Net rack bolt sphere strengthening node after rod piece instability

Abstract

The invention relates to the technical field of building steel structure connection, and discloses a net rack bolt sphere strengthening node after rod piece instability, which comprises a bolt sphere, a sealing plate connected with the end part of a rod piece, a connecting bolt and a sleeve arranged on the connecting bolt in a sleeving manner and positioned between the sealing plate and the bolt sphere, the end face, facing the bolt ball, of the sleeve is constructed to be capable of forming non-area-fixed contact with the surface of the bolt ball when the joint rotates due to buckling of the rod piece, so that the bending moment acting on the connecting bolt is reduced. Only by optimizing the local geometrical shape of one end face of the sleeve, on the premise that all other standard components such as a bolt ball, a connecting bolt, a sealing plate and a rod piece are not changed, the fracture resistance of the joint under the extreme condition is remarkably improved with extremely low transformation cost, and the joint is easy to apply and popularize in new construction and reinforcement projects.

Description

Technical Field

[0001] This invention relates to the field of building steel structure connection technology, specifically to a space frame bolt ball reinforcement node after member instability. Background Technology

[0002] Bolted ball joints are one of the most commonly used connection methods in modern space steel grid structures. They mainly consist of bolt balls, high-strength bolts, sleeves, pins, end plates, and members. The members are connected by screwing bolts into the threaded holes within the bolt balls. This type of joint offers advantages such as reliable connection, clear force transmission, high standardization, and convenient construction.

[0003] However, under extreme loads (such as strong earthquakes), when the grid structure members (members) experience excessive axial pressure and large displacement buckling, the traditional bolt ball joint reveals a significant technical defect: the buckled members exert huge rotational and bending moments on the joint, and the traditional hexagonal sleeve and bolt ball are in planar contact, forming a rigid constraint. This constraint causes the sleeve at the joint to exert significant shear and bending effects on the connecting bolts. Under the above-mentioned combined stress state, the connecting bolts (especially at their thread roots or at the transition between the bolt and the bolt head) are very prone to crack initiation due to stress concentration and rapid propagation, eventually leading to brittle fracture of the joint. Once this fracture occurs, it will cut off the force transmission path between the members, which may cause the structure to collapse continuously, posing a great danger.

[0004] Existing technologies mainly focus on how to improve the strength and stiffness of nodes under normal use conditions, such as increasing bolt diameter, using higher strength grade steel, or optimizing sphere wall thickness. Although these methods can improve the ultimate bearing capacity of nodes, they fail to fundamentally change the stress mechanism and failure mode of nodes after member buckling instability. They also fail to solve the safety hazard of brittle fracture of nodes after member instability under the design concept of "strong nodes, weak members".

[0005] Currently, there is no effective technical solution in the industry that can actively adapt to buckling deformation and unload bending moment by modifying the local geometry of the sleeve, thereby delaying or preventing node fracture. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a bolt-ball reinforced joint for space frame structures after member buckling based on arc-shaped surface unloading of bending moment. This joint optimizes the geometry of the contact surface between the sleeve and the bolt ball, allowing for a larger rotation angle when the member undergoes large displacement buckling. The arc-shaped contact surface converts part of the bending moment into a gentler contact pressure, effectively unloading or reducing harmful bending moments and shear forces acting on the connecting bolts, delaying joint fracture, and improving the robustness and anti-collapse capability of the space frame structure under extreme conditions.

[0007] The present invention proposes a bolt ball reinforcement node for a space frame after member instability, comprising a bolt ball, a sealing plate connected to the end of the member, a connecting bolt, and a sleeve sleeved on the connecting bolt and located between the sealing plate and the bolt ball. The end face of the sleeve facing the bolt ball is configured to form a non-fixed contact with the surface of the bolt ball when the member buckles and causes the node to rotate, so as to reduce the bending moment acting on the connecting bolt. The end face of the sleeve facing the bolt ball is designed to form a non-fixed contact area with the ball surface when the node is rotated under force, such as point contact or line contact, and the contact position moves as the rotation angle increases, thereby changing the line of action of the force, reducing the lever arm, and effectively reducing the additional bending moment transmitted to the connecting bolt.

