Analysis of viscoelastic tapered pylons used in transmission lines due to ground vibrations including soil-structure-interaction effects

Abstract

This work reports on the influence that mass attachments and soft soil support conditions have on the vibratory motion of flexible pylons with non-uniform cross-section, both for axial and flexural vibrations induced by ground motion. The use of such structures is pervasive, both in civil and in mechanical engineering. In particular, the tapered pylon considered here is used in electrified railways to support transmission lines and possibly other types of apparatus. We first present an analytical solution to the governing equations of motion of an inhomogeneous beam, which entails the recovery of the natural frequencies in the presence of an attached top mass and of a compliant base support represented by soil springs. This is followed by the complete solution for the case of harmonic ground motion. Results are presented in term of transmissibility functions, defined as the ratio of the top pylon displacement amplitude to that of the base motion. The aim here is to identify the frequency range for which the presence of a top mass, which may also act as a passive damper, and of compliant soil support, which may also act as a base isolator, is either beneficial or detrimental in terms of minimizing the kinematic field induced in the pylon by ground vibrations.