Design method for controllable plastic hinge of variable cross-section steel beam grouting connection joint

Abstract

The invention relates to a design method for a controllable plastic hinge of a variable cross-section steel beam grouting connection node in a modular steel structure building, which comprises the following steps: S1, establishing a model in structural calculation software according to actual engineering parameters, S2, extracting a bending moment envelope diagram curve, S3, calculating a resistance bending moment value, and S4, calculating a deformation moment value. S4, according to the bending moment envelope diagram extracted in the step S2 and the calculated resistance bending moment value calculated in the step S3, under the conditions that the design of the variable cross section is considered and the resistance bending moment is larger than the beam end bending moment in the envelope diagram, the inertia moment value of the beam end cross section meeting plastic hinge outward movement is determined, and then the specific design size of the beam end cross section is obtained; and S6, the final section size is obtained, specifically, various section sizes of the beam end are obtained finally, the plastic hinge is moved out of the node area, the situation that the overall structure is unstable due to node damage is avoided, the effect of energy dissipation can be achieved through generation of the beam end plastic hinge, and the effect of protecting the structure against damage is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of beam-column node design in civil engineering steel structures, and relates to a design method for a controllable plastic hinge of a variable-section steel beam grouting connection node, and in particular to a design method for a controllable plastic hinge of a variable-section dog-bone steel beam grouting connection node. Background Art

[0002] In recent years, the country has vigorously promoted the industrialization, digitalization and green transformation and upgrading of the construction industry, which has pointed out the direction for my country to continuously promote the industrialization of new buildings. Modular steel structure buildings have the advantages of fast construction speed, good engineering quality, energy saving and environmental protection, and low labor consumption. They are gradually emerging in the field of modern construction. As building industrialization has received more and more attention and application at home and abroad, it provides new ideas for the transformation of the traditional construction industry.

[0003] The connection nodes between modules are the components that ensure the reliability of the connections between modules. The reliability of the nodes directly determines the overall performance of the structure. In modular steel structures, each module needs to be connected to each other through nodes to form a stable overall structure. If the node design is unreasonable and the load cannot be smoothly transmitted, it will cause local stress concentration, thereby affecting the load-bearing capacity and stability of the structure. In addition, the nodes in modular buildings refer not only to the connection between the upper and lower columns, but also to the connection between the floor beams and the ends of the ceiling beams. For the existing double beam connections using bolts, their on-site construction is often affected by the interference of the internal decoration of the modules and the limitations of the on-site construction space.

[0004] Current research on double-beam connections, both domestically and internationally, primarily focuses on bolted connections. By employing different types of bolts or different forms of beam-end perforations, the twin beams achieve a certain degree of integrity, thereby improving the overall performance of the joint. Bolted connections require high construction precision and sufficient construction space at the construction site. Furthermore, structural failure at large inter-story drift angles often results in tearing of the column wall or damage to the welds at the beam-column joint. These failures, all occurring in the joint region, are highly detrimental to the structure and prevent it from fully utilizing its energy dissipation capacity. Consequently, researchers at home and abroad are continuously improving and experimenting with new node connection methods and new design approaches for energy dissipation at beam-column joints.

[0005] Based on the node form of grouting connection, the present invention proposes a new type of beam end connection form of variable-section dog-bone beam, so that the grouting area of ​​the beam end has certain overall performance under the bite of the new connector. The location where the plastic hinge of the beam is generated is far away from the node area through the design of variable cross-section and dog-bone beam, and based on this design, a design method for controllable plastic hinge of the structural beam end is proposed. Summary of the Invention

[0006] In view of this, the present invention provides a design method for controllable plastic hinges in grouting connection nodes of variable-section steel beams in order to solve the problem that structural damage in current modular steel structure buildings mainly occurs at beam-column nodes when the inter-story displacement angle is large, which is detrimental to the overall structure and cannot fully utilize the structural energy absorption capacity. When designing, the present invention adopts this design method according to different engineering conditions to achieve the design purpose while maximizing the performance of the steel, thereby achieving the purpose of cost saving.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A design method for a controllable plastic hinge of a grouting connection node of a variable-section steel beam comprises the following steps:

