Advanced Analytical Methods for Fatigue Assessment of Ancillary Systems in Highway Bridges

Abstract

Fatigue failure is a major concern for highway sign structures due to sustained wind-loading events, which have been recognized in many states. To ensure public safety, AASHTO specifies that structures should be designed for infinite life by maintaining wind-induced stress below their constant amplitude fatigue threshold (CAFT). However, existing structures that were not designed for fatigue may contain unnoticed fatigue cracks that are difficult to detect through visual inspection, which is also time-consuming. To address this issue, a simplified analytical inspection tool was developed and implemented into computer software. The tool assesses all critical components according to AASHTO specifications for fatigue and was used to examine a failed structure, which revealed a fatigue damage crack in the vertical weld of the mast-to-arm box connection at the upper chord level. In addition, a spatial interpolation technique was proposed using Isoparametric finite element shape functions to derive wind speed records for unsampled locations from actual data recorded at known locations. This provides a better understanding of the wind events that might be the driving source for fatigue failure of these flexible structures and facilitates fatigue-life prediction by generating a full range of wind loading. Overall, this chapter contributes to improving the safety and efficiency of highway sign structures by providing effective inspection tools and wind-speed interpolation techniques.