Beam-column joint design method for strengthening reinforced concrete frame columns with increased cross-section

Abstract

The present invention provides a beam-column node design method for reinforced concrete frame columns with increased cross-section reinforcement. By structurally designing the beam-column node for reinforcement with increased cross-section, a structural form in which newly added longitudinal reinforcement transmits force to the beam outer hoop steel plate through a connecting steel plate is adopted, thereby avoiding the newly added longitudinal reinforcement from passing through the beam. The beam-column node is set at the connection between the original frame column and the original frame beam, and a structural form in which newly added longitudinal reinforcement transmits force to the beam outer hoop steel plate through a connecting steel plate is adopted. Thus, the beam-column node includes: the beam outer hoop steel plates welded to the four sides of the original frame beam, the connecting steel plates welded to the top and bottom surfaces of the beam outer hoop steel plates respectively, and a number of newly added longitudinal reinforcements welded to the connecting steel plates. 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 beam outer hoop steel plate. 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.

Description

Technical Field

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

[0002] Currently, facing the challenges of high-performance building functions and the aging of existing buildings due to long-term use, it is necessary to rationally reinforce existing buildings if they cannot be demolished and rebuilt due to economic and social considerations. As a result, there are more and more reinforcement projects for existing concrete structures.

[0003] As a primary load-bearing component, frame columns require significant reinforcement, and the most common method is to increase the cross-section. This method requires calculating the required reinforcement in the newly added cross-section. The lower end of the longitudinal reinforcement should extend into the foundation or lower-level beams and columns and meet anchorage requirements. Longitudinal reinforcement outside the original structural envelope (i.e., outside the horizontal projection of the beam) should pass through the floor slab and into the upper column footings, or be anchored at the roof slab. Longitudinal reinforcement within the original structural envelope (i.e., within the horizontal projection of the beam) must pass through the beam and into the upper column footings, or be anchored at the roof slab.

[0004] In actual projects, the reinforcement at the ends of existing structural beams is often dense and difficult to detect accurately. The diameter of the longitudinal bars used for reinforcement is large, which inevitably breaks the steel bars inside the beam when passing through it, reducing or even destroying the structural bearing capacity. It can even make it impossible to drill holes for planting rebar, making construction difficult. Therefore, it is necessary to design a beam-column joint for increasing the cross-section of reinforced concrete frame columns. This joint avoids inserting new longitudinal bars through the beam when increasing the cross-section of the concrete frame column, thus avoiding breaking the existing structural beam reinforcement. It also meets the reinforcement requirements of the frame column and ensures 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 force to the outer hoop steel plate of the beam through the 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 joint 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 to the four sides of the original frame beam, the connecting steel plates welded to the beam outer hoop steel plates on the top and bottom surfaces respectively, and a plurality of newly added longitudinal reinforcements welded to the connecting steel plates;

[0008] Based on the beam-column node structure, 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 must satisfy:

[0011]

[0012] Where: b is the width of the original frame beam, unit is mm; t1 is the thickness of the outer hoop steel plate located on the left and right sides of the original frame beam, unit is mm; d1 is the diameter of the newly added longitudinal reinforcement, unit is mm; D is the net spacing between the newly added longitudinal reinforcements, unit is mm; the maximum 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 must meet the following requirements:

[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 bars, N2 is the maximum tensile design value of the newly added longitudinal bars; A is the cross-sectional area of ​​the newly added longitudinal bars, 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 improvement coefficient of the original frame beam concrete under compression, c The strength of the original frame beam concrete, unit 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 beam outer hoop steel plate must 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, unit 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, The design value of tensile strength of fillet weld, unit N / mm 2 ;h f is the solder foot 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 to 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, the newly added longitudinal reinforcement is avoided from passing through the beam, thereby avoiding breaking the original structural beam reinforcement. The protection of the original structural beam can be achieved when the longitudinal reinforcement is anchored. Moreover, 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 ensures that the force transmission is safe and reliable by considering 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 reinforcement in the beam-column node.

[0028] (3) The present invention ensures that the local compression of the original frame beam meets the design requirements by specifically designing the length of the outer hoop steel plate of the beam, 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 This is a schematic structural diagram of a beam-column node with increased cross-section and reinforcement 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 and ensures the realization of the purpose of strengthening the existing structure.

[0037] like Figure 1 and Figure 2 As shown, the beam-column joint designed in this embodiment is used to reinforce reinforced concrete frame columns by increasing their cross-sections. The reinforced concrete frame column comprises: an original frame column 1 and an original frame beam 2; the original frame column 1 is arranged vertically, and the original frame beam 2 is arranged horizontally on the four sides of the original frame column 1. The width of the original frame beam 2 is less than the width of the side surface that connects 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 passing through the beam; based on this, the structure of the beam-column node includes: beam outer hoop steel plate 3, connecting steel plate 4 and newly added longitudinal reinforcement 5; beam outer hoop steel plates 3 are set on the top surface, bottom surface and two side surfaces of the connection end of the original frame beam 2 and the original frame column 1, that is, four beam outer hoop steel plates 3 are used to surround the connection end of the original frame beam 2 and the original frame column 1. 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; therefore, 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 portion of the newly added longitudinal reinforcement 5 below the original frame beam 2 is welded to the corresponding connecting steel plate 4 (i.e., the lower connecting steel plate), with the lower end supported on the structural bottom plate. The lower portion of the newly added longitudinal reinforcement 5 (not shown) above the original frame beam 2 is welded to the corresponding connecting steel plate 4 (i.e., the lower connecting steel plate), with the upper end supported on the structural top plate. Because 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 installed on the plane of the original frame beam 2, 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, and thus avoid breaking the steel bars inside the original frame beam 2 during reinforcement.