[0008] As a further optimization of the present invention, the end face of the sleeve facing the bolt ball is a non-planar structure, preferably a non-planar shape such as a convex curved surface or an inclined surface, such as a spherical surface, a conical surface or a chamfered surface. This design allows the contact area to move smoothly during the rotation of the node, avoiding stress concentration caused by rigid surface contact.

[0009] As a further optimization of the present invention, the non-planar structure is a convex surface, which is preferably a part of a sphere. Its radius of curvature can be greater than or equal to the radius of the bolt ball to ensure that the contact line or contact point can move smoothly during rotation and realize the dynamic unloading of bending moment.

[0010] As a further optimization of the present invention, the convex surface is a part of a sphere, a part of an ellipsoid, or other rotating convex surface formed by rotating a smooth curve around the sleeve axis. The convex surface can be a standard sphere, an ellipsoid, or other rotationally symmetrical smooth surface, all of which can provide continuously changing contact positions when the node rotates, achieving a similar bending moment unloading effect.

[0011] As a further optimization of the present invention, the non-planar structure is an inclined surface, which can be a conical surface or a large chamfered surface that is inclined from the edge of the end face to the center, such as a 45° chamfer. The inclined surface design can also guide the contact area to move from the edge to the center when the node rotates, thereby reducing the lever arm.

[0012] As a further optimization of the present invention, the inclined surface is a conical surface that is rotationally symmetrical about the axis of the sleeve, or a chamfered surface formed by the edge of the end face tilting towards the center. The conical surface is symmetrical about the axis of the sleeve, and the chamfered surface is evenly distributed along the circumference of the end face. Both of these shapes can be achieved by conventional machining, which is simple and cost-controllable.

[0013] As a further optimization of the present invention, the outer contour of the sleeve cross section is polygonal or circular, and the outer contour of the sleeve is preferably regular hexagonal, which is convenient for tightening with a wrench. Its inner hole is circular to accommodate the bolt rod. The shape of the outer contour does not affect the mechanical behavior of the end face contact and can be selected according to construction habits.

[0014] As a further optimization of the present invention, the other end face of the sleeve away from the bolt ball is a plane, which is used to contact the sealing plate to ensure a stable and uniform surface contact with the sealing plate, reliably transmit axial pressure, and not interfere with the normal stress performance of the node.

[0015] As a further optimization of the present invention, a locking component is also included, which passes through the side wall of the sleeve and engages with the shaft of the connecting bolt to prevent relative rotation between the two. The locking component can be a pin, which passes through the hole in the side wall of the sleeve and engages with the groove on the bolt shank to prevent relative rotation between the bolt and the sleeve during installation or use, thus ensuring the stability of the joint.

[0016] As a further optimization of the present invention, the sleeve is made of a metal material, such as 45 steel, 40Cr or alloy steel, and after heat treatment, it has sufficient strength, hardness and toughness to withstand the contact pressure and local deformation of the node under extreme conditions.

[0017] The working principle of this invention is to change the constraint conditions and force transmission path of the node under extreme deformation by changing the geometry of the contact surface at the end of the sleeve. Under normal working conditions, the reinforced node functions exactly the same as the traditional node. The sleeve and the bolt ball fit tightly together, and the axial force is reliably transmitted through the preload of the high-strength bolt. When a member buckles due to excessive axial pressure, the end of the member will generate angular and lateral displacement relative to the bolt ball. In a conventional joint, the flat end of the hexagonal sleeve will form a rigid compression with the surface of the bolt ball, immediately applying a huge lever arm to the connecting bolt that passes through, generating significant bending stress and root shear force. In this invention, the end of the sleeve facing the bolt ball is an arc-shaped curved surface (such as a part of a sphere) or a large chamfered slope. When the node begins to rotate, the contact between this end face of the sleeve and the bolt ball is no longer the entire plane, but starts from a "line" or "point" on the edge. As the rotation angle increases, the contact area moves smoothly along the arc-shaped surface. This movement process allows the sleeve to have a certain "rolling" or "sliding" tendency relative to the bolt ball, rather than a pure "prying". Moreover, the lower sleeve stiffness allows the node to allow greater angular deformation before fracture, so that it still has a certain deformation coordination ability after the structure becomes unstable. This geometric change has a dual mechanical effect: first, it unloads the bending moment, as the line of action of the contact force is closer to the bolt axis, and the lever arm is significantly reduced, thereby directly reducing the bending moment acting on the bolt; second, it redistributes stress, avoiding extreme stress concentration in local areas of the bolt (such as at the end of the thread), and converting some of the energy into local plastic deformation or frictional slip energy at the contact surface between the sleeve and the ball. Therefore, the combined stress state of tension (compression) + bending + shear borne by the connecting bolts is greatly improved, the time required to reach the material limit state is extended, and the fracture of the joint is effectively delayed, thus buying time for early warning and emergency treatment of the structural system.

