1. Application principles of reinforcement technology for reinforced concrete structures
According to the relevant provisions of the Code for Seismic Design of Industrial and Civil Buildings, the application principles of reinforced concrete reinforcement construction technology can be summarized as follows:
1. 1 maintainability principle
According to the original design standard, the safety factor of reinforced concrete structure is improved to the level before the reduction, usually by strengthening the local parts that weaken the performance or reduce the bearing capacity of the original structure. This principle can refer to the standard code "Standard for Seismic Appraisal of Buildings", and is applicable to the reinforced concrete structure of building engineering built according to the requirements of seismic strengthening design code. However, due to subjective and objective reasons, the seismic grade of the reinforced concrete structure of this building project has declined, especially the reinforced concrete structure that has been used for more than 40 years, which needs to meet the current national standards and norms as much as possible.
1.2 generalization principle
For those reinforced concrete structures that do not meet the current seismic fortification standards, whether the seismic fortification level is reduced or not. This kind of seismic strengthening can not continue to use the previous standards, but strengthen the parts with different seismic grades based on the current standards, especially those building structures that do not strictly consider the seismic fortification problem during construction. It is difficult to hoist and strengthen the earthquake. Before reinforcement, the reinforced concrete structure has been subjected to stress compression or bending deformation under a certain load. The original load has not been removed, but the bearing capacity has been added, which slows down the compression of the load, thus achieving the reinforcement effect.
2. Suggested measures for the application of reinforced concrete structure reinforcement technology
In view of the basic principle of the application of reinforced concrete structure reinforcement technology, this paper will focus on three methods: bonded steel reinforcement, carbon fiber sheet reinforcement and bonded steel reinforcement. On the basis of understanding the principles of these reinforcement methods, how to apply these methods and the scope of application of these methods are discussed as follows:
2. 1 bonded steel reinforcement technology
The concrete principle of the application of bonded steel reinforcement method is to find out the tensile area on the surface of the reinforced concrete structural members of the building, and then paste a certain specification of steel plates on it. By using the bonding ability of steel plates, the tensile force and shear force of the original concrete members are transferred to the steel plates as a part of the reinforced concrete structure of the building to improve the bearing capacity of the building structure. This reinforcement method has been applied since the end of 1960s, which is not only simple in construction, but also will not affect the appearance of the building structure.
(1) There are four main application forms of steel-bonded reinforcement technology: the first is to stick steel plates at the bottom of reinforced concrete structures of beams or slabs to enhance the bending level and bearing level of the cross-section of the structures; The second is to stick steel plates on the upper part of the beam plate of the beam structure or above the neutral axis to enhance the bending level and bearing level of the normal section of the manufacturing part; Thirdly, the U-shaped steel plate is used as the anchor steel plate and pasted on the reinforced concrete structure of the beam building to enhance the shear level and bearing level of the inclined section of the structure; Fourthly, the U-shape is pasted on the frame column of reinforced concrete structure in the form of overlapping, and the stressed part of the structure is constrained into a ring shape to improve the ductility level of the column.
(2) Application requirements of steel-bonded reinforcement technology: Steel-bonded reinforcement requires that the joint surface between the steel plate and the reinforced part is well handled, and the bond strength of the concrete at the joint surface is high. When strengthening, we should control the strength grade of concrete, which is above C 15 in principle. The thickness of steel plate also depends on the strength of concrete, and the anchorage length of steel plate is determined at the same time. Generally speaking, the greater the thickness of steel plate, the longer the anchorage length of steel plate, which will obviously affect the bonding effect, while the thinner the steel plate, the more glue will be used, which will increase the difficulty of steel plate anticorrosion. According to the construction experience, the author thinks that there are three optimal thicknesses of steel plates strengthened with bonded steel. The first is that when the strength grade of concrete is less than C20, the thickness of steel plate is 2-3 mm; The second is that when the concrete grade is C20-C25, the thickness of the steel plate is 3-4 mm; Third, when the concrete grade is greater than C25, the thickness of the steel plate is 4-5 mm. As for the anchorage length of the steel plate, it depends on the structural requirements of the reinforced concrete structure of the building to be strengthened while meeting the calculation requirements. For anchorage in tension zone, the anchorage length should be at least 200 times the thickness of steel plate and not less than 600mm；; If it belongs to the compression zone anchorage, the anchorage length should be at least 160 times of the thickness of the steel plate, and not less than 490 mm In addition, while using epoxy resin chemical grouting and steel bar bonding for reinforcement, anti-corrosion materials should be used for protection to prevent structural adhesive from aging and peeling at high temperature.
