Seismic assessment of transmission towers

In the 21st century, necessity for the electricity is growing more and more every day. In order to transfer huge amount of electricity, engineering is finding its way between mountains, rivers and valleys with the help of electricity transmission lines. However, external obstacles are not limited to geographical characteristics of the environment but also natural hazards such as earthquakes as the supply of electricity must be continuous in terms of economic and social outcomes. In order to keep continuous supply, seismic design of electricity transmission lines is proven to be very crucial in the late decades as a lot of catastrophic events were witnessed. In light of this need, an electrical transmission line in Istanbul region is instrumented with accelerometers and a modal identification study is conducted. Natural frequencies of the system are obtained by frequency domain decomposition method. These results are compared with modal values obtained from finite element model (FEM) of the system created according to the technical drawings. Furthermore, as transmission lines covers long spans, spatially varying ground motion excitations are simulated and applied in time history analysis to capture the realistic response of the system. In this study, it is shown that spatially varying ground motions and FEM updating based on modal identification results are significant in the determination of seismic demand on electrical transmission lines.