Shape memory alloy reinforced concrete column and post-earthquake self-resetting method thereof

Abstract

The invention discloses a shape memory alloy reinforced concrete column and a post-earthquake self-resetting method thereof.The shape memory alloy reinforced concrete column comprises a concrete bearing platform, a prefabricated concrete section, an outer wrapping reinforced material, a reserved hole channel, a prestressed steel strand, Fe-SMA ribs, FRP ribs, an electrified wire, a power source device and a controller, and longitudinal ribs in the prefabricated concrete section are formed by mixing the FRP ribs and the Fe-SMA ribs; the concrete column and the structure form a whole through the reserved hole channel and grouting, and an unbonded section is arranged in a plastic hinge area at the bottom of the concrete column; the Fe-SMA rib is provided with an electrified wire, a socket is reserved on a precast concrete section, the Fe-SMA rib is excited to generate self-resetting stress by connecting a power supply device and a controller, the controller has two functions of switching on and switching off a power supply and monitoring temperature, and when the temperature reaches the required temperature, the power supply is switched off, so that the magnitude of the applied self-resetting stress is controlled.

Description

Technical Field

[0001] The invention relates to the technical field of structural engineering, and in particular to a shape memory alloy reinforced concrete column and a post-earthquake self-resetting method thereof. Background Art

[0002] With the rapid improvement of economic level and the improvement of urban functions, the concept of developing earthquake-resistant cities has received keen attention from the international community. The traditional concept of earthquake-resistant design of buildings relies on increasing the strength and ductility of the structure itself to resist earthquakes. Although this method can greatly reduce the possibility of overall collapse of the structure under strong earthquakes, the plastic deformation that is difficult to recover after the disaster will lead to high economic costs and technical difficulties in structural maintenance. Studies have found that when the residual displacement angle of the damaged bridge piers after the earthquake exceeds 1% rad, from an economic and technical perspective, the structure has lost its repair value and can only be demolished and rebuilt, causing huge economic losses.

[0003] Prefabricated segmental piers are modular prefabricated by dividing the reinforced concrete pier body into several segments along the longitudinal direction. During construction, the prefabricated segments are mechanically assembled and assembled into a whole through post-tensioned prestressed tendons, concrete post-casting strips and channel grouting. It has the characteristics of small impact on the environment, rapid construction, outstanding self-reset effect, and small residual displacement after earthquake. It is a typical ductile structure. However, its low energy dissipation capacity leads to its large seismic response, which limits its application in high-intensity areas.

[0004] Some scholars have proposed the use of fiber reinforced polymer (FRP) and steel bars mixed reinforcement to reduce residual displacement while ensuring energy dissipation capacity. FRP has the advantages of light weight, high strength, elasticity, fatigue resistance, and corrosion resistance. Mixing FRP with steel bars can provide a stable post-yield stiffness for the structure. On the premise of ensuring that the hysteretic energy dissipation of the structure remains basically unchanged, it can reduce the residual displacement and the discreteness of the residual displacement, thereby improving the repairability of the structure. However, the structure will still produce irreversible residual deformation due to the yielding of the steel bars, and the difference in the elastic-plastic characteristics of the structure will cause a large discreteness of the residual displacement. As well as the complexity and randomness of the earthquake motion, it is difficult to accurately predict the residual displacement of the structure under strong earthquakes, and the structure is still at risk of being irreparable.

[0005] Iron-based Shape Memory Alloys (Fe-SMAs) have the characteristics of high strength, good ductility, strong energy dissipation capacity, fatigue resistance, corrosion resistance, and low price. They can recover deformation through stimulation and can generate certain prestress by imposing constraints. They are expected to be used as energy-absorbing reinforcements that have good energy dissipation effects and are easy to repair after earthquakes.

