A method for multiple activation of SMA in SMA reinforced steel beams

Abstract

The present invention discloses a method for activating SMA multiple times in an SMA reinforced steel beam, belonging to the field of construction engineering technology. The present invention first installs a strain gauge at the bottom of the span of the reinforced steel beam, and installs a heating device on the SMA; applies a load to the reinforced steel beam, and measures the change value of the strain gauge at the bottom of the loaded steel beam through the above steps for the loading of the reinforced steel beam; activates the SMA by heating the obtained strain gauge value through the heating device; and repeats the above steps to achieve multiple activations. The method of the present invention utilizes the characteristic that SMA can be excited multiple times to generate restoring stress, performs real-time monitoring and evaluation of the structure throughout its life cycle, and repairs it in time to avoid the structure being in a "sub-healthy" working state for a long time.

Description

Technical Field

[0001] The invention belongs to the technical field of construction engineering, and particularly relates to a method for activating SMA multiple times in an SMA reinforced steel beam. Background Art

[0002] Shape memory alloy (SMA) is an intelligent material that can remember its original shape, so that it can be deformed under stress at room temperature, and when the external force is removed and heated, it can recover to its shape and volume before deformation when the temperature reaches a certain value. This property is called shape memory effect. By using this property, the pre-tensioned SMA is fixed on the reinforced component, and then the SMA is activated by a heating device to generate recovery stress, so that prestress can be applied to the reinforced component, thereby improving the bearing capacity of the component and inhibiting the development of cracks. Therefore, shape memory alloy (SMA) has a wide range of application prospects in the field of structural reinforcement. The required SMA cross-sectional area of ​​the reinforced component can be calculated from the required bearing capacity of the reinforced component and the recovery stress generated by the SMA under a certain pre-tensioning level and activation temperature. However, during the entire life cycle, the reinforced structure may experience changes in usage requirements or design standards, resulting in further increases in the requirements for structural bearing capacity. At the same time, SMA material property tests show that long-term fatigue loads will affect the recovery stress of SMA. After two million loadings, the SMA recovery stress decreased by 12~15%. Therefore, for reinforced components, in their subsequent service process, due to the decrease or insufficiency of SMA prestress, their bearing capacity may no longer meet the requirements of current normal use, and they may face the need for reinforcement again.

[0003] In the patent with publication number CN114263126A, a method for intelligently controlling the crack threshold of a concrete beam by using the strain of an SMA wire or reinforcement is disclosed. The method determines whether to activate the SMA wire or reinforcement electric heating device to heat the SMA wire or reinforcement by electric heating, thereby generating restoring stress and reducing the crack width of the concrete beam. The patent method only determines the first excitation of the SMA and does not involve multiple excitations of the SMA. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a method for multiple activation of SMA in SMA reinforced steel beams, which utilizes the characteristic that SMA can be repeatedly excited to generate recovery stress, performs real-time monitoring and evaluation of the structure throughout its life cycle, and repairs it in time to avoid the structure being in a "sub-healthy" working state for a long time.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for activating SMA multiple times in an SMA reinforced steel beam, comprising the following steps:

[0007] S1. Install the strain gauge at the bottom of the reinforced steel beam span and install the heating device on the SMA.

[0008] S2, apply load to the reinforced steel beam;

[0009] S3, through step S2, the loading condition of the reinforced steel beam is measured to obtain the change value of the strain gauge at the bottom of the steel beam after loading;

[0010] S4, according to the change of the value of the strain gauge obtained in S3, the SMA is activated by heating through a heating device;

[0011] S5. Repeat steps S2 to S4.

[0012] Further, in step S3, by n The value of the strain gauge at the bottom of the steel beam after adding the additional load is e s,n , get the n Activation temperature at the first activation T n = f ( e s,n , T n-1 , e 0), where T n-1 It is n - Activation temperature at 1st activation, e 0 is the SMA pre-tension strain.

