Vertical connection node of round bamboo and construction method thereof

Abstract

The application discloses a vertical connecting node of round bamboo and a construction method thereof and belongs to the technical field of connecting technologies of fabricated bamboo structures. The vertical connecting node of round bamboo comprises a bamboo cylinder, a first horizontal through hole, a through rod assembly, a vertical composite shear core, a hoop self-tightening band and a buckling half-steel ring. The vertical composite shear core is arranged in the bamboo cylinder and comprises a steel sleeve, a resin wrapping layer outside the steel sleeve and a filled resin filling layer. The vertical composite shear core is provided with a second horizontal through hole. The hoop self-tightening band is arranged outside the bamboo cylinder and comprises a shape memory alloy. The buckling half-steel ring is arranged outside the bamboo cylinder, and the through rod assembly penetrates through the buckling half-steel ring. After the hoop self-tightening band is activated, hoop pre-pressure is generated, cooperates with an FRP outer constraint layer and forms a hoop self-tightening constraint system to inhibit hole splitting and local buckling. The vertical composite shear core provides the required shear resistance and slip resistance of the node, reduces stress concentration, avoids the fracture of the end of the bamboo cylinder and realizes overall sealing, corrosion resistance and durability.

Description

Technical Field

[0001] This invention relates to the field of prefabricated bamboo structure connection technology, specifically to a vertical connection node for round bamboo and its construction method. Background Technology

[0002] Bamboo boasts advantages such as easy propagation, rapid growth, short maturation period, and high yield, making it an energy-saving and environmentally friendly renewable material. China is extremely rich in bamboo resources, ranking first in the world in both bamboo forest area and stock volume. In recent years, under the major trend of green, energy-saving, and environmentally friendly practices, the government has successively issued documents to encourage the application of wood-bamboo structure buildings, indicating that bamboo structures have broad development prospects.

[0003] Traditional bamboo structural joints commonly use steel sleeves and high-strength bolts for clamping and hole grouting. Firstly, because bamboo has limited resistance to splitting, perforation and sudden changes in stiffness can easily induce end splitting, and the connection performance deteriorates over time. Secondly, the large number of exposed steel sleeves and steel connectors in traditional joints are prone to corrosion and rust expansion in humid, hot and salt spray environments, leading to reduced load-bearing capacity and stiffness, and exacerbated hole cracking. Furthermore, they are highly dependent on protective coatings, have high maintenance costs, and their durability is difficult to guarantee in the long term. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems in the prior art and provide a vertical connection node for round bamboo and its construction method.

[0005] This invention provides a vertical connection node for round bamboo, including a connection assembly for connecting vertically positioned bamboo poles, comprising: a bamboo tube, vertically positioned; a first connector, configured as a vertical composite shear-resistant core placed inside the bamboo tube, including a steel sleeve, a resin-coated layer on the outside of the steel sleeve, and a resin-filled layer, wherein an FRP outer constraint layer is wound around the outside of the resin-coated layer; a second connector, including interlocking semi-steel rings, several circumferential self-tightening bands, and several FRP outer constraint layers, wherein the several circumferential self-tightening bands are all wrapped around the outside of the bamboo tube and are made of shape memory alloy, the several FRP outer constraint layers are sleeved on the outside of the bamboo tube, the interlocking semi-steel rings are sleeved on the outside of the bamboo tube, and both the interlocking semi-steel rings and the bamboo tube have first horizontal through holes, and the vertical composite shear-resistant core has a second horizontal through hole; the circumferential self-tightening bands generate circumferential preload after activation, working in conjunction with the FRP outer constraint layers to form a circumferential self-tightening constraint system; and a through-bar assembly, which sequentially passes through the first horizontal through hole and the second horizontal through hole.

[0006] Preferably, the outer surface of the steel sleeve is provided with an electrically insulating transition layer, which is disposed between the steel sleeve and the resin coating layer.

[0007] Preferably, the electrically insulating transition layer is a glass fiber reinforced polymer thin layer or a polyimide film.

[0008] Preferably, the FRP outer constraint layer is woven with 40° to 45° zoned fiber angles, and the bamboo tube is wound with the FRP outer constraint layer in a 90° sequence.

