A variable cross-section double-tube SMA-ECC concrete column

Abstract

The present invention relates to a variable cross-section double-tube SMA-ECC concrete column, which comprises an SMA outer tube, an SMA inner tube and an ECC filling layer; the SMA inner tube is a variable-diameter tube with a larger upper end and a smaller lower end, the SMA inner tube is sleeved inside the SMA outer tube at intervals, and the ECC filling layer is filled in the gap between the SMA outer tube and the SMA inner tube. The difference between the present invention and the traditional double-steel-tube concrete column lies in: on the one hand, the use of SMA and ECC materials enhances the ductile deformation and energy dissipation capacity of the column body and endows it with the ability of self-resetting after earthquake, reducing the influence of residual deformation on the used structure; on the other hand, by adjusting the design parameters of the variable cross-section inner tube, the position and length of the plastic hinge area of the column body can be optimized, further enhancing the energy dissipation and self-resetting ability of the structural column. This product not only inherits the advantages of the existing steel-tube concrete column, but also is superior to the existing steel-tube concrete column, having excellent mechanical properties and self-resetting ability, and having good engineering application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of construction engineering, and particularly relates to a variable cross-section double-tube SMA-ECC concrete column. Background Art

[0002] Concrete-filled steel tube is a composite member formed by pouring concrete into a steel tube. Compared with the unidirectional compression of traditional reinforced concrete, concrete-filled steel tube has good plastic properties. Although concrete is a brittle material, under the action of axial compressive stress, a confinement effect is generated, and the concrete in the steel tube is in a state of triaxial compression, having a high bearing capacity. In addition, the stability of the steel tube is also enhanced, giving full play to the advantages of concrete and steel. It can improve its bearing capacity, enhance its ductility, and reduce the cross-sectional area, thereby reducing the consumption of steel and concrete. Therefore, it is widely used in the column structures of bridges, factories, and buildings. Research shows that the end of a concrete-filled steel tube column is prone to plastic buckling under the action of seismic force, forming "elephant foot" buckling, and the height is reduced due to the damage of the internal concrete, which exacerbates the damage of non-structural components and leads to unstable hysteretic bearing capacity of the structure.

[0003] How to further optimize and solve the above problems based on concrete-filled steel tube components has been a problem studied by the academic community. With the vigorous development of the material science and the maturity of processing technology, it has become possible to optimize concrete-filled steel tube by using new materials in the field of civil engineering. There are several solutions to this problem: using high-performance materials to replace ordinary steel and concrete: In recent years, some scholars have used fiber-reinforced composite materials to replace ordinary steel or cover the outer surface of the steel tube, and used high-performance concrete to replace ordinary concrete materials; optimizing the structural form of components: adopting structural forms such as hollow sandwich and composite columns, and these methods have achieved good results.

[0004] In recent years, domestic and foreign researchers have gradually become enthusiastic about the research on self-centering structural components. The purpose of the self-centering function research is to enable the building structure to automatically reduce the residual deformation after experiencing a strong earthquake, thereby reducing the strong earthquake disaster. Shape memory alloy (SMA) materials have unique shape memory effects and superelastic properties, and have the ability to automatically recover their initial shape and strain after experiencing large strains. SMA materials have attracted extensive attention from researchers in the field of civil engineering.

[0005] With the improvement of production technology and the perfection of processes, the processing means of SMA have gradually matured, and the cost has been continuously reduced. It can be processed into various forms of components, such as wire, rib, bar, stranded wire, etc. The basic components of SMA are important parts that make up SMA components or structural systems, and usually determine the functionality, safety and economy of the structure. A large number of studies have shown that SMA materials are uniformly stressed, showing typical flag-shaped hysteretic characteristics, having excellent self-centering characteristics, stable hysteretic performance and good energy dissipation capacity. Some scholars have used SMA ribs to replace ordinary steel bars at beam-column joints, showing outstanding self-centering performance and seismic bearing capacity. Since the surface of the used SMA ribs is smooth and the bonding force in concrete is low, the superior performance of SMA materials cannot be fully exerted. Some scholars have tried to process ribbed SMA ribs, which greatly improve their performance. Summary of the Invention

[0006] Based on the hollow sandwich double steel pipe concrete column, using SMA materials and ECC materials, and adopting the structural form of variable cross-section inner pipe, the present invention proposes a new type of self-centering variable cross-section double pipe SMA-ECC concrete column, which effectively solves the problem of poor seismic performance of existing steel pipe concrete columns and improves and optimizes the mechanical seismic performance of steel pipe concrete columns.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a variable cross-section double pipe SMA-ECC concrete column, including an SMA outer pipe, an SMA inner pipe and an ECC filling layer; the SMA inner pipe is a variable diameter pipe with a large upper end and a small lower end, and the SMA inner pipe is spacedly sleeved inside the SMA outer pipe in the shape of a large upper end and a small lower end, and the ECC filling layer is filled in the gap between the SMA outer pipe and the SMA inner pipe.

