FRP rib fire-resistant anchoring structure in concrete slab and design method

Abstract

The invention provides an FRP rib fire-resistant anchoring structure in a concrete slab and a design method. By designing the FRP rib fire-resistant anchoring structure with the FRP rib externally connected with the sleeve in a pressing mode, even if bonding failure occurs between the FRP rib and concrete in the plate span in the fire disaster, the sleeve at the position of the support can provide the anchoring effect for the FRP rib, it is guaranteed that the FRP rib and the concrete are cooperatively stressed in the fire disaster, and the anchoring problem of the FRP rib in the concrete in the fire disaster environment is solved; according to the design method of the FRP rib fire-resistant anchoring structure, the reasonable engineering crimping amount is determined through a crimping amount test, the FRP rib cannot be damaged during crimping, the anchoring strength of the sleeve structure is determined through a pull-out test, the design requirement can be met when the anchoring strength of the structure is larger than the ultimate strength of the FRP rib in a fire disaster, and the scientific sleeve structure design method is provided; and the stable anchoring effect is ensured.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering technology, specifically relating to a fire-resistant anchorage structure and design method for FRP reinforcement in concrete slabs. Background Technology

[0002] Fiber-reinforced polymer (FRP) bars, due to their high strength, lightweight, and corrosion resistance, are an effective way to solve the problem of steel corrosion in reinforced concrete structures. FRP-reinforced concrete structures have high load-bearing capacity, high durability, and green and low-carbon characteristics, and have been applied to some extent in concrete structures.

[0003] Currently, scholars have conducted extensive research on the mechanical properties of FRP-reinforced concrete structures, and the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials" (GB50608-2020) has been established for FRP structure design.

[0004] However, the glass transition temperature T of FRP bars currently on the market... g At temperatures below 200℃, the temperature of FRP-reinforced concrete structures (especially concrete slabs) will quickly exceed the glass transition temperature of the FRP bars in a fire. Once the glass transition temperature is exceeded, the FRP bars will gradually change from a monolithic rod shape to a loose filament shape. Therefore, the bonding performance of FRP bars will decrease sharply as the temperature exceeds the glass transition temperature, which may lead to bonding failure of FRP-reinforced concrete structures in a fire.

[0005] Currently, domestic and international standards (such as ACI 440.1R-15 and JSCE-1997) only focus on the high-temperature resistance of FRP reinforcement for fire protection design, but do not consider the bond slip degradation problem. FRP reinforced concrete structures may be damaged in a fire due to the bonding aging problem of FRP reinforcement.

[0006] Therefore, it is urgent to design a fire-resistant anchoring structure for FRP reinforcement in concrete slabs to solve the fire-resistant anchoring problem of FRP reinforcement concrete structures. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a fire-resistant anchoring structure and design method for FRP bars in concrete slabs. This anchoring structure can maintain effective anchoring between the ends of the FRP bars and the concrete even when the bond between the FRP bars and the concrete fails due to fire, ensuring the coordinated stress distribution between the FRP bars and the concrete in a fire environment, thereby solving the problem of fire anchoring of FRP bars in concrete.

[0008] The technical solution of this invention is: a design method for fire-resistant anchorage structure of FRP reinforcement in concrete slabs, comprising the following steps:

[0009] S1, FRP rib preparation, using pultrusion molding process, directly forming a threaded structure on the outer surface of the FRP rib;

[0010] S2, Sleeve preparation: Cut the pipe into sections according to the designed sleeve length;

[0011] S3, Determine the crimping amount. Select several crimping amount gradients and crimp the sleeve to the outside of the FRP bar according to the selected crimping amount. Determine the engineering crimping amount based on the crimping situation.

[0012] S4, Anchorage strength determination: According to the engineering compression amount determined in S3, several FRP fire-resistant anchorage structures are made, and the FRP fire-resistant anchorage structures are made into concrete pull-out specimens. The anchorage strength between the FRP fire-resistant anchorage structure and the concrete is determined by pull-out test.

[0013] S5, the anchorage location is determined, the sleeve is arranged in the beam support, and the temperature rise value ΔT of the FRP fire-resistant anchorage at the support location after being exposed to fire is calculated according to the technical standard. It is necessary to ensure that ΔT≤50℃.

