ON MODELING THE DYNAMIC RESPONSE OF THE 190M-HIGH TL TOWER FOR THE CROSSING OF TROMBETAS RIVER IN THE AMAZON REGION

SUMMARY A challenging design of a transmission line (TL) is presently being carried out in Brazil: a double circuit 500kV TL in the Amazon region. In addition to the significant length (over 1400 km) in the rain forest region, the design has to cope with huge river crossings and very severe environmental constrains. Some of these crossings demand single spans of more than 2000 meters. The crossing of the Trombetas River is one of the most important, having a total length of 5100 meters. The proposed design alternative for crossing the river has located a tower on an island. Each one of the two main spans is approximately 1600m long and demands two suspension towers 190m high and a third a 120m high. Moreover, these towers must be erected on concrete foundations that reaxh 10m above terrain level, to maintain the base of the towers above maximum river flood level. The present article describes the structural analysis of the special TL towers for this crossing. The focus is on numerical predictions of the dynamic response of the 160m high structure subjected to Extended Pressure Systems (EPS) and thunderstorm (TS) wind loads, as well as to cable rupture (conductors and shield wires). The entire crossing section is modeled, including the two highest towers and all other elements: foundations, conductors, shield cables, as well as the insulator strings. The loading resulting from the numerically simulated wind velocity field, acting on the spans, is applied directly to the entire section. Cable rupture is modeled by removing a cable element from the system, thus closely simulating the real phenomenon. To perform the analysis, direct explicit numerical integration of the equations of motion in the time domain is adopted, using the finite central differences scheme. The responses obtained by such approach are then compared to responses determined by standard practice (IEC 60826). The results furnish very valuable information on the uncertainties in modeling the system response. An additional feature of this study was the consideraation of the dynamic structural interaction between the structure and the foundation, which attained particular importance in view of the soft soil foundation at the site.