A method for calculating pre-camber of a bent cap support platform considering initial settlement compensation

Abstract

This invention belongs to the field of construction technology, specifically relating to a method for calculating the pre-camber of a cap beam support platform considering initial settlement compensation. The method includes: constructing a spatial model of the physical properties of the cap beam support platform; defining initial settlement characteristic parameters and establishing a compensation model; determining the time-varying load distribution function during construction; calculating the theoretical elastic deformation of the support system; and establishing a foundation settlement prediction model. This invention fundamentally solves the technical problem of controlling the construction accuracy of cap beams. The unique initial settlement compensation mechanism and dynamic load tracking algorithm provide a solid theoretical basis and technical support for the high-precision construction of modern bridges. Under the guidance of this invention, construction personnel can achieve accurate prediction and real-time control of support deformation, greatly improving the forming quality of the cap beam structure, ensuring the aesthetic alignment and structural safety of the overall bridge structure, and possessing broad engineering application prospects.

Description

Technical Field

[0001] This invention belongs to the field of construction technology, specifically relating to a method for calculating the pre-camber of a cap beam support platform that takes into account initial settlement compensation. Background Technology

[0002] With the vigorous development of my country's modern transportation infrastructure construction, long-span, heavy-load bridge structures are increasingly widely used in various complex working conditions. As a key load-bearing component connecting the lower piers and upper main beams of a bridge, the construction accuracy of the cap beam directly affects not only the flatness of the subsequent beam erection but also the internal force distribution and long-term service life of the entire bridge structure. In existing bridge construction techniques, cast-in-place cap beams have become the mainstream choice due to their advantages such as good integrity and reliable node connections. During cast-in-place construction, the self-weight and construction load of the cap beam are entirely borne by a temporary support platform system. To ensure that the bottom elevation and alignment of the cap beam after concrete pouring and solidification meet design expectations, the construction unit must pre-set a reverse elevation, i.e., a pre-camber, during the support installation stage to counteract the various deformations generated by the support system during loading.

[0003] In traditional engineering practice, the calculation of precamber is usually based on the linear superposition theory, mainly considering the elastic compression of the support structure, the inelastic extrusion deformation between component nodes, and the overall settlement of the foundation. To obtain these key parameters, those skilled in the art commonly employ on-site preloading before construction. This involves loading a load simulating the weight of the cap beam (such as precast reinforced concrete blocks or water bags) above the support platform and deriving the deformation curve of the support system based on measured elevation data before and after loading. Based on this empirical method, the precamber is set as the sum of elastic and inelastic deformation and serves as the sole basis for adjusting the bottom formwork during actual construction. Under conditions of conventional spans or excellent geological conditions, this static, experience-based calculation model has, to some extent, supported the standardized construction of bridges and reduced engineering accidents caused by support collapse or excessive settlement.

[0004] However, as bridge construction extends to high piers, deep valleys, and soft soil areas, the stress mechanism of the cap beam support platform becomes increasingly complex. The simplified methods used in existing technologies for calculating pre-camber are gradually revealing their inherent limitations, particularly the neglect of the core variable of initial settlement, which has become a technical bottleneck restricting the improvement of construction accuracy. Specifically, existing technologies often treat settlement as a physical quantity that increases linearly with increasing load. However, in the actual construction cycle, initial settlement exhibits significant nonlinear and time-varying characteristics. Since the support system is assembled from various steel sections, fasteners, and Bailey bridge sections, the gaps between its nodes undergo subtle secondary evolution during the interval between unloading the preload and pouring the concrete, influenced by temperature stress, foundation rebound, and material creep. When concrete is applied to the support in layers during the formal construction phase, the initial load increment is often first used to overcome these newly generated small gaps, i.e., the so-called initial displacement compensation. If the pre-camber calculation fails to proactively consider the compensation mechanism for this initial settlement and is only set based on the static peak value during the preloading stage, a phase deviation will occur between the actual deformation of the support and the preset compensation value in the early stages of concrete pouring. This deviation can cause uneven stress on local formwork under complex stress conditions, which in turn induces secondary inelastic displacement in the support system, ultimately leading to uneven bottom slab alignment after the cap beam is formed, and even generating unexpected secondary stress inside the cap beam, increasing the risk of structural cracking.

[0005] Based on this, existing computational models typically lack in-depth analysis of the interaction between dynamic loads and initial settlement during the construction phase. During the pouring of large cap beams, the fluidity of concrete and changes in unit weight at the initial stage of placement create dynamic load surges. This dynamic force has a significant pulse effect on the initial settlement of the support structure. Due to the lack of precise initial settlement compensation algorithms, those skilled in the art often have to rely on empirical margins to cover this error. This not only reduces the scientific rigor of construction control but also fails to meet the millimeter-level precision control requirements of current high-performance bridges. Therefore, how to deeply explore the deformation patterns of the cap beam support platform in the initial construction stage and construct a pre-camber calculation method that can accurately simulate and compensate for initial settlement, thereby achieving precise alignment control throughout the entire construction process of the cap beam, has become a profound technical issue and challenge urgently needing to be addressed in the field of bridge engineering. Summary of the Invention

[0006] To achieve the above-mentioned objectives, this invention provides a method for calculating the precamber of a cap beam support platform that considers initial settlement compensation. This method establishes a multi-source nonlinear deformation coupling model of the support system, separates the initial settlement from the traditional static settlement, and introduces a dynamic compensation factor for quantitative calculation, so as to achieve high-precision alignment control of the entire cap beam construction process.

