Keywords: buckling, differential settlement, dynamic analysis, transmission line, steel tower, earthquake.

The electric power supply system mainly consists of power plants, electric power transmission facilities and substations and electric power can be supplied only when all of those facilities function together. Therefore maintaining a functioning system is critical matter for securing the electric power supply. Damage of transmission towers located on trunk line network especially cause a huge social impact. Many large typhoons have seriously damaged transmission facilities in Japan. With this experience the Japanese design guideline was reviewed in terms of wind load which is a dominant element in steel tower design. Electric power transmission facilities designed with static load converted from wind and icing loads have been traditionally regarded as secure against seismic loading. Therefore tower bodies are becoming larger as much more electric power is needed to be transmitted at high voltages. However in September 1999 when the Ji-Ji earthquake hit Taiwan, many transmission line towers collapsed. This was an unprecedented quake disaster of transmission line towers in Japan. Studies [1,2,3] conducted in the past focused on towers that collapsed even though Taiwan's design specification was slightly stricter than that of Japan. The importance of seismic performance evaluation of steel towers has been pointed out. In a previous study [4], the effects of ground differential settlement on seismic performance of transmission line towers were confirmed by using a single tower model. This paper describes the development of a simplified model for a transmission line tower considering the influence of adjacent transmission line towers. Eigenvalue analysis and dynamic response analyses were conducted using two types of models. Differences of vibration characteristics and dynamic behaviour between both models were compared. A simplified model for a 220kV transmission line tower considering the influence of adjacent transmission line towers was proposed. The models can accurately simulate the dynamic behaviour of the steel tower during an earthquake. Vibration characteristics and dynamic behaviour were made clear by the dynamic response analysis using the proposed models. The influence of adjacent transmission line towers was clarified. This led to the conclusion that transmission lines greatly affect the seismic response of a central tower in the longitudinal direction at the time of earthquakes.

1

Japan Society of Civil Engineers, "The 1999 Ji-Ji Earthquake, Taiwan - Investigation into Damage to Civil Engineering Structures", 1999.

2

T. Mazda, H. Otsuka, H. Uchida, S. Ikeda, "A study on earthquake responses of steel tower with additional damping", ASME PVP-Vol.428-2, Seismic Engineering 2001, 43-48, July 2001.

3

T. Mazda, H. Otsuka, S. Ikeda, K. Uno, "A study on damage of transmission steel tower with unequal legs in the Chi-Chi earthquake Taiwan", Proceedings of 13th World Conference of Earthquake Engineering, Vol. DVD No.739, 2004.

4

T. Mazda, M. Matsumoto, N. Oka, N. Ishida, "Evaluation of the Seismic Behaviour of Steel Transmission Towers with Different Boundary Conditions", in B.H.V. Topping, J.M. Adam, F.J. Pallarés, R. Bru, M.L. Romero, (Editors), "Proceedings of the Tenth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 329, 2010. doi:10.4203/ccp.93.329

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