# Safe and Sustainable Design of Composite Smart Poles for Wireless Technologies
## 2 Materials and Methods
### Finite Element Modelling and Mechanical Analysis  
In this study, two different shaft cross-sections, i.e., shaft designs, were analyzed: (1) traditional circular profile and (2) a near-rectangular diamond-shaped profile. The near-rectangular cross-section, as illustrated in Figure 4, can accommodate radios, other devices and cabling while optimizing the coverage of the transmitting devices around the surroundings of the pole. Moreover, such design can be further divided into internal slots to manage the cabling and piping inside the pole and to separate different equipment by standard modules. The composite shaft structure--the two cross-sections--were modelled by using the ABAQUS standard/explicit (2017) software code. In order to widely characterize the behaviour and loading conditions, different 3D models of the shaft were analyzed with finite element analysis (FEA). The full-scale model of the pole was simulated to characterize deformation under a mechanical load and thermal expansion due to temperature increase by solar radiation. Furthermore, material was removed in specific pole locations of the model to simulate the machining processes needed to accommodate and mount electronic devices (i.e., via so-called maintenance cutouts and doors) in the root and top section of the pole. In this case, curvature radii as well as dimensions of the holes were analyzed, together with their effect on the pole's structural integrity for the static loads mentioned above. The results obtained were then used to properly design the cutouts for electronic components and maintenance doors also at the base of the 5 GP. In order to keep the consistency of the results between the different analyses, continuum shell elements (SC8R) were used in all of the finite element  
Figure 3: Testing of GFRP mechanics: (**a**) the QS indentation of a half-circular specimen with a semi-rigid boundary; (**b**) the drop-weight impact testing of a half-circular specimen with an ‘open’ boundary, and; (**c**) the drop-weight impact testing of a tubular pole specimen. models of the pole shaft. The mechanical properties of the laminate and the local impact performance have been reported elsewhere [27; 28]; the elastic constants used in the modelling here are shown in Table 1 and the strength values for the laminate are 500 MPa, 200 GPa, 50 MPa, 100 MPa and 40 MPa for the longitudinal tensile strength, longitudinal compressive strength, tensile transverse strength, compressive transverse strength and shear strength, respectively. For most of the composite materials, the thermal expansions are lower than those for any steel alloy. Thermal expansion coefficients of fibrous composites depends on the applied constituent materials and the lay-up of reinforcement, along with many factors of measurements [29; 30]. In this study, the linear thermal expansion coefficients (CTEs) of the GFRP composite were determined using an experimental arrangement and an iterative FEA of the CTE values based on the residual strain, as described in Section 2.4 and Appendix A. The boundary conditions and loads (wind load distribution), shown in Figure 4, reflect a standard specification [31]. The wind loads represent the primary mechanical load against which the pole structure must be verified. The wind reference speed is given by the standard, e.g., here it is 21 m/s for the terrain category II of Scandinavia. The services for \begin{table}
\begin{tabular}{l l l} \hline
**Constant** & **Parameter** & **Value (Units)** \\ \hline Axial Young’s modulus & \(E_{11}\) & 35 GPa \\ Transverse Young’s modulus & \(E_{22}\) & 7.0 GPa \\ Out-of-plane Young’s modulus & \(E_{33}\) & 4.5 GPa \\ Poisson’s ratios & \(v_{12},v_{23}\) & 0.3 \\ Poisson’s ratio & \(v_{13}\) & 0.05 \\ Shear modulus & \(G_{12}\) & 3.6 GPa \\ Shear modulus & \(G_{13}\) & 3.6 GPa \\ Shear modulus & \(G_{23}\) & 2.0 GPa \\ \hline \end{tabular}
\end{table} 
Table 1: Elastic constants of the GFRP (unidirectionally reinforced layer) used in this work for the pole shaft FEA [27; 28].