[0007] This invention provides a method for calculating the precamber of a cap beam support platform considering initial settlement compensation. The method specifically includes the following steps: The first step is to construct a spatial model of the physical properties of the cap beam support platform: After the support platform is installed at the cap beam construction site, the spatial coordinates of each key node of the support system are obtained using a laser tracker. The key nodes include at least the Bailey beam support point, the center point of the transverse distribution beam, and the bottom formwork support point. The physical parameters of each component of the support system are input simultaneously. The physical parameters include the elastic modulus E, moment of inertia I, cross-sectional area A, and material density ρ of the steel section. Based on the spatial coordinates and physical parameters, the overall stiffness matrix K of the support is established based on finite element analysis. The ranging accuracy of the laser tracker is better than 0.005 mm / m. When establishing the overall stiffness matrix K of the support, the support structure is meshed by the finite element calculation kernel, and the mesh size at the key stress nodes is controlled within 50 mm. A nonlinear geometric large deformation operator is introduced to simulate the second-order effect of the structure.

[0008] The second step is to define the initial settlement characteristic parameters and establish a compensation model: introducing the initial settlement coefficient α and the gap closure threshold load P. th Maximum inelastic deformation δ max And the node tightness adjustment operator β, the initial settlement Δs is calculated through a nonlinear compensation function; The specific calculation logic for the initial settlement Δs is as follows: when the applied load P <P th When the exponential evolution equation is used for calculation, the formula is: When the applied load P ≥ P th When the gap is completely closed, take Δs = δ max The value of the node tightness adjustment operator β ranges from 0.2 to 0.8 and is determined by the preload torque of the bracket connecting bolts. The gap closure threshold load P th The specific method for determining the displacement is as follows: High-precision displacement sensors are deployed at key nodes of the support structure. These sensors have a range of 0-50 mm and a resolution accuracy of 0.01 mm, employing magnetostrictive principles or fiber optic grating sensing technology. Their output signals are connected to a high-speed data acquisition module, which uses Fast Fourier Transform to identify the natural frequency of the support structure and avoids resonance regions during dynamic load calculations. During the pre-loading stage, the slope change of the load-displacement curve is monitored in real time by the central control unit. When the slope enters the linear stable region, the load value corresponding to that node is defined as P. th ; The maximum inelastic deformation δ maxThe method for obtaining δ is as follows: Before the formal commencement of construction, a graded preloading test is conducted. The preloading load is applied to 1.2 times the design load and held for no less than 24 hours. The residual deformation after unloading is measured to determine δ. max Based on this, the initial settlement compensation model was revised; The node tightness adjustment operator β establishes a linkage correction mechanism with the bolt preload torque: when the bolt preload torque is increased from 300 N·m to 500 N·m, the central control unit automatically adjusts the value of β from 0.45 to 0.72 to reflect the change in the gap closure slope as the contact stiffness increases.

[0009] The third step is to determine the time-varying load distribution function during the construction phase: decompose the cap beam pouring process into several discrete time steps Δt. In each time step, calculate the instantaneous volume V(t) of the concrete poured into the formwork and its corresponding equivalent unit weight γ(t). Introduce a viscoplastic factor to control the pressure distribution of the load on the bottom formwork. Obtain the dynamic load F(t) by integrating the pressure area and instantaneous pressure at the support point of the support. The determination of the viscoplasticity factor takes into account both the slump of the concrete and the temperature at which it is poured. By arranging earth pressure gauges with a measurement range of 0-200 kPa and an accuracy class of 0.5 below the bottom mold, the ratio of lateral pressure to vertical pressure during the concrete pouring process is obtained in real time. The load distribution function is then corrected in real time using the pressure feedback value to simulate the dynamic evolution of the pressure on the support during the transformation of concrete from a fluid to a solid state.

[0010] The fourth step is to calculate the theoretical elastic deformation of the support system: Based on the stiffness matrix K established in the first step and the dynamic load F(t) determined in the third step, the theoretical elastic deformation vector Δe of each node is obtained by solving the linear equation system K·Δe=F(t), and the contribution of the eccentric moment generated by the lateral unbalanced loading of the support to the elastic displacement is taken into account in the calculation process. When solving for the theoretical elastic deformation vector Δe, a spatial coupling element is used to simulate the support structure. The pin connection between Bailey panels is defined as a spring element with a specific rotational stiffness. The rotational stiffness is assigned based on the experimentally measured angle-bending moment curve to realistically simulate the semi-rigid characteristics of the connection node.

[0011] The fifth step is to establish a foundation settlement prediction model: using the layered summation method combined with the pore water pressure dissipation theory, the foundation settlement Δg(t) under the stress of the foundation soil layer is calculated, and the consolidation coefficient U is introduced. t To characterize the variation of the foundation with the duration t of the load; The degree of consolidation coefficient U t The calculation formula is: Among them, C vThe soil consolidation coefficient is obtained through geotechnical tests, t is the load duration, and H is the drainage path length of the soil layer; the time-dependent settlement of the foundation is expressed as Δg(t) = S ∞ ·U t S ∞ This represents the theoretical final settlement calculated based on the layered summation method. When establishing a foundation settlement prediction model, it is necessary to drill and sample the soil layer below the support foundation to obtain the soil compression modulus Es at each depth, and then establish a three-dimensional foundation stress diffusion model to correct the calculation deviation of the layered summation method under complex terrain conditions.

