Influence line theory supported single sensor-based strain feature for bridge defect diagnosis

This study established a theoretical foundation for single-sensor-based M -value feature derived from field bridge strain responses. Its ability to detect bridge structural damage was validated and explained through the influence line theories. More importantly, the variations of such a feature were further connected to the shifts of neutral axis (NA) positions. By correlating the NA position with the cracking depth of the section, the application of a single-sensor-based M -value feature was innovatively expanded to quantify bridge minor defects, such as small cracks within the section, where a design value for intact structures was proposed, offering a benchmark for quantitative bridge condition assessment and guidance for practical bridge management. A case study involving a two-span continuous bridge demonstrates the practical application of the developed feature in scenarios that lack original design information of bridge sections.