Rectangular steel tube concrete column with built-in composite constraints and construction method thereof

Abstract

The present invention discloses a rectangular steel tube concrete column with built-in composite constraints. The composite constraints include rectangular spiral stirrups, circular spiral stirrups and a straight hoop assembly. The straight hoop assembly consists of two cross-arranged straight hoops, which tie the two long sides of the rectangular spiral stirrups together to form a whole, and divide the interior of the rectangular spiral stirrups into multiple cavities. A circular spiral stirrup is arranged inside each cavity, and a distance is provided between the outer side of the rectangular spiral stirrup and the inner wall of the rectangular steel tube. The present invention also provides a construction method for a rectangular steel tube concrete column with built-in composite constraints. The present invention improves the uneven and weak constraints of the long and short sides of the rectangular steel tube, delays the local bulging of the side of the rectangular steel tube and strengthens the constraints on the core concrete, significantly improves the mechanical properties at room temperature, and greatly improves the fire resistance performance throughout the life cycle, thereby achieving the goal of exempting the surface of the rectangular steel tube from fire protection while meeting the fire resistance limit requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of improving safety, comprehensive performance and disaster resilience of building structures throughout their life cycle, and specifically relates to a rectangular steel tube concrete column with built-in composite constraints and a construction method thereof. Background Art

[0002] As we all know, steel tube concrete columns have good mechanical properties and construction performance. In recent years, they have been widely used in construction projects and have good application prospects. At present, the cross-sectional forms of steel tube concrete columns used in practice mainly include circular, rectangular and polygonal. Rectangular steel tube concrete columns have the advantages of good stability, flexible building space layout and relatively simple beam-column node connection structure. They are widely used in multi-story and high-rise steel structure residential or high-rise buildings, and super high-rise building structures. However, the long and short sides of the rectangular steel tube have uneven effects on the restraint of the core concrete, and the restraint effect is worse than that of the circular cross-section steel tube concrete column, which limits the actual use of rectangular steel tube concrete in engineering. In order to improve the comprehensive performance and disaster resistance resilience, domestic and foreign scholars have proposed a series of measures to enhance the mechanical properties of rectangular steel tube concrete columns, including welding stiffeners, studs, steel stiffeners inside the steel tube, setting restraint tie rods and internal stirrups, etc.

[0003] Currently, regarding the measure of internal stirrup reinforcement, Chinese patent application number 201921921547.X proposes a double-cavity rectangular steel tube concrete column, Chinese patent application number 202011397979.2 proposes a rectangular steel tube concrete column and preparation method and applies for an invention patent, and the master's thesis "Research on Axial Compression and Eccentric Load Mechanical Properties of Rectangular Steel Tube Concrete Short Columns with Internal Elliptical Stirrups" proposes a method of internal elliptical stirrup reinforcement. However, the above-mentioned steel tube concrete columns have the following disadvantages:

[0004] 1. The rectangular concrete-filled steel tube column, application number 201921921547.X, utilizes a central steel plate for separation. This plate is welded at both ends to the inner wall of the rectangular steel tube. This method consumes a large amount of steel and is cumbersome to weld to the inner wall of the rectangular steel tube. Furthermore, in the event of a fire, due to the high thermal conductivity of steel, heat from the rectangular steel tube can easily transfer through the central steel plate to the interior of the rectangular concrete-filled steel tube column, severely degrading the concrete inside and potentially compromising the fire resistance of the rectangular concrete-filled steel tube column.

[0005] 2. The rectangular concrete-filled steel tube column with application number 202011397979.2 utilizes multiple layers of restraining stirrups. The upper and lower layers of restraining stirrups are discontinuous, and their performance improvement is not significant. Furthermore, the restraining stirrups are a combination of "U" and "arc," making processing very complex, requiring higher equipment requirements and requiring more manpower. The internal elliptical stirrups also have similar shortcomings to those in this patent.

[0006] Furthermore, the scale and frequency of fires are increasing, resulting in approximately 200 billion yuan in economic losses worldwide. The inherent fire resistance of steel pipes is not very high, and to meet these requirements, fire-retardant coatings are often applied to their surfaces. Over the life of a structure, fire-retardant coatings are inevitably subject to complex factors such as environmental erosion and material aging, potentially causing severe pulverization, cracking, and even shedding. This raises questions about the reliability of the coating's long-term fire resistance, poses significant safety risks, and incurs high costs for regular maintenance.