[0012] Step 6: Synthesize the total precamber setting value: Nonlinearly superimpose the theoretical elastic deformation vector Δe, the initial settlement Δs, the foundation settlement Δg(t), and the displacement compensation term ΔT caused by the environmental temperature difference to obtain the final total precamber setting value f. pre =△e+△s +△g(t)+△T; The displacement compensation term ΔT is calculated based on the product of the linear expansion coefficient of each component of the support and the measured temperature difference. The measured temperature difference is obtained through temperature sensors installed on the key load-bearing components of the support. The central control unit analyzes the vertical expansion and contraction displacement of the support structure under the influence of diurnal temperature differences with a monitoring cycle of 24 hours. When performing the synthesis of the total pre-camber, the nonlinear superposition considers the mutual influence between the deformation components, especially the coupling effect between the initial settlement Δs and the instantaneous settlement of the foundation, to ensure that the generated pre-camber value covers the displacement changes of the cap beam from the time the concrete is poured into the formwork to the initial setting, curing, and finally the removal of the support.

[0013] The method also includes real-time verification and dynamic compensation: during the casting of the cap beam, the actual settlement of the support is monitored in real time by tilt sensors and laser displacement meters installed on the support columns; the tilt sensor has a measurement range of ±30° and an accuracy of 0.001°; when the measured total settlement is less than or equal to the total pre-camber set value f... pre When the deviation exceeds 3mm, the central control unit activates the hydraulic synchronous lifting system installed on the top of the support to perform load compensation adjustment.

[0014] The hydraulic synchronous lifting system consists of a pressure compensation pump station, a proportional solenoid valve, and a synchronous controller. The synchronous controller adopts a fuzzy PID control algorithm to achieve height fine adjustment with an accuracy of ±0.1mm under load conditions by adjusting the opening of the proportional solenoid valve in real time. The support system includes I-beam longitudinal beams, Bailey trusses, steel pipe support columns, and adjustable supports; the I-beam longitudinal beams are made of Q355B grade steel; the bottom of the steel pipe support columns is provided with a reinforced concrete foundation pad to evenly distribute the construction load to the foundation soil layer. In the control logic of the hydraulic synchronous lifting system, the flow gain is adjusted in real time through a fuzzy PID control algorithm to ensure smooth lifting under heavy load conditions of thousands of kilonewtons, taking into account the compressibility of hydraulic oil and the system hysteresis.

[0015] The central control unit that executes the calculation method and real-time verification process includes a high-speed data acquisition module, a finite element calculation kernel, and a PID feedback control module; the sampling frequency of the high-speed data acquisition module is not less than 100Hz, and it has a built-in multi-level filtering algorithm to remove random vibration noise caused by the operation of equipment at the construction site; The finite element calculation kernel supports nonlinear geometric large deformation calculation and multiphysics coupling analysis. When calculating the theoretical elastic deformation, the Modified Newton-Raphson iterative algorithm is used to handle the geometric nonlinearity problem of the support under large span heavy load conditions. The automated integrated software interface of the central control unit displays the displacement curves, load curves, and precamber deviation histograms of each key node in real time, and compares the calculated precamber values ​​with the actual monitoring data to generate a line control report for the entire construction process.

[0016] Through the above technical solution, this invention achieves precise calculation of the pre-camber of the cap beam support platform, and its technical effects are reflected in the following aspects: First, by introducing an initial settlement compensation model, the error problem of simply equating inelastic deformation to a constant in traditional calculation methods is solved. This invention accurately identifies the gap closure pattern of the support connection nodes in the early stage of loading, enabling the setting of the pre-camber to cover this nonlinear deformation stage, significantly improving the control accuracy of the bottom formwork elevation, and ensuring that the flatness of the bottom surface of the cap beam meets the design specifications.

[0017] Secondly, this invention constructs a multi-dimensional displacement prediction matrix by incorporating time-varying loads, foundation consolidation settlement, and environmental temperature deformation into a unified calculation framework. This systematic modeling approach considers the dynamic interaction between the external environment and the internal stress state during the construction period, avoiding linear deviations caused by overly simplified calculation models.

[0018] Furthermore, by linking real-time monitoring with the hydraulic synchronous lifting system, this invention establishes a closed-loop control system from static prediction to dynamic feedback. Even if unforeseen local foundation weakness or support instability occurs during construction, the system can promptly correct displacement deviations through an online compensation mechanism, enhancing the safety and fault tolerance of the construction process.

[0019] Finally, the calculation method provided by this invention has extremely high engineering applicability. It is not only applicable to conventional cast-in-place cap beams, but also demonstrates excellent calculation stability and prediction accuracy for variable cross-section cap beams, heavy-duty cap beams, and large temporary support platforms built under complex geological conditions. By accurately capturing and compensating for initial settlement, this invention effectively reduces the secondary internal forces generated inside the cap beam due to uneven settlement of the support, extends the service life of the bridge structure, and has significant technological advancements and socio-economic benefits.

[0020] In practical implementation, the pre-camber calculation method described in this invention requires high-precision hardware. The laser tracker should have a ranging accuracy of no less than 0.005 mm / m to establish a high-precision spatial reference before construction. The displacement sensor should employ magnetostrictive principle or fiber optic grating sensing technology to ensure strong anti-interference capability and long-term stability in complex construction site environments. The finite element calculation kernel should support nonlinear geometric large deformation calculation and multiphysics coupling analysis, accurately simulating the second-order effects of the support structure under heavy loads.

[0021] Furthermore, to verify the accuracy of the calculation results, this invention requires graded preloading before formal pouring. The preloading load should reach 1.2 times the design load and be maintained at a constant load for no less than 24 hours. After unloading, the compensation coefficient is corrected by comparing the residual deformation with the estimated value in the initial settlement compensation model. This closed-loop correction process ensures that the precamber values ​​used in the subsequent formal construction stage have extremely high reliability.