[0014] S6, Anchorage strength verification: Calculate the highest temperature of the FRP bar under the fire resistance limit according to the technical standard, and the FRP bar strength change curve with temperature to determine the ultimate strength of the FRP bar at the highest temperature. If the anchorage strength of the fire-resistant anchorage structure of the FRP bar is greater than the ultimate strength of the FRP bar, the anchorage requirement is met; otherwise, the sleeve size and crimping amount need to be redesigned.

[0015] Once the S7 FRP fire-resistant anchoring structure meets the anchoring requirements, the FRP fire-resistant anchoring structure can be mass-produced.

[0016] Furthermore, in S1, the thread pitch of the outer threaded structure of the FRP rib is 10-15mm, and the thread depth is ≥0.15mm.

[0017] Furthermore, in S2, the sleeve material is selected as a pipe with a thickness of 3-5mm and an inner diameter 2mm larger than the diameter of the FPR rib.

[0018] Furthermore, in S2, the pipe is a 6061-T6 aluminum alloy pipe, and the designed sleeve length is 50-100mm.

[0019] Furthermore, in S3, the method for determining the amount of engineering pressing is as follows:

[0020] S31, Check whether the surface of the FRP rib is damaged after crimping, and whether any sound is made during the crimping process; S32, the maximum amount of crimping without either of these phenomena is the limit amount of crimping.

[0021] S33, select a pressing amount that is one level lower than the ultimate pressing amount as the engineering pressing amount.

[0022] Furthermore, in S3, the crimping amount ranges from 0.5 to 1.5 mm, and the gradient value of the crimping amount gradient is 0.1 mm.

[0023] Furthermore, in S4, the calculation formula for the anchorage strength between the FRP reinforcement fire-resistant anchorage structure and the concrete is as follows:

[0024]

[0025] Where τ is the anchorage strength, F is the pull-out force, d is the diameter of the FRP bar, and l1 is the bond length.

[0026] Furthermore, in S4, the concrete pull-out specimen includes an FRP bar fire-resistant anchoring structure and a concrete cubic test block. The sleeve is embedded in the concrete cubic test block, and an anchoring sleeve is provided at one end of the FRP bar away from the concrete cubic test block.

[0027] Furthermore, the concrete cubic test block is a concrete cubic test block with a side length of 150mm. The bonding length between the concrete cubic test block and the FRP fire-resistant anchoring structure is l1 = 100mm, and the unbonded length is l2 = 50mm. The concrete cubic test block is provided with spiral stirrups with a pitch of 40mm and an outer diameter of 100mm inside.

[0028] The fire-resistant anchorage structure for FRP reinforcement in concrete slabs is manufactured using the design method for the fire-resistant anchorage structure for FRP reinforcement in concrete slabs as described in any of the above items.

[0029] The beneficial effects of this invention are:

[0030] (1) In this invention, by designing the structure of the external compression sleeve of FRP bar, even if the FRP bar and concrete in the middle of the slab span fail to bond under fire, the sleeve at the support can provide anchorage for the FRP bar, ensuring that the FRP bar and concrete are stressed together under fire, thus solving the problem of anchorage of FRP bar in concrete under fire environment.

[0031] (2) The present invention proposes a sleeve construction design method. By testing the amount of compression, a reasonable amount of engineering compression is determined. The compression will not damage the FRP reinforcement. The sleeve construction anchorage strength is determined by pull-out test. The construction anchorage strength is greater than the ultimate strength of the FRP reinforcement under fire conditions to meet the design requirements. This provides a scientific sleeve construction design method to ensure that it can stably play its anchorage role. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the design method for the fire-resistant anchorage structure of FRP reinforcement in concrete slabs according to the present invention.

[0033] Figure 2A schematic diagram of a concrete pull-out specimen fabricated for the fire-resistant anchoring structure of FRP reinforcement.

[0034] Figure 3 Designed for fire resistance t The relationship between the time of exposure to fire (t≤120min) and the time of exposure to fire.

[0035] Figure 4 Designed for fire resistance t The relationship between the time of exposure to fire (t>120min) and the time of exposure to fire.

[0036] Figure 5 For temperature T y A graph showing the relationship between the distance y of the FRP reinforcement fire-resistant anchorage structure and the beam side.

[0037] Figure 6 This is a graph showing the relationship between the strength of the FRP reinforcement and temperature in this invention.