[0009] Preferably, it also includes a viscoelastic interface layer with a thickness of 0.2mm to 0.5mm, disposed between the inner wall of the bamboo tube and the vertical composite shear-resistant core, wherein the viscoelastic interface layer is made of elastomer-modified epoxy or polyurethane material.

[0010] Preferably, the circumferential self-tightening band is a nickel-titanium alloy closed ring, activated by resistance heating or induction heating.

[0011] Preferably, the interlocking semi-steel ring is composed of two stainless steel semi-rings, with an elastic buffer layer on the inner side, the elastic buffer layer being made of polyurethane or rubber material.

[0012] Preferably, the through-bar assembly includes a screw, a nut, and a washer, wherein the screw passes through the first horizontal through-hole and the second horizontal through-hole in sequence, and the nut and the washer are sleeved on the screw.

[0013] A preferred method for constructing a vertical connection node for round bamboo includes the following steps: The first horizontal through hole is processed on the side wall of the bamboo tube, and the hole diameter is adapted to the second horizontal through hole of the through rod assembly and the vertical composite shear core; the resin coating layer is wrapped around the outside of the steel sleeve, and resin is injected to form the resin filling layer, which constitutes the vertical composite shear core; the vertical composite shear core is vertically inserted into the bamboo tube. The FRP constraint layer is wound around the resin coating layer and the bamboo tube respectively; the circumferential self-tightening band is wrapped around the outside of the FRP constraint layer; the two interlocking semi-steel rings are aligned along the axial direction of the bamboo tube and attached to the outer wall of the bamboo tube; the screw is passed through the first horizontal through hole and the second horizontal through hole in sequence for temporary fixation; the shape memory effect of the circumferential self-tightening band is triggered by resistance heating to generate circumferential preload.

[0014] Compared with the prior art, the beneficial effects of the present invention are: The circumferential self-tightening band, made of shape memory alloy, surrounds the outside of the bamboo tube. Upon activation, it generates contraction force, applying circumferential preload. This preload is quantifiable and long-term maintained, effectively preventing loosening of connections caused by preload decay in traditional bamboo structures. Simultaneously, the circumferential self-tightening band works in conjunction with the FRP constraint layer to form a circumferential self-tightening constraint system, providing more uniform constraint stress and suppressing orifice splitting and local buckling. Interlocking semi-steel rings are fitted onto the outside of the bamboo tube and penetrated by through-bar components, further strengthening the circumferential constraint and ensuring the stability of the joint under vertical loads. The vertical composite shear-resistant core undertakes the main shear and anti-slip functions. Through the rigid support of the steel sleeve and the flexible filling of the resin layer, it achieves efficient shear force dispersion, reduces stress concentration, prevents breakage at the bamboo tube ends, and possesses excellent sealing, corrosion resistance, and durability. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall three-dimensional structure of the present invention.

[0016] Figure 2 This is a schematic diagram of the internal structure of the bamboo tube according to the present invention.

[0017] Figure 3 This is a schematic diagram of the vertical composite shear-resistant core structure of the present invention.

[0018] Figure 4 This is a schematic diagram of the mating structure of the interlocking half steel ring and the through-bar tie rod assembly of the present invention.

[0020] Explanation of reference numerals in the attached drawings: 1. Bamboo tube; 2. FRP outer restraint layer; 3. Circumferential self-tightening band; 4. Interlocking half steel ring; 5. Through-through tie rod assembly; 6. Resin wrapping layer; 7. Resin filling layer; 8. Steel sleeve. Detailed Implementation

[0021] The following is in conjunction with the appendix Figures 1-4 To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art.

[0022] The terms "first," "second," and similar terms used in this invention and its claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the term encompasses the elements or objects listed after the term and their equivalents, without excluding other elements or objects. Terms such as "inner," "outer," "upper," "lower," "far," "near," "front," and "rear" are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. The drawings in this invention are not strictly drawn to scale; the specific dimensions and quantity of each structure can be determined according to actual needs. The drawings described in this invention are merely structural schematic diagrams.