[0006] In summary, the present invention proposes a concrete structure with low residual deformation after earthquake by hybrid reinforcement of FRP bars and Fe-SMA bars. When an earthquake occurs, the secondary stiffness of the hybrid reinforcement of FRP bars and Fe-SMA bars is used to reduce the residual displacement of the structure for the first time. After the earthquake, the residual deformation is further pulled back by stimulating the Fe-SMA bars to generate self-resetting stress, thereby helping the structure to quickly restore its use function, avoiding the need to rebuild the structure due to excessive residual deformation, and achieving the purpose of toughness earthquake resistance. Summary of the invention

[0007] The present invention proposes a shape memory alloy reinforced concrete column and a post-earthquake self-resetting method thereof, which are particularly suitable for reducing the post-earthquake residual displacement of the structure. The prestressed prefabricated assembled concrete column is reinforced by mixed reinforcement of Fe-SMA bars and FRP bars. When an earthquake occurs, the post-yield stiffness of the structure after the mixed reinforcement is utilized, which not only ensures the structural energy dissipation capacity, but also reduces the residual displacement and its discreteness. After the earthquake, the residual displacement is further pulled back by stimulating Fe-SMA, thereby avoiding the structure having to be demolished due to excessive residual displacement. Compared with traditional structures, the present invention has higher life cycle cost-effectiveness.

[0008] In order to achieve the above object, the present invention adopts the following technical scheme:

[0009] A shape memory alloy reinforced concrete column, comprising a concrete cap, a precast concrete segment, an external reinforcement material, a reserved channel, a prestressed steel strand, a Fe-SMA tendon, a FRP tendon, an energized conductor, a power supply device and a controller;

[0010] The precast concrete segment is installed on the concrete cap, the lower part of the precast concrete segment is provided with an outer reinforcement material, and the middle position and the longitudinal reinforcement position in the precast concrete segment are provided with longitudinal reserved channels;

[0011] The concrete cap and the precast concrete segment are connected by applying prestress after the prestressed steel strand passes through the reserved channel in the middle of the precast concrete segment. Due to the existence of prestress, it can provide self-resetting ability for the structure and reduce the residual displacement after the earthquake;

[0012] The longitudinal reinforcement in the precast concrete segment is a mixed reinforcement of FRP and Fe-SMA, and is grouted through the reserved channel to form a whole with the structure, and a non-bonded section is set in the plastic hinge area at the bottom of the concrete column, which can improve the deformation and energy dissipation capacity of the structure on the one hand, and improve the recovery effect of Fe-SMA on the structure on the other hand;

[0013] The Fe-SMA tendons are equipped with powered wires and reserved sockets on the precast concrete segments. The Fe-SMA tendons are connected to power supply equipment and controllers to stimulate the Fe-SMA tendons to generate self-resetting stress. The controller has two functions: switching power supply and monitoring temperature. When the temperature reaches the required temperature, the power supply is turned off, thereby controlling the magnitude of the applied self-resetting stress.

[0014] Preferably, the precast concrete segment may be a whole segment, or a plurality of segments, and shear keys may be provided on the upper and lower surfaces of the precast concrete segment to improve the shear resistance of the structure.

[0015] Preferably, the concrete cap and precast concrete segment are made of ECC or UHPC material. The ECC material has high crack resistance, and its cracking strain can reach 3%, which is beneficial to the energy consumption and earthquake resistance of the structure. The UHPC has extremely high strength and can reduce structural damage.

[0016] Preferably, the outer reinforcement material is made of steel pipe, FRP cloth, shape memory alloy and the like, and prestress can be applied to further enhance the restraint effect on the concrete segment, because the damage of the prefabricated segment assembly column is often concentrated on the concrete segment in the bottom plastic hinge area.

[0017] Preferably, the reserved channel adopts a metal bellows or a PE pipe, and according to the "Metal Bellows for Prestressed Concrete (JG 225-2007)", the length of the corrugated pipe buried in the concrete cap is not less than 36d, d is the diameter of the longitudinal reinforcement, and the longitudinal reinforcement can be in the form of "parallel reinforcement", at this time, d is the equivalent diameter of the longitudinal reinforcement of equal area.

[0018] Preferably, the FRP bars are CFRP bars, BFRP bars or GFRP bars.

[0019] Preferably, the Fe-SMA tendons have a certain initial pre-deformation, which can be 4%, 6%, or 8% according to the use requirements. Under a pre-strain of 4%, it can generate a pre-stress greater than 200 MPa when heated to 200 degrees Celsius, which can be used to restore the residual displacement of the structure after an earthquake.

