Sandwich combination structure underhanging steel beam coordinate precision control method

Abstract

The application provides a sandwich combination structure lower hanging steel beam coordinate precision control method, and belongs to the technical field of wind tunnel construction. The application establishes an independent reference control network, sets a forced closed control point to block error linear transmission, calculates the lower hanging steel beam camber, and offsets the dead load deflection through reverse prefabricated bending processing. A buried part rigid positioning frame is installed and the position deviation is monitored. A hydraulic synchronous jacking device is used to iteratively adjust the posture of the steel beam. Pre-stressed tension is applied to realize reverse arch shaping. Finally, the least squares adjustment technology and the minimum spanning tree optimization algorithm are used to reasonably distribute the section cumulative error between the forced closed control points, thereby solving the technical problem of excessive steel beam coordinate precision caused by large-span multi-section construction cumulative error.

Description

Technical Field

[0001] This invention belongs to the field of wind tunnel construction technology, and specifically relates to a method for controlling the coordinate accuracy of a steel beam suspended under a sandwich composite structure. Background Technology

[0002] In the construction of wind tunnel structures, the installation of steel beams under sandwich composite structures traditionally employs a segmented sequential construction method. The independent measured coordinates of each segment serve as the positioning benchmark for subsequent segments, and the coordinates of the overall structure are transferred by accumulating the measured data from each segment. However, in the construction of large-span steel beams, due to factors such as the large deflection caused by the beam's self-weight, the large number of segments, and the long construction period, the traditional linear cumulative measurement method leads to the continuous amplification of errors along the construction direction. Especially when there are hundreds of construction segments and a single span exceeds 30 meters, the cumulative error may exceed the allowable structural deviation by several times, severely affecting the coaxiality accuracy of the wind tunnel structure. In other words, existing technologies suffer from a technical problem where the cumulative error from large-span, multi-segment construction leads to excessive coordinate accuracy of the steel beams. Summary of the Invention

[0003] In view of this, the present invention provides a method for controlling the coordinate accuracy of the steel beam under the sandwich composite structure, which can solve the technical problem in the prior art where the cumulative error of the construction of large spans and multiple sections leads to the steel beam coordinate accuracy exceeding the standard.

[0004] This invention is implemented as follows: This invention provides a method for controlling the coordinate accuracy of the suspended steel beam in a sandwich composite structure, including: establishing an independent reference control network; setting forced closure control points within the wind tunnel construction area; establishing a spatial coordinate reference system using a 3D laser scanner and a total station; calculating the pre-camber of the suspended steel beam; establishing a finite element analysis model considering the semi-rigid connection characteristics of nodes and the incomplete constraint conditions of supports; calculating the elastic deflection value of the steel beam under its own weight; determining the parameters of the reverse prefabrication bending curve; implementing reverse prefabrication bending processing of the steel beam; performing reverse cold bending or hot bending treatment on the suspended steel beam; installing a rigid positioning frame for embedded parts; fixing the embedded parts to the rigid positioning frame before concrete pouring; and using three points to... The upper spatial constraints are connected to the independent benchmark control network; the lower steel beam is hoisted and hydraulically synchronously lifted and adjusted. A hydraulic synchronous lifting device is installed at the connection node between the steel beam and the steel grid. The lifting amount of each lifting point is adjusted according to the coordinate data measured in real time by the total station, and iterative adjustments are made; prestressed tensioning is applied to adjust the arch shape. High-strength steel strands are inserted into the anchor holes reserved on the lower flange of the lower steel beam, and jacks are used to apply tension to the high-strength steel strands; the cumulative error adjustment of the section is carried out. The least squares adjustment technique is used to distribute the manufacturing error and installation error of the construction section among the forced closed control points. Fine-tuning operations are performed on the adjustable connection device set at the key node. The error distribution path is determined by solving the minimum spanning tree optimization problem.

[0005] The forced closure control point is a high-precision coordinate reference point set artificially within a large construction area to prevent the linear accumulation and transmission of errors.

[0006] The independent reference control network is an independent measurement coordinate system that is not attached to the construction components themselves. It is established by burying deep foundation measurement piers and installing highly stable measurement supports.

[0007] The pre-camber calculation uses a deflection prediction function, with inputs including the steel beam span, the steel beam section moment of inertia, and the steel beam line load, and output being the pre-camber setting value.

[0008] The deflection prediction function is expressed as follows: the product of the fourth power of the steel beam span and the steel beam line load is divided by the product of the moment of inertia and the elastic modulus of the steel beam section, and then multiplied by the span correction factor.