[0013] further, T n and e s,n The relationship between is obtained by the following formula:

[0014] The value of the strain gauge passing through the bottom of the steel beam is e s,n , and obtain the additional recovery stress Δ required by SMA s r,n , used to offset additional loads P The resulting steel beam strain e s,n

[0015] (1.1)

[0016] in, E SMA , E s are the elastic moduli of SMA and steel, A SMA ,A s are the cross-sectional areas of SMA and steel beam, h is the height of the steel beam, d is the width of the steel beam flange, I s is the moment of inertia of the steel beam section;

[0017] The additional recovery stress Δ required for SMA obtained by formula (1.1) s r,n , calculate the first n The recovery stress that SMA should reach after the first activation s r,n

[0018] (1.2)

[0019] in s r,n-1 For the n −1 activation, the recovery stress of SMA is calculated according to equations (1.1), (1.2), T n = f ( s r,n, T n−1 , e 0), we get T n = f ( e s,n , T n−1 , e 0).

[0020] Further, in n Activation temperature when SMA is activated for the first time T n The recovery stress generated by the SMA is not less than the recovery stress that the SMA should achieve. s r,n .

[0021] Further, in step S2, a fatigue load is applied to the reinforced steel beam, and the value of the strain gauge at the bottom of the steel beam after the fatigue load is measured. e s , according to a predetermined threshold C 1； Determine and reactivate SMA when the measured bottom strain of the mid-span steel beam is When the SMA heating device is started to reactivate the SMA, the loss of SMA prestress caused by fatigue load is restored; when the strain at the bottom of the mid-span of the steel beam is The heating device is not started.

[0022] Furthermore, the threshold C 1 is the strain gauge reading corresponding to the specified upper limit of SMA recovery stress loss, specifically:

[0023] (1.3)

[0024] in, E SMA , E s are the elastic moduli of SMA and steel, A SMA , A s are the cross-sectional areas of SMA and steel beam, h is the height of the steel beam, d is the width of the steel beam flange, I s is the moment of inertia of the steel beam section, s r,0 is the recovery stress of SMA when first activated, oh is the allowed SMA recovery stress loss rate.

[0025] Further, the activation temperature when the SMA is activated again is the same as the activation temperature when it is activated for the first time.

[0026] Furthermore, the SMA in the reinforced steel beam involved in step S1 has been activated and has recovery stress, and the reinforced steel beam has been subjected to a certain external load.

[0027] Furthermore, the connection between the strain gauge and the heating device involved in step S1 is permanent, and the strain gauge and the heating device are connected to a computer control terminal to perform real-time monitoring and evaluation throughout the life cycle of the structure.

[0028] The beneficial effects of the present invention are:

[0029] (1) Intelligence: The shape memory alloy (SMA) in the present invention is an intelligent material. When the prestress is lost, it can be powered on to quickly replenish the prestress. Combining this technology with structural monitoring and evaluation technology can achieve real-time repair of the structure, avoid the structure being in a "sub-healthy" working state for a long time, and greatly save labor costs and construction time, and improve the efficiency of secondary repair.

[0030] (2) High applicability. The present invention is not limited by space when reinforcing the structure on the basis of the original reinforcement. The structure can be reinforced again by using only the original reinforcement device.

[0031] (3) Wide application: The present invention can be applied to the repair of concrete beams, steel beams and other types of components reinforced by SMA.

[0032] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art may be taught from the practice of the present invention. The objectives and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0034] Figure 1 This is a flow chart of Embodiment 1 of the present invention;

[0035] Figure 2 This is a flow chart of Example 2 of the present invention. DETAILED DESCRIPTION

[0036] In the material property test of SMA, the SMA that has already generated recovery stress is heated again by an electric heating device. The results show that if the shape memory effect of SMA still remains after the first activation, then under the secondary activation at a higher activation temperature, the residual ε-type martensite will transform into γ-type austenite again, thereby generating higher recovery stress. The property of SMA that can be repeatedly excited provides the feasibility of increasing the prestress level of the structure multiple times during its life cycle.

[0037] Example 1, a method for multiple excitation of SMA in SMA reinforced steel beams of the present invention, scenario 1 is to improve the bearing capacity of the reinforced component. Figure 1 As shown, the specific steps are as follows:

[0038] S1. Place the strain gauge close to the bottom of the reinforced steel beam span and the thermocouple close to the SMA.

