A steel-recombined bamboo composite truss and a calculation method for its node bearing capacity

Abstract

The present invention relates to a steel-reorganized bamboo composite truss, the composite truss comprises a steel chord, a reorganized bamboo web and a vertical connector, the reorganized bamboo web comprises a vertical web and an oblique web; the vertical connector is arranged on the steel chord, the vertical connector and the reorganized bamboo web are preset with bolt holes, the vertical connector is connected to the reorganized bamboo web by bolts, and the angle between the vertical web and the oblique web is 30° to 60°. On the other hand, the present invention also proposes a method for calculating the node bearing capacity of the above-mentioned steel-reorganized bamboo composite truss. The steel-reorganized bamboo composite truss makes full use of the characteristics of reliable and convenient steel connection and excellent mechanical properties of reorganized bamboo in the direction of grain, which not only ensures that the truss is reasonably and efficiently stressed, but also effectively reduces the carbon emissions of the truss structure. The node bearing capacity calculation method proposed in the present invention has laid a theoretical foundation for its promotion and application in practical engineering applications, and has higher feasibility.

Description

Technical Field

[0001] The invention relates to the technical field of building structures, and in particular to a steel-recombined bamboo combined truss structure. Background Art

[0002] Truss structure members are generally straight or curved to suit the building form. They are highly adaptable to the building form and are widely used in large-span structures. Truss structures are generally composed of chords and webs, with clear force transmission, simple and efficient force bearing. The web only bears axial force (tension or compression), while the chord is mainly axial force and only bears small bending moment. Steel is the most commonly used material for truss structures because of its good performance, reliable and convenient connection.

[0003] As one of the main areas of energy consumption and carbon emissions in my country, the construction sector should transform towards a low-carbon and green direction as soon as possible under the background of "dual carbon". The carbon emissions of steel structures in the physical, use and consumption stages are relatively high, second only to concrete structures. They are non-renewable materials and do not have a carbon fixation effect. Bamboo structures are negative carbon building materials, and my country is rich in bamboo resources. The bamboo forest area, bamboo production and bamboo species are all among the best in the world. The application prospects of domestic bamboo structures are broader. The recombinant bamboo, which was first industrialized by Chinese enterprises, is a green and high-strength bamboo-based composite material processed from original bamboo as the base material. It has the advantages of low carbon and environmental protection, excellent and stable physical and mechanical properties, high strength, good toughness, strong weather resistance, excellent flame retardancy, etc. It has excellent tensile and compressive properties in the direction of the grain, which can reach more than 100MPa.

[0004] However, due to processing and transportation conditions, the length of reconstructed bamboo rods is limited. If a large-span truss structure is made entirely of reconstructed bamboo, the webs are generally shorter and do not need to be spliced, but since the chords are longer, they need to be spliced ​​on site. On the one hand, the splicing nodes affect the architectural effect, and on the other hand, according to existing research data, the on-site splicing nodes of reconstructed bamboo cannot achieve a completely rigid connection, which will reduce the bearing capacity of the truss and even affect the structural safety. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a steel-recombined bamboo composite truss and a method for calculating the bearing capacity of its nodes. The present invention is achieved through the following technical solutions:

[0006] A steel-reorganized bamboo combined truss, the combined truss comprises a steel chord, a reorganized bamboo web and a vertical connector, the reorganized bamboo web comprises a vertical web and a diagonal web; the vertical connector is arranged on the steel chord, the vertical connector and the reorganized bamboo web are preset with bolt holes, the vertical connector is connected to the reorganized bamboo web by bolts, and the angle between the vertical web and the diagonal web is 30° to 60°.

[0007] Furthermore, when the cross-section of the end of the reorganized bamboo web is circular, the vertical connector is a steel filling plate or a circular steel sleeve; when the cross-section of the end of the reorganized bamboo web is rectangular, the vertical connector is a steel filling plate, a steel clamping plate or a rectangular steel sleeve.

