A Key Contribution for Concrete Durability: Harnessing Force‐Magnetic Coupling for Stress State Detection in Reinforced Concrete Beams

Over the past 20 years, more than 200 major bridge‐collapsed accidents have occurred during their service life. The durability of reinforced concrete (RC) beams is a serious threat to the safety performance of the structures. To accurately grasp the service performance of RC beams, a four‐point bending loading experiment was conducted on RC rectangular beams, and magnetic field data were detected. The results show that during four‐point bending loading, the damage modes of RC beams can be categorized into the elastic stress stage, stage of work with cracks, and yield stage. The change rule of the rebar tangential magnetic induction intensity ( B x ) curves varies from overlapping each other to rotating counterclockwise, finally generating abrupt changes. The force‐magnetic coupling model is optimized based on the magnetization angle. The “force‐magnetic area parameter” K σ x is proposed to quantitatively analyze the rebar stress. Finally, the stress state assessment model of RC beam rebars is established. The relative error of the assessment results is near 6.61%. The nondestructive testing and assessment of the rebar stress state inside the RC beams are realized through the comparison and verification of the experimental phenomenon analysis and the force‐magnetic coupling model. It lays a theoretical foundation for ensuring the safe operation of bridge structures and building structures during the service life.