Seismic reinforcement method for reinforced concrete frame joint with force defects

Abstract

The application provides an anti-seismic reinforcing method for a reinforced concrete frame joint with a stress defect, which comprises the following steps: determining the number of reinforcing steel bars when target specification steel bars are used as reinforcing steel bars; alternately opening a first installation hole and a second installation hole in the joint core area along the width direction of the beam; opening a first channel and a second channel, which respectively communicate with the first installation hole and the second installation hole, on a lower reinforcing section close to the lower side of the joint core area; installing the reinforcing steel bars; and wrapping FRP cloth around a lower reinforcing section and an upper reinforcing section close to the upper side of the joint core area. After the reinforcing steel bar parameters are determined, the first installation hole and the second installation hole are opened in the joint core area, the first channel and the second channel are opened in the concrete protective layer at the column end, the reinforcing steel bars are installed, and finally the FRP cloth is used to wrap the upper reinforcing section and the lower reinforcing section, so that the shear performance of the joint core area and the bending performance of the column end are improved.

Description

Technical Field

[0001] This invention relates to the field of building engineering technology, and in particular to a seismic reinforcement method for reinforced concrete frame joints with stress defects. Background Technology

[0002] Reinforced concrete (RC) frame structures are one of the most commonly used structural forms in buildings. Frame joints play a crucial role in transferring internal forces and maintaining the overall structural integrity. However, many existing frame joints, designed according to earlier codes, suffer from insufficient shear capacity due to inadequate stirrup reinforcement in the joint core area. As an example, the aforementioned joint core area can be formed by the intersection of a beam and a column.

[0003] Some frame structures fail to consider the reinforcement of beam bending strength by floor slabs, resulting in a "strong beam, weak column" phenomenon. Consequently, during earthquakes, columns fail before beams, leading to structural collapse and serious harm to life and property. Therefore, implementing effective seismic reinforcement measures for these RC frame joints with insufficient seismic performance is essential.

[0004] Currently, common reinforcement methods for improving the seismic performance of RC joints mainly include the concrete enlargement method, steel bonding method, and fiber-reinforced composite material bonding method. The concrete enlargement method is difficult to construct and will affect the usable space of the building; although the steel bonding method is convenient to construct, it has problems with poor corrosion resistance and fire resistance; the fiber-reinforced composite material bonding method is prone to delamination failure in the later stage of loading and is not very suitable for spatial joints. Summary of the Invention

[0005] The summary section of this invention provides a brief overview of the concepts, which will be described in detail in the detailed description section that follows. This summary section is not intended to identify key or essential features of the claimed technical solutions, nor is it intended to limit the scope of the claimed technical solutions.

[0006] Some embodiments of the present invention provide a seismic strengthening method for reinforced concrete frame joints with stress defects, in order to solve the technical problems mentioned in the background section above.

[0007] The method includes determining the number of reinforcing bars when using target specification steel bars as reinforcing bars, wherein the reinforcing bars include inclined joint sections and column end sections, and the number of reinforcing bars is even; Along the width direction of the beam, a first mounting hole and a second mounting hole are alternately opened in the core area of ​​the node, wherein the axis of the first mounting hole is parallel to one diagonal of the cross section of the core area of ​​the node; and the axis of the second mounting hole is parallel to the other diagonal of the cross section of the core area of ​​the node. A first channel and a second channel, respectively communicating with the first mounting hole and the second mounting hole, are vertically opened on the lower reinforced section near the lower side of the node core area. The reinforcing steel bar is installed such that it is installed into the first mounting hole and the first channel, or into the second mounting hole and the second channel; FRP fabric is wrapped around the lower reinforcement section and the upper reinforcement section near the core area of ​​the node.

[0008] The above embodiments of the present invention have the following beneficial effects: the seismic strengthening method for reinforced concrete frame joints with stress defects of the present invention can significantly improve the overall seismic performance of the frame joints.

[0009] Specifically, by creating a first and second mounting hole spaced apart within the core area of ​​the node, and aligning these holes with the two diagonals of the core area's cross-section, the node segments of the two reinforcing bars installed in the first and second mounting holes are spaced apart and staggered. This angular staggered arrangement of the two node segments enhances the shear capacity of the core area and covers the entire core area, thereby improving the overall strength of the core area.