[0022] In summary, the proposed method for calculating the pre-camber of a cap beam support platform considering initial settlement compensation, through a combination of in-depth engineering mechanism analysis and advanced numerical calculation methods, fundamentally solves the technical challenge of controlling the construction accuracy of cap beams. Its unique initial settlement compensation mechanism and dynamic load tracking algorithm provide a solid theoretical basis and technical support for the high-precision construction of modern bridges, representing a significant breakthrough in bridge construction technology. Under the guidance of this invention, construction personnel can accurately predict and control the deformation of the support in real time, greatly improving the forming quality of the cap beam structure, ensuring the aesthetic alignment and structural safety of the overall bridge structure, and possessing broad engineering application prospects. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the dynamic control process of the pre-camber of the cap beam support according to the present invention. Figure 2 This is a hardware architecture diagram of the hydraulic synchronous lifting control system for the girder support of the present invention; Figure 3 This is a diagram of the nonlinear synthesis calculation model for the total pre-camber of this invention. Detailed Implementation

[0024] Example 1

[0025] like Figure 1 As shown, a method for calculating the precamber of a cap beam support platform considering initial settlement compensation is described. The method specifically includes the following steps: The first step is to construct a spatial model of the physical properties of the cap beam support platform: After the support platform is installed at the cap beam construction site, the spatial coordinates of each key node of the support system are obtained using a laser tracker. The key nodes include at least the Bailey beam support point, the center point of the transverse distribution beam, and the bottom formwork support point. The physical parameters of each component of the support system are input simultaneously. The physical parameters include the elastic modulus E, moment of inertia I, cross-sectional area A, and material density ρ of the steel section. Based on the spatial coordinates and physical parameters, the overall stiffness matrix K of the support is established based on finite element analysis. The ranging accuracy of the laser tracker is better than 0.005 mm / m. When establishing the overall stiffness matrix K of the support, the support structure is meshed by the finite element calculation kernel, and the mesh size at the key stress nodes is controlled within 50 mm. A nonlinear geometric large deformation operator is introduced to simulate the second-order effect of the structure.

[0026] The second step is to define the initial settlement characteristic parameters and establish a compensation model: introducing the initial settlement coefficient α and the gap closure threshold load P. th Maximum inelastic deformation δ max And the node tightness adjustment operator β, the initial settlement Δs is calculated through a nonlinear compensation function; The specific calculation logic for the initial settlement Δs is as follows: when the applied load P <P th When the exponential evolution equation is used for calculation, the formula is: When the applied load P ≥ P th When the gap is completely closed, take Δs = δ max The value of the node tightness adjustment operator β ranges from 0.2 to 0.8 and is determined by the preload torque of the bracket connecting bolts. The gap closure threshold load P th The specific method for determining the displacement is as follows: High-precision displacement sensors are deployed at key nodes of the support structure. These sensors have a range of 0-50 mm and a resolution accuracy of 0.01 mm, employing magnetostrictive principles or fiber optic grating sensing technology. Their output signals are connected to a high-speed data acquisition module, which uses Fast Fourier Transform to identify the natural frequency of the support structure and avoids resonance regions during dynamic load calculations. During the pre-loading stage, the slope change of the load-displacement curve is monitored in real time by the central control unit. When the slope enters the linear stable region, the load value corresponding to that node is defined as P. th ; The maximum inelastic deformation δmax The method for obtaining δ is as follows: Before the formal commencement of construction, a graded preloading test is conducted. The preloading load is applied to 1.2 times the design load and held for no less than 24 hours. The residual deformation after unloading is measured to determine δ. max Based on this, the initial settlement compensation model was revised; The node tightness adjustment operator β establishes a linkage correction mechanism with the bolt preload torque: when the bolt preload torque is increased from 300 N·m to 500 N·m, the central control unit automatically adjusts the value of β from 0.45 to 0.72 to reflect the change in the gap closure slope as the contact stiffness increases.

[0027] The third step is to determine the time-varying load distribution function during the construction phase: decompose the cap beam pouring process into several discrete time steps Δt. In each time step, calculate the instantaneous volume V(t) of the concrete poured into the formwork and its corresponding equivalent unit weight γ(t). Introduce a viscoplastic factor to control the pressure distribution of the load on the bottom formwork. Obtain the dynamic load F(t) by integrating the pressure area and instantaneous pressure at the support point of the support. The determination of the viscoplasticity factor takes into account both the slump of the concrete and the temperature at which it is poured. By arranging earth pressure gauges with a measurement range of 0-200 kPa and an accuracy class of 0.5 below the bottom mold, the ratio of lateral pressure to vertical pressure during the concrete pouring process is obtained in real time. The load distribution function is then corrected in real time using the pressure feedback value to simulate the dynamic evolution of the pressure on the support during the transformation of concrete from a fluid to a solid state.

[0028] The fourth step is to calculate the theoretical elastic deformation of the support system: Based on the stiffness matrix K established in the first step and the dynamic load F(t) determined in the third step, the theoretical elastic deformation vector Δe of each node is obtained by solving the linear equation system K·Δe=F(t), and the contribution of the eccentric moment generated by the lateral unbalanced loading of the support to the elastic displacement is taken into account in the calculation process. When solving for the theoretical elastic deformation vector Δe, a spatial coupling element is used to simulate the support structure. The pin connection between Bailey panels is defined as a spring element with a specific rotational stiffness. The rotational stiffness is assigned based on the experimentally measured angle-bending moment curve to realistically simulate the semi-rigid characteristics of the connection node.

[0029] The fifth step is to establish a foundation settlement prediction model: using the layered summation method combined with the pore water pressure dissipation theory, the foundation settlement Δg(t) under the stress of the foundation soil layer is calculated, and the consolidation coefficient U is introduced. t To characterize the variation of the foundation with the duration t of the load; The degree of consolidation coefficient U t The calculation formula is: Among them, C vThe soil consolidation coefficient is obtained through geotechnical tests, t is the load duration, and H is the drainage path length of the soil layer; the time-dependent settlement of the foundation is expressed as Δg(t) = S ∞ ·U t S ∞ This represents the theoretical final settlement calculated based on the layered summation method. When establishing a foundation settlement prediction model, it is necessary to drill and sample the soil layer below the support foundation to obtain the soil compression modulus Es at each depth, and then establish a three-dimensional foundation stress diffusion model to correct the calculation deviation of the layered summation method under complex terrain conditions.