2.2 carbon fiber sheet reinforcement technology
The strengthening method of carbon fiber sheet began in the late 1980s. This strengthening method can effectively avoid the problem of interfacial bond strength, and greatly improve the bending, shearing, torsion, tension and bearing level of the strengthened members, which belongs to a new type of seismic strengthening technology for building structures.
(1) The principle of strengthening with carbon fiber sheets is to wrap carbon fiber materials vertically on the reinforced concrete members to be strengthened, so as to enhance the ductility level, bearing level and seismic energy consumption level of the members. The self-weight of carbon fiber cloth is only 2N, and the thickness is only 0. 167mm, which will not increase the self-weight and cross-sectional area of the original reinforced concrete structure. But also can be manually operated and constructed, and is suitable for corrosive environments such as acid, alkali, salt and the like, and does not need post-maintenance and has a wide application range.
(2) There are four main application forms of carbon fiber sheet strengthening technology: the first one is to stick carbon fiber sheet on the bottom of reinforced concrete structural members of beams or slabs to improve the flexural level and bearing level of cross-section of members; The second is to stick carbon fiber cloth on the upper part of the beam slab of the beam reinforced concrete structural member or below the neutral axis of the member to enhance the bending level or bearing level of the normal section of the bearing; Thirdly, the U-shaped carbon fiber cloth is used as the longitudinal anchoring steel plate and pasted on the beam reinforced concrete member to enhance the shear level and bearing level of the inclined section of the member; The fourth is to stick the U-shaped carbon fiber cloth in the direction of the column hoop of the building frame, and constrain the seismic strengthening part of the structure into a ring shape to improve the ductility level of the column.
(3) The construction method of strengthening with carbon fiber cloth is as follows: Because the ultimate tensile strain of carbon fiber cloth is large, the tensile stress of steel bar should be controlled within the design value of tensile strength of steel bar as far as possible after strengthening, and the temperature of external bonding should be kept to ensure that the concrete strength of the reinforced member is above C 15; Before pasting, the concrete and oil stains peeled off from the surface of steel bars must be removed. When pasting, it is necessary to control the direction of the carbon fiber cloth and the reinforcement, and keep the axial direction of the carbon fiber cloth and the reinforcement vertical. A variety of close packing methods can be used to ensure the reliable adhesion between protective materials and carbon fiber cloth.
2.3 externally bonded steel reinforcement technology
In addition to the above two technical methods for strengthening reinforced concrete structures, the externally bonded steel reinforcement technology also has a certain reinforcement effect, and its reinforcement part is mainly the surface or corner of reinforced concrete structural members. Pouring modified epoxy resin glue improves the mechanical properties of the structure, which is suitable for strengthening beams, columns, walls, trusses and frames of reinforced concrete structures. During construction, angle steel is used to cooperate with batten plates, all steel plates are welded, and loose honeycomb, holes and cracks are filled with epoxy resin, so that the * * * of the old and new reinforced concrete structures bear the same force, but all operations must be completed before the initial setting of cement to ensure the fastening of bonding.
3. Concluding remarks
To sum up, the reinforcement of reinforced concrete structure is one of the key tasks in the current building structure construction. In order to further improve the seismic level of reinforced concrete structures, we can adhere to the basic principles of the application of reinforcement technology and select the appropriate reinforcement technology in combination with the reinforcement needs of specific reinforced concrete structures. In this paper, strengthening with bonded steel, strengthening with carbon fiber sheet and strengthening with bonded steel outside are the research focuses of seismic strengthening of reinforced concrete structures. Through research, it is found that these reinforcement methods are obviously practical, but the specific application methods need to be summarized in practical work to continuously improve the application level of these methods.
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