Fatigue life of piles in integral-abutment bridges: Case study

Piles in integral-abutment bridges (IABs) may experience plastic deformation and low cycle fatigue as a result of cyclic loading induced by daily and seasonal temperature variations. This paper presents guidelines that will help to determine the amount of deformation in piles, evaluate the type of deformation (elastic versus plastic), and establish the fatigue life of the piles in IABs. To illustrate the steps of the process, the case of an IAB is studied in which the length of the bridge is varied as a parameter between 122 and 549 m. The effect of bridge length on daily and seasonal strain amplitude in piles and daily and seasonal fatigue life is evaluated. Plastic deformation was observed in all bridges analyzed, indicating a possibility of low cycle fatigue in these bridges. Palmgren-Miner is used to evaluate the combination effects of both daily and seasonal temperature cycles and the contribution of each cycle type. The results show that daily cycles are the main cause of damage and that the contribution of seasonal temperature cycles is negligible. The fatigue life was found to be about 42 years in a bridge with a length of 122 m and decreases exponentially as the length of the bridge increases to 9.5 years in a 549-m-long bridge.