[0038] Figure 7 This is a schematic diagram of the structure of the concrete slab with added FRP reinforcement fire-resistant anchoring structure in this invention. Detailed Implementation

[0039] Various exemplary embodiments of the invention will now be described in detail with reference to the accompanying drawings. The descriptions of the exemplary embodiments are merely illustrative and are in no way intended to limit the invention or its application or use. The invention can be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to make the invention thorough and complete, and to fully express the scope of the invention to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, the composition of materials, numerical expressions, and values ​​set forth in these embodiments should be interpreted as merely exemplary and not as limiting.

[0040] The terms "first," "second," and similar words used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. Words such as "including" or "comprising" mean that the element preceding the word encompasses the element listed after it, without excluding the possibility of encompassing other elements. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0041] like Figure 1 As shown, a design method for fire-resistant anchorage structure of FRP reinforcement in concrete slabs is disclosed, characterized by the following steps:

[0042] S1, FRP rib preparation, using pultrusion molding process, directly forming a threaded structure on the outer surface of the FRP rib;

[0043] S2, Sleeve preparation: Cut the pipe into sections according to the designed sleeve length;

[0044] S3, Determine the crimping amount. Select several crimping amount gradients and crimp the sleeve to the outside of the FRP bar according to the selected crimping amount. Determine the engineering crimping amount based on the crimping situation.

[0045] S4, Anchorage strength determination: According to the engineering compression amount determined in S3, several FRP fire-resistant anchorage structures are made, and the FRP fire-resistant anchorage structures are made into concrete pull-out specimens. The anchorage strength between the FRP fire-resistant anchorage structure and the concrete is determined by pull-out test.

[0046] S5, the anchorage location is determined, the sleeve is arranged in the beam support, and the temperature rise value ΔT of the FRP fire-resistant anchorage at the support location after being exposed to fire is calculated according to the technical standard. It is necessary to ensure that ΔT≤50℃.

[0047] S6, Anchorage strength verification: Calculate the highest temperature of the FRP bar under the fire resistance limit according to the technical standard, and the FRP bar strength change curve with temperature to determine the ultimate strength of the FRP bar at the highest temperature. If the anchorage strength of the fire-resistant anchorage structure of the FRP bar is greater than the ultimate strength of the FRP bar, the anchorage requirement is met; otherwise, the sleeve size and crimping amount need to be redesigned.

[0048] S7, mass production: Once the FRP fire-resistant anchorage structure meets the anchorage requirements, mass production of the FRP fire-resistant anchorage structure can begin.

[0049] In the above embodiments, the present invention proposes a sleeve construction design method. Through compression tests, a reasonable engineering compression amount is determined, ensuring that the FRP reinforcement is not damaged during compression. The sleeve construction anchorage strength is determined through pull-out tests. As long as the construction anchorage strength is greater than the ultimate strength of the FRP reinforcement under fire conditions, the design requirements are met. This provides a scientific sleeve construction design method to ensure its stable anchorage function. A threaded structure is directly formed on the outer surface of the FRP reinforcement to ensure the bonding performance between the FRP reinforcement and the concrete.

[0050] In some embodiments, in S1, the thread pitch of the outer threaded structure of the FRP reinforcement is 10-15 mm, and the thread depth is ≥0.15 mm; wherein the FRP reinforcement can be glass fiber reinforcement, basalt fiber reinforcement, aramid fiber reinforcement, carbon fiber reinforcement, etc.; preferably carbon fiber reinforcement.

[0051] In some embodiments, in step S2, the sleeve material is selected as a pipe with a thickness of 3-5mm and an inner diameter 2mm larger than the diameter of the FPR reinforcement; specifically, in step S2, the pipe is 6061-T6 aluminum alloy pipe, and the sleeve length is designed to be 50-100mm, with the specific sleeve length determined according to the required anchoring strength.

[0052] In some embodiments, in step S3, the sleeve is crimped onto the outside of the FRP reinforcement. Different anchoring effects between the sleeve and the FRP reinforcement are achieved by controlling the crimping amount. Since the shear strength of the FRP reinforcement is weaker than its tensile strength, a reasonable crimping amount needs to be determined to ensure that the FRP reinforcement is not damaged after the sleeve is added. After crimping, the surface of the FRP reinforcement is checked for damage, and whether any sound is made during the crimping process. The maximum crimping amount that does not exhibit either of these phenomena is the ultimate crimping amount. A crimping amount that is one level lower than the ultimate crimping amount should be selected as the engineering crimping amount. This ensures that the FRP reinforcement is not damaged during batch processing while maximizing the structural anchoring effect.