[0008] Further, the SMA inner pipe is a one-piece unidirectional variable diameter pipe, and the SMA inner pipe gradually becomes smaller from one end to the other end.

[0009] Further, the SMA inner pipe is a two-piece structure, which includes an upper section pipe and a lower section pipe. Both the upper section pipe and the lower section pipe are uniformly variable diameter pipes with a large end and a small end. The large ends of the upper section pipe and the lower section pipe are butted together and are correspondingly spacedly sleeved inside the SMA outer pipe.

[0010] Further, the large end diameters of the upper section pipe and the lower section pipe are equal.

[0011] Further, the SMA inner pipe is a three-piece structure, which includes an upper section pipe, a middle section pipe and a lower section pipe. The upper section pipe and the lower section pipe are both uniformly variable diameter pipes with a large end and a small end, and the middle section pipe is a columnar pipe, and the upper section pipe and the lower section pipe are butted at both ends of the middle section pipe.

[0012] Furthermore, the large ends of the upper pipe section and the lower pipe section are matingly docked with both ends of the middle pipe section.

[0013] Furthermore, a cover plate is provided at the upper end of the SMA inner pipe.

[0014] The beneficial effects of the above technical solution are as follows: By adjusting the cross-sectional size of the SMA inner pipe, the thickness of the concrete at the column end is increased, which is equivalent to applying an effective lateral restraint to the dangerous area at the middle or bottom column end of the SMA double-pipe concrete column, controlling the local buckling of the steel pipe, improving the mechanical properties of the steel pipe, and having the following beneficial effects.

[0015] 1. The construction of this product is simple and the construction period is shortened. The pipe body is equivalent to formwork, longitudinal bars and stirrups, and the steel pipe itself can be used as a load-bearing skeleton during the construction stage, saving scaffolding. The economic effect is prominent, achieving the purpose of saving materials and reducing the floor area of the structure. At the same time, the reduction of material consumption greatly reduces the self-weight of the structure, has good ductility and good seismic performance.

[0016] 2. The present invention uses SMA materials. On the basis of the characteristics of concrete-filled steel tubular columns, not only does the column have higher bearing capacity and stronger ductility, but also the self-centering effect is increased, which is beneficial for post-earthquake recovery, overcomes some defects of the above-mentioned concrete-filled steel tubular columns, and has more excellent mechanical properties.

[0017] 3. Using ECC materials can better cooperate with SMA materials, and has good ductility, high energy dissipation capacity and self-centering performance.

[0018] 4. This product improves the problem that plastic failure is likely to occur at the column end of components. Taking the one-way one-section SMA double-pipe variable-section inner pipe concrete column as an example, the size of the inner pipe is appropriately reduced at the lower part where plastic failure occurs, and the thickness of the ECC material is increased to prevent local buckling at this part.

[0019] Generally speaking, the difference between the double steel pipe concrete column and the SMA double-pipe ECC column of the present invention is that the use of SMA and ECC materials increases stronger deformation ability, enhanced ductility and self-centering ability. Due to the residual deformation of the column body under cyclic seismic action, after the earthquake, the use of SMA can restore to the original state after the earthquake through the self-centering performance of the inner and outer pipes of SMA, reducing the influence of the residual deformation on the structure, and the bearing capacity is also improved. This product inherits the advantages of the existing concrete-filled steel tubular columns. On the other hand, this product is superior to the existing concrete-filled steel tubular columns, has excellent mechanical properties and good engineering application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a sectional view of the present invention;

[0021] Figure 2This is a schematic diagram of a one-way reducer structure;

[0022] Figure 3 It is a schematic diagram of the two-stage one-way reducer structure;

[0023] Figure 4 It is a schematic diagram of the three-section one-way reducer structure;

[0024] Figure 5 Schematic diagram of the layout position of the cover.

