Disease analysis of existing steel mixed girder bridge

• bridge bearing capacity is insufficient, which can not meet the existing traffic load requirements.

• Corrosion of bare steel beams

• Steel beam fatigue

• Longitudinal cracking of concrete wing of steel-concrete composite continuous beam

• Transverse cracking of concrete deck slab in negative bending area of steel-concrete composite continuous beam

• Partial rupture or corrosion of concrete bridge deck

• Shear bond is cut of

Other problems with low design load at early stage are easy to be replaced or reinforced because of overloading and long exposure to wet air and rain, which easily make the connecting bolts or rivets loose or broken. In recent years, due to the heavy use of ice melting salt in cold areas, the subsidiary facilities such as the expansion joint drainage pipe of the steel concrete composite beam are badly damaged, and the lack of regular maintenance makes the bridge state less obvious to the steel concrete continuous beam bridge, the web or floor of the steel beam compression zone will be caused by accidental overloading or heating up. Local drums are produced, that is, local instability. If the local instability is not repaired in time, it will also reduce the overall structure's ability to resist instability and indirectly reduce the bearing capacity of the bridge.

Strengthening and reforming strategy

• Externally prestressed reinforcement

• Externally bonded FRP 

• Repair of cracks or corrosion defects of steel beams

• Replacement of concrete bridge deck

• Change the shear bond

• Treatment of partial instability of steel plate

Summary

(1) the most common and most likely diseases of existing steel-concrete composite girder bridges include: Due to corrosion, fatigue, high stress accumulation and welding residual stress, cracks appear in the members of steel beams, resulting in brittle fracture of members. The special structure and construction process of the steel-concrete composite beam bridge cause the cracking of the deck slab and the longitudinal cracking of the deck slab in the negative moment area of the composite continuous girder bridge. Local damage and corrosion of concrete bridge deck; shear key or shear failure.

(2) the existing research shows that when the bearing capacity of the existing steel composite beam bridge is insufficient or the load level is required to be raised, the strengthening method of prestressing or sticking carbon fiber fabric can be used in vitro. These two methods can effectively improve the bearing capacity of existing steel reinforced concrete composite girder bridges, and the increase can be achieved in general.

(3) the shear bond is the key to ensure the joint work of the steel beam and the concrete bridge deck. If it is damaged because of its fatigue or excessive longitudinal shear, it must be replaced. Otherwise, the combined action of steel-concrete composite beams will no longer exist, and will be degenerated into composite beams, and its bearing capacity will reduce the bridge.

(4) the steel concrete composite beam bridge has the common problems of the reinforced concrete structure and the steel structure, such as the open, damaged and steel girder corrosion, the fatigue crack, the drum and the other diseases of the concrete bridge deck, as well as its unique personality problems. For example, the fatigue and cutting questions of the shear bond must be analyzed specifically for the concrete diseases. And then adopt targeted reinforcement strategy to achieve the purpose of reinforcement.