FRP rib reinforced concrete composite beam

Abstract

The utility model discloses an FRP (fiber reinforce plastic) bar reinforced UHPC (ultra high performance concrete)-common concrete composite beam structure, which belongs to the field of structural engineering and comprises an FRP bar cage, a beam lower UHPC layer and a beam upper common concrete layer, the FRP bar cage penetrates through the beam lower UHPC layer and the beam upper common concrete layer, and the beam lower UHPC layer and the beam upper common concrete layer are connected into a whole through the FRP bar cage. The characteristics of high strength and good ductility of UHPC (Ultra High Performance Concrete) are fully utilized, the advantage of high tensile strength of FRP (Fiber Reinforced Plastic) ribs is fully exerted, the durability of the member is improved in a corrosion and severe environment, the crack width requirement in a use limit state is met, and the UHPC-FRP reinforced concrete member has the technical advantages of good stress performance, high material utilization rate, good economical efficiency and the like.

Description

Technical Field

[0001] The utility model relates to a FRP bar reinforced concrete composite beam, belonging to the technical field of structural engineering. Background Art

[0002] Conventional reinforced concrete structures are prone to corrosion of steel bars in corrosive or harsh environments, which also leads to serious deterioration of structural performance and requires expensive repair costs. Fiber-reinforced polymer (FRP) bars are considered to be an effective measure to overcome the corrosion problem of concrete structures. FRP bars have many obvious advantages over steel bars, including high tensile strength and fatigue strength, high corrosion resistance, light weight, easy transportation and handling, thermal and electrical insulation properties, and insensitivity to magnetic fields. These advantages have led to their increasing application in the field of structural engineering. However, due to the low elastic modulus of FRP bars, concrete components reinforced with FRP bars often show larger deformations and wider cracks than reinforced concrete components. Therefore, the design of FRP-reinforced concrete components is often restricted by the normal service limit state, which in turn prevents the high tensile strength of FRP bars from being fully utilized. In addition, due to the linear elastic properties of FRP bars, structures using FRP bars often need to be designed as over-reinforced components to obtain greater ductility. However, ordinary concrete with low ultimate compressive strain is a quasi-brittle material, which makes FRP-reinforced ordinary concrete structures at risk of compressive failure.

[0003] Ultra-high performance concrete (UHPC) is an innovative cement-based engineering material, which is a mixture of silicate cement, fine silica sand, silica fume, quartz powder, high-efficiency water reducer and steel or organic short fibers, with a water-cement ratio of less than 0.25. Compared with ordinary concrete, UHPC has excellent properties such as better compressive and tensile strength, significant durability and ductility, and small shrinkage after thermal curing. Existing research results have shown that UHPC beams reinforced with FRP bars have higher flexural stiffness. The addition of short steel fibers prevents the development of UHPC microcracks into macro cracks. The flexural stiffness after cracking can still be maintained at a high level, and due to the strain hardening characteristics of UHPC, the crack width requirements are met under the service limit state. It can be seen that combining the unique advantages of FRP bars and UHPC is expected to produce structural components with high ductility, light weight and significant durability.

[0004] However, some disadvantages limit the widespread application of UHPC in the construction industry, such as high initial cost, lack of design specifications for UHPC structures, and relatively scattered material properties of concrete due to the random distribution of fibers, and demanding preparation and curing conditions. The production and application of UHPC is cost- and energy-intensive, and it is difficult for contractors to use mechanical pumps to transport UHPC due to its high viscosity. In short, it is not realistic to use ultra-high performance concrete to construct new structural units. At present, the application of UHPC is limited to the renovation and repair of existing structures, which does not fully reflect the superior performance of this material. In fact, it is more realistic to use ultra-high performance concrete in critical parts of the structure, such as the plastic hinge area of ​​beams and beam-column joints. Summary of the invention

[0005] The purpose of the utility model is to provide a concrete composite beam reinforced with FRP bars, which can improve the durability of the component under corrosion and harsh environments while meeting the crack width requirements under the limit state of use. This type of beam component has technical advantages such as good stress performance, high material utilization rate, and good economy.

[0006] In order to achieve the above-mentioned purpose, the technical solution of the utility model is: an FRP reinforcement concrete composite beam, comprising an FRP reinforcement cage, a UHPC layer at the lower part of the beam, and an ordinary concrete layer at the upper part of the beam, wherein the FRP reinforcement cage runs through the UHPC layer at the lower part of the beam and the ordinary concrete layer at the upper part of the beam, and the UHPC layer at the lower part of the beam and the ordinary concrete layer at the upper part of the beam are connected as a whole through the FRP reinforcement cage.