[0053] As a specific method for determining the amount of engineering pressing, the method for determining the amount of engineering pressing is as follows:

[0054] S31, Check whether the surface of the FRP rib is damaged after crimping, and whether any sound is made during the crimping process; S32, the maximum amount of crimping without either of these phenomena is the limit amount of crimping.

[0055] S33, select a pressing amount that is one level lower than the ultimate pressing amount as the engineering pressing amount.

[0056] Specifically, the sleeve is crimped onto the outside of the FRP rib using a 360° annular hydraulic crimping machine. The 360° annular hydraulic crimping machine utilizes existing equipment and consists of multiple annular wedges. Driven by hydraulics, the annular wedges press towards the center during crimping to achieve the crimping effect. During operation, the FRP rib 1 is first placed in the center of the 360° annular hydraulic crimping machine, then the sleeve is inserted into the FRP rib. The sleeve is adjusted into the 360° annular hydraulic crimping machine, and finally, the annular wedges of the 360° annular hydraulic crimping machine are pushed inward to achieve the required crimping depth.

[0057] In some embodiments, in step S3, the crimping amount ranges from 0.5 to 1.5 mm, and the gradient value of the crimping amount gradient is 0.1 mm. In the specific implementation process, five crimping amount gradients can be selected, with a gradient of 0.1 mm and a range of 0.5 mm to 1.5 mm. After the gradient is determined, the FRP bars are crimped according to the five crimping amounts, and five FRP bars are crimped for each crimping amount.

[0058] In some embodiments, the formula for calculating the anchorage strength between the FRP reinforcement fire-resistant anchorage structure and the concrete in step S4 is as follows:

[0059]

[0060] Where τ is the anchorage strength, F is the pull-out force, d is the diameter of the FRP bar, and l1 is the bond length.

[0061] In some embodiments, in S4, such as Figure 2As shown, the concrete pull-out specimens are prepared in accordance with the standard "Test Methods for Basic Mechanical Properties of Fiber Reinforced Composite Reinforcement Bars" (GB / T 30022-2013). The concrete pull-out specimens include the fire-resistant anchoring structure of the FRP bar and the concrete cubic test block 4. The sleeve 2 is embedded in the concrete cubic test block 4, and the end of the FRP bar 1 facing away from the concrete cubic test block 4 is provided with the anchoring sleeve 7. In the specific implementation process, five concrete pull-out specimens can be prepared for testing separately.

[0062] In some embodiments, the concrete cubic test block is a concrete cubic test block with a side length of 150mm. The bonding length between the concrete cubic test block and the fire-resistant anchoring structure of the FRP reinforcement is l1 = 100mm, and the unbonded length is l2 = 50mm. The unbonded section of the FRP reinforcement 1 is externally fitted with a PVC pipe 6. In order to prevent the concrete from splitting and breaking, the interior of the concrete cubic test block is provided with spiral stirrups 5 with a pitch of 40mm and an outer diameter of 100mm.

[0063] In some embodiments, in S5, the sleeve is arranged in the beam support, usually at the center of the beam. According to the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials" (GB50608-2020), the position of the fire-resistant anchoring structure at the support under the fire resistance limit is calculated. It is necessary to ensure that its ΔT≤50℃. Under this temperature field, the performance of the aluminum sleeve is not affected and can perform the anchoring performance of the fire-resistant anchoring structure normally.

[0064] In some embodiments, in S6, the ultimate strength of the FRP reinforcement under fire conditions will be weakened to some extent. First, the highest temperature of the FRP reinforcement under the fire resistance limit is calculated according to the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials" (GB50608-2020). Then, the ultimate strength of the FRP reinforcement at that temperature is determined according to the strength-temperature change curve of the FRP reinforcement. Specifically, the highest temperature of the FRP reinforcement under the fire resistance limit is determined by ΔT = k t T y The calculations were performed based on the distance y between the FRP reinforcement fire-resistant anchorage structure and the beam side, and the temperature field was calculated according to a 1-hour single-sided fire exposure time. Figures 3 to 5 We can get k t and T y The value of .

