Fatigue Reliability Assessment of Potential Crack Initiation of Tube-to-Transverse Plate Connections for Cantilever Sign Support Structures

Abstract

Tube-to-transverse plate stiffened connection details are widely used in cantilevered sign support structures in New Jersey and many other states. This stiffened fillet-welded connection showed a lower stress level than the socket connection at the fillet weld toe at the base. However, the tip of stiffener location on the tube wall becomes a more critical fatigue crack location according the AASHTO. This paper evaluates a reliability-based fatigue assessment for the potential crack initiation at the tip of stiffener. A synthetic analysis of 1-h averaged wind speed wind data from two New Jersey weather stations was performed. The wind data were transformed to the transient domain to represent the turbulent natural wind phenomena and the effective stress ranges and number of cycles were obtained using the rainflow counting technique. To evaluate fatigue resistance of these connection details, existing fatigue test data of fatigue crack initiation at the tip of stiffener were analyzed and a statistical analysis of linear stress-life (S–N) fatigue data provided fatigue coefficients. The probability of fatigue crack initiation versus time of sign structures with different orientations of sign panel was determined using a reliability-based fatigue assessment approach. Results showed that the probability of crack initiation during the life span is dependent on wind cycles, orientation, and fatigue coefficients obtained from experimental S–N curves. The results can be used to estimate inspection frequencies of this critical detail in sign structures.