## 3 Monitoring Program and Results  
In order to ensure the safety and stability of the leveling process of T-shaped rigid bridges [30; 31], it is necessary to monitor the stresses of some bridge members in real time [32; 33]. However, the stress at the steel spherical hinge cannot be directly monitored by the sensor. Therefore, the monitoring scheme in this paper is to install vibrating string stress gauges underneath the steel spherical hinge, the spherical hinge steel frame, and the circular track. By monitoring the stress change in the steel support structure in the lower turntable, the deflection of the T-shaped rigid bridge in the process of turning can be derived, which indirectly reacts to the change rule of the stress at the steel spherical hinge. For this monitoring, nineteen vibrating string surface stress gauges were placed. The arrangement scheme of the stress gauges is shown in Figure 25, where all the stress gauges are welded to the steel support structure of the lower turntable at the same depth of arrangement. The actual arrangement of the stress gauges is shown in Figure 26a, where changes in stress values are accurately monitored by welding the iron blocks at the ends of the stress gauges to the steel support structure. The actual arrangement of the encoder is shown in Figure 26b; its function is to monitor the turning angle of the T-shaped rigid bridge in real time and summarize the data through the collection box, so as to obtain the correspondence table between the turning angle and the stress value. The data collection box is shown in Figure 26c. Figure 23: Cloud diagram of upper steel spherical hinge (eccentricity is 257.4 mm): (**a**) equivalent stress cloud; (**b**) total deformation cloud. Figure 24: Cloud diagram of lower steel spherical hinge (eccentricity is 257.4 mm): (**a**) equivalent stress cloud; (**b**) total deformation cloud. As the T-shaped rigid bridge turned, the stress values monitored by each stress gauge are shown in Figure 27,b. Stress gauges were installed at the concrete steel support structure directly below the steel spherical hinge; the variation curves of the monitored stresses are shown in Figure 27. Stress gauges were installed at the concrete steel support structure below the lower steel spherical hinge base bracket and supporting legs; their monitored stress profiles are shown in Figure 27. It is obvious that the stress values at each stress monitoring point will change with the turn of the body. This suggests that multiple unfavorable factors, such as unbalanced traction forces and wind loads, can have an impact on the smoothness of the bridge rotation during the actual turning process. Initial stress of the sensor at 0\({}^{\circ}\) is the increment of the stress value at each monitoring point during the period from the lower turntable concrete placement to the completion of bridge construction. From the figure, it can be seen that with the rotation of the bridge, the stress value of each monitoring point under the steel spherical hinge changed significantly; the magnitude of the change was within 5 MPa. The stress difference between the start of the turn (0\({}^{\circ}\)) and the end of the turn (88\({}^{\circ}\)) is less than 5 MPa. This indicates that the transfer bridge complies with the construction requirements despite the slight deflection. In the data, only the stress value numbered 1-1 decreased by 1.76 MPa; the stress values of the rest of the monitoring points increased to varying degrees, indicating that the right side of the bridge weighed the most before the turnaround. Figure 26: Test apparatus: (**a**) stress gauge; (**b**) encoder; (**c**) data collection. Figure 25: Stress gauge arrangement scheme. The magnitude of the change in stress values at the lower steel spherical hinge base bracket was greater. It indicates that the bridge was not in a smooth condition during the turning process. Slight deflection occurs under the influence of external unstable factors.