PUSHOVER AND DYNAMIC BEHAVIOR OF TRANSMISSION TOWERS UNDER HIGH INTENSITY WIND

Abstract

In January 2010, 81 towers had failed at Aswan, Egypt, as a result of high intensity wind (HIW). The wind speed reached a value of 200 km/h., and the pressure induced from this wind was 193 kg/m2, which is strongly higher than the design values. The economic drawbacks from the interruption of the electrical network are huge. Thus the study of the modes of failure and the causes of collapse of these towers are essential. The lessons drawn from this disaster leads to the necessity to re-evaluate the design wind speed and the requirement of mitigate the (HIW) effects. The main focus of this research was directed to study the behavior of the transmission tower under high intensity wind and the reasons for failure to mitigate the HIW. The capacity assessment and failure mechanism of two types transmission towers in Aswan region have been studied.500 kv tower designed in the 1964 and 220 kV tower designed in the 1980. Transmission tower design is modeled in the structural analysis software SAP 2000, which is selected due to its handling of nonlinear material properties and 3-D numerical simulation capability. The analysis considers both material and geometric nonlinearity. A comparison is made between two methods for nonlinear inelastic analysis, the nonlinear static pushover method and incremental dynamic analysis method. The feasibility of employing nonlinear pushover analysis and incremental dynamic analysis to capture the maximum capacity of transmission towers to the wind loads have been examined. Recommendations for the design engineer regarding the mitigation of the failed towers are illustrated.