Fatigue performance of externally post-tensioned steel–concrete composite girders

Understanding the fatigue behavior of retrofitted beams in bridge structures is vital. The effects of pre-fatigue conditions on the efficacy of retrofitting tend to be overlooked. In this paper, five specimens were experimentally tested under fatigue. The effects of external retrofitting on the cyclic crack patterns on the concrete flanges, cyclic incremental deformations, and strains were investigated with various pre-fatigue conditions. The pre-fatigue conditions included exposure to outdoor environmental changes, plastic deformations, and prior cyclic loading. The results showed that external PT enhanced the performance of the individual components of the composite specimens, which improved the overall fatigue performance of the strengthened specimens. However, the strengthened specimens experienced longitudinal fatigue cracks in the concrete flanges because of post-tensioning. The pre-damage conditions due to prior cyclic loading and environmental changes caused greater damage in concrete around the studs relative to the plastically pre-deformed strengthened specimen and led to more incremental deformations and strains.