Dynamic testing of wood utility poles

Reliability of timber utility poles is important because breakdown or failure can cause damages to the infrastructure or even loss of life. Timber utility poles safety relies on both the material strength and the structural integrity of the pole. The former is influenced by both the original quality of timber and by the rate of the deterioration of the material in service; the latter mostly depends on the type of pole foundation, the soil nature as well as the eventual presence of in-ground decay. In order to develop and verify a method for assessing the structural condition of timber poles and to predict failure in a closed form, disregarding the specific nature and cause of damage, a research program based on dynamic testing of timber poles has been carried out at the University of Trento. Dynamic behaviour of structures depends on both geometrical and mechanical features, which are often also responsible for the structural safety. In case of timber poles, the dynamic response is influenced by multiple factors, such as end-boundary conditions (foundation and over-head cables), size and tapering of the pole, stiffness and density of timber. In order to evaluate the influence of the cited factors on the dynamic behaviour of timber poles an experimental campaign has been carried out. Discarded and new poles, used for the telephonic network in Italy, were dynamically tested in laboratory, using quantifiable boundary conditions. In a preliminary survey, geometrical and physical characteristics of the test material were measured. Static bending tests using the cantilever method were carried out on full-size poles, and static bending properties were determined. Experimental results are presented in this paper and, from them, some conclusions are drawn.