Analytical and Experimental Modal Analysis of Electrical Transmission Tower to Study the Dynamic Characteristics and Behaviors

Abstract

Experimental modal analysis of electrical transmission tower has been a challenging task for transmission tower researchers and design engineers in industry all over the world. Requirement of large numbers of sensors and accelerometers have been major constrain. In this study an innovative approach has been developed to investigate the dynamic characteristics and behavior of tower structure through analytical and experimental modal analysis. Firstly, a scale down (1:15) prototype model of transmission tower structure has been constructed with mild steel straps, joint together by welding, for modal testing. Modal hammer test has been conducted on the prototype tower model for extracting modal parameters; modal frequency, modal damping and modes, of the tower model which representing the actual tower structure. Secondly, the transmission tower structure has been modeled in standard finite element tools and analyzed analytically for natural frequencies. The first six natural frequencies and corresponding mode shapes have been determined analytically and first six natural frequencies have also been determined experimentally and compared with each other. The first six natural frequencies are determined analytically, the frequency range of 2–9 Hz has been found. The analytical and experimental modal analysis of transmission tower structure has been found to be in correlation with some differences. The maximum natural frequencies percentage difference 11.1% has been found; between the scale down model and the stand software model. Additionally, the tower structure has been modified and optimized to improve the stiffness of the diaphragm as per specification and practical limitations. The first order natural frequency of the modified tower has been reduced to 2.171 Hz from the 2.1773 Hz.