[0010] Furthermore, a first channel and a second channel connected to the first mounting hole and the second mounting hole are provided in the lower reinforcement section below the core area of ​​the node, so that the column end section of the reinforcing steel provides vertical support to the corresponding node section, and at the same time enhances the bending bearing capacity of the lower reinforcement section. Attached Figure Description

[0011] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0012] Figure 1 The flowchart shows some embodiments of the seismic strengthening method for reinforced concrete frame joints with stress defects according to the present invention. Figure 2 A schematic diagram of the structure for reinforcing steel bars; Figure 3 A top view of the frame structure after the first mounting hole, the second mounting hole, the first channel, and the second channel have been opened; Figure 4 for Figure 3 Sectional view at point AA; Figure 5 for Figure 4 Sectional view at point BB; Figure 6 A cross-sectional view of the reinforced node frame; Figure 7 Another sectional view of the reinforced node frame; Figure 8 This is the front view after the reinforcement bars have been installed. Figure 9 This is a side view after the reinforcing steel bars have been installed. Figure 10 A 3D view of the reinforced steel bars after installation; Figure 11 A schematic diagram of the reinforced node frame.

[0013] Explanation of reference numerals in the attached figures: 1: Beam; 2: Column; 3: Node core area; 31: First mounting hole; 32: Second mounting hole; 33: First channel; 34: Second channel; 4: Reinforcing steel; 41: Node section; 42: Column end section; 43: Upsetting part; 5: FRP fabric. Detailed Implementation

[0014] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0016] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly; for example, they may refer to a fixed connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0017] This disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] Please refer to the following first. Figure 1 , Figure 1 This is a flowchart 100 of some embodiments of the seismic strengthening method for reinforced concrete frame joints with stress defects according to the present invention. For example... Figure 1 As shown, the method includes: Step 101: Determine the quantity of reinforcing steel bars when using steel bars of the target specification as reinforcing steel bars.

[0019] In some embodiments, firstly combined Figure 2 Describe the structure of the reinforcing steel. Figure 2 This is a structural diagram for reinforcing steel bars. (Example) Figure 2 As shown, the reinforcing steel bar 4 includes an inclined joint section 41 and a column end section 42. Upsetting can be performed at both ends of the reinforcing steel bar 4 using an upsetting machine. The length of the upset portion 43 is not less than twice the diameter of the reinforcing steel bar 4, and the diameter of the upset portion 43 is at least 4 mm larger than the diameter of the reinforcing steel bar.

[0020] Furthermore, the length of the column end section 42 is equal to the effective height of the column section; the length of the node section 41 is 0.7 to 0.8 times the diagonal length of the node core area 3 section.

[0021] Shear bearing capacity of the target core area of ​​the node and the existing shear bearing capacity of the node core area V j The difference is used to determine the nominal tensile strength of the aforementioned reinforcing steel bars. The target shear bearing capacity of the core area of ​​the aforementioned node can be characterized as the expected shear bearing capacity of the core area of ​​the building at that node, or it can be the design value of the shear bearing capacity of the core area of ​​the node.

[0022] The following description uses a specific example. In a certain frame node structure, the column's cross-sectional dimensions are 500×500mm. 2 The beam's cross-sectional dimensions are 350×500mm. 2 Spacing between column inflection points H c =2500mm, beam inflection point spacing L b =2500mm, the longitudinal reinforcement of both columns and beams is symmetrically arranged with 3C25 steel, and the stirrups are all C10@150mm. The measured tensile strength of the longitudinal reinforcement is 518MPa, and the tensile strength of the stirrups is 456MPa. No stirrups are provided in the core area of ​​the joint. The axial compressive strength N=600kN. The measured axial compressive strength of the concrete is... f c =25.6MPa.

[0023] First, based on the seismic requirements for Class I seismic-resistant frame structures in the "Code for Design of Concrete Structures" (GB50010-2010), the column-beam flexural strength ratio of this frame structure before reinforcement is calculated:

[0024]

[0025] in, This refers to the bending bearing capacity at the column end. This refers to the bending capacity at the beam end. This is the seismic adjustment coefficient for bearing capacity; This refers to the axial pressure of the column. The height of the column section; The width of the column section; The coefficient is set to 1.0; This refers to the axial compressive strength of concrete. These are the tensile strength and compressive strength of the longitudinal reinforcement, respectively. These are the cross-sectional areas of the tension longitudinal reinforcement and the compression longitudinal reinforcement, respectively. The effective height of the beam section; This refers to the thickness of the protective layer.

