Steel-concrete composite support active anti-instability control method

Abstract

The application provides a steel-concrete composite support active anti-instability control method, comprising the following steps: S1: determining the basic parameters of the composite steel-concrete composite support; S2: in the service process of the steel-concrete composite support, the central control device collects real-time monitoring data through a sensing unit; S3: identifying the real axial force for stability analysis; S4: identifying the end equivalent eccentricity based on the end strain; S5: inverting the end rotation stiffness of the steel-concrete composite support; S6: dynamically correcting the calculation length coefficient and calculating the critical buckling bearing capacity; S7: performing stability safety factor discrimination; S8: implementing boundary enhancement control or boundary-axial force collaborative active control. The application relates to the technical field of geotechnical engineering deep foundation pit support and intelligent monitoring control, and can solve the problem that the prior art cannot combine the field monitoring information to identify the end constraint state in real time and dynamically correct the stability calculation parameters.

Description

Technical Field

[0001] This invention relates to the field of deep foundation pit support and intelligent monitoring and control technology in geotechnical engineering, and in particular to an active anti-instability control method for steel-concrete composite support. Background Technology

[0002] In the construction of complex underground structures, steel-concrete composite supports have been increasingly used in large-span foundation pits and special underground space construction scenarios due to their high load-bearing capacity, high overall stiffness, and fast construction speed. Compared with ordinary steel supports, this type of support has a larger span, heavier components, and more complex constraint conditions. During long-term service, it is not only subjected to axial pressure, but also affected by multiple factors such as temperature changes, concrete creep and shrinkage, deformation of the retaining structure, and degradation of the constraint at the support ends.

[0003] In existing engineering projects, the control of support safety is usually based on monitoring the total axial force or performing static calculations according to predetermined boundary conditions. However, for steel-concrete composite supports, the monitored total axial force often includes components related to temperature, time, and the actual deformation of the retaining structure. If the monitored total axial force is directly used as the basis for stability judgment and control, it can easily lead to deviations in the judgment of the actual compressive state of the support. Especially in open or semi-open foundation pits, changes in ambient temperature will cause fluctuations in the axial force of the composite support, while concrete creep and shrinkage will lead to slow adjustments in stress over a long period of time. If these additional effects are not isolated, it is difficult to accurately obtain the actual axial pressure for stability analysis.

[0004] On the other hand, existing stability calculations for struts typically assume that the boundary conditions at the support ends are fixed, such as performing a one-time design calculation based on ideal hinged, semi-rigid, or fixed connections. However, during actual construction, the rotational constraint stiffness at the ends dynamically changes due to the development of horizontal displacement of the diaphragm wall, local torsion of the capping or lintel beams, changes in node gaps, and loosening of the support end connections. Even without a significant increase in axial force, the calculated length of the support may increase due to a decrease in end rotational stiffness, leading to a decrease in the critical buckling bearing capacity and insufficient stability safety reserve. Existing technologies lack a method that can identify the end constraint state in real time and dynamically correct stability calculation parameters by combining on-site monitoring information, making it difficult to detect such "boundary degradation type" instability risks in a timely manner.

[0005] In addition, although existing monitoring systems can collect tilt angle, deflection or strain data, most of them are only used for alarm display. They have not yet formed a closed-loop control chain of "real force identification - end stiffness inversion - calculated length correction - active control execution", which results in a lack of direct correlation between monitoring data and actuators, and cannot achieve active defense against the stable state of combined supports.

[0006] Therefore, there is a need to provide an active anti-instability control method for steel-concrete composite supports, which can solve the problem in the existing technology that cannot identify the end constraint state in real time and dynamically correct the stability calculation parameters by combining on-site monitoring information. Summary of the Invention

[0007] The purpose of this invention is to provide an active anti-instability control method for steel-concrete composite supports, which can solve the problem in the prior art that it is impossible to identify the end constraint state in real time and dynamically correct the stability calculation parameters by combining on-site monitoring information.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A method for active instability prevention and control of steel-concrete composite supports includes the following steps: Step S1: Determine the foundation parameters of the composite steel-concrete composite support; Step S2: During the service of the steel-concrete composite support, the central control device collects real-time monitoring data through the sensing unit; Step S3: Identify the actual axial forces used for stability analysis; Step S4: Identify the equivalent end eccentricity based on end strain; Step S5: Invert the end rotational stiffness of the steel-concrete composite support; Step S6: Dynamically correct the calculated length factor and calculate the critical buckling capacity; Step S7: Determine the stability and safety factor; Step S8: Implement boundary enhancement control or boundary-axial force coordinated active control.

[0009] In step S1, sensing units are deployed inside and on the surface of the steel-concrete composite support, an end active control device is installed between the end of the steel-concrete composite support and the foundation pit retaining structure, a mid-span control unit is set between the mid-span of the steel-concrete composite support and the bottom of the foundation pit, and a central control device electrically connected to the sensing units is set outside the foundation pit. The sensing unit includes several distributed fiber optic gratings or distributed fiber optic sensors embedded in the core concrete of the steel-concrete composite support, an axial force monitoring device and an end rotation sensor installed at the end of the steel-concrete composite support, and a sensor group installed on the surface of the steel-concrete composite support, which includes one or more tilt sensors, a mid-span displacement sensor and one or more temperature sensors. The end active control device includes a servo hydraulic actuator, a lockable ball joint support, and a ball joint mechanical locking device, used to adjust the support axial force and end rotation constraint of the steel-concrete composite support; The mid-span control unit includes adjustable lattice columns and their vertical adjustment actuators; The central control unit is used to perform real force identification, end stiffness inversion, equivalent calculated length correction, stability safety factor determination, and control command output.

