Hydraulically Actuated Macrobending Fiber-Optic Load Sensor with Symmetric Deformation for Weigh-In-Motion Applications

A hydraulically actuated fiber-optic load sensor with a four-sided deformer was developed to address limitations in macrobending-based sensing for weigh-in-motion (WIM) applications. Finite element analysis showed that the proposed design remained within safe operating limits, with a maximum stress of 0.202 MPa and a strain of 68.65% at 5.1 mm deflection. Sensitivity increases with the number of fiber coils, with the six-coil configuration achieving 0.1142 V/kg. Laboratory testing showed that the sensor exhibited nonlinear behavior at low loads and hysteresis due to the viscoelastic response of the silicone-rubber sensor housing. Static field tests produced axle-load errors below 4%, whereas dynamic measurements at 5 km/h showed larger deviations, mainly because of the hydraulic lag and structural compliance. The proposed sensor is feasible for WIM systems, but the mechanical and hydraulic designs need improvement to enhance its dynamic performance.