A stiffness compensation type composite beam system for inhibiting cracking in the negative bending moment region of an integral bridge

Abstract

The present application belongs to the technical field of bridge engineering, and relates to a stiffness compensation type composite beam system for inhibiting cracking in the negative bending moment area of a whole bridge, which comprises: a pre-deformation locking unit, which installs a stiffness compensator in the negative bending moment area of a steel beam and loads to generate a pre-deformation of upward arch, so as to lock elastic strain energy in the steel beam; a composite structure construction unit, which pre-buries a sensor above the steel beam and pours concrete, and forms a composite structure through a shear connector; a state monitoring and analysis unit, which collects multi-dimensional time-varying data to calculate the material state, compares an energy release window model to determine the application time; an energy controlled release unit, which controls the stiffness compensator to be unlocked to release energy to drive the steel beam to bend downward; and a pre-compression stress generation and verification unit, which utilizes the deformation of the whole structure to introduce a compressive stress in the bridge deck slab. The present application solves the technical problems of complex construction process of traditional prestressing technology and insufficient accuracy of prestress application timing control.

Description

Technical Field

[0001] This invention belongs to the technical field of bridge engineering and relates to a stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of an integral bridge. Background Technology

[0002] In the design and service of steel-concrete composite girder bridges, the negative bending moment section above the pier supports is a critical stress area. Under the long-term effects of vehicle loads, structural self-weight, and the inherent shrinkage and creep effects of concrete, the upper edge of the concrete bridge deck in this section will bear significant tensile stress. Since the tensile strength of concrete is lower than its compressive strength, when this tensile stress exceeds the tensile strength of the concrete, transverse cracks are prone to form in the bridge deck. These cracks not only affect the appearance of the bridge but also provide pathways for the intrusion of corrosive substances such as moisture and chloride ions, which in turn can lead to corrosion of the internal steel reinforcement, posing a potential impact on the long-term durability and safety of the structure.

[0003] To address cracking in the negative bending moment zone, the industry typically employs methods such as increasing the reinforcement ratio or applying prestress. Increasing the reinforcement ratio controls crack width by using more reinforcing steel bars, a passive crack control method. A more proactive technique is prestressing, with external prestressing or internal unbonded prestressing being widely used. This technique artificially introduces prestress into the concrete bridge deck by tensioning high-strength prestressed tendons to counteract the tensile stress generated during future operation, thereby inhibiting or delaying crack formation.

[0004] However, traditional prestressing methods have certain limitations in practice. External prestressing systems require external steering blocks and anchoring devices, resulting in a relatively complex structure, and the exposed prestressing tendons require additional corrosion protection. Internal prestressing technology requires pre-embedding corrugated pipes before concrete pouring and grouting of the ducts after tensioning, making the construction process cumbersome, and the grouting quality directly affects the durability of the prestressing system. Furthermore, the timing of tensioning in traditional prestressing technology usually relies on fixed age standards. This time-based control strategy is difficult to accurately match the actual development state of concrete material properties, especially when tensioning is performed before shrinkage strain has stabilized. This can easily lead to significant prestress loss due to shrinkage later, thus affecting the long-term effect of prestressing. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a stiffness-compensating composite beam system that suppresses cracking in the negative bending moment zone of an integral bridge.

[0006] A stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of a monolithic bridge includes: A pre-deformation locking unit is used to construct a steel beam pre-deformation locking system. A stiffness compensator is installed on the steel beam in the negative bending moment section of the composite steel beam. An external loading device induces an upward camber pre-deformation in the steel beam, and the stiffness compensator locks the elastic strain energy generated by this pre-deformation within the steel beam. The system includes a stiffness compensator at the bottom of the steel beam, comprising a wedge-shaped locking block, a drive actuator, and a stress monitoring sensor. The external temporary loading device is controlled to apply force to the steel beam until the vertical displacement reaches the design target value. The wedge-shaped locking block inside the stiffness compensator forms a mechanical self-lock with the steel beam, and the external temporary loading device is removed, storing the elastic strain energy generated by the upward camber pre-deformation in a mechanically locked form. The composite structure construction unit is configured to pour concrete bridge decks that work in conjunction with steel beams. A monitoring sensor network is pre-embedded above the locked steel beams, and the concrete is poured and cured, so that the concrete bridge decks and steel beams form a composite structure through shear connectors. The condition monitoring and analysis unit is used to acquire real-time material state parameters of concrete bridge decks. It uses a monitoring sensor network to collect multi-dimensional time-varying data and calculates material state parameters based on the multi-dimensional time-varying data. The material state parameters are compared with a preset energy release window model based on concrete compressive strength, elastic modulus and shrinkage strain to determine the timing of prestressing application that meets the model conditions. The controlled energy release unit is used to trigger the controlled energy release of the pre-deformation locking system. When the prestressing application time is reached, the control stiffness compensator is released from the locking state, releasing the elastic strain energy stored inside the steel beam and driving the steel beam to produce downward bending deformation. The prestress generation and verification unit is used to generate prestress in the bridge deck to suppress cracking. It utilizes the overall composite structure to transfer the downward bending deformation of the steel beam and introduces compressive stress in the negative bending moment section of the concrete bridge deck.

[0007] A further embodiment of the present invention provides a combined structural construction unit for performing the following steps: With the pre-deformation locking system in a locked state, the steel reinforcement binding of the bridge deck is completed; A network of monitoring sensors is deployed inside the concrete bridge deck to collect data on hydration heat, shrinkage strain, and elastic modulus. Concrete pouring and curing are carried out, and shear connectors are used to establish a shear-resistant connection between the concrete bridge deck and the steel beams.

[0008] A further aspect of the present invention includes a status monitoring and analysis unit, which is used to perform the following operations: The monitoring sensor network was activated to continuously collect multi-dimensional time-varying data on the hydration heat, elastic modulus, and shrinkage strain of the concrete bridge deck. Based on multi-dimensional time-varying data, the compressive strength growth curve, elastic modulus development curve, and shrinkage strain development trend of concrete bridge deck are calculated as material state parameters. The compressive strength growth curve, elastic modulus development curve, and shrinkage strain development trend are compared with the preset energy release window model. When the material state parameters meet the threshold requirements of the energy release window model, it is determined to be the time to apply prestress.

[0009] A further aspect of the present invention provides an energy-controlled release unit for performing the following steps: Generate an energy release control command containing the target unlocking rate and send it to the stiffness compensator; The stiffness compensator responds to the command and releases the mechanical self-locking state of its internal locking mechanism in a controlled manner; As the mechanical self-locking is released, the steel beam springs back from its pre-deformed, arched state to its original straight state.

[0010] A further aspect of the present invention includes a prestress generation and verification unit, which performs the following operations: The downward bending deformation caused by the springback of the steel beam is forcibly transferred to the concrete bridge deck through shear connectors. This forces the concrete bridge deck located on the upper part of the overall composite structure to bend downwards synchronously with the steel beams; The downward bending deformation generates prestress in the concrete bridge deck in the negative bending moment zone, corresponding to the release of elastic strain energy.

[0011] A further aspect of the present invention utilizes a stress monitoring sensor to continuously monitor the stress changes of the steel beam and confirm that the stress value remains above a preset percentage of the target locked stress, thereby verifying that the elastic strain energy is effectively locked.

[0012] In a further embodiment of the present invention, the energy release window model defines the compressive strength threshold, the elastic modulus plateau criterion, and the shrinkage strain rate stability criterion for allowing the application of prestress. The specific timing for applying prestress is determined as follows: when the real-time calculated compressive strength is higher than the compressive strength threshold, the growth rate of the elastic modulus meets the elastic modulus plateau criterion, and the shrinkage strain change rate meets the shrinkage strain rate stability criterion, the timing for applying prestress is determined.

[0013] A further aspect of the present invention, specifically including the controlled release of the mechanical self-locking state of its internal locking mechanism, includes: During the process of releasing the mechanical self-locking state, the locking stress monitoring value fed back by the stress monitoring sensor is received in real time; Calculate the slope of the change in the locking stress monitoring value and control the absolute value of the slope to not exceed the preset safe release rate threshold to achieve closed-loop control.

[0014] In a further embodiment of the present invention, the prestress generation and verification unit is also used to perform the following operations: The measured rebound deformation was calculated based on the difference in the pre-arch deformation of the steel beam before and after energy release. Based on the converted section stiffness of the overall composite structure, the actual prestress of the concrete bridge deck acting on the negative bending moment section of the concrete bridge deck is calculated. The actual prestress of the bridge deck is compared with the design value of tensile stress generated by long-term operational loads.

[0015] In summary, the present invention has the following beneficial technical effects: 1. The elastic strain energy of the steel beam is stored and converted into prestress in the concrete bridge deck through a pre-deformation locking system. This mechanism directly utilizes the steel beam itself as the force-bearing body, replacing the prestressing tendons, anchorages, and tensioning equipment required in traditional technologies. This simplifies the structural construction of the composite beam, reduces construction procedures, and avoids potential quality problems such as insufficient compaction that may exist in traditional prestressed duct grouting processes.

[0016] 2. By embedding a monitoring sensor network and combining it with an energy release window model, the timing of prestressing application is determined in real time using multi-dimensional data such as the heat of hydration, elastic modulus, and shrinkage strain of concrete. Compared with traditional control methods based on fixed age, this invention can determine the energy release time point according to the actual performance development state of concrete materials, which helps to reduce stress relaxation caused by premature prestressing and prestress loss caused by shrinkage and creep, thereby improving the long-term retention effect of prestress.

[0017] 3. By utilizing the locking mechanism within the stiffness compensator in conjunction with the control system, the controlled release of the elastic strain energy of the steel beam is achieved. By controlling the unlocking rate, the elastic rebound process of the steel beam is kept smooth and gradual, effectively mitigating the dynamic impact effect that instantaneous energy release may have on the composite structure. This facilitates the uniform establishment of a prestressed stress field in the concrete bridge deck during the quasi-static process, ensuring the stability of the structure during construction. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings are used to provide a further understanding of the present invention.

[0019] Figure 1 This discloses a schematic diagram of the framework in the embodiments of this application.

[0020] Figure 2 This discloses a flowchart of an embodiment of this application. Detailed Implementation

[0021] The following is in conjunction with the appendix Figure 1 - Figure 2 A preferred description of the present invention is provided below.

[0022] See attached document Figure 1 - Figure 2 This invention proposes a stiffness-compensating composite beam system for suppressing cracking in the negative bending moment region of an integral bridge, comprising the following modules: The pre-deformation locking unit is used to construct a pre-deformation locking system for steel beams. A stiffness compensator is installed on the steel beam in the negative bending moment section of the steel composite beam. An external loading device is used to induce an upward arching pre-deformation in the steel beam, and the elastic strain energy generated by the upward arching pre-deformation is locked inside the steel beam through the stiffness compensator. The composite structure construction unit is configured to pour concrete bridge decks that work in conjunction with steel beams. A monitoring sensor network is pre-embedded above the locked steel beams, and the concrete is poured and cured, so that the concrete bridge decks and steel beams form a composite structure through shear connectors. The condition monitoring and analysis unit is used to acquire real-time material state parameters of concrete bridge decks. It uses a monitoring sensor network to collect multi-dimensional time-varying data and calculates material state parameters based on the multi-dimensional time-varying data. The material state parameters are compared with a preset energy release window model based on concrete compressive strength, elastic modulus and shrinkage strain to determine the timing of prestressing application that meets the model conditions. The controlled energy release unit is used to trigger the controlled energy release of the pre-deformation locking system. When the prestressing application time is reached, the control stiffness compensator is released from the locking state, releasing the elastic strain energy stored inside the steel beam and driving the steel beam to produce downward bending deformation. The prestress generation and verification unit is used to generate prestress in the bridge deck to suppress cracking. It utilizes the overall composite structure to transfer the downward bending deformation of the steel beam and introduces compressive stress in the negative bending moment section of the concrete bridge deck.

[0023] In one embodiment of the present invention, the pre-deformation locking unit is used to perform the following steps: A stiffness compensator, including a wedge-shaped locking block, a drive actuator, and a stress monitoring sensor, is installed at the bottom of the steel beam. An external temporary loading device is controlled to apply force to the steel beam until the vertical displacement of the steel beam reaches the design target value. The wedge-shaped locking block inside the drive stiffness compensator forms a mechanical self-lock with the steel beam, and the external temporary loading device is removed, storing the elastic strain energy generated by the pre-deformation of the arch in the form of mechanical locking.

[0024] Specifically, this step is executed by a bridge construction control system integrating a data acquisition module, a logic control module, and a command sending module. First, the system operator, according to the construction drawings, installs the stiffness compensator on the centerline of the lower flange plate of the steel beam in the negative bending moment section of the steel composite beam. It should be understood that the stiffness compensator is a mechanical device made of high-strength steel. Its core component is a locking mechanism equipped with wedge-shaped locking blocks and a matching drive actuator. In this embodiment, a wedge self-locking principle is adopted, with the self-locking angle designed to be smaller than the friction angle between materials, ensuring that the locked state is maintained solely by the preset axial pressure generated by the rebound of the steel beam after the driving force is removed. During installation, the fiber optic grating stress monitoring sensor integrated inside the stiffness compensator is connected to the data acquisition module via optical cable to establish a monitoring link for the initial stress state. The initial reading is calibrated to 0 MPa. The measurement range and accuracy of the stress monitoring sensor should meet the requirements of steel beam stress monitoring; for example, the measurement range should cover -200 MPa to +200 MPa to quantify the stress state of the steel beam before and after locking.

[0025] Next, the control system drives one or more hydraulic jacks with sufficient loading capacity. These jacks, acting as external temporary loading devices, are placed below the mid-span of the steel beam corresponding to the negative bending moment section, applying a downward force to the beam. During loading, a laser displacement sensor positioned directly above the negative bending moment section measures the vertical displacement of the steel beam's upward arch in real time at a preset high-frequency sampling frequency, such as 10 Hz-50 Hz, to capture minute dynamic changes during loading. The acquired displacement data is then sent to the data acquisition module. Here, the upward arch pre-deformation refers to the upward vertical displacement of the steel beam's geometric centerline relative to its original horizontal position within the negative bending moment section. The logic control module compares the received real-time displacement data with the preset design target value within the system.

[0026] It should be noted that this design target value is calculated in reverse based on the finite element model of the bridge structure. It is the pre-deformation amount used to completely or partially offset this tensile stress by simulating the total tensile stress generated during future operation due to vehicle loads, structural self-weight, and concrete shrinkage and creep effects. The specific setting is based on the following: Design Target Value Span is usually taken of to For example, regarding span Based on finite element analysis, the maximum tensile stress at the supports of the beam segment under shrinkage, creep, and secondary dead load 20 years after bridge completion is calculated to be... Then the pre-deformation amount calculated in reverse Conditions to be met: In the formula, Let be the elastic modulus of the steel beam. Let be the moment of inertia of the steel beam section. The target value for the pre-deformation amount is designed. For the span of the beam segment, This represents the maximum tensile stress at the support after the bridge is completed. 1.1 is a geometric coefficient, and 1.1 is a safety factor that takes into account construction losses. In a typical scenario, this is the design target value. Set to 85 mm. This is the distance from the tension edge of the steel beam to the neutral axis.

[0027] When the real-time displacement data reaches the design target value, the logic control module stops the loading action of the hydraulic jacks. Then, the logic control module sends a locking command to the electric actuator inside the stiffness compensator via the command sending module. The electric actuator drives a wedge-shaped locking block made of high-strength alloy steel, engaging it with a groove on the stiffness compensator housing, thus putting the stiffness compensator into a mechanical self-locking state. After self-locking is complete, the control system controls the hydraulic jacks to unload at a preset slow rate. During unloading, the fiber optic stress monitoring sensor continuously monitors the stress changes in the lower flange of the steel beam, confirming that the stress value remains above a preset effective percentage of the target locking stress, typically above 98%, indicating that the elastic strain energy generated by the pre-deformation of the upward arch has been effectively locked inside the steel beam. Elastic strain energy is the potential energy stored inside the steel beam that undergoes elastic deformation due to external forces; its value is proportional to the square of the pre-deformation of the upward arch. Finally, the external temporary loading equipment is completely removed. At this point, the pre-deformation locking system, including the steel beam in the upward arch state and the stiffness compensator in the locked state, is complete.

[0028] For example, suppose this method is applied to a steel-concrete composite beam bridge with a main span of 40 m, where the design target value for the negative bending moment section of the steel beam is 85 mm. First, the construction control system confirms that a stiffness compensator has been installed at the bottom of the steel beam in this section and that the sensor link has been debugged, with an initial stress reading of 0 MPa. Next, two 500-ton hydraulic jacks located in the middle of the span are activated to apply downward force synchronously. At the same time, a laser displacement sensor begins to monitor the change in arch height in the negative bending moment section. When the laser displacement sensor reading reaches 85 mm, loading is stopped, and at this moment, the stress monitoring sensor measures a compressive stress of 160 MPa on the lower flange of the steel beam. Subsequently, a locking command is issued, and the wedge-shaped locking block inside the stiffness compensator is driven to the self-locking position. Finally, the hydraulic jacks are completely unloaded, and the steel beam cannot rebound because it is locked by the stiffness compensator. After unloading, the final stable reading of the stress monitoring sensor was 157 MPa, and the final reading of the laser displacement sensor was 84.5 mm, indicating that approximately 1.8% stress loss and 0.5 mm deformation recoil occurred due to mechanical backlash and minor slippage, but more than 98% of the elastic strain energy was successfully locked. The final locked deformation of 84.5 mm and the locking stress of 157 MPa were recorded, and a status report was generated, marking that the pre-deformation locking system had been constructed according to design requirements.

[0029] In one embodiment of the present invention, the combined structural construction unit is used to perform the following steps: With the pre-deformation locking system in a locked state, the steel reinforcement binding of the bridge deck is completed; a monitoring sensor network for collecting data on hydration heat, shrinkage strain, and elastic modulus is arranged inside the concrete bridge deck; concrete is poured and cured, and shear connections are established between the concrete bridge deck and the steel beams using shear connectors.

[0030] Specifically, this step continues under the condition that the pre-deformation locking system constructed by the pre-deformation locking module remains locked, and is then executed by the bridge construction control system. First, the control system reads the status report of the pre-deformation locking system from the storage unit to confirm that it is in stable locking mode and that the locking stress monitoring value is a valid locking value. In this state, construction personnel, according to the design drawings, carry out the reinforcement binding construction of the bridge deck above the steel beam, binding the longitudinal main reinforcement and transverse distribution reinforcement that meet the design specifications into a mesh structure with a preset spacing, and fixing the end reinforcement of the bridge deck according to the drawing requirements.

[0031] After the steel reinforcement is tied, a network of monitoring sensors is pre-embedded inside the bridge deck area corresponding to the negative bending moment section of the steel beam. This monitoring sensor network is a distributed data acquisition system composed of multiple functional sensor nodes, specifically arranged as follows: At a predetermined level of the concrete slab thickness, typically at the center of the slab thickness or 50 mm from the top surface, a cross-section is arranged at predetermined intervals along the longitudinal direction of the bridge, for example, every 2 to 5 m. A key dense area is located within 5 m on either side of the support centerline, where a hydration heat wireless temperature sensor is installed to acquire the hydration reaction temperature field inside the concrete in real time. Its operating range should cover the conventional temperature range of concrete hydration reaction, for example, 0℃ to 100℃. At a predetermined position above the neutral axis of the slab thickness, a vibrating wire strain sensor is arranged at predetermined intervals to directly measure the axial strain of the concrete caused by shrinkage and temperature changes. Its range should meet the monitoring requirements; a sensor with a range of ±3000 με and a resolution better than 1 με is recommended. At a predetermined height of the slab thickness, pairs of ultrasonic pulse transmitter and receiver probes are arranged at predetermined intervals to indirectly reflect changes in the dynamic elastic modulus by measuring the propagation speed of ultrasonic waves. The transmission frequency can be selected, for example, 50 kHz. All sensors are connected to a moisture-proof junction box located on the side of the bridge deck via pre-embedded waterproof cables, and then connected to the data acquisition module via an RS-485 bus to form a complete real-time monitoring link.

[0032] Subsequently, the concrete pouring of the bridge deck began. Compensating shrinkage concrete, such as C50 or C60, meeting the design strength requirements, was used. The concrete was evenly poured into the formwork above the steel beams using pumping equipment, and compacted using an immersion vibrator during the pouring process. After pouring, the concrete was immediately covered with geotextile and automatic spray curing was initiated. The ambient temperature and relative humidity were controlled within standard curing conditions, and the curing period was preset to reach the design age. Throughout the curing period, the steel beams and bridge decks bonded and mechanically interlocked through shear connectors, which in this embodiment are cylindrical head studs determined based on shear force calculations. The function of the shear connectors is to transfer the horizontal shear force between the steel beams and the concrete bridge deck, ensuring coordinated deformation. After the curing period, core sampling was conducted to test the concrete compressive strength, confirming that it exceeded the design strength threshold, and that there were no signs of relative slippage in the stud shear connector area. This indicated that the concrete bridge deck and steel beams had formed an integral composite structure through the shear connectors. This means that the concrete bridge deck and the steel beams are reliably connected and can jointly withstand loads such as bending moment and shear force, and that its cross section conforms to the plane section assumption during the elastic working stage.

[0033] For example, based on the foregoing example, the pre-deformation locking system remains locked, and the laser displacement sensor continuously monitors the arch height as 84.5 mm. The construction control system first authorizes bridge deck construction based on the lock status report. Construction workers complete the reinforcement mesh binding on the steel beams. Next, within the bridge deck area corresponding to the negative bending moment section (approximately 20 m long), 10 hydration heat sensors are pre-embedded longitudinally at locations x = 2 m, 4 m, ..., 20 m; 6 vibrating wire strain sensors are pre-embedded at x = 3 m, 6 m, ..., 18 m; and 4 sets of ultrasonic probes are pre-embedded at x = 4 m, 8 m, 12 m, 16 m. All sensor wiring is connected to the junction box and integrated into the system. Subsequently, C50 shrinkage-compensating concrete is pumped for pouring and vibration. Sensor data is continuously collected after curing begins. On the 28th day of curing, three core samples were drilled from the bridge deck. The compressive strength test results were 52.1 MPa, 50.8 MPa, and 53.4 MPa, all exceeding 50 MPa. Simultaneously, no abnormal slippage signals were detected at any of the stud connections. Based on this, the control system generated a status report, confirming that the concrete bridge deck and steel beams had formed an integral composite structure, providing a basis for subsequent steps.

[0034] In one embodiment of the present invention, the status monitoring and analysis unit is configured to perform the following steps: A monitoring sensor network is activated to continuously collect multi-dimensional time-varying data on the hydration heat, elastic modulus, and shrinkage strain of the concrete bridge deck. Based on the multi-dimensional time-varying data, the compressive strength growth curve, elastic modulus development curve, and shrinkage strain development trend of the concrete bridge deck are calculated as material state parameters. The compressive strength growth curve, elastic modulus development curve, and shrinkage strain development trend are compared with a preset energy release window model. When the material state parameters meet the threshold requirements of the energy release window model, it is determined to be the time to apply prestress.

[0035] Specifically, this step is executed by the bridge construction control system, the core of which is processing the real-time data stream from the monitoring sensor network embedded in the composite structure construction unit. First, the control system's command sending module sends a start command to the monitoring sensor network, putting it into continuous operation mode. The data acquisition module then begins to synchronously acquire raw readings from the hydration heat wireless temperature sensor, vibrating wire strain sensor, and ultrasonic pulse transmitter-receiver pair at preset time intervals, such as every 30 or 60 minutes. For each acquisition cycle, data from different types of sensors at the same longitudinal location are packaged into a data packet; for example, at location x=8 m, the data packet contains the temperature value. Strain gauge frequency value And the ultrasonic wave propagation time t.

[0036] Next, the logic control module invokes the built-in computing engine to perform real-time processing and analysis of multi-dimensional time-varying data. For concrete compressive strength, an estimation method based on a mature hydration heat model is adopted, such as the International Federation of Concrete Industries (ICEI) model CEB-FIP or a maturity method based on the Arrhenius equation. Specifically, this is achieved through formulas... To calculate the maturity of concrete, the formula is: For time The maturity of the time For actual measured temperature, The reference temperature is usually -10℃. This represents the time interval for temperature data acquisition. Then, using the pre-calibrated maturity-intensity relationship curve In the formula, To estimate the current compressive strength, The preset ultimate compressive strength, Let be the hydration rate constant. The current level of maturity, as described above. , This represents the initial maturity level for strength development. Based on this, the compressive strength growth curve of the concrete bridge deck can be fitted in real time. This curve is an empirical function curve describing the increase of concrete compressive strength with equivalent curing age. For shrinkage strain, the frequency change of the vibrating wire strain sensor is directly read. After subtracting the temperature strain compensation value calculated from the temperature sensor data at the same point, the net shrinkage strain value is obtained. Linear regression analysis is then performed on its development over time to generate a shrinkage strain development trend line. This trend line and its slope are used to quantify the change law of concrete drying shrinkage deformation over time. The temperature strain compensation value is calculated as follows: In the formula, This is the temperature strain compensation value. The coefficient of linear expansion of concrete, such as , This represents the change in temperature.

[0037] Simultaneously, the ultrasonic pulse transmitting and receiving probe is used to measure the ultrasonic wave propagation time t and the known fixed propagation path length. According to the formula: Calculate the dynamic elastic modulus of concrete In the formula, For concrete density, The time it takes for the ultrasound to travel is 1000 rpm. It is Poisson's ratio. This is used as an auxiliary criterion for the development of material stiffness.

[0038] Finally, the logic control module compares the real-time calculated current compressive strength, current elastic modulus, and current shrinkage strain rate with the energy release window model pre-stored in the system database. This energy release window model is essentially a set of logical judgment thresholds based on physical parameters such as strength, modulus, and shrinkage, stored in the control system. It aims to define the state window of concrete materials for the safe and effective release of elastic strain energy. This model defines three conditions that must be simultaneously met for the expected timing of prestressing application: The compressive strength reaches a certain percentage above the design strength, such as a compressive strength threshold of 90%, to ensure that the concrete is not crushed, because applying prestress too early will cause microcracks to form in the concrete at low strength. The development of elastic modulus has entered a plateau period, that is, the growth rate is less than the preset stability threshold. The criteria for the plateau period of elastic modulus, such as a 24-hour growth rate of less than 1%, indicate that the macroscopic stiffness of the material has stabilized. At this time, applying prestress can ensure the maximum stress transfer efficiency. The shrinkage strain rate tends to stabilize, that is, the absolute value of the linear regression slope is less than the preset shrinkage rate threshold. The criterion for stabilizing the shrinkage strain rate is, for example, the absolute value of the slope is less than 0.5 microstrains / day, to ensure that the subsequent additional stress loss is minimized and to prevent the prestress established by the release of the steel beam from being quickly offset due to the severe shrinkage of the concrete in the later stage.

[0039] When the real-time data meets all the conditions, it is determined that the concrete bridge deck has entered the expected prestressing application time, and a status sign indicating that the time is ready is generated.

[0040] For example, continuing the previous example, after the 28th day of maintenance, the control system starts continuous monitoring. Assume that at a certain data acquisition moment, the sensor data packet at location x = 8 m contains: temperature... strain gauge frequency Initial calibration frequency Ultrasonic propagation time First, the equivalent age is calculated. Based on historical temperature data, the current equivalent age is determined to be 30 days. Substituting this into the strength model, the current compressive strength is estimated to be 52.5 MPa, reaching 105% of the design strength of 50 MPa. Shrinkage strain is then calculated based on the frequency difference. and sensor sensitivity coefficient The total strain is 80 microstrains per Hz; the temperature strain is calculated to be 50 microstrains using temperature T and the material's coefficient of linear expansion; therefore, the net shrinkage strain is 30 microstrains. A linear regression of the net shrinkage strain values ​​from all strain sensors over the past 7 days yields a trend line with a slope of -0.3 microstrains per day. The dynamic elastic modulus is calculated given the concrete density. Poisson's ratio μ is taken as 0.2, and the propagation path length is... , Then wave speed Substituting into the formula, we get Check for 24 consecutive hours. Historical data shows a maximum fluctuation of 0.3 GPa and a growth rate of 0.8%, less than 1%. The current strength value (52.5 MPa > 45 MPa), elastic modulus growth rate (0.8% < 1%), and shrinkage strain rate (absolute value of -0.3 microstrain / day < 0.5) are compared with the conditions of the energy release window model, and all are satisfied. Therefore, the logic control module determines that the concrete bridge deck has entered the expected prestressing application period and updates the system status to "ready."

[0041] In one embodiment of the present invention, the energy-controlled release unit is configured to perform the following steps: An energy release control command containing the target unlocking rate is generated and sent to the stiffness compensator; the stiffness compensator responds to the command and releases the mechanical self-locking state of its internal locking mechanism in a controlled manner; as the mechanical self-locking state is released, the steel beam springs back from the pre-deformed arched state to its original straight state.

[0042] Specifically, after the condition monitoring and analysis unit determines that the concrete bridge deck has entered the expected prestressing application phase, this step is continued by the bridge construction control system. First, the control system's logic control module generates a structured energy release control command based on the timing-ready status flag. This control command is a system-generated digital command containing a command header, command type, control parameters, and a cyclic redundancy check code, specifically including the control mode, target unlocking rate, and security check code. The command sending module transmits this command to the embedded controller installed on the stiffness compensator via the established industrial Ethernet network using the Modbus TCP protocol.

[0043] After receiving an instruction and completing a safety verification, the embedded controller within the stiffness compensator activates its internal electric actuator. Based on the target unlocking rate in the instruction, the electric actuator drives the wedge-shaped locking block in a linear motion opposite to the locking action in the pre-deformation locking module in a synchronous and controlled manner, thereby gradually releasing the mechanical self-locking state of the locking mechanism. The synchronous and controlled manner refers to a closed-loop control formed by the unlocking action and monitoring feedback; the target unlocking rate is a parameter controlling the movement speed of the locking block, set based on the relationship between the mechanical transmission ratio of the stiffness compensator and the stiffness of the steel beam, aiming to keep the stress release rate below a safety threshold. Preferably, the target unlocking rate is set to 0.05 mm / s to 0.2 mm / s, or the target stress unloading rate is set to not exceed 2 MPa / min. This low-speed release strategy is to simulate a quasi-static loading process, avoiding the amplification effect of the dynamic impact coefficient caused by instantaneous energy release.

[0044] During the unlocking process, the fiber optic stress monitoring sensor monitors the stress attenuation of the lower flange of the steel beam in real time at a sampling frequency of, for example, 50Hz, and transmits the data back to the data acquisition module in real time. The logic control module continuously calculates the slope of the locked stress monitoring value, that is, the amount of change in the stress monitoring reading per unit time, ensuring that its absolute value does not exceed the preset safe release rate threshold. It should be noted that this safe release rate threshold is the maximum allowable stress change rate determined based on bridge dynamic characteristic simulation, such as -1.5 MPa / s, to ensure that the energy release process is smooth and does not induce harmful structural vibrations or impact the already formed overall composite structure.

[0045] As the locking mechanism is released, the elastic strain energy stored inside the steel beam in the pre-deformation locking module begins to be released. This drives the steel beam to spring back from its final upward arch state reached in the pre-deformation locking module to its original straight state, resulting in downward bending deformation. Simultaneously, a laser displacement sensor mounted on the steel beam monitors the decrease in arch height, confirming that the springback deformation and stress release occur synchronously. When the reading of the fiber optic stress monitoring sensor drops from the initial locked value to a stable residual value close to zero, for example, less than 5 MPa (typically caused by mechanical friction), and the arch height value monitored by the laser displacement sensor decreases to a stable displacement value close to zero, the logic control module determines that the elastic strain energy release is complete and sends a stop command to the embedded controller of the stiffness compensator, ending the entire release process.

[0046] For example, continuing the previous example, under the conditions of system status being ready, current locking stress being 157 MPa, and current arch height being 84.5 mm, the logic control module generates an energy release control command, specifying the control mode as "controlled linear release" and the target unlocking rate as 0.1 mm / s. The system sends the command via Ethernet to a location located at... The controller of the stiffness compensator was activated. After the controller was verified to be correct, the electric actuator was started to slowly pull back the wedge-shaped locking block at a speed of 0.1 mm / s. As the locking block moved, the reading of the fiber optic stress monitoring sensor began to decrease. The stress change slope was calculated in real time. Ten seconds after the release began, the stress dropped to 149 MPa, and the average change slope over the past 10 seconds was -0.8 MPa / s, which was below the safety threshold of -1.5 MPa / s, indicating that the release process was under control. At the same time, the laser displacement sensor showed that the arch height had dropped to 78 mm. This process continued, and after about 157 seconds, the stress monitoring sensor reading dropped to 5 MPa, and the laser displacement sensor reading dropped to 2 mm. At this point, it was determined that the energy release was basically complete, a stop command was sent, and the electric actuator stopped operating. The residual stress of 5 MPa and the residual arch height of 2 mm after the final release were recorded, marking the completion of the controlled energy release step of the pre-deformation locking system, and the steel beam had produced obvious downward bending deformation.

[0047] In one embodiment of the present invention, the prestress generation and verification unit is used to perform the following steps: The shear connectors forcefully transfer the downward bending deformation caused by the springback of the steel beam to the concrete bridge deck; the concrete bridge deck located on the upper part of the overall composite structure is forced to undergo downward bending deformation synchronously with the steel beam; based on the downward bending deformation, the bridge deck prestress corresponding to the release of elastic strain energy is generated in the negative bending moment section of the concrete bridge deck.

[0048] Specifically, after the controlled energy release unit completes the controlled energy release in this step, the bridge construction control system performs analysis and verification. The control system's logic control module first reads the residual arch height value and the geometric and material properties of the steel beam recorded at the end of the controlled energy release unit, including its elastic modulus. Moment of inertia of cross section Based on the principles of mechanics of materials, the measured springback deformation of the steel beam from its final locked state in the pre-deformation locking module to its current state was calculated. The rebound deformation quantifies the tendency of the steel beam to change from an upward arching state to its original straight or downward bending state after energy release. Due to the integral composite structure formed in the composite structure construction unit, the steel beam and the concrete bridge deck are rigidly connected by shear connectors. During this process, the shear connectors transmit the interface shear force to ensure that the deformation of the two is coordinated. Therefore, the rebound deformation of the steel beam will forcefully drive the concrete bridge deck bonded to it to undergo downward bending deformation simultaneously.

[0049] Next, the logic control module calls the composite beam section conversion method calculation program. The program calculates the cross-section of the concrete bridge deck based on its current elastic modulus. With the elastic modulus of steel beams ratio Converted to an equivalent steel section; where the elastic modulus of concrete is... The value is taken from the current dynamic elastic modulus measured in the condition monitoring and analysis unit. This is because it can more accurately reflect the actual stiffness of a material at the moment of stress. Combined with measured springback deformation... Based on the bridge span and the equivalent section stiffness of the overall composite structure, the fiber stress acting on the top surface of the negative bending moment section of the concrete bridge deck due to this energy release was calculated.

[0050] In the formula, This refers to the prestress on the top surface of the concrete bridge deck. The elastic modulus of concrete. This is the distance from the top surface of the concrete to the neutral axis of the converted section of the composite beam. Based on the measured springback deformation The curvature of the beam obtained from the structural boundary conditions, for the typical negative bending moment region transitioning from simply supported to continuous, has the following approximate calculation formula: ;in, It refers to the equivalent internal bending moment generated on the composite section when the steel beam is unlocked due to the elastic rebound tendency. Its value is calculated by back-calculating the difference in elastic potential energy or the amount of rebound deformation before and after the steel beam rebounds. It refers to the equivalent elastic modulus of steel-concrete composite structures; It refers to the moment of inertia of the overall composite structure about its composite neutral axis, calculated based on the transformed section method; curvature It can be obtained by numerical differentiation or analytical analysis based on the assumed deformation mode, according to the springback deformation curve.

[0051] Calculation results This refers to the prestressing stress generated to suppress cracking in the bridge deck. It should be understood that prestressing stress refers to the initial compressive stress actively generated within the concrete bridge deck using this method, with a direction opposite to the tensile stress caused by the service load. Finally, the calculated prestressing stress value is compared with the design value of the maximum tensile stress predicted by finite element analysis during the design phase, which is expected to be generated in this area during long-term operation due to vehicle loads, structural self-weight, and concrete shrinkage and creep. This verifies that the prestressing stress can effectively partially or completely offset the tensile stress. Offsetting here means that the prestressing stress and the future tensile stress are superimposed on the same cross-section, reducing the net tensile stress on the concrete or even converting it into compressive stress, thereby improving its crack resistance safety factor. The verification standard is usually set as follows: , The design value is the maximum tensile stress generated during long-term operation; or the net tensile stress after superposition is less than the standard tensile strength of concrete, to ensure that no through cracks appear in the structure under normal serviceability limit state. After completing the above comparison, the closed-loop logic verification from energy release to stress generation is completed, and an initial stress state report is provided for the bridge to enter the operation phase.

[0052] Among them, downward bending deformation refers to the trend of the geometric center line of the steel beam changing from an upward arched state to its original straight or downward bending state after energy release. Its quantitative index is the measured springback deformation. The role of shear connectors in this step is to ensure deformation coordination between the steel beam and the concrete bridge deck, transfer interfacial shear force, and allow them to bend together like a single component. Prestress refers to the initial compressive stress actively generated within the concrete bridge deck using this method, with a direction opposite to the tensile stress caused by the service load. Tensile stress refers to the stress component that causes cracking of the concrete during long-term operation, resulting from standard vehicle loads, structural dead loads, and the shrinkage and creep effects of the concrete material itself, collectively on the top surface of the bridge deck in the negative bending moment zone. Its design value is usually calculated based on bridge design specifications, taking into account partial factors in the load combination. Offset is a mechanical equilibrium concept, referring to the algebraic superposition of prestress and future tensile stress at the same concrete section location, reducing the net tensile stress on the concrete or even converting it into compressive stress, thereby improving its crack resistance safety factor. Concrete elastic modulus. The value is taken from the current dynamic elastic modulus measured in the state monitoring and analysis unit. Because it can more accurately reflect the actual stiffness of a material at the moment of stress.

[0053] For example, continuing from the previous example, the residual arch height of 2 mm and the locked arch height of 84.5 mm were read, and the measured rebound deformation was calculated. Assuming calculations based on structural mechanics, the curvature produced by this deformation mode at mid-span... The converted neutral axis distance of the composite section is the distance from the top surface of the concrete. Elastic modulus of concrete Substitute the values ​​into the formula to calculate: Calculations show that the prestress generated on the top surface of the concrete bridge deck... The compressive stress was approximately 3.33 MPa. The maximum tensile stress design value for the bridge's negative bending moment zone under long-term load combinations was retrieved from the design database; this value was 4.0 MPa. Comparison showed that the generated 3.33 MPa pre-compression stress could offset approximately 83% of the tensile stress, reducing the net tensile stress of the concrete to 0.67 MPa, lower than the standard tensile strength value of C50 concrete (approximately 2.65 MPa). This verifies that the method can effectively suppress cracking in the negative bending moment zone. The final pre-compression stress value, offset ratio, and initial stress state report were archived.

[0054] Each of the modules can be implemented in whole or in part through software, hardware, or a combination thereof. It supports hardware embedded in or independent of the processor in the computer device, and also supports software stored in the memory of the computer device, so that the processor can call and execute the operations corresponding to each of the above modules.

[0055] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of an integral bridge, characterized in that, include: The pre-deformation locking unit is used to construct a pre-deformation locking system for steel beams. A stiffness compensator is installed on the steel beam in the negative bending moment section of the steel composite beam. An external loading device is used to induce an upward arching pre-deformation in the steel beam, and the elastic strain energy generated by the upward arching pre-deformation is locked inside the steel beam through the stiffness compensator. The system includes a stiffness compensator installed at the bottom of the steel beam, comprising a wedge-shaped locking block, a drive actuator, and a stress monitoring sensor; controlling an external temporary loading device to apply force to the steel beam until the vertical displacement of the steel beam reaches the design target value; driving the wedge-shaped locking block inside the stiffness compensator to form a mechanical self-lock with the steel beam, and removing the external temporary loading device to store the elastic strain energy generated by the pre-deformation of the arch in the form of mechanical locking. The composite structure construction unit is configured to pour concrete bridge decks that work in conjunction with steel beams. A monitoring sensor network is pre-embedded above the locked steel beams, and the concrete is poured and cured, so that the concrete bridge decks and steel beams form a composite structure through shear connectors. The condition monitoring and analysis unit is used to acquire real-time material state parameters of concrete bridge decks. It uses a monitoring sensor network to collect multi-dimensional time-varying data and calculates material state parameters based on the multi-dimensional time-varying data. The material state parameters are compared with a preset energy release window model based on concrete compressive strength, elastic modulus and shrinkage strain to determine the timing of prestressing application that meets the model conditions. The controlled energy release unit is used to trigger the controlled energy release of the pre-deformation locking system. When the prestressing application time is reached, the control stiffness compensator is released from the locking state, releasing the elastic strain energy stored inside the steel beam and driving the steel beam to produce downward bending deformation. The prestress generation and verification unit is used to generate prestress in the bridge deck to suppress cracking. It utilizes the overall composite structure to transfer the downward bending deformation of the steel beam and introduces compressive stress in the negative bending moment section of the concrete bridge deck.

2. The stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of an integral bridge according to claim 1, characterized in that, A combined structural construction unit is used to perform the following steps: With the pre-deformation locking system in a locked state, the steel reinforcement binding of the bridge deck is completed; A network of monitoring sensors is deployed inside the concrete bridge deck to collect data on hydration heat, shrinkage strain, and elastic modulus. Concrete pouring and curing are carried out, and shear connectors are used to establish a shear-resistant connection between the concrete bridge deck and the steel beams.

3. The stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of an integral bridge according to claim 1, characterized in that, The condition monitoring and analysis unit is used to perform the following operations: The monitoring sensor network was activated to continuously collect multi-dimensional time-varying data on the hydration heat, elastic modulus, and shrinkage strain of the concrete bridge deck. Based on multi-dimensional time-varying data, the compressive strength growth curve, elastic modulus development curve, and shrinkage strain development trend of concrete bridge deck are calculated as material state parameters. The compressive strength growth curve, elastic modulus development curve, and shrinkage strain development trend are compared with the preset energy release window model. When the material state parameters meet the threshold requirements of the energy release window model, it is determined to be the time to apply prestress.

4. The stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of an integral bridge according to claim 1, characterized in that, Controlled energy release unit, used to perform the following steps: Generate an energy release control command containing the target unlocking rate and send it to the stiffness compensator; The stiffness compensator responds to the command and releases the mechanical self-locking state of its internal locking mechanism in a controlled manner; As the mechanical self-locking is released, the steel beam springs back from its pre-deformed, arched state to its original straight state.

5. A stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of an integral bridge according to claim 1, characterized in that, The prestress generation and verification unit is used to perform the following steps: The downward bending deformation caused by the springback of the steel beam is forcibly transferred to the concrete bridge deck through shear connectors. This forces the concrete bridge deck located on the upper part of the overall composite structure to bend downwards synchronously with the steel beams; The downward bending deformation generates prestress in the concrete bridge deck in the negative bending moment zone, corresponding to the release of elastic strain energy.

6. A stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of an integral bridge according to claim 1, characterized in that, Stress monitoring sensors are used to continuously monitor the stress changes of the steel beam and confirm that the stress value is maintained above the preset percentage of the target locked stress, thus verifying that the elastic strain energy is effectively locked.

7. A stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of an integral bridge according to claim 3, characterized in that, The energy release window model defines the compressive strength threshold, elastic modulus plateau criterion, and shrinkage strain rate stability criterion for allowing prestress to be applied; The specific timing for applying prestress is determined as follows: when the real-time calculated compressive strength is higher than the compressive strength threshold, the growth rate of the elastic modulus meets the elastic modulus plateau criterion, and the shrinkage strain change rate meets the shrinkage strain rate stability criterion, the timing for applying prestress is determined.

8. A stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of an integral bridge according to claim 4, characterized in that, The controlled release of the mechanical self-locking state of its internal locking mechanism specifically includes: During the process of releasing the mechanical self-locking state, the locking stress monitoring value fed back by the stress monitoring sensor is received in real time; Calculate the slope of the change in the locking stress monitoring value and control the absolute value of the slope to not exceed the preset safe release rate threshold to achieve closed-loop control.

9. A stiffness-compensating composite beam system for suppressing cracking in the negative bending moment zone of an integral bridge according to claim 5, characterized in that, The prestress generation and verification unit is also used to perform the following operations: The measured rebound deformation was calculated based on the difference in the pre-arch deformation of the steel beam before and after energy release. Based on the converted section stiffness of the overall composite structure, the actual prestress of the concrete bridge deck acting on the negative bending moment section of the concrete bridge deck is calculated. The actual prestress of the bridge deck is compared with the design value of tensile stress generated by long-term operational loads.

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