[0007] In summary, it is very important to find a fire protection technology that is easy to construct, can improve the fire resistance of the rectangular steel tube concrete column structure itself, can achieve fire protection-free and low maintenance, and ensure that the fire protection has the same life span as the structure. Summary of the Invention

[0008] The object of the present invention is to provide a rectangular steel tube concrete column with built-in composite constraints and a construction method thereof.

[0009] On the one hand, the composite restraints built into the present invention are easy to manufacture and construct, and effectively restrain the core concrete. While maintaining the same total steel usage as conventional rectangular concrete-filled steel tube columns, by reducing the wall thickness of the rectangular steel tube and installing composite restraints within the tube, the uneven and weak restraints on the long and short sides of the rectangular tube are addressed, slowing localized lateral buckling of the tube and strengthening the restraints on the core concrete, significantly improving the room-temperature mechanical properties of the rectangular concrete-filled steel tube columns.

[0010] On the other hand, under fire, when the mechanical properties of the outer rectangular steel tube degrade severely, the built-in composite constraint can constrain the core concrete and improve the high-temperature performance of the core concrete, thereby greatly improving the fire resistance of the rectangular steel tube concrete column throughout its life cycle, and thus achieving the goal of exempting the rectangular steel tube surface from fire protection while meeting the fire resistance limit requirements.

[0011] The present invention is achieved through the following technical solutions:

[0012] A rectangular steel tube concrete column with built-in composite restraints, characterized by comprising composite restraints, core concrete, a rectangular steel tube, and fixing steel bars; the composite restraints being placed inside the rectangular steel tube and continuously arranged along the height direction of the rectangular steel tube concrete column; the core concrete being filled inside the rectangular steel tube, and the composite restraints being buried in the core concrete;

[0013] The composite constraint includes a rectangular spiral stirrup, at least two circular spiral stirrups and at least one straight stirrup assembly; the straight stirrup assembly consists of two straight stirrups arranged in a cross pattern; the straight stirrup assembly ties the two long sides of the rectangular spiral stirrup together to form a whole, and divides the interior of the rectangular spiral stirrup into at least two cavities, with a circular spiral stirrup arranged inside each cavity; the straight stirrup is embedded between the pitches of the rectangular spiral stirrups, and the pitch is the height advanced by the spiral stirrup extending one circle in a spiral; the distance between two adjacent bending parts on the same side of the straight stirrup is twice the pitch of the rectangular spiral stirrups; a distance is provided between the outer side of the rectangular spiral stirrup and the inner wall of the rectangular steel tube; the fixing steel bars are used to fix the rectangular spiral stirrups, and are disconnected and discontinuously arranged along the height direction of the rectangular steel tube concrete column.

[0014] Furthermore, the straight hoop is formed by bending a complete steel bar back and forth, and multiple bending parts are formed on both sides of the straight hoop. The bending parts of the two straight hoop of the straight hoop assembly alternately tie the long sides of the rectangular spiral stirrups.

[0015] Furthermore, the outer side of the circular spiral stirrup and the inner side of the rectangular spiral stirrup are closely attached to each other.

[0016] Furthermore, the rectangular spiral stirrups and the one-stroke stirrup assembly, the rectangular spiral stirrups and the circular spiral stirrups, and the rectangular spiral stirrups and the fixing steel bars are connected into one piece by spot welding or binding, and then placed into the rectangular steel pipe in an integrated form.

[0017] Furthermore, the rectangular steel pipe is a normal strength or high strength steel pipe, and the circular spiral stirrups, straight stirrups and rectangular spiral stirrups are made of normal strength or high strength steel bars with a diameter of 6 to 12 mm.

[0018] Furthermore, the distance between the outer side of the rectangular spiral stirrup and the inner wall of the rectangular steel pipe is 25 to 50 mm.

[0019] Furthermore, the fixing steel bars are HPB 300 grade steel bars with a diameter of 6 to 12 mm.

[0020] Furthermore, the core concrete is natural aggregate concrete, recycled aggregate concrete, or recycled block concrete.

