to evaluate the potential of some indicator properties to be used as structural grading parameters on this resource. A large number of non-destructive measurements were performed on all samples (i.e. X-ray density scanning, acoustic frequency measurement, year-ring measurements and stiffness measurement) before it was destructively tested in bending and tension. The young P. patula timber tested in this study had good bending strength (MOR) properties with higher characteristic grade values than required. The timber, however, had low stiffness and did not comply with the SANS 10163-1 requirements for mean modulus of elasticity on edge (MOE_edge) for any of the structural grades. Dynamic MOE (MOE_dyn), calculated from acoustic frequency tests on the timber, was found to be the best single predictor of MOE_edge, MOR and tension strength. Multiple regression analysis showed that a combination of MOE_dyn, density and knot parameters can be used to improve the predictability of some of the strength and stiffness characteristics of the timber.

Keywords: non-destructive evaluation, structural grading, young Pinus patula

Southern Forests 2013, 75(1): 7–17