Beam-column joint design method for increasing section and reinforcing reinforced concrete frame column

Abstract

According to the beam-column joint design method for reinforcing the increased cross section of the reinforced concrete frame column, structural design is conducted on the beam-column joint for reinforcing the increased cross section, the structural form that a newly-added longitudinal bar transmits force to a beam outer hoop steel plate through a connecting steel plate is adopted, and the situation that the newly-added longitudinal bar penetrates through a beam is avoided. The beam column joint is arranged at the joint of an original frame column and an original frame beam, and the structural form that a newly-added longitudinal bar transmits force to a beam outer hoop steel plate through a connecting steel plate is adopted. The beam-column joint comprises beam outer hoop steel plates welded to the four side faces of an original frame beam, connecting steel plates welded to the beam outer hoop steel plates on the top face and the bottom face respectively, and a plurality of newly-added longitudinal bars welded to the connecting steel plates. On the basis of a beam-column joint structure, key parameters of a beam-column joint are designed, and the key parameters comprise the number of newly-added longitudinal bars and the length of a beam outer hoop steel plate; the number of the newly added longitudinal bars and the length of the beam outer hoop steel plate ensure that the tensile bearing capacity of the beam outer hoop steel plate and the local compression of the original frame beam meet the design requirements.

Description

Technical Field

[0001] The invention relates to a design method, in particular to a design method for a beam-column node with an enlarged cross-section and reinforcement, and belongs to the technical field of civil engineering. Background Art

[0002] At present, facing the problems of high-performance building functions and aging of existing buildings due to long-term use, if the economic and social impacts are taken into consideration, it is necessary to reasonably reinforce the existing buildings, so there are more and more reinforcement projects for existing concrete structures.

[0003] As a major load-bearing component, frame columns have great demand for reinforcement, and the most commonly used reinforcement method is the increased section method. The increased section method sets the calculated reinforcement required for reinforcement in the newly added section, where the lower end of the longitudinal force-bearing steel bars should extend into the foundation or lower beams and columns and meet the anchorage requirements; the longitudinal bars outside the original structural range (i.e., outside the horizontal projection range of the beam) at the upper end should pass through the floor slab and extend into the upper column foot or be capped and anchored at the roof slab, and the longitudinal bars within the original structural range (i.e., within the horizontal projection range of the beam) need to pass through the beam and extend into the upper column foot or be capped and anchored at the roof slab.

[0004] In actual projects, the reinforcement at the ends of the original structural beams is often dense and the exact position cannot be detected. The diameter of the column longitudinal reinforcement used for reinforcement is large, which will inevitably break the steel bars in the beam when passing through the beam, reducing or even destroying the structural bearing capacity, and even making it impossible to drill holes for planting reinforcement, which brings construction difficulties. Therefore, it is necessary to design a beam-column node for increasing the cross-section and strengthening the reinforced concrete frame column. When the concrete frame column is increased in cross-section and reinforced, it is necessary to avoid adding new longitudinal reinforcement through the beam, thereby avoiding breaking the original structural beam steel bars, and meeting the reinforcement requirements of the frame column to ensure the realization of the purpose of strengthening the existing structure. Summary of the invention

[0005] In view of this, the present invention provides a beam-column node design method for increasing the cross-section and reinforcing reinforced concrete frame columns. By structurally designing the beam-column node for increasing the cross-section and reinforcing, a structural form is adopted in which newly added longitudinal reinforcement transmits the force to the outer hoop steel plate of the beam through a connecting steel plate, thereby avoiding the newly added longitudinal reinforcement passing through the beam, thereby ensuring that the purpose of reinforcing the concrete column is achieved while avoiding secondary damage to the original structural beam.

