Prestress UHPC reinforced RC beam structure and construction method thereof

Abstract

The invention relates to a prestressed UHPC reinforced RC beam structure and a construction method thereof, and belongs to the field of concrete structure reinforcement. The construction method of the prestressed UHPC reinforced RC beam structure comprises the following steps: step 1, manufacturing a CFRP-UHPC composite groove; step 2, the CFRP-UHPC composite groove is wrapped and fixed on the RC beam, in the step 1, the bending resistance of the UIPC equivalent rectangular plate, the flexural capacity of the UIPC-RC beam and the flexural capacity of the RC beam reinforced by the CFRP-UHPC composite groove are calculated, and finally, the shear resistance of the RC frame node reinforced by the CFRP-UHPC composite groove is analyzed to obtain a final CFRP-UHPC composite groove model. The CFRP-UHPC composite groove is formed by pouring a reinforcing rib and a CFRP plate in the UHPC composite groove, and a prestressed steel noose device is mounted in the CFRP-UHPC composite groove; the CFRP rib material is adopted to reinforce the UHPC prefabricated slab, a high-performance composite board is formed, the stress state of the RC beam structure is effectively improved, and the reinforcing efficiency is improved; and a final reinforcement model is obtained through calculation and analysis, so that the CFRP-UHPC composite groove performs targeted reinforcement on different RC beams, and the reinforcement effect is improved.

Description

Technical Field

[0001] The invention relates to a prestressed UHPC-reinforced RC beam structure and a construction method thereof, belonging to the field of concrete structure reinforcement. Background Technique

[0002] Due to low reinforcement ratio or performance degradation (such as steel bar corrosion, concrete cracking, etc.) of reinforced concrete beams, the ductility of RC beams is poor, the bearing capacity is reduced, and cracking occurs, which will bring serious structural hidden dangers. Reinforced concrete (RC) beams are the most important load-bearing members in engineering structures such as building construction and bridge construction. The insufficient bearing capacity and durability caused by internal and external factors will pose a huge threat to the safety of building structures. Therefore, seeking an effective reinforcement method to improve the structural performance and durability of RC bridges is one of the important research directions at present. Some researchers have studied the reinforcement effect of using UHPC on reinforced concrete beams. However, for the post-cast conventional UHPC layer reinforcement, the stress state of the structure cannot be improved, and damage cracks are likely to reopen under the action of external loads. For RC beams with serious cracking or those that need to increase the load level, the reinforcement efficiency still needs to be improved. Therefore, a prestressed UHPC-reinforced RC beam structure and a construction method thereof are proposed. The RC beam is passively reinforced by a composite plate with high strength, high toughness and high durability to improve the reinforcement effect. Summary of the Invention

[0003] In order to overcome the problems existing in the background technique, the invention uses CFRP bars to reinforce UHPC precast slabs to form a composite plate with high strength, high toughness and high durability for joint reinforcement, effectively improving the stress state of the RC beam structure and enhancing the reinforcement efficiency; by calculating the flexural force of the UIPC equivalent rectangular plate, the flexural bearing capacity of the UIPC-RC beam and the flexural bearing capacity of the CFRP-UHPC composite groove-reinforced RC beam, and finally analyzing the shear resistance of the CFRP-UHPC composite groove-reinforced RC frame joint, the final reinforcement model is obtained, so that the CFRP-UHPC composite groove can be used for targeted reinforcement of different RC beams to improve the reinforcement effect.

[0004] In order to overcome the problems existing in the background technique and solve the above problems, the invention is realized through the following technical solutions:

[0005] A prestressed UHPC-reinforced RC beam structure includes a CFRP-UHPC composite groove, a bottom plate, prestressed steel strands, anchor bars, a UHPC composite groove, reinforcing bars, and a CFRP plate. The HPC composite groove is filled with reinforcing bars and a CFRP plate. The bottom plate is installed at the bottom of the CFRP-UHPC composite groove, and the anchor bars are installed at the upper ends of both sides of the CFRP-UHPC composite groove. The prestressed steel strands connect the bottom plate and the anchor bars.

[0006] A construction method for prestressed UHPC-reinforced RC beams includes the following steps:

[0007] Step 1, fabricate a CFRP-UHPC composite groove;

[0008] Step 2, wrap and fix the CFRP-UHPC composite groove on the RC beam.