[0010] In step S1, the initial installation time of the steel-concrete composite support (3) is obtained. The basic parameters include the elastic modulus of steel. , elastic modulus of concrete cross-sectional area of ​​steel components Effective cross-sectional area of ​​concrete Coefficient of linear expansion of steel Coefficient of linear expansion of concrete Component length Initial installation temperature Initial axial force during installation and the initial equivalent flexural stiffness of the steel-concrete composite support (3) ; Steel-concrete composite support (3) at time The equivalent axial stiffness is: Steel-concrete composite support (3) at time The equivalent linear expansion coefficient is: in, The value of is the reduction factor for the time-varying effect of concrete, which ranges from 0.30 to 1.00.

[0011] In step S2, the real-time monitoring data includes total axial force. Average temperature Strain values ​​at both sides or multiple points of the end section End angle Mid-span displacement or deflection ; Among them, total axial force Obtained by axial force monitoring device (6) or strain inversion; real-time temperature Temperature sensor obtained from distributed fiber optic sensor (9) or sensor group (10); end strain value The end rotation angle is measured by a distributed fiber optic grating or a distributed fiber optic sensor (9) installed at the end section of the steel-concrete composite support (3). Obtained by end angle sensor (15); mid-span displacement or deflection The displacement is obtained from the mid-span displacement sensor of the sensor group (10).

[0012] Step S3 includes the following sub-steps: Step S31: Based on real-time temperature With initial installation temperature The difference is used to calculate the temperature increment. The calculation formula is: Step S32: Calculate the temperature component The calculation formula is: In the formula, This is the temperature constraint correction factor, with a value ranging from 0.10 to 1.00; Step S33: Calculate the time effect component The calculation formula is: In the formula, This is the time effect correction factor, and its value ranges from 0.10 to 1.20; This is the function for the influence of concrete creep, with a value range of 0 to 1; Step S34: Calculate the true axial force after eliminating the effects of temperature and time. The calculation formula is: In the formula, The correction factor for on-site calibration has a value range of 0.80 to 1.20. This is the actual axial force after eliminating the effects of temperature and time.

[0013] Step S4 includes the following sub-steps: Step S41: Select a control section at the end of the steel-concrete composite support (3), and use a distributed fiber optic grating or a distributed fiber optic sensor (9) to measure the strain values ​​on the upper and lower sides of the control section, and calculate the average axial strain of the control section. and curvature The calculation formula is: in, and These represent the strain at two measuring points on the upper and lower sides of the control section, respectively. The distance between the two measuring points; Step S42: Calculate the end bending moment based on the bending relationship of the control section at the end of the steel-concrete composite support (3). The calculation formula is: in, For steel-concrete composite support (3) at time The equivalent bending stiffness; Step S43: Define the equivalent eccentricity at the end Its defining formula is: .

[0014] Step S5 includes the following sub-steps: Step S51: Simplify the steel-concrete composite support (3) into a compression-bending member with rotational springs at both ends. The rotational stiffness of the end of this compression-bending member is denoted as... ; Step S52: Calculate the current end rotational stiffness based on the relationship between the end bending moment and end rotation angle of the compression-bending member. The calculation formula is: in, The end angle is measured by the end angle sensor (15); The end bending moment obtained in step S4; In step S52, when end rotation sensors (15) are installed at both ends of the steel-concrete composite support (3), the rotational stiffness of the left end is calculated respectively. Rotational stiffness at the right end .

[0015] Step S6 includes the following sub-steps: Step S61: To characterize the instability sensitivity of the steel-concrete composite support (3) under the current boundary conditions, a calculation length factor is introduced. ; The calculation of the length coefficient This refers to the equivalent calculated length of a compression member under actual boundary conditions as a hinged compression member at both ends, compared to the member length. The ratio, that is: In the formula, For a moment The equivalent computational length; Step S62: Based on the end rotational stiffness Equivalent bending stiffness and component length Establish boundary stiffness parameters : Step S63: Based on the stability theory of semi-rigid compression members, the current calculation length coefficient is obtained through numerical iteration of the characteristic equation. : in, and These are the left and right boundary stiffness parameters, based on the rotational stiffness of the left end. Rotational stiffness at the right end Using boundary stiffness parameters respectively Calculated; This represents the length coefficient solution function determined by the semi-rigid boundary conditions; Step S64: Calculate the time. Critical buckling capacity of steel-concrete composite bracing (3) under current boundary conditions : .

[0016] Step S7 includes the following sub-steps: Step S71: Define the real-time stability safety factor for: Among them, the real-time stability safety factor The smaller the value, the closer the steel-concrete composite support (3) is to the critical state of instability; Step S72: Set the stability control threshold and stable early warning threshold And satisfy: in, To ensure stable control, the threshold value is set between 1.20 and 1.50. To stabilize the early warning threshold, a range of 1.50 to 2.00 is adopted; when When the steel-concrete composite support (3) is determined to have entered the normal stable zone, the current support state of the steel-concrete composite support (3) is maintained, monitoring continues and the next cycle begins; when When the steel-concrete composite support (3) is determined to have entered the warning zone, the boundary reinforcement control in step S8 is initiated. when When the steel-concrete composite support (3) is determined to be in the active control zone, the boundary-axial force collaborative active control step S8 is entered.