[0007] Furthermore, the cross-section of the UHPC layer at the lower part of the beam and / or the ordinary concrete layer at the upper part of the beam is a rectangular, trapezoidal or arc-shaped structure.

[0008] Furthermore, the height of the UHPC layer at the lower part of the beam is less than or equal to 1 / 2 of the height of the entire concrete composite beam.

[0009] Furthermore, a group of anchor bolts are implanted between the UHPC layer at the lower part of the beam and the ordinary concrete layer at the upper part of the beam.

[0010] Furthermore, the FRP reinforcement cage includes FRP longitudinal reinforcement, FRP stirrups and regional restrained FRP reinforcement, and the FRP stirrups and regional restrained FRP reinforcement are evenly arranged along the length of the FRP longitudinal reinforcement.

[0011] Furthermore, the anchor bolts are spaced the same as the spacing of the FRP stirrups and are arranged in a staggered manner with the FRP stirrups.

[0012] Furthermore, the top surface of the UHPC layer at the lower part of the beam is provided with a UHPC top sandblasted rough surface.

[0013] Due to the adoption of the above technical scheme, the advantages of the utility model are as follows: the utility model fully utilizes the characteristics of UHPC with high strength and good ductility, and at the same time gives full play to the advantages of FRP tendons with high tensile strength, improves the durability of components under corrosion and harsh environments, and meets the crack width requirements under the limit state of use, and has technical advantages such as good stress performance, high material utilization rate, and good economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and other aspects and advantages of the present invention will become more readily apparent by describing in more detail exemplary embodiments of the present invention with reference to the accompanying drawings, in which:

[0015] Figure 1 It is a structural schematic diagram of the first embodiment of the utility model;

[0016] Figure 2 for Figure 1 Middle AA section;

[0017] Figure 3 This is a schematic diagram of the FRP cage of the first embodiment of the utility model;

[0018] Figure 4 This is a schematic diagram of the end of the UHPC layer at the lower part of the beam of the first embodiment of the utility model;

[0019] Figure 5 This is a schematic diagram of the sandblasted rough surface of the UHPC top in the first embodiment of the utility model;

[0020] Figure 6 for Figure 5 Middle BB section;

[0021] Figure 7 It is a structural schematic diagram of the second embodiment of the utility model.

[0022] Explanation of reference numerals: 1-FRP reinforcement cage; 11-FRP longitudinal reinforcement; 12-FRP stirrups; 13-regional restrained FRP reinforcement; 2-UHPC layer at the lower part of the beam; 3-ordinary concrete layer at the upper part of the beam; 4-sandblasted rough surface of the UHPC top; 5-UHPC-ordinary concrete interface anchor bolt. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the utility model clearer, the utility model is further described in detail below with reference to the accompanying drawings and embodiments, wherein the materials described can be obtained through commercial channels.

[0024] Embodiment 1

[0025] The structural schematic diagram of a FRP reinforced concrete composite beam of the utility model is as follows Figures 1 to 6As shown, it includes an FRP cage 1, a UHPC layer 2 at the bottom of the beam, and an ordinary concrete layer 3 at the top of the beam. The FRP cage 1 runs through the UHPC layer 2 at the bottom of the beam and the ordinary concrete layer 3 at the top of the beam, and the UHPC layer 2 at the bottom of the beam and the ordinary concrete layer 3 at the top of the beam are connected as a whole through the FRP cage 1. In this embodiment, the cross-section of the UHPC layer 2 at the bottom of the beam or the ordinary concrete layer 3 at the top of the beam is a rectangular structure. The height of the UHPC layer 2 at the bottom of the beam is less than 1 / 2 of the height of the entire concrete composite beam. The FRP cage 1 includes FRP longitudinal bars 11, FRP stirrups 12, and regional constrained FRP bars 13. The FRP stirrups 12 and regional constrained FRP bars 13 are evenly arranged along the length of the FRP longitudinal bars 11.

