Monitoring of Vertical Displacement of Concrete Slab End at Pavement Joint Based on FBG-Dowel Bar Signal

The vertical displacement of pavement concrete slab end at the joint is prone to emerge in its long-term service. It would lead to the occurrence of the joint faulting and other diseases, bringing safety hazards to the vehicles; therefore, the monitoring for the vertical displacement of joint slab end is of great practical significance. According to the Timoshenko classic theory, the shear force transmitted on the dowel bar and the bending moment on both sides of the joint can be calculated according to the strain of four points on the dowel bar, and the vertical displacement of the slab end can be calculated by the bending moment and the shear force. In this paper, relying on the calculation method of the strain of dowel bar converting to the displacement of concrete slab end, a new kind of dowel bar contained four fiber Bragg gratings (FBG) for strain measuring, which is called an FBG-dowel bar, was presented to monitor the vertical displacement of slab end. The feasibility of monitoring the vertical displacement of slab end based on the signal of FBG-dowel bar was verified by the experiment loading on the joint of concrete slab specimens. A curvilinear model ($\mathrm{\Delta }\lambda -{\omega }_s$ model) between the wavelength drift ($\mathrm{\Delta }\lambda$) of FBG on the dowel bar node and the vertical displacement of the slab end (${\omega }_s$) at joint was established by regression fitting. In addition, the numerical simulation of a full-scale concrete slab within the vertical displacement of slab end in the range of $0–1.0\mathrm{mm}$ was used to verify the validity of the calculation method and the $\mathrm{\Delta }\lambda -{\omega }_s$ model applied to actual working conditions.