[0017] Step S8 includes the following sub-steps: Step S81: Based on the real-time stability safety factor and end rotational stiffness In response to changes in [the situation], the following control strategy will be implemented: ① Boundary enhancement control; when And the end rotational stiffness was identified. When the price continues to fall, boundary augmentation control is prioritized. Boundary augmentation control includes: Action A: Drive the ball joint mechanical locking device (14) at the end of the steel-concrete composite support (3) to improve the end rotation constraint and increase the end rotation stiffness. ; Action B: Adjust the height of the mid-span lattice column of the mid-span control unit (4) to change the mid-vertical constraint conditions and flexural shape of the steel-concrete composite support (3); ② Boundary-axial force coordinated active control; when At the same time, while performing the boundary enhancement control mentioned above ①, the servo hydraulic actuator (12) is driven to perform compensatory unloading or force redistribution on the steel-concrete composite support (3), so that the actual axial force is applied. Descend to a safe range; Step S82: After performing boundary reinforcement control, update the boundary parameters and recalculate the end rotational stiffness. Calculate the length coefficient Critical buckling bearing capacity Real-time stability safety factor ; After implementing boundary-axial force coordinated active control, the boundary parameters are updated and the actual axial force is recalculated. End rotational stiffness Calculate the length coefficient Critical buckling bearing capacity Real-time stability safety factor ; Step S83: The central control device (8) outputs the end rotation stiffness based on the real-time calculation results. The control commands for the target value of the control, the height adjustment of the mid-span lattice column, and the unloading amount of the servo hydraulic actuator (12); Step S84: After executing the control command, determine whether the steel-concrete composite support (3) meets the conditions: That is, whether the state of the steel-concrete composite support (3) has returned to the normal stable zone. If yes, then end the current round of control and return to real-time monitoring. If no, return to step S7 and re-determine the stability safety factor.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a method for identifying the true force for stability analysis. Instead of directly using the monitored total axial force as the input for stability analysis, it removes the temperature and time effects to obtain the true axial force that better characterizes the deformation and earth pressure changes of the retaining structure. This reduces the interference of temperature and time effects on stability judgment, improves the accuracy of the stability analysis input from the source, and thus improves the reliability of the stability analysis results.

[0019] 2. This invention provides a rotational stiffness inversion method based on end monitoring information. Inclination sensors and distributed fiber optic strain sensors are arranged at the ends of steel-concrete composite supports to obtain the end rotation angle and the bending strain state of the end section. Then, the equivalent eccentricity and end bending moment of the end are identified, and the current rotational constraint stiffness of the end is inverted. This method can dynamically reflect the degradation or enhancement of the end constraint of steel-concrete composite supports during actual construction, breaking through the assumption of static invariance of boundary conditions in traditional stability verification.

[0020] 3. By dynamically correcting the calculated length, this invention can directly transform the "change in end stiffness" into a calculable result of the "change in stable safety reserve", thus transforming the risk of instability of steel-concrete composite supports from empirical judgment to real-time quantitative identification.

[0021] 4. This invention provides an active instability prevention control method based on dynamic correction of calculated length. According to the end rotation stiffness obtained by real-time inversion, the calculated length coefficient and critical buckling bearing capacity of the steel-concrete composite support are updated. Through the stability safety factor discrimination logic, the end locking device, the mid-span lattice column adjustment mechanism and the servo axial force adjustment device are linked to form an active instability prevention system that coordinates boundary condition control and axial force control. The end boundary reinforcement, mid-span lattice column adjustment and axial force control are integrated into a unified active control system, which can actively intervene before the instability risk develops into significant deformation, thereby improving the stability and safety of steel-concrete composite supports in the construction of complex underground structures. Attached Figure Description

[0022] The above and other objects, features and advantages of this disclosure will become more apparent from the accompanying drawings, in which like reference numerals generally denote like parts.

[0023] Figure 1 This is a schematic diagram illustrating the end equivalent eccentricity identification and rotational stiffness inversion principle of the active anti-instability control method for steel-concrete composite supports of the present invention. Figure 2 This is a flowchart of the dynamic correction of the calculation length and the stability judgment of the active anti-instability control method for steel-concrete composite supports of the present invention; Figure 3This is a flowchart of the boundary-axial force coordinated active control of the active anti-instability control method for steel-concrete composite supports of the present invention; Figure 4 This is a schematic diagram illustrating the application scenario of the active anti-instability control method for steel-concrete composite supports of the present invention; Figure 5 This is a schematic diagram of the deployment of the internal sensing unit of the steel-concrete composite support in the active anti-instability control method of the steel-concrete composite support of the present invention; Figure 6 This is a schematic diagram of the deployment of the end sensing unit of the steel-concrete composite support in the active anti-instability control method of the steel-concrete composite support of the present invention.

[0024] In the diagram, 2 is the foundation pit retaining structure (diaphragm wall), 3 is the steel-concrete composite support, 3a is the steel pipe shell, 3b is the core concrete, 4 is the mid-span control unit, 5 is the end active control device, 6 is the axial force monitoring device, 7 is the data transmission line, 8 is the central control device (data processing terminal), 9 is the distributed fiber optic grating or distributed fiber optic sensor, 10 is the sensor group, 11 is the flange connection node, 12 is the servo hydraulic actuator, 13 is the lockable ball joint support, 14 is the ball joint mechanical locking device, and 15 is the end angle sensor. Detailed Implementation

[0025] The active anti-instability control method for steel-concrete composite supports proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0026] Please see the appendix Figure 1 and attached Figure 2 A method for active instability prevention and control of steel-concrete composite supports includes the following steps: Step S1: Determine the foundation parameters of the composite steel-concrete composite support 3.

[0027] Please see the appendix Figure 4 and attached Figure 5 In step S1, sensing units are deployed inside and on the surface of the steel-concrete composite support 3. An end active control device 5 is installed between the end of the steel-concrete composite support 3 and the foundation pit retaining structure (usually a diaphragm wall) 2 through a flange connection node 11. A mid-span control unit 4 is set between the mid-span of the steel-concrete composite support 3 and the bottom of the foundation pit. A central control device (data processing terminal) 8 is set outside the foundation pit and electrically connected to the sensing units through a data transmission line 7.