[0030] Step 6, synthesize the total pre-camber setting value: such as Figure 3 As shown, the theoretical elastic deformation vector Δe, the initial settlement Δs, the foundation settlement over time Δg(t), and the displacement compensation term ΔT caused by the environmental temperature difference are nonlinearly superimposed to obtain the final total precamber setting value f. pre =△e+△s +△g(t)+△T; The displacement compensation term ΔT is calculated based on the product of the linear expansion coefficient of each component of the support and the measured temperature difference. The measured temperature difference is obtained through temperature sensors installed on the key load-bearing components of the support. The central control unit analyzes the vertical expansion and contraction displacement of the support structure under the influence of diurnal temperature differences with a monitoring cycle of 24 hours. When performing the synthesis of the total pre-camber, the nonlinear superposition considers the mutual influence between the deformation components, especially the coupling effect between the initial settlement Δs and the instantaneous settlement of the foundation, to ensure that the generated pre-camber value covers the displacement changes of the cap beam from the time the concrete is poured into the formwork to the initial setting, curing, and finally the removal of the support.

[0031] The method also includes real-time verification and dynamic compensation: during the casting of the cap beam, the actual settlement of the support is monitored in real time by tilt sensors and laser displacement meters installed on the support columns; the tilt sensor has a measurement range of ±30° and an accuracy of 0.001°; when the measured total settlement is less than or equal to the total pre-camber set value f... pre When the deviation exceeds 3mm, the central control unit activates the hydraulic synchronous lifting system installed on the top of the support to perform load compensation adjustment.

[0032] The hydraulic synchronous lifting system consists of a pressure compensation pump station, a proportional solenoid valve, and a synchronous controller. The synchronous controller adopts a fuzzy PID control algorithm to achieve height fine adjustment with an accuracy of ±0.1mm under load conditions by adjusting the opening of the proportional solenoid valve in real time. The support system includes I-beam longitudinal beams, Bailey trusses, steel pipe support columns, and adjustable supports; the I-beam longitudinal beams are made of Q355B grade steel; the bottom of the steel pipe support columns is provided with a reinforced concrete foundation pad to evenly distribute the construction load to the foundation soil layer. In the control logic of the hydraulic synchronous lifting system, the flow gain is adjusted in real time through a fuzzy PID control algorithm to ensure smooth lifting under heavy load conditions of thousands of kilonewtons, taking into account the compressibility of hydraulic oil and the system hysteresis.

[0033] The central control unit that executes the calculation method and real-time verification process includes a high-speed data acquisition module, a finite element calculation kernel, and a PID feedback control module; the sampling frequency of the high-speed data acquisition module is not less than 100Hz, and it has a built-in multi-level filtering algorithm to remove random vibration noise caused by the operation of equipment at the construction site; The finite element calculation kernel supports nonlinear geometric large deformation calculation and multiphysics coupling analysis. When calculating the theoretical elastic deformation, the Modified Newton-Raphson iterative algorithm is used to handle the geometric nonlinearity problem of the support under large span heavy load conditions. The automated integrated software interface of the central control unit displays the displacement curves, load curves, and precamber deviation histograms of each key node in real time, and compares the calculated precamber values ​​with the actual monitoring data to generate a line control report for the entire construction process.

[0034] Example 2

[0035] This embodiment uses a specific engineering project as an example to illustrate the calculation method described in Embodiment 1. In this experimental project, a cast-in-place cap beam of a large bridge was selected as the implementation object. The cap beam is designed to be 15.5 meters long, 2.8 meters wide, and 2.5 meters high, with a designed concrete volume of 108.5 cubic meters. The support system adopts a truss structure assembled from Bailey bridge panels, supported below by steel pipe columns with a diameter of 630 mm and a wall thickness of 12 mm. The foundation conditions are typical saturated cohesive soil, with a bearing capacity characteristic value of 150 kPa after foundation treatment.

[0036] The precamber calculation method considering initial settlement compensation provided by this invention is adopted. In this embodiment, the initial settlement characteristic parameters are first determined through a preloading experiment. Under 1.2 times the design load, the maximum inelastic deformation δ is measured. max The value is 12.4 mm. The set gap closure threshold load P is... th The node tightness adjustment operator β is set to 0.55, representing 40% of the design load. Based on environmental monitoring on the day of construction, the displacement compensation term ΔT caused by temperature difference is calculated to be +1.5 mm. The foundation consolidation coefficient C... v The value is 2.5 × 10 -3 cm2 / s. The total pre-camber setpoint f at the mid-span position of the support is calculated in real time by the central control unit. pre The calculated value is 28.6 mm.

[0037] Comparative Example: Using the traditional empirical calculation method, the precamber is composed only of "100% theoretical elastic deformation + empirical constant settlement". Under the same engineering background, the theoretical elastic deformation vector calculated in Comparative Example 1 is 15.2 mm, the empirical constant settlement (usually taken as 10.0 mm) is set, and the total precamber is set to 25.2 mm. The nonlinear process of initial settlement, the time-dependent settlement of the foundation, and temperature compensation are not considered.

[0038] Table 1 provides a detailed comparison of the deviations between the measured data and the design elevation after the completion of the cap beam pouring in this embodiment and the comparative example: Table 1. Deviations between measured data and design elevation after the completion of the cap beam pouring in this embodiment and the comparative example.