[0026] The column-beam bending strength ratio is determined according to the following formula: 1.33 < 1.40, which does not meet the specifications. Therefore, the frame structure needs to be reinforced. This is the sum of the flexural bearing capacities at the beam ends; This is the sum of the bending bearing capacity of the column ends; Next, the target shear bearing capacity of the node core area is determined using the following formula. :

[0027] in, For the target shear bearing capacity of the core area of ​​the node; These are the effective height of the beam section and the beam section height, respectively. H c The distance between the inflection points of the column.

[0028] Next, the existing shear bearing capacity of the node core area is determined using the following formula. :

[0029] in, The existing shear bearing capacity of the node core area; The compressive stress in the column section is determined according to the following formula:

[0030] The angle between the diagonal compression member and the column axis is approximately determined by the following formula:

[0031] The cross-sectional area of ​​the diagonal compression member; The compressive strength of the concrete cylinder is taken as 0.8. f c ; This represents the effective width of the node's core area.

[0032] The nominal tensile strength of concrete is determined according to the following formula:

[0033] For the tensile strength of plain concrete, take... ; A sv This represents the total area of ​​the longitudinal reinforcement bars in the middle of the column; f yv This represents the tensile strength of the longitudinal reinforcement bars in the middle of the column. The contribution of the nominal tensile strength of the reinforcing steel is taken as 0 when calculating the existing shear capacity.

[0034] Shear bearing capacity of the target core area of ​​the node V J Existing shear bearing capacity of the core area of ​​the node V j The difference is the minimum increase required to improve the shear bearing capacity of the core area of ​​that node. =543kN. Use this as the new... , bring in The calculation formula is used to determine the nominal tensile strength contribution of the reinforced steel bars. f ts .

[0035] Next, we will determine the cross-sectional area of ​​the reinforcing steel required for the core area of ​​the above-mentioned nodes and the column ends when using HRB400 grade steel bars of the target specification as reinforcing steel bars.

[0036] The minimum cross-sectional area of ​​reinforcing steel required for unilateral shear reinforcement in the core area of ​​a node is determined using the following formula. A ssj :

[0037] in, The angle between the joint section and the column end section for reinforcing steel reinforcement; This refers to the tensile strength of the steel bars of the aforementioned target specifications.

[0038] The required cross-sectional area of ​​the reinforcing steel for unilateral bending reinforcement at the column end is determined using the following formula. :

[0039] in, This corresponds to the column-beam flexural strength ratio limit in the code under the seismic resistance level. The compressive strength of the steel bars of the target specification.

[0040] Since the minimum cross-sectional area of ​​the steel bars required for shear reinforcement in the core area of ​​the node is greater than the cross-sectional area of ​​the steel bars required for bending reinforcement at the column end, the number of steel bars of the target specification is determined by the minimum cross-sectional area of ​​the steel bars required for shear reinforcement in the core area of ​​the node.

[0041] Specifically, the aforementioned reinforcing bars are installed in pairs, and each side of the frame node structure can use two ribbed steel bars with a diameter of 22mm as reinforcing bars.

[0042] Reinforced steel cross-sectional area A ss >750mm 2 Ultimately, it was determined that a total of four reinforcing steel bars with a diameter of 22mm were needed on both sides of the frame node structure.

[0043] Step 102: Alternately open the first mounting hole and the second mounting hole in the core area of ​​the node along the width direction of the beam.

[0044] Please see Figure 3 , Figure 4 , Figure 5 . Figure 3 A top view of the frame structure after the first mounting hole, the second mounting hole, the first channel, and the second channel have been opened; Figure 4 for Figure 3 Sectional view at point AA; Figure 5 for Figure 4 Sectional view at point BB.

[0045] like Figure 3 As shown, the width direction of beam 1 is... Figure 3 Up and down direction.

[0046] Because reinforcement is required using four reinforcing steel bars 4, there are two of each: the first mounting hole 31 and the second mounting hole 32. Figure 4 and Figure 5 As shown, the first mounting hole 31 and the second mounting hole 32 are used to accommodate the node section 41 of the reinforcing steel bar 4.

[0047] Two first mounting holes 31 and two second mounting holes 32 are alternately provided. The axis of the first mounting hole 31 is parallel to one diagonal of the cross-section of the node core region 3. The axis of the second mounting hole 32 is parallel to the other diagonal of the cross-section of the node core region 3. Therefore, adjacent first mounting holes 31 and second mounting holes 32 are arranged opposite each other.