[0065] In some embodiments, a fire-resistant anchoring structure for FRP bars in concrete slabs is disclosed, which is manufactured using the design method for fire-resistant anchoring structures for FRP bars in concrete slabs as described in any of the preceding embodiments. By designing the structure of the external compression sleeve for FRP bars, even if the FRP bars in the middle of the slab span fail to bond with the concrete under fire, the sleeve at the support can provide anchoring for the FRP bars, ensuring that the FRP bars and concrete share the load under fire, thus solving the problem of anchoring FRP bars in concrete under fire conditions.

[0066] A more specific implementation method for the design of fire-resistant anchorage structure of FRP reinforcement in concrete slabs, such as Figure 7 As shown, this embodiment discloses a concrete slab with an additional FRP (Fiber Reinforced Plastic) fire-resistant anchoring structure. The concrete slab has dimensions of 3000mm × 2000mm × 200mm, a protective layer thickness of 15mm, and uses 8mm diameter CFRP (Crystal Fiber Reinforced Plastic) bars arranged in a double-layer, bidirectional configuration. The concrete beam has dimensions of 400mm × 300mm, and the design fire resistance rating of the FRP-reinforced concrete slab is 1 hour. The design method for the FRP-reinforced fire-resistant anchoring structure includes the following steps:

[0067] S1, FRP reinforcement fabrication: Embossed CFRP reinforcement is selected, with a thread pitch of 14mm, a thread depth of 0.17mm, an ultimate strength ≥2400MPa, and an effective stress f of the carbon fiber reinforcement. fe =1242MPa, elastic modulus ≥155GPa;

[0068] S2, Sleeve preparation, using 6061-T6 aluminum alloy, the aluminum alloy sleeve length is 50mm, the thickness should be 5mm, and the inner diameter is 10mm;

[0069] S3. Crimping Amount Determination: Five crimping amount gradients (0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm) were selected. CFRP bars were crimped according to these five amounts. When the crimping amount was 1.0mm, the CFRP bars produced a brittle sound during crimping. No sound was produced when the crimping amount was 0.9mm or less. Pull-out tests were performed on the crimped structure. The failure mode of the CFRP bars was pull-out failure, and they did not break at the crimping point. Therefore, crimping amounts of 0.9mm and below provide reliable anchoring. To meet the requirements of batch crimping in the project, 0.8mm, which is one order of magnitude smaller than the maximum crimping amount of 0.9mm, was selected as the project crimping amount.

[0070] S4. Anchorage strength determination: Five FRP (Fire Reinforced Polymer) rebar fire-resistant anchorage concrete pull-out specimens were fabricated using a 0.8mm compression allowance. Pull-out tests were conducted 28 days after concrete pouring and curing to obtain the pull-out force F. The anchorage strength of the FRP rebar fire-resistant anchorage structure was determined. It is determined that τ is the anchorage strength, F is the pull-out force, d is the diameter of the CFRP bar, l1 is the bond length, and the average anchorage strength is 737 MPa.

[0071] S5, the anchorage location is determined. The anchorage is selected and placed at the center of the beam fabrication, 200mm from the side of the beam (i.e., y = 200mm). The temperature field is calculated based on a single-sided fire exposure for 1 hour. (Refer to...) Figure 5 Get k t =0.1, ΔT=k t T y=0.1×50=5℃, indicating that the temperature rises by 5℃ after the anchoring structure is exposed to fire for 1 hour, which satisfies ΔT≤50℃. Under this temperature field, the performance of the aluminum sleeve is not affected and can perform the anchoring performance of the fire-resistant anchoring structure normally.

[0072] S6, Anchorage strength verification: First, calculate the fire resistance limit temperature of the CFRP reinforcement and check... Figures 3-5 When the fire resistance is 1 hour, calculated based on a one-dimensional temperature field, y = 19 mm. The fire resistance limit of the carbon fiber reinforced concrete slab is taken as 1 hour, k. t =0.68, T y =650℃, ΔT=k t ×T y =0.68 × 650 = 442℃, check Figure 6 It can be seen that the strength of the carbon fiber reinforcement remains at 30% at 442℃, and the strength is f = f fe ×30%=1242×30%=373MPa, the anchoring strength 737MPa is greater than 373MPa, therefore, the anchoring structure meets the design requirements.

