CorTen Steel Lattice Tower Analysis
Analysis of Deteriorating CorTen Lattice Towers (46 Transmission Lines/1,400 Miles/1,370 Towers)
Realtime’s Client had a population of structures constructed with CorTen steel, a specific type of structural steel that develops a surface patina to protect the base metal. While CorTen steel does not require painting or other surface coating, it has shown a tendency, over time, to not completely protect the base against loss of structural integrity, and has the ability to develop pack rust in the joints and crevices of a lattice structure. Items all of which tend to shorten the expected service life of a CorTen structure.
Realtime Utility Engineers was contracted to inspect a sampling of CorTen structures exhibiting rusting issues, examine the severity of the problem, and advise how the structural stability of the NYPA’s aging lattice tower system may be affected by this issue.
The initial analysis performed utilized uniform corrosion of the towers, identifying the sensitivity of significant members. This provided relative member failure sensitivity, as well as overall tower lifecycle analysis graphed over time. After a uniform corrosion analysis, individual member thicknesses were reduced in 10% increments, while other member thicknesses remained at 100% to develop a specific sensitivity analysis, indicating which members were the most critical. Finally, the extrapolated corrosion rates of individual members were applied to predict a tower failure mode. Actual field measurements of member sizes were then plotted on the graph to understand where any particular tower and tower member was in its life cycle.
Twenty percent of NYPA’s 1,370 lattice tower structures were inspected by RUE’s sister company, Quanta Technology. There were (16) different tower types inspected across (8) different transmission lines. At the same time, PLSCADD Tower models were developed for common tower types and families of the tower lines being inspected. Structural analysis models exhibiting various corrosion rates were created and field data plotted to determine reinforcement remediation priorities. This information determined the future schedule for tower remediation depending on where the tower’s physical measurements plotted in its life cycle of any given tower.