[0026] A group of anchor bolts 5 are implanted between the UHPC layer 2 at the bottom of the beam and the ordinary concrete layer 3 at the top of the beam; the spacing between the anchor bolts 5 is the same as the spacing between the FRP stirrups 12, and they are arranged alternately with the FRP stirrups 12. As an important interface connection element, the anchor bolts 5 are used to firmly connect the UHPC layer 2 at the bottom of the beam and the ordinary concrete layer 3 at the top of the beam to form a whole, which can withstand large tensile and shear forces, provide secondary protection for the integrity and stability of the beam component, and avoid excessive stress at the bonding interface between the UHPC layer 2 at the bottom of the beam and the ordinary concrete layer 3 at the top of the beam. The anchor bolts 5 are commercial hexagonal full-thread chemical anchor bolts made of 8.8 grade carbon steel, with a yield strength of 640MPa and an ultimate strength of 800MPa. They are surface treated with blue-white zinc plating to effectively improve their anti-corrosion effect.

[0027] The top surface of the UHPC layer 2 at the lower part of the beam is provided with a UHPC top sandblasting rough surface 4. The UHPC top sandblasting rough surface 4 is intended to improve the bonding performance of the UHPC layer 2 at the lower part of the beam and the ordinary concrete layer 3 at the upper part of the beam, thereby making the interlayer bonding firm, improving the shear strength, and enhancing the overall force performance and deformation resistance of the beam component. During the sandblasting process, the abrasive is selected as quartz sand with a particle size greater than 0.6 mm, the minimum air pressure of the dry sandblasting machine is 0.5 MPa, the spray angle is selected as a fixed value between 30 and 75°, the spray distance is less than 200 mm, and the spray time is between 20 and 30 seconds, finally forming a uniform and rough UHPC top sandblasting rough surface 4.

[0028] The composite beam of the utility model can effectively solve a series of problems encountered in the promotion of FRP bar reinforced concrete structure, such as large deflection, wide cracks, etc., which do not meet the requirements of the normal use limit state. In this embodiment, the specific materials used are as follows:

[0029] The FRP bars used in the utility model include carbon fiber reinforced polymer (CFRP) bars, basalt fiber reinforced polymer (BFRP) bars, glass fiber reinforced polymer (GFRP) bars, and aramid fiber reinforced polymer (AFRP) bars. The ultimate tensile strength of the FRP bars is greater than 1000MPa, the elastic modulus can reach 120GPa, and the ultimate elongation can reach 0.019.

[0030] Ultra-high performance concrete (UHPC) is made by mixing active powder concrete and discrete steel fibers on site. It has a compressive strength greater than 150MPa, a sustained tensile strength greater than 6MPa after cracking, and an elastic modulus greater than 40GPa. Steel fibers can significantly improve the energy dissipation capacity of concrete and reduce the brittleness of the material. The material of the UHPC layer 2 at the bottom of the beam is a commercial premix, which is made of cement (767kg / m 3 )、fine sand (1067kg / m 3 ), silica fume (280kg / m 3 ) and high performance water reducing agent (27kg / m 3 ) with a water-cement ratio of 0.23. The main cementitious material is PO 52.5 ordinary Portland cement. The average particle size of fine sand is 0.3mm and the fineness modulus is 2.1. The chemical composition of silica fume is CaO 0.39%, SiO2 97.56%, Al2O3 0.17%, MgO 0.83%, K2O 0.26%, P2O5 0.27% and Na2O 0.37%. The steel fiber added to the premix is ​​a direct copper-plated type with a length of 14mm and a diameter of 0.15mm. The steel fiber accounts for 1% to 2% of the volume of the mixture.

[0031] Ordinary concrete with a strength grade not less than C30 can be provided by commercial concrete companies. Compared with UHPC, the construction technology and methods of ordinary concrete are quite mature, and the construction and preparation process is relatively simple, which is easy for construction personnel to master. In addition, its material sources are wide, so the cost is low and it is suitable for large-scale production and application. Ordinary concrete has good fluidity and can fill various shapes of templates to meet different construction needs. At the same time, its hardening process is relatively stable, which can ensure the integrity and stability of the structure. In view of the low elastic modulus of FRP bars, its high strength advantage can only be exerted under higher strains. At this time, the ordinary concrete in the upper compression zone will be crushed due to reaching the ultimate compressive strain, resulting in brittle failure of the beam member. Therefore, regional restrained FRP bars are added in the compression zone to enhance the compressive performance of ordinary concrete and avoid the above-mentioned adverse damage phenomena.

[0032] The specific manufacturing process of the first embodiment of the present utility model is as follows:

[0033] 1. First, a template is made according to the size of the beam component, and then the FRP longitudinal reinforcement 11, FRP stirrups 12 and regional restraining FRP reinforcement 13 are tied into an FRP reinforcement cage 1 using thin iron wires, while satisfying the protective layer thickness of the FRP reinforcement in the concrete.