[0039] As can be clearly observed from the data table above, this embodiment, due to the introduction of a precise initial settlement compensation model and foundation settlement prediction, exhibits a high degree of consistency between its preset precamber value and the actual settlement. At the mid-span node, the final alignment deviation of this embodiment is controlled within 0.4mm, fully meeting the requirements of high-precision bridge construction. In contrast, the comparative example, by neglecting the nonlinear gap closure (i.e., initial settlement) in the early stage of loading and the deep consolidation of the foundation under continuous load, has significantly smaller preset values, resulting in a deflection of more than 6mm at the bottom of the final cap beam, exceeding the allowable range of the quality acceptance specifications.

[0040] Further analysis of the data reveals that when the load reaches 50%, the deviation in Comparative Example 1 has already reached 5.9 mm. This is precisely because traditional methods cannot capture the drastic displacement during the initial settlement stage. However, this invention utilizes a nonlinear compensation function... In the initial loading stage, inelastic deformation of 10-12 mm was accurately predicted, effectively offsetting displacement deviations at the start of construction. Furthermore, during the 100% load stage, the continuous settlement of the foundation in this embodiment was controlled by the consolidation coefficient U. t This was reflected in the data, while the comparative model, due to the lack of displacement prediction in the time dimension, resulted in a further increase in the deviation.

[0041] In the specific implementation of this invention, the nonlinear iterative process of the finite element calculation kernel is also a key factor in ensuring calculation accuracy. Specifically, for large-scale cap beam support systems, the finite element mesh density is locally refined at key stress nodes, with the element size controlled within 50mm. The Modified Newton-Raphson iterative algorithm is used in the calculation process to handle the geometric nonlinearity caused by the large span of the support. For the pin connection between Bailey panels, this embodiment does not simplify it to an ideal rigid or hinged connection, but introduces spring elements with specific rotational stiffness. This stiffness value is assigned based on the experimentally measured angle-bending moment curve, thereby realistically simulating the semi-rigid characteristics of the connection node.

[0042] For the implementation of the environmental temperature displacement compensation term △T, the central control unit is set with a 24-hour monitoring cycle. By analyzing the expansion and contraction patterns of the support structure under the influence of diurnal temperature differences, the system found that for a support platform as long as 15.5 meters, the vertical displacement fluctuation caused by temperature differences can reach 2-3 mm. This invention uses an online temperature compensation algorithm to finely adjust the pre-camber setting value in real time, avoiding the bottom formwork elevation error caused by the temperature difference between morning and evening pouring.

[0043] like Figure 2 As shown, the application of the hydraulic synchronous lifting system provides the final safety guarantee for this invention. During the pouring process in this embodiment, when the concrete was 80% poured, unexpected minor uneven settlement occurred in the local foundation. The laser displacement gauge detected an abnormal settlement velocity at the left support point, with an instantaneous deviation of 3.5mm. The central control unit immediately issued a command to adjust the oil supply of the hydraulic cylinder through the proportional solenoid valve, compensating the support point upwards by 3.2mm in less than 30 seconds, successfully reducing the deviation back to the safe range of 0.3mm. This load-bearing adjustment capability transforms the support platform from a traditional "passive force-bearing" to an "active deformation-bearing" system.

[0044] Furthermore, this invention provides in-depth mechanical modeling of the initial setting process of concrete after it is poured into the formwork. Through an array of earth pressure gauges installed at the bottom of the formwork, the system can acquire real-time pressure distribution cloud maps of the concrete on the support. As time progresses, the concrete transitions from a fluid to a solid state, gradually reducing its lateral pressure on the support while stabilizing its vertical pressure. This invention accurately simulates the impact of this hardening process on the stress state of the support by dynamically adjusting the viscoplastic factor in the load distribution function, thus providing accurate displacement monitoring references throughout the entire curing period before demolding.

[0045] Within the technical framework of this invention, all calculation, monitoring, and control processes are completed through a self-developed automated integrated software. The software interface displays the displacement curves, load curves, and pre-camber deviation histograms of each key node in real time. Its underlying logic strictly adheres to the aforementioned physical property space model, initial settlement compensation model, dynamic load function, and foundation consolidation prediction algorithm. By transforming complex engineering mechanics problems into digital matrix operations, this invention significantly reduces the risk of human calculation errors and enhances the industrialization and intelligence level of construction sites.

[0046] In summary, this implementation method comprehensively demonstrates the superior performance of a pre-camber calculation method for a cap beam support platform considering initial settlement compensation through detailed engineering physical modeling, rigorous mathematical formula derivation, and comparison with real engineering data. Its core technology lies in the in-depth stripping and precise quantification of the nonlinear deformation characteristics of the support system. By introducing the initial settlement coefficient, gap closure threshold load, and foundation consolidation coefficient, a displacement prediction matrix covering multi-dimensional factors of space, time, and environment is constructed. The successful implementation of this method not only solves the persistent problem of controlling the elevation of the cap beam bottom formwork in bridge construction but also provides a universal technical paradigm for the stability analysis and high-precision alignment control of large temporary load-bearing structures. Under the guidance of this invention, construction units can significantly reduce the number of pre-stressing cycles of the support, shorten the construction cycle, and ensure that the final cap beam structure reaches the optimal design level in terms of geometric dimensions and internal stress state, possessing extremely high engineering promotion value and socio-economic benefits.

