Influence of spatial variation of ground motions on dynamic responses of supporting towers of overhead electricity transmission systems: An experimental study

Abstract

An overhead electricity transmission system typically consists of a series of steel lattice towers supporting transmission lines (referred to herein as the tower-line system). Recent major earthquakes suggest that the tower-line system constructed based upon existing knowledge can be vulnerable. A tower-line system typically extends over a large region and it may be subjected to spatially varying ground motions during an earthquake event. The influence of spatial variation of ground motions is not explicitly considered in current design of the system and very limited research (particularly, experimental research) has been completed in this regard. A two-phase experimental program was conducted using an array of three shake tables to quantitatively assess the respective impact of three factors causing non-uniform excitations (namely, the wave passage effect, the ground motion coherency loss effect, and the local site effect) on dynamic response of the supporting towers. Test results show that neglecting the wave passage effect may result in underestimates of peak dynamic responses of the towers. Additionally, it is found that non-uniform ground motions with a higher degree of coherency loss tend to amplify tower dynamic responses. Furthermore, test results reveal that when the soil at the bases of adjacent towers becomes more flexible, the resulting spatially varying ground motions cause larger tower dynamic responses.