Recent design improvements for traffic signal and sign structures incorporate fatigue load criteria related to wind. The Fourth Edition of the AASHTO Luminaire and Traffic Signal Specification (2001 with interims) specification is a significant change from past practice and often results in much larger and more costly structures. Conservative principles (envelope wind demands and infinite fatigue life) for design resulted in increased cost even for those regions historically not adversely affected by wind-induced fatigue. States that do not have steady, sustained winds and have notexperienced significant fatigue failures have rightly concerns with the larger and more costly structures. A rational basis for lowering the fatigue design loads may be appropriate. This study compares fatigue failures with respect to wind power (expressed as a function of average wind velocity). Inspection reports for approximate 2500 cantilevered traffic structures were collected and analyzed for suspected fatigue cracking. Each structure was located spatially and the associated wind power classification forthat location was determined. The inspected structures were classified as cracked or non-cracked and categorized by their wind power classification and ambient average wind velocity. The probability of a structure havingfatigue 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 fatigue performance. Structures in lower wind power classes have a lower probabilityof developing fatigue cracks. A rational procedure for designing these structures for low wind demand regions is presented.
Abstract