[0020] Preferably, since the price of Fe-SMA bars is relatively high compared to ordinary steel bars, and the maximum deformation of concrete often occurs in the plastic hinge zone at the bottom of the column, the Fe-SMA bars can be the entire length, or Fe-SMA bars can be used at the bottom of the concrete column and ordinary steel bars can be used at the top, and they can be connected by steel bar connectors to reduce costs.

[0021] The present invention also provides a post-earthquake self-resetting method for a shape memory alloy reinforced concrete column, comprising the following steps:

[0022] S1: Under earthquake action, the post-yield stiffness of the mixed reinforcement of FRP bars and Fe-SMA bars reduces the residual deformation and reduces the discreteness of the residual deformation. Secondly, the high energy dissipation capacity of Fe-SMA bars dissipates the seismic energy, which not only ensures the energy dissipation capacity of the structure, but also reduces the residual displacement and enhances the repairability of the structure.

[0023] S2: After the earthquake, due to the elastic-plastic characteristics of the structure and the complexity and randomness of the earthquake motion, the structure may still have residual displacement. This part of the residual displacement is controlled by the controller to control the power supply equipment to stimulate the Fe-SMA tendons to generate self-resetting stress, which further reduces the residual displacement, improves the repairability of the structure, and prevents the structure from being demolished.

[0024] The beneficial effects of the present invention are:

[0025] 1. The present invention adopts Fe-SMA tendons to dissipate earthquake energy through their high energy dissipation capacity, reduce earthquake response, and effectively restore post-earthquake residual displacement through their shape memory effect.

[0026] 2. The present invention adopts Fe-SMA and FRP hybrid reinforcement, and utilizes the high strength and elastic characteristics of FRP to provide a stable post-yield stiffness for the structure, which can effectively reduce the post-earthquake residual displacement and its discreteness.

[0027] 3. The present invention adopts prestressed segment prefabricated assembled concrete columns to reduce the pollution caused by construction to the environment, increase the construction speed, and because of the presence of prestressed tendons, it can provide a self-resetting effect.

[0028] 4. The bottom plastic hinge zone segment of the present invention adopts external reinforcement materials to reduce the damage to the structure caused by earthquake action.

[0029] 5. When an earthquake occurs, the present invention firstly utilizes the secondary stiffness of the mixed reinforcement of FRP bars and Fe-SMA bars to reduce the residual displacement of the structure. Secondly, after the earthquake, the residual displacement of the structure is further pulled back by energizing the Fe-SMA bars. The construction is convenient, fast and effective. The structure that has to be demolished due to excessive residual displacement and does not meet the repair conditions can be turned into a repairable structure, reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the structure of a shape memory alloy reinforced concrete column described in Example 1;

[0031] Figure 2 is a schematic cross-sectional view of a shape memory alloy reinforced concrete column described in Example 1;

[0032] Figure 3 is a schematic diagram of reinforcing bars of a shape memory alloy reinforced concrete column described in Example 1;

[0033] Figure 4 Schematic diagram of the post-earthquake self-resetting mechanism of a shape memory alloy reinforced concrete column described in Example 1;

[0034] Figure 5 This is a schematic diagram of the post-earthquake self-reset of a shape memory alloy reinforced concrete column described in Example 1;

[0035] Figure 6 This is a schematic diagram of the structure of a shape memory alloy reinforced concrete column described in Example 2. DETAILED DESCRIPTION

[0036] The following embodiments of the present invention are described in detail with reference to the accompanying drawings to further describe the present invention. The following embodiments are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0037] Example 1: Figure 1-3 As shown, a shape memory alloy reinforced concrete column includes a concrete cap 1, a precast concrete segment 2, an external reinforcement material 3, a reserved channel 4, a prestressed steel strand 5, a Fe-SMA tendon 6, a FRP tendon 7, a power conductor 8, a power supply device 9 and a controller 10;

