The existing codes for the inspection and evaluation of highway bridges utilize a semi-empirical framework to determine the residual bearing capacity of concrete structures. This approach primarily relies on inspectors’ subjective assessments for classifying the condition of the bridges, which is both time-consuming and potentially inconsistent to the design codes. Since such a method is inadequate for managing the expanding infrastructure of bridges, there is an urgent need for a more efficient and objective technique that aligns with established design codes. To address this, we propose utilizing the reduction of bending stiffness as an indicator of the residual bearing capacity of a bridge girder, in accordance with the design code and the results from a failure test of a prestressed concrete T-girder. Following this, we introduce the Tap-scan technique for damage identification, which is capable of efficiently detecting the reduction of bending stiffness without the need for traffic blocking. By integrating these two strategies, we have developed an innovative approach for assessing the residual bearing capacity of concrete girder bridges. The effectiveness of this approach is confirmed through a practical application on an existing bridge.