In this study, the high-cycle fatigue behavior of bridge connections subjected to distortion-induced loadings (generating multiaxial stresses) and strengthened with prestressed elements were experimentally investigated. Thereafter, appropriate critical plane-based multiaxial fatigue thresholds based on the modified Wohler curve method (MWCM) and Fatemi-Socie's (FS) criteria were used to predict the initiation of cracks in the angles considering the estimated fully reversed uniaxial and shear fatigue limits as well as residual stresses. The prestressed strengthening system was effective in reducing the mean values as a result of the prestressing force, enabling a shift in the stress state to below the initiation threshold.