[0048] Furthermore, the diameters of the first mounting hole 31 and the second mounting hole 32 are not less than 1.5 times the diameter of the reinforcing steel bar 4, and the lengths of the first mounting hole 31 and the second mounting hole 32 are equal to the length of the node section 41. The net distance between adjacent first mounting holes 31 and second mounting holes 32 is not less than the larger of 50 mm and 3 times the diameter of the reinforcing steel bar 4.

[0049] Step 103: On the lower reinforced section near the core area of ​​the above-mentioned node, a first channel and a second channel are vertically opened along the direction, respectively communicating with the first mounting hole and the second mounting hole.

[0050] like Figure 4 and Figure 5 As shown, the first channel 33 and the second channel 34 are used to accommodate the column end section 42 of the reinforcing steel bar 4. The width of the first channel 33 and the second channel 34 is not less than 1.5 times the diameter of the reinforcing steel bar 4. The depth of the first channel 33 and the second channel 34 is at least 5 mm greater than the diameter of the reinforcing steel bar 4, and the length of the first channel 33 and the second channel 34 is equal to the effective height of the column section.

[0051] The first mounting hole, the second mounting hole, the first channel, and the second channel can be chiseled using cutting machines, electric drills, and other related tools. The inner walls of the channels should be roughened and cleaned.

[0052] Step 104: Install reinforcing bars, such that the reinforcing bars are installed into the first mounting hole and the first channel, or into the second mounting hole and the second channel.

[0053] In some embodiments, combined with Figure 6 and Figure 7 To explain, Figure 6 A cross-sectional view of the reinforced node frame; Figure 7 This is another sectional view of the reinforced node frame. (See attached image.) Figure 6 and Figure 7 As shown, four reinforcing steel bars 4 are respectively installed into the corresponding first mounting hole 31, first channel 33, second mounting hole 32, and second channel 34.

[0054] Next, combine Figure 8 , Figure 9 and Figure 10 This diagram shows the reinforcement bars after installation. Figure 8 This is the front view after the reinforcement bars have been installed. Figure 9 This is a side view after the reinforcing steel bars have been installed. Figure 10 This is a three-dimensional view of the reinforced steel bars after installation. In this way, the node segments 41 of the two reinforced steel bars 4 installed in the first mounting hole 31 and the second mounting hole 32 are spaced apart and staggered. The staggered arrangement of the two node segments 41 improves the shear bearing capacity of the node core area 3 and covers the entire node core area 3. This improves the overall strength of the node core area.

[0055] During installation, two-thirds of the required structural adhesive volume can be injected into the first mounting hole 31, the first channel 33, and the second mounting hole 32 and the second channel 34. Then, the reinforcing steel bar 4 is installed centered in the first mounting hole 31 or the first channel 33, or the second mounting hole 32 or the second channel 34. The gaps are then filled with structural adhesive, and finally, excess structural adhesive is removed with a scraper.

[0056] Step 105: Wrap FRP cloth around the lower reinforcement section and the upper reinforcement section near the core area of ​​the node.

[0057] See Figure 11 , Figure 11 This is a structural diagram illustrating the reinforced node frame. Figure 11 As shown, structural adhesive is used to wrap two layers of FRP cloth 5 in the upper and lower reinforcement sections of column 2 near the core area of ​​the node. The single layer of FRP cloth 5 is 0.167mm thick, and the wrapping width is greater than the length of the column section of the reinforcing steel bar 4.

[0058] The present invention provides a seismic reinforcement method for reinforced concrete frame joints with stress defects. Specifically, for the defective reinforced concrete frame joint, the parameters of the reinforcing steel are first determined. Then, by opening a first and a second mounting hole in the core area of ​​the joint, and by opening a first and a second channel in the concrete protective layer at the column end, pre-bent reinforcing steel is installed. Finally, FRP fabric is used to wrap around the upper and lower reinforcing sections to improve the seismic resistance of the core area of ​​the joint.

[0059] This invention embeds reinforcing bars in the core area of ​​the node and the adjacent lower reinforcement section, and uses FRP cloth rings to wrap the column ends, which can effectively improve the shear strength of the core area of ​​the node and the bending strength of the column ends, and transfer the potential plastic hinge out, thus significantly improving the overall seismic performance of the node frame structure.