[0008] Furthermore, the steel filler plate is inserted into the pre-grooved end of the reconstructed bamboo web bar.

[0009] Furthermore, the steel filling plates inserted into the vertical web members and the diagonal web members are integrated as a whole.

[0010] Furthermore, the thickness of the steel filler plate is not less than 10 mm and not less than 0.8 times the bolt diameter, and the height-to-thickness ratio of the steel filler plate is not greater than 40ε k , where ε k is the steel grade correction coefficient, and its value is the square root of the ratio of 235 to the yield point value in the steel grade. The angle between the vertical web member and the diagonal web member is 30° to 45°.

[0011] Furthermore, the steel clamping plate includes a first plate and a second plate, and the first plate and the second plate are respectively arranged on both sides of the end of the reconstructed bamboo web rod.

[0012] Furthermore, the first plate or the second plate arranged on both sides of the vertical web member and the diagonal web member is an integral whole.

[0013] Furthermore, the thickness of the steel clamp is not less than 8 mm and not less than 0.7 times the bolt diameter, and the height-to-thickness ratio of the steel clamp is not greater than 80ε k , where ε k It is the steel grade correction factor, and its value is the square root of the ratio of 235 to the yield point value in the steel grade.

[0014] Furthermore, the circular steel sleeve or the rectangular steel sleeve is sleeved on the outer side of the end of the reconstructed bamboo web bar, the wall thickness of the steel sleeve is not less than 8 mm, and the angle between the vertical web bar and the oblique web bar is 45° to 60°.

[0015] Furthermore, a steel sealing plate is provided between the first plate and the second plate, and the steel sealing plate seals the gap between the first plate and the second plate.

[0016] Furthermore, the diameter d of the bolt is not less than 12 mm, the diameter of the circular end of the reconstructed bamboo web rod or the side length D of the rectangular end is not less than 90 mm, and the thickness-to-diameter ratio D / d is 4-15.

[0017] Furthermore, the bolt end distance is not less than 6d, the column distance is not less than 4d, the edge distance is not less than 3d and the row distance is not less than 2d.

[0018] Furthermore, when the reconstructed bamboo web is a circular web with a rectangular end section, the bolt end distance is not less than 7d.

[0019] On the other hand, the present invention also proposes a method for calculating the node bearing capacity of the above-mentioned steel-recombined bamboo composite truss, the method comprising at least the following steps:

[0020] a) Obtain the thickness t of the edge member of the steel-reconstructed bamboo node s ;

[0021] b) obtaining the screw diameter d of the bolt;

[0022] c) The minimum effective length coefficient k of the pin groove of the reorganized bamboo bolt connection node under pressure is obtained according to the following formula min ,

[0023]

[0024] where k Ⅰ , k Ⅲ , k Ⅳ The pin slot pressure-bearing effective length coefficients corresponding to the pin slot pressure failure, the bolt single plastic hinge failure, and the bolt double plastic hinge failure shall be determined according to the provisions of the Timber Structure Design Standard;

[0025] is the correction coefficient of the effective length coefficient of the pin groove pressure corresponding to the pin groove pressure failure, the single plastic hinge failure of the bolt, and the two plastic hinge failures of the bolt. For the vertical connector being a steel-filled plate node: when t s / d≤4,

[0026] When t s / d≥4, For the vertical connectors that are steel plates or steel sleeve nodes: when t s / d≤4, When 7 ≥ t s / d≥4, t s / d≥7,

[0027] d) Obtain the compressive strength standard f of the edge components of the steel-reconstructed bamboo node es , among which, the compressive strength of the reconstructed bamboo pin along the grain is f e,0 Determined according to the following formula, where ρ k The air-dry density of reconstituted bamboo is

[0028] f e,0 =0.082(1-0.01d)ρ k ;

[0029] e) Obtain the reference design value of bearing capacity Z(N) according to the following formula:

[0030] Z=kmin t s df es ;

[0031] f) Obtain the design value of the bearing capacity Z of a single shear surface of the bolt according to the following formula: d (N),