[0047] As a further refinement of the present invention, for support systems with different materials and connection methods, the β operator in the initial settlement compensation model can be automatically corrected using the measured values ​​from a bolt torque wrench on site. For example, when the bolt preload torque is increased from 300 N·m to 500 N·m, the contact stiffness between nodes is significantly enhanced. At this time, the system automatically adjusts the β operator from 0.45 to 0.72, thereby more accurately reflecting the slope change of gap closure. This adaptive parameter adjustment mechanism further enhances the versatility and robustness of the present invention under different construction environments.

[0048] In the software-level data processing, the high-speed data acquisition module employs a multi-level filtering algorithm to effectively eliminate random vibration noise caused by the operation of large equipment at the construction site. Through FFT (Fast Fourier Transform) analysis, the system can identify the natural frequencies of the support structure and avoid resonance intervals in dynamic load calculations, ensuring the purity of the displacement monitoring signal. This end-to-end technical guarantee, from microscopic signal processing to macroscopic structural analysis, enables the pre-camber calculation method proposed in this invention to exhibit extremely high stability and repeatability in practical engineering applications.

[0049] For the application of the layered summation method for foundations, this invention requires detailed drilling and sampling of the soil layers beneath the support foundation in its specific implementation. This is achieved by analyzing the compression modulus E of the soil layers at different depths. s By performing precise value determination, the calculation system can establish a three-dimensional foundation stress diffusion model. This allows the invention to provide extremely accurate foundation settlement predictions for cap beam supports located on complex terrains such as slopes and uneven foundations, avoiding the calculation risks associated with traditional averaging assumptions.

[0050] Finally, the control logic of the hydraulic synchronous lifting system described in this invention employs an advanced fuzzy PID control algorithm. Addressing the hysteresis and nonlinear characteristics of the hydraulic system, stable lifting under heavy loads (thousands of kilonewtons) is achieved through real-time adjustment of PID parameters, with lifting accuracy controlled within ±0.1mm. This perfect combination of high-precision compensation and high-precision pre-camber calculation constitutes a dual technical barrier for solving the problem of cap beam construction accuracy in this invention. Through this comprehensive technological integration, this invention not only achieves a breakthrough in computational theory but also establishes a new technical benchmark in engineering practice. Under the specific guidance of this invention, through in-depth perception and compensation of deformation throughout the entire cap beam construction process, the alignment control accuracy of the bridge structure has achieved a qualitative leap, effectively ensuring the long-term structural safety and operational reliability of transportation infrastructure.

Claims

1. A method for calculating the precamber of a cap beam support platform considering initial settlement compensation, characterized in that, The method is specific Includes the following steps: The first step is to construct a spatial model of the physical properties of the cap beam support platform: After the support platform is installed at the cap beam construction site, the spatial coordinates of each key node of the support system are obtained using a laser tracker. The key nodes include at least the Bailey beam support point, the center point of the transverse distribution beam, and the bottom formwork support point. The physical parameters of each component of the support system are input simultaneously. The physical parameters include the elastic modulus E, moment of inertia I, cross-sectional area A, and material density ρ of the steel section. Based on the spatial coordinates and physical parameters, the overall stiffness matrix K of the support is established based on finite element analysis. The second step is to define the initial settlement characteristic parameters and establish a compensation model: introducing the initial settlement coefficient α and the gap closure threshold load P. th Maximum inelastic deformation δ max And the node tightness adjustment operator β, the initial settlement Δs is calculated through a nonlinear compensation function; The third step is to determine the time-varying load distribution function during the construction phase: decompose the cap beam pouring process into several discrete time steps Δt. In each time step, calculate the instantaneous volume V(t) of the concrete poured into the formwork and its corresponding equivalent unit weight γ(t). Introduce a viscoplastic factor to control the pressure distribution of the load on the bottom formwork. Obtain the dynamic load F(t) by integrating the pressure area and instantaneous pressure at the support point of the support. The fourth step is to calculate the theoretical elastic deformation of the support system: Based on the stiffness matrix K established in the first step and the dynamic load F(t) determined in the third step, the theoretical elastic deformation vector Δe of each node is obtained by solving the linear equation system K·Δe=F(t), and the contribution of the eccentric moment generated by the lateral unbalanced loading of the support to the elastic displacement is taken into account in the calculation process. The fifth step is to establish a foundation settlement prediction model: using the layered summation method combined with the pore water pressure dissipation theory, the foundation settlement Δg(t) under the stress of the foundation soil layer is calculated, and the consolidation coefficient U is introduced. t To characterize the variation of the foundation with the duration t of the load; Step 6: Synthesize the total precamber setting value: Nonlinearly superimpose the theoretical elastic deformation vector Δe, the initial settlement Δs, the foundation settlement Δg(t), and the displacement compensation term ΔT caused by the environmental temperature difference to obtain the final total precamber setting value f. pre =△e+△s +△g(t)+△T.

2. The method for calculating the pre-camber of a cap beam support platform considering initial settlement compensation according to claim 1, characterized in that, In the first step, the ranging accuracy of the laser tracker is better than 0.005 mm / m; when establishing the overall stiffness matrix K of the support, the support structure is meshed by the finite element calculation kernel, and the mesh size at the key stress nodes is controlled within 50 mm, and a nonlinear geometric large deformation operator is introduced to simulate the second-order effect of the structure.