[0025] Figure numerals: 1 is an SMA outer tube, 2 is an SMA inner tube, 21 is a one-stage one-way reducer, 22 is a two-stage structure, 221 is an upper tube one, 222 is a lower tube one, 23 is a three-stage structure, 231 is a middle tube, 232 is an upper tube two, 233 is a lower tube two, 3 is an ECC filling layer, and 4 is a cover plate. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0027] Example 1. This example aims to provide a variable-section double-tube SMA-ECC concrete column, which is mainly used for steel tube concrete components. The ends of steel tube concrete columns are prone to plastic buckling under the action of seismic forces, forming "elephant leg" buckling, and the height is reduced due to the destruction of the internal concrete, thereby aggravating the damage to non-structural components and causing unstable hysteretic bearing capacity of the structure. According to research, under the action of an earthquake, the column body is subjected to reciprocating action and swings, and local buckling is prone to occur at the column end, affecting normal force. This example changes the cross-sectional area of the inner tube so that the end force-bearing area is larger and the stress is reduced, which is equivalent to enhancing the stability of the column.

[0028] At present, components with constant cross-sectional dimensions are used in engineering projects. Although the use of constant cross-sectional dimensions is more convenient for construction and installation, it is often wasteful. In today's era of increasingly mature processing technology, it is necessary to use advanced technology in exchange for low costs. According to actual conditions, the weak areas of the columns are different. Small-sized inner tubes are set in the weak areas, and the thickness of the ECC material here is thickened to prevent local buckling. The weak parts of steel tube concrete columns are usually the column ends, which can cause local and overall buckling failures, affecting normal stress. In response to this situation, the present invention adopts the form of a variable cross-sectional inner tube, appropriately reducing the cross-sectional dimensions of the inner tube in the weak area of the column, increasing the thickness of the ECC material, improving the stress concentration phenomenon here, and preventing damage.

[0029] In this embodiment, the cross-sectional dimensions of the SMA inner tube are adjusted to increase the thickness of the concrete at the column end, which is equivalent to applying effective lateral constraints to the dangerous areas in the middle or bottom column end of the SMA double-tube concrete column, thereby controlling the local buckling of the steel tube and improving the mechanical properties of the steel tube.

[0030] The differences between double concrete-filled steel tubes and SMA double-tube ECC columns lie in that the use of SMA and ECC materials increases stronger deformation capacity, enhanced ductility, and self-centering ability. Since the columns will have residual deformation after seismic reciprocating actions, after using SMA, through the self-centering performance of the inner and outer SMA tubes, they can return to their original state after the earthquake, reducing the influence of residual deformation on the structure, and the bearing capacity is also improved; SMA has unique shape memory effect, superelasticity, high damping, and electrical resistance characteristics. The recoverable strain of superelastic SMA can be as high as 6%-8%, the yield stress reaches 400-600 MPa, its ultimate strength exceeds 1000 Mpa, and the ultimate deformation is as high as 20%, far higher than that of general metals. The superelastic characteristics endow SMA with large hysteretic energy dissipation and self-centering ability. Utilizing these characteristics, passive control of structural vibration can be achieved, such as being used to develop dampers, energy-dissipating braces, composite isolation bearings, energy-dissipating coupling beams, bridge displacement limiters, bridge cable shock absorbers, as well as energy-dissipating keys, energy-dissipating plates, fasteners, and bolts in steel frame energy-dissipating joints.

[0031] In terms of structure, as Figures 1-4 shown in [reference], a variable cross-section double-tube SMA-ECC concrete column includes an outer SMA tube 1, an inner SMA tube 2, and an ECC filling layer 3; the ECC filling layer 3 fills the gap between the outer SMA tube 1 and the inner SMA tube 2.

[0032] In a specific implementation structure, as Figure 2 shown in [reference], the inner SMA tube 2 is a stepped tube with a larger upper end and a smaller lower end, and the wall thickness of the stepped tube is uniform, that is, its inner cavity changes with the surface shape. The inner SMA tube 2 is sleeved inside the outer SMA tube 1 at intervals in the form of a larger upper end and a smaller lower end; the inner SMA tube 2 is a one-piece unidirectional stepped tube 21, and the inner SMA tube 2 gradually becomes smaller from one end to the other end. The inner tube of the one-piece SMA double-tube variable cross-section inner tube concrete column is in the form of unidirectional variable cross-section, with the largest cross-sectional size at the top and the smallest at the bottom; the one-piece SMA double-tube variable cross-section inner tube concrete column strengthens the lower column end, which is equivalent to increasing the lateral restraint at the bottom column end and controlling local buckling here.

[0033] As Figure 3 shown in [reference], the inner SMA tube is of a two-piece structure 22, which includes an upper tube one 221 and a lower tube one 222. Both the upper tube one 221 and the lower tube one 222 are uniformly stepped tubes with a larger end and a smaller end. The large ends of the upper tube one 221 and the lower tube one 222 are butted together and are sleeved inside the outer SMA tube 1 at corresponding intervals. The diameters of the large ends of the upper tube one 221 and the lower tube one 222 are equal. The cross-sectional sizes of the inner SMA tube of the two-piece SMA double-tube variable cross-section inner tube concrete column are the smallest at both ends and gradually increase along the column length direction until reaching the maximum at the middle.