[0038] The precast concrete segment 2 is installed on the concrete cap 1, and the lower part of the precast concrete segment 2 is provided with an external reinforcement material 3, and the middle position and the longitudinal reinforcement position of the precast concrete segment 2 are provided with a longitudinal reserved channel 4; the concrete cap 1 and the precast concrete segment 2 are selected from ECC materials, and the ECC material has a high crack resistance, and its cracking strain can reach 3%, which is beneficial to the energy consumption and earthquake resistance of the structure. The precast concrete segment 2 can be a whole segment, or a plurality of segments, which can be prefabricated in the factory to reduce environmental pollution on the site and speed up the construction progress. Shear keys can be set on the upper and lower surfaces of the precast concrete segment 2 to improve the shear resistance of the structure. The precast concrete segment 2 is equipped with stirrups 14. The external reinforcement material 3 is made of materials such as steel pipes, FRP cloth, shape memory alloys, etc., and prestress can be applied to further enhance the restraint effect on the concrete segment. This is because the damage of the precast segment assembly column is often concentrated on the concrete segment in the bottom plastic hinge area.

[0039] The concrete cap 1 and the precast concrete segment 2 are connected by applying prestress after the prestressed steel strand 5 passes through the reserved channel 4 in the middle of the precast concrete segment 2. Due to the existence of prestress, it can provide self-resetting ability for the structure and reduce the residual displacement after earthquake; the reserved channel 4 adopts a metal bellows or a PE pipe, and according to the "Metal Bellows for Prestressed Concrete (JG 225-2007)", the length of the corrugated pipe buried in the concrete cap 1 is not less than 36d, d is the diameter of the longitudinal reinforcement, and the longitudinal reinforcement can be in the form of "parallel reinforcement". At this time, d is the equivalent diameter of the longitudinal reinforcement of equal area, and the form of parallel reinforcement is as follows Figure 3 As shown, the reinforcement is formed into a whole through the reserved channel 4 and the grouting material 17.

[0040] The longitudinal reinforcement in the precast concrete segment 2 is a mixed reinforcement of FRP bars 7 and Fe-SMA bars 6, and is grouting through the reserved channel 4 to form a whole with the structure, and a non-bonded section 15 is set in the plastic hinge area at the bottom of the concrete column, which can improve the deformation and energy dissipation capacity of the structure on the one hand, and improve the recovery effect of Fe-SMA on the structure on the other hand; the type of FRP bars 7 used is CFRP bars, BFRP bars or GFRP bars. The Fe-SMA bars 6 have a certain initial pre-deformation, which is selected according to the use requirements. 4%, 6%, 8%. Under the pre-strain of 4%, it is heated to 200 degrees Celsius and can produce a prestress greater than 200MPa, which can be used to restore the post-earthquake residual displacement of the structure. The Fe-SMA bars are the entire length.

[0041] The Fe-SMA tendon 6 is provided with a power-carrying conductor 8, and a socket 11 is reserved on the precast concrete segment 2. The Fe-SMA tendon 6 is connected to a power supply device 9 and a controller 10, and a plug 16 is inserted into the socket 11 to stimulate the Fe-SMA tendon to generate self-resetting stress. The controller 10 has two functions of switching the power supply and monitoring the temperature. When the temperature reaches the required temperature, the power supply is turned off, thereby controlling the magnitude of the applied self-resetting stress.

[0042] like Figure 4-5 As shown, Example 1 also provides a post-earthquake self-reset method for shape memory alloy reinforced concrete columns: under earthquake action, the residual deformation is reduced by the post-yield stiffness of the mixed reinforcement of FRP bars and Fe-SMA bars, and the discreteness of the residual deformation is reduced. Secondly, the seismic energy is dissipated by the high energy dissipation capacity of the Fe-SMA bars, which not only ensures the energy dissipation capacity of the structure, but also reduces the residual displacement and enhances the repairability of the structure. After the earthquake, due to the elastic-plastic characteristics of the structure and the complexity and randomness of the earthquake motion, the structure may still have residual displacement. This part of the residual displacement is controlled by the controller to control the power supply to stimulate the Fe-SMA bars to generate self-reset stress, which further reduces the residual displacement, improves the repairability of the structure, and prevents the structure from being demolished.