[0039] S2. Apply additional load to the reinforced steel beam P .

[0040] S3, measured value of the strain gauge at the bottom of the steel beam e s,n .

[0041] S4. Obtain the additional recovery stress Δ required for SMA s r,n .

[0042] S5. Obtain the recovery stress that SMA should reach after reactivation s r,n .

[0043] S6. Start the SMA electric heating device to reactivate the SMA, generate a higher recovery stress, and restore the normal use of the steel beam.

[0044] S7. Repeat steps S2 to S6.

[0045] Furthermore, the SMA in the reinforced steel beam involved in step S1 has been activated and has recovery stress, and the reinforced steel beam has been subjected to a certain external load.

[0046] Furthermore, the connection between the strain gauge and the thermocouple involved in step S1 and the structure is permanent and cannot be removed, and certain protective measures need to be taken. The strain gauge and the thermocouple are connected to a computer control terminal to perform real-time monitoring and evaluation throughout the life cycle of the structure.

[0047] Further, the additional recovery stress Δ required for the SMA obtained in step S4 s r,n To offset additional loads P The resulting steel beam strain e s,n , specifically:

[0048] (1.1)

[0049] In the formula, E SMA , E s are the elastic moduli of SMA and steel, A SMA , A s are the cross-sectional areas of SMA and steel beam, h is the height of the steel beam, d is the width of the steel beam flange, I s is the moment of inertia of the steel beam section.

[0050] Further, in step S5, the n The recovery stress that SMA should reach after the first activation s r,n Specifically:

[0051] (1.2)

[0052] In the formula, s r,n-1 For the n −1 Recovery stress of SMA after activation.

[0053] Further, the step S6 involves nThe activation temperature when activating the SMA for the first time should satisfy the following requirement: the recovery stress generated by the SMA at this activation temperature is not lower than the recovery stress that the SMA should reach in step S5. s r,n . Establish the relationship between the bottom strain of the steel beam and the reactivation temperature; according to equations (1.1), (1.2), T n = f ( s r,n, T n−1 , e 0), we get T n = f ( e s,n , T n−1 , e 0), where T n It is n The excitation temperature at the first activation, T n−1 It is n −1 activation temperature, e s,n It is n The bottom strain of the steel beam after the load increase is: e 0 is the SMA pre-tension strain.

[0054] Example 2, a method for multiple excitation of SMA in SMA reinforced steel beams of the present invention, scenario 2: the prestressing level of SMA decreases after fatigue load, the flow chart is as follows Figure 2 As shown, the specific steps are as follows:

[0055] S1. Place the strain gauge close to the bottom of the reinforced steel beam span and the thermocouple close to the SMA.

[0056] S2. Apply fatigue load to the reinforced steel beam.

[0057] S3, measured value of the strain gauge at the bottom of the steel beam after fatigue load e s .

[0058] S4. Determine the threshold C 1.

[0059] S5. Determine and reactivate SMA.

[0060] When the measured steel beam bottom strain When the SMA is powered on and heated, the SMA is activated again to restore the loss of SMA prestress caused by fatigue load. When the SMA is powered on, the heating device is not started to reactivate the SMA.

[0061] S6 repeats steps S2 to S5.

[0062] Furthermore, the SMA in the reinforced steel beam involved in step S1 has been activated and has recovery stress.

[0063] Furthermore, the connection between the strain gauge and the thermocouple involved in step S1 and the structure is permanent and cannot be removed, and certain protective measures need to be taken. The strain gauge and the thermocouple are connected to a computer control terminal to perform real-time monitoring and evaluation throughout the life cycle of the structure.

[0064] Furthermore, the threshold value in step S4 C 1 Refers to the strain gauge reading corresponding to the specified upper limit of SMA recovery stress loss, specifically:

[0065] (1.3)

[0066] In the formula, E SMA , E s are the elastic moduli of SMA and steel, A SMA , A s are the cross-sectional areas of SMA and steel beam, h is the height of the steel beam, d is the width of the steel beam flange, I s is the moment of inertia of the steel beam section, s r,0 is the recovery stress of SMA when first activated, oh is the allowed SMA recovery stress loss rate.