[0009] S1. Model establishment: Establish a double-beam end model in the structural calculation software based on actual engineering parameters;

[0010] S2. Extracting a bending moment envelope curve: extracting a bending moment envelope curve of the double beams according to the simulation calculation results of the double beam end model by the structural calculation software in step S1;

[0011] S3. Calculate the resistance bending moment value: According to the resistance bending moment formula of the dog bone section of a single beam when the flange is plastic, the calculated resistance bending moment value of the double beam end is obtained;

[0012] S4. Determine the moment of inertia and dimensions of the beam end section: Based on the bending moment envelope diagram extracted in step S2 and the resisting bending moment value calculated in step S3, under the condition that the design of a variable cross-section is considered and the resisting bending moment is greater than the bending moment at the beam end in the envelope diagram, determine the moment of inertia value of the beam end section that satisfies the outward displacement of the plastic hinge, and thus obtain the specific design dimensions of the beam end section;

[0013] S5. Design the dogbone weakening dimensions: Determine the dogbone position, length, depth and other parameters based on the fact that the bending moment at the dogbone under the most unfavorable conditions is equal to the most unfavorable bending moment and the corresponding specifications, and then design the dogbone weakening dimensions after the cross-section is changed;

[0014] S6. Obtain the final cross-sectional dimensions: Combine the calculation results of steps S4 and S5 to obtain the various cross-sectional dimensions of the specific beam end, and move the plastic hinge outward to outside the node area.

[0015] Furthermore, the specific structure of the double-beam end model in step S1 includes a box beam installed in the upper floor beam grouting area, a box beam in the lower ceiling beam grouting area, an H-shaped steel beam with dog bones connected to the two grouting area box beams respectively, and a beam end connector. A grouting sealing plate is provided at the connection between the grouting area box beam and the H-shaped steel beam, and corresponding positions of the bottom of the box beam in the floor beam grouting area and the top of the box beam in the ceiling beam grouting area are provided with sockets for facilitating the insertion of the beam end connectors.

[0016] Furthermore, in step S1, the beam end connector includes a support plate and an integrally formed plug-in plate connected to both sides of the support plate. A plurality of through holes are evenly opened on the plug-in plate. The plug-in plate is inserted into the plug-in hole of the box beam in the grouting area. The height of the box beam in the grouting area is adapted to the height of the plug-in plate.

[0017] Furthermore, in step S1, a reserved hole is opened on the beam column wall of the box beam in the grouting area to facilitate the injection of grouting material into the grouting area at the beam end.

[0018] Furthermore, in step S3, the relationship between the bending moment at the beam end and the bending moment at the dog bone is expressed as follows:

[0019] ( )× (1)

[0020] The beam length is l, the length from the beam end to the dog bone is l1, and the bending moment at the beam end is M b1 , the bending moment at the dog bone is M b2 , the external conditions for controlling the generation of plastic hinges are obtained from the relationship between the bending moment at the beam end and the bending moment at the dog bone;

[0021] The expression for the bending moment resistance of the dog-bone section of a single beam when the flange is plastic is as follows:

[0022] (2)

[0023]

[0024]

[0025]

[0026] Among them, M u1 is the bending moment of the dogbone beam, f y is the yield strength of steel; t1 is the thickness of the I-beam flange; t2 is the thickness of the I-beam web; b is the width of the I-beam; h w is the web height of the I-beam; h is the height of the I-beam; is the resisting bending moment generated by the upper and lower webs of the beam, The resisting bending moment generated by the upper and lower flanges of the beam.

