Building usage

The milling training room is located in the basement of the Engineering Skills Training Center Building. The building was completed in 1997 and is a fully cast-in-place frame structure building with a frame-shear structure in the basement. The building has been used for office, teaching and experimentation for a long time. Recently, due to changes in the use of functions, a large number of training machine tools have been arranged, resulting in cracks in the plate, shear wall and other parts of the milling training room during use. After crack detection, it was found that a large part of the cracks had exceeded the national safety standards, which affected the normal use of the building and required reinforcement.  The bearing capacity of the positive bending moment section does not meet the requirements, and the negative moment section can meet the requirements.

Classification and characteristics of reinforcement methods

The methods often used in reinforcement projects are: increasing section reinforcement method, encased steel reinforcement method, prestressed reinforcement method, and reinforcement method of changing the structural force transmission path. With the continuous progress of science and technology, the application of new technologies, new materials, and new techniques for engineering reinforcement methods. For example, the external bonding steel reinforcement method for concrete components and the carbon fiber wrap reinforcement and repair structure technology emerged as the times require, and began to be widely used in various reinforcement projects.

Determination of reinforcement plan

(1) Determination of the plan. First of all, we must follow the principles of safety, economy, speed, and ease of construction. Only in this way can the reinforcement project receive good social and economic benefits; secondly, suitable reinforcement plans should be formulated according to the different actual conditions of the building. In view of the actual situation of this project, the technology of reinforcing and repairing structure with carbon fiber wrap is initially adopted. Compared with other reinforcement schemes, this scheme has the following advantages:

1) High strength, high efficiency, wide application, easy quality assurance. Carbon fiber material has extremely high tensile strength and elastic modulus, and its tensile strength can reach more than 4500MPa. After forming a composite material, it can reach more than 3500MPa, which is more than 10 times the tensile strength of ordinary steel bars. The carbon fiber material is flexible and can achieve a 100% effective bonding rate in the pasting construction. If bubbles are found, the method of injecting resin can also be used to remedy it.

2) The construction is convenient, the work efficiency is high, there is no wet operation, no on-site fixed facilities, and the construction takes up less space. Carbon fiber wrap reinforcement does not require large construction machinery and heavy equipment, and can be operated in a small space without wet operation. The carbon fiber wrap is flexible and can be cut arbitrarily with scissors or blades according to the design size. The operation is simple and the construction speed is fast. According to relevant statistics, the reinforcement efficiency of pasting carbon fiber is 4-8 times that of pasting steel reinforcement.

3) Excellent corrosion resistance and durability. Carbon fiber can effectively protect the concrete and steel bars of the components from the corrosion of acid, alkali, salt, water and other media, greatly reducing anti-corrosion and maintenance costs, and also protects the internal concrete structure. The carbon fiber and glue structure itself and its reinforced components can withstand ultraviolet rays and nuclear radiation for a long time at -54°C-80°C, and the strength will not decrease; it can last for 40 years after accelerated exposure aging test. ; and after surface coating, durability is more prominent.

4) After reinforcement and repair, the weight of the original structure and the size of the original components are basically not increased. The beautiful appearance of the carbon fiber sheet is easy to attach to the original shape of the component, and the section size of the component is basically unchanged. After pasting, the weight per square meter is less than 1kg, and the thickness is only about 1mm. It has little effect on the weight and size of the structure, and the additional load on the structure is small.

(2) Proposed reinforcement plan

A single layer of carbon fiber wrap (CFRP) is pasted on the bottom of the slab with a thickness of 0.167mm. According to experience calculation, after using carbon fiber wrap to reinforce and repair the structure, the flexural bearing capacity of the floor slab meets the requirements, which can ensure the normal use of training and teaching.