Dynamic response analysis of transmission tower under thunderstorm downburst

Abstract

Many transmission towers around the world collapsed due to thunderstorm downbursts. It is essential to understand mechanisms of downbursts and to predict dynamic responses of transmission towers under down bursts. In this regard, a deterministic-stochastic hybrid model of downbursts is employed to simulate the time history of wind speed caused by a down burst at the site of a tower. The hybrid model is factorized as a time-varying mean wind speed component and a fluctuating wind speed component. The former is represented by the product of a vertical profile and a time function, and the latter is treated as the amplitude modulated stationary stochastic process. Both wind speeds are transformed into downburst loads acting on the tower at different levels, taking consideration of flow accelerations induced by varying wind speed and direction. A 50.5 m tall transmission tower is selected as a case study. A finite element model of the tower is established using the commercial software ANSYS, and dynamic responses of the tower subjected to downburst load are analyzed using the Newmark's method. The results show that the dynamic responses of the transmission tower under downburst taking wind direction into consideration are different from that without considering wind direction. The sensitive locations of the goblet-type transmission tower to damage under downburst are the comer of the goblet head and the first level of the mast tower.