## 3 Structural Method of Reinforcement and Construction Stages  
### Theoretical Basis of Hollow Girder Reinforcement  
The prefabricated slab bridges that are commonly used in China are divided into solid slabs and hollow slabs according to the section form. The span of the solid slab is small. To adapt to the larger span, the hollow slab not only reduces the weight, but also gives full play to the role of materials. Therefore, the existing slab bridge is basically a hollow slab girder. To ensure that he assembled plate girder jointly bears the vehicle load, it is necessary to set the transverse connection with sufficient strength in the transverse direction. Welded steel plate and concrete hinge connections are the most commonly used connection methods. However, due to the high cost of welded steel plate connections, the use of this application is not always practical. At present, the transverse connection of the hollow plate usually adopts a concrete hinge. The common forms of the concrete hinge are round, diamond and funnel, as shown in Figure 3. Usually, the hinge joints are filled with fine aggregate concrete. In the case of a small vehicle load, this hinge joint can theoretically ensure the transfer of the transverse shear force and ensures that each plate cooperates with the force. This is also the basis of the hinged plate method in the calculation of the transverse distribution coefficient. This method is based on the fact that the hinge joints only transmit vertical shear, and the pavement structure layer does not participate in the force [21]. The calculation model is shown in Figure 4a. Figure 2: Status of the pavement of the bridge. Due to the structural characteristics of hollow slab girders and the long-term use of overload, the hinge joints and the integrated layer are common areas of deterioration, and these typically manifest as the fracture of hinge joints and longitudinal cracking of the integrated layer [22]. As a result, a large number of small hinge joint bridges built in the early stages, exhibit hinge joint cracking, and may form a single beam bearing load. To strengthen the overall effect of the linkage of hinge joints, researchers in China have changed the original small hinge joints to deep hinge joints, which increases the size of the concrete joints. The rebar in the prefabricated plate can be extended and bound with adjacent rebar and then poured into the pavement layer, and the strengthened rebar is set in the hinge joints. The purpose of this design is to ensure that the adjacent girders share the force. Inspired by this method, for a large number of existing hollow girders with small hinge joints, the transverse connection can be realized through the hinge joints and the force transfer of the stronger integral layer, especially by adding or recasting the integral layer of the pavement structure method to improve the structural performance of the hollow girder bridge. The main method of reinforcing the plate top is to set a steel plate at the hinge joints to strengthen the local stiffness so that the integrity of the plate beam is restored; however, the construction is relatively complex Another method is to recast the pavement just after cleaning the damaged bridge deck, to recover the pavement and reduce the stress transfer to the hinge joints; however, this will increase the weight. Based on these two ideas, another method involves the original pavement and common concrete structure layer. The hinge joint concrete is removed and the hinge concrete is recast, and the pavement structure layer is recast with rebar. This is the method used in this study and in the implementation. Figure 4: Different mechanics modes of hinge joints. (**a**) Mechanics mode of the common hinge for transmission of shear. (**b**) New mechanics mode of the hinge with a stronger pavement structure. Note: P1–load; gi–shear effect by hinge; Mi–bending (moment) load effect by reinforced pavement. Figure 3: Common hinge joint form of the hollow plate beam.