Reinforcement of reinforced concrete structures: concept, definition, calculation, technical characteristics, classification and compliance with GOST requirements

Reinforced concrete structures often play a key role in construction and large-scale industries, performing the functions of frames, ceilings and functional platforms of various buildings. They account for multi-ton loads acting in both static and dynamic modes. Over time, the voltage can not affect the state of the structure. As a result, reinforcement of reinforced concrete structures is required in one way or another. The specific methodology for conducting such operations depends on the operating conditions of the facility, technical and physical parameters and planning requirements.

What is reinforcement of reinforced concrete structures?

To begin with, it is necessary to determine what a reinforced concrete structure is in principle. In capital construction, this is part of the structure that takes on increased operational loads. The structure is formed by the concrete structure, and reinforcing bars are used as its basic reinforcement. At the same time, reinforcement and restoration of reinforced concrete structures can be carried out comprehensively and partially. If the diagnosis revealed a defective zone on the surface, the repair will primarily concern this part, although the causes of destruction should be investigated first, which can justify the feasibility of reconstruction of other parts of the structure.

What is meant by amplification as such? This is a technical operation in construction, due to which the operational life of buildings and individual structures in particular is extended. There are various methods of repair and reinforcement of reinforced concrete structures. All of them, to varying degrees, involve solving the following problems:

• Strengthening the strength of nodes and bearing components of the structure due to the inclusion of new elements. As the latter can be beams, lintels, cantilever parts, stiffeners, etc.
• Unloading or redistribution of mass that affects the reinforced concrete base. In this case, the structure of structures that mechanically act on the target area of ​​reinforcement is affected. Unloading reduces the requirements for reinforcement of reinforced concrete structures.
• Improving the basic strength characteristics of an object and its elements by replacement.

When is reinforcement of reinforced concrete structures necessary?

Even at the stage of erection of the supporting frame in accordance with future loads, technical solutions and building materials are selected with the expectation of long-term operation. Over time, due to various factors, the technical condition of the structure deteriorates and a need arises to support its critical elements. Full reinforcement of reinforced concrete structures should be performed in the following cases:

• Loss of design strength due to aging and material fatigue. This is especially true for the concrete structure, which is exposed to chemical negative influences and natural mechanical stresses.
• Redevelopment of the building, as a result of which the configuration of the bearing walls, beams, columns, trusses and consoles changes. Strength buildup or mass unloading at reference points in the structure may be required.
• Change the number of storeys. There is also a redistribution of weight along the columns, ceilings and walls, which requires a review and the bearing capacity of the building elements.
• Soil shifts, which either have already deformed or changed the configuration of the impact on the foundation, and therefore on the supporting nodes of the frame. It also requires restoration of the power balance between the structures.
• Destruction or partial damage to bearing parts or individual elements due to accidents, natural disasters, earthquakes, man-made disasters.
• Upon detection of errors made at the design stage or identified during the operation of the building.

In this case, the main and most common reasons that entail the need to strengthen reinforced concrete structures in one way or another are considered. The specific nature of wear or damage should be determined in the course of a comprehensive examination, on the basis of which a design for strengthening the structure is developed and the optimal method for its implementation is selected.

Diagnostics and structural troubleshooting

Technical inspection is carried out in accordance with the schedule or unscheduled with obvious signs of building destruction. This part of the measures is regulated by the standards of non-destructive testing in accordance with GOST 22690 and 17624. The assessment according to the results of the inspection is made in accordance with the set of rules (SP) on reinforcement of reinforced concrete structures under the number 63.13330.

Diagnostic procedures begin with a visual inspection, during which external damage is detected - defects, chips, cracks, etc. Nondestructive testing methods are used to detect hidden damage. Similar tasks are solved by means of special equipment, for example, using electromagnetic or ultrasonic flaw detectors. In particular, it is precisely for the troubleshooting of reinforced concrete that ultrasonic devices operating by georadar and echo-pulse methods are more often used. During the examination, voids, the presence of aggressive components in the structure, the destruction of reinforcing rods, traces of corrosion, etc. can be detected.

Based on the data obtained, a further strategy is developed to eliminate damage, repair, restore or redistribute the loads. At the same stage, defectologists can give recommendations on reinforcing reinforced concrete structures, taking into account the specifics of damage, which only non-destructive testing tools can record. An important role in determining ways to strengthen the structure will also be played by the specific technical and physical parameters on which the structure is operated.

