Compared to today’s most common concrete structures, the steel structure has a significant advantage. The steel structure is light, the seismic performance is good, and the value of resources is high, referred to as reusable and environmentally friendly green buildings. Today, the number of steel structures is more marked with economic strength in a country or region, and the number of steel structures in my country has also been an upward trend after \”active and reasonable steel\” in the architecture.
Increasing section welding reinforcement
The convenience and reliability of welding reinforcement construction is often the most direct selection of steel structural reinforcement. Welding reinforcement is the role of welding metal cover or steel in a structural damaged site, and the steel structure acts as a reinforcement. The welding reinforcement is long, the technology is high, but the material properties of the soldering have deteriorated, and the risk of the operator has highly affected.
Increasing cross section method is a basic reinforcement method, especially under load capacity, considering the long-term carrying and reinforcement steel structure, in accordance with CECS: 7796 and YB9257-96 two standards Declarative, but due to the differences in the value of the stress specificity and the value of the related parameters, there is still a lot of unreasonableness.
Based on this, the national standard \”Steel Structure Reinforcement Design Specification\” preparation group launched research work under carrying performance of steel structural components under carrying conditions to provide basic data and theoretical support for increasing cross-section welding reinforcement. Contains new technical points.
Adhesive steel reinforcement
adhesive steel reinforcing method, also known as sticky steel reinforcement technology, its process is to stick the steel plate with a special building structure adhesive, so that the bond is formed. Together, improve the stability of the structure. From the perspective of the experimental study of sticky steel reinforcement technology from domestic scholars, the technology has a series of advantages such as non-fire, small work surface, does not affect the structure shape, but due to the reinforcing member and the reinforced connection interface The stress is complex, and it is easy to crack under the action of various factors, and the reinforcement effect is too dependent on the function of the structural rubber layer, and this method is questioned in the engineering community.
Further, the steel structure reinforcement can also be reinforced by the steel structure in the form of riveting and screwing in the original steel structure. Disadvantages is that weakened the opening, which is easy to generate new stress concentrations.
1, process status
The advantage of fiber reinforced composites is mainly intensity than stiffness, fatigue resistance and corrosion resistance The live operability is strong, the construction period is short, the protected protector, etc., and is now widely used in the reinforcement of concrete structures and masonry structures due to their excellent physical and mechanical properties. To date, domestic and foreign scholarsThe application of fiber reinforcing composites in the field of steel structure reinforcement has launched a large number of research work, and foreign research is mainly focused on carrying performance and fatigue reinforcement of the bending member; The test study, combined with the stress mechanism of the paste surface, and the calculation formula of carbon fiber bonding strain, bond shear stress, and effective bond length provides theoretical support for the reinforcement of the fiber reinforced composite material.
In 2016, the industry standard YB / T 4558-2016 \”Fiber Enhancement Composite Reinforcement and Repairing Steel Structure\” is also published in 2016. This is also our carbon fiber. The reinforcing steel structure provides a strong basis, and the carbon fiber plus solid steel structure is applied in a plurality of steel structural components such as Baosteel, Tailang Plant. The earliest carbon fiber plus solid steel structure has been 15 years, and it has achieved good Effect.
2, the treatment of the adhesive surface
When adopting the steel structure, the steel surface and the carbon fiber composite material (specifically referred to as carbon fiberboard) when adopting a bonding carbon fiber composite material The treatment of the surface is one of the important steps of the reinforcing steel structure of carbon fiber composites, and is one of the key factors of reinforcement or failure. Under normal circumstances, there are some different degrees of oxides, rust, oil and other impurities. Similarly, the carbon fiber composite material also places in a series of processes, transportation, and storage. Adsorne, and the carbon fiber composite reinforced steel structure is borrowed to bond the carbon fiber material and the steel, so that the purpose of reinforcement, if impurities are present on the surface, will directly affect the bonding surface The cohesive strength.