[0034] 2. The height of the UHPC layer 2 at the bottom of the cast beam shall not exceed half of the overall height of the beam, and shall be cured for at least 7 days under standard conditions until the compressive strength reaches 80% of that at 28 days of age.

[0035] 3. The top surface of the UHPC layer 2 at the lower part of the beam is sandblasted for 20 to 30 seconds to form a uniform UHPC top sandblasted rough surface 4.

[0036] 4. Evenly spaced anchor bolts 5 are buried on the top surface of the UHPC layer 2 at the lower part of the beam. The main operation steps are: (a) drilling holes; (b) cleaning holes; (c) inserting drug tubes; (d) implanting anchor bolts 5; (e) solidification and hardening, which takes at least one hour at room temperature. The spacing between anchor bolts 5 is the same as the spacing between FRP stirrups 12, and they are staggered, such as Figure 6 Finally, pour the ordinary concrete layer 3 on the upper part of the beam and cure it for 28 days under standard conditions.

[0037] Embodiment 2

[0038] like Figure 7 As shown, the structure and materials used in the composite beam in this embodiment are the same as those in the composite beam in the first embodiment, and the distinguishing feature is that the cross-section of the UHPC layer 2 at the bottom of the beam in this embodiment is a rectangular structure, while the cross-section of the ordinary concrete layer 3 at the top of the beam is a trapezoidal structure, thereby forming a FRP bar reinforced UHPC-ordinary concrete T-shaped composite beam. Compared with the first embodiment, only the cross-sectional shape of the beam component is changed, and the size and arrangement position of the FRP stirrups and the regional constraint FRP bars are changed accordingly, while the height regulation and interface treatment method of the UHPC layer 2 at the bottom of the beam remain unchanged. The above description is only a preferred embodiment of the utility model, and is not intended to limit the utility model. Although the utility model is described in detail with reference to the above embodiments, it is still possible for those skilled in the art to modify the above technical solutions, or to replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the utility model shall be included in the protection scope of the utility model.

[0039] In summary, the composite beam of the utility model fully utilizes the characteristics of UHPC with high strength and good ductility, and gives full play to the advantages of FRP tendons with high tensile strength, improves the durability of components under corrosion and harsh environments, and meets the crack width requirements under the service limit state, and has technical advantages such as good stress performance, high material utilization rate, and good economy.

Claims

1. A FRP reinforced concrete composite beam, comprising an FRP reinforcement cage (1), a UHPC layer (2) at the lower part of the beam, and a common concrete layer (3) at the upper part of the beam, characterized in that: The FRP reinforcement cage (1) penetrates the UHPC layer (2) at the bottom of the beam and the ordinary concrete layer (3) at the top of the beam, and the UHPC layer (2) at the bottom of the beam and the ordinary concrete layer (3) at the top of the beam are connected as a whole through the FRP reinforcement cage (1).

2. The FRP reinforced concrete composite beam according to claim 1, characterized in that: The cross-section of the UHPC layer (2) at the lower part of the beam and / or the ordinary concrete layer (3) at the upper part of the beam is a rectangular, trapezoidal or arc-shaped structure.

3. The FRP bar reinforced concrete composite beam according to claim 1, characterized in that: The height of the UHPC layer (2) at the lower part of the beam is less than or equal to 1 / 2 of the height of the entire concrete composite beam.

4. The FRP bar reinforced concrete composite beam according to claim 1, characterized in that: A group of anchor bolts (5) are implanted between the UHPC layer (2) at the lower part of the beam and the ordinary concrete layer (3) at the upper part of the beam.

5. The FRP bar reinforced concrete composite beam according to claim 1, characterized in that: The FRP reinforcement cage (1) comprises FRP longitudinal reinforcement (11), FRP stirrups (12) and regional restraining FRP reinforcement (13), wherein the FRP stirrups (12) and regional restraining FRP reinforcement (13) are evenly arranged along the length of the FRP longitudinal reinforcement (11).

6. The FRP bar reinforced concrete composite beam according to claim 4, characterized in that: The spacing between the anchor bolts (5) is the same as the spacing between the FRP stirrups (12), and the anchor bolts (5) are arranged in a staggered manner with the FRP stirrups (12).

7. The FRP bar reinforced concrete composite beam according to claim 1, characterized in that: The top surface of the UHPC layer (2) at the lower part of the beam is provided with a UHPC top sandblasted rough surface (4).

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