## 2 Up-to-Date Numerical Modelling of Wooden Utility Poles  
As mentioned at the outset, wood has complex mechanical behaviour with highly nonlinear performance [11]. However, in existing studies, wood is sometimes simulated as a homogeneous and isotropic material. This assumption will not be able to illustrate the practical mechanics performance [12]. For analysing the failure and fatigue behaviour of wood structures like piles or poles, it is well recognised that it is necessary to model wood as an orthotropic material with elastic-plastic behaviour based on [PERSON]'s criterion [13; 14]. Besides, [PERSON] developed FE models to forecast the performance of the uniform-diameter wood poles subjected to the loads [15]. Five orthotropic models were developed using ANSYS and were verified with experimental results. In the research, three-dimensional (3D) 10-node tetrahedral solid element was used in the modelling of wood laminated poles, which has a nonlinear displacement behaviour, plasticity, large deflection, and large strain capabilities. The predicted deflection by these models agreed well with those of the experiments, and the predicted normal stress agreed with those calculated. [PERSON] and [PERSON] employed 3D FE models to investigate the stress distribution and failure of wood poles subjected to cantilever bending [16]. Orthotropic and isotropic material models with linear-elastic material properties were built and verified with the theoretical results. It can be concluded that orthotropic models are more sensitive to support conditions affecting the bending stress distribution near the boundary. [PERSON] and [PERSON] developed an isotropic material model to investigate the usage of guided wave velocity measurements to distinguish between strength-reducing decay and non-strength-reducing growth ring separations (ringshake). The results from the field testing and FE analysis indicated that the guided wave velocity measurements alone were not sufficient to confidently differentiate between ringshake and decay [17]. On the other hand, the soil is also a complex material, which consists of particles with various mineralogy, size and shape [18]. Therefore, soil modelling plays an essential role in pile or pole testing research, because the piles and poles are generally embedded in the soil, the boundary condition of which will directly affect the wave propagation behaviour in structures when stress wave-based NDE techniques are adopted for tests. High strain testing of piles or poles is typically performed to evaluate the driving system for assessing the static or bearing capacity. For this kind of testing, soil behaviour is always considered as elasto-plastic and simulated by the Mohr-Coulomb model to describe the stability of foundation structures. [PERSON] and [PERSON] created numerical models to illustrate the behaviour of medium dense sand when the piles are under an inclined load [19]. [PERSON] et al. used a Mohr-Coulomb elasto-plastic model to describe the soil behaviour and pile foundation stability when a strong earthquake occurred [20]. Moreover, low strain methods have also been developed for the integrity assessment of embedded length estimation of piles. For a very low strain level (less than \(10^{-5}\)), the elastic and linear behaviour of soil is obvious [21]. Accordingly, soil could be simulated as linear-elastic, which provides the most basic soil behaviour without considering the nonlinear and plastic behaviour at failure of the soil. [PERSON] et al. adopted a linear-elastic model to describe the soil behaviour under integrity testing [22]. In this work, low strain testing is conducted and the strain level is less than \(10^{-5}\). Consequently, the material constitutive in this paper will be simulated as linear-elastic. Furthermore, to effectively analyse the wave propagation in wood poles, the effect of soil-pole interaction should be also considered.