[0018] The bolt ball reinforcement node for space frame after member instability proposed in this invention has the following beneficial effects: (i) When the member buckles and becomes unstable, the rotation of the node is rigidly restricted by the traditional planar sleeve. However, the arc / chamfered sleeve of the present invention provides a larger rotation space. The contact between the sleeve and the bolt ball changes from "surface contact" to "line contact" or "point contact". As the rotation angle increases, the contact position moves smoothly along the arc surface. This process can effectively absorb deformation energy and significantly reduce the additional bending moment and concentrated shear force generated by the sleeve on the root of the connecting bolt, thereby greatly delaying the process of the bolt initiating cracks and propagating fracture due to composite stress. (ii) The core innovation of this invention lies in the optimization of the geometry of one end of the sleeve. The specifications, dimensions and connection methods of all other components of the node (bolt ball, bolt, pin, end plate, rod) are consistent with those of the traditional standard node. This makes it possible to upgrade the performance of this reinforced node without changing the existing design, production and installation system. Only the sleeve needs to be replaced. The modification cost is extremely low and it is easy to promote and apply in new construction and reinforcement projects. (III) This design achieves complex mechanical performance optimization through simple geometric changes. The arc surface acts as a "mechanical insurance". When the structure encounters a disaster exceeding the design intensity, it allows the nodes to undergo large controllable plastic rotation, providing valuable time and space for the redistribution of internal forces and energy dissipation, enhancing the robustness and collapse resistance of the overall structure, and improving the safety reserve. (iv) The arc-shaped curved surface or chamfered surface of the sleeve of the present invention can be achieved by conventional machining (such as turning, milling) or forging processes. The process is mature, the quality is controllable, and no new processing difficulties or reliability risks will be introduced.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structural assembly of an embodiment of the present invention; Figure 2 This is a schematic cross-sectional view of the overall structure of an embodiment of the present invention; Figure 3 This is a schematic diagram showing the disassembly of an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the sleeve of the present invention; Figure 5 This is a schematic diagram of the connecting bolt of the present invention; Figure 6 This is a schematic diagram of the end face structure of the bolt ball of the present invention; Figure 7 This is a schematic diagram of the structure of the rod of the present invention; Figure 8 This is a schematic diagram of the experimental device for displacement loading according to the present invention; Figure 9 This is a feature diagram of the entire deformation process of the TR-0 control group in this invention; Figure 10 This is a feature diagram of the entire deformation process of the TR-1 test group of this invention; Figure 11 This is a feature diagram of the entire deformation process of the TR-2 test group in this invention; Figure 12 This is a feature diagram of the entire deformation process of the TR-3 test group in this invention; Figure 13 This is a schematic diagram showing the damage at each test node in this invention; Figure 14 This is a schematic diagram showing the comparison and analysis of the force-displacement curves of the control group TR-0 and the experimental group TR-1 in this invention; Figure 15 This is a schematic diagram showing the comparison and analysis of the force-displacement curves of the control group TR-0 and the experimental group TR-2 in this invention; Figure 16 This is a schematic diagram showing the comparison and analysis of the force-displacement curves of the control group TR-0 and the experimental group TR-3 in this invention.

[0021] Figure descriptions: 101, Bolt ball; 102, Sleeve; 103, Pin; 104, Sealing plate; 105, Rod; 201, Connecting bolt. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar symbols denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0023] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0024] Example: A bolt-ball reinforced node for space frame after member instability based on arc-surface unloading bending moment. See Figures 1-7 This embodiment aims to address the risk of brittle fracture at joints due to member buckling in extreme conditions of a large stadium's steel space frame roof structure. By adopting a simple and low-cost reinforced joint, the ductility and fracture resistance of the joint are significantly improved without altering the existing design, production, and construction systems.

