1 Physical reinforcement bridge conditions

The expressway is on a circular curve with a radius of 9000m on a certain bridge, and the optimal design is changed to a prestressed concrete wide hollow slab bridge of 8-30m, with a length of 247.02m and continuous deck. Due to the adjustment of the longitudinal slope, the elevation of the entire bridge has dropped, and the longitudinal slope is 0%. The wide hollow slab girder is 1.4m high, and 10cm waterproof concrete is used for this bridge deck pavement. The bridge deck width is 24.5m, and the bridge deck cross slope is 2%. It was completed and opened to traffic in 1998. Due to severe overloading and the earthquake in 2005, the beams were cracked and the concrete fell off, and repeated maintenance and reinforcement could not reach the ideal state. In 2011, a bridge disease inspection was carried out. The "Bridge Test Inspection Report" showed that the diseases were mainly as follows:

(1) The total number of cracks is as high as 126, the total length is calculated to be 7852.52m, and the maximum crack width is 0.6mm. Among them, the longest crack on the bottom plate is 27.5m, and the maximum crack width of the horizontal crack on the bottom plate is 0.4mm. The longest crack in the web is 1.55m, and the maximum crack width is 0.4mm. The width of most cracks exceeds the specification limit.

(2) The cap beam concrete of the left and right piers is damaged, the steel bar is corroded and exposed, the cap beam of the abutment sees water, and the stopper is seriously damaged.

(3) The steel plate is severely corroded, and some of the supports are deformed.

2 Analysis and evaluation of existing problems in bridge reinforcement

In the early stage of the design, materials were saved due to economic considerations, resulting in lower safety and poor durability. Accurate identification of design defects, diseases caused by construction or other external causes should be provided to provide a basis for the formulation of reinforcement plans. For the dangerous bridge that is already on the verge of structural damage, the structure is already in a very unfavorable state. For the bridge that has been opened to traffic, it needs to maintain normal traffic, so it will be interfered by traffic during reinforcement.

Although the application of carbon fiber sheet for reinforcement can increase the bearing capacity of the positive bending moment in the span of the beam and the negative bending moment at the beam end, it is still constrained by the basic principles of reinforcement (it should rely on the original structure). Overcoming the transition of the new and old structural systems and realizing the organic combination between the reinforced structure and the original structure are also problems to be solved. The symptoms and causes of bridge damage are different, and the solutions are different. The main reason:

(1) The old standard design load level is low;

(2) The severe traffic environment such as heavy traffic and overweight vehicles are the main factors that damage the bridge;

(3) The influence of natural service conditions such as atmospheric corrosion, temperature, humidity, and hydrogeological changes;

(4) The structural stress limit and fatigue life are low due to material limitations;

(5) Conditions such as construction quality, construction management, construction technology and construction technical equipment are not well controlled.

3 Bridge reinforcement plan

The superstructure of the bridge has low bearing capacity, and vertical and diagonal cracks of the beam appear; spalling steel bars are corroded and exposed. According to the design check calculation and expert demonstration, the bridge half of the superstructure is replaced by beams. Pave the bridge deck, guardrails, and prestressed steel bars; remove and transport the wide hollow slab to the designated location, and use prestressed reinforced concrete box girder for the new beam. Overhaul and strengthen the substructure columns and cover beams, and repair and reform other auxiliary projects. The other half of the beam slab of the original bridge is reinforced with carbon fiber plates.

4 Carbon fiber cloth reinforcement technology

The longitudinal main reinforcement of the bridge was severely corroded, and the insufficient bearing capacity of the main girder caused serious cracks in the main girder, and the expansion joints in the bridge deck system were also damaged under the conditions of vehicle load and other factors. Therefore, through the demonstration, the technology of pasting carbon fiber cloth method is adopted to strengthen the beam and slab.

Carbon fiber sheets are pasted on the beams and slabs that are subject to greater stress and weak points to replace the reinforcing steel bars to bear a certain tensile stress for the beam body to control the development of cracks and improve the bearing capacity of the beam body.

300gsm, 0.167mm carbon fiber for bridge strengthening.

5 Conclusion

The entire process of maintenance, repair and reinforcement of the old bridge is equivalent to a system engineering. According to the characteristics and causes of actual bridge diseases, corresponding reinforcement methods are adopted. The construction of carbon fiber sheets is an important part of the strong technical and strict construction in the reinforcement of the old bridge. It is required that the reinforcement plan must be reliable, effective and reasonable. The choice of the plan has a very direct impact on the actual effect of reinforcement. It is required to be completed by a professional construction team specializing in reinforcement technology, and to conduct regular monitoring and evaluation of the reinforced bridge.