Lattice Tower Deflection and Modeling of the Structure and Spans in Practice

Within the power delivery industry, it is traditionally assumed that a lattice steel tower will not deflect enough to cause structural concerns during conductor stringing operations. However, on a recent project, an existing tower deflected significantly during stringing-ultimately affecting the stringing sequencing. The deflection was attributed to the tower’s high level of structural utilization combined with construction constraints that resulted from stringing over two major freeways. Engineers used finite element (FE) modeling software to model the tower’s observed deflection and the discrepancy in the sag of the supported spans. The FE model served to determine the cause of the deflection and provide a conductor stringing sequence to mitigate it. Field crews fabricated custom extension links that were temporarily installed to adjust the length of each conductor in the supported spans. After the conductor stringing mitigation sequence was completed, the tower and spans moved to their expected positions per the original design.