Abstract: In-situ stresses are critical to the assessment of a bridge state and reliability. According to the long serving time, complex stress state, large component size and predominant axial load of bridge concrete structures, the influence functions for uniaxial stresses are established, which correlate the relaxed strains on the surface with the unknown in-situ stresses. A thin-wall ring is adopted as a stress release zone, and the influence functions for different measurement fields are calibrated using the finite element method. Incremental drilling experiments are conducted to identify the in-situ stresses of concrete specimens subjected to uniform uniaxial stresses. The results show that: the influence functions give an effective description of the correlation between the in-situ stresses and relaxed strains on the surface, which is in an agreement with the experimental results and verifies the feasibility and applicability of the proposed method; the accuracy loss caused by the inhomogeneity and randomness of concrete can be reduced via the synthesis of multiple strain gages and the optimization of multi-step results; the identification stability is also affected by the sensitive grid size of strain gages.