[0027] Furthermore, in step S4, when the flange of the single beam box section yields under the action of the grouting material, the influence of the bearing capacity obtained based on the cross-sectional force balance is as follows:

[0028]

[0029] The offset of the neutral axis can be obtained as:

[0030]

[0031] The moment of inertia after offset is obtained according to the parallel axis shift formula:

[0032] (8)

[0033]

[0034] Then the resistance bending moment value can be obtained:

[0035] (10)

[0036] in is the distance from the bottom after the neutral axis is offset, are the section moments of inertia after section offset, before steel offset, and grouting material respectively; is the offset of the neutral axis; H is the beam height; B is the beam width; t is the beam thickness; is the cross-sectional area of ​​the steel.

[0037] Furthermore, the influence of the double beams when the connector acts in step S4 is as follows:

[0038] Among them, the relationship between the axial forces of the double beams is as follows:

[0039]

[0040]

[0041]

[0042] Section bending moment calculation:

[0043] (14)

[0044] Calculation of cross-sectional curvature:

[0045]

[0046] Bring in:

[0047]

[0048] According to the geometric relationship, we can get:

[0049]

[0050] According to the relationship between strain and curvature, we can get:

[0051]

[0052] (19)

[0053]

[0054]

[0055] The strain difference between the lower flange of the floor beam and the upper flange of the ceiling beam is calculated as follows:

[0056]

[0057]

[0058] in Represents the floor beam, Represents the ceiling beams, is the beam curvature, is the strain difference between the contact surface of the double beam and the connector; is the axial force; is the beam shear force; is the slip proportional coefficient; is the cross-sectional area of ​​the beam; For beam height; is the thickness of the connecting piece; The front spacing of the beam neutral axis offset; are the strains at the contact surfaces of floor beams and ceiling beams with connectors, respectively;

[0059] By superimposing the above-mentioned calculations of the influence of grouting materials and the influence of connectors, the resistance bending moment of the grouting area at the beam end can be obtained, and then the bending moment of the beam section and the resistance bending moment diagram of each section can be obtained. The design size of the connector and the design size of the beam end can be obtained through the above-mentioned design method of the section plastic hinge.

[0060] Furthermore, step S6 can determine the dogbone weakening parameters based on the cross-sectional parameters and the Technical Code for Steel Structures of High-Rise Civil Buildings and the Steel Structure Design Standard: the distance from the column a, the dogbone length b, and the dogbone depth c, and finally obtain the specific dimensional parameters of the beam end.

[0061] The beneficial effects of the present invention are:

[0062] 1. The present invention discloses a method for designing a controllable plastic hinge for a grouting connection node of a variable-section steel beam. Through the plug-in design of the box beam in the grouting area of ​​the ceiling beam, the box beam in the grouting area of ​​the lower floor beam and the beam end connector, the beam end can be designed to have a controllable plastic hinge so that the location of the plastic hinge at the beam end is far away from the node area when encountering a rare earthquake, thereby avoiding the instability of the entire structure due to node damage. The generation of the plastic hinge at the beam end can play a good role in dissipating energy, thereby protecting the structure from damage, so that the overall structure can achieve the ideal effect of "strong node, weak component".

[0063] 2. The present invention discloses a design method for a controllable plastic hinge of a grouting connection node of a variable-section steel beam. By designing the beam section of a variable-section dog-bone beam, the beam end section size is optimized according to actual engineering needs, so that the structure can maximize the performance of the steel while meeting the design requirements; at the same time, it can avoid waste of steel and achieve the purpose of saving costs.

[0064] 3. The present invention discloses a design method for a controllable plastic hinge of a grouting connection node of a variable-section steel beam. The node form of the grouting connection is adopted. Compared with the traditional bolt connection, it reduces the requirements for construction accuracy and construction space, reduces the construction difficulty, reduces the on-site construction time, and improves the construction efficiency.

