Building reinforcement technology: structural earthquake resistance

1 Common structural reinforcement technology

1.1 Increasing the section reinforcement method For the reinforced concrete structure, the method of increasing the section method is to increase the cross-sectional area of ​​the original concrete structure by using the same material (reinforced concrete), thereby achieving the purpose of improving the structural bearing capacity. When the resistance of the beam and column members is insufficient, the method of increasing the section is often adopted, and the advantages are as follows:

1) The construction technology is mature and easy to construct; 2) the quality is good and the reliability is strong; 3) the resistance and the stiffness of the component are large, especially for the column.

To increase the section and increase the stiffness, we must first consider the analysis of the overall structure, which can not be increased only by local enlargement, which will cause a major accident in the local weak layer of the overall structure. In addition, there are some disadvantages to the enlarged section method, which should be considered when using it.

1) Due to the large variation of component quality and stiffness, the natural frequency of the structure will change. Therefore, the natural frequency after structural reinforcement should be avoided to enter the resonance region of earthquake or wind shock, resulting in new forms of damage; 2) On-site wet work Large amount, long curing time, has a certain impact on production and life; 3) The cross-section of the component increases the appearance of the structure and the clearance of the house or bridge.

The increased section reinforcement method is mainly used for general structures such as beams, plates, columns, and walls.

1.2 Outsourcing steel reinforcement method The outer steel reinforcement method is a method in which the angle steel is outsourced to the four corners of the component, and the angle steel is connected by the splicing plate. The outer steel reinforcement method is divided into dry and wet.

1) The wet outsourcing steel method is to bond between the steel and the original component with latex cement or epoxy resin, so that the new and old materials have better working ability, and the overall performance is good, but the wet work is large. 2) The dry-out steel method is that the steel has no bond with the original component. Sometimes it is filled with cement mortar, but it does not ensure the effective transmission of the joint shear force and tensile force. The steel and the original component cannot work as a whole. They can only be stressed by each other. Compared with wet-out steel, the construction of the outer steel is easier, but the improvement of the bearing capacity is not as effective as that of the wet outer steel.

The method can greatly improve the bearing capacity of the member and increase the ductility and rigidity without substantially changing the cross-sectional dimensions of the original structural members, and is suitable for structural members and structures such as concrete columns, beams, roof trusses and brick windows, and chimneys. Reinforcement. The outer steel reinforcement method is particularly suitable for the reinforcement of the axial center and the eccentric compression member which are not allowed to increase the sectional size and which need to greatly increase the bearing capacity. The method has a fast construction speed, a small amount of work on site, and a good reinforcement effect, but the amount of steel used is large and the reinforcement cost is high.

1.3 Prestressed reinforcement method The prestressed reinforcement method is a method of reinforcing the structure by using an externally prestressed steel tie rod (a horizontal tie rod and a combined tie rod) or a steel struts. By applying prestressing force to force the steel tie rod or the steel struts, the stress distribution of the original structure is affected and changed, and the original stress level of the structure is reduced, so that the influence of the stress and strain hysteresis generally existing in the general reinforcement method can be better eliminated. Therefore, the post-addition part and the original structure can work well together, and the overall carrying capacity of the structure can be significantly improved. The prestressed reinforcement method has the triple effect of reinforcing, unloading and changing the structural stress distribution. It is suitable for large-span structural reinforcement, and large-scale structural reinforcement under high stress and strain conditions that cannot be strengthened or strengthened by other methods.

The main advantages of the prestressed reinforcement method are as follows:

1) External reinforcement tension prestressing can increase the strength of the main rib, increase the positive section and the oblique section, and also increase the rigidity, effectively improving the performance and good effect.

2) Prestressing can eliminate or slow down the stress hysteresis of the post-added rods, so that the post-adding rods work effectively.

3) The negative bending moment generated by the prestress can offset the partial load bending moment, reduce the deflection of the original component, reduce the crack width of the original component or even completely close the original crack.

Therefore, the prestressed reinforcement method is a reinforcement method with good reinforcement effect and low cost, and has broad application prospects. The disadvantage of this method is the addition of processes and equipment to apply pre-stress.

1.4 External bonded steel reinforcement method The external bonded steel reinforcement method is to pass the steel plate through the adhesive and paste it on the surface of the concrete or steel structure according to the reinforcement design requirements to make it work together. The advantage of the reinforcement method is that the material is easy to take, the construction is convenient and fast, and the bearing capacity of the structural member and the performance in the normal use stage can be greatly improved under the condition that the appearance and the use space of the member are hardly changed.

When externally bonded steel is used for reinforcement, the steel plate is usually adhered to the tension receiving portion of the beam bottom to improve the bearing capacity of the beam. When the steel plate is attached to the beam side, the bearing capacity of the oblique section of the beam can be improved.

At present, the external bonded steel reinforcement method is mainly used for reinforcing and strengthening the general flexural members and tensile members subjected to static force, and the ambient temperature should not exceed 60 ° C, the relative humidity should not be greater than 70%, and no chemical corrosion is required. When the working conditions do not meet the above requirements, corresponding measures should be taken. The bonding steel plate has high requirements on the construction process, and a professional construction team is generally required to ensure the construction quality.

1.5 Adding fulcrum reinforcement method Adding fulcrum reinforcement method is to reduce the structural calculation span by adding support points, and to achieve the reinforcement method of reducing the internal force of the structure and improving its bearing capacity. The method is simple and reliable, but has certain influence on the use space, and is suitable for the reinforcement of horizontal structures such as beams, plates, trusses and grids.

