Analysis of Environmental and Typhoon Effects on Modal Frequencies of a Power Transmission Tower

Abstract

The structural health monitoring of power transmission towers (PTTs) has drawn increasing attention from researchers in recent years; however, no long-term monitoring of the dynamic parameters of PTTs has previously been reported in the literature. This study performed the long-term monitoring of an instrumented PTT. An automated subspace identification technique was used to extract the dynamic parameters of the PTT from ambient vibration measurements taken over approximately ten months in 2017. Ten target modal frequencies were selected to explore the effects of environmental factors, such as temperature and wind speed, as well as the root-mean-square (RMS) acceleration response of the PTT. Variations in the modal frequencies of approximately 2% to 8% were observed during the study period. In general, among the environmental factors, the temperature was found to be the primary cause of decreases in the modal frequencies, except in the case of some of the higher modes. Typhoon Nesat, which affected the PTT on July 29th, 2017, seems to have decreased the modal frequencies of the PTT, especially for the higher modes. This reduction in the modal frequencies seems to have lasted for approximately two and a half months, after which they recovered to their normal state, probably due to a seasonal cool down in temperature. The reduction percentages in the modal frequencies due to Typhoon Nesat were quantified as approximately −0.89% to −1.34% for the higher modes, but only −0.07% to −0.46% for the remaining lower modes. Although the unusual reductions in the modal frequencies are reported in this study, the reason for this phenomenon is not clear yet. Further studies would be required in the future in order to find the cause.

Stochastic stress response and dynamic reliability evaluation for transmission towers with semi-rigid behaviors

“…where 𝜹(𝑡), 𝜹(𝑡), and 𝜹(𝑡) are the vector of acceleration, velocity, and displacement of nodes, respectively; K (𝚯 𝑠 ), M (𝚯 𝑠 ), and C (𝚯 𝑠 ) are the stochastic stiffness, mass, and damping matrices of STTTs-SRB, respectively, which are determined in the following subsections; F(𝚯 𝑤 , 𝑡) is the external stochastic wind load vector and is calculated as [23] F (𝚯 𝑤 , 𝑡) = 0.5𝜌 𝑎 [ v(ℎ) + 𝒗 (𝚯 𝑤 , 𝑡)] 2 𝜇 𝑠 𝐴 𝑠 (10) where v(ℎ) is the mean wind speed at the tower height of ℎ; 𝒗 (𝚯 𝑤 , 𝑡) is the stochastic vector of fluctuating wind speeds, which is simulated and determined by the dimension-reduced probabilistic simulation approach [17] ; 𝜇 𝑠 is the drag coefficient of transmission towers; 𝜌 𝑎 is the air density; 𝐴 𝑠 is the projected area of transmission towers.…”

“…Shen et al and Li et al studied the effect of conductor and insulator breakages on the dynamic response of transmission tower-line systems, respectively [6,7] . Additionally, some studies [8][9][10][11][12][13][14] focused on the determination of dynamic characteristics (e.g., modal parameters) of tower structures, and other research efforts [15,16] aimed to conduct the size and shape optimization and wind-induced vibration control for guyed structures. Furthermore, owing to the uncertainties associated with wind loads, materials, and dimensions, structural responses of transmission towers would exhibit random characteristics.…”

Identification of modal parameters of long-span bridges under various wind velocities

“…Through wind tunnel tests and field measurements, Chang et al (2022) found that the aerodynamic damping ratio increases approximately linearly with the wind velocity. Hsu et al (2020) showed that the modal parameters, especially the modal damping ratios, are significantly affected by the wind velocity. Meng et al (2019) found that the modal frequencies of the first lateral and vertical modes depend on the wind velocity, and the modal frequency decreases with the increase of the wind velocity.…”