Generally, the treatment of steel surface is generally manifested as three aspects:
1, remove the oil and loose layers of the steel surface, improve the bonding ability of the structural glue
2, increasing the effective paste area of \u200b\u200bsteel and carbon fiber composites;
3, improve the cohesive strength of the bonding surface;
and these three aspects The influencing factors are the cleanliness and roughness of the bonding surface. The steel materials in the actual use are not passivated, and there is often a layer of oxides or impurities of oil in its surface, and these impurity structures are loose, and the binding to the matrix The strength is very low, affecting the bonding ability of structural glue, reducing the bond strength of the interface, so it is necessary to clean the surface of the bonding surface is necessary.
For steel structures with small cross-section, properly roughening the bonding surface, on the one hand, not only increases the bonding surface area, but also forms a microscopic between the adhesive and the projections of the surface. Mechanical bite force and improves the friction of the bonding surface, and effectively improve carbon fiber composites.Adhesion to the surface of the steel structure.
Carbon fiber cloth does not need to be treated, and for preforming carbon fiberboards, sand blasting should be taken at its surface to increase the roughness of the carbon fiberboard to increase its adhesion strength. In the process of processing, the degree and effort should be controlled, and do not cause the carbon fiber to naked or damage, and remove the surface residue surface with a dry cloth.
Combined reinforcing method is to use the principle of reinforcing concrete by combined structures, and the steel structure is reinforced by internal filled concrete and outer concrete. The inner filled concrete reinforcement method is mainly used to reinforce the steel pipe member, so that the structure load as much as possible, but in most cases, the initial load is difficult to remove due to the influence of the initial stress level on the supporting capacity of the structural member, and it also leads to outsourcing When the concrete is reinforced, the phenomenon of stress hysteresis due to the load levels of the original member.
In order to facilitate the use of the designer in the reinforcement, the two combinational reinforcement method can adopt the concept of intensity reduction coefficient, based on the existing research results, establish quantization relationship between the strength reduction coefficient and the initial stress level, thus Reduce the load capacity of the reinforcement cross section.
The principle of prestressing reinforcement
steel structure prestressed reinforcement is to reinforce the steel structure as a whole or component of the steel structure, and the essence is to Custom Steel Fabrication reduce the original Steel structure stress level, thereby changing the internal force distribution in the protocol structure.
Supplies with prestressed steel structures are mainly suitable for larger span and high stress, unimactless or reinforced effects, which can be used to reinforce or reinforcement, and reinforcement. There is a steel structure, changing the effect of the original structure and internal force, the construction is convenient, the cost is low, the prestressed beam can be protected alone or replaced.
1) reinforcement operation can be carried out without unloading, non-discontinued;
2) Application of prestress can be directly Reduce the deformation, quickly eliminate the peak of exceeding stress and internal force;
3) can eliminate stress hysteresis compared to non-prestressed methods, and make full use of high-strength characteristics of carbon fibers to improve reinforcement efficiency.
4) Combining reliable anchoring, reducing the stripping stress of the bonding interface, avoiding the entire carbon fiber to peel off, improve the reliability of reinforcement;
5) Reduce the reinforcement cost and use cost.
1) Do not withstand the force of the damaged carbon plate;
2) The degree of flatness of the surface of the steel structure determines the determination of the difficulty of construction operation;
3) Determination of structural adhesive and steel structural bonding effect. The prestressed carbon fiber sheet reinforced steel structure shall follow the principles and calculation principles of the prestressed carbon plate reinforcement in accordance with the criteria of the general steel structure reinforcement.
Summary The steel structure in the construction project is inevitably present in various defects and injuries.Under the role of factors such as load and environment, the material changes, causing deterioration of macroscopic mechanical properties to cause steel structural engineering accidents. To ensure the safety of the structure, the extended service life must be replaced or reinforced with the damaged components, and the replacement of these components will cause great waste and affect the normal use of the structure.
At the same time, structural damage has local and multiple characteristics, which is impossible to retire immediately when there is damage.Therefore, seeking economic efficient steel structural reinforcement techniques are both technical issues in the field of civil engineering, and a problem related to social sustainable development.