Dongzhi Bridge

After nearly 10 years of use of the original Nanzhi old bridge in Harbin, cracks appeared in many T beams. Because the newly built Dongzhi bridge needs to reuse the 13-span Nanzhi old bridge, it is reinforced and repaired. In 2000, the Harbin Second Ring Road Headquarters commissioned the National Industrial Building Diagnostic and Renovation Engineering Technology Research Center to conduct reliability evaluation and testing of T beam structural components.

Field testing showed that the bearing capacity of T-beams did not meet the seismic requirements. Cracks existed on the webs and flanges of T-beams, and the width was generally too large or equal to 0.15 mm. Therefore, considering safety, applicability, and durability, the T beam needs to be reinforced. Cracks below 0.15 mm are sealed with sealant, and cracks above 0.15 mm are filled with AB-filling resin to block them. The contact between air and steel bars reduces oxidation. The bottom of the web of the T beam is reinforced with carbon fiber material.

Carbon fiber composite material reinforcement and repair of concrete structures is a new type of reinforcement technology that has emerged in developed countries in recent years. The technology is to apply carbon fiber, a high-performance fiber, to civil engineering, and stick the carbon fiber to the surface of the structure or component with resin materials. The composite material body CFRP is formed, and through its cooperation with the structure or components, the purpose of strengthening and strengthening the structural components and improving the force performance is achieved.

There are two main types of carbon fiber materials used in the reinforcement and repair of concrete structures: carbon fiber and supporting resin. Among them, the tensile strength of carbon fiber is ten times that of construction steel, and the elastic modulus is equivalent to that of steel. Some types of carbon fiber (such as high elasticity) have a modulus of elasticity more than twice that of steel, and have good construction performance and durability. They are a good reinforcement and repair material. The supporting resin includes bottom resin, leveling material and pasting tree fingers. The first two functions are to improve the bonding quality of carbon fiber, while the latter function is to make carbon fiber and concrete form a complex whole and work together.

Construction technology of carbon fiber reinforced T beam

The old T beams of Dongzhi Bridge are being reinforced. The carbon fiber uses HM-20. Its performance indicators are: single fiber direction, unit weight 200 g, thickness 0.111mm, tensile strength 3550mpa, elastic modulus 235000mpa.

Resin glue HM-180C3P glue for sticking carbon fiber. Its performance indicators are: tensile strength 30MPa, shear strength 10MPa, and adhesive strength 2.0MPa. Applicable temperature: 5-35℃, available time: 20-120rain

Reinforcement effect

In the Dongzhi Bridge reinforcement of the old T beam project, a total of 130 T beams of 20m length were reinforced, and 240 square meters of carbon fiber were actually glued. It took 15 days to complete all the reinforcement construction. After the reinforcement of the T beam is completed, the bridge deck construction begins and the T beam is stressed. After six months of observation of the reinforced joints, the surface of the carbon fiber cloth and the T-beam were in good condition, without hollows and cracks. The construction quality of the reinforcement was approved by the supervision, design and owner, and satisfactory results were achieved. Carbon fiber concentrates many excellent material properties, and it has a wide range of applications. The construction is convenient, the construction performance is good, the carbon fiber material is light and thin, and it is easy to operate. And compared with sticky steel, its masking quality is easier to guarantee.