[0028] Steel-concrete composite support 3 refers to a support member formed by the joint stress of steel components (steel pipe shell 3a) and concrete components (core concrete 3b), including but not limited to steel pipe concrete support, steel-concrete composite support, steel box-concrete composite support, and the above-mentioned types of composite supports formed by precast segment assembly.

[0029] Please see the appendix Figure 4 To be continued Figure 6 The sensing unit includes several distributed fiber optic gratings or distributed fiber optic sensors 9 embedded in the core concrete 3b of the steel-concrete composite support 3, an axial force monitoring device 6 and an end rotation angle sensor 15 installed at the end of the steel-concrete composite support 3, and a sensor group 10 installed on the surface of the steel-concrete composite support 3, etc. The sensor group 10 includes one or more tilt sensors, a mid-span displacement sensor and one or more temperature sensors.

[0030] Among them, the distributed fiber optic grating or distributed fiber optic sensor 9 is used to acquire concrete temperature data and strain data of steel-concrete composite support 3, the axial force monitoring device 6 is used to acquire axial force data of steel-concrete composite support 3, the tilt sensor is used to acquire tilt data of steel-concrete composite support 3, the mid-span displacement sensor is used to acquire displacement data of steel-concrete composite support 3, the temperature sensor is used to acquire surface temperature data of steel-concrete composite support 3, and the end rotation sensor 15 is used to acquire end rotation data of steel-concrete composite support 3.

[0031] Preferably, the sensors in the sensor group 10 can be surface-mounted MEMS sensors, distributed fiber optic gratings or distributed fiber optic sensors 9, axial force monitoring devices 6 and end angle sensors 15. The sensor group 10 is a conventional monitoring and sensing device in the art. The appropriate type and specification of the sensor can be selected according to the actual monitoring needs, and it can be installed at a suitable position on the steel-concrete composite support 3 according to the data acquisition requirements. The data acquisition process and working principle will not be described in detail here.

[0032] Please see the appendix Figure 6 The end active control device 5 includes a servo hydraulic actuator (for adjusting axial force) 12, a lockable ball joint support (for adjusting stiffness) 13, and a ball joint mechanical locking device (e.g., locking bolt or wedge) 14, for adjusting the support axial force and end rotation constraint of the steel-concrete composite support 3.

[0033] The mid-span control unit 4 includes an adjustable lattice column and its vertical adjustment actuator, used to adjust the mid-span support elevation and constraint status.

[0034] The mid-span control unit 4, the servo hydraulic actuator 12, the lockable ball joint support 13, and the ball joint mechanical locking device 14 are all installation and adjustment equipment for steel-concrete composite support 3 in this field, and their specific installation and adjustment processes will not be described in detail here.

[0035] The central control device (data processing terminal) 8 is used to perform real force identification, end stiffness inversion, equivalent calculation length correction, stability safety factor discrimination and control command output.

[0036] Preferably, the central control device (data processing terminal) 8 can be a computer device equipped with a corresponding execution program, used to collect sensor data from the sensing unit, execute the calculation steps of steps 1 to 7, and execute the control step of step 8.

[0037] In step S1, the initial installation time of the steel-concrete composite support 3 is obtained. The basic parameters include the elastic modulus of steel. , elastic modulus of concrete cross-sectional area of ​​steel components Effective cross-sectional area of ​​concrete Coefficient of linear expansion of steel Coefficient of linear expansion of concrete Component length Initial installation temperature Initial axial force during installation and the initial equivalent bending stiffness of the steel-concrete composite support 3 .

[0038] According to the support requirements of the foundation pit, in addition to the initial installation temperature In addition, the aforementioned basic parameters were determined during the design of the steel-concrete composite support 3 to ensure that the steel-concrete composite support 3 could meet the safety requirements of the foundation pit. Initial installation temperature. The ambient temperature during the installation of the steel-concrete composite support 3.

[0039] Steel-concrete composite support 3 at time The equivalent axial stiffness is: Steel-concrete composite support 3 at time The equivalent linear expansion coefficient is: in, It is the reduction factor for time-varying effects of concrete, used to characterize the stiffness reduction of concrete caused by creep, shrinkage and long-term service.

[0040] The time-varying effect reduction factor for concrete ranges from 0.3 to 1.00, preferably from 0.60 to 1.00; it can be taken as 1.00 at the initial installation of the steel-concrete composite support 3, and gradually decreases with the increase of service time. For temporary foundation pit support projects, a typical value can be 0.75 to 0.95. This time-varying effect reduction factor for concrete can be determined based on the concrete age, ambient humidity, cross-sectional dimensions, concrete strength grade, and creep shrinkage test results, or it can be calibrated on-site based on monitoring data from similar projects.

[0041] Preferably, the time-varying effect reduction factor of concrete can be determined according to the following relationship: time-varying effect reduction factor of concrete = 1 / [1 + modified creep coefficient], wherein the modified creep coefficient can be obtained by multiplying the concrete creep coefficient by the constraint influence coefficient, and the constraint influence coefficient is taken as 0.20 to 1.00.

[0042] Step S2: During the service of the steel-concrete composite support 3, the central control device (data processing terminal) 8 collects real-time monitoring data through the sensing unit.

[0043] In step S2, the real-time monitoring data includes total axial force. Average temperature Strain values ​​at both sides or multiple points of the end section End angle Mid-span displacement or deflection .