[0042] In addition, if Figure 5 As shown, since the outsourced beam 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 hoop steel plate 3, and the welding length is 10d.

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

[0044] First, 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 transmit the tensile force through the beam outer hoop steel plate 3. The number n of newly added longitudinal reinforcement 5 that needs to transmit the tensile force within the range of the beam outer hoop steel plate 3 must meet the following requirements:

[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 plates 3. The length of the beam hoop steel plates 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 f is the strength improvement coefficient of the original frame beam 2 concrete under compression, c is the strength of the original frame beam 2 concrete, A ln is the local compressed 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 length of the selected 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, where 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 on both sides of the beam 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 bars 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 The outer hoop steel plates 3 of the beam are butt welded to form an equal strength connection. 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 increase coefficient of concrete under compression The concrete grade is assumed to be C30, f c =14.3N / mm 2 , from this calculation we can get: 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 compressive net area of ​​the original frame beam 2 is A. 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 as follows:

[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, which should be p2 is the design value of tensile strength of 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 solder foot 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 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 scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. Design method for beam-column joints for increasing the cross-section and strengthening reinforced concrete frame columns. The reinforced concrete frame columns include: An original frame column (1) and original frame beams (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 newly added longitudinal reinforcement (5) transmits force to the beam outer hoop steel plate (3) through the connecting steel plate (4); based on this, the beam-column node includes: the beam outer hoop steel plates (3) welded to the four side surfaces of the original frame beam (2), the connecting steel plates (4) respectively welded to the beam outer hoop steel plates (3) on the top and bottom surfaces, and a plurality of newly added longitudinal reinforcements (5) welded to the connecting steel plates (4); Based on the structure of the beam-column node, key parameters of the beam-column node are designed, and the key parameters include: the number of the newly added longitudinal reinforcements (5) and the length of the beam outer hoop steel plate (3); The number of the 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; The key parameters of the beam-column joint also include the height of the connecting steel plate (4) ; The height of the connecting steel plate (4) Need to meet: in: is the calculated length of the fillet weld, , is the design value of tensile strength of the newly added longitudinal reinforcement (5), in units of , A is the cross-sectional area of ​​the newly added longitudinal reinforcement (5), unit: mm 2 , is the calculated thickness of the fillet weld, ; is the design value of tensile strength of fillet weld, unit ; is the solder foot size, .

2. The beam-column joint design method for increasing the cross-section and strengthening reinforced concrete frame columns according to claim 1, characterized in that: In the beam-column joint, the newly added longitudinal reinforcement (5) transmits tension through the beam outer hoop steel plate (3), and the number of the newly added longitudinal reinforcement (5) is Need to meet: （1） in: is the width of the original frame beam (2), in mm; is the thickness of the outer hoop steel plate (3) located on the left and right sides of the original frame beam (2), in mm, is the diameter of the newly added longitudinal reinforcement (5), in mm; is the clear spacing between the newly added longitudinal reinforcements (5), in mm; The number of newly added longitudinal reinforcement (5) can be calculated from formula (1): The maximum value of .

3. The beam-column joint design method for increasing the cross-section and strengthening reinforced concrete frame columns according to claim 2, characterized in that: The length of the outer hoop steel plate (3) of the beam Need to meet: （2） in: is the local compression design value of the original frame beam (2), , is the number of newly added longitudinal reinforcement (5), 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 , is the design value of tensile strength of the newly added longitudinal reinforcement (5), in units of ; is the width of the original frame beam (2); is the concrete strength coefficient of the original frame beam (2); is the strength improvement coefficient of the concrete of the original frame beam (2) under compression, is the strength of the concrete of the original frame beam (2), in units of .

4. The beam-column joint design method for increasing the cross-section and strengthening reinforced concrete frame columns according to claim 3, characterized in that: Furthermore, the number of the newly added longitudinal bars (5) and the length of the outer hoop steel plate (3) of the beam Need to meet: in: is the maximum tensile design value of the newly added longitudinal reinforcement (5), is the maximum tensile design value that the outer hoop steel plates (3) on both sides of the beam can withstand, ; is the design value of tensile strength of the outer hoop steel plate (3) of the beam, in units of .

5. The beam-column joint design method for increasing the cross-section and strengthening reinforced concrete frame columns 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 beam outer hoop steel plate (3); 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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