[0034] like Figure 4 As shown in the figure, the SMA inner tube is a three-section structure 23, which includes an upper tube 232, a middle tube 231 and a lower tube 233. The upper tube 232 and the lower tube 233 are both uniformly variable tubes with one end large and the other end small. The middle tube 231 is a columnar tube, and the upper tube 232 and the lower tube 233 are connected to the two ends of the middle tube 231. The large end diameters of the upper tube 2 and the lower tube 2 are equal to the diameter of the middle tube.

[0035] The inner tube of the three-section SMA double-tube variable-section inner tube concrete column is divided into three sections from top to bottom: the first and third sections are the smallest at both ends, and gradually become larger as they extend to the middle. The two-section and three-section types have strengthened the upper and lower column ends, which is equivalent to increasing the lateral constraints of the dangerous areas of the upper and lower column ends, which is one step closer than the one-section type. If the column is long, a three-section form can be adopted, and the cross-sectional size in the middle part remains constant. The specific length of each section can be set according to usage. The same construction method as the steel tube concrete column is adopted. First, the inner and outer tubes are prefabricated in the factory, and then the ECC material in the inner and outer tube interlayer is poured, and finally the components are formed and maintained.

[0036] This invention utilizes a self-resetting, variable-section, double-tube SMA-ECC concrete column with a hollow sandwich cross-section. The SMA, made of the most common nickel-titanium alloy, primarily comprises an SMA outer tube, an SMA variable-section inner tube, and ECC material within the inner and outer tubes. To effectively coordinate with the SMA material and achieve excellent practical results, it is advantageous to use ECC material instead of ordinary concrete within the tubes. ECC has garnered widespread attention in the engineering field in recent years. As an alternative to ordinary concrete, ECC exhibits significant strain hardening properties, ultra-high tensile and compressive toughness, excellent durability, good deformation capacity, and energy dissipation capabilities. Combining SMA and ECC can unleash superior performance. This embodiment differs from conventional double-tube concrete columns in that, on the one hand, the use of SMA and ECC enhances the column's ductile deformation and energy dissipation capacity, providing post-earthquake self-resetting capabilities and reducing the impact of residual deformation on the structure. On the other hand, by adjusting the design parameters of the variable-section inner tube, the location and length of the column's plastic hinge zone can be optimized, further enhancing the column's energy dissipation and self-resetting capabilities.

[0037] Example 2: This example is basically the same as Example 1, except that a cover plate 4 is provided at the upper end of the SMA inner tube.

[0038] This embodiment uses Figure 5 For example, in Figure 2 A cover plate 4 is added on the basis of Figure 3 and Figure 4Similarly, it can be obtained that a cover plate 4 is provided at the upper end of the SMA inner tube. The cover plate structure is used to seal the upper end opening of the SMA inner tube in a contact manner, which does not affect the mechanical properties of the tube body of the SMA inner tube, and the SMA inner tube is placed inside the SMA outer tube.

Claims

1. A variable cross-section double-tube SMA-ECC concrete column, characterized in that: It includes an SMA outer tube, an SMA inner tube and an ECC filling layer; the ECC filling layer is filled in the gap between the SMA outer tube and the SMA inner tube; the SMA inner tube is of a two-section structure, which includes an upper section tube one and a lower section tube one, both the upper section tube one and the lower section tube one are uniformly tapered tubes with one end large and the other end small, the large ends of the upper section tube one and the lower section tube one are butted together and are correspondingly and spacedly sleeved inside the SMA outer tube; or the SMA inner tube is of a three-section structure, which includes an upper section tube two, a middle section tube and a lower section tube two, wherein both the upper section tube two and the lower section tube two are uniformly tapered tubes with one end large and the other end small, the middle section tube is a columnar tube, and the large ends of the upper section tube two and the lower section tube two are butted at both ends of the middle section tube; the diameters of the large ends of the upper section tube two and the lower section tube two are equal to the diameter of the middle section tube.

2. The variable cross-section double-tube SMA-ECC concrete column according to claim 1, characterized in that: The upper section tube one and the lower section tube one are of a symmetric structure.

3. The variable cross-section double-tube SMA-ECC concrete column according to any one of claims 1-2, characterized in that: A cover plate is arranged at the upper end of the SMA inner tube.

Images