Integrated self-aware and self-stimulating prestressed concrete intelligent beam construction method

Abstract

The application discloses a kind of integrated self-sensing and self-excitation prestressed concrete intelligent beam construction method, belong to bridge prestressed beam construction and monitoring technical field.The present application is to solve the technical problems that the existing prestressed beam construction lacks real-time accurate monitoring, and the prestress loss during service period cannot be actively compensated.The scheme divides the excitation section and lays the Fe-SMA steel strand with built-in electric heating wire and stress FBG sensor, converts the real-time stress value using temperature correction, establishes the basic prestress after concrete curing through pre-tensioning, heats to 85~90% of the design stress value at full power with the upper limit of the phase change temperature during the construction period, and then stabilizes and fine-tunes to the design value through residual heat and short-time pulse, and if the loss exceeds the threshold during the service period, it will be heated and excited again to compensate.The application is used to realize real-time sensing, accurate application and dynamic compensation during the whole process of prestressed beam construction, and improve the long-term service safety and durability.

Description

Technical Field

[0001] This invention relates to the field of prestressed concrete beam construction technology. More specifically, this invention relates to an integrated self-sensing and self-excitation intelligent prestressed concrete beam construction method. Background Technology

[0002] Prestressed concrete beams, with their strong crack resistance, large stiffness, and excellent span capacity, are widely used in bridge engineering. Currently, the commonly used prestressing application method in prestressed beam construction mainly relies on traditional tensioning equipment, controlling the prestress magnitude through preset tension values. During construction, operators use jacks and other tensioning equipment to tension the prestressed steel strands according to the design drawings, and anchor them after reaching the preset tension value. While this traditional tensioning process is technically mature and easy to operate, it is essentially an open-loop control method. This means that the prestress distribution within the beam cannot be known in real time during construction; the magnitude of the prestress can only be indirectly inferred from the hydraulic pressure gauge readings of the tensioning equipment, making it difficult to accurately control the actual stress state of the beam.

[0003] Existing prestressed construction technologies suffer from the following significant drawbacks: First, prestress loss is difficult to monitor and accurately compensate for in real time. Under the influence of multiple factors such as concrete shrinkage and creep, anchor deformation, and strand relaxation, prestress loss begins immediately after tensioning of the prestressed steel strands, and this loss accumulates over time. Current monitoring methods primarily employ traditional sensors such as resistance strain gauges. These sensors suffer from low accuracy, poor electromagnetic interference resistance, and insufficient durability, making it impossible to achieve long-term, accurate, and real-time monitoring of the stress within the beam and the prestressed steel strands. In particular, they cannot meet the need for continuous tracking of the prestress state throughout the entire lifespan of the bridge. Due to the lack of effective monitoring methods, insufficient or excessive prestressing during construction frequently occurs, leading to structural defects such as beam cracking, decreased stiffness, and excessive mid-span deflection, severely impacting the beam's service life and safety performance.

[0004] Secondly, once traditional prestressed beams are constructed, their prestress state remains fixed and cannot be adaptively adjusted according to load changes, structural damage, and material deterioration during later service. When the beam suffers fatigue damage due to repeated vehicle loads, or when the prestress decays over a long period, it is difficult to restore the structural stress balance through active adjustment. Existing technologies can only rely on later reinforcement and maintenance to address prestress loss. Common reinforcement methods include bonding carbon fiber cloth and adding external prestressing cables. These methods not only increase maintenance costs but also have long construction cycles and disrupt traffic. More importantly, these reinforcement measures cannot achieve proactive prevention and real-time compensation of prestress loss, nor can they provide dynamic intervention during the prestress decay process.

[0005] In recent years, iron-based shape memory alloys (Fe-SMA), as a novel smart material, have been explored for application in the reinforcement and adaptive adjustment of prestressed structures due to their unique shape memory effect and superelasticity, which allows them to generate stable restoring forces under temperature excitation. However, existing Fe-SMA prestressing application technologies still have significant limitations. On the one hand, there is a lack of precise real-time monitoring methods for the prestressing effect of Fe-SMA materials. Construction personnel cannot accurately determine whether the magnitude of the prestress generated after Fe-SMA excitation meets the design requirements, nor can they capture the stress decay and performance degradation of Fe-SMA during long-term service. On the other hand, the temperature excitation process of Fe-SMA lacks linkage control with the stress state of the beam. Existing technologies mostly use fixed heating parameters for open-loop excitation, which cannot dynamically adjust the heating strategy according to the real-time stress changes of the beam, resulting in poor adaptive adjustment effects and difficulty in achieving stress balance control throughout the entire life cycle of the beam. Although fiber optic grating (FBG) sensors have excellent characteristics such as high measurement accuracy, strong resistance to electromagnetic interference, corrosion resistance, and the ability to achieve distributed monitoring, they have been applied in strain and stress monitoring in the field of civil engineering. However, there is no existing technology that can apply fiber optic grating stress monitoring technology to the entire process of prestressed beam construction and deeply integrate it with Fe-SMA temperature excitation to form a monitoring-judgment-excitation-feedback closed-loop control system.

[0006] In summary, existing prestressed beam construction technologies face several technical challenges, including a lack of real-time and accurate monitoring of the prestressing application process, an inability to actively compensate for prestress loss during service life, and a lack of linkage control between Fe-SMA adaptive adjustment and the monitoring system. There is an urgent need to develop an integrated intelligent construction method that can achieve real-time perception, accurate application, and dynamic compensation throughout the entire prestressed beam construction process. Summary of the Invention

[0007] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0008] Another objective of this invention is to achieve real-time stress sensing, precise application, and dynamic compensation throughout the entire construction process of prestressed beams, thereby improving the construction quality, load-bearing capacity, and long-term service safety and durability of prestressed beams in bridges.

[0009] Another objective of this invention is to provide an integrated self-sensing and self-excitation prestressed concrete smart beam construction method, which forms a monitoring-excitation closed-loop control to achieve independent control of zones; it enables rapid and accurate force building during construction and stable compensation for losses during service life, overcoming the problem of difficult compensation for prestress loss.

[0010] To achieve these objectives and other advantages according to the present invention, an integrated self-sensing and self-excitation prestressed concrete smart beam construction method is provided, comprising: S1. Divide the steel reinforcement cage of the beam into multiple excitation sections. A high-temperature resistant corrugated pipe is reserved in any excitation section, and a set of Fe-SMA prestressed steel strands are inserted into the corrugated pipe. Each set of Fe-SMA prestressed steel strands is independently equipped with a heating wire and a stress-type FBG sensor. Temperature sensors are embedded in non-stressed areas of the same environment to collect temperature data synchronously. The wavelength drift data collected in real time by the stress-type FBG sensor is corrected for temperature and converted into the real-time stress value of the Fe-SMA prestressed steel strands. S2. After the concrete has cured to the design strength, the Fe-SMA prestressed steel strands of each group are pre-stretched and temporarily anchored so that the Fe-SMA prestressed steel strands of each group reach the foundation prestress value. S3. During construction, the stress data of Fe-SMA prestressed steel strands in each excitation section are calculated in real time. For excitation sections where the prestress does not meet the design requirements, the corresponding heating wires are used to heat and excite the Fe-SMA prestressed steel strands so that the prestress in each excitation section reaches the design prestress value and permanent anchoring is completed. S4. During the service of the beam, based on the obtained prestress loss value of Fe-SMA prestressed steel strand in each excitation section, if the prestress loss value monitored in a certain excitation section exceeds the preset compensation threshold, the Fe-SMA prestressed steel strand in that excitation section will be reheated and excited using the corresponding heating wire until the prestress reaches the design prestress value. In step S3, when heating excitation is performed, the upper limit of the phase transformation temperature range of Fe-SMA prestressed steel strand is used as the target heating temperature. The temperature is rapidly increased to 85-90% of the design prestress value using full-power heating. After the power is cut off and the stress stabilizes, the excitation section that has not reached the design prestress value is heated with a short pulse until the design prestress value is reached.

[0011] Preferably, during the reheating excitation in step S4, the lower limit of the phase transformation temperature range of the Fe-SMA prestressed steel strand is used as the target heating temperature. A duty cycle modulation heating method is employed for excitation, with an initial duty cycle set to 30-50%, based on the stress change rate and stress fluctuation amplitude of each excitation zone. When the rate of change of stress is less than the preset lower threshold, the duty cycle is gradually increased, with each increase being 5-10%. When the rate of change of stress exceeds the preset upper limit threshold, the duty cycle is gradually reduced, with each reduction being 5-10%. If the stress fluctuation exceeds the amplitude threshold, pause heating for 10-30 seconds, reduce the duty cycle before pausing heating by 10-20%, and then restart heating. Repeat the above process until the stress in the excitation section recovers to the design prestress value.

[0012] Preferably, the process includes the following step between S1 and S2: After the concrete is poured and before it sets, the wavelength drift of the sensor is monitored in real time by the stress-type FBG sensor. When the detected wavelength drift exceeds the preset protection threshold, the concrete is sprayed to cool it down. During the spraying and cooling process, the rate of decrease of wavelength drift is kept within the preset cooling rate range.

[0013] Preferably, the temperature sensor in step S1 is a temperature-compensated FBG sensor, which collects data synchronously with the stress-type FBG sensor to separate the temperature contribution component in the wavelength drift of the stress-type FBG sensor; the foundation prestress value in step S1 is 80~95% of the design prestress value.

[0014] Preferably, the full-power heating method in step S3 is to heat the heating wire with a constant rated power, and the heating power is the rated power value of the heating wire; the short-time pulse heating is to turn off the power after each 3-8s of power-on, and the interval between adjacent pulses is 5-7s.

[0015] Preferably, the preset lower threshold of the stress change rate in step S4 is 0.1~0.5MPa / s, and the preset upper threshold is 2~5MPa / s; the threshold of the stress fluctuation amplitude is 2~4% of the design prestress value.

[0016] Preferably, the protection threshold for the wavelength drift corresponds to 90-95% of the wavelength drift corresponding to the deformation limit of the Fe-SMA prestressed steel strand, and the deformation limit of the Fe-SMA prestressed steel strand is the maximum thermal strain that the Fe-SMA prestressed steel strand can withstand in the unactivated state.

[0017] Preferably, the heating wire is arranged parallel to or spirally wound along the Fe-SMA prestressed steel strands, with an independent set of heating wires on each group of Fe-SMA prestressed steel strands, and the control circuits of the heating wires and stress-type FBG sensors on each group of Fe-SMA prestressed steel strands are independently led out to the control center.

[0018] Preferably, the control center includes a data acquisition module, a data processing module, a heating control module, a spray control module, and a storage module; the data acquisition module acquires wavelength data from each FBG sensor in real time; the data processing module performs temperature correction on the wavelength data and converts it into stress values; the heating control module independently controls the energizing time and duty cycle of the heating wires in each excitation section according to preset control logic; the spray control module controls the start / stop and spray intensity of the automatic spray curing system according to preset protection thresholds and cooling rate ranges; and the storage module records the initial reference values ​​and historical monitoring data of each excitation section.

[0019] The present invention has at least the following beneficial effects: Firstly, this invention achieves active control of the entire process of prestressed beams from construction to service by deploying independently controlled Fe-SMA prestressed units in zones and constructing a closed-loop control system for the entire life cycle of monitoring, judgment, excitation and feedback. This overcomes the technical defects of traditional prestressed beams with fixed prestress state and inability to adaptively adjust, and significantly improves the long-term service safety and durability of the beam. Secondly, this invention employs differentiated heating control strategies for the construction and service periods: during construction, the upper limit of the phase change temperature is targeted, and full-power rapid heating combined with short-time pulse fine-tuning is used to achieve rapid and accurate establishment of prestress, shortening the construction cycle; during service, the lower limit of the phase change temperature is targeted, and duty cycle modulation heating combined with stress fluctuation monitoring and a pause-restart mechanism is used to achieve stable compensation of prestress and prevent stress overshoot from damaging the structure; the two strategies work together to achieve a balance between construction efficiency and long-term service stability. Thirdly, this invention monitors the wavelength drift in real time during the concrete curing period using a stress-type FBG sensor. Utilizing the single correspondence between wavelength drift and temperature under zero stress, the invention uses the wavelength drift corresponding to the deformation limit of Fe-SMA as a protection threshold to control spray cooling, effectively preventing hydration heat from damaging the embedded heating wire and FBG sensor. At the same time, it protects the performance of the Fe-SMA prestressed steel strand from premature activation or deterioration, ensuring the normal functioning of the subsequent shape memory effect. Fourth, this invention integrates data acquisition, data processing, heating control, spray control and storage modules in the control center, realizing full-process automation of sensor data acquisition, stress conversion, heating excitation decision-making and spray cooling control, forming a highly integrated intelligent construction and operation and maintenance management system, which greatly reduces the need for manual intervention and improves the controllability of construction quality and the efficiency of operation and maintenance management.

[0020] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the construction process of the construction method described in one of the technical solutions of the present invention. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0023] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0024] like Figure 1 As shown, this invention provides an integrated self-sensing and self-excitation prestressed concrete smart beam construction method, comprising: S1. Divide the steel reinforcement cage of the beam into multiple excitation sections. A high-temperature resistant corrugated pipe is reserved in any excitation section, and a set of Fe-SMA prestressed steel strands are inserted into the corrugated pipe. Each set of Fe-SMA prestressed steel strands is independently equipped with a heating wire and a stress-type FBG sensor. Temperature sensors are embedded in non-stressed areas of the same environment to collect temperature data synchronously. The wavelength drift data collected in real time by the stress-type FBG sensor is corrected for temperature and converted into the real-time stress value of the Fe-SMA prestressed steel strands. S2. After the concrete has cured to the design strength, the Fe-SMA prestressed steel strands of each group are pre-stretched and temporarily anchored so that the Fe-SMA prestressed steel strands of each group reach the foundation prestress value. S3. During construction, the stress data of Fe-SMA prestressed steel strands in each excitation section are calculated in real time. For excitation sections where the prestress does not meet the design requirements, the corresponding heating wires are used to heat and excite the Fe-SMA prestressed steel strands so that the prestress in each excitation section reaches the design prestress value and permanent anchoring is completed. S4. During the service of the beam, based on the obtained prestress loss value of Fe-SMA prestressed steel strand in each excitation section, if the prestress loss value monitored in a certain excitation section exceeds the preset compensation threshold, the Fe-SMA prestressed steel strand in that excitation section will be reheated and excited using the corresponding heating wire until the prestress reaches the design prestress value. In step S3, when heating excitation is performed, the upper limit of the phase transformation temperature range of Fe-SMA prestressed steel strand is used as the target heating temperature. The temperature is rapidly increased to 85-90% of the design prestress value using full-power heating. After the power is cut off and the stress stabilizes, the excitation section that has not reached the design prestress value is heated with a short pulse until the design prestress value is reached.

[0025] In the above technical solution, or where the temperature sensor is a temperature-compensated FBG sensor, the temperature-compensated FBG sensor is placed in a stress-free area of ​​the same environment (encapsulated in a stress-free sleeve). It synchronously collects data with the stress-type FBG sensor to separate the temperature contribution component Δε in the wavelength drift of the stress-type FBG sensor. The specific method for temperature correction is: Δε = (Δλ) s -K T ×Δλ T ) / Kε ; where Δλ s Δλ represents the wavelength shift of the stress-type FBG sensor. T K represents the wavelength shift of a temperature-compensated FBG sensor. T K is the temperature sensitivity coefficient. ε is the strain sensitivity coefficient.

[0026] In the above technical solution, the threshold of 85-90% of the designed prestress value as the power cut-off value is determined by the following method: According to the residual heat thermal effect characteristics of Fe-SMA prestressed steel strand material, after the power is cut off, the material will still generate an additional prestress increment of 3-8% due to residual heat. Setting the target value of 85-90% can ensure that the stress naturally rises to 88%-98% of the designed prestress value after the power is cut off. The remaining 2-12% stress deviation is finely adjusted by subsequent short-time pulse heating.

[0027] In the above technical solution, in step S2, the temporary anchoring adopts a self-locking anchor. The self-locking anchor locks the Fe-SMA prestressed steel strand after mechanical pre-tensioning and maintains the locked state during subsequent heating and excitation, so that the shrinkage recovery force generated by the Fe-SMA prestressed steel strand is effectively transferred to the beam.

[0028] In the above technical solution, after permanent anchoring is completed in step S3, the beam is initially calibrated, and the wavelength drift of each excitation section under the design prestress value and the design prestress value is recorded as the initial reference value, which is used as the calculation reference for the prestress loss value in step S4.

[0029] In the above technical solution, the preset compensation threshold is determined by the following method: based on the beam structure design specifications and long-term service performance requirements, the maximum allowable prestress loss value is determined, and 5-15% of the design prestress value is taken as the compensation trigger threshold. When the monitored prestress loss value reaches this threshold, the reheating excitation is initiated.

[0030] In the above technical solution, after the reheating excitation is completed in step S4, the prestress stability of each excitation section is continuously monitored by the stress-type FBG sensor. The prestress value after compensation can be recorded as a new reference value, or the design prestress value after permanent anchoring is completed in step S3 can always be used as the reference value for the initial reference of prestress loss monitoring during subsequent service.

[0031] The aforementioned technical solution constructs a closed-loop control system for prestressing throughout its entire lifecycle, from construction to service, to address two major technical challenges in traditional prestressed beam construction: inaccurate prestressing application due to a lack of real-time and accurate monitoring, and the inability to actively compensate for prestress loss during service. First, multiple independent excitation zones are longitudinally divided within the beam's steel reinforcement cage, with high-temperature resistant corrugated pipes pre-installed in each zone. Then, a set of Fe-SMA prestressed steel strands, each with independently mounted heating wires and stress-type FBG sensors, is inserted. This zoned pre-embedded structure solves the problem of differentiated control of different parts of the beam, a limitation of traditional techniques, laying the physical foundation for subsequent precise zoned control. To achieve accurate stress sensing, temperature sensors are pre-embedded in non-stressed areas within the same environment to synchronously collect temperature data. Temperature correction is applied to the wavelength drift data collected in real-time by the stress-type FBG sensors, thereby calculating the real-time stress value of the steel strands. This overcomes the inherent limitation of FBG sensors being sensitive to both temperature and strain, ensuring the reliability of stress data acquired during subsequent construction and service, and providing accurate feedback signals for closed-loop control. After the concrete has cured to its design strength, each group of steel strands is pre-stretched and temporarily anchored to achieve a prestress value lower than the final design value. This provides space for subsequent stress adjustment using the properties of Fe-SMA material, solving the drawback of traditional techniques where tensioning is done once and cannot be adjusted. During construction, based on real-time calculated stress data for each excitation zone, the system uses corresponding heating wires to excite sections where the prestress has not met design requirements. By precisely controlling the heating process, the stress in each area ultimately reaches the design prestress value, thus achieving a transition from open-loop tensioning to closed-loop control. Finally, during service, by continuously monitoring the prestress loss value of each excitation zone, if the loss in a certain zone exceeds a preset compensation threshold, that zone is immediately reheated to restore the prestress to the design value. This solves the long-standing technical problem of traditional prestressed beams where prestress attenuation cannot be actively compensated during service and can only rely on post-construction reinforcement.

[0032] A specific construction process of the above technical solution is as follows: First, in the construction preparation stage, technicians fix the stress-type FBG sensor to the surface of the Fe-SMA prestressed steel strand using special adhesive or metal clamps. The heating wire is attached parallel to or spirally wound around the outside of the steel strand, and the steel strand is threaded into a high-temperature resistant corrugated pipe embedded in the beam's reinforcing steel skeleton. Simultaneously, the temperature-compensated FBG sensor is freely placed in a non-stressed area of ​​the same environment (e.g., encapsulated in a non-stressed sleeve). All sensor and heating wire signal and power lines are independently led out to the control center outside the beam via high-temperature resistant cables. After the concrete has cured to the design strength (usually 28 days or reaching 100% design strength), operators use hydraulic through-hole jacks to mechanically pre-stretch the Fe-SMA steel strand in each excitation section. By controlling the hydraulic pressure of the jacks, the steel strand reaches 80-95% of the design prestress value. Then, self-locking anchors are used to temporarily anchor it to the beam end. During the construction control phase, the control center activates the temperature excitation module. For sections where the stress value does not meet the design requirements, the upper limit of the phase transformation temperature range of the Fe-SMA material (e.g., 180℃~200℃ within the range of 120~200℃) is used as the target. A heating wire with constant rated power is used for full-power heating. When the real-time stress value fed back by the FBG sensor reaches 85~90% of the design prestress value, the power is immediately cut off. The residual heat effect of the Fe-SMA material is used to allow the stress to rise naturally. After the stress stabilizes, if it still does not meet the standard, a short-time pulse eddy current heating method with 3~8 seconds of power-on and 5~7 seconds of interval is used for precise fine-tuning until the prestress of the section reaches the design value. Then, permanent anchoring is completed. During its decades-long service life, the system operated continuously. The data acquisition module in the control center periodically collected wavelength data from the stress-type FBG sensors in each excitation section and compared and corrected it with temperature compensation data to convert it into real-time stress values. When the prestress loss value of a certain section reached 5% to 15% of the design prestress value, the control center automatically determined that the section needed compensation and restarted the corresponding heating wire of the section. A slow-start strategy different from that during construction was used for secondary heating until the stress recovered to the design allowable range.

[0033] In the above technical solution, during the specific construction process, to further ensure the safety of the embedded parts and sensors and the reliability of the system, a thick layer of heat insulation cotton is wrapped around the contact point between the reserved corrugated pipe and the concrete to reduce the heat conduction of hydration heat to the embedded parts; the concrete pouring adopts a layered pouring process, and the pouring speed is strictly controlled to avoid damaging the embedded heating wires and sensors; during the concrete curing period, an automatic sprinkler curing system electrically connected to the control information is used for curing, and the curing time is not less than 15 days, and the top of the beam is covered with geotextile to maintain stable humidity and temperature; after the concrete reaches the design strength, jacks are used to pre-stretch each group of Fe-SMA prestressed steel strands, and self-locking anchors are used for temporary anchoring; after the construction is completed, the beam's external dimensions, concrete strength, Fe-SMA prestressed steel strand anchoring status, and monitoring system operation are comprehensively inspected, and only after the inspection is passed can the service monitoring stage begin.

[0034] In the above technical solution, Fe-SMA prestressed steel strands are used to replace traditional prestressed steel strands, which can realize the adaptive adjustment of prestress and effectively compensate for the prestress loss during service. By using stress-type and temperature-compensated FBG sensors together, the stress changes inside the beam and Fe-SMA prestressed steel strands can be accurately monitored, and the subsequent maintenance process of traditional prestressed beams can be simplified, reducing maintenance costs.

[0035] The above technical solution deeply integrates the partitioned pre-embedded structure, temperature-corrected FBG precise sensing, and the shape memory effect of Fe-SMA material to construct a full life cycle closed-loop control system of monitoring-judgment-excitation-feedback. It realizes a fundamental transformation from traditional open-loop tensioning to closed-loop adaptive control. It not only solves the technical problem of inaccurate prestressing application caused by the inability to sense stress in real time during construction, but more importantly, it endows the prestressed beam with the ability to actively identify and dynamically compensate for prestress loss during long-term service, so that the stress of the beam is always maintained within the safe design range, fundamentally improving the long-term safety and durability of the bridge structure.

[0036] In one technical solution, during the reheating excitation in step S4, the lower limit of the phase transformation temperature range of the Fe-SMA prestressed steel strand is used as the target heating temperature. A duty cycle modulation heating method is employed for excitation, with the initial duty cycle set to 30-50%, based on the stress change rate and stress fluctuation amplitude of each excitation zone. When the rate of change of stress is less than the preset lower threshold, the duty cycle is gradually increased, with each increase being 5-10%. When the rate of change of stress exceeds the preset upper limit threshold, the duty cycle is gradually reduced, with each reduction being 5-10%. If the stress fluctuation exceeds the amplitude threshold, pause heating for 10-30 seconds, reduce the duty cycle before pausing heating by 10-20%, and then restart heating. Repeat the above process until the stress in the excitation section recovers to the design prestress value.

[0037] In the above technical solution, the duty cycle refers to the ratio of the energizing time to the cycle time within one cycle, which is achieved by a solid-state relay or a thyristor regulator. The control center outputs a control signal to drive the solid-state relay to adjust the energizing time.

[0038] The above technical solution uses the lower limit of the phase transformation temperature range of Fe-SMA material as the target heating temperature and adopts a low duty cycle slow start method to avoid thermal shock damage that may be caused to the in-service structure by high-power rapid heating. By dynamically adjusting the duty cycle through real-time monitoring of the stress change rate, the duty cycle is increased to improve compensation efficiency when the change rate is too low, and decreased to prevent stress overshoot when the change rate is too high, thus achieving a balance between compensation speed and stability. At the same time, by introducing a stress fluctuation amplitude monitoring and pause-restart mechanism, heating is automatically paused when the stress fluctuation exceeds the limit, and restarted with a lower duty cycle after the stress stabilizes. This effectively prevents stress oscillations caused by uneven material phase transformation or structural response lag during secondary heating, ensuring a stable and controllable compensation process. It avoids the overpressure damage that is prone to occur in traditional open-loop heating methods, significantly improves the safety and reliability of maintenance operations during service, and truly achieves stable, accurate, and safe compensation for prestress loss.

[0039] In one of the technical solutions, the step between S1 and S2 also includes: After the concrete is poured and before it sets, the wavelength drift of the sensor is monitored in real time by the stress-type FBG sensor. When the detected wavelength drift exceeds the preset protection threshold, the concrete is sprayed to cool it down. During the spraying and cooling process, the rate of decrease of wavelength drift is kept within the preset cooling rate range.

[0040] In the above technical solution, since the steel strands are in a zero-stress state before pre-stretching, the wavelength drift is caused solely by temperature changes and has a single corresponding relationship with the internal temperature of the concrete. The control center dynamically adjusts the opening of the spray control valves or the start / stop frequency of the water pumps in the spray system based on the difference between the real-time monitored wavelength drift and the protection threshold, to keep the rate of decrease in wavelength drift within a preset range. This protective control mechanism during the curing period effectively ensures the integrity of the embedded heating wires and FBG sensors. More importantly, it ensures that the performance of the Fe-SMA material is not damaged by high temperatures before activation, laying a reliable foundation for the normal functioning of the subsequent shape memory effect. This ensures the reliability and effectiveness of the entire adaptive prestressing control system from the outset.

[0041] In one of the technical solutions, the temperature sensor in step S1 is a temperature-compensated FBG sensor, which collects data synchronously with the stress-type FBG sensor to separate the temperature contribution component in the wavelength drift of the stress-type FBG sensor; the foundation prestress value in step S1 is 80~95% of the design prestress value.

[0042] In the above technical solution, the foundation prestress value is determined by the following method: Before construction, material performance tests are conducted on the same batch of Fe-SMA prestressed steel strands to determine their elastic modulus, ultimate tensile strength, and shape memory effect recovery rate. Based on the design prestress value and the maximum additional prestress value that the Fe-SMA prestressed steel strand material can generate after heating excitation, the foundation prestress value is determined to be 80-95% of the design prestress value, ensuring that the remaining 5-20% of the prestress increment is provided by subsequent heating excitation. This technical solution improves the accuracy of stress monitoring through temperature compensation and reserves space for subsequent thermal regulation by pre-setting the foundation prestress range, thereby ensuring the precise implementation and adaptive adjustment capability of closed-loop control.

[0043] In one technical solution, the full-power heating method in step S3 involves energizing the heating wire with a constant rated power, where the heating power is the rated power value of the heating wire. The short-time pulse heating involves energizing for 3-8 seconds and then de-energizing, with an interval of 5-7 seconds between adjacent pulses. Precise control of the energizing time and pulse interval enables accurate stress fine-tuning, avoiding overshoot. Using full-power heating ensures rapid and stable temperature rise, improving construction efficiency.

[0044] In one of the technical solutions, the preset lower threshold of the stress change rate in step S4 is 0.1~0.5MPa / s, and the preset upper threshold is 2~5MPa / s; the threshold of the stress fluctuation amplitude is 2~4% of the design prestress value.

[0045] The preset lower and upper threshold values ​​for the stress change rate described in the above technical solution were determined by conducting heating excitation tests on the same batch of Fe-SMA prestressed steel strands before construction. The stress change rate under different heating powers was recorded. A stress change rate of 0.1~0.5 MPa / s was set as the lower threshold value to determine whether the heating power was insufficient and whether the duty cycle needed to be increased. A stress change rate of 2~5 MPa / s was set as the upper threshold value to determine whether the heating power was excessive and whether the duty cycle needed to be reduced. The amplitude threshold for stress fluctuation was determined based on the allowable stress fluctuation range of the beam structure during service, taking 2~4% of the design prestress value as the amplitude threshold. When the real-time stress value fluctuates within this threshold range, it is considered a stable stress state; when the fluctuation amplitude exceeds this threshold range, it is considered an unstable stress state, triggering a heating pause mechanism. For different Fe-SMA prestressed steel strands, all thresholds in this application can be appropriately adjusted according to the threshold determination method provided in this application.

[0046] The above technical solution provides a clear control boundary for duty cycle modulation heating during service life by accurately quantifying the lower and upper thresholds of the stress change rate and the amplitude threshold of the stress fluctuation. This enables the reheating excitation to achieve stable compensation within a safe range, effectively preventing stress overshoot or oscillation, and significantly improving the reliability and safety of the compensation process.

[0047] In one of the technical solutions, the protection threshold for the wavelength drift corresponds to 90-95% of the wavelength drift corresponding to the deformation limit of the Fe-SMA prestressed steel strand, and the deformation limit of the Fe-SMA prestressed steel strand is the maximum thermal strain that the Fe-SMA prestressed steel strand can withstand in the unactivated state.

[0048] In the above technical solution, the protection threshold for wavelength drift is determined by the following method: Before construction, a temperature loading test is conducted on the same batch of Fe-SMA prestressed steel strands to determine the wavelength drift corresponding to the maximum allowable thermal strain in the unactivated state. 90-95% of this wavelength drift is used as the protection threshold. The preset cooling rate range is the cooling rate corresponding to a wavelength drift change rate of 0.05-0.5 nm / min. During spraying, the cooling rate is maintained within this range to prevent excessively rapid cooling from causing concrete temperature difference cracks or excessively slow cooling from causing the hydration heat peak to last too long. By setting the protection threshold for spray cooling during the curing period to 90-95% of the wavelength drift corresponding to the deformation limit of the Fe-SMA prestressed steel strands, the cooling control benchmark is directly linked to the material's own performance indicators. This provides a safety margin for hydration heat shock and avoids performance degradation or premature activation of the material due to overheating, ensuring the reliable performance of the subsequent shape memory effect from the source.

[0049] In one technical solution, the heating wires are arranged parallel to or spirally wound along the Fe-SMA prestressed steel strands. Each group of Fe-SMA prestressed steel strands has an independently installed set of heating wires. The control circuits for the heating wires and stress-type FBG sensors on each group of Fe-SMA prestressed steel strands are independently led out to the control center. By arranging the heating wires parallel to or spirally wound along the steel strands, the uniformity and efficiency of heating are ensured. The independent lead-out of control circuits to the control center for each group provides the hardware foundation for achieving independent zone control, enabling reliable execution of precise excitation during construction and fixed-point compensation during service life, significantly improving the system's flexibility and reliability.

[0050] In the above technical solution, the heating excitation in step S3 and the reheating excitation in step S4 are both controlled by the control center to form a closed-loop control loop of monitoring-judgment-excitation-feedback: the control center receives real-time monitoring data from the stress-type FBG sensor and the temperature-compensated FBG sensor, compares the monitoring data with a preset threshold, determines whether heating excitation and reheating excitation are needed, and then drives the heating wire to heat through the control signal. During the heating process, the heating parameters are dynamically adjusted by continuously receiving feedback data from the stress-type FBG sensor and the temperature-compensated FBG sensor until the monitoring data reaches the target threshold.

[0051] In one technical solution, the control center includes a data acquisition module, a data processing module, a heating control module, a spray control module, and a storage module. The data acquisition module acquires wavelength data from each FBG sensor in real time. The data processing module performs temperature correction on the wavelength data and converts it into stress values. The heating control module independently controls the energizing time and duty cycle of the heating wires in each excitation section according to preset control logic. The spray control module controls the start / stop and spray intensity of the automatic spray curing system according to preset protection thresholds and cooling rate ranges. The storage module records the initial reference values ​​and historical monitoring data of each excitation section.

[0052] In the above technical solution, the data acquisition module is connected to the stress-type FBG sensor and the temperature-compensated FBG sensor via fiber optic patch cords, and multi-channel synchronous acquisition is achieved using wavelength division multiplexing or space division multiplexing. After receiving the wavelength data from the stress-type FBG sensor and the temperature-compensated FBG sensor, the data processing module first calculates the wavelength drift of both, then performs temperature compensation calculations based on preset temperature sensitivity coefficients and strain sensitivity coefficients, and finally outputs the pure strain value and converts it into a stress value. The heating control module is independently connected to the heating wires of each excitation section via solid-state relays or thyristor power regulators, and controls the heating power using PID regulation or duty cycle regulation. The spray control module controls the opening and closing of the spray solenoid valves via relays and adjusts the water pump speed via a frequency converter to control the spray intensity. The storage module records the real-time stress value, wavelength drift, heating record, spray record, and alarm information of each excitation section in a time-series manner, with a storage period of no less than the design service life of the beam.

[0053] The aforementioned technical solution modularizes the control center into five functional modules: data acquisition, data processing, heating control, sprinkler control, and storage. This constructs a highly integrated and fully functional intelligent construction and operation management system. The five modules work together organically to form a complete automated closed loop from sensor signal acquisition, data analysis, control decision-making to execution feedback. This significantly reduces the need for manual intervention, improves the stability of construction quality and the level of intelligent operation and maintenance management, and truly achieves automated control of the entire process of prestressed beams from construction to service.

[0054] The number of devices and processing scale described herein are for simplification of the invention. Applications, modifications, and variations of the integrated self-sensing and self-excitation prestressed concrete smart beam construction method of this invention will be readily apparent to those skilled in the art.

[0055] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. An integrated self-sensing and self-excitation prestressed concrete smart beam construction method, characterized in that, include: S1. Divide the steel reinforcement cage of the beam into multiple excitation sections. A high-temperature resistant corrugated pipe is reserved in any excitation section, and a set of Fe-SMA prestressed steel strands are inserted into the corrugated pipe. Each set of Fe-SMA prestressed steel strands is independently equipped with a heating wire and a stress-type FBG sensor. Temperature sensors are embedded in non-stressed areas of the same environment to collect temperature data synchronously. The wavelength drift data collected in real time by the stress-type FBG sensor is corrected for temperature and converted into the real-time stress value of the Fe-SMA prestressed steel strands. S2. After the concrete has cured to the design strength, the Fe-SMA prestressed steel strands of each group are pre-stretched and temporarily anchored so that the Fe-SMA prestressed steel strands of each group reach the foundation prestress value. S3. During construction, the stress data of Fe-SMA prestressed steel strands in each excitation section are calculated in real time. For excitation sections where the prestress does not meet the design requirements, the corresponding heating wires are used to heat and excite the Fe-SMA prestressed steel strands so that the prestress in each excitation section reaches the design prestress value and permanent anchoring is completed. S4. During the service of the beam, based on the obtained prestress loss value of Fe-SMA prestressed steel strand in each excitation section, if the prestress loss value monitored in a certain excitation section exceeds the preset compensation threshold, the Fe-SMA prestressed steel strand in that excitation section will be reheated and excited using the corresponding heating wire until the prestress reaches the design prestress value. In step S3, when heating excitation is performed, the upper limit of the phase transformation temperature range of Fe-SMA prestressed steel strand is used as the target heating temperature. The temperature is rapidly increased to 85-90% of the design prestress value using full-power heating. After the power is cut off and the stress stabilizes, the excitation section that has not reached the design prestress value is heated with a short pulse until the design prestress value is reached.

2. The integrated self-sensing and self-excitation prestressed concrete smart beam construction method as described in claim 1, characterized in that, In step S4, during the reheating excitation, the lower limit of the phase transformation temperature range of the Fe-SMA prestressed steel strand is used as the target heating temperature. A duty cycle modulation heating method is employed for excitation, with the initial duty cycle set to 30-50%. The heating temperature is determined based on the stress change rate and stress fluctuation amplitude of each excitation zone. When the rate of change of stress is less than the preset lower threshold, the duty cycle is gradually increased, with each increase being 5-10%. When the rate of change of stress exceeds the preset upper limit threshold, the duty cycle is gradually reduced, with each reduction being 5-10%. If the stress fluctuation exceeds the amplitude threshold, pause heating for 10-30 seconds, reduce the duty cycle before pausing heating by 10-20%, and then restart heating. Repeat the above process until the stress in the excitation section recovers to the design prestress value.

3. The integrated self-sensing and self-excitation prestressed concrete smart beam construction method as described in claim 2, characterized in that, Between steps S1 and S2, the following is also included: After the concrete is poured and before it sets, the wavelength drift of the sensor is monitored in real time by the stress-type FBG sensor. When the detected wavelength drift exceeds the preset protection threshold, the concrete is sprayed to cool it down. During the spraying and cooling process, the rate of decrease of wavelength drift is kept within the preset cooling rate range.

4. The integrated self-sensing and self-excitation prestressed concrete smart beam construction method as described in claim 3, characterized in that, In step S1, the temperature sensor is a temperature-compensated FBG sensor, which collects data synchronously with the stress-type FBG sensor to separate the temperature contribution component in the wavelength drift of the stress-type FBG sensor; the foundation prestress value in step S1 is 80~95% of the design prestress value.

5. The integrated self-sensing and self-excitation prestressed concrete smart beam construction method as described in claim 4, characterized in that, The full-power heating method in step S3 is to use a constant rated power to heat the heating wire, and the heating power is the rated power value of the heating wire; the short-time pulse heating is to turn off the power after each 3-8 seconds of power-on, and the interval between adjacent pulses is 5-7 seconds.

6. The integrated self-sensing and self-excitation prestressed concrete smart beam construction method as described in claim 5, characterized in that, In step S4, the preset lower threshold for the stress change rate is 0.1~0.5MPa / s, and the preset upper threshold is 2~5MPa / s; the threshold for the stress fluctuation amplitude is 2~4% of the design prestress value.

7. The integrated self-sensing and self-excitation prestressed concrete smart beam construction method as described in claim 6, characterized in that, The protection threshold for the wavelength drift corresponds to 90-95% of the wavelength drift corresponding to the deformation limit of the Fe-SMA prestressed steel strand. The deformation limit of the Fe-SMA prestressed steel strand is the maximum thermal strain that the Fe-SMA prestressed steel strand can withstand in the unactivated state.

8. The integrated self-sensing and self-excitation prestressed concrete smart beam construction method as described in claim 7, characterized in that, The heating wires are arranged parallel to or spirally wound along the Fe-SMA prestressed steel strands. Each group of Fe-SMA prestressed steel strands has an independent set of heating wires. The control circuits of the heating wires and stress-type FBG sensors on each group of Fe-SMA prestressed steel strands are independently led out to the control center.

9. The integrated self-sensing and self-excitation prestressed concrete smart beam construction method as described in claim 8, characterized in that, The control center includes a data acquisition module, a data processing module, a heating control module, a spray control module, and a storage module. The data acquisition module acquires wavelength data from each FBG sensor in real time. The data processing module performs temperature correction on the wavelength data and converts it into stress values. The heating control module independently controls the energizing time and duty cycle of the heating wires in each excitation section according to preset control logic. The spray control module controls the start-up, shutdown, and spray intensity of the automatic spray maintenance system according to the preset protection threshold and cooling rate range; the storage module records the initial reference value and historical monitoring data of each excitation section.

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