[0025] The bolt-ball reinforced joint specifically includes the following components: Bolt ball 101: Forged from 45# steel or higher strength steel, it is a hollow sphere. The surface of the sphere is drilled with multiple threaded holes according to the space frame design. In this embodiment, one of the threaded holes is used to connect with this node. The internal thread specification of the threaded hole matches the connecting bolt 201. Member 105: A circular steel pipe or other cross-sectional shape of space frame load-bearing member, whose ends are beveled for welding sealing plate 104; Sealing plate 104: It is a circular steel plate with a circular hole in the center. Sealing plate 104 is welded to the end of rod 105. The diameter of its central circular hole is slightly larger than the diameter of the thread of connecting bolt 201, but smaller than the diameter of the bolt head, and is used to accommodate and hold the bolt head. Connecting bolt 201: A high-strength bolt (e.g., grade 8.8 or 10.9), see [link / reference]. Figure 5 It includes a screw and a bolt head. The bolt head is confined inside the sealing plate 104. The screw passes through the center hole of the sealing plate 104 and the sleeve 102 in sequence, and is finally screwed into the corresponding screw hole of the bolt ball 101. The screw has a groove or through hole for installing the pin 103. Pin 103: It is a short cylindrical pin that passes through a small hole on the side wall of sleeve 102 and is inserted into a groove on the rod of connecting bolt 201. Its function is to prevent the connecting bolt 201 from loosening due to relative rotation during installation or under stress. Sleeve 102: A hollow hexagonal prism (hexagonal sleeve) made of high-strength steel, with a circular inner hole that fits with the threaded rod of connecting bolt 201 with clearance. Figure 4 As shown, the sleeve 102 has two end faces. The first end face is kept as a plane for contacting the outer surface of the sealing plate 104. The second end face is the improvement of the present invention. It is processed into an arc-shaped surface that convexes towards the bolt ball. Specifically, the surface is part of a sphere, and its radius of curvature R is determined by calculation. It is usually larger than the radius of the bolt ball to ensure that there is still a reasonable contact area in the initial state and under small deformation. As another equivalent implementation, the second end face of the sleeve 102 can also be processed into a conical chamfer or a large arc chamfer that smoothly transitions from the hexagonal edge to the center; During installation, the sleeve 102 is fitted onto the connecting bolt 201, with the flat surface of its first end face fitting against the sealing plate 104 and the arc-shaped surface of its second end face facing the outer spherical surface of the bolt ball 101. After tightening the bolt, the sleeve is pressed between the sealing plate 104 and the bolt ball 101.

[0026] The working principle of this invention is as follows: Under normal operating conditions, the sleeve 102 is pressed between the sealing plate 104 and the bolt ball 101 by the preload of the connecting bolt 201, and transmits axial force as reliably as a conventional node; When member 105 buckles and becomes unstable, rotation occurs at the node. At this time, the conventional flat sleeve will form a rigid compression with the spherical surface, which will generate a huge bending moment arm on the connecting bolt 201, causing stress concentration at the bolt root and rapid fracture. In this invention, the contact between the convex curved end of the sleeve 102 and the bolt ball 101 begins in a certain area (such as a line or a small surface). As the rotation angle increases, the contact area smoothly moves or changes along the convex curved surface. This process generates two core mechanical effects: ①Moment unloading: The line of action of the contact force can be closer to the axis of the connecting bolt 201, which significantly reduces the lever arm and thus directly reduces the harmful bending moment acting on the bolt; ② Stress redistribution: avoids extreme stress concentration at weak points such as the thread end of the connecting bolt 201 or the transition area of ​​the bolt head, and converts some deformation energy into local elastic-plastic deformation or frictional slip energy at the contact surface between the sleeve and the ball. Therefore, the combined stress state of tension (compression) + bending + shear borne by the connecting bolt 201 is greatly improved. The process of reaching the strength limit, initiating cracks and expanding fracture is effectively delayed. This buys valuable time for the redistribution of internal forces and energy dissipation of the structure under extreme loads (such as strong earthquakes), and improves the robustness and progressive collapse prevention of the entire space frame structure.

[0027] It should be noted that the sleeve end face shape that realizes the above-mentioned core idea of ​​"variable contact and reduced lever arm" is not limited to a spherical convex surface. As an equivalent technical solution of the present invention, the second end face of the sleeve 102 can also be other forms of convex surface, such as a part of an ellipsoid, or a convex surface of revolution formed by rotating a smooth curve around the sleeve axis. In addition, the end face can also be an inclined surface, such as a conical surface that is rotationally symmetrical about the sleeve axis, or a chamfered surface that is inclined from the edge of the end face to the center. These inclined surface designs can also make the contact area move from the edge to the center when the member buckles and the node rotates, thereby adjusting the line of action of the contact force and partially unloading the bending moment.