[0065] 4. The present invention discloses a design method for a controllable plastic hinge of a grouting connection node of a variable-section steel beam. Through the design of the beam end connector, the double beams can work together better when subjected to stress, thereby improving the overall bearing capacity of the structure. Reasonable design of the connector and cross-sectional form can effectively avoid stress concentration, reduce the risk of local damage, and improve the reliability and durability of the structure.

[0066] 5. The present invention discloses a design method for a controllable plastic hinge of a grouting connection node of a variable-section steel beam. The design method can be adjusted according to different engineering parameters and requirements, has high flexibility, and can meet diverse engineering design requirements; it is suitable for various types of steel structure buildings and has wide applicability.

[0067] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0069] Figure 1 Schematic diagram of the structure of the double-beam beam end model in an embodiment of the present invention;

[0070] Figure 2 The diagram is an envelope diagram of the bending moments generated by different loads on the ends of the double beams and a diagram of the resisting bending moments of the beam sections in an embodiment of the present invention;

[0071] Figure 3 The bending moment resistance diagram of the dog-bone section of a single beam when the flange is plastic in an embodiment of the present invention;

[0072] Figure 4This is a schematic diagram of the bearing capacity obtained based on the cross-sectional force balance when the flange of a single beam box section yields under the action of grouting material according to an embodiment of the present invention;

[0073] Figure 5 This is a schematic diagram of the axial forces acting on the floor beams, ceiling beams and connectors according to an embodiment of the present invention:

[0074] Figure 6 Schematic diagram of the strain at the contact surface between the floor beams, ceiling beams and connectors according to an embodiment of the present invention:

[0075] Figure 7 Schematic diagram of the offset when the floor beams, ceiling beams and connectors interact in an embodiment of the present invention.

[0076] Reference numerals: ceiling beam 1, floor beam 2, grouting area box beam 3, H-shaped steel beam 4, beam end connector 5, grouting sealing plate 6, socket 7. DETAILED DESCRIPTION

[0077] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0078] A design method for a controllable plastic hinge of a grouting connection node of a variable-section steel beam comprises the following steps:

[0079] S1. Model building: According to the actual engineering parameters, the model is built in the structural calculation software. Figure 1 The double-beam end model shown provides a basis for subsequent structural calculations and analysis, ensuring that the model can accurately reflect the actual engineering conditions.

[0080] The double-beam beam end model includes a box beam 3 in the grouting area of ​​the upper floor beam 2, a box beam 3 in the grouting area of ​​the lower ceiling beam 1, an H-shaped steel beam 4 with dog bones connected to the two box beams 3 in the grouting area respectively, and a beam end connector 5. A grouting sealing plate 6 is provided at the connection between the box beam 3 in the grouting area and the H-shaped steel beam 4. Sockets 7 for facilitating the insertion of the beam end connector 5 are provided at the corresponding positions of the bottom of the box beam 3 in the grouting area of ​​the floor beam 2 and the top of the box beam 3 in the grouting area of ​​the ceiling beam 1. The H-shaped steel beam 4 is cross-shaped, and a reserved hole is provided on the beam column wall of the box beam 3 in the grouting area to facilitate the injection of grouting material into the beam end grouting area.

[0081] When installing the double beams, first install the ceiling beam 1, then insert the lower plug-in plate of the beam end connector 5 into the socket 7 of the box beam 3 in the grouting area of ​​the ceiling beam 1, dock the socket 7 of the box beam 3 in the grouting area of ​​the floor beam 2 with the upper plug-in plate of the beam end connector 5, complete the installation of the upper floor beam 2, and finally inject the grouting material into the beam end grouting area through the reserved holes in the beam column wall.

[0082] The through-holes in the plug-in plate of the beam end connector 5 ensure sufficient engagement with the grouting material at the beam end, maximizing the coordinated load-bearing effect of the two beams. The choice of a plate-type connector minimizes cross-sectional damage to the box beam when the hole is cut, thus preventing damage to the beam end at the point where the hole is inserted into the box beam. The beam end connector 5 must be installed with tolerances in mind, and a single insertion hole is provided to avoid unnecessary installation hassles.

