Finite element-based analyses of natural frequencies of long tapered hollow steel poles

Long tapered poles are commonly used to support Closed Circuit Television Cameras (CCTV) for security and traffic monitoring. Images received from CCTV are normally distorted due to the camera’s wind-induced vibration. To minimize the vibration experienced by the CCTV through development of a damping device to be placed at the interface between the pole and the camera, identification of the poles’ different frequencies as functions of poles’ geometric variables is essential. Thus, this study presents the development of natural frequency equations for long tapered hollow poles as functions of their geometric variables based on three-dimensional finite element model (FEM) analyses by taking into account the couplings between material, contact and geometric nonlinearities. The FEM results are compared and verified with the experimental data obtained from the instrumentation of a 60 ft pole. Sensitivity study is performed to identify the effect of different geometric parameters on the overall natural frequencies of the pole. Using the results from the parametric study, empirical formulae between the geometric parameters and the first, second and third mode natural frequencies for the long tapered hollow steel poles are obtained.