[0021] The construction method of the rectangular steel tube concrete column with built-in composite constraints is characterized by comprising the following steps:

[0022] Step 1: Manufacturing and processing rectangular steel pipes;

[0023] Step 2: Process and manufacture circular spiral stirrups, straight stirrups, and rectangular spiral stirrups according to a preset longitudinal center spacing; embed the straight stirrups on the rectangular spiral stirrups, and insert circular spiral stirrups into the cavity; connect the circular spiral stirrups, straight stirrups, rectangular spiral stirrups, and fixing steel bars into one by spot welding or binding, and then place them inside the rectangular steel pipe and fix them, ensuring that the rectangular spiral stirrups coincide with the central axis of the rectangular steel pipe, and that a distance is left between the outer side of the rectangular spiral stirrups and the inner wall of the rectangular steel pipe;

[0024] Step 3: Carry out on-site lifting and splicing of rectangular steel pipes, then pour concrete from the top of the rectangular steel pipes and vibrate them thoroughly until dense.

[0025] Compared with the prior art, the present invention has the following advantages and effects:

[0026] (1) The built-in circular spiral stirrups, rectangular spiral stirrups, straight stirrups and rectangular steel pipes can all be processed and assembled in the factory, which is convenient for construction and has a high degree of assembly. In addition, no additional construction process of rectangular steel tube concrete columns is required on site.

[0027] (2) Composite constraints are built into the rectangular steel tube to improve the problems of long and short side constraints and weak constraints of the rectangular steel tube, delay the local buckling of the long side of the rectangular steel tube and strengthen the constraints on the core concrete, further improving the comprehensive performance and disaster resistance toughness of the rectangular steel tube concrete column.

[0028] (3) Under fire conditions, when the mechanical properties of the outer rectangular steel tube deteriorate severely, the built-in composite constraint can constrain the core concrete and improve the high-temperature performance of the core concrete, thereby significantly improving the fire resistance of the rectangular steel tube concrete column throughout its life cycle. This can achieve the goal of exempting the rectangular steel tube surface from fire protection while meeting the fire resistance limit requirements, which is green, low-carbon, environmentally friendly and energy-saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the structure of a rectangular steel tube concrete column according to Example 1 of the present invention;

[0030] Figure 2 1 is a schematic structural diagram of a circular spiral stirrup according to Example 1 of the present invention;

[0031] Figure 3 1 is a schematic structural diagram of a pen hoop assembly according to embodiment 1 of the present invention;

[0032] Figure 4 Schematic diagram of the structure of the rectangular spiral stirrups of Example 1 of the present invention.

[0033] Meaning of the reference numerals in the figure:

[0034] 1-Circular spiral stirrups; 2-Straight stirrups; 3-Rectangular spiral stirrups; 4-Core concrete; 5-Rectangular steel pipe; 6-Fixing steel bars; 7-Bend part. DETAILED DESCRIPTION

[0035] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0036] Example 1:

[0037] like Figures 1 to 4 As shown, a rectangular steel tube concrete column with built-in composite restraints includes a composite restraint, core concrete 4, a rectangular steel tube 5, and fixing steel bars 6. The composite restraint includes a rectangular spiral stirrup 3, two circular spiral stirrups 1, and a straight stirrup assembly, which is composed of two straight stirrups 2 arranged in a cross pattern.

[0038] The composite constraint is placed inside the rectangular steel tube 5 and is continuously arranged along the height direction of the rectangular steel tube concrete column. A distance of 40 mm is left between the outer side of the rectangular spiral stirrup 3 and the inner wall of the rectangular steel tube 5. Two straight hoops 2 tie the two long sides of the rectangular spiral stirrup 3 together to form a whole, and divide the interior of the rectangular spiral stirrup 3 into two cavities. A circular spiral stirrup 1 is set inside each cavity, and the outer side of the circular spiral stirrup 1 is close to the inner side of the rectangular spiral stirrup 3. The fixing steel bar 6 is only used to fix the rectangular spiral stirrup 3. It can be disconnected and discontinuously arranged along the height direction of the rectangular steel tube concrete column, that is, the fixing steel bar 6 can be disconnected and arranged into multiple sections along the height direction of the rectangular spiral stirrup 3. The fixing steel bar 6 separated into multiple sections makes the internal composite constraint easier to construct.

[0039] The steel bars of the rectangular spiral stirrups 3 and the circular spiral stirrups 1 are both extended in a spiral form. The pitches of the rectangular spiral stirrups 3 and the circular spiral stirrups 1 can be the same or different.