[0044] Among them, total axial force It can be obtained from the axial force monitoring device 6 or strain inversion; real-time temperature (average temperature) The end strain value can be obtained from the temperature sensor of the distributed fiber optic sensor 9 or the sensor group 10. Preferably, the end rotation angle is measured by a distributed fiber optic grating or distributed fiber optic sensor 9 located near the ends of the steel-concrete composite support 3. Preferably obtained by the end angle sensor 15; mid-span displacement or deflection. Preferably, the displacement is obtained by the mid-span displacement sensor of the sensor group 10, but it can also be obtained by existing inclinometer systems or optical measuring devices.

[0045] Step S3: Identify the actual axial forces used for stability analysis.

[0046] Step S3 includes the following sub-steps: Step S31: Based on real-time temperature With initial installation temperature The difference is used to calculate the temperature increment. The calculation formula is: Step S32: Calculate the temperature component The calculation formula is: In the formula, The temperature constraint correction coefficient has a value range of 0.10 to 1.00, preferably 0.30 to 0.90. When the steel-concrete composite support 3 is nearly fully constrained at both ends and the temperature distribution is relatively uniform, its value is close to 1.00. When there is a releaseable displacement at the end of the steel-concrete composite support 3, a node gap, or the temperature effect is only partially converted into axial internal force, its value is reduced accordingly.

[0047] The temperature constraint correction coefficient can be calibrated on-site by regression analysis of the axial force-temperature response curve during the initial temperature change phase of installation, or it can be pre-determined based on the end boundary constraint stiffness, support length, and node construction conditions.

[0048] Step S33: Calculate the time effect component The calculation formula is: In the formula, The time-effect correction factor ranges from 0.10 to 1.20, preferably from 0.30 to 0.90. For temporary support projects with short service periods, stable environmental conditions, and minimal impact from concrete creep, a smaller value can be used for this time-effect correction factor; for projects with long service periods, short concrete ages, or significant variations in environmental humidity, a larger value can be used. This time-effect correction factor can be determined by adjusting for concrete material testing, design creep and shrinkage parameters, empirical values ​​from similar projects, or long-term axial force monitoring data from the field. The function representing the effect of concrete creep is a dimensionless function whose value increases monotonically with time and gradually stabilizes. Its value ranges from 0 to 1. The function is 0 at the initial installation time and gradually increases with the service time.

[0049] Step S34: Calculate the true axial force after eliminating the effects of temperature and time. The calculation formula is: In the formula, The field calibration correction factor has a value range of 0.80 to 1.20, preferably 0.90 to 1.10, and a typical value of 1.00. This field calibration correction factor can be determined by comparing the initial loading test after the steel-concrete composite support 3 is installed, the jack loading calibration, the axial force gauge readings and strain inversion results, or by comparing multi-source monitoring data of the same steel-concrete composite support 3 under stable working conditions. This represents the actual axial force after eliminating the effects of temperature and time. Actual axial force. This serves as the basis for subsequent stability analysis and active control.

[0050] Step S4: Identify the equivalent end eccentricity based on end strain.

[0051] Step S4 includes the following sub-steps: Step S41: Select a control section near the end of the steel-concrete composite support 3 (a distributed fiber optic grating or distributed fiber optic sensor 9 has been installed at this control section). Use the distributed fiber optic grating or distributed fiber optic sensor 9 to measure the strain values ​​at different locations in the control section, and calculate the average axial strain of the control section. and curvature .

[0052] Preferably, distributed fiber optic gratings or distributed fiber optic sensors 9 can be arranged on the upper and lower sides of the control section at the end of the steel-concrete composite support 3, so that the average axial strain can be measured. and curvature The calculation formula is: in, and These represent the strain at two measuring points on the upper and lower sides of the control section, respectively. The distance between the two measuring points is denoted as .

[0053] Step S42: Calculate the end bending moment based on the bending relationship of the control section at the end of the steel-concrete composite support (3). The calculation formula is: in, For steel-concrete composite support (3) at time The equivalent bending stiffness.

[0054] Step S43: Define the equivalent eccentricity at the end Its defining formula is: .

[0055] The equivalent eccentricity at the end is used to characterize the degree of deviation of the actual compressive line at the end of the support from the centroid of the control section. Therefore, the "equivalent eccentricity at the end measured by the distributed fiber grating or the distributed fiber sensor 9" is not the eccentricity value directly output by the sensor, but is the equivalent force eccentricity calculated by inverting the curvature through the strain distribution of the control section at the end and then converting it according to the relationship between bending moment and axial force.

[0056] Step S5: Invert the end rotational stiffness of the steel-concrete composite support 3.

[0057] Step S5 includes the following sub-steps: Step S51: Simplify the steel-concrete composite support 3 into a compression-bending member with rotational springs at both ends. The end rotational stiffness of this compression-bending member is denoted as... .

[0058] Step S52: Calculate the current end rotational stiffness based on the relationship between the end bending moment and end rotation angle of the compression-bending member. The calculation formula is: in, The end angle is measured by the end angle sensor 15; The end bending moment is obtained in step S4.

[0059] In step S52, when end rotation sensors 15 are installed at both ends of the steel-concrete composite support 3, the rotational stiffness of the left end can be calculated separately. Rotational stiffness at the right end This is used for subsequent stability analysis under asymmetric boundary conditions.

[0060] Step S6: Dynamically correct the calculated length factor and calculate the critical buckling bearing capacity.

[0061] Step S6 includes the following sub-steps: Step S61: To characterize the instability sensitivity of the steel-concrete composite support 3 under the current boundary conditions, a calculation length factor is introduced. .