[0060] This invention is applicable to various spatial nodes with insufficient reinforcement in the core area of ​​the node and at the column end. It is easy to construct and has obvious effects, and has broad application prospects.

[0061] Finally, it should be noted that the above 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 with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A seismic strengthening method for reinforced concrete frame joints with stress defects, characterized in that, The method includes: The method involves determining the quantity of reinforcing steel bars of a target specification when using them as reinforcement, wherein the reinforcing steel bars include inclined joint sections and column end sections; the length of the column end section is equal to the effective height of the column section; the length of the joint section is 0.7 to 0.8 times the diagonal length of the joint core area section; the method further includes: determining the cross-sectional area of ​​the reinforcing steel bars required for the joint core area and column end reinforcement respectively; and determining the diameter of the reinforcing steel bars by using the larger value between the cross-sectional areas of the joint core area and column end reinforcement. The number of reinforcing steel bars is an even number; Along the width direction of the beam, a first mounting hole and a second mounting hole are alternately opened in the core area of ​​the node, wherein the axis of the first mounting hole is parallel to one diagonal of the cross section of the core area of ​​the node; and the axis of the second mounting hole is parallel to the other diagonal of the cross section of the core area of ​​the node. A first channel and a second channel, respectively communicating with the first mounting hole and the second mounting hole, are vertically opened on the lower reinforced section near the lower side of the node core area. The reinforcing steel bar is installed such that it is installed into the first mounting hole and the first channel, or into the second mounting hole and the second channel; FRP fabric is wrapped around the lower reinforcement section and the upper reinforcement section near the core area of ​​the node.

2. The seismic strengthening method for reinforced concrete frame joints with stress defects according to claim 1, characterized in that, When determining the target specification steel bars as reinforcement, the cross-sectional area of ​​the reinforcement bars required for the core area of ​​the node and the column end reinforcement includes: Based on the target shear bearing capacity of the core area of ​​the node V J and the existing shear bearing capacity of the node core area V j The difference is used to determine the nominal tensile strength of the reinforcing steel. f ts ; The cross-sectional area of ​​the reinforcing steel bars required for unilateral reinforcement of the node core area is determined according to the following formula. A ssj : in, The tensile strength of the steel bars of the target specification; The effective width of the node's core area; The height of the column section; The angle between the node section and the column end section of the reinforcing steel bar.

3. The seismic strengthening method for reinforced concrete frame joints with stress defects according to claim 2, characterized in that, The cross-sectional area of ​​the reinforcing steel bars required for the single-sided reinforcement of the column end. It is determined by the following formula: in, This corresponds to the column-beam flexural strength ratio limit in the code under the seismic resistance level. This is the sum of the flexural bearing capacities at the beam ends; This is the sum of the bending bearing capacity of the column ends; The effective height of the column section; This refers to the thickness of the protective layer at the column end. The compressive strength of the steel bar of the target specification.

4. The seismic strengthening method for reinforced concrete frame joints with stress defects according to claim 1, characterized in that, The reinforcing steel bars are upset at both ends using an upsetting machine. The length of the upset portion is not less than twice the diameter of the reinforcing steel bar, and the diameter of the upset portion is at least 4 mm larger than the diameter of the reinforcing steel bar.

5. The seismic strengthening method for reinforced concrete frame joints with stress defects according to claim 1, characterized in that, The diameter of the first mounting hole and the second mounting hole is not less than 1.5 times the diameter of the reinforcing bar, and the length of the first mounting hole and the second mounting hole is equal to the length of the node section.

6. The seismic strengthening method for reinforced concrete frame joints with stress defects according to claim 1, characterized in that, The net distance between adjacent first and second mounting holes shall not be less than the larger of 50 mm and 3 times the diameter of the reinforcing steel bar.

7. The seismic strengthening method for reinforced concrete frame joints with stress defects according to claim 1, characterized in that, The width of the first channel and the second channel is not less than 1.5 times the diameter of the reinforcing steel bar; the depth of the first channel and the second channel is at least 5 mm greater than the diameter of the reinforcing steel bar; and the length of the first channel and the second channel is equal to the effective height of the column section.

8. The seismic strengthening method for reinforced concrete frame joints with stress defects according to claim 1, characterized in that, The width of the FRP fabric loop is greater than the length of the column end section.

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