A BFRP-steel composite chord truss and its assembly implementation method

Abstract

The present invention discloses a BFRP-steel composite chord truss and its assembly method. The truss comprises an upper chord (tube) attached to a steel tube along its length. The upper chord (tube) is a composite tube made by directly attaching BFRP fibers to the steel tube after high-temperature treatment; a lower chord (tube) wrapped with BFRP perpendicular to the length of the steel tube, with the tube ends internally threaded with positive screw threads; and a lower chord (tube) wrapped perpendicular to the length of the steel tube. The upper chord and lateral vertical tubes of the steel tube are impregnated with epoxy resin and wrapped along the diameter of the tube, with the tube ends internally threaded with positive screw threads. The truss also includes a three-joint node connector using stainless steel triple-bolts; a double-joint node connector using stainless steel studs; and a chord sleeve bolt connector using stainless steel sleeves with bolted joints. The truss exhibits superior durability, high load-bearing capacity, and high-temperature resistance.

Description

Technical Field

[0001] The invention belongs to the field of structural engineering and relates to a BFRP-steel composite chord truss and an assembly implementation method thereof. Background Art

[0002] Steel trusses are important transverse load-bearing components in steel structures, primarily carrying the loads of long-span, lightweight steel roof structures. Steel trusses generally consist of upper and lower chords, webs, and end risers, with steel pipes typically used as fittings. Typically, the upper chord and end risers bear compression, while the lower chord bears tension. The direction of force applied to the middle webs changes with the load.

[0003] Steel trusses offer advantages such as light weight, high load-bearing capacity, high steel consumption, diverse forms, and flexible layout. However, similar to other steel structures, rust is an almost unavoidable durability issue for steel trusses subjected to long-term service in complex environments, which directly affects the steel trusses' mechanical properties. Rust can have a particularly significant impact on the upper chord, which bears pressure, and the lower chord, which bears tension. To prevent this, the conventional practice is to apply anti-rust paint or galvanize the surface of the pipes. However, the coating or plating can still crack and peel during long-term service in various complex environments. Using stainless steel for all pipes would be costly and unsuitable for large-scale application.

[0004] Fiber-reinforced polymers (FRP) are a new type of building material that is corrosion-resistant, rust-resistant, lightweight, and high-strength. Using FRP in trusses can prevent truss corrosion. However, there are still various problems.

[0005] For example, the patent document with publication number CN208933015U discloses a GFRP truss. The pipe fittings in this patent are made of GFRP material. Although the strength of GFRP material is higher than that of steel, its ductility is poor. The truss nodes are connected by adhesive bonding and polypropylene-stainless steel composite plywood. This patent obviously cannot overcome the creep problem of GFRP under long-term high stress. There is also the problem of asynchrony between the colloid and the bolt tightening force.

[0006] Patent document CN108825605 discloses a method for assembling carbon fiber composite trusses and branch pipes. This method involves gluing, bolting, or attaching the composite pipes to the main structure. This method weakens the composite pipes at the joints and still fails to address the problem of loose connections caused by creep in the FRP pipes.

[0007] Patent document CN111173194A discloses a method for implementing an FRP truss node structure. This method focuses on the special node structure of the FRP truss. The FRP truss node is processed by inserting a steel box and steel pipe into the FRP pipe and pouring micro-expansive concrete. Although this node is tightly connected, the structure is too complex and on-site assembly is still difficult.

[0008] In summary, the truss structure and node operating principles in existing patents are completely different from those of the present invention. The present invention provides a novel structure that is corrosion-resistant and rust-proof, low-carbon and environmentally friendly, lightweight, high-strength, easy to construct, and high-temperature resistant, which is of great significance for the further promotion and application of BFRP materials. Summary of the Invention

[0009] Purpose of the invention:

[0010] The present invention aims to provide a novel BFRP-steel composite chord-tube truss and its assembly method. This new truss breaks through the limitations of using only FRP instead of steel for chord tubes. Instead, it employs low-carbon, environmentally friendly BFRP combined with steel pipe fittings as the truss's pipes. This design offers advantages such as corrosion and rust resistance, energy conservation and environmental protection, and lightweight and high strength. Its joints utilize joint kits, with the pipes screwed together for assembly. This overcomes the shortcomings of traditional joints, such as poor connection tightness and complex construction, and has high promotional value.

[0011] Technical solution:

[0012] The present invention discloses a BFRP-steel composite chord truss structure and an assembly method thereof, comprising an upper chord tube with BFRP fibers attached along the length direction of a steel pipe, wherein the upper chord tube with BFRP fibers attached along the length direction of the steel pipe is a composite pipe material in which fibers are extracted from the BFRP material after high-temperature treatment and directly attached to the steel pipe; a lower chord tube with BFRP fibers wound around the length direction perpendicular to the steel pipe, wherein the pipe end has a positive screw thread inside; the lower chord tube with BFRP fibers wound around the length direction perpendicular to the steel pipe is an upper chord and side vertical pipe fitting in which BFRP fibers are wound around the outside of the steel pipe impregnated with epoxy resin material along the pipe diameter, wherein the pipe end has a positive screw thread inside; a node three-joint bolt connector, wherein the node three-joint bolt connector is a stainless steel three-head bolt; a node double-joint bolt connector, wherein the node double-joint bolt connector is a stainless steel double-head bolt; and a chord sleeve bolt connector, wherein the chord sleeve bolt connector is a stainless steel sleeve with a bolt joint.