[0009] Preferably, in Step 1 of fabricating the CFRP-UHPC composite groove, CFRP plates are added to the UHPC precast slab and extended along the beam axis direction, and a prestressed steel strand structure is added to improve the shear strength of the joint core area and the flexural capacity of the RC beam.

[0010] Preferably, the materials of the CFRP-UHPC composite groove in Step 1 include Portland cement, quartz sand, quartz powder, silica fume, fly ash, steel fibers, and high-range water reducer. To enhance the tensile toughness of UHPC, hybrid steel fibers are used with a volume fraction of 3%, including 1% short straight steel fibers and 2% hooked-end steel fibers; to reduce the water-binder ratio of UHPC and improve its fluidity, polycarboxylate superplasticizer is used with a volume content of 1.5% and a water reduction rate exceeding 30%, and the water-binder ratio of UHPC is 0.18.

[0011] Preferably, in Step 1, according to the dimensions, reinforcement, and stress conditions of the RC beam to be reinforced, determine the dimensions of the CFRP-UHPC composite groove, the quantity and distribution of the CFRP plates, and determine the installation hole positions of the CFRP-UHPC composite groove according to the steel bar positions of the RC beam.

[0012] Preferably, when fabricating the CFRP-UHPC composite groove in Step 1, first conduct the flexural calculation of the UIPC equivalent rectangular plate, then calculate the flexural bearing capacity of the UIPC-RC beam, then calculate the flexural bearing capacity of the RC beam reinforced with the CFRP-UHPC composite groove, and finally conduct the shear analysis of the RC frame joint reinforced with the CFRP-UHPC composite groove.

[0013] Preferably, when fabricating the CFRP-UHPC composite groove in Step 1, based on the relevant calculations of the CFRP-UHPC composite plate reinforced RC frame, obtain the design of the RC frame joint reinforced with the CFRP-UHPC composite groove, obtain the cross-sectional area of the CFRP-UHPC composite groove and the CFRP reinforcement area, and fabricate the CFRP-UHPC composite groove.

[0014] Preferably, Step 1 specifically further includes: after completing the fabrication of the CFRP-UHPC composite groove, cure the CFRP-UHPC composite groove for a certain period of time to improve its quality.

[0015] Preferably, step 2 is to paste the CFRP-UHPC composite groove on the surface of the RC beam using an adhesive, and then mechanically anchor the CFRP-UHPC composite groove and the RC beam through anchor bolts.

[0016] The beneficial effects of the present invention are as follows:

[0017] The present invention uses CFRP reinforcement to strengthen the UHPC precast slab to form a composite slab with high strength, high toughness and high durability, which is used for joint reinforcement, effectively improving the stress state of the RC beam structure and enhancing the reinforcement efficiency; by calculating the bending resistance of the UIPC equivalent rectangular plate, the bending bearing capacity of the UIPC-RC beam and the flexural bearing capacity of the CFRP-UHPC composite groove reinforced RC beam, and finally analyzing the shear resistance of the CFRP-UHPC composite groove reinforced RC frame joint to obtain the final reinforcement model, so that the CFRP-UHPC composite groove can be specifically reinforced for different RC beams, improving the reinforcement effect. Description of the Drawings

[0018] Figure 1 is the structural schematic diagram of the present invention;

[0019] Figure 2 is the right view of the CFRP-UHPC composite groove of the present invention;

[0020] Figure 3 is the front view of the CFRP-UHPC composite groove of the present invention.

[0021] The reference numerals in the figure are: 1-RC beam, 2-CFRP-UHPC composite groove, 3-anchor bolt, 4-bottom plate, 5-prestressed steel strand, 6-anchoring strip, 201-UHPC composite groove, 202-reinforcing rib, 203-CFRP plate. Detailed Embodiments

[0022] In order to make the purpose, technical solutions and beneficial effects of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings for the convenience of those skilled in the art to understand.