[0028] To verify the effectiveness of the invention, a comparative axial compression test was conducted. The test involved loading at one side of the bolt ball, with the load transferred to the member 105 via the bolt ball 101, achieving axial loading. During loading, a monotonic displacement was applied along the member's axis. The longest specimen length was 3600mm. The axial pressure was only converted into a bending moment and transferred to the bolt ball joint when the member buckled significantly. Therefore, this test required a device capable of large displacement loading. A custom-designed 50T double-acting hydraulic jack with a stroke of 2000mm and an electric hydraulic pump were used to achieve the required large displacement loading. To ensure axial compression of the specimen, a sliding trolley and a chute were installed on one side of the loading bolt ball 101. The bolt ball 101 was connected to the trolley, and the chute restricted the trolley's lateral and vertical displacement, allowing it to move only along the axis of the composite member. The model was installed as follows... Figure 8 As shown; To allow for adjustment of the height of the specimen on both sides to achieve a horizontal effect, an elongated hole was made on one side of the trolley to retain vertical adjustment space. During the test, the height of one side of the support was measured in advance, and then the height of the trolley was measured. After adjusting the bolt ball steel pipe assembly specimen to a horizontal position by adding or subtracting shims, the bolt ball joint was connected to the sliding trolley using high-strength bolts to achieve the purpose of axial loading. The test jack is connected to the jack support by high-strength bolts. The jack support is fixed to the ground by ground anchor bolts. The reaction force of the jack load is transmitted to the jack support through the bolts and then to the ground to ensure the normal loading and stability of the jack. To ensure that the trolley connected to the bolt ball can move only along the axis of the rod during the test, two chutes anchored to the ground are designed. The chutes are welded from steel. A slot is cut out on the chute surface adjacent to the trolley. A solid round steel with the same diameter as the slot is welded at the corresponding position of the trolley. During installation, the round steel on the trolley is inserted into the slots on both sides of the chutes to limit the vertical displacement of the trolley. Channel steel is welded to the outside of the chutes to reinforce them. A perforated steel plate is welded to the outside of the chutes to insert ground anchor bolts for fixing to the ground. At the same time, stiffening ribs are welded at both ends of the chutes to prevent excessive vertical deformation of the chutes during loading. During installation, first install one side of the slide rail. After inserting the round steel on one side of the trolley into the slot, align the other side of the round steel on the trolley and install the other side of the slide rail. After the two slide rails are tightly attached to the trolley, insert ground anchor bolts through the reserved holes on the outer welded steel plate of the slide rail and secure it to the laboratory floor. During the test, the left and right and up and down displacement of the slide rail trolley is restricted, and it can only move along the axial direction of the rod. To ensure that the trolley can move forward with the jack when the limit trolley is loaded without generating excessive resistance, four directional one-way wheels are installed under the trolley. The bolt ball is connected to the trolley with large-diameter high-strength bolts to achieve a fixed connection on the loading side. A support connected to the ground is designed, and the bolt ball support is connected to the support with high-strength bolts to achieve a fixed connection. Thus, the experimental device achieves a fixed connection on one side, and the loading side only retains the constraint of the degree of freedom along the axis of the member. This allows the constraints on both sides of the member to be provided by the bolt ball joint, so as to study the effect of member buckling on the force of the bolt ball joint.

[0029] To ensure experimental safety, the height of the loading device was kept low during design to prevent bolt breakage and potential ejection of the member, which could pose a danger. However, the buckling direction of the steel pipe member cannot be predicted beforehand. If the pipe buckles downwards, the test cannot proceed normally. Therefore, during specimen installation, a dial indicator is used to pinpoint the defect location and position the defect upwards so that if the member buckles, it will buckle upwards. The specific procedure is as follows: When installing the component, the ball joints of the bolts are not tightened initially, leaving a certain gap to allow the member to rotate freely. Then, the dial indicator... Place the specimen at the midpoint of the strut, perpendicular to the strut. After alignment, turn on the dial indicator and zero the reading. Then, slowly rotate the strut in one direction (clockwise or counterclockwise) and carefully observe the dial indicator reading. When the dial indicator reading rises, it indicates that the convex direction of the strut is approaching the dial indicator position. When the dial indicator reading falls, it indicates that the concave direction of the strut is approaching the dial indicator position. Record the position of the strut corresponding to the maximum dial indicator reading, which is the position where the convex direction of the strut is the greatest. Adjust this position to face directly above the ceiling, and then tighten the bolts on both sides of the component. At this point, the installation of the specimen and the control of the buckling direction are completed.