[0023] This invention provides a vertical connection node for round bamboo, such as... Figures 1-3 The diagram shows a connecting assembly for connecting vertically positioned bamboo poles, including a bamboo tube 1, which is vertically positioned; a first connector, configured as a vertical composite shear-resistant core placed inside the bamboo tube 1, including a steel sleeve 8, a resin-coated layer 6 on the outside of the steel sleeve 8, and a resin-filled layer 7, with an FRP outer constraint layer 2 wrapped around the outside of the resin-coated layer 6; a second connector, including interlocking semi-steel rings 4, several circumferential self-tightening bands 3, and several FRP outer constraint layers 2, with the several circumferential self-tightening bands 3 all surrounding the outside of the bamboo tube 1 and made of shape memory alloy, the several FRP outer constraint layers 2 fitted on the outside of the bamboo tube 1, the interlocking semi-steel rings 4 fitted on the outside of the bamboo tube 1, and a first horizontal through-hole on both the interlocking semi-steel rings 4 and the bamboo tube, and a second horizontal through-hole on the vertical composite shear-resistant core; the circumferential self-tightening bands 3 generate circumferential pre-pressure after activation, working in conjunction with the FRP outer constraint layers 2 to form a circumferential self-tightening constraint system; and a through-bar assembly 5, which sequentially passes through the first and second horizontal through-holes.

[0024] In this embodiment, the circumferential pre-pressure generated after the activation of the circumferential self-tightening band 3 works synergistically with the resin-coated layer 6 constraint layer of the vertical composite anti-shear core to form an adaptive circumferential self-tightening constraint system. The bamboo tube 1 is provided with a first horizontal through hole through which the through-through tie rod assembly 5 passes to achieve basic fixation of the node. The vertical composite anti-shear core is placed inside the bamboo tube 1, and its steel sleeve 8 provides core support. The resin-coated layer 6 and the resin-filled layer 7 jointly enhance the shear resistance and buffering performance. The anti-shear core is provided with a second horizontal through hole to ensure the smooth passage of the through-through tie rod assembly 5.

[0025] The circumferential self-tightening band 3, made of shape memory alloy, surrounds the outside of the bamboo tube 1. Upon activation, it generates contraction force, applying circumferential preload. This preload is quantifiable and long-term maintained, effectively preventing loosening of connections caused by preload decay in traditional bamboo structures. Simultaneously, the circumferential self-tightening band 3 works in conjunction with the FRP constraint layer 2 to form a circumferential self-tightening constraint system, providing more uniform constraint stress and suppressing orifice splitting and local buckling. The interlocking semi-steel rings 4 are fitted onto the outside of the bamboo tube 1 and are penetrated by the through-bar assembly 5, further strengthening the circumferential constraint and ensuring the stability of the joint under vertical loads. The vertical composite shear core undertakes the main shear force transmission function. Through the rigid support of the steel sleeve 8 and the flexible filling of the resin layer, it achieves efficient shear force dispersion, reduces stress concentration, and prevents breakage at the end of the bamboo tube 1.

[0026] Preferred, such as Figures 1-3 As shown, the outer surface of the steel sleeve 8 is provided with an electrically insulating transition layer, which is disposed between the steel sleeve 8 and the resin coating layer 6. The electrically insulating transition layer is a glass fiber reinforced polymer thin layer or a polyimide film.

[0027] In this embodiment, the electrically insulating transition layer prevents electrochemical corrosion between the steel sleeve 8 and the resin layer due to potential difference, prolongs the node life, avoids galvanic corrosion in humid environments, and thus maintains the integrity of the resin coating layer 6. On the other hand, it also enhances the bonding strength between the steel sleeve 8 and the resin layer, reduces internal stress caused by the difference in the thermal expansion coefficient of the materials by providing a uniform transition interface, and improves the stability of the node under temperature changes.

[0028] Glass fiber reinforced polymer films have high strength and corrosion resistance, effectively bearing mechanical stress while maintaining insulation properties; polyimide films are known for their excellent high temperature resistance and dielectric properties, making them suitable for extreme temperature environments.

[0029] Preferred, such as Figures 1-3 As shown, the FRP outer constraint layer 2 is woven with 40° to 45° partitioned fiber angles, and the bamboo tube 1 is wound with the FRP outer constraint layer 2 in a 90° sequence.