[0083] S2. Extract the bending moment envelope curve: Figure 2 As shown, according to the simulation calculation results of the double-beam end model by the structural calculation software in step S1, the bending moment envelope curve of the double beam is extracted to understand the bending moment distribution of the double beam under various loads, providing key data for subsequent design.

[0084] S3. Calculate the resistance bending moment value: According to the resistance bending moment formula of the dog-bone section of a single beam when the flange is plastic, the calculated resistance bending moment value of the double beam end is obtained, and the resistance bending moment capacity of the beam end under different working conditions is determined to provide a basis for subsequent section design.

[0085] The relationship between the bending moment at the beam end and the bending moment at the dog bone is expressed as:

[0086] ( )× (1)

[0087] The beam length is l, the length from the beam end to the dog bone is l1, and the bending moment at the beam end is M b1 , the bending moment at the dog bone is M b2 The external conditions that control the generation of plastic hinges are obtained from the relationship between the bending moment at the beam end and the bending moment at the dog bone.

[0088] like Figure 3 The expression for the bending moment resistance of the dog-bone section of a single beam is obtained when the flange is plastic as shown below:

[0089] (2)

[0090]

[0091]

[0092]

[0093] Among them, M u1 is the bending moment of the dogbone beam, f y is the yield strength of steel; t1 is the thickness of the I-beam flange; t2 is the thickness of the I-beam web; b is the width of the I-beam; h w is the web height of the I-beam; h is the height of the I-beam; is the resisting bending moment generated by the upper and lower webs of the beam, The resisting bending moment generated by the upper and lower flanges of the beam.

[0094] S4. Determine the moment of inertia and dimensions of the beam end section: Based on the bending moment envelope diagram extracted in step S2 and the resistance bending moment value calculated in step S3, and considering the design of a variable cross-section and the condition that the resistance bending moment is greater than the bending moment at the beam end in the envelope diagram, determine the moment of inertia value of the beam end section that satisfies the outward shift of the plastic hinge, and then obtain the specific design dimensions of the beam end section. By rationally designing the beam end section, the location where the plastic hinge is generated can be kept away from the node area, thereby improving the overall performance and safety of the structure.

[0095] like Figure 4 The influence of the cross-sectional force balance on the bearing capacity of the single beam box section shown below when the flange yields under the action of grouting material is as follows:

[0096]

[0097] The offset of the neutral axis can be obtained as:

[0098]

[0099] The moment of inertia after offset is obtained according to the parallel axis shift formula:

[0100] (8)

[0101]

[0102] Then the resistance bending moment value can be obtained:

[0103] (10)

[0104] in is the distance from the bottom after the neutral axis is offset, are the section moments of inertia after section offset, before steel offset, and grouting material respectively; is the offset of the neutral axis; H is the beam height; B is the beam width; t is the beam thickness; is the cross-sectional area of ​​the steel.

[0105] like Figures 5-7 The effects of the double beam shown when the connector is acting are as follows:

[0106] Figure 5 It is a schematic diagram of the overall structure. Figure 6 The comparison diagram of the strain of the double beam with and without the connector is shown in Fig. Figure 7 is a schematic diagram of the cross section of a double box beam, where the axial forces of the double beams are related as follows:

[0107]

[0108]

[0109]

[0110] Section bending moment calculation:

[0111] (14)

[0112] Calculation of cross-sectional curvature:

[0113]

[0114] Bring in:

[0115]

[0116] According to the geometric relationship, we can get:

[0117]

[0118] According to the relationship between strain and curvature, we can get:

[0119]

[0120] (19)

[0121]

[0122]

[0123] The strain difference between the lower flange of the floor beam and the upper flange of the ceiling beam is calculated as follows:

[0124]

[0125]

[0126] in Represents the floor beam, Represents the ceiling beams, is the beam curvature, is the strain difference between the contact surface of the double beam and the connector; is the axial force; is the beam shear force; is the slip proportional coefficient; is the cross-sectional area of ​​the beam; For beam height; is the thickness of the connecting piece; The front spacing of the beam neutral axis offset; are the strains at the contact surfaces of floor beams and ceiling beams with connectors, respectively.