[0030] The test subjects were divided into four groups: one group used the node of the traditional flat end sleeve as the control group TR-0, and the other three groups used the node of the rounded chamfer end sleeve of this embodiment as the test groups TR-1, TR-2 and TR-3; like Figure 9 The image shown is a feature diagram of the entire deformation process of TR-0; like Figure 10 The image shown is a feature diagram of the entire deformation process of TR-1. like Figure 11 The image shown is a feature diagram of the entire deformation process of TR-2; like Figure 12 The image shown is a feature diagram of the entire deformation process of TR-3; The damage status of each test node is as follows: Figure 13 As shown; Comparative analysis of force-displacement curves of each group of tests is as follows: Figure 14 , Figure 15 , Figure 16 As shown; The test results show that during axial loading, all composite components failed due to the fracture of high-strength bolts at the joints. Furthermore, the bolt-ball-steel-pipe composite components instantly lost their load-bearing capacity after joint failure, exhibiting brittle failure characteristics. This indicates that the integrity of the bolt-ball joints is a key factor affecting the load-bearing capacity of bolt-ball-steel-pipe composite components under large displacement axial loading. Greater sleeve stiffness results in smaller failure displacements under large displacement axial loading, making joint failure more likely. Conversely, reduced sleeve stiffness at the joints delays joint failure under large displacement axial loading.

[0031] In summary, this invention achieves a significant improvement in the fracture resistance of nodes under extreme conditions by optimizing only the local geometry of one end face of the sleeve, without changing any other standard components such as bolt balls, connecting bolts, sealing plates, and rods, based on the reverse mechanism discovered in the above experiments, at extremely low modification costs. It is easy to promote and apply in new construction and reinforcement projects.

[0032] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A bolt-ball reinforcement node for a space frame after member instability, comprising a bolt ball, a sealing plate connected to the end of the member, a connecting bolt, and a sleeve sleeved on the connecting bolt and located between the sealing plate and the bolt ball, characterized in that, The end face of the sleeve facing the bolt ball is configured to form a non-fixed contact with the surface of the bolt ball when the member buckles, causing the node to rotate, thereby reducing the bending moment acting on the connecting bolt.

2. The bolt-ball reinforced joint for space frame after member instability as described in claim 1, characterized in that, The end face of the sleeve facing the bolt ball has a non-planar structure.

3. The bolt-ball reinforced joint for space frame after member instability as described in claim 2, characterized in that, The non-planar structure is a convex curved surface.

4. The bolt-ball reinforced joint for space frame after member instability as described in claim 3, characterized in that, The convex surface is a part of a sphere, a part of an ellipsoid, or another convex surface formed by rotating a smooth curve about the axis of the sleeve.

5. The bolt-ball reinforced joint for space frame after member instability according to claim 2, characterized in that, The non-planar structure is an inclined surface.

6. The bolt-ball reinforced joint for space frame after member instability as described in claim 5, characterized in that, The inclined surface is either a conical surface that is rotationally symmetrical about the axis of the sleeve, or a chamfered surface formed by the edge of the end face tilting towards the center.

7. The bolt-ball reinforced joint for space frame after member instability as described in claim 1, characterized in that, The outer contour of the cross-section of the sleeve is polygonal or circular.

8. The bolt-ball reinforced joint for space frame after member instability according to claim 1, characterized in that, The end face of the sleeve away from the bolt ball is a flat surface, which is used to contact the sealing plate.

9. The bolt-ball reinforced joint for space frame after member instability according to claim 1, characterized in that, It also includes a locking component that passes through the side wall of the sleeve and engages with the shaft of the connecting bolt to prevent relative rotation between the two.

10. The bolt-ball reinforced joint for space frame after member instability according to claim 1, characterized in that, The sleeve is made of metal.

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