[0040] A straight hoop 2 is formed by bending a complete steel bar back and forth, and multiple bending parts 7 are formed on both sides of the straight hoop 2. The distance between two adjacent bending parts 7 on the same side of the straight hoop 2 is twice the pitch of the rectangular spiral hoop 3. The two straight hoop 2 are close to each other and arranged crosswise. The bending parts of the two straight hoop 2 of the straight hoop assembly are arranged alternately. The bending parts 7 on both sides of the straight hoop 2 are embedded between the pitches of the rectangular spiral hoop 3 and tie the two long sides of the rectangular spiral hoop 3 together.

[0041] In this embodiment, the rectangular steel tube 5 is formed by welding two cold-bent steel sections. The cross-sectional dimensions of the rectangular steel tube 5 are 350 mm × 580 mm, the wall thickness is 10 mm, and the height is 5000 mm. The steel material is Q345B steel plate, and the measured yield strength is 390 MPa.

[0042] In this embodiment, the circular spiral stirrups 1 are made of HRB 400 grade steel bars with a diameter of 10 mm and a measured yield strength of 490 MPa; the pitch of the circular spiral stirrups 1 is 80 mm.

[0043] In this embodiment, the diameters of the two circular spiral stirrups 1 are both 220 mm.

[0044] In this embodiment, the straight hoop 2 uses HRB 400 grade steel bars with a diameter of 10 mm and a measured yield strength of 490 MPa; the two cross-arranged straight hoop 2 are set at the half position of the long side of the rectangular spiral hoop 3; the distance between the two adjacent bending parts 7 on the same side of the straight hoop 2 is 160 mm.

[0045] In this embodiment, the rectangular spiral stirrups 3 are made of HRB 400 grade steel bars with a diameter of 10 mm and a measured yield strength of 490 MPa; the pitch of the rectangular spiral stirrups 3 is 80 mm.

[0046] In this embodiment, the long side (center distance) of the rectangular spiral stirrup 3 is 480 mm, and the short side (center distance) is 240 mm.

[0047] In this embodiment, the fixing steel bar 6 is a HPB 300 steel bar with a diameter of 10 mm and a length of 4870 mm.

[0048] In this embodiment, the rectangular spiral stirrups 3 and the fixing steel bars 6 are connected as a whole by binding. Four fixing steel bars 6 are arranged at the corners of the rectangular spiral stirrups 3 to fix the shape of the rectangular spiral stirrups 3. The fixing steel bars 6 are arranged vertically.

[0049] In this embodiment, the composite restraint is spot welded together as a whole and fixed by short steel bars arranged at the upper, middle and lower positions to ensure the distance between the outer side of the rectangular spiral stirrup 3 and the inner wall of the rectangular steel pipe 5.

[0050] In this embodiment, the core concrete 4 is made of natural aggregate concrete, and the compressive strength of 150 mm cube of natural aggregate concrete is 45 MPa.

[0051] In this embodiment, the welding rod for tailor welding the rectangular steel pipe 5 and the welding between the composite constraints is E50, the flux is F4A0, and the weld quality grade is level one.

[0052] The construction method of the rectangular steel tube concrete column with built-in composite constraints in this embodiment includes the following steps:

[0053] Step 1: Manufacturing and processing the rectangular steel tube 5;

[0054] Step 2: Process and manufacture circular spiral stirrups 1, straight stirrups 2 and rectangular spiral stirrups 3 according to the preset longitudinal center spacing; then cross-arrange the straight stirrups 2 on the rectangular spiral stirrups 3, and insert the circular spiral stirrups 1 into the cavity; connect the circular spiral stirrups 1, straight stirrups 2, rectangular spiral stirrups 3 and fixing steel bars 6 into one by spot welding or binding, and then place them inside the rectangular steel pipe 5 in an integrated form and fix them. They can be welded and fixed by short steel bars to ensure that the central axis of the rectangular spiral stirrups 3 coincides with the central axis of the rectangular steel pipe 5, and a distance of 40 mm is left between the outer side of the rectangular spiral stirrups 3 and the inner wall of the rectangular steel pipe 5;

[0055] Step 3: hoist and splice the rectangular steel pipe 5 on site, then pour concrete into the top of the rectangular steel pipe 5 and fully vibrate it until it is dense.

[0056] Example 2:

[0057] A rectangular steel tube concrete column with a built-in composite restraint includes a composite restraint, a core concrete 4, a rectangular steel tube 5, and fixing steel bars 6. The composite restraint includes a rectangular spiral stirrup 3, three circular spiral stirrups 1, and two sets of straight stirrup assemblies, each consisting of two straight stirrups 2 arranged in a cross pattern.

