Use of wind power maps to establish fatigue design criteria for traffic signal and variable message structures

Recent design improvements for traffic signal and sign structures incorporated fatigue load criteria related to wind that are producing significant increases in joint size and cost. The Fourth Edition of the AASHTO Luminaire and Traffic Signal Specification (2002 with interims) specification is a significant change to past practice and typically results in much larger and more costly structures. The revised specification applies conservative principles (envelope wind demands and infinite fatigue life) for design in critical regions; hence, the larger and more costly structures for all regions. Thus, the states that do not have high wind demands and have not experienced significant fatigue failures have concerns with the larger and more costly structures. States are searching for justification before accepting the new fatigue design requirements. This study examines and compares fatigue failures with respect to wind power (expressed as a function of wind velocity). In this study inspection reports for cantilevered traffic structures and high-mast luminaires were collected and analyzed for suspected fatigue cracking. Each structure was located spatially and the associated wind power classification for that location was noted. Finally the structures were classified as cracked or non-crack and then categorized by their wind power classification. This study found that probability of a structure having fatigue cracks increases with greater wind power classifications. Structure orientation, pole diameter, mast arm length, in-service age, along with other details were also studied for their roles in in-service structure fatigue cracking. The study shows that structures in wind power class one have a lower probability of having fatigue cracks (less than 8.5%) at any given time.;Keywords. Cantilevered Traffic Structures, High-Mast Luminaires, Fatigue Cracking, Wind Velocity, and Wind Power Classification.