Dynamic analysis due to cable rupture of a transmission line tower for large river crossing in Brazil considering the soil-structure interaction

A challenging design of a transmission line (TL) is presently being carried out in Brazil: a double circuit 500kV TL in the Amazonian region. In addition to the significant length, over 1400 km in the rain forest, the design has to cope with large river crossings and severe environmental constrains. Some of these crossings demand single spans more than 2000 meters long. The crossing of the Trombetas River is one of the most important, having a total length of 5100 meters. The proposed design has located a tower on an island. Each of the two main spans is approximately 1600m long and demands two latticed steel suspension towers 190m high and a third 120m high. Moreover, these towers must be erected on concrete foundations that reach 10m above terrain level, to maintain the base of the towers above maximum river flood level. The present work describes the structural analysis of the special TL towers for this crossing. The focus is on numerical predictions of the dynamic response of the 190m high latticed steel structure subjected to cable rupture (conductors and shield wires). The entire crossing section is modeled including the two highest towers and all other elements: foundations, conductor cables, shield wires and insulator strings. To perform the analysis, direct explicit numerical integration of the equations of motion in the time domain is adopted, using the central finite differences scheme. The responses obtained by such approach are then compared to responses determined by standard practice. An additional feature of this study was the consideration of the dynamic structural interaction between the structure and the foundation (soil-structure interaction), which attained particular importance in view of the soft soil foundation at the site.