Pre-damage effect on the residual behavior of externally post-tensioned fatigued steel-concrete composite beams

Steel-concrete composite beams in highway bridges are susceptible to various types of damage during their service life. These damages can greatly affect the structural performance and shorten the fatigue life of bridges. The efficacy of adding external post-tensioning, as a strengthening technique, to steel-concrete composite beams that are subjected to fatigue loading is not well investigated. Therefore, this study includes fatigue testing of post-tensioned steel-concrete composite beams with various types of pre-damage. Three of the tested samples were subjected to outdoor environmental changes, cyclic preloading, and static overloading as pre-damages before applying the external post-tensioning. The strengthened samples were exposed to fatigue tests to a million cycles under four-point bending. Samples without pre-damage were tested as references to those with pre-damages. The crack patterns in the concrete decks were evaluated during these tests. Static tests to failure were performed to explore the residual capacities, deformations, and strains of all fatigued samples. The crack patterns in concrete decks were significantly affected by the type of pre-damage that was applied before the post-tensioning. The static overloading pre-damage reduced the number of cracks and their rate of propagation while the exposure to outdoor environment pre-damage induced more cracks, which negatively affected the crack patterns during fatigue loading. Subjecting the sample to plastic deformation pre-damage slightly improved its performance in terms of residual stiffness and ultimate load. The residual ultimate load was increased by 7% relative to the fatigued sample without pre-damage. However, the ductility was reduced by 40% due to the initial plastic deformation. This reduction in ductility was combined with a decrease in the interface slippage between the concrete deck and steel flange.