## 4 Rehabilitation Measures and Rehabilitation Effect  
As highlighted in the previous analysis results, the exact cause of the abnormal deformation of the bridge is the inconsistency of the temperature field between the top and bottom plates of the box girder. However, the internal force due to the temperature gradient was stored in the steel box girder, and it is difficult to release by cutting and reforming the box girder of the formed bridge. To solve the abnormal deformation, rehabilitation measures should consider technology, cost, and the necessary construction period. From the monitoring and numerical simulation, the following steps were taken and put into engineering practice. Step 1: Increase the force of the tie rods by 1000 kN based on the original design, and adopt the temporary concrete block, shown in Figure 31a, to position the end of the box girder downwards while pre-stressing the tie rods. Step 2: Remove the temporary concrete block, jack up the steel box girder and lower the pad-stones by 45 mm, and remove the bearing anchor bolts and the original bearing. Drop the elevation of the box girder, replace the new bearings, and then position the whole steel box girder in place, as shown in Figure 31b. Figure 31: Rehabilitation measures: (**a**) Adopt the temporary concrete block to position the end of the box girder downwards. (**b**) Replace bearings by jacking up the overall box girder. Figure 30: Theoretical deformation of the temperature gradient in the China standard (JTGD60-2015) (unit: mm). Step 3: Adjust the force of the hanging rods to improve the whole deformation of the box girder. Add the pressure weight by casting concrete inside the compartment cell at the end of the box girder, to increase the reserve force of the support reaction. After the above adjustment, the side support (support away from the bridge axis) could have a sufficient pressure reserve to prevent the negative reaction force of the support. The rehabilitation-measures process mainly involved the following steps: After the overall jacking-up of the box girder, all the bearings were removed to adjust the padstone height; the elevation at the whole bearing supports was lowered by 4.5 cm in stages; and the force of the hanging rods was adjusted according to the FE simulation. The primary issue dates before and after the rehabilitation measures are shown in Table 3.  
The changes in the elevation of the box girder are shown in Figure 32. Figure 32a shows the elevation change of the end of the box girder above abutment #0. The elevation of this section increased by 4 cm after the rehabilitation measures. Figure 32b shows the elevation change of the mid-span of the main span of the box girder, and the overall elevation at this section increased by 3 cm after rehabilitation. Figure 32c shows the elevation change of the box girder at the section of hanging rod #11, and the overall elevation of this section increased by 5 cm. Figure 32d shows the elevation change of the end of the box girder above abutment #3. The elevation of this section increases by 6 cm after the rehabilitation measures. The contour map deformation of the box girder in the main span is shown in Figures 33 and 34. The deformation before treatment demonstrated obvious parabolic characteristics between the longitudinal section and the cross-section, and the maximum deformation was \(-11.5\) cm, forming a concave \"pot cover\" shape as shown in Figure 33. After the treatment, the deformation ranged from \(-0.6\) cm to \(-0.8\) cm, and the error was close to the error value of \(-0.7\) cm. This result means that rehabilitation measures improved the overall linearity of the bridge deck. To ensure that bridge deformation after rehabilitation does not develop in service, long-term monitoring of the deformation was performed at different temperatures. Representative deformation monitoring data are shown in Figure 35, from 16 January 2020, 30 March 2020, and 7 June 2020, with temperatures of 3 \({}^{\circ}\)C, 19 \({}^{\circ}\)C, and 24 \({}^{\circ}\)C, respectively.