[0030] In this embodiment, the FRP outer constraint layer 2 provides primary circumferential constraint for the bamboo tube 1 and is used to uniformly distribute and transmit the circumferential preload generated after the SMA circumferential self-tightening band 3 is activated. Specifically, the 40°–45° layup is beneficial for bearing and dispersing in-plane shear forces, enhancing the shear resistance of the nodes; the 90° layup provides the main circumferential constraint, improving the resistance to swelling and buckling at the opening of the bamboo tube 1 and in local areas. By using a combination of different layup angles for winding, the transmission path and distribution uniformity of the constraint force can be improved, reducing local stress concentration.

[0031] Preferred, such as Figures 1-3As shown, it also includes a viscoelastic interface layer with a thickness of 0.2mm to 0.5mm, which is disposed between the inner wall of the bamboo tube 1 and the vertical composite shear core. The viscoelastic interface layer is made of elastomer-modified epoxy or polyurethane material.

[0032] In this embodiment, the viscoelastic interface layer acts as a buffer and sealant, effectively filling the gap between the bamboo tube 1 and the vertical composite shear core, preventing moisture intrusion and fretting wear; the elastic properties of the viscoelastic interface layer allow the nodes to absorb energy when they undergo minor deformation under load, reducing impact stress, while improving the adhesion between the bamboo tube 1 and the vertical composite shear core.

[0033] Preferred, such as Figures 1-3 As shown, the circumferential self-tightening band 3 is a nickel-titanium alloy closed ring, which is activated by resistance heating or induction heating.

[0034] In this embodiment, the nickel-titanium shape memory alloy possesses superelastic phase transformation properties, which, upon activation, generate controllable and reversible pre-stress, achieving precise quantification of the circumferential self-tightening function. Resistance heating or induction heating makes the activation process convenient and efficient, suitable for on-site construction; after heating, the alloy shrinks, applying circumferential compressive stress, and this pre-stress can be maintained for a long time and is easily reset.

[0035] Preferred, such as Figures 1-3 As shown, the snap-fit ​​semi-steel ring 4 is composed of two stainless steel semi-rings, with an elastic buffer layer on the inner side, which is made of polyurethane or rubber material.

[0036] In this embodiment, the elastic buffer layer protects the surface of the bamboo tube 1, preventing direct contact with the steel ring that could cause damage or stress concentration in the bamboo. Polyurethane or rubber materials possess high elasticity and wear resistance, absorbing vibration energy and reducing noise and wear at the joints under dynamic loads.

[0037] Preferred, such as Figures 3-4 As shown, the through-rod assembly 5 includes a screw, a nut, and a washer. The screw passes through the first horizontal through hole and the second horizontal through hole in sequence, and the nut and washer are sleeved on the screw.

[0038] In this embodiment, the screw provides axial tension, while the nut and washer ensure that the tightening force is adjustable and uniform, enabling rapid assembly of the nodes. The washer disperses the contact pressure, preventing local damage to the bamboo tube 1. The tightening of the nut allows for precise control of the preload, forming a dual constraint system in conjunction with the circumferential self-tightening band 3.

[0039] The method of using a vertical connection node for round bamboo according to the present invention is as follows: The vertical composite anti-shear core is inserted into the bamboo tube 1, ensuring a pre-existing gap between the inner wall of the bamboo tube 1 and the anti-shear core. Then, the FRP constraint layer 2 is wound around the outside of the bamboo tube in a sequence of inner layer ±45° and outer layer 90°, with the circumferential self-tightening band 3 wrapped around the outside of the FRP constraint layer 2. Next, the screw of the through-bar assembly 5 is sequentially passed through the first horizontal through-hole of the bamboo tube 1 and the second horizontal through-hole of the anti-shear core. The snap-fit ​​semi-steel ring 4 is fitted onto the outside of the bamboo tube 1, allowing the screw to pass through. An elastic buffer layer protects the surface of the bamboo tube 1, and washers and nuts are installed at both ends of the screw, initially tightened to fix the node. Then, the circumferential self-tightening band 3 is activated, working in conjunction with the FRP outer constraint layer to form a self-tightening constraint system. Finally, a torque wrench is used to tighten the nuts twice to complete the node installation and assembly.