[0043] Implementation Case 2: Figure 6 As shown, this embodiment is different from Embodiment 1 in that, since the price of Fe-SMA bars 6 is relatively high compared to ordinary steel bars, and the maximum deformation of concrete often occurs in the plastic hinge area at the bottom of the column, Fe-SMA bars 6 are used at the bottom of the concrete column, and ordinary steel bars 12 are used at the top, and they are connected by steel bar connectors 13 to reduce costs.

[0044] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention.

Claims

1. A shape memory alloy reinforced concrete column, characterized in that: It includes concrete cap, precast concrete segments, external reinforcement materials, reserved channels, prestressed steel strands, Fe-SMA tendons, FRP tendons, power conductors, power supply equipment and controllers; The precast concrete segment is installed on the concrete cap, the lower part of the precast concrete segment is provided with an outer reinforcement material, and the middle position and the longitudinal reinforcement position in the precast concrete segment are provided with longitudinal reserved channels; The concrete cap and the precast concrete segment are connected by applying prestress after the prestressed steel strand passes through the reserved channel in the middle of the precast concrete segment; The longitudinal reinforcement in the precast concrete segment is a mixed reinforcement of FRP and Fe-SMA, and is grouting through the reserved channel to form a whole with the structure, and a non-bonded section is set in the plastic hinge area at the bottom of the concrete column; The Fe-SMA tendons are equipped with powered wires and reserved sockets on the precast concrete segments. The Fe-SMA tendons are connected to power supply equipment and controllers to stimulate the Fe-SMA tendons to generate self-resetting stress. The controller has two functions: switching power supply and monitoring temperature. When the temperature reaches the required temperature, the power supply is turned off, thereby controlling the magnitude of the applied self-resetting stress.

2. The shape memory alloy reinforced concrete column according to claim 1, characterized in that: The precast concrete segment is a whole segment, or a plurality of segments, and shear keys are arranged on the upper and lower surfaces of the precast concrete segment.

3. The shape memory alloy reinforced concrete column according to claim 2, characterized in that: The concrete cap and precast concrete segments are made of ECC or UHPC materials.

4. The shape memory alloy reinforced concrete column according to claim 3, characterized in that: The outer reinforcement material is a steel pipe, FRP cloth or shape memory alloy, and prestress is applied.

5. The shape memory alloy reinforced concrete column according to claim 4, characterized in that: The reserved channel adopts metal corrugated pipe or PE pipe, and according to "Metal Corrugated Pipe for Prestressed Concrete (JG 225-2007)", the length of the corrugated pipe buried in the concrete cap shall not be less than 36d, d is the diameter of the longitudinal reinforcement, and when the longitudinal reinforcement adopts the form of "parallel reinforcement", d is the equivalent diameter of the longitudinal reinforcement of equal area.

6. The shape memory alloy reinforced concrete column according to claim 5, characterized in that: The FRP bars are of the type CFRP bars, BFRP bars or GFRP bars.

7. The shape memory alloy reinforced concrete column according to claim 6, characterized in that: The Fe-SMA tendons have an initial pre-deformation, which is selected from 4%, 6% and 8% according to use requirements.

8. The shape memory alloy reinforced concrete column according to claim 7, characterized in that: The Fe-SMA bars are throughout the entire length, or the bottom of the concrete column uses Fe-SMA bars and the upper part uses ordinary steel bars, which are connected by steel bar connectors.

9. A method for self-resetting a shape memory alloy reinforced concrete column after an earthquake according to claim 1, 2, 3, 4, 5, 6, 7 or 8, characterized in that: The following steps are involved: S1: Under earthquake action, the post-yield stiffness of the mixed reinforcement of FRP bars and Fe-SMA bars reduces the residual deformation and reduces the discreteness of the residual deformation. Secondly, the high energy dissipation capacity of Fe-SMA bars dissipates the seismic energy, which not only ensures the energy dissipation capacity of the structure, but also reduces the residual displacement and enhances the repairability of the structure. S2: After the earthquake, due to the elastic-plastic characteristics of the structure and the complexity and randomness of the earthquake motion, the structure may still have residual displacement. This part of the residual displacement is controlled by the controller to control the power supply equipment to stimulate the Fe-SMA tendons to generate self-resetting stress, which further reduces the residual displacement, improves the repairability of the structure, and prevents the structure from being demolished.

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