[0032] Z d =C m C n C t k g Z

[0033] Among them, C m is the moisture content adjustment coefficient: the reconstructed bamboo component takes a value of 1.0;

[0034] C n The adjustment coefficient for the design service life is: 1.1 for 5 years; 1.05 for 25 years; 1.0 for 50 years;

[0035] C t Temperature adjustment coefficient: in long-term production high temperature environment, when the surface temperature of reconstructed bamboo reaches 40-50℃, the value is 0.8;

[0036] In other cases, the value is 1.0;

[0037] k g It is the group bolt combination coefficient and is determined according to the provisions of the Timber Structure Design Standard.

[0038] The steel-reorganized bamboo composite truss of the present invention comprises a chord, a web and a vertical connector, wherein the chord and the vertical connector are made of steel, and the web is reorganized bamboo. The vertical connector is arranged on the steel chord, and the vertical connector and the reorganized bamboo web are preset with bolt holes and connected by bolts, providing a variety of steel-reorganized bamboo node connection forms. The steel-reorganized bamboo composite truss makes full use of the characteristics of reliable and convenient steel connection and excellent mechanical properties of reorganized bamboo along the grain direction, which not only ensures that the truss is reasonably and efficiently stressed, but also effectively reduces the carbon emissions of the truss structure, promotes the transformation of the construction field to a low-carbon and green direction, and can solve the problem of safety hazards in the splicing of the chord of the large-span reorganized bamboo truss, and can comprehensively select the node connection form in terms of beautiful appearance, convenient construction, safety and reliability. While proposing the steel-reorganized bamboo composite truss, in order to facilitate its engineering application, the present invention also proposes a node bearing capacity calculation method of the steel-reorganized bamboo composite truss, which lays a theoretical foundation for its promotion and application in actual engineering applications, and has higher feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1a It is a schematic diagram of a curved truss involved in the present invention.

[0041] Figure 1b It is a schematic diagram of a straight truss involved in the present invention.

[0042] Figure 2 The invention is a schematic diagram of a reconstructed bamboo belly pole.

[0043] Figure 3 The invention is a schematic diagram of connecting a steel chord rod and a reconstructed bamboo web rod with a circular cross section by using a steel filling plate and bolts.

[0044] Figure 4 The invention is a schematic diagram of connecting a steel chord rod and a reconstructed bamboo web rod with a circular cross section by using a circular steel sleeve and bolts.

[0045] Figure 5 The invention is a schematic diagram of connecting a steel chord rod and a rectangular cross-section reorganized bamboo web rod by using steel filling plates and bolts.

[0046] Figure 6 The invention is a schematic diagram of connecting a steel chord rod and a rectangular cross-section reorganized bamboo web rod by using steel clamping plates and bolts.

[0047] Figure 7 The invention is a schematic diagram of connecting a steel chord rod and a rectangular cross-section reconstructed bamboo web rod by using a rectangular steel sleeve and bolts.

[0048] Figure 8 It is a partial structural layout diagram of the steel-recombined bamboo composite truss according to an embodiment of the present invention.

[0049] Figure 9a It is a node structure diagram when a steel clamp plate and bolts are used for connection in an embodiment of the present invention.

[0050] Figure 9b yes Figure 9a BB cross-section diagram.

[0051] Fig.9c yes Figure 9a AA cross-section diagram.

[0052] Fig.10a It is a schematic diagram of the pin groove pressure bearing thickness ts of the reconstituted bamboo-steel plywood connection node of the present invention.

[0053] Fig.10b It is a schematic diagram of the pin groove pressure bearing thickness ts of the reconstituted bamboo-steel filler plate connection node of the present invention.

[0054] Fig.11 It is a schematic diagram of bolt arrangement involved in the present invention.