[0073] S7, mass production, mass production of FRP reinforcement fire-resistant anchoring structure.

[0074] A more specific implementation method for the design of fire-resistant anchorage structure of FRP reinforcement in concrete slabs, such as Figure 7 As shown, this embodiment discloses a concrete slab with an additional FRP reinforcement fire-resistant anchoring structure, measuring 3000mm×2000mm×200mm, with a protective layer thickness of 20mm. The FRP reinforcement is 8mm diameter CFRP reinforcement, arranged in a double layer and bidirectional manner. The concrete beam dimensions are 400mm×300mm. The design fire resistance rating of the FRP reinforcement concrete slab is 1.5h. The design method of the FRP reinforcement fire-resistant anchoring structure includes the following steps:

[0075] S1, FRP reinforcement fabrication: Embossed CFRP reinforcement is selected, with a thread pitch of 14mm, a thread depth of 0.17mm, an ultimate strength ≥2400MPa, and an effective stress f of the carbon fiber reinforcement. fe =1242MPa, elastic modulus ≥155GPa;

[0076] S2, Sleeve preparation, using 6061-T6 aluminum alloy, the aluminum alloy sleeve length is 50mm, the thickness should be 5mm, and the inner diameter is 10mm;

[0077] S3. Crimping Amount Determination: Five crimping amount gradients (0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm) were selected. CFRP bars were crimped according to these five amounts. When the crimping amount was 1.0mm, the CFRP bars produced a brittle sound during crimping. No sound was produced when the crimping amount was 0.9mm or less. Pull-out tests were performed on the crimped structure. The failure mode of the CFRP bars was pull-out failure, and they did not break at the crimping point. Therefore, crimping amounts of 0.9mm and below provide reliable anchoring. To meet the requirements of batch crimping in the project, 0.8mm, which is one order of magnitude smaller than the maximum crimping amount of 0.9mm, was selected as the project crimping amount.

[0078] S4. Anchorage strength determination: Five FRP (Fire Reinforced Polymer) rebar fire-resistant anchorage concrete pull-out specimens were fabricated using a 0.8mm compression allowance. Pull-out tests were conducted 28 days after concrete pouring and curing to obtain the pull-out force F. The anchorage strength of the FRP rebar fire-resistant anchorage structure was determined. It is determined that τ is the anchorage strength, F is the pull-out force, d is the diameter of the CFRP bar, l1 is the bond length, and the average anchorage strength is 737 MPa.

[0079] S5, the anchorage location is determined. The anchorage is selected and placed at the center of the beam fabrication, 200mm from the side of the beam (i.e., y = 200mm). The temperature field is calculated based on a single-sided fire exposure of 1.5 hours. (See attached diagram). Figure 5 Get k t =0.45, ΔT = k t T y =0.45×50=22.5℃, indicating that the temperature rises to 22.5℃ after 1.5 hours of exposure to fire at the anchoring location, satisfying ΔT≤50℃. Under this temperature field, the performance of the aluminum sleeve is not affected and it can perform the anchoring performance of the fire-resistant anchoring structure normally.

[0080] S6, Anchorage strength verification: First, calculate the fire resistance limit temperature of the CFRP reinforcement. See attached... Figures 3-5 When the fire resistance is 1.5 hours, calculated based on a one-dimensional temperature field, y = 24 mm. The fire resistance limit of the carbon fiber reinforced concrete slab is taken as 1.5 hours, k. t =0.85, T y =600℃, ΔT=k t ×T y =0.85×600=510℃, check Figure 6 It can be seen that the strength of the carbon fiber reinforcement remains at 20% at 510℃, and the strength is f = f fe ×20%=1242×20%=248.4MPa, the anchoring strength 737MPa is greater than 248.4MPa, therefore, the anchoring structure meets the design requirements.

[0081] S7, mass production, mass production of FRP reinforcement fire-resistant anchoring structure.

[0082] The various embodiments of the present invention have now been described in detail. To avoid obscuring the concept of the invention, some details known in the art have not been described. Those skilled in the art will fully understand how to implement the technical solutions disclosed herein based on the above description.

