The client wanted to replace three (3) aging tangent lattice tower structures with Valmont Pyramax structures, HD-3, HD-4 and HD-5, on the Higgins – East Clearwater 115kV transmission line that crosses over Old Tampa Bay near Safety Harbor, Florida. An inspection had been performed to document the condition of the existing marine foundations above and below water. The condition assessment helped determine if the existing marine foundations could be reused for the new structures. Various conductor types had been investigated for use on this crossing to meet the ampacity requirements, vertical clearance requirements and the goal of reducing the overall structure heights as compared to the existing lattice towers.
The conductors selected were 1272 ACSS/TW (pheasant) and 1622 ACCR/TW (Pecos) for the 230kV line. The structures were also designed for two OPGW cables.
A goal of the project was to be able to reuse the existing foundations. Analysis of the existing foundations indicated this was feasible with moderate structural upgrades consisting of steel bracing. Condition upgrades were included in our design package to ensure a suitable service life for the foundations.