[0055] In the figure: 1-steel chord; 2-recombined bamboo web; 2a-vertical web; 2b-diagonal web; 3-vertical connector; 4-bolt; 5-steel filler plate; 6-circular steel sleeve; 7-steel splint; 8-rectangular steel sleeve; 9-first plate; 10-second plate; 11-steel sealing plate. DETAILED DESCRIPTION

[0056] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. In the absence of conflict, the following embodiments and the features in the embodiments can be combined with each other; it is understandable to those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0057] The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be noted that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate directions or positional relationships, they are based on the directions or positional relationships shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0058] The specific implementation modes of the present invention are described in detail below with reference to the embodiments.

[0059] like Figure 1a , Figure 1bAs shown, the steel-reorganized bamboo composite truss of the present invention can be a straight or curved truss structure according to the building form. The composite truss includes a steel chord 1, a reorganized bamboo web 2 and a vertical connector 3. The steel chord can be a round tube or a rectangular tube. The steel chord preferably has a strength grade of Q355B or above, and the reorganized bamboo web preferably has a strength grade of Ep14 or above. The vertical connector 3 is welded on the steel chord 1, and the weld grade is not less than level 2. Bolt holes are reserved for the vertical connector and the reorganized bamboo web in the factory, and the vertical connector is connected to the reorganized bamboo web by bolts 4 on site, thereby realizing the hinged connection between the reorganized bamboo web and the steel chord. The reorganized bamboo web 2 includes a vertical web 2a and an oblique web 2b, and the angle between the vertical web 2a and the oblique web 2b is 30° to 60°.

[0060] like Figure 2 As shown, the reorganized bamboo web member 2 can be a round rod or a rectangular cross-section member, or a combined cross-section member with a round middle cross-section and a rectangular end cross-section. When the cross-section of the end of the reorganized bamboo web member 2 is round, the vertical connector 3 can be a steel filler plate 5 or a round steel sleeve 6; when the cross-section of the end of the reorganized bamboo web member 2 is rectangular, the vertical connector 3 can be a steel filler plate 5, a steel clamping plate 7 or a rectangular steel sleeve 8.

[0061] like Figure 3 and 5 As shown, when the steel filler plate is used as a vertical connector, the steel filler plate 5 is inserted into the end of the pre-grooved reconstructed bamboo web 2. This arrangement allows the steel filler plate to be hidden inside the reconstructed bamboo web, and the connection is beautiful, but the reconstructed bamboo web needs to be grooved in advance in the factory, which requires high processing accuracy.

[0062] like Figure 6 , Figure 9a , Figure 9b , Fig.9c As shown, when a steel clamp is used as a vertical connector, the steel clamp 7 includes a first plate 9 and a second plate 10, and the first plate 9 and the second plate 10 are respectively arranged on both sides of the end of the reconstructed bamboo web 2. The arrangement and construction of the steel clamp on both sides of the reconstructed bamboo is more convenient, but the aesthetics is slightly poor. Therefore, in order to improve the aesthetics, a steel sealing plate 11 can be further used to seal the gap between the first plate 9 and the second plate 10, and spot welding can be used between the steel sealing plate 11 and the steel clamp.

[0063] The above-mentioned steel filler plates and steel splints are one steel filler plate or two steel splints (i.e., the first plate 9 and the second plate 10) for each web member. However, this connection method has problems such as inconvenient construction and positioning of vertical connectors, a large number of types and quantities, and insufficient welding length with the chord. Combining the steel filler plates inserted into the diagonal web members and the vertical web members into one, or combining the steel splints (the first plate or the second plate) arranged on each side of the ends of the diagonal web members and the vertical web members into one can perfectly solve the above problems and enhance the integrity of the node. Figure 3As shown, the steel filler plates inserted into the vertical web members 2a and the diagonal web members 2b can be integrated into one body; or Figure 6 As shown, the first plate 9 or the second plate 10 on both sides of the vertical web member 2a and the diagonal web member 2b are combined into a whole, and a smooth curve transition can be used in the middle (such as Figure 9a shown).