[0062] The calculation of the length coefficient This refers to the equivalent calculated length of a compression member under actual boundary conditions (the compression member being the end compression member in the existing compression member stability calculation, a conventional component and calculation method in this field, which will not be elaborated here) compared to the component length when it is converted into an equivalent two-end hinged compression member. The ratio, that is: In the formula, For a moment The equivalent computational length; The larger the value, the weaker the boundary constraints, and the more easily the steel-concrete composite support 3 becomes unstable.

[0063] Step S62: Based on the end rotational stiffness Equivalent bending stiffness and component length Establish boundary stiffness parameters : .

[0064] Step S63: Based on the stability theory of semi-rigid compression members, the current calculation length coefficient is obtained through numerical iteration of the characteristic equation. : in, and These are the left and right boundary stiffness parameters, which can be based on the rotational stiffness of the left end. Rotational stiffness at the right end Using boundary stiffness parameters respectively Calculated; This represents the length coefficient solution function determined by the semi-rigid boundary conditions.

[0065] Step S64: Calculate the time. Critical buckling capacity of steel-concrete composite brace 3 under current boundary conditions : .

[0066] Step S7: Determine the stability and safety factor.

[0067] Step S7 includes the following sub-steps: Step S71: Define the real-time stability safety factor for: Among them, the real-time stability safety factor The smaller the value, the closer the steel-concrete composite support 3 is to the critical state of instability.

[0068] Step S72: Set the stability control threshold and stable early warning threshold And satisfy: in, To ensure stable control, a threshold value of 1.20 to 1.50 is preferred. To ensure a stable early warning threshold, a value of 1.50 to 2.00 is preferred.

[0069] when When the steel-concrete composite support 3 is determined to have entered the normal stable zone, the current support state of the steel-concrete composite support 3 is maintained, monitoring continues, and the cycle begins.

[0070] when When the steel-concrete composite support 3 is determined to have entered the warning zone, the boundary reinforcement control in step S8 is initiated.

[0071] when When the steel-concrete composite support 3 is determined to be in the active control zone, step S8 is entered into the boundary-axial force coordinated active control.

[0072] Please see the appendix Figure 3 Step S8: Implement boundary enhancement control or boundary-axial force coordinated active control.

[0073] Step S8 includes the following sub-steps: Step S81: Based on the real-time stability safety factor and end rotational stiffness In response to changes in [the situation], the following control strategy will be implemented: ① Boundary enhancement control; when And the end rotational stiffness was identified. When the price continues to fall, boundary augmentation control is prioritized. Boundary augmentation control includes: Action A: Drive the ball joint mechanical locking device 14 at the end of the steel-concrete composite support 3 to improve the end rotation constraint and increase the end rotation stiffness. .

[0074] Action B: Adjust the height of the mid-span lattice column of the mid-span control unit 4, change the mid-vertical constraint conditions and flexural shape of the steel-concrete composite support 3, and suppress the development of unfavorable bending modes.

[0075] Adjusting the height of the mid-span lattice column can reduce the equivalent calculation length. The reason is that the mid-span lattice column not only provides vertical support but also constrains the lateral deformation of the supporting bending members. When the height or stress state of the mid-span lattice column is adjusted, the mid-span constraint conditions of the steel-concrete composite support 3 change accordingly, transforming the original deflection pattern, which was close to the overall buckling of a single span, into a segmented deflection pattern constrained by the midpoint. This reduces the effective half-wave length of the instability waveform and decreases the calculated length factor. and equivalent computational length This improves the critical buckling bearing capacity. .

[0076] ② Boundary-axial force coordinated active control.

[0077] when At the same time, while performing the boundary enhancement control described above ①, the servo hydraulic actuator 12 is driven to perform compensatory unloading or force redistribution on the steel-concrete composite support 3, so that the actual axial force is applied. Descending to a safe range.

[0078] The safe zone refers to the range within which the actual axial force is allowed under the conditions of satisfying the deformation control requirements of the foundation pit retaining structure 2 and the stability requirements of the steel-concrete composite support 3. The safe zone includes a lower safety limit and a higher safety limit, where the lower safety limit is the minimum support axial force required to maintain the deformation control of the foundation pit retaining structure 2, and the higher safety limit is the maximum allowable actual axial force determined based on the current critical buckling bearing capacity and the stability warning threshold.

[0079] Preferably, the safety range satisfies: lower safety limit ≤ actual axial force ≤ upper safety limit; wherein, the lower safety limit can be taken as 0.70 to 0.90 of the design support axial force, or as the minimum support axial force calculated based on the deformation control of the foundation pit retaining structure 2; the upper safety limit can be taken as the ratio of the current critical buckling bearing capacity to the stability warning threshold, so that the steel-concrete composite support 3, after adjustment, satisfies that the real-time stability safety factor is not less than the stability warning threshold.

[0080] When the lower safety limit is greater than the upper safety limit, it indicates that unloading or force redistribution alone cannot simultaneously meet the deformation control and support stability control requirements of the foundation pit retaining structure 2. At this time, the central control device stops unloading and issues an alarm command to increase boundary constraints, add temporary supports, or adjust the construction conditions.

[0081] Step S82: After performing boundary reinforcement control, update the boundary parameters and recalculate the end rotational stiffness. Calculate the length coefficient Critical buckling bearing capacity Real-time stability safety factor .

[0082] After implementing boundary-axial force coordinated active control, the boundary parameters are updated and the actual axial force is recalculated. End rotational stiffness Calculate the length coefficient Critical buckling bearing capacity Real-time stability safety factor .

[0083] Step S83: The central control device (data processing terminal) 8 outputs the end rotation stiffness based on the real-time calculation results. The control commands include the target value of the control, the height adjustment of the mid-span lattice column, and the unloading amount of the servo hydraulic actuator 12.