[0006] A beam-column node design method for increasing the cross-section and strengthening a reinforced concrete frame column, wherein the reinforced concrete frame column comprises: an original frame column and original frame beams arranged on four sides of the original frame column in a horizontal direction;

[0007] The beam-column node is set at the connection between the original frame column and the original frame beam, and adopts a structural form in which the newly added longitudinal reinforcement transmits the force to the beam outer hoop steel plate through the connecting steel plate; based on this, the beam-column node includes: the beam outer hoop steel plates welded on the four sides of the original frame beam, the connecting steel plates welded on the top and bottom surfaces of the beam outer hoop steel plates respectively, and a plurality of newly added longitudinal reinforcements welded on the connecting steel plates;

[0008] Based on the beam-column node structure, the key parameters of the beam-column node are designed, and the key parameters include: the number of newly added longitudinal reinforcements and the length of the outer hoop steel plate of the beam;

[0009] The number of newly added longitudinal reinforcements and the length of the beam outer hoop steel plate ensure that the tensile bearing capacity of the beam outer hoop steel plate and the local compression of the original frame beam meet the design requirements.

[0010] As a preferred embodiment of the present invention, in the beam-column joint, the newly added longitudinal reinforcement transmits tension through the beam outer hoop steel plate, and the number n of the newly added longitudinal reinforcement needs to satisfy:

[0011]

[0012] Wherein: b is the width of the original frame beam, in mm; t1 is the thickness of the outer hoop steel plate on the left and right sides of the original frame beam, in mm; d1 is the diameter of the newly added longitudinal reinforcement, in mm; D is the net spacing between the newly added longitudinal reinforcements, in mm; the maximum value of the number of newly added longitudinal reinforcements n can be calculated by the above formula.

[0013] As a preferred embodiment of the present invention, the length b1 of the outer hoop steel plate of the beam needs to satisfy:

[0014] b1≥F L / 1.35β c β l f c b (2)

[0015] Among them: F L is the local compression design value of the original frame beam, F L =nN2=n×A×p2, n is the number of newly added longitudinal reinforcements, N2 is the maximum tensile design value of the newly added longitudinal reinforcements; A is the cross-sectional area of ​​the newly added longitudinal reinforcements, unit: mm 2 , p2 is the design value of tensile strength of the newly added longitudinal reinforcement, unit N / mm 2 ;

[0016] b is the width of the original frame beam; β c is the concrete strength coefficient of the original frame beam; β l f is the strength enhancement factor of the original frame beam when the concrete is under compression, c is the strength of the original frame beam concrete, in N / mm 2 .

[0017] As a preferred embodiment of the present invention, further, the number of newly added longitudinal reinforcements and the length b1 of the outer hoop steel plate of the beam need to satisfy:

[0018] nN2≤2N1

[0019] Where: N2 is the maximum tensile design value of the newly added longitudinal reinforcement, N1 is the maximum tensile design value that the outer hoop steel plates on both sides of the beam can withstand, N1 = b1 × t1 × p1; p1 is the tensile strength design value of the outer hoop steel plates of the beam, unit N / mm 2 .

[0020] As a preferred embodiment of the present invention, the key parameters of the beam-column node also include the height l of the connecting steel plate;

[0021] The height l of the connecting steel plate must meet the following requirements:

[0022] l≥l e +2h f

[0023] Among them: e is the calculated length of the fillet weld, p2 is the design value of tensile strength of the newly added longitudinal reinforcement, in N / mm 2 , A is the cross-sectional area of ​​the newly added longitudinal reinforcement, unit: mm 2 ,h e is the calculated thickness of the fillet weld, It is the design value of tensile strength of fillet weld, in N / mm 2 ;h f is the weld leg size,

[0024] As a preferred embodiment of the present invention, the width of the connecting steel plate is the same as the width of the outer hoop steel plate of the beam; the newly added longitudinal reinforcement outside the range of the connecting steel plate in the newly added section passes through the structural plate at the corresponding position.

[0025] Beneficial effects:

[0026] (1) The present invention connects the newly added longitudinal reinforcement with the connecting steel plate at the beam-column node, and transmits the force to the outer hoop steel plate of the beam through the connecting steel plate. Therefore, when the cross-section of the concrete frame column is increased for reinforcement, it is avoided that the newly added longitudinal reinforcement passes through the beam, thereby avoiding breaking the original structural beam steel bars, and can achieve protection of the original structural beam when the longitudinal reinforcement is anchored. In addition, by designing the beam-column node, it is ensured that the tensile bearing capacity design requirements of the outer hoop steel plate of the beam and the local compression of the original frame beam meet the design requirements; so that it meets the reinforcement requirements of the frame column and ensures the realization of the purpose of strengthening the existing structure.

