1. Overview

The life cycle of bridges must undergo three stages: construction, operation and aging. Although the bridge construction in the early stage fully considered the near and long-term economic development and social needs, using the most advanced technology and materials, but still difficult to get rid of historical limitations. With the development of science and technology, the vehicle load increases gradually, and the vehicle speed increases one after another. People put forward higher requirements for the safety and comfort of driving. However, the early construction of bridges, low load standards, poor construction level, after many years of operation of the bridge disease has emerged, so the old bridge maintenance and reinforcement has become an urgent problem to be solved.

At present, the developed countries in the world have invested a lot of manpower and material resources in the old bridge reinforcement technology research, while building new bridges, still attach great importance to the use of the old bridge value. At present, China is vigorously developing infrastructure, and the demand for funds is large. To rebuild dangerous bridges on grade highways in a short time, not only a large amount of funds, but also contrary to the sustainable development of bridge construction. The following author according to the highway network in recent years in the process of transformation, for small and medium-span bridges often used in some maintenance and reinforcement methods to do some introduction.

2. Sticking carbon fiber wrap reinforcement method

Carbon fiber is a new type of material, which has the advantages of high strength, light weight, corrosion resistance and easy construction, and becomes an ideal material for strengthening old bridges. When strengthening concrete members, CFRP sheets are bonded to the surface of the members according to the different mechanical characteristics of the members, so that the deformation of the members can be restrained and the bearing capacity of the members can be improved.

This reinforcement method is widely used in strengthening flexural rigidity, reducing deflection and restraining concrete crack propagation. When the shape of reinforcement structure is complex, it is very difficult to construct with concrete enclosure or steel plate bonding method, and the bonding of steel plate may cause damage to the original structure. At this time, carbon fiber cloth can be used to construct arbitrarily with the shape of the structure, thus reducing the construction difficulty.

3. Bolt shotcrete reinforcement method

Anchor shotcrete is a composite structure that first anchors the anchor rod into the reinforced part of the structure, and then sprays a certain thickness of concrete to make it bear the external force together with the original structure.

This reinforcement method is used more frequently in the reinforcement of masonry slab arch bridges. At present, slab arch bridges on low-grade highways are not strictly selected materials according to the strength and specifications in early construction, and the mortar is not full when masonry slabs, and the mortar mix proportion is not strictly controlled, in addition to the long-term effect of overweight vehicles. There are widespread weathering of flakes in the main arch ring, different sizes of stone, crushing and fragmentation of flakes, uneven strength of stone and other phenomena. Masonry mortar loosening and shedding and there are more cavities, some arch ring has been found longitudinal cracks. In view of this situation, anchoring and shotcreting concrete reinforcement will not only interrupt traffic but also solve these problems.

4. Outsourcing concrete reinforcement method

Enlarged section reinforcement method is a reinforcement method that enlarges the section and reinforcement of components to improve the strength and stiffness of components. This reinforcement method is widely used to increase the lateral connection of bridges. The cross-tied beams or diaphragms of early bridges are small in size and weak in strength and stiffness. Under the current large external load, large deformation occurs, resulting in cracking and shedding of the cross-tied beams, and the lateral load can not be effectively distributed. At this point, the size of the transverse girder is increased by using the enclosing concrete reinforcement method. With the strengthening of the transverse connection, the transverse overall mechanical performance of the main girder is improved, thus increasing the bearing capacity of the bridge and improving the stiffness and stability of the bridge.

5. Concluding remarks

The above methods are often used in the conventional reinforcement of medium and small span bridges. Due to the limited temporary economic capacity of our country, in order to ensure the safe operation of bridges, the maintenance and reinforcement of bridges is inevitable in a certain period of time.

(1) Because of the incomplete data of the old bridge, there are some differences between the actual stress situation and the structural calculation model, so the bridge reinforcement is strictly calculated by the design unit and meticulously constructed by the construction unit according to the drawings. It is suggested that the strengthened bridge should be inspected, and the detailed observation and record of the data should be made. Compared with the theoretical calculation, the safe and reliable conclusion can be drawn after the analysis before the vehicle can be opened.

(2) We should carry out the idea of "building and paying equal attention" and "prevention first" for bridge disease treatment. Bridges should be regularly inspected and periodically maintained, and some minor diseases found should be repaired in time to avoid enlargement of the disease and loss of bearing capacity.

(3) At present, bridge construction should take the road of sustainable development, and new bridges should consider its detectability, reinforcement and replaceability.