[0040] When activating the circumferential self-tightening band 3, a special heating device is used to uniformly heat the nickel-titanium alloy band, and the temperature is controlled above the phase change point to ensure accurate quantification of preload. At the same time, the nuts of the through-rod assembly 5 should be tightened in stages, and a torque wrench is used to control the axial preload to avoid over-tightening that could cause the bamboo tube 1 to split. After installation, load tests are conducted to verify the shear force transfer function and circumferential constraint effect of the nodes. For example, deformation behavior is observed through vertical loading tests to ensure that the circumferential self-tightening system can adapt to the expansion and contraction of bamboo and maintain a tight state in the long term.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A vertical connection node for round bamboo, characterized in that, Includes a connecting assembly for connecting vertically positioned bamboo poles, comprising: Bamboo tubes, set vertically; The first connector, configured as a vertical composite shear-resistant core placed inside the bamboo tube, includes a steel sleeve, a resin wrapping layer on the outside of the steel sleeve, and a resin filling layer. An FRP outer constraint layer is wrapped around the outside of the resin wrapping layer. The second connector includes interlocking semi-steel rings, several circumferential self-tightening bands, and several FRP outer constraint layers. The several circumferential self-tightening bands are all wrapped around the outside of the bamboo tube and are made of shape memory alloy. The several FRP outer constraint layers are sleeved on the outside of the bamboo tube, and the interlocking semi-steel rings are sleeved on the outside of the bamboo tube. The interlocking semi-steel rings and the bamboo tube are both provided with first horizontal through holes, and the vertical composite shear core is provided with second horizontal through holes. When the circumferential self-tightening bands are activated, they generate circumferential preload and work together with the FRP outer constraint layers to form a circumferential self-tightening constraint system. The through-rod assembly passes through the first horizontal through-hole and the second horizontal through-hole in sequence.

2. The vertical connection node for round bamboo as described in claim 1, characterized in that, The outer surface of the steel sleeve is provided with an electrically insulating transition layer, which is disposed between the steel sleeve and the resin coating layer.

3. A vertical connection node for round bamboo as described in claim 2, characterized in that, The electrically insulating transition layer is a glass fiber reinforced polymer thin layer or a polyimide film.

4. A vertical connection node for round bamboo as described in claim 1, characterized in that, The FRP outer constraint layer is woven with 40° to 45° zoned fiber angles, and the bamboo tube is wound with the FRP outer constraint layer in a 90° sequence.

5. A vertical connection node for round bamboo as described in claim 1, characterized in that, It also includes a viscoelastic interface layer with a thickness of 0.2mm to 0.5mm, which is disposed between the inner wall of the bamboo tube and the vertical composite shear-resistant core. The viscoelastic interface layer is made of elastomer-modified epoxy or polyurethane material.

6. A vertical connection node for round bamboo as described in claim 1, characterized in that, The circumferential self-tightening band is a nickel-titanium alloy closed ring, which is activated by resistance heating or induction heating.

7. A vertical connection node for round bamboo as described in claim 1, characterized in that, The interlocking semi-steel ring is composed of two stainless steel semi-rings, with an elastic buffer layer on the inner side, which is made of polyurethane or rubber.

8. A vertical connection node for round bamboo as described in claim 1, characterized in that, The through-hole assembly includes a screw, a nut, and a washer. The screw passes through the first horizontal through-hole and the second horizontal through-hole in sequence, and the nut and the washer are sleeved on the screw.

9. A construction method for a vertical connection node of round bamboo according to any one of claims 1 to 8, characterized in that, Includes the following steps: The first horizontal through hole is processed on the side wall of the bamboo tube, and the hole diameter is adapted to the second horizontal through hole of the through rod assembly and the vertical composite shear core; the resin coating layer is wrapped around the outside of the steel sleeve, resin is injected to form the resin filling layer, and the upper and lower ends are sealed with structural adhesive to form the vertical composite shear core; the vertical composite shear core is vertically inserted into the bamboo tube. The FRP constraint layer is wound around the resin coating layer and the bamboo tube respectively; the circumferential self-tightening band is wrapped around the outside of the FRP constraint layer; the two interlocking semi-steel rings are aligned along the axial direction of the bamboo tube and attached to the outer wall of the bamboo tube; the screw is passed through the first horizontal through hole and the second horizontal through hole in sequence for temporary fixation; the shape memory effect of the circumferential self-tightening band is triggered by resistance heating to generate circumferential preload.

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