# A New Top-Mounted Shear-Hinge Structure Based on Modal Theory and Rubber-Pad Damping Theory
## 6 Conclusions  
To address the problem of damage to TMSHs under long-term train loads, a field investigation was conducted on an old and a new SSFST line. A refined model of the TMSH was established for dynamic characteristic analysis, and the simulation results were verified via indoor hammering tests on both structures. The following conclusions were obtained:  
1. Through field research, it was determined that the main damage to the top-mounted shear hinges was mainly characterized by shear-rod fracture, bolt loosening, and broken bolts. Among these, bolt loosening was common in both the new and old lines and the curved section had more damage compared to the straight section. Based on rubber-damping theory, a new structure was formed by adding rubber mats between the shear-hinge structure and the metal pad. It is expected that the service life will be extended by reducing the shear hinge's natural frequency so that the natural frequency is located in the region of a lower vibration level of the floating-slab excitation, while also reducing the vibration amplitude in the higher part of the floating-slab excitation in the range of 400-3000 Hz. 2. By establishing a refined FEM of the SSFST and a refined model of the TMSH, the strength of the TMSH structure after the addition of the rubber pad was verified to be adequate. The pre-stress modal analysis of the TMSH assembly proved that the second-, third-, and seventh-order modes were the main causes of shear-rod fracture, and the reduced pre-stressing force under the third- and fifth-order modes of transverse vibration caused the bolts to loosen. 3. Upon comparing the vibration levels of the TMSH structure before adding the rubber pad and after adding the rubber pad under four different working conditions, it was found that, except for the linear section, the vibration level caused by floating-slab excitation can be effectively reduced in the curved section. It was reduced by eight times in the 4.8 m curved section and by at least three times in the 3.6 m curved section. Therefore, it is tentatively believed that adding rubber padding to the curved section can effectively extend the service life of the TMSH. 4. After adding the rubber pad, some natural frequencies higher than 3000 Hz were reduced to 400-3000 Hz in the high-vibration area of the floating slab. Due to the damping effect of the rubber pad, the transverse vibration amplitude of the easily damaged parts was reduced by more than 30 dB. Additionally, the transverse vibration energy of the shear rod was attenuated by 59.71 dB, the vertical vibration amplitudes of the rear-end bolt and mid-end bolt were slightly increased, and the vertical vibration amplitudes of the shear rod and the front-end bolt were reduced by 47.97 dB and 5.28 dB, respectively. It has been proven that the rubber pad can effectively reduce the problems of shear-hinge fracture, bolt loosening, and broken bolts. 5. The old and new TMSH structures were tested indoors using hammering tests to assess their modalities and validate the two simulation models separately. It was finally demonstrated, from both the test and simulation perspectives, that the new structure can effectively reduce the vibration amplitude of TMSHs when resonance occurs at the excited intrinsic frequency, thus delaying the occurrence of damage. Discussion: This study innovatively analyzed the causes of damage to TMSHs (which have not been investigated in any of the current published literature). In order to reduce the occurrence of damage, a new type of TMSH was designed according to modal theory and the principle of damping using rubber pads. Through tests and simulations, it was proven that, after adding a rubber pad, the natural frequency of the TMSH decreased to that of the low-vibration region of the floating slab.