[0058] The composite restraint is placed inside the rectangular steel tube 5 and continuously arranged along the height of the rectangular steel tube concrete-filled column. A 40mm gap is left between the outer side of the rectangular spiral stirrup 3 and the inner wall of the rectangular steel tube 5. Two sets of straight hoop assemblies tie the two long sides of the rectangular spiral stirrup 3 together and divide the interior of the rectangular spiral stirrup 3 into three cavities. Each cavity is equipped with a circular spiral stirrup 1, with the outer side of the circular spiral stirrup 1 tightly attached to the inner side of the rectangular spiral stirrup 3. The fixing steel bars 6 are used only to secure the rectangular spiral stirrup 3 and can be disconnected and discontinuous along the height of the rectangular steel tube concrete-filled column.

[0059] In this embodiment, the rectangular steel tube 5 is formed by welding two cold-bent steel sections. The cross-sectional dimensions of the rectangular steel tube 5 are 350 mm × 810 mm, the wall thickness is 10 mm, and the height is 4000 mm. The steel material is Q345B steel plate, and the measured yield strength is 390 MPa.

[0060] In this embodiment, the circular spiral stirrups 1 are made of HRB 400 grade steel bars with a diameter of 10 mm and a measured yield strength of 490 MPa; the pitch of the circular spiral stirrups 1 is 75 mm.

[0061] In this embodiment, the diameter of the circular spiral stirrups 1 is 220 mm.

[0062] In this embodiment, the straight hoop 2 is made of HRB 400 grade steel bars with a diameter of 10 mm and a measured yield strength of 490 MPa; the distance between two adjacent bent portions 7 on the same side of the straight hoop 2 is 150 mm.

[0063] In this embodiment, the rectangular spiral stirrups 3 are made of HRB 400 grade steel bars with a diameter of 10 mm and a measured yield strength of 490 MPa; the pitch of the rectangular spiral stirrups 3 is 75 mm.

[0064] In this embodiment, the long side (center distance) of the rectangular spiral stirrup 3 is 700 mm, and the short side (center distance) is 240 mm.

[0065] In this embodiment, the fixing steel bar 6 is HPB 300 steel bar with a diameter of 10 mm and a length of 3850 mm.

[0066] In this embodiment, the rectangular spiral stirrups 3 and the fixing steel bars 6 are connected into a whole by binding.

[0067] In this embodiment, the composite restraint is spot welded together as a whole and fixed by short steel bars arranged at the upper, middle and lower positions to ensure the distance between the outer side of the rectangular spiral stirrup 3 and the inner wall of the rectangular steel pipe 5.

[0068] In this embodiment, the core concrete 4 is made of recycled block concrete, and the 150 mm cube compressive strength of the recycled block concrete is 50 MPa.

[0069] In this embodiment, the welding rod for tailor welding the rectangular steel pipe 5 and the welding between the composite constraints is E50, the flux is F4A0, and the weld quality grade is level one.

[0070] The construction method of the rectangular steel tube concrete column with built-in composite constraints in this embodiment includes the following steps:

[0071] Step 1: Manufacturing and processing the rectangular steel tube 5;

[0072] Step 2: Process and manufacture the circular spiral stirrups 1, the straight stirrups 2 and the rectangular spiral stirrups 3 according to the preset longitudinal center spacing; then cross-arrange the straight stirrups 2 on the rectangular spiral stirrups 3, and insert the circular spiral stirrups 1 into the cavity; spot weld or tie the circular spiral stirrups 1, the straight stirrups 2, the rectangular spiral stirrups 3 and the fixing steel bars 6 into one piece, and then place them in the rectangular steel tube 5 as a whole and fix them, ensuring that the central axis of the rectangular spiral stirrups 3 coincides with the central axis of the rectangular steel tube 5, and that a distance of 40 mm is left between the outer side of the rectangular spiral stirrups 3 and the inner wall of the rectangular steel tube 5;

[0073] Step 3: hoist and splice the rectangular steel pipe 5 on site, then pour concrete into the top of the rectangular steel pipe 5 and fully vibrate it until it is dense.