[0027] (2) The present invention considers the maximum tensile design value of the newly added longitudinal reinforcement and the maximum tensile design value that the outer hoop steel plates of the beam on both sides can withstand when designing the number of newly added longitudinal reinforcements in the beam-column joint, thereby ensuring that the force transmission is safe and reliable.

[0028] (3) The present invention specifically designs the length of the outer hoop steel plate of the beam to ensure that the local compression of the original frame beam meets the design requirements, thereby improving the structural stability of the reinforced concrete frame column after adding the beam-column node. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of a beam-column node with an enlarged cross-section and reinforced in the present invention;

[0030] Figure 2 for Figure 1 AA cross section in;

[0031] Figure 3 This is a schematic diagram of the tensile calculation of the outer hoop steel plate of the beam;

[0032] Figure 4 This is a schematic diagram of the local compression of the original frame beam;

[0033] Figure 5 Schematic diagram of floor slab reinforcement cutting.

[0034] Among them: 1-original frame column; 2-original frame beam; 3-beam outer hoop steel plate; 4-connecting steel plate; 5-newly added longitudinal reinforcement. DETAILED DESCRIPTION

[0035] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0036] This embodiment provides a beam-column node design method for increasing the cross-section and strengthening reinforced concrete frame columns. By designing the beam-column node for increasing the cross-section and strengthening, it meets the reinforcement requirements of the frame columns, ensuring the realization of the purpose of strengthening the existing structure.

[0037] like Figure 1 and Figure 2 As shown, the beam-column node designed in this embodiment is used to reinforce the reinforced concrete frame column based on the increased cross-section reinforcement. The reinforced concrete frame column includes: an original frame column 1 and an original frame beam 2; the original frame column 1 is vertically arranged, and the original frame beam 2 is horizontally arranged on four sides of the original frame column 1, and the width of the original frame beam 2 is less than the width of the side that is connected to the original frame column 1.

[0038] The beam-column node designed in this embodiment is set at the connection between the original frame column 1 and the original frame beam 2, which is used to achieve increased cross-section reinforcement. First of all, the structural design idea of ​​the beam-column node is: the newly added longitudinal reinforcement 5 transfers the force to the beam outer hoop steel plate 3 through the connecting steel plate 4 to avoid the newly added longitudinal reinforcement from penetrating the beam; based on this, the structure of the beam-column node includes: the beam outer hoop steel plate 3, the connecting steel plate 4 and the newly added longitudinal reinforcement 5; the beam outer hoop steel plates 3 are arranged on the top surface, the bottom surface and the two side surfaces of the connection end of the original frame beam 2 and the original frame column 1, that is, the connection end of the original frame beam 2 and the original frame column 1 is surrounded by four beam outer hoop steel plates 3. A connecting steel plate 4 is vertically welded upward on the beam outer hoop steel plate 3 located on the top surface, and a connecting steel plate 4 is vertically welded downward on the beam outer hoop steel plate 3 located on the bottom surface. The width of the connecting steel plate 4 is the same as the width of the beam outer hoop steel plate 3.

[0039] There is a gap between the connecting steel plate 4 and the side surface corresponding to the original frame column 1, and the connecting steel plate 4 is used to weld the newly added longitudinal reinforcement 5; thus, the gap between the connecting steel plate 4 and the side surface corresponding to the original frame column 1 depends on the size of the newly added section; during design, the distance between the newly added longitudinal reinforcement 5 and the original frame column 1 can be determined based on the size of the newly added section, and then the distance value between the connecting steel plate 4 and the original frame column 1 can be obtained.

[0040] The upper part of the newly added longitudinal reinforcement 5 located below the original frame beam 2 is welded to the connecting steel plate 4 at the corresponding position (i.e., the lower connecting steel plate), and the lower end is supported on the structural bottom plate; the lower part of the newly added longitudinal reinforcement 5 (not shown in the figure) located above the original frame beam 2 is welded to the connecting steel plate 4 at the corresponding position (i.e., the lower connecting steel plate), and the upper end is supported on the structural top plate. Since the width of the connecting steel plate 4 is the same as the width of the outer hoop steel plate 3 of the beam, and the structural plate is set on the plane where the original frame beam 2 is located, the newly added longitudinal reinforcement outside the range of the connecting steel plate 4 in the newly added section passes through the structural plate at the corresponding position.