[0023] As Figures 1 to 3As shown in the figure, a prestressed UHPC-reinforced RC beam structure includes an RC beam 1, a CFRP-UHPC composite groove 2, anchor bolts 3, a bottom plate 4, prestressed steel strands 5, anchoring bars 6, a UHPC composite groove 201, reinforcing bars 202, and a CFRP plate 203. Reinforcing bars 202 and a CFRP plate 203 are cast in the UHPC composite groove 201 to enhance the flexural bearing capacity of the UHPC composite plate. The bottom plate 4 is a square steel bar cast at the middle position of the bottom of the CFRP-UHPC composite groove 2. Square steel anchoring bars 6 are installed at the upper ends of both sides of the CFRP-UHPC composite groove 2. The prestressed steel strands 5 are tightened between the bottom plate 4 and the anchoring bars 6 to increase the prestress of the CFRP-UHPC composite groove.

[0024] The construction method of the prestressed UHPC-reinforced RC beam includes Step 1: fabricating the CFRP-UHPC composite groove. When fabricating the CFRP-UHPC composite groove, CFRP plates are added to the UHPC precast slab and extended along the beam axis direction, and a prestressed steel strand structure is added to improve the shear strength of the joint core area and the flexural capacity of the RC beam. The UHPC reinforcement layer can significantly improve the flexural stiffness and ultimate bearing capacity of the structure, and can effectively inhibit the formation and expansion of cracks in the RC beam, enhancing the crack resistance performance of the structure. The overall working performance of the CFRP and UHPC composite structure is good. The time-varying effect of the CFRP and UHPC composite components is mainly controlled by the autogenous shrinkage of UHPC within 90 days after casting, and there will be no peeling failure phenomenon. The main components of the UHPC material include Portland cement (42.5R), quartz sand (particle size 450um - 900um), quartz powder (average particle size 50.2um), silica fume (particle size 2nm - 280nm), fly ash, steel fibers (tensile strength 2000MPa, elastic modulus 200GPa), and high-range water reducer, etc. To enhance the tensile toughness of UHPC, hybrid steel fibers are used with a volume fraction of 3%, including 1% short straight steel fibers with a diameter of 0.12mm and a length of 8mm, and 2% end-hooked steel fibers with a diameter of 0.20mm and a length of 13mm. At the same time, to reduce the water-binder ratio of UHPC and improve its fluidity, polycarboxylate superplasticizer is used with a volume content of 1.5% and a water reduction rate exceeding 30%. The water-binder ratio of UHPC is 0.18.

[0025] In step 1, according to the dimensions, reinforcement, and stress conditions of the RC beam to be strengthened, determine the dimensions of the CFRP-UHPC composite groove, the quantity and distribution of the CFRP plates, and determine the installation hole positions of the CFRP-UHPC composite groove according to the positions of the steel bars in the RC beam. When calculating the flexural bearing capacity of the beam end of the RC frame joint strengthened by the CFRP-UHPC composite plate, the following basic assumptions are adopted: the cross-section strains of all materials in the strengthened beam section satisfy the plane section assumption; when the beam end of the strengthened beam does not reach the ultimate bearing capacity, the interfacial bonding between the UHPC strengthening layer, CFRP bars and the matrix is good, without interfacial cracks and relative slippage; the stress-strain relationship of concrete satisfies the provisions of the Code for Design of Concrete Structures;

[0026] When calculating the flexural bearing capacity of the CFRP-UHPC composite groove, use the UHCP groove to strengthen the joint, symmetrically arrange CFRP bars along the central axis of the side UHPC precast slab. Based on the assumption, the bottom CFRP-UHPC composite plate is equivalently calculated as a UHPC single-reinforced rectangular beam in isolation; the two side CFRP-UHPC composite plates are equivalently calculated as UHPC single-reinforced rectangular beams in isolation, and finally the compressive bearing capacity formula of the RC frame joint strengthened by the CFRP-UHPC composite plate is jointly derived.

[0027] First, perform the flexural calculation of the UIPC equivalent rectangular plate. When the UHPC in the compression zone reaches the ultimate compressive strain, the section enters the failure stage. Based on the moment equilibrium formula and the plane section assumption of strain, determine the magnitude and action point position of the section stress resultant force, and equivalently transform the stress distribution diagrams of the UHPC sections in the compression and tension zones into rectangles. Through the flexural bearing capacity analysis of the beam's normal section, the flexural bearing capacity formula of the UHPC beam is derived.