[0074] According to the method of the present invention, a series of implementation examples can also be developed, which does not impose any formal limitation on the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above examples based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A rectangular steel tube concrete column with built-in composite constraints, characterized by: The invention comprises a composite constraint, core concrete (4), a rectangular steel tube (5) and fixing steel bars (6); the composite constraint is placed inside the rectangular steel tube (5) and is continuously arranged along the height direction of the rectangular steel tube concrete column; the core concrete (4) is filled inside the rectangular steel tube (5), and the composite constraint is buried in the core concrete (4); The composite constraint comprises a rectangular spiral stirrup (3), at least two circular spiral stirrups (1) and at least one straight stirrup assembly; the straight stirrup assembly is composed of two straight stirrups (2) arranged in a cross pattern; the straight stirrup assembly binds the two long sides of the rectangular spiral stirrup (3) to form a whole, and divides the interior of the rectangular spiral stirrup (3) into at least two cavities, and one circular spiral stirrup (1) is arranged in each cavity; the straight stirrup (2) is embedded between the pitches of the rectangular spiral stirrup (3), and the pitch is the height of the spiral stirrup extended in one circle; the distance between two adjacent bending parts (7) on the same side of the straight stirrup (2) is twice the pitch of the rectangular spiral stirrup (3); a distance is provided between the outer side of the rectangular spiral stirrup (3) and the inner wall of the rectangular steel tube (5); the fixing steel bar (6) is used to fix the rectangular spiral stirrup (3), and is disconnected and discontinuously arranged along the height direction of the rectangular steel tube concrete column; The straight hoop (2) is formed by bending a complete steel bar back and forth, and a plurality of bending portions (7) are respectively formed on both sides of the straight hoop (2). The bending portions (7) of the two straight hoops (2) of the straight hoop assembly alternately tie the long sides of the rectangular spiral hoop (3).

2. The rectangular steel tube concrete column with built-in composite restraint according to claim 1, characterized in that: The outer side of the circular spiral stirrup (1) and the inner side of the rectangular spiral stirrup (3) are closely attached to each other.

3. The rectangular steel tube concrete column with built-in composite restraint according to claim 1, characterized in that: The rectangular spiral stirrups (3) and the one-hoop assembly, the rectangular spiral stirrups (3) and the circular spiral stirrups (1), and the rectangular spiral stirrups (3) and the fixing steel bars (6) are connected into one piece by spot welding or binding, and then placed into the rectangular steel pipe (5) in an integrated form.

4. The rectangular steel tube concrete column with built-in composite restraint according to claim 1, characterized in that: The rectangular steel pipe (5) is a normal strength or high strength steel pipe, and the circular spiral stirrup (1), the straight stirrup (2) and the rectangular spiral stirrup (3) are made of normal strength or high strength steel bars with a diameter of 6 to 12 mm.

5. The rectangular steel tube concrete column with built-in composite restraint according to claim 1, characterized in that: The distance between the outer side of the rectangular spiral stirrup (3) and the inner wall of the rectangular steel pipe (5) is 25 to 50 mm.

6. The rectangular steel tube concrete column with built-in composite restraint according to claim 1, characterized in that: The fixing steel bars (6) are HPB 300 grade steel bars with a diameter of 6 to 12 mm.

7. The rectangular steel tube concrete column with built-in composite restraint according to claim 1, characterized in that: The core concrete (4) is natural aggregate concrete, recycled aggregate concrete, or recycled block concrete.

8. The construction method of rectangular steel tube concrete column with built-in composite constraints according to any one of claims 1 to 7, characterized in that: The steps include: Step 1: manufacturing and processing the rectangular steel tube (5); Step 2: The circular spiral stirrup (1), the straight hoop (2) and the rectangular spiral stirrup (3) are respectively processed and manufactured according to a preset longitudinal center spacing; the straight hoop (2) is embedded in the rectangular spiral stirrup (3), and the circular spiral stirrup (1) is placed in the cavity; the circular spiral stirrup (1), the straight hoop (2), the rectangular spiral stirrup (3) and the fixing steel bar (6) are connected into one by spot welding or binding, and then placed inside the rectangular steel pipe (5) and fixed, ensuring that the rectangular spiral stirrup (3) coincides with the central axis of the rectangular steel pipe (5), and a distance is left between the outer side of the rectangular spiral stirrup (3) and the inner wall of the rectangular steel pipe (5); Step 3: hoisting and splicing the rectangular steel pipe (5) on site, then pouring concrete from the top of the rectangular steel pipe (5) and fully vibrating it until it is dense.

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