[0041] In the beam-column joint of this structural form, the newly added longitudinal reinforcement 5 is only connected to the connecting steel plate 4, and the force is then transmitted to the outer hoop steel plate 3 of the beam through the connecting steel plate 4, which can avoid the newly added longitudinal reinforcement passing through the beam, thereby avoiding breaking the steel bars inside the original frame beam 2 during reinforcement.

[0042] In addition, if Figure 5 As shown, since the outsourced beam outer hoop steel plate 3 needs to cut off part of the floor slab steel bars, the cut floor slab steel bars can be double-sided welded for 5d (d is the original floor slab steel bar diameter) and welded to the beam outer hoop steel plate 3, and the welding length is 10d.

[0043] Based on the above beam-column node structure, the key parameters of the beam-column node are further designed. The key parameters of the above beam-column node include: the number of newly added longitudinal bars 5 welded to the connecting steel plate 4 (hereinafter referred to as newly added longitudinal bars 5 refer to newly added longitudinal bars welded to the connecting steel plate 4), the length of the outer hoop steel plate 3 of the beam, and the length of the connecting steel plate 4.

[0044] Firstly, the number of newly added longitudinal bars 5 welded to the connecting steel plate 4 and the length of the beam outer hoop steel plate 3 are designed to ensure that the tensile bearing capacity of the beam outer hoop steel plate 3 and the local compression of the original frame beam 2 meet the requirements.

[0045] In the above beam-column joint, the newly added longitudinal reinforcement 5 needs to transfer the tension through the beam outer hoop steel plate 3. The number n of newly added longitudinal reinforcement 5 that needs to transfer the tension within the beam outer hoop steel plate 3 needs to satisfy:

[0046] b+2t1≥nd1+(n-1)×D

[0047]

[0048] Wherein: n is the number of newly added longitudinal reinforcements 5, b is the width of the original frame beam 2 (unit: mm), t1 is the thickness of the outer hoop steel plate 3 located on the left and right sides of the original frame beam 2 (unit: mm), d1 is the diameter of the newly added longitudinal reinforcement 5 (unit: mm), and D is the net spacing between the newly added longitudinal reinforcements 5 (unit: mm). D is usually taken as 50 mm.

[0049] The maximum value of the number n of newly added longitudinal reinforcements 5 can be calculated by the above formula (1); therefore, the number of newly added longitudinal reinforcements 5 selected should not exceed the maximum value.

[0050] The original frame beam 2 is equipped with indirect reinforcement and is surrounded by a circle of beam hoop steel plate 3. The length of the beam hoop steel plate 3 should ensure that the local compression of the original concrete beam (i.e., the original frame beam 2) meets the requirements; the schematic diagram of the local compression of the original frame beam 2 is as follows Figure 4 shown.

[0051] The length b1 of the outer hoop steel plate 3 of the beam should meet the following requirements:

[0052] F L ≤1.35β c β l f c A ln

[0053] A ln =b×b1

[0054] That is: b1 ≥ F L / 1.35β c β l f c b (2)

[0055] Among them: F L is the local compression design value of the original frame beam 2, F L =nN2=n×A×p2, A is the cross-sectional area of ​​the newly added longitudinal reinforcement 5 (unit: mm 2 ), p2 is the tensile strength design value of the newly added longitudinal reinforcement 5 (unit: N / mm 2 );

[0056] β c is the concrete strength coefficient of the original frame beam 2; β l is the strength enhancement factor of the concrete of the original frame beam 2 under compression, f c is the strength of the original frame beam 2 concrete, A ln is the local compressive net area of ​​the original frame beam 2, and b is the width of the original frame beam 2.

[0057] The minimum value of the length b1 of the beam outer hoop steel plate 3 can be calculated by the above formula (2); therefore, the selected length of the beam outer hoop steel plate 3 should not be less than the minimum value.