[0084] Step S84: After executing the control command, determine whether the steel-concrete composite support 3 meets the conditions: That is, whether the state of the steel-concrete composite support 3 has returned to the normal stable zone. If yes, then end the current round of control and return to real-time monitoring. If no, return to step S7 and re-determine the stability safety factor.

[0085] This invention first eliminates the effects of temperature and time from the monitored total axial force to obtain the true axial force for stability analysis; then, it combines end strain, tilt angle, and mid-span deformation information to invert the rotational constraint stiffness at the ends of the steel-concrete composite support 3, and dynamically corrects the calculated length and critical buckling bearing capacity of the support accordingly; finally, based on the real-time stability safety factor, it triggers boundary control and axial force control to achieve proactive identification and defense against the instability risk of the steel-concrete composite support 3, and is applicable to complex underground structure construction scenarios such as large-span foundation pits, basements under existing buildings, and pipe jacking starting shafts.

[0086] In a preferred embodiment, the central control device (data processing terminal) 8 receives monitoring data at set time intervals and first calculates the actual axial force. Then calculate the equivalent eccentricity at the end. End rotational stiffness Calculate the length coefficient and real-time stability safety factor When the real-time stability safety factor is detected... Upon entering the warning zone, priority is given to adjusting the end locking state (i.e., end rotation constraint) and the height of the mid-span lattice column; when the real-time stability safety factor is detected... When entering the active control zone, the servo hydraulic actuator 12 is linked to implement unloading control, thereby forming a graded intervention mechanism for the stability risk of the steel-concrete composite support 3.

[0087] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A method for active instability prevention and control of steel-concrete composite supports, characterized in that, Includes the following steps: Step S1: Determine the foundation parameters of the composite steel-concrete composite support (3); Step S2: During the service of the steel-concrete composite support (3), the central control device (8) collects real-time monitoring data through the sensing unit; Step S3: Identify the actual axial forces used for stability analysis; Step S4: Identify the equivalent end eccentricity based on end strain; Step S5: Invert the end rotational stiffness of the steel-concrete composite support (3); Step S6: Dynamically correct the calculated length factor and calculate the critical buckling capacity; Step S7: Determine the stability and safety factor; Step S8: Implement boundary enhancement control or boundary-axial force coordinated active control.

2. The active anti-instability control method for steel-concrete composite supports as described in claim 1, characterized in that, In step S1, sensing units are deployed inside and on the surface of the steel-concrete composite support (3), an end active control device (5) is installed between the end of the steel-concrete composite support (3) and the foundation pit retaining structure (2), a mid-span control unit (4) is set between the mid-span of the steel-concrete composite support (3) and the bottom of the foundation pit, and a central control device (8) electrically connected to the sensing units is set outside the foundation pit. The sensing unit includes several distributed fiber optic gratings or distributed fiber optic sensors (9) embedded in the core concrete (3b) of the steel-concrete composite support (3), an axial force monitoring device (6) and an end rotation sensor (15) installed at the end of the steel-concrete composite support (3), and a sensor group (10) installed on the surface of the steel-concrete composite support (3). The sensor group (10) includes one or more tilt sensors, a mid-span displacement sensor and one or more temperature sensors. The end active control device (5) includes a servo hydraulic actuator (12), a lockable ball joint support (13), and a ball joint mechanical locking device (14), used to adjust the support axial force and end rotation constraint of the steel-concrete composite support (3); The mid-span control unit (4) includes adjustable lattice columns and their vertical adjustment actuators; The central control device (8) is used to perform real force identification, end stiffness inversion, equivalent calculation length correction, stability safety factor discrimination and control command output.

3. The active anti-instability control method for steel-concrete composite supports as described in claim 1, characterized in that, In step S1, the initial installation time of the steel-concrete composite support (3) is obtained. The basic parameters include the elastic modulus of steel. , elastic modulus of concrete cross-sectional area of ​​steel components Effective cross-sectional area of ​​concrete Coefficient of linear expansion of steel Coefficient of linear expansion of concrete Component length Initial installation temperature Initial axial force during installation and the initial equivalent flexural stiffness of the steel-concrete composite support (3) ; Steel-concrete composite support (3) at time The equivalent axial stiffness is: Steel-concrete composite support (3) at time The equivalent linear expansion coefficient is: in, The value of is the reduction factor for the time-varying effect of concrete, which ranges from 0.30 to 1.

00.

4. The active anti-instability control method for steel-concrete composite supports as described in claim 1, characterized in that, In step S2, the real-time monitoring data includes total axial force. Average temperature Strain values ​​at both sides or multiple points of the end section End angle Mid-span displacement or deflection ; Among them, total axial force Obtained by axial force monitoring device (6) or strain inversion; real-time temperature Temperature sensor obtained from distributed fiber optic sensor (9) or sensor group (10); end strain value The end rotation angle is measured by a distributed fiber optic grating or a distributed fiber optic sensor (9) installed at the end section of the steel-concrete composite support (3). Obtained by end angle sensor (15); mid-span displacement or deflection The displacement is obtained from the mid-span displacement sensor of the sensor group (10).

5. The active anti-instability control method for steel-concrete composite supports as described in claim 1, characterized in that, Step S3 includes the following sub-steps: Step S31: Based on real-time temperature With initial installation temperature The difference is used to calculate the temperature increment. The calculation formula is: Step S32: Calculate the temperature component The calculation formula is: In the formula, This is the temperature constraint correction factor, with a value ranging from 0.10 to 1.00; Step S33: Calculate the time effect component The calculation formula is: In the formula, This is the time effect correction factor, and its value ranges from 0.10 to 1.20; This is the function for the influence of concrete creep, with a value range of 0 to 1; Step S34: Calculate the true axial force after eliminating the effects of temperature and time. The calculation formula is: In the formula, The correction factor for on-site calibration has a value range of 0.80 to 1.