[0028] Next, calculate the flexural bearing capacity of the UIPC-RC beam. When the concrete in the compression zone reaches the ultimate compressive strain, the beam section enters the failure stage. According to the constitutive curve of the UHPC stress-strain relationship described in the basic assumption, assume that the UHPC strengthening layers on the tension side and the compression side are completely in the plastic stage, and the tensile and compressive stresses remain unchanged. According to the force balance condition, the flexural bearing capacity formula of the UIPC-RC beam can be obtained.

[0029] Then, calculate the flexural bearing capacity of the RC beam strengthened by the CFRP-UHPC composite groove. Based on the plane section assumption and on the basis of the same neutral axis height, the compressive resultant force formula of the composite beam and the tensile resultant force formula of the composite beam can be obtained, and the compressive resultant moment and the tensile resultant moment are obtained from the force balance formula.

[0030] Finally, the shear analysis of the RC frame nodes reinforced with CFRP-UHPC composite slots was carried out. The force analysis of the nodes is mostly based on the diagonal strut mechanism and the frame mechanism. The shear formula of the node constructed based on the frame model is mostly calculated with empirical guidance during structural design. The reason is that the section strain of the node does not conform to the flat section assumption, and the direct application of the formula cannot meet its actual stress state. Considering the internal force transmission of the node from the overall force can more accurately reflect the stress characteristics of the core area of ​​the node. Through the shear analysis of the prestressed concrete frame node, the dissipation of the internal force of the diagonal strut in the compression area of ​​the beam and column is considered, and the role of the tie rod is played by the shear reinforcement. The revised model is more in line with the actual force mechanism of the node. Based on the average stress distribution, the shear contribution of the core area concrete, stirrups, column center reinforcement, CFRP bars and UHPC precast panels are considered respectively. If there are no stirrups and column center reinforcement in the reinforced node, the horizontal stirrups, column side longitudinal reinforcement and CFRP bars are fixed in position, and the main source of contribution is their respective components; while UHPC has no fixed force transmission route and covers the entire core area of ​​the node. Considering its inhibitory effect on cracks in the core area, the calculation of the core area of ​​the node reinforced with CFRP cloth can be used to calculate and analyze the effective reinforced cross-sectional area.

[0031] When making CFRP-UHPC composite troughs, based on the relevant calculations of CFRP-UHPC composite panels to reinforce RC frames, the node design of CFRP-UHPC composite troughs to reinforce RC frames is obtained, the cross-sectional area of ​​CFRP-UHPC composite troughs and the area of ​​CFRP reinforcement are obtained, and CFRP-UHPC composite troughs are prepared. After the CFRP-UHPC composite troughs are made, the CFRP-UHPC composite troughs are cured for a certain period of time to improve their quality, that is, they are covered with moisturizing protection within 12 hours after pouring. After the UHPC ultra-high performance concrete is added with water reducer, the amount of water used will be greatly reduced. If the concrete itself is not protected in time, the UHPC ultra-high performance concrete will produce micro-cracks after losing moisture. After 7-15 days of moisturizing protection, it can be demolded and left to stand for curing. After demolding without cracks, UHPC still needs to be sprayed and cured for 15-30 days in time. In addition, the temperature difference of UHPC protection does not exceed 20 degrees. It cannot be exposed to the sun during curing and cannot be in an environment with a large temperature difference. Insulation measures should be taken in cold winter. Large temperature differences can cause cracks to appear in concrete slabs.

[0032] The second step is to wrap and fix the CFRP-UHPC composite trough on the RC beam, and use an adhesive to stick the CFRP-UHPC composite trough to the surface of the RC beam, so that the CFRP-UHPC composite trough is closely fitted to the exposed surface of the RC beam, and then pass the anchor nails through the CFRP-UHPC composite trough installation hole and mechanically anchor it to the RC beam to further reinforce the CFRP-UHPC composite trough.

[0033] The present invention uses CFRP reinforcement to strengthen UHPC precast slabs, forming composite slabs with high strength, high toughness and high durability performance for joint reinforcement, effectively improving the stress state of RC beam structures and enhancing the reinforcement efficiency; through the calculation of the flexural force of the equivalent rectangular plate of UIPC, the flexural bearing capacity of the UIPC-RC beam and the flexural bearing capacity of the RC beam strengthened by the CFRP-UHPC composite groove, and finally analyzing the shear resistance of the CFRP-UHPC composite groove strengthened RC frame joint to obtain the final reinforcement model, so that the CFRP-UHPC composite groove can be specifically reinforced for different RC beams, improving the reinforcement effect.