[0009] The parameters of the reverse prefabricated bending curve include the location of the maximum arch height and the arch height distribution function coefficient, with the location of the maximum arch height taken at the span of the steel beam.

[0010] The reverse prefabrication bending process refers to artificially applying an initial curvature that is opposite to the deflection direction during the steel beam fabrication stage, so that the actual deformation of the steel beam after installation and loading matches the theoretical straight profile.

[0011] The rigid positioning frame is a spatial truss structure welded from H-beams and connected to an independent reference control network through three or more spatial constraints.

[0012] The hydraulic synchronous lifting device consists of a hydraulic cylinder, a pressure sensor, a displacement sensor, and an electrical control unit, and achieves coordinated action of multiple lifting points through a central control system.

[0013] The iterative adjustment refers to the repeated execution of a cyclical process of measuring the current coordinate deviation, adjusting the lifting amount, and measuring and verifying again, with the coordinate deviation gradually decreasing after each round of adjustment.

[0014] The coordinate deviation is calculated using a deviation evaluation function. The inputs include the measured coordinates of the measuring point, the theoretical coordinates of the measuring point, and the weight coefficient of the measuring point. The output is a comprehensive deviation index.

[0015] The tension force is applied by using a tension force distribution function to determine the tension force of each high-strength steel strand. The inputs include the anchor point location, the target deflection curve parameters, and the elastic modulus of the high-strength steel strand.

[0016] The adjustable connection device is a mechanical device installed at the steel structure node that allows for minute three-dimensional displacement, including an elongated hole bolt connection, a wedge-shaped pad adjustment mechanism, and a screw fine-tuning device.

[0017] The minimum spanning tree optimization problem is used to determine the optimal allocation path for the cumulative error of a segment, and the minimum spanning tree is solved by Prim's algorithm or Kruskal's algorithm.

[0018] The coaxiality deviation refers to the spatial distance between the actual position of the central axis of the wind tunnel structure and the theoretically designed axis position, which is calculated using an axis fitting function.

[0019] The sandwich structure refers to a composite load-bearing system consisting of three layers: an upper concrete roof panel, a middle steel grid frame, and a lower suspended concrete roof slab.

[0020] This invention establishes an independent benchmark control network and sets forced closure control points. It combines techniques such as pre-camber calculation, reverse prefabrication bending, hydraulic synchronous jacking and posture adjustment, and prestressed tensioning for reverse camber adjustment to achieve multi-level active control of the steel beam coordinates. This method utilizes forced closure control points to block the linear transmission of errors and employs least squares adjustment techniques to rationally distribute manufacturing and installation errors among control points, avoiding the unidirectional accumulation and amplification of errors inherent in traditional methods. Simultaneously, it pre-counters the steel beam's self-weight deflection through pre-camber calculation, achieves precise spatial posture adjustment through hydraulic jacking, and corrects the deflection curve through prestressed tensioning. This ensures that the final coordinate deviation of the steel beam is controlled within ±5mm, solving the technical problem mentioned in the background art where accumulated errors from large-span, multi-segment construction lead to excessive steel beam coordinate accuracy. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method of the present invention.

[0022] Figure 2 This is a schematic diagram of the overall sandwich structure in the embodiment.

[0023] Figure 3 This is a graph showing the change in the comprehensive deviation index during the hydraulic synchronous lifting iterative adjustment process in the embodiment.

[0024] Figure 4 This is a schematic diagram of the hydraulic synchronous lifting device in the embodiment.

[0025] Figure 5 This is a schematic diagram of the rigid positioning frame for the embedded part in the embodiment.

[0026] Figure 6 This is a schematic diagram of the prestressed tensioning anti-arch shaping device in the embodiment. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0028] like Figure 1 As shown, the invention provides a method for controlling the coordinate accuracy of a steel beam suspended from a sandwich composite structure, comprising:

[0029] S10. Establish an independent benchmark control network, set up forced closure control points in the wind tunnel construction area, set up one forced closure control point for every 50 construction sections, and use a three-dimensional laser scanner and total station to establish a spatial coordinate benchmark system.

[0030] S20. Perform the pre-camber calculation of the lower steel beam, establish a finite element analysis model considering the semi-rigid connection characteristics of the nodes and the incomplete constraint conditions of the supports, calculate the elastic deflection value of the steel beam under its own weight, and determine the parameters of the reverse prefabrication bending curve.

[0031] S30. Implement reverse prefabrication bending of steel beams. Based on the pre-camