Structural reinforcement methods can be categorized into two types: direct reinforcement and indirect reinforcement.
Direct Reinforcement Method
Direct reinforcement method is a technique that directly enhances the load-bearing capacity and stiffness of structural sections through various reinforcement measures. In engineering practice, the following methods are commonly used:
Enhanced Cross-Section Reinforcement Method
The Increased Section Reinforcement Method involves reinforcing the original structure using the same materials, namely concrete and ordinary rebar. By increasing the cross-sectional area of the concrete and rebar and implementing certain structural measures, it ensures reliable connection between the reinforced sections and the original components, working together to enhance the section's bearing capacity and stiffness. This is an extremely effective reinforcement technique, which can be used to improve the flexural and compressive bearing capacity of the components' cross-sections, as well as the shear-bearing capacity of oblique sections. It can also be employed to repair cracked sections. It is widely applicable for reinforcing steel-reinforced concrete beams, slabs, columns, walls, and other structural components, as well as general constructions.
2. Outsourced Steel Reinforcement Method
The external steel reinforcement method involves reinforcing and reinforcing original components with dissimilar materials, significantly enhancing structural load-bearing capacity without altering the original component's cross-sectional dimensions. The external reinforcement methods can be categorized into dry and wet types. When there is no connection between the external material and the original component, or even if cement mortar is used to fill but still cannot ensure effective transfer of shear force at the bonding surface, it is referred to as dry external reinforcement. When bonded using methods such as latex cement粘贴 or epoxy resin grouting, it is called wet external reinforcement. Dry external reinforcement transfers loads to the newly added structure through the deformation of the original object, whereas wet external reinforcement combines the old and new materials into a single unit, working and bearing forces together. This method is suitable for reinforcing axially and eccentrically loaded components where increasing the cross-sectional dimensions of the components is not permitted for use but a substantial increase in load-bearing capacity is required. When chemical grouting external reinforcement is used, the surface temperature of the external material should not exceed 60 degrees Celsius, and reliable anticorrosion measures must be in place.
3. Prestressed reinforcement method
Pre-stressed reinforcement is a method that utilizes non-standard materials (such as high-strength steel bars or shapes) to apply pre-stress, forcing the added materials to work together with the original materials. This approach strengthens the structure and offers advantages such as overcoming the issue of excessive force ahead of reinforcement in the cross-section of the component, reducing the width of cracks and deflection in the original component. It is suitable for concrete bending and compression components that require enhanced load-bearing capacity, stiffness, and crack resistance, as well as those that require minimal space after reinforcement. However, this method is not suitable for concrete structures in environments with temperatures above 60 degrees Celsius or for structures with significant concrete shrinkage and creep.
4. Auxiliary Structure Reinforcement Method
The auxiliary structure reinforcement method is a technique that employs different materials for in-situ reinforcement. It involves creating simple or complex frameworks from other materials to bear the load of the original component, thereby forming a composite structure. By transferring the load to the added structure through the deformation of the original component, this method achieves the goal of working together to enhance load-bearing capacity. This method offers convenient construction schedules, minimal increase in structural weight, and can significantly improve load-bearing capacity. It is suitable for components with severe damage or even destruction, where a substantial increase in load-bearing and stiffness is required for concrete bending elements. However, anti-corrosion measures for the external structure should be implemented.
External steel bonding reinforcement method
The External Bonded Reinforcement Method involves adhering reinforcing materials to the concrete surface of the bending members using construction adhesive, which enhances the tensile, compressive, and shear resistance of the cross-section, thereby improving the bearing capacity of the reinforced structural elements and limiting crack propagation. This method is simple to implement, highly flexible, and an extremely effective reinforcement technique. It is selected for general bending and tensile members subjected to static loads. For full or partial reinforcement of both vertical and diagonal sections, since the reinforcing materials are bonded to the members using adhesives like epoxy cement, forming an integrated structure that works together, the environmental temperature should not exceed 60 degrees Celsius, the relative humidity should not exceed 70%, and there should be no chemical corrosion. Otherwise, protective measures should be taken.
6. Carbon Fiber Reinforcement Method
General Regulations:
When reinforcing and repairing concrete structures with adhesive carbon fiber sheets, the sheets should be bonded to the surface of the components using compatible adhesive materials. This allows the carbon fiber sheets to bear tensile stresses and coordinate with the deformation of the concrete, sharing the load together.
(2) Carbon fiber sheet materials are primarily used for reinforcing concrete structures in the following forms:
When reinforcing beams and slab components with carbon fiber sheet materials in the tension zone, the fiber direction should align with the direction of the applied stress in the reinforcement.
When reinforcing beam and column members with closed-side bonding, U-shaped bonding, or side bonding, the fiber direction should ideally be perpendicular to the member's axis.
When reinforcing columns with seismic reinforcement using closed-loop stitching, the fiber direction should be perpendicular to the column's axis.
When reliable evidence is available, carbon fiber sheets can also be used for reinforcement of other concrete structural components and load-bearing forms.
When reinforcing and repairing concrete structures with carbon fiber reinforced sheets, the design for load-bearing capacity and serviceability should be calculated and verified using the limit state design method based on probability theory, in accordance with the current national codes. The strength design indicators for steel and concrete materials should be determined based on the actual strength obtained from structural inspections, in line with the current national codes. Alternatively, these indicators can be determined according to the type of steel and the design strength grade of concrete, using the corresponding material strength design indicators as specified by the current national codes. The stress of the carbon fiber sheets should be determined based on the strain at the ultimate state of the component, in accordance with the linear elastic stress-strain relationship.
(4) The carbon fiber sheet material takes the ultimate tensile strength with a minimum guarantee rate of not less than 95% provided by the manufacturer as the tensile strength standard value, fcfk. The ultimate tensile strain of the carbon fiber sheet material is obtained by dividing the ultimate tensile strength standard value, fcfk, by the elastic modulus, Ecf.
When reinforcing or repairing structures or components with adhesive carbon fiber sheet materials, consider the potential impact on other components within the structure or on other performance characteristics of the components.
(6) Reinforce and repair the structure using bonded carbon fiber sheet materials. It is advisable to remove the live load on the structure when necessary. When it is not possible to fully unload for reinforcement, consider the effects of secondary loading.
(7) During flexural reinforcement and shear reinforcement, the actual concrete strength grade of the reinforced concrete structures and components should not be lower than C15. When using closed-lay carbon fiber sheets to reinforce concrete columns, the concrete strength grade should not be lower than C10.
II. Indirect Reinforcement
Indirect reinforcement involves altering the load paths of the original structure through certain components and local measures, reducing the load effects, tapping into the potential of the components, and ultimately aiming to decrease the probability of structural failure and reinforce the structure. A commonly used method in engineering is:
1. Addition of Component Method
The Addition Component Method involves adding a new component between existing components of a structure (such as adding a new truss between two existing ones, a new beam between two large beams, or a new column between column grids, etc.). This is done to reduce the load on the original components, thereby reinforcing the structure. This method is generally suitable for single-story industrial buildings or for reinforcing floor beams and columns in multi-story buildings where the addition of new components does not affect the usage requirements. The construction process does not damage the original structure, ensuring safety.
2. Additional Pivot Method
The method of adding fulcrums involves adding support points to beams, slabs, and columns to reduce the calculated span of the structure, thereby decreasing the load effect, tapping into the potential of the components, enhancing bearing capacity, and reinforcing the structure. According to the load-bearing performance of the supporting structure, the reinforcement method of adding fulcrums to beams is divided into rigid fulcrum and elastic fulcrum methods. The rigid fulcrum method transmits the load directly to the foundation or other load-bearing components through the axial compression of the supporting components, at which point, the deformation of the fulcrum is relatively very small compared to the deflection of the reinforced beam, and can be neglected. The elastic fulcrum reinforcement method transmits the load indirectly through the bending or truss action of the supporting components. In this case, the deformation of the fulcrum cannot be ignored. The reinforcement of column fulcrum methods can adopt the inter-column lateral support method. The method of adding fulcrums is suitable for reinforcing large-span beams, slabs, or tall columns where the clear height of the building is not restricted.
3. Enhance overall structural integrity reinforcement method
The enhancement of structural integrity is achieved by adding supports to form a spatially integrated whole of multiple components, working together. Since the probability of overall failure is less than that of individual component failure, the reliability of the structure is improved without reinforcing any single component.
4. Stiffness Ratio Modification Reinforcement Method
In the construction of buildings, altering the stiffness ratio of components, adjusting the internal force distribution of the original structure, and improving the structural load-bearing condition can also achieve the purpose of structural reinforcement. This method is commonly used to enhance the structural horizontal resistance capacity.
Enhanced Categorization
The reinforced engineering can be categorized into four major types based on the materials used for reinforcement.
Steel
To ensure that the welding of rebars, steel sections, and steel plates is beneficial during the transverse tension construction of steel frame connections, steel section frame connections, and prestressed reinforcement methods, it is advisable to use Grade 1 or Grade 2 rebars for concrete structure reinforcement. Steel sections, steel plates, flat bars, and steel pipes should be selected from No. 3 steel or 16Mn steel. For large-span prestressed reinforcement methods, high-strength materials such as Grades 3 to 4 rebars, carbon钢丝, or steel strands can also be reasonably selected based on the actual structure. Jack tension should be employed.
2. Concrete
To enhance the bond between new and old concrete components, considering that the original structural concrete strength is generally low, the concrete strength grade used for concrete structure reinforcement should be one level higher than that of the original structure and components during design. When the original component concrete strength is high, the same concrete strength grade as the original component can usually be adopted, but technical measures should be taken to ensure sufficient bonding strength between the new and old concrete. To accelerate construction progress, minimize impact on usage, and ensure reinforcement effectiveness, it is advisable to use early-strength concrete.
3. Soft Materials
Soft materials are mainly represented by flexible materials such as carbon fiber fabrics.
Features: 1. Stable performance with minimal corrosion issues. 2. Lightweight, without adding to the structural static load. 3. High strength. 4. Easy for manual operation, no specialized machinery required. 5. Construction is dust and noise pollution-free, allowing for continuous production and operation.
Utilizing carbon fiber reinforcement in reinforced concrete short columns can prevent or limit the development of diagonal cracks, significantly enhancing the column's shear-bearing capacity. The failure of carbon fiber-reinforced concrete columns is somewhat sudden, yet it is preceded by a sound warning, making the failure predictable. Applying carbon fiber reinforcement before the axial force results in a more effective constraint on the column, leading to a greater increase in its shear strength. Under cyclic loading, the load-displacement hysteresis loop of carbon fiber-reinforced concrete short columns is stable, exhibiting good energy dissipation capabilities and less strength degradation compared to conventional concrete columns.
4. Connecting Materials
When using chemical slurry grouting for connection, it is advisable to use a slurry with good groutability, low shrinkage, high bonding strength, adjustable curing time, good durability, and non-toxic properties. The bond strength of the slurry after curing should be higher than the tensile and shear strengths of the concrete structure being bonded.