According to the deformation performance of the added support structure, the additional fulcrum method can be divided into two cases: rigid fulcrum and elastic fulcrum. The rigid fulcrum method transmits the load directly to the foundation or column and other members through the axial compression of the support structure or the axial tension. Since the axial deformation of the support structure is much smaller than the flexural deformation of the reinforced structure, the reinforced structure is In other words, the support structure can be simplified according to the fixed fulcrum, the structural force is more clear, and the internal force calculation is greatly simplified. The elastic fulcrum method is a reinforcement method that transfers the load indirectly through the bending or truss action of the support structure. Since the deformation of the support structure and the deformation of the reinforced structure are of the same order of magnitude, the support structure can only be considered according to the elastic fulcrum, and the internal force analysis is more complicated. Relatively speaking, rigid fulcrum reinforcement has a greater increase in the bearing capacity of the structure, and the effect of elastic fulcrum reinforcement on the space of the structure is lower.

1.6 Chemical grouting reinforcement method Chemical grouting reinforcement is to make a certain chemical material into a slurry, which is poured into the crack of the concrete structure by pressure feeding equipment to spread, gel or solidify to achieve the purpose of reinforcement. There are two kinds of chemical grouting materials: one is an epoxy resin grouting material prepared by using epoxy resin as main agent, which has good chemical stability, can be cured at room temperature, has small shrinkage, high strength and strong adhesion. The advantages of the series, and because the cohesive force and cohesion of the epoxy grouting material are greater than the cohesion of the concrete, it can effectively repair the crack of the concrete and restore the integrity of the structure. At present, it is a better reinforcing and consolidation chemical grouting material. It is generally used to repair cracks with a width of 0.2 mm to 0.5 iD2n; the other is a methacrylate grouting material prepared with methyl methacrylate as the main agent, which has good irrigability. It can be filled into fine cracks of 0.05 nlnl width, which is generally used to repair cracks with slit widths below 0.2 Inrn.

The chemical grouting reinforcement method is mainly used to repair structures that affect the use of functions due to cracks, such as pools, water towers, dams, etc. It can also be used to repair concrete beams, plates, columns and other components and structural durability due to corrosion of steel bars. member.

1.7 Cement grouting reinforcement method The cement grouting reinforcement method is a method of hydraulically pushing cement slurry into honeycombs, holes or cracks of structural members by pressure equipment, filling and consolidating these defects to achieve reinforcement and reinforcement. . Cement grouting has the advantages of high strength, wide material source, low price, convenient transportation and storage, and relatively simple grouting process. It is still the most widely used grouting material. The shortcoming of this method is that special equipment is needed, which is mainly used for repairing cracks in brick walls caused by earthquakes, temperature, settlement and the like.

1.8 shotcrete reinforcement method shotcrete reinforcement method is a concrete jet machine to spray concrete mix and water (dry spray machine) or concrete wet material (wet spray machine) onto the concrete structure at high speed, and Reinforcement method for rapid solidification. The shotcrete does not need vibrating, it is densified by the continuous impact between the cement and the aggregate, and it does not need the supporting die or only part of the supporting die. The construction is convenient, the speed is fast, the construction period is short, and the sprayed solidified layer is sticky with the original structure. It has strong strength, so it has unique advantages in large-scale reinforcement engineering. Its shortcoming is that it requires special equipment, and the design of concrete has higher requirements. This method is commonly used to:

Partial or complete replacement of weak concrete; addition of concrete under beams, plates, etc.; filling of holes, gaps and concrete walls of concrete and masonry.

1.9 Adhesive fiber composite material as a new type of reinforcement reinforcement material for concrete structure is gradually emerging in China. Fiber reinforced composite material is made by sticking fiber cloth to concrete surface with resin cement material to achieve structural members. Reinforce and strengthen the structure and improve the mechanical performance of the structure. FRP (fiber reinforced composite materials) commonly used in structural reinforcement are: CFRP (carbon fiber reinforced plastic), GFRP (glass fiber reinforced plastic) and AFRP (aramid fiber reinforced composite), which are obvious compared with traditional concrete structure reinforcement technology. Superiority.

1) High strength and high efficiency. In the reinforcement and repair of concrete structures, the high-strength characteristics can be fully utilized to improve the bearing capacity and ductility of the concrete structure, improve its mechanical performance, achieve the purpose of high-efficiency reinforcement and repair, and is especially important for seismic strengthening of columns. 2) Convenient construction. The construction work efficiency is high, there is no wet operation, no large construction equipment is needed, no on-site fixed facilities are needed, and the construction takes up less space. 3) Excellent corrosion resistance and durability. 4) Construction quality is easy to guarantee. 5) The FRP material is light and thin, and the weight per square meter after bonding is less than 1.0 kg (including the weight of the resin). After the layer is pasted, the thickness is only about 1.0 mill: after the reinforcement, the original structure is not increased. And the original component size. 6) Wide application.

2 Conclusion

For the above-mentioned reinforcement methods, many research institutes at home and abroad have carried out a lot of research work, and most of them have been used in practical projects. However, these reinforcement methods have certain defects. In addition to the common chemical corrosion problems, like the steel reinforcement method, it will increase the weight of the components, the nodes are difficult to handle, and the construction is difficult. Therefore, in the actual reinforcement, a simple and technically high reinforcement technology should be sought. H has become a popular new material in the field of civil engineering with its excellent performance, especially in combination with the traditional reinforced concrete structure. FRP has great research and promotion value and huge social and economic benefits. With the deepening of research work, this material will be widely used. China has a huge construction market. With the rapid development of economic construction, it is believed that FRP will have a bright and broad prospect in the field of civil engineering in China.