Amplification Specifications

The parameters of the amplification means may vary depending on the configuration of the additional force application and the specific requirements for structural support. The most common characteristics are the elastic modulus of the support means and tensile strength. So, the optimal reinforcement of reinforced concrete structures with composite materials on average provides elasticity in the range of 70,000-640,000 MPa and tensile strength indicators from 1,500 to 5,000 MPa. Of course, it is not necessary in each case to strive for maximum performance. The choice of a specific power potential of the support and strengthening elements depends on the current state of the reinforced concrete structure.

As for the dimensional parameters, they will depend on the strengthening scheme, which is compiled on the basis of the planning decision. For example, fragmented reinforcement of a reinforced concrete slab can be accomplished by additional support for a beamless monolithic module 300 mm thick. Reinforcing columns usually have an average section of 400x400 mm and are placed under the ceiling in increments of 5-7.5 m. The span is determined by the stress-strain state of the ceilings and load-bearing walls.

In a complex form, for example, reinforcement of reinforced concrete structures with carbon fiber can have the following technical characteristics:

• The thickness of the element is 0.3 mm.
• Width - 300 mm.
• Mass - 500 g / m ² .
• The modulus of elasticity is 230,000 N / mm ² .
• Density - 1.7 g / cm ³ .
• Tensile strength indicators - 4000 N / mm ² .
• The shear strength of the structure is 7 N / mm ² .
• The compressive strength of the material is 70 N / mm ² .
• The deformation at break of the structure is 1.6%.
• The adhesion of the composite fiber to the concrete structure is 4 N / mm ² .
• Young's modulus - 400 N / mm ² .

The specifics of using modern composite materials is due to the fact that the adhesive composition plays a significant role in installation operations with them. Often, it acts as an independent termination and restoration tool for strengthening the concrete structure. For example, epoxy compounds may well perform the function of sealing technological joints and joints.

Regulatory requirements

In the process of calculating, designing and performing installation works, one should focus on several GOSTs, including 31937, 22690 and 28570. These documents regulate, to varying degrees, measures for maintenance and reconstruction of buildings and structures. It is also necessary to take into account the standards of SP 63.13330, which gives specific instructions on the organization and implementation of repair and restoration measures, including the reinforcement of reinforced concrete structures with composite materials. SP 164.1325800 will also help in the use of other plastic and fiberglass materials for reinforcement. General regulatory rules that you should focus on are as follows:

• The development of the reinforcement project should be carried out only on the basis of data from a field survey of structures.
• By the time of calculation based on materials and configuration of installation work, information should be prepared on the dimensions of the target object, its condition, methods of reinforcement, concrete strength, etc.
• After the inspection, a fundamental decision is made on the admissibility of the structure for repair with further operation.
• Reinforcing measures should be carried out so that composite fibers or metal rods provide joint loading work with the concrete structure.
• It is not allowed to reinforce structures in which foci of corrosion damage are observed.
• In the process of preparing the project, it is important to calculate the need to provide additional protective properties of the material, for example, to include refractory or moisture resistant coatings in the structure.

Reinforced concrete reinforcement guides

Along with the rules governing the sphere of repair and restoration of building structures, it will be useful to initially prepare a base of methodological materials that will help to practically solve the tasks. To date, there are many illustrative instructions that step by step and clearly describe the technology of applying specific methods of reconstruction of certain structures. For example, Interaqua LLC and NIIIZhB offer a comprehensive guide to reinforcing reinforced concrete structures with composite materials based on the set of rules SP 52-101-2003. The material describes the choice of structural solutions, principles for calculating the strengthening of walls and floors, as well as technological methods for using carbon parts.

If we are talking about industrial facilities, then highly specialized manuals can be applied, in which the emphasis is also made on the special conditions of operation of structures. In particular, Far East PromstroyNIIproekt LLC offers instructions for reinforcing reinforced concrete structures of the 1.400.1-18 series. This material highlights the nuances of strengthening load-bearing walls and ceilings in the structure of industrial buildings.