20. This is the actual axial force after eliminating the effects of temperature and time.

6. The active anti-instability control method for steel-concrete composite supports as described in claim 1, characterized in that, Step S4 includes the following sub-steps: Step S41: Select a control section at the end of the steel-concrete composite support (3), and use a distributed fiber optic grating or a distributed fiber optic sensor (9) to measure the strain values ​​on the upper and lower sides of the control section, and calculate the average axial strain of the control section. and curvature The calculation formula is: in, and These represent the strain at two measuring points on the upper and lower sides of the control section, respectively. The distance between the two measuring points; Step S42: Calculate the end bending moment based on the bending relationship of the control section at the end of the steel-concrete composite support (3). The calculation formula is: in, For steel-concrete composite support (3) at time The equivalent bending stiffness; Step S43: Define the equivalent eccentricity at the end Its defining formula is: 。 7. The active anti-instability control method for steel-concrete composite supports as described in claim 1, characterized in that, Step S5 includes the following sub-steps: Step S51: Simplify the steel-concrete composite support (3) into a compression-bending member with rotational springs at both ends. The rotational stiffness of the end of this compression-bending member is denoted as... ; Step S52: Calculate the current end rotational stiffness based on the relationship between the end bending moment and end rotation angle of the compression-bending member. The calculation formula is: in, The end angle is measured by the end angle sensor (15); The end bending moment obtained in step S4; In step S52, when end rotation sensors (15) are installed at both ends of the steel-concrete composite support (3), the rotational stiffness of the left end is calculated respectively. Rotational stiffness at the right end .

8. The active instability control method for steel-concrete composite supports as described in claim 1, characterized in that, Step S6 includes the following sub-steps: Step S61: To characterize the instability sensitivity of the steel-concrete composite support (3) under the current boundary conditions, a calculation length factor is introduced. ; The calculation of the length coefficient This refers to the equivalent calculated length of a compression member under actual boundary conditions as a hinged compression member at both ends, compared to the member length. The ratio, that is: In the formula, For a moment The equivalent computational length; Step S62: Based on the end rotational stiffness Equivalent bending stiffness and component length Establish boundary stiffness parameters : Step S63: Based on the stability theory of semi-rigid compression members, the current calculation length coefficient is obtained through numerical iteration of the characteristic equation. : in, and These are the left and right boundary stiffness parameters, based on the rotational stiffness of the left end. Rotational stiffness at the right end Using boundary stiffness parameters respectively Calculated; This represents the length coefficient solution function determined by the semi-rigid boundary conditions; Step S64: Calculate the time. Critical buckling capacity of steel-concrete composite bracing (3) under current boundary conditions : 。 9. The active instability prevention and control method for steel-concrete composite supports as described in claim 1, characterized in that, Step S7 includes the following sub-steps: Step S71: Define the real-time stability safety factor for: Among them, the real-time stability safety factor The smaller the value, the closer the steel-concrete composite support (3) is to the critical state of instability; Step S72: Set the stability control threshold and stable early warning threshold And satisfy: in, To ensure stable control, the threshold value is set between 1.20 and 1.

50. To stabilize the early warning threshold, a range of 1.50 to 2.00 is adopted; when When the steel-concrete composite support (3) is determined to have entered the normal stable zone, the current support state of the steel-concrete composite support (3) is maintained, monitoring continues and the next cycle begins; when When the steel-concrete composite support (3) is determined to have entered the warning zone, the boundary reinforcement control in step S8 is initiated. when When the steel-concrete composite support (3) is determined to be in the active control zone, the boundary-axial force collaborative active control step S8 is entered.

10. The active anti-instability control method for steel-concrete composite supports as described in claim 1, characterized in that, Step S8 includes the following sub-steps: Step S81: Based on the real-time stability safety factor and end rotational stiffness In response to changes in [the situation], the following control strategy will be implemented: ① Boundary enhancement control; when And the end rotational stiffness was identified. When the price continues to fall, boundary augmentation control is prioritized. Boundary augmentation control includes: Action A: Drive the ball joint mechanical locking device (14) at the end of the steel-concrete composite support (3) to improve the end rotation constraint and increase the end rotation stiffness. ; Action B: Adjust the height of the mid-span lattice column of the mid-span control unit (4) to change the mid-vertical constraint conditions and flexural shape of the steel-concrete composite support (3); ② Boundary-axial force coordinated active control; when At the same time, while performing the boundary enhancement control mentioned above ①, the servo hydraulic actuator (12) is driven to perform compensatory unloading or force redistribution on the steel-concrete composite support (3), so that the actual axial force is applied. Descend to a safe range; Step S82: After performing boundary reinforcement control, update the boundary parameters and recalculate the end rotational stiffness. Calculate the length coefficient Critical buckling bearing capacity Real-time stability safety factor ; After implementing boundary-axial force coordinated active control, the boundary parameters are updated and the actual axial force is recalculated. End rotational stiffness Calculate the length coefficient Critical buckling bearing capacity Real-time stability safety factor ; Step S83: The central control device (8) outputs the end rotation stiffness based on the real-time calculation results. The control commands for the target value of the control, the height adjustment of the mid-span lattice column, and the unloading amount of the servo hydraulic actuator (12); Step S84: After executing the control command, determine whether the steel-concrete composite support (3) meets the conditions: That is, whether the state of the steel-concrete composite support (3) has returned to the normal stable zone. If yes, then end the current round of control and return to real-time monitoring. If no, return to step S7 and re-determine the stability safety factor.

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