[0127] By superimposing the above-mentioned calculations of the influence of grouting materials and the influence of connectors, the resistance bending moment of the grouting area at the beam end can be obtained, and then the bending moment of the beam section and the resistance bending moment diagram of each section can be obtained. The design size of the connector and the design size of the beam end can be obtained through the above-mentioned design method of the section plastic hinge.

[0128] S5. Design dogbone weakening dimensions: Determine parameters such as dogbone position, length, and depth based on the fact that the bending moment resistance at the dogbone under the most unfavorable conditions is equal to the most unfavorable bending moment and the corresponding specifications. Then, design the dogbone weakening dimensions after the cross-section is changed. Under the premise of ensuring structural safety, the seismic performance and energy consumption capacity of the structure can be further improved by optimizing the dogbone weakening dimensions.

[0129] S6. Obtain the final cross-sectional dimensions: Combined with the calculation results of steps S4 and S5, the various cross-sectional dimensions of the specific beam ends are finally obtained, and the plastic hinge is moved outward outside the node area, completing the design of the controllable plastic hinge at the beam end, and ensuring the reliability and economy of the structure under extreme working conditions such as rare earthquakes.

[0130] Then, based on the cross-sectional parameters and the Technical Code for Steel Structures of High-Rise Civil Buildings and the Steel Structure Design Standards, the dogbone weakening parameters can be determined: length from the column a, dogbone length b, and dogbone depth c, and finally the detailed parameters of the beam end can be obtained.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A design method for controllable plastic hinges of grouting connection nodes of variable-section steel beams, characterized in that: The following steps are involved: S1. Model establishment: Establish a double-beam end model in the structural calculation software based on actual engineering parameters; S2. Extracting a bending moment envelope curve: extracting a bending moment envelope curve of the double beams according to the simulation calculation results of the double beam end model by the structural calculation software in step S1; S3. Calculate the resistance bending moment value: According to the resistance bending moment formula of the dog bone section of a single beam when the flange is plastic, the calculated resistance bending moment value of the double beam end is obtained; S4. Determine the moment of inertia and dimensions of the beam end section: Based on the bending moment envelope diagram extracted in step S2 and the resisting bending moment value calculated in step S3, under the condition that the design of a variable cross-section is considered and the resisting bending moment is greater than the bending moment at the beam end in the envelope diagram, determine the moment of inertia value of the beam end section that satisfies the outward displacement of the plastic hinge, and thus obtain the specific design dimensions of the beam end section; S5. Design the dogbone weakening dimensions: Determine the parameters of the dogbone position, length, and depth based on the fact that the bending moment at the dogbone under the most unfavorable conditions is equal to the most unfavorable bending moment and the corresponding specifications, and then design the dogbone weakening dimensions after the cross-section is changed; S6. Obtain the final cross-sectional dimensions: Combine the calculation results of steps S4 and S5 to finally obtain the various cross-sectional dimensions of the specific beam end, and realize the outward movement of the plastic hinge to outside the node area.

2. A design method for a controllable plastic hinge of a grouting connection node of a variable-section steel beam according to claim 1, characterized in that: The specific structure of the double-beam beam end model includes a box beam in the upper ceiling beam grouting area, a box beam in the lower floor beam grouting area, an H-shaped steel beam with dog bones connected to the two grouting area box beams respectively, and a beam end connector. A grouting sealing plate is provided at the connection between the grouting area box beam and the H-shaped steel beam. Sockets for facilitating the insertion of beam end connectors are provided at the corresponding positions of the bottom of the box beam in the floor beam grouting area and the top of the box beam in the ceiling beam grouting area.