[0034] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A prestressed UHPC reinforced RC beam structure, characterized by: The prestressed UHPC reinforced RC beam structure comprises a CFRP-UHPC composite trough (2), a bottom plate (4), a prestressed steel strand (5), an anchor bar (6), a UHPC composite trough (201), a reinforcing rib (202), and a CFRP plate (203); the reinforcing rib (202) and the CFRP plate (203) are cast in the UHPC composite trough (201); the bottom plate (4) is installed at the bottom of the CFRP-UHPC composite trough (2); the anchor bar (6) is installed at the upper ends of both sides of the CFRP-UHPC composite trough (2); and the prestressed steel strand (5) connects the bottom plate (4) and the anchor bar (6).

2. A construction method for prestressed UHPC reinforced RC beams, characterized in that: The prestressed UHPC reinforced RC beam construction method comprises the following steps: Step 1, making a CFRP-UHPC composite tank; Step 2: The CFRP-UHPC composite trough is wrapped and fixed on the RC beam.

3. The construction method of prestressed UHPC reinforced RC beam according to claim 2 is characterized in that: The step 1 manufactures a CFRP-UHPC composite trough, adds a CFRP plate to the UHPC prefabricated plate and extends it along the beam axis, and adds a prestressed steel cable structure to improve the shear strength of the node core area and the bending resistance of the RC beam.

4. The construction method of prestressed UHPC reinforced RC beam according to claim 2 is characterized in that: Step 1: The materials of the CFRP-UHPC composite tank include silicate cement, quartz sand, quartz powder, silica fume, fly ash, steel fiber, and high-efficiency water reducing agent. In order to enhance the tensile toughness of UHPC, mixed steel fiber is used with a volume content of 3%, including 1% short straight steel fiber and 2% end hook steel fiber; To reduce the water-binder ratio of UHPC and improve its fluidity, a polycarboxylic acid high-performance water-reducing agent is used with a volume content of 1.5%, a water reduction rate of more than 30%, and a UHPC water-binder ratio of 0.

18.

5. The construction method of prestressed UHPC reinforced RC beam according to claim 2 is characterized in that: The step 1 determines the size of the CFRP-UHPC composite trough and the number and distribution of the CFRP plates according to the size, reinforcement and stress conditions of the RC beam to be reinforced, and determines the installation hole position of the CFRP-UHPC composite trough according to the reinforcement position of the RC beam.

6. The construction method of prestressed UHPC reinforced RC beam according to claim 2 is characterized in that: When making the CFRP-UHPC composite trough in step 1, the bending resistance calculation of the UIPC equivalent rectangular plate is first performed, then the bending bearing capacity of the UIPC-RC beam is calculated, and then the bending bearing capacity of the CFRP-UHPC composite trough reinforced RC beam is calculated, and finally the shear resistance analysis of the CFRP-UHPC composite trough reinforced RC frame node is performed.

7. The construction method of prestressed UHPC reinforced RC beam according to claim 2, characterized in that: When making the CFRP-UHPC composite trough in the step 1, based on the relevant calculation of the CFRP-UHPC composite plate reinforced RC frame, the node design of the CFRP-UHPC composite trough reinforced RC frame is obtained, the cross-sectional area of ​​the CFRP-UHPC composite trough and the CFRP reinforcement area are obtained, and the CFRP-UHPC composite trough is prepared.

8. The construction method of prestressed UHPC reinforced RC beam according to claim 2, characterized in that: The step 1 specifically also includes: after the CFRP-UHPC composite tank is manufactured, the CFRP-UHPC composite tank is cured for a certain period of time to improve its quality.

9. The construction method of prestressed UHPC reinforced RC beam according to claim 2, characterized in that: The step 2 specifically includes: using an adhesive to adhere the CFRP-UHPC composite trough to the surface of the RC beam, and then mechanically anchoring the CFRP-UHPC composite trough and the RC beam by anchor nails.

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