Design reinforcement design

The main task of this stage is to propose a specific technical solution for the implementation of strengthening the structure of the target object. In the process of development, specialists are guided by data on the characteristics of construction materials, their geometric parameters, operating conditions and existing damage. Currently, the following design principles for reinforcing reinforced concrete structures have been developed:

• Interconnectivity of components. A common mistake that occurs during construction is to consider a work site in an isolated format. That is, the load-bearing wall, for example, will be calculated according to direct loads on it without an emphasis on short-range influence factors. In fact, a high-quality and durable system can be designed only with a comprehensive consideration of all operating factors.
• Optimization. The tasks of reinforcing structures can be solved in different ways, and in almost every case there is a solution that will allow the object to maintain a high working resource. But it is advisable at the same time to strive to minimize the amount of work, the mass of auxiliary supporting parts and rationalize the use of consumables. The lower the degree of interference in the structure of the structure, the higher its reliability. By the way, to minimize the inclusion volumes of foreign elements just allow modern technology to strengthen reinforced concrete structures with composite materials, which have a smaller size and weight compared to metal counterparts.
• Economic rationalization. Even if it is possible to use large financial resources during the implementation of the amplification project, it is important to take into account that complex and massive technical solutions always require large expenditures already during maintenance during the operation of the facility.
• Compliance with established requirements. Each design stage should take into account both general regulatory rules and the specific requirements of the technical and construction device in relation to the target building.

Rules for calculating reinforcement of reinforced concrete structures

The technical calculation of structures is the basis of design work, during which actual loads are correlated with the power potentials of the materials used for reinforcement. The initial data for a comprehensive calculation are taken from the design scheme, its dimensions, current loads and the nature of the damage. Separate articles in the evaluation of materials for reinforcing a reinforced concrete structure are calculated indicators for compressive strength, height of the compression zone, stability along inclined sections, etc.

The fundamental value of the design, determining the ability to cope with actual loads, will be the moment of maximum bending. For its calculation, reliability factors for material and load are used. It also determines the nature of the distribution of damage over the cross section of the structure, taking into account the degree of elasticity. If the initial maximum bending moment exceeds the crack formation process over the cross section, then the calculation should be performed the same as for the cross section with cracks without taking into account the potential for the development of deformation.

In the calculations, constant values ​​of the target materials are also used to strengthen the structures. Modern guidelines for reinforcing reinforced concrete structures, in particular, are based on the following indicators:

• Strength - a range from 1000 to 1500 MPa, but not less.
• The modulus of elasticity is from 50 to 150 GPa.
• Glass transition temperature (used for composites) - not less than 40 ° .

Dimensional parameters and mounting configuration are determined individually for a particular design.

Classification of gain methods

Modern technologies allow the use of an extensive list of means of technical strengthening of various structures, adapting to specific operating conditions. At a basic level, it is worth sharing all the ways to reinforce concrete structures based on their physical condition. In particular, liquid, woven and solid-state elements can be distinguished. In the first case, the reinforcement will be carried out by the method of sealing external damage. This can be the elimination of cracks by means of a sand-cement mortar, and the sealing of joints with adhesive construction compounds. Fabric materials are used less often and for the most part as a reinforcing agent, which is applied to the filling area with the same reinforcing solutions.

As for solid-state elements, they are structural parts that are integrated in one way or another or superimposed on a damaged structure. In this case, methods for reinforcing reinforced concrete structures can be divided both by the type of material used (metal, composites, stone), and by the mounting configuration. The most popular way of reinforcing with solid-state products is a belt reinforcement, in which profile overlays clamp the damaged area. .

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The advantages of the metal include its versatility, high strength and affordable cost. By the way, reinforcing reinforced concrete structures with carbon fiber, with all the positive technical and physical qualities, can cost 20-30% more than using even high-quality stainless steel. How are such costs justified? Yet composites exhibit unrivaled tensile strengths that are superior even to steel. Also, unlike concrete, carbon fiber is characterized by a higher resource of fatigue strength, which excludes intermediate restoration measures during the long-term operation of the building. Are there any drawbacks to composites besides the high price? There are environmental nuances, since plastic is still laid at the base of the material, but the significance of the effect of synthetic additives is minimal from the point of view of danger to humans.

Conclusion

Measures for the repair, restoration and strengthening of reinforced concrete structures, as a rule, require a lot of organizational and financial costs. This is due to the complexity of their design and the technological problems of installation operations. Even minor cosmetic procedures need to be carried out in several stages - from troubleshooting with the preparation of the object for work to the direct repair of damage or increase the strength properties of materials. Therefore, in the recommendations for designing reinforcement of reinforced concrete structures, experts note the need to consider the most technically flexible options for solving the problem. For example, the simplest replacement of steel reinforcement with a diameter of 12 mm with a carbon fiber rod with a thickness of 8 mm with the same reinforcing effect will minimize up to 50% of the effort. But of course, such optimization is not always possible. In any case, the principles of maintaining the required strength, elasticity and rigidity of structures should come to the fore. Following normative plans and high-quality installation schemes will allow rationalizing the strengthening, postponing the deadline for the need for a complete reconstruction of the building with the replacement of the reinforced concrete structure.