[0013] Furthermore, the inner diameter of the BFRP-steel composite rod is consistent with the outer diameter of the connecting bolt, and the BFRP-steel pipe is connected to the stainless steel connecting piece by screwing.

[0014] Furthermore, epoxy resin needs to be applied to the connector before the pipes are screwed to prevent water from invading the inner steel pipe.

[0015] Furthermore, the upper and lower chord sleeve connectors use reverse-thread bolts, and the belly tube simultaneously tightens the upper and lower chords during the screwing process.

[0016] The present invention also provides a method for assembling and constructing the novel truss structure, which comprises the following steps:

[0017] (1) The upper chord tube with BFRP fibers attached along the length of the steel pipe, the lower chord tube with BFRP fibers wrapped perpendicular to the length of the steel pipe, the belly tube, and the end tube are manufactured to the predetermined lengths, and stainless steel bolt connectors are prepared.

[0018] (2) Apply epoxy resin to the bolt head of the top connector, and screw the lower chord tube and the middle vertical web tube wrapped with BFRP fiber in the length direction of the vertical steel pipe into the connector.

[0019] (3) Insert the chord tube clamp bolt connector through the clamp into the upper chord tube to the predetermined design position.

[0020] (4) Screw the double-headed stainless steel bolt connectors onto the two ends of the upper chord tube.

[0021] (5) Insert the chord tube clamp bolt connector through the clamp into the lower chord tube to the predetermined design position.

[0022] (6) Use the belly tube and end tube to connect the upper and lower chord sleeve connectors, and screw until the upper and lower sleeve connectors are tightened.

[0023] Beneficial effects:

[0024] The present invention provides a BFRP-steel composite chord truss and an assembly method thereof, which can achieve the following beneficial effects:

[0025] (1) Effectively prevent truss chord tubes from rusting and increase component durability

[0026] BFRP is a green building material with exceptional corrosion resistance. Truss structures are commonly used in industrial plants with large spans, often operating in open-air environments or in complex environments with significant corrosion potential. This places high demands on the trusses, particularly the chords that bear the bending moment, for corrosion resistance, a requirement that existing steel chords clearly cannot meet. Using BFRP-steel composite tubes as chords effectively prevents corrosion and increases component durability.

[0027] (2) Effectively increase the bearing capacity of the truss

[0028] The tensile strength of BFRP material is generally between 600-1500MPa, which is higher than the ultimate tensile strength of steel. Therefore, using a BFRP-steel composite tube with the fiber direction in the same direction as the steel tube as the lower chord tube can effectively increase the tensile strength of the lower chord tube. At the same time, the upper chord pressure tube uses a BFRP transversely wrapped composite steel tube to avoid buckling of the upper chord tube. Therefore, the present invention can significantly improve the ultimate bearing capacity of the truss.

[0029] (3) Effectively reduce the deadweight of the truss and increase the span of the component

[0030] BFRP is lightweight and high-strength, with an ultimate tensile strength up to 2.5 times that of steel. Meanwhile, its unit volume density is only 26% of that of steel. Based on the ultimate strength and unit volume density, a BFRP material bearing the same load weighs only 12% of the equivalent steel. Therefore, this invention effectively reduces the weight of trusses, not only improving seismic resistance but also facilitating the application requirements of large-span spatial structures.

[0031] (4) Effectively prolong the destruction time of trusses under high temperature

[0032] Another important characteristic of BFRP is its thermal insulation. One of the main disadvantages of steel is its poor high-temperature resistance. In the event of a fire, steel components can buckle rapidly under the influence of high temperatures, causing the truss to lose its load-bearing capacity prematurely. The present invention utilizes BFRP-steel composite pipes as the upper and lower chords and side risers, fully utilizing the thermal insulation properties of BFRP. This effectively prolongs the time it takes for the core steel pipes in the truss to heat up and fail in high-temperature environments.

[0033] (5) The assembly method is simple and easy to assemble and construct

[0034] This assembly method is easy to manufacture and operate on-site. Truss tubes are connected by bolts, and the bolt heads are coated with epoxy resin to ensure a strong and dense connection. Chord tubes and web tubes are connected by chord tube clamp bolt connectors to prevent damage to the upper and lower chord tubes of the BFRP-steel composite. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the assembled BFRP-steel composite chord-tube truss.

[0036] Figure 2 This diagram illustrates the assembly method of the upper chord tube and the middle tube.

