Fiber Bragg Grating-based smart cable force sensing under bending-tension coupling

In beam string structures, cables bend under the action of struts, and the combined effects of bending, tension, and joint friction complicate force variation. Additionally, limited installation space in bent sections poses significant challenges to accurate force monitoring. This study investigates the reliability of force monitoring in fiber Bragg grating (FBG) smart cables under coupled bending-tension effects. Theoretical principles for force monitoring and the mechanical behavior of cables under bending-tension coupling are derived. Calibration tests show a maximum deviation of 1.61% between the load sensitivity coefficients and theoretical values, with maximum nonlinearity, repeatability, and lag errors of 1.13%, 0.89%, and 1.33%, respectively. Finite element simulations and experiments reveal that as the bending joint height increases, the strain at FBG measurement points rises, with a faster increase on the loading-end side. When the bending joint moves closer to the fixed end, the strain at the fixed-end FBG measurement point increases, while the strain at the loading-end point decreases, consistent with simulation results. The maximum deviation between monitored cable forces and dynamometer readings is 5.5%, with a minimum deviation of 0.2%. Finally, 95% ultimate breaking force tests show that the FBGs fractured at 8300με and 8100με, respectively, achieving a 72–89% range increase over conventional FBG sensors. These findings demonstrate the excellent monitoring accuracy of smart cables under bending-tension coupling, providing reliable technical support for force monitoring in beam string structures under complex loading conditions.