[0083] The embodiments described above only illustrate some implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A design method for fire-resistant anchorage structure of FRP reinforcement in concrete slabs, characterized in that, Includes the following steps: S1, FRP rib preparation, using pultrusion molding process, directly forming a threaded structure on the outer surface of the FRP rib; S2, Sleeve preparation: Cut the pipe into sections according to the designed sleeve length; S3, Determine the crimping amount. Select several crimping amount gradients and crimp the sleeve to the outside of the FRP bar according to the selected crimping amount. Determine the engineering crimping amount based on the crimping situation. S4, Anchorage strength determination: According to the engineering compression amount determined in S3, several FRP fire-resistant anchorage structures are made, and the FRP fire-resistant anchorage structures are made into concrete pull-out specimens. The anchorage strength between the FRP fire-resistant anchorage structure and the concrete is determined by pull-out test. S5, the anchorage location is determined, the sleeve is arranged in the beam support, and the temperature rise value ΔT of the FRP fire-resistant anchorage at the support location after being exposed to fire is calculated according to the technical standard. It is necessary to ensure that ΔT≤50℃. S6, Anchorage strength verification: Calculate the highest temperature of the FRP bar under the fire resistance limit according to the technical standard, and the FRP bar strength change curve with temperature to determine the ultimate strength of the FRP bar at the highest temperature. If the anchorage strength of the fire-resistant anchorage structure of the FRP bar is greater than the ultimate strength of the FRP bar, the anchorage requirement is met; otherwise, the sleeve size and crimping amount need to be redesigned. Once the S7 FRP fire-resistant anchoring structure meets the anchoring requirements, the FRP fire-resistant anchoring structure can be mass-produced.

2. The design method for the fire-resistant anchorage structure of FRP reinforcement in concrete slabs according to claim 1, characterized in that: In S1, the thread pitch of the outer threaded structure of the FRP rib is 10-15mm, and the thread depth is ≥0.15mm.

3. The design method for the fire-resistant anchorage structure of FRP reinforcement in concrete slabs according to claim 1, characterized in that: In S2, the sleeve material is selected with a thickness of 3-5mm and an inner diameter that is 2mm larger than the diameter of the FPR rib.

4. The design method for the fire-resistant anchorage structure of FRP reinforcement in concrete slabs according to claim 3, characterized in that: In S2, the tubing is 6061-T6 aluminum alloy tubing, and the sleeve length is designed to be 50-100mm.

5. The design method for the fire-resistant anchorage structure of FRP reinforcement in concrete slabs according to claim 1, characterized in that, In S3, the method for determining the amount of engineering pressing is as follows: S31, After crimping, check whether the surface of the FRP rib is damaged and whether any sound is made during the crimping process; S32, the maximum amount of crimping without either of the two phenomena is the ultimate crimping amount; S33, select a pressing amount that is one level lower than the ultimate pressing amount as the engineering pressing amount.

6. The design method for the fire-resistant anchorage structure of FRP reinforcement in concrete slabs according to claim 1, characterized in that: In S3, the crimping amount ranges from 0.5 to 1.5 mm, and the gradient value of the crimping amount gradient is 0.1 mm.

7. The design method for the fire-resistant anchorage structure of FRP reinforcement in concrete slabs according to claim 1, characterized in that: In S4, the calculation formula for the anchorage strength between the FRP reinforcement fire-resistant anchorage structure and the concrete is as follows: Where τ is the anchorage strength, F is the pull-out force, d is the diameter of the FRP bar, and l1 is the bond length.

8. The design method for the fire-resistant anchorage structure of FRP reinforcement in concrete slabs according to claim 1, characterized in that: In S4, the concrete pull-out specimen includes an FRP bar fire-resistant anchoring structure and a concrete cubic test block. The sleeve is embedded in the concrete cubic test block, and an anchoring sleeve is provided at the end of the FRP bar away from the concrete cubic test block.

9. The design method for the fire-resistant anchorage structure of FRP reinforcement in concrete slabs according to claim 8, characterized in that: The concrete cubic test block is a concrete cubic test block with a side length of 150mm. The bonding length between the concrete cubic test block and the FRP fire-resistant anchoring structure is l1 = 100mm, and the unbonded length is l2 = 50mm. The concrete cubic test block is equipped with spiral stirrups with a pitch of 40mm and an outer diameter of 100mm inside.

10. A fire-resistant anchoring structure for FRP reinforcement in a concrete slab, characterized in that: It is manufactured using the design method for the fire-resistant anchorage structure of FRP reinforcement in concrete slabs as described in any one of claims 1 to 9.

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