3. The design method of a controllable plastic hinge of a grouting connection node of a variable-section steel beam according to claim 2, characterized in that: The connecting plate of the beam end connecting piece inserted into the plug hole of the box beam in the grouting area is provided with a plurality of through holes of the same size, and the height of the box beam in the grouting area is adapted to the height of the connecting plate.

4. The method for designing a controllable plastic hinge for a grouting connection node of a variable-section steel beam according to claim 2, wherein: Reserved holes are provided on the beam and column walls of the box beams in the grouting area.

5. The method for designing a controllable plastic hinge for a grouting connection node of a variable-section steel beam according to claim 1, characterized in that: The relationship between the bending moment at the beam end and the bending moment at the dog bone in step S3 is expressed as follows: （ ）× （1） The beam length is l, the length from the beam end to the dog bone is l1, and the bending moment at the beam end is M b1 , the bending moment at the dog bone is M b2 , the external conditions for controlling the generation of plastic hinges are obtained from the relationship between the bending moment at the beam end and the bending moment at the dog bone; The expression for the bending moment resistance of the dog-bone section of a single beam when the flange is plastic is as follows: （2） Among them, M u1 is the bending moment of the dogbone beam, f y is the yield strength of steel; t1 is the thickness of the I-beam flange; t2 is the thickness of the I-beam web; b is the width of the I-beam; h w is the web height of the I-beam; h is the height of the I-beam; is the resisting bending moment generated by the upper and lower webs of the beam, The resisting bending moment generated by the upper and lower flanges of the beam.

6. A design method for a controllable plastic hinge of a grouting connection node of a variable-section steel beam according to claim 5, characterized in that: In step S4, when the flange of the single beam box section yields under the action of the grouting material, the influence of the bearing capacity obtained based on the cross-sectional force balance is as follows: The offset of the neutral axis can be obtained as: The moment of inertia after offset is obtained according to the parallel axis shift formula: （8） Then the resistance bending moment value can be obtained: （10） in is the distance from the bottom after the neutral axis is offset, are the section moments of inertia after section offset, before steel offset, and grouting material respectively; is the offset of the neutral axis; H is the beam height; B is the beam width; t is the beam thickness; is the cross-sectional area of ​​the steel.

7. A method for designing a controllable plastic hinge for a grouting connection node of a variable-section steel beam according to claim 6, characterized in that: The influence of the double beams in step S4 when the connecting member acts is as follows: Among them, the relationship between the axial forces of the double beams is as follows: Section bending moment calculation: （14） Calculation of cross-sectional curvature: Bring in: According to the geometric relationship, we can get: According to the relationship between strain and curvature, we can get: （19） The strain difference between the lower flange of the floor beam and the upper flange of the ceiling beam is calculated as follows: in Represents the floor beam, Represents the ceiling beams, is the beam curvature, is the strain difference between the contact surface of the double beam and the connector; is the axial force; is the beam shear force; is the slip proportional coefficient; is the cross-sectional area of ​​the beam; For beam height; is the thickness of the connecting piece; is the front spacing of the beam neutral axis offset; are the strains at the contact surfaces of floor beams and ceiling beams with connectors, respectively; By superimposing the above-mentioned calculations of the influence of grouting materials and the influence of connectors, the resistance bending moment of the grouting area at the beam end can be obtained, and then the bending moment of the beam section and the resistance bending moment diagram of each section can be obtained. The design size of the connector and the design size of the beam end can be obtained through the above-mentioned design method of the section plastic hinge.

8. A method for designing a controllable plastic hinge for a grouting connection node of a variable-section steel beam according to claim 7, characterized in that: In step S6, the dogbone weakening parameters can be determined based on the cross-sectional parameters and the Technical Code for Steel Structures of High-Rise Civil Buildings and the Steel Structure Design Standard: the distance from the column a, the dogbone length b, and the dogbone depth c, and finally the specific dimensional parameters of the beam end are obtained.

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