[0058] Furthermore, the tensile bearing capacity of the beam outer hoop steel plate 3 is calculated based on the number of newly selected longitudinal bars 5 and the length b1 of the beam outer hoop steel plate 3:

[0059] The tensile diagram of the outer hoop steel plate 3 of the beam is as follows: Figure 3 As shown, N2 is the maximum tensile design value of the newly added longitudinal reinforcement 5, and N1 is the maximum tensile design value that the outer hoop steel plates 3 of the beam on both sides can withstand. It is necessary to ensure that:

[0060] nN2≤2N1 (3)

[0061] Where: 2N1=2×b1×t1×p1

[0062] nN2=n×A×p2

[0063] p1 is the design value of tensile strength of the outer hoop steel plate 3 of the beam (unit: N / mm 2 ).

[0064] That is, the number of newly added longitudinal reinforcements 5 and the length b1 of the outer hoop steel plate 3 of the beam can be selected to satisfy the above formulas (1), (2), and (3).

[0065] As an example, the thickness of the outer hoop steel plate 3 of the beam is t1 = 20 mm, the material is Q235, and its tensile strength design value is p1 = 205 N / mm 2 ; Butt welds are used between the outer hoop steel plates 3 of the beam to provide equal strength connections; the diameter of the newly added longitudinal reinforcement 5 is d1 = 25 mm, the material is HRB400, and its tensile strength design value is p2 = 360 N / mm 2 ;at this time:

[0066]

[0067] When b=200, n=3; b=250, n=4; b=300, n=5; b=350, n=5.

[0068] Take b=300 and n=5 as an example:

[0069] Original frame beam 2 local compression design value FL =5N2=883620N, concrete strength coefficient β c =1.0; strength enhancement factor of concrete under compression The concrete grade is assumed to be C30, f c =14.3N / mm 2 , from which we can calculate: b1≥162.56mm, take b1=300mm;

[0070] Verify the tensile bearing capacity of the outer hoop steel plate 3 of the beam:

[0071] 2N1=2×300×20×205=2460000N

[0072] 5N2=5×490.9×360=883620N≤2N1

[0073] This indicates that the tensile bearing capacity of the outer hoop steel plate 3 of the beam meets the requirements.

[0074] The width of the original frame beam 2 is 300mm. When b1 = 300mm, the local net compression area A of the original frame beam 2 is ln =300×300=90000mm 2 ;

[0075] at this time

[0076] The local compression of the original frame beam 2 meets the requirements.

[0077] The design process of the height of the connecting steel plate 4 is:

[0078] The newly added longitudinal reinforcement 5 and the connecting steel plate 4 are connected by double-sided fillet welds. The height l of the connecting steel plate 4 is the welding length between the newly added longitudinal reinforcement 5 and the connecting steel plate 4, which should meet the following requirements:

[0079] l≥l e +2h f

[0080] Among them: e is the calculated length of the fillet weld, p2 is the design value of tensile strength of the newly added longitudinal reinforcement 5 (unit: N / mm 2 ), A is the cross-sectional area of ​​the newly added longitudinal reinforcement 5 (unit: mm 2 ), h e is the calculated thickness of the fillet weld, is the design value of tensile strength of fillet weld (unit: N / mm 2 );h f is the weld leg size,

[0081] As an example, the thickness of the connecting steel plate 4 is t2 = 20 mm, and the material is Q235; the diameter of the newly added longitudinal reinforcement 5 is d1 = 25 mm, and the material is HRB400, and the weld leg size is h f =12.5, calculated thickness of fillet weld h e =12.5×0.7=8.75; Design value of tensile strength of fillet weld

[0082] The calculated length of the fillet weld is l e for:

[0083]

[0084] Then the height l of the connecting steel plate 4 should satisfy:

[0085] l≥l e +2h f ≥126.23+2×12.5=151.23mm

[0086] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A beam-column joint design method for increasing the cross-section and strengthening reinforced concrete frame columns, wherein the reinforced concrete frame columns include: An original frame column (1) and an original frame beam (2) arranged on four sides of the original frame column (1) in a horizontal direction; The invention is characterized in that: the beam-column node is arranged at the connection between the original frame column (1) and the original frame beam (2), and adopts a structural form in which the newly added longitudinal reinforcement (5) transmits the force to the beam outer hoop steel plate (3) through the connecting steel plate (4); based on this, the beam-column node comprises: the beam outer hoop steel plate (3) welded to the four side surfaces of the original frame beam (2), the connecting steel plate (4) respectively welded to the beam outer hoop steel plate (3) on the top surface and the bottom surface, and a plurality of newly added longitudinal reinforcements (5) welded to the connecting steel plate (4); Based on the beam-column node structure, key parameters of the beam-column node are designed, wherein the key parameters include: the number of newly added longitudinal reinforcements (5) and the length of the beam outer hoop steel plate (3); The number of newly added longitudinal bars (5) and the length of the beam outer hoop steel plate (3) ensure that the tensile bearing capacity of the beam outer hoop steel plate (3) and the local compression of the original frame beam (2) meet the design requirements.

2. The beam-column node design method for increasing the cross-section and strengthening the reinforced concrete frame column according to claim 1, characterized in that: In the beam-column node, the newly added longitudinal reinforcement (5) transmits tension through the beam outer hoop steel plate (3), and the number n of the newly added longitudinal reinforcement (5) needs to satisfy: Wherein: b is the width of the original frame beam (2), in mm; t1 is the thickness of the outer hoop steel plates (3) located on the left and right sides of the original frame beam (2), in mm; d1 is the diameter of the newly added longitudinal reinforcement (5), in mm; D is the clear spacing between the newly added longitudinal reinforcements (5), in mm; The maximum number n of newly added longitudinal reinforcements (4) can be calculated from the above formula (1).

3. The beam-column node design method for increasing the cross-section and strengthening the reinforced concrete frame column according to claim 2, characterized in that: The length b1 of the beam outer hoop steel plate (3) must satisfy: b1≥F L / 1.35b c b l f c b (2) Among them: F L is the local compression design value of the original frame beam (2), F L =nN2=n×A×p2, n is the number of newly added longitudinal reinforcement (4), N2 is the maximum tensile design value of the newly added longitudinal reinforcement (5); A is the cross-sectional area of ​​the newly added longitudinal reinforcement (5), unit: mm 2 , p2 is the design value of tensile strength of the newly added longitudinal reinforcement (5), unit: N / mm 2 ; b is the width of the original frame beam (2); β c is the concrete strength coefficient of the original frame beam (2); β l is the strength enhancement factor of the concrete of the original frame beam (2) under compression, f c is the strength of the concrete of the original frame beam (2), in N / mm 2 .

4. The beam-column node design method for increasing the cross-section and strengthening the reinforced concrete frame column according to claim 3, characterized in that: Furthermore, the number of the newly added longitudinal reinforcements (5) and the length b1 of the outer hoop steel plate (3) of the beam need to satisfy: nN2≤2N1 Where: N2 is the maximum tensile design value of the newly added longitudinal reinforcement (5), N1 is the maximum tensile design value that the beam outer hoop steel plates (3) on both sides can withstand, N1 = b1 × t1 × p1; p1 is the tensile strength design value of the beam outer hoop steel plates (3), unit N / mm 2 .

5. The beam-column joint design method for increasing the cross-section and strengthening the reinforced concrete frame column according to any one of claims 1 to 4, characterized in that: The key parameters of the beam-column node also include the height l of the connecting steel plate (4); The height l of the connecting steel plate (4) must satisfy: l≥l e +2h f Among them: e is the calculated length of the fillet weld, p2 is the design value of tensile strength of the newly added longitudinal reinforcement (5), in N / mm 2 , A is the cross-sectional area of ​​the newly added longitudinal reinforcement (5), unit: mm 2 ,h e is the calculated thickness of the fillet weld, It is the design value of tensile strength of fillet weld, in N / mm 2 ;h f is the weld leg size, 6. The beam-column joint design method for increasing the cross-section and strengthening the reinforced concrete frame column according to any one of claims 1 to 4, characterized in that: The width of the connecting steel plate (4) is the same as the width of the outer hoop steel plate (3) of the beam; the newly added longitudinal reinforcement outside the range of the connecting steel plate (4) in the newly added section passes through the structural plate at the corresponding position.

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