[0067] Further, the activation temperature when reactivating the SMA in step S5 is the same as the activation temperature when first activated, so as to completely recover the SMA recovery stress lost due to fatigue load.

[0068] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for multiple activation of SMA in SMA reinforced steel beams, characterized in that: The following steps are involved: S1. Install the strain gauge at the bottom of the reinforced steel beam span and install the heating device on the SMA. S2, apply load to the reinforced steel beam; S3, through step S2, the loading condition of the reinforced steel beam is measured to obtain the change value of the strain gauge at the bottom of the steel beam after loading; S4, according to the change of the value of the strain gauge obtained in S3, the SMA is activated by heating through a heating device; S5, repeat steps S2 to S4; In step S3, by n The value of the strain gauge at the bottom of the steel beam after adding the additional load is ε s,n , get the n Activation temperature at the first activation T n = f ( ε s,n , T n−1 , ε 0), where T n-1 It is n −1 activation temperature, ε 0 is the SMA pre-tension strain; T n and ε s,n The relationship between is obtained by the following formula: The value of the strain gauge passing through the bottom of the steel beam is ε s,n , and obtain the additional recovery stress Δ required by SMA σ r,n , used to offset additional loads P The resulting steel beam strain ε s,n （1.1） in, E SMA , E s are the elastic moduli of SMA and steel, A SMA , A s are the cross-sectional areas of SMA and steel beam, respectively, h is the height of the steel beam, d is the width of the steel beam flange, I s is the moment of inertia of the steel beam section; The additional recovery stress Δ required for SMA obtained by formula (1.1) σ r,n , calculate the first n The recovery stress that SMA should reach after the first activation σ r,n （1.2） in σ r,n-1 For the n -The recovery stress of SMA after the first activation is calculated according to equations (1.1), (1.2), T n = f ( σ r,n, T n-1 , ε 0), we get T n = f ( ε s,n , T n-1 , ε 0).

2. A method for multiple activation of SMA in SMA reinforced steel beam according to claim 1, characterized in that: In the n Activation temperature when SMA is activated for the first time T n The recovery stress generated by the SMA is not less than the recovery stress that the SMA should achieve. σ r,n .

3. The method for multiple activation of SMA in SMA reinforced steel beam according to claim 1, characterized in that: In step S2, a fatigue load is applied to the reinforced steel beam, and the value of the strain gauge at the bottom of the steel beam after the fatigue load is measured. ε s , according to a predetermined threshold C 1； Determine and reactivate SMA when the measured bottom strain of the mid-span steel beam is When the SMA is heated, the SMA heating device is started to reactivate the SMA to restore the loss of SMA prestress caused by fatigue load; When the measured steel beam bottom strain The heating device is not started.

4. A method for multiple activation of SMA in SMA reinforced steel beam according to claim 3, characterized in that: The threshold C 1 is the strain gauge reading corresponding to the specified upper limit of SMA recovery stress loss, specifically: （1.3） in, E SMA , E s are the elastic moduli of SMA and steel, A SMA , A s are the cross-sectional areas of SMA and steel beam, respectively, h is the height of the steel beam, d is the width of the steel beam flange, I s is the moment of inertia of the steel beam section, σ r，0 is the recovery stress of SMA when first activated, ω is the allowed SMA recovery stress loss rate.

5. A method for multiple activation of SMA in SMA reinforced steel beam according to claim 4, characterized in that: The activation temperature when the SMA is activated again is the same as the activation temperature when it was activated for the first time.

6. A method for multiple activation of SMA in an SMA reinforced steel beam according to any one of claims 1 to 5, characterized in that: The SMA in the reinforced steel beam involved in step S1 has been activated and has recovery stress, and the reinforced steel beam has been subjected to a certain external load.

7. A method for multiple activation of SMA in SMA reinforced steel beams according to claim 6, characterized in that: The connection between the strain gauge and the heating device involved in step S1 is permanent, and the strain gauge and the heating device are connected to a computer control terminal to perform real-time monitoring and evaluation throughout the life cycle of the structure.

Images