Softwood timber poles: Proving of strength and stiffness

The method of classification of softwood timber poles within Australia is adopted directly from the United States of America, whereby a pole is classified by its groundline circumference which was determined from a given pole tip load and a fibre stress value (as determined from previous testing). Consequently, the derivation of the basis for classification is based on strength and stiffness values determined from the testing of American timber. This study was conducted to determine the strength and stiffness of Queensland plantation grown softwood. The strength and stiffness of timber is expressed by the Modulus of Rupture (MOR) and Modulus of Elasticity (MOE), respectively. The samples selected for testing were two lots of 40 specimens of the species Slash Pine (Pinus Elliotti). One sample consisted of poles 9.1m in length, the other 7.6m in length. The species and length of the specimens represent the product of timber poles most commonly utilised by industry. The size of the sample was determined so to be both economic and also to produce results which were a valid indication of the entire population. Specimens were tested by cantilever loading. Full size poles were placed horizontally into a rigid clamp. A load was then applied to the tip of the pole until failure occurred. The load at failure and corresponding deflection were measured, from which the MOR and MOE of each pole was determined.