Beam and slab reinforcement with carbon fiber(CFRP)

carbon fiber(CFRP)

Project Overview

A project is a multi-functional building integrating high-end hotels, offices, apartments, large conferences, and boutique shops. The apartment part of this project is a frame-shear structure, with 1 floor underground and 12 floors above ground. The part of the hotel is a frame-shear structure, with 1 floor underground and 11 floors above ground, with a total construction area of 140,000 square meters.

Engineering difficulties

According to the requirements of the owner, some building functions of this hotel need to be adjusted. At this time, all the masonry and plastering works inside the hotel have been completed, and the installation of ventilation and fire protection works have been basically completed. At this time, there are two issues to be dealt with when adjusting the building function. On the one hand, the bearing capacity of the original structure cannot meet the requirements of existing building functions, and structural reinforcement measures are required to deal with the main structure. On the other hand, the structural reinforcement and reconstruction will now conflict with the installation project under construction. In order to ensure the construction period required by the owner, it is necessary to arrange the interleaving construction between the various processes reasonably. Therefore, in order to ensure the quality of the project, it is difficult to choose a fast, economical and convenient construction reinforcement plan and arrange the construction reasonably in order to ensure the quality of the project due to the difficulties of many engineering procedures, tight deadlines and large engineering volume.

Structural strengthening

The construction characteristics of the steel-bonded reinforcement method and the carbon fiber cloth reinforcement method are in line with the construction requirements of this project. However, in accordance with the principle of being responsible for the interests of the owners, the best construction plan should be selected from them. The selection of the optimal plan in engineering is mainly based on quality, economic benefit, and construction period. The relationship between quality, economic benefit and duration is not independent, but interrelated. If the quality is improved, it may be necessary to increase economic investment or extend the duration. For this reason, it is necessary to compare the two reinforcement schemes in detail from these three aspects, so as to select the most economical solution suitable for this project.

(1) Quality aspect. The factors that affect the quality of the project mainly include the performance of the reinforcing material, the working performance of the reinforcing material and concrete, the impact on the original structure after reinforcement, the construction efficiency and durability. From these aspects, the comparison of the two reinforcement methods is listed in Table 1.

Item	steel-bonded reinforcement	carbon fiber cloth reinforcement
Performance of reinforced materials	No.3 steel: tensile strength: 210mpa, elastic modulus: 2.1*10⁵	tensile strength is more than 3400mpa, elastic modulus: 2.35*10⁵
Working performance with concrete	Bonded by a structural glue, and additionally anchored with anchor bolts, insufficient bonding	Through 3 bonding materials to form composite materials and work together
Influence on original structure	The thickness of one layer is 3 to 6 mm, and the mass of each layer is 23.6 to 47.2 kg/m².	The thickness of one layer is 0.5-0.6mm, and the mass of each layer is 400-600g/m2. Basically does not increase the original structure weight and cross-sectional size
The effectiveness of construction	It is difficult to match with the actual structure. Due to its high stiffness, the effective bonding area is difficult to reach the level that can be achieved by sticky carbon fiber, and the hollow drum is difficult to remedy.	Lightweight and soft, easy to attach. The effective bonding area can reach more than 95%, and local bubbles can be repaired by injection with needle.
Durability	Under the action of temperature, it is easy to cause the deformation of the steel plate and the concrete to be out of sync, leading to the destruction of the bonding layer. The steel plate itself is easily corroded and needs regular maintenance. Poor durability. .	Carbon fiber materials have excellent durability, and are resistant to acid, alkali, salt and atmospheric environment corrosion

By comparing the information in the table, it can be seen that in terms of quality assurance, the carbon fiber cloth reinforcement method is better than the bonded steel reinforcement method.

(2) Construction period. The carbon fiber cloth reinforced concrete structure does not require large-scale machinery and equipment. Under the premise of ensuring construction quality and no accidental interference, the time required under the same conditions is less than 1/2 of the time required for the currently widely used sticky steel plate method in China. Under the condition of good construction organization in China, the workload of 1000 m can be completed in 10 working days. The finished carbon fiber cloth is a fabric with a width of 20, 30, 50 cm and a length of 50-100 m. It is packaged in rolls. When used on site, it can be arbitrarily cut with scissors or blades. Like cutting steel plates, special cutting tools are required. According to the relevant statistical data, the same method is used to paste and strengthen. The paste of carbon fiber cloth is 4 to 8 times the work efficiency of paste steel plates. Therefore, from the perspective of construction period, the carbon fiber cloth reinforcement method can greatly save the construction period, which is better than the sticky steel reinforcement method.

(3) In terms of economic benefits. The main factors that affect the economic benefits of this project are the cost price of materials, construction costs, and maintenance costs at a later stage. The shortened carbon fiber construction period is also equivalent to saving construction costs. Therefore, from the perspective of economic benefits, the carbon fiber cloth reinforcement method is better than the bonded steel reinforcement method.

In summary, although the steel-bonded reinforcement method and the carbon fiber reinforcement method have the advantages of sturdiness and durability, fast construction, simple and lightweight, and economical and reasonable. However, further analysis from three aspects of quality, construction period and economic benefits, the carbon fiber cloth reinforcement method is better than the bonded steel reinforcement method, so this project will use the carbon fiber reinforcement method to strengthen the structure.

slab reinforcement with carbon fiber

Reinforcement scheme of beam and slab in engineering

Through optimization and selection, the carbon fiber reinforcement method was selected to reinforce the main part of the hotel, and the following reinforcement schemes were adopted for the beams and plates of the K1 axis ~ C1 axis / 2 axis ~ 3 axis of the hotel from the 3rd to 9th floors of the hotel through design and calculation.

Slab reinforcement scheme

(1) The top and bottom of the board are 100 mm wide, 300 g/m² carbon fiber cloth, and the center spacing is 300 mm.

(2) At the ends of the top and bottom plates, 100 mm wide, 200 g/m² carbon fiber cloth is used, and two bead bars are provided, with a center spacing of 200 mm.

Beam reinforcement scheme

(1) Two layers of carbon fiber cloth with the same beam width and a weight of 300 g are attached to the bottom of the beam.

(2) Within the range of 1.5 times the beam height, paste a layer of carbon fiber U-shaped hoops with a width of 100 mm and a weight of 300 g and a center distance of 200 mm.

Conclusion

Due to the correct selection of the reinforcement plan and the reasonable arrangement of the interpenetrating construction, the construction period of this project has been saved by 50%, and the cost of the reinforcement project has been reduced by 45%. At the same time, it is proved once again that the use of carbon fiber cloth for structural reinforcement has the characteristics of convenient operation, short construction period and high efficiency.