Civil Engineering Association

Condition Indexing and Hazards Analysis for Communications Towers

Design and construction of the Missouri Department of Transportation (MoDOT) two-way radio network was initiated in the 1950’s and 60’s and was motivated primarily by the need to provide a statewide communication system for civil defense related issues. Today, the system is one of the largest networks in the state for providing voice and data communications associated with daily field operations as well as during times of emergency. Increasing reliance on the network is envisioned in the future to support wireless interoperability (e.g., with police and fire) and to support an increasing load of data communications for intelligent transportations system (ITS) infrastructure. Growing concern regarding the network’s performance during natural hazard events, most notably the possibility for significant earthquakes originating from the New Madrid Seismological Zone, has stimulated the desire for a comprehensive analysis of the network and the development of systematic asset management tools. A recent statewide emergency preparedness exercise involving a mock 6.7 magnitude earthquake revealed that the chief obstacle encountered as field crews attempted to communicate with each other was failure of the radio towers. Many of the towers are over 40 years old and in relatively poor physical condition. The primary objectives of this project were (1) to develop a rational condition indexing (CI) system as an asset management tool that may be used to systematically quantify the physical condition of towers in the network; (2) to conduct detailed dynamic and static structural analyses of key towers under seismic, wind and ice loading; (3) to evaluate the general effects of physical deterioration (e.g., corrosion related to aging) on tower dynamic response and stability; and (4) to develop a centralized electronic database. A CI system has been developed to quantify the physical condition of guyed communications towers. Use of the proposed system is demonstrated for two towers (Taum Sauk and Ashland) selected to represent towers in relatively poor and relatively good condition, respectively. Results from structural analysis indicate that the Taum Sauk tower (as built condition) is not loaded to near its capacity under simulated seismic loading. The Taum Sauk tower is shown to pass TIA-222-F code specifications with respect to wind and ice loading. Deterioration to the Taum Sauk tower was simulated by reducing the cross sectional areas of the guy cables, diagonal braces, and axial leg members. A free standing tower in Kansas City was also analyzed and is shown to be loaded to 2% over capacity according to TIA-222-C but meets the more recent 222-F code requirements. An electronic web-based database was developed for implementation into management of the tower network. General recommendations for implementing the results of these efforts are provided, which includes a recommendation to consider the proposed CI approach for a wide range of infrastructure managed by MoDOT.