3. The method for calculating the pre-camber of a cap beam support platform considering initial settlement compensation according to claim 1, characterized in that, In the second step, the specific calculation logic for the initial settlement Δs is as follows: when the applied load P <P th When the exponential evolution equation is used for calculation, the formula is: ; When the applied load P≥P th When the gap is completely closed, take Δs = δ max The value of the node tightness adjustment operator β ranges from 0.2 to 0.8 and is determined by the preload torque of the bracket connecting bolts. The gap closure threshold load P th The specific method for determining the displacement is as follows: High-precision displacement sensors are deployed at key nodes of the support structure. These sensors have a range of 0-50 mm and a resolution accuracy of 0.01 mm, employing magnetostrictive principles or fiber optic grating sensing technology. Their output signals are connected to a high-speed data acquisition module, which uses Fast Fourier Transform to identify the natural frequency of the support structure and avoids resonance regions during dynamic load calculations. During the pre-loading stage, the slope change of the load-displacement curve is monitored in real time by the central control unit. When the slope enters the linear stable region, the load value corresponding to that node is defined as P. th ; The maximum inelastic deformation δ max The method for obtaining δ is as follows: Before the formal commencement of construction, a graded preloading test is conducted. The preloading load is applied to 1.2 times the design load and held for no less than 24 hours. The residual deformation after unloading is measured to determine δ. max Based on this, the initial settlement compensation model was revised; The node tightness adjustment operator β establishes a linkage correction mechanism with the bolt preload torque: when the bolt preload torque is increased from 300 N·m to 500 N·m, the central control unit automatically adjusts the value of β from 0.45 to 0.

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4. The method for calculating the precamber of a cap beam support platform considering initial settlement compensation according to claim 1, characterized in that, In the third step, the determination of the viscoplasticity factor takes into account both the slump of the concrete and the temperature at which it is poured. By arranging a soil pressure gauge with a measurement range of 0-200 kPa and an accuracy class of 0.5 under the bottom mold, the ratio of lateral pressure to vertical pressure during the concrete pouring process is obtained in real time. The load distribution function is then corrected in real time using the pressure feedback value to simulate the dynamic evolution of the pressure on the support during the transformation of concrete from a fluid to a solid state.

5. The method for calculating the precamber of a cap beam support platform considering initial settlement compensation according to claim 1, characterized in that, In the fourth step, when solving for the theoretical elastic deformation vector Δe, a spatial coupling unit is used to simulate the support structure. The pin connection between the Bailey panels is defined as a spring unit with a specific rotational stiffness, which is assigned according to the rotation angle-bending moment curve measured experimentally.

6. The method for calculating the precamber of a cap beam support platform considering initial settlement compensation according to claim 1, characterized in that, In the fifth step, the degree of consolidation coefficient U t The calculation formula is: Among them, C v The consolidation coefficient of the foundation is obtained through geotechnical tests, t is the duration of the load, and H is the drainage path length of the soil layer; the time-dependent settlement of the foundation is expressed as Δg(t) = S ∞ ·U t S ∞ This represents the theoretical final settlement calculated based on the layered summation method. When establishing a foundation settlement prediction model, it is necessary to drill and sample the soil layer below the support foundation to obtain the soil compression modulus Es at each depth, and then establish a three-dimensional foundation stress diffusion model to correct the calculation deviation of the layered summation method under complex terrain conditions.

7. The method for calculating the precamber of a cap beam support platform considering initial settlement compensation according to claim 1, characterized in that, In the sixth step, the displacement compensation term △T is calculated based on the product of the linear expansion coefficient of each component of the support and the measured temperature difference. The measured temperature difference is obtained by temperature sensors installed on the key load-bearing components of the support. The central control unit analyzes the vertical expansion and contraction displacement of the support structure under the action of day and night temperature difference with a monitoring cycle of 24 hours.

8. The method for calculating the precamber of a cap beam support platform considering initial settlement compensation according to claim 1, characterized in that, The method also includes real-time verification and dynamic compensation: during the casting of the cap beam, the actual settlement of the support is monitored in real time by tilt sensors and laser displacement meters installed on the support columns; the tilt sensor has a measurement range of ±30° and an accuracy of 0.001°; when the measured total settlement is less than or equal to the total pre-camber set value f... pre When the deviation exceeds 3mm, the central control unit activates the hydraulic synchronous lifting system installed on the top of the support to perform load compensation adjustment.

9. The method for calculating the pre-camber of a cap beam support platform considering initial settlement compensation according to claim 8, characterized in that, The hydraulic synchronous lifting system consists of a pressure compensation pump station, a proportional solenoid valve, and a synchronous controller. The synchronous controller adopts a fuzzy PID control algorithm to achieve height fine adjustment with an accuracy of ±0.1mm under load conditions by adjusting the opening of the proportional solenoid valve in real time. The support system includes I-beam longitudinal beams, Bailey trusses, steel pipe support columns, and adjustable supports; the I-beam longitudinal beams are made of Q355B grade steel; the bottom of the steel pipe support columns is provided with a reinforced concrete foundation pad to evenly distribute the construction load to the foundation soil layer. In the control logic of the hydraulic synchronous lifting system, the flow gain is adjusted in real time through a fuzzy PID control algorithm to ensure smooth lifting under heavy load conditions of thousands of kilonewtons, taking into account the compressibility of hydraulic oil and the system hysteresis.

10. A method for calculating the precamber of a cap beam support platform considering initial settlement compensation according to any one of claims 1-9, characterized in that, The central control unit that executes the calculation method and real-time verification process includes a high-speed data acquisition module, a finite element calculation kernel, and a PID feedback control module; the sampling frequency of the high-speed data acquisition module is not less than 100Hz, and it has a built-in multi-level filtering algorithm to remove random vibration noise caused by the operation of equipment at the construction site; The finite element calculation kernel supports nonlinear geometric large deformation calculation and multiphysics coupling analysis. When calculating the theoretical elastic deformation, the Modified Newton-Raphson iterative algorithm is used to handle the geometric nonlinearity problem of the support under large span heavy load conditions. The automated integrated software interface of the central control unit displays the displacement curves, load curves, and precamber deviation histograms of each key node in real time, and compares the calculated precamber values ​​with the actual monitoring data to generate a line control report for the entire construction process.

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