[0037] Figure 3 Schematic diagram of the structure of the ferrule upper chord tube connector.

[0038] Figure 4 This is a diagram of the lower chord tube assembly method.

[0039] In the figure: 100 - upper chord tube; 200 - lower chord tube; 300 - end belly tube; 400 - middle belly tube; 500 - node three-joint bolt connector; 600 - node double-joint bolt connector.

[0040] The upper chord and end risers of the assembled BFRP-steel composite chord-tube truss are made of BFRP fibers wrapped transversely around composite steel tubes; the lower chord is made of BFRP fibers attached longitudinally to composite steel tubes and a steel web tube painted with anti-rust paint. It has the advantages of high bearing capacity, strong durability, and good thermal insulation. The trusses are connected by bolt joints, and epoxy resin is applied to the nodes before the bolts are tightened. Figure 1 Section 1-1 is the cross section of the composite chord tube with BFRP fibers wrapped transversely, and section 2-2 is the cross section of the composite chord tube with BFRP fibers attached longitudinally. DETAILED DESCRIPTION

[0041] The truss pipes designed in this invention are assembled and connected using threaded steel connectors. To ensure that there is no moisture or rust inside the pipes, epoxy resin is applied to the bolt heads before tightening the bolts at the ends of the pipes. The specific steps for pipe assembly are as follows:

[0042] (1) Upper chord tube assembly

[0043] First, apply epoxy resin to the steel three-way bolt joint, then wrap the pre-made BFRP fiber horizontally around the chord tube and the vertical tube in the truss and screw it clockwise to close the ends of the chord tube and the vertical tube in the truss (see the attached picture). Figure 2 );

[0044] (2) Upper chord connector in place

[0045] Put the sleeve connector into the upper chord tube to the specified position, and tighten the short fastening bolt counterclockwise with a wrench, and screw the chord tube end connector into the chord tube end (attached Figure 3 );

[0046] (3) Assemble with the lower chord

[0047] Align the lower chord tube assembled according to the above methods 1 and 2 with the assembled upper chord tube, connect the connectors at both ends with steel belly tubes painted with anti-rust paint and screw them clockwise. The threads of the upper and lower connectors are designed to be reversed. During the screwing process of the belly tube, the connectors and the chord tube, and the belly tube and the upper and lower chord tubes should be screwed in the tightening direction to ensure the overall stability of the truss and the dense joints without gaps (see Appendix). Figure 4 ).

[0048] The above embodiments are only preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and equivalent substitutions without departing from the principles of the present invention.

[0049] The technical solutions after improvements and equivalent replacements in the claims all fall within the protection scope of the present invention.

Claims

1. A method for assembling and installing a corrosion-resistant, lightweight, high-strength BFRP-steel tube composite chord-tube truss, characterized by: It includes an upper chord tube with BFRP fibers attached. The upper chord tube is wound horizontally with BFRP fibers to prevent buckling of the upper chord tube components. The lower chord tube has BFRP fibers longitudinally attached and has a right-handed screw thread inside the tube end. The upper and lower chord tubes are connected to the end web tubes by threaded stainless steel connectors. The length of the threaded section of the connector matches the length of the internal threaded section of the tube component, and the length of the threaded section is 5mm < L < 10m. The other web tubes are both truss components and connection components for strengthening the connection of the upper chord web tubes. The middle web tube is connected to the chord tube by a sleeve with threaded parts. The inner diameter of the sleeve matches the outer diameter of the chord tube, and the diameter-thickness ratio D / t of the sleeve ranges in the interval of (1 / 20 - 1 / 10). During the screwing of the web tube, it not only protects the BFRP shell of the chord tube from damage but also plays a role in connecting the tube components. The specific installation method includes the following steps: (1) Fabricate the upper chord tube wound horizontally with BFRP fibers, the lower chord tube with BFRP fibers longitudinally attached, the web tubes, and the end tubes according to the established length, and prepare the stainless steel bolt connectors; (2) Apply epoxy resin to the bolt head of the top connector, and screw the lower chord tube with BFRP fibers longitudinally attached and the middle vertical web tube into the connector; (3) Insert the chord tube hoop bolt connector through the hoop into the upper chord tube to the established position; (4) Screw the double-headed stainless steel bolt connector onto both ends of the upper chord tube; (5) Insert the chord tube hoop bolt connector through the hoop into the lower chord tube to the established position; (6) Use the web tubes and end tubes to connect the hoop connectors of the upper and lower chords, and screw them until all the upper and lower hoop connectors are tightened; The inner diameter of the BFRP-steel composite tube component matches the outer diameter of the connector bolt. The upper and lower chord sleeve connectors use reverse-thread bolts, and the web tube tightens both the upper and lower chords during the screwing process; The upper chord tube with BFRP fibers attached is a composite pipe in which BFRP material is processed at high temperature to extract fibers and directly attached to the steel pipe.

Images