[0064] Figure 8 It is a specific implementation method. According to the building plan, the truss is selected to be a curved type. The upper chord and the lower chord are both steel round tubes with a diameter of 402mm and a material of Q355C. The web is made of reconstructed bamboo, and the rod adopts a combined section rod with a square end section and a circular middle section. The side length and diameter are both 250mm. The cross-section change part of the reconstructed bamboo web is processed to make it a smooth transition. The length direction of the reconstructed bamboo web is the direction of the bamboo grain, and the material strength grade is Ep14. Steel plywood is used as the vertical connector, and the top and side surfaces of the two plates are closed with steel sealing plates.

[0065] When the steel-recombined bamboo composite truss is combined with steel filler plates, Figure 3 , Figure 5 As shown, this type of connection has a simple and beautiful appearance, but the node out-of-plane stiffness is poor. In order to avoid instability of the steel filler plate, the size of the steel filler plate should not be too large. Its thickness should not be less than 10mm and not less than 0.8 times the bolt diameter. The height-to-thickness ratio should not be greater than 40ε k (where ε k is the steel grade correction factor, and its value is the square root of the ratio of 235 to the yield point value in the steel grade). The angle range between the vertical web member and the diagonal web member is 30°~45°.

[0066] When the steel-recombined bamboo composite truss uses the first plate and the second plate of the steel splint to be combined into one, such as Figure 6 As shown, this type of connection node has good out-of-plane stiffness and is easy to construct, but it is slightly bulky and lacks aesthetics. In order to ensure that the truss has a good visual effect after construction, the node height should not exceed one-fourth of the net height of the web member, the thickness of the steel splint should not be less than 8mm, and not less than 0.7 times the bolt diameter, and the height-to-thickness ratio should not be greater than 80ε k (where ε k is the steel grade correction factor, whose value is the square root of the ratio of 235 to the yield point value in the steel grade), and the angle range between the vertical web member and the diagonal web member is 30° to 60°. Furthermore, the steel cover plate can be a steel plate with a thickness of not less than 6 mm.

[0067] like Figure 4 , Figure 7As shown, the vertical connector can be adjusted to a circular or rectangular steel sleeve, and the circular steel sleeve 6 or the rectangular steel sleeve 8 is sleeved on the outside of the end of the reorganized bamboo web 2. Such a connection node is simple, beautiful, and has good rigidity, and is convenient to construct. The force mode of this type of node bolt is the same as that of the steel plywood connection node. The node is simpler and more visually transparent. The inner and outer rigidity of the sleeve surface are the same, and the node stability is good. However, there is a large intersection surface between the diagonal web sleeve and the vertical web sleeve, thereby weakening the connection between the diagonal web sleeve and the steel chord. Therefore, the angle between the vertical web 2a and the diagonal web 2b is set to 45°~60°, and the wall thickness of the steel sleeve should not be less than 8mm.

[0068] When the reconstructed bamboo web and the vertical connector are connected by bolts 4, ordinary bolts can be used to achieve a hinged connection between the reconstructed bamboo web and the steel chord. The number of bolts is determined based on calculations, and the number of bolts for a single web should not be less than 2; the bolts can be arranged in a single row, double row, or multiple rows. When the number of bolts is greater than 3, a single row arrangement should not be used; when the vertical connector is a steel sleeve, the bolts can be arranged on one side or in a cross-shaped arrangement along the longitudinal direction. The diameter d of the bolt 4 shall not be less than 12 mm, the diameter of the circular end of the reconstructed bamboo web 2 or the side length D of the rectangular end shall not be less than 90 mm, and the thickness-to-diameter ratio D / d should be controlled within the range of 4 to 15. Bolt arrangement as follows Fig.11 As shown in the figure, the direction of the reconstructed bamboo web is the direction of force along the grain (indicated by the black arrow). Under different working load conditions, the web may be tensile or compressed, so the end distance of the bolts at both ends is the same. To avoid splitting and failure of the node, the bolt end distance e1 is not less than 6d, the spacing s is not less than 4d; the edge distance e2 is not less than 3d and the row spacing r is not less than 2d; in particular, for circular webs with rectangular end sections, the bolt end distance is not less than 7d.

[0069] In order to facilitate the engineering application of the steel-recombined bamboo composite truss, the present invention also proposes a method for calculating the node bearing capacity of the steel-recombined bamboo composite truss.

[0070] When there is no external force on the steel chord members of the truss, the chord is an axially tensile (compressive) member, and the member section strength and stability calculations shall be carried out in accordance with the current specifications, and the allowable slenderness ratio limit requirements of the current relevant standards shall be met. When the metal roof or equipment load acts on the truss chord, the truss chord is a tension (compression) bending member, and the strength and stability calculations shall be carried out in accordance with the current specifications, and the structural requirements of the current relevant standards shall be met. The reconstructed bamboo web is connected to the steel chord at both ends by a hinged connection. Therefore, the reconstructed bamboo member is only subjected to axial force (tension or pressure). The strength and stability calculations shall be carried out in accordance with the current specifications, and the structural requirements of the current relevant standards shall be met.

[0071] The bolts of the steel-reorganized bamboo connection node are long, the aspect ratio is large, and the bolts are sheared, so the bolt strength grade should be B or A. The reorganized bamboo-steel splint connection node, the reorganized bamboo-steel filler plate connection node, and the reorganized bamboo-steel sleeve connection node are all double shear connections. Under the action of axial load, there is extrusion between the bolts and the reorganized bamboo, the pin groove is under pressure, and the bolt is under bending, which will produce four failure modes: pressure failure of the pin groove of the steel plate (steel splint or steel filler plate or steel sleeve), pressure failure of the reorganized bamboo pin groove, single plastic hinge failure of the bolt, and two plastic hinge failures of the bolt.

[0072] For the steel plate pin groove pressure failure mode, the design value of the steel plate pin groove pressure bearing capacity should be calculated according to the "Steel Structure Design Standard" At present, there is relatively little experience in reconstructed bamboo structure engineering, and the relevant specifications are still immature. There is no clear calculation method for the bearing capacity of reconstructed bamboo bolt connection nodes under the three failure modes of "reconstructed bamboo pin groove pressure failure", "bolt single plastic hinge failure" and "bolt two plastic hinge failure". The current main design method is to refer to the "Wood Structure Design Standard" to calculate the bearing capacity design value of a single shear surface of the bolt. However, the physical and mechanical properties of reconstructed bamboo are better than those of glued wood. Existing studies have shown that the bearing capacity of reconstructed bamboo nodes is generally greater than that of glued wood nodes. Therefore, the present invention calculates the bearing capacity Z of a single shear surface of the bolt. d The calculation is carried out in accordance with the "Wood Structure Design Standard", and some corrections are made. At the same time, the values ​​of some parameters in the calculation formula are clarified, which specifically includes at least the following steps:

[0073] a) If Fig.10a , 10b As shown, the thickness t of the edge member of the steel-reconstructed bamboo node is obtained s ;

[0074] b) obtaining the screw diameter d of the bolt;

[0075] c) The minimum effective length coefficient k of the pin groove of the reorganized bamboo bolt connection node under pressure is obtained according to the following formula min ,

[0076]

[0077] where k Ⅰ , k Ⅲ , k Ⅳ The pin slot pressure-bearing effective length coefficients corresponding to the pin slot pressure failure, the bolt single plastic hinge failure, and the bolt double plastic hinge failure shall be determined according to the provisions of the Timber Structure Design Standard;

[0078] is the correction coefficient of the effective length coefficient of the pin groove pressure corresponding to the pin groove pressure failure, the single plastic hinge failure of the bolt, and the two plastic hinge failures of the bolt. For the vertical connector being a steel-filled plate node: when ts / d≤4,

[0079] When t s / d≥4, For the vertical connectors that are steel plates or steel sleeve nodes: when t s / d≤4, When 7 ≥ t s / d≥4, t s / d≥7,

[0080] d) Obtain the compressive strength standard f of the edge components of the steel-reconstructed bamboo node es , among which, the compressive strength of the reconstructed bamboo pin along the grain is f e,0 Determined according to the following formula, where ρ k The air-dry density of reconstituted bamboo is

[0081] f e,0 =0.082(1-0.01d)ρ k ;

[0082] e) Obtain the reference design value of bearing capacity Z(N) according to the following formula:

[0083] Z=k min t s df es ;

[0084] f) Obtain the design value of the bearing capacity Z of a single shear surface of the bolt according to the following formula: d (N),

[0085] Z d =C m C n C t k g Z

[0086] Among them, C m is the moisture content adjustment coefficient: the reconstructed bamboo component takes a value of 1.0;

[0087] C n The adjustment coefficient for the design service life is: 1.1 for 5 years; 1.05 for 25 years; 1.0 for 50 years;

[0088] C t Temperature adjustment coefficient: in long-term production high temperature environment, when the surface temperature of reconstructed bamboo reaches 40-50℃, the value is 0.8;

[0089] In other cases, the value is 1.0;

[0090] k gIt is the group bolt combination coefficient and is determined according to the provisions of the Timber Structure Design Standard.

[0091] At the same time, the bolts also have to bear shear force, and the shear bearing capacity of a single bolt should be determined according to the "Steel Structure Design Standard". Calculate. Then the design value of the bearing capacity of a single bolt in the reorganized bamboo bolt connection node is:

[0092]

[0093] Among them, n v is the number of sheared surfaces;

[0094] In order to reduce the complexity of the design, the bolt specifications are consistent, and the number of bolts is determined according to the design value of the axial force of the reorganized bamboo web and the design value of the bearing capacity of a single bolt.

[0095] The steel-reconstructed bamboo composite truss of the present invention has a clear force transmission path and simple force analysis. It rationally utilizes the physical and mechanical properties of different materials, transforms the composition form of a single material of a traditional truss into a combination of different materials, and makes the force of the truss structure more reasonable and efficient. The composite truss can greatly reduce the amount of construction steel, promote the further use of reconstructed bamboo in the construction field, effectively reduce the carbon emissions of the truss structure, and promote the transformation of the construction field to a low-carbon and green direction. The composite truss is easy to construct, and only the vertical connectors and chords need to be welded on site. The reconstructed bamboo web is pre-drilled in the factory and connected to the vertical connectors on site by bolts, which has good assemblability. The composite truss also increases the diversity of building structures.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating the node bearing capacity of a steel-recombined bamboo composite truss, characterized in that: The combined truss comprises a steel chord (1), a reorganized bamboo web member (2) and a vertical connector (3), wherein the reorganized bamboo web member (2) comprises a vertical web member (2a) and a diagonal web member (2b); The vertical connecting member (3) is arranged on the steel chord (1), the vertical connecting member (3) and the reorganized bamboo web member (2) are pre-set with bolt holes, the vertical connecting member (3) and the reorganized bamboo web member (2) are connected by bolts (4), and the angle between the vertical web member (2a) and the diagonal web member (2b) is 30° to 60°; When the cross section of the end of the reorganized bamboo web bar (2) is circular, the vertical connection member (3) is a steel filling plate (5); when the cross section of the end of the reorganized bamboo web bar (2) is rectangular, the vertical connection member (3) is a steel filling plate (5) or a steel clamping plate (7); The steel filler plate (5) is inserted into the interior of the pre-grooved end of the reconstructed bamboo web bar (2); The steel filler plate (5) inserted into the vertical web member (2a) and the diagonal web member (2b) is a whole; The steel clamping plate (7) comprises a first plate (9) and a second plate (10), wherein the first plate (9) and the second plate (10) are respectively arranged on both sides of the end of the reconstructed bamboo web rod (2); The first plate (9) or the second plate (10) arranged on both sides of the vertical web member (2a) and the diagonal web member (2b) is an integral body; A steel sealing plate (11) is further arranged between the first plate (9) and the second plate (10), and the steel sealing plate (11) seals the gap between the first plate (9) and the second plate (10); The calculation method comprises at least the following steps: a) Obtain the thickness t of the edge member of the steel-reconstructed bamboo node s ; b) obtaining the screw diameter d of the bolt (4); c) The minimum effective length coefficient k of the pin groove of the reorganized bamboo bolt connection node under pressure is obtained according to the following formula min , where k Ⅰ , k Ⅲ , k Ⅳ The pin slot pressure-bearing effective length coefficients corresponding to the pin slot pressure failure, the bolt single plastic hinge failure, and the bolt double plastic hinge failure shall be determined according to the provisions of the Timber Structure Design Standard; is the correction coefficient of the effective length coefficient of the pin groove pressure corresponding to the pin groove pressure failure, the single plastic hinge failure of the bolt, and the double plastic hinge failure of the bolt. For the vertical connection member (3) being a steel-filled plate node: when t s / d≤4, When t s / d≥4, For the vertical connection member (3) being a steel plate node: when t s / d≤4, When 7 ≥ t s / d≥4, t s / d≥7, d) Obtain the compressive strength standard f of the edge components of the steel-reconstructed bamboo node es , among which, the compressive strength of the reconstructed bamboo pin along the grain is f e,0 Determined according to the following formula, where ρ k The air-dry density of reconstituted bamboo is f e,0 =0.082(1-0.01d)ρ k ; e) Obtain the reference design value of bearing capacity Z(N) according to the following formula: Z=k min t s df es ; f) Obtain the design value Z of the bearing capacity of a single shear surface of the bolt (4) according to the following formula: d (N), Z d =C m C n C t k g Z Among them, C m is the moisture content adjustment coefficient: the reconstructed bamboo component takes a value of 1.0; C n The adjustment coefficient for the design service life is: 1.1 for 5 years; 1.05 for 25 years; 1.0 for 50 years; C t The temperature adjustment coefficient is 0.8 in a long-term high-temperature production environment when the surface temperature of the reconstructed bamboo reaches 40-50°C; 1.0 in other cases; k g It is the group bolt combination coefficient and is determined according to the provisions of the Timber Structure Design Standard.

2. The method for calculating the node bearing capacity of the steel-recombined bamboo composite truss according to claim 1 is characterized in that: The thickness of the steel filler plate (5) is not less than 10 mm and not less than 0.8 times the bolt diameter, and the height-to-thickness ratio of the steel filler plate (5) is not greater than 40ε k , where ε k is a steel grade correction coefficient, and its value is the square root of the ratio of 235 to the yield point value in the steel grade. The angle between the vertical web member (2a) and the diagonal web member (2b) is 30° to 45°.

3. The node bearing capacity calculation method of the steel-recombined bamboo composite truss according to claim 1 is characterized in that: The thickness of the steel clamping plate (7) is not less than 8 mm and not less than 0.7 times the bolt diameter, and the height-to-thickness ratio of the steel clamping plate (7) is not greater than 80ε k , where ε k It is the steel grade correction factor, and its value is the square root of the ratio of 235 to the yield point value in the steel grade.

4. The method for calculating the node bearing capacity of the steel-recombined bamboo composite truss according to any one of claims 1 to 3, characterized in that: The diameter d of the bolt (4) is not less than 12 mm, the diameter of the circular end of the reconstructed bamboo web rod (2) or the side length D of the rectangular end is not less than 90 mm, and the thickness-diameter ratio D / d is 4-15.

5. The method for calculating the node bearing capacity of the steel-recombined bamboo composite truss according to claim 4 is characterized in that: The bolt end distance is not less than 6d, the column distance is not less than 4d, the edge distance is not less than 3d and the row distance is not less than 2d.

6. The method for calculating the node bearing capacity of the steel-recombined bamboo composite truss according to claim 5 is characterized in that: When the reorganized bamboo web (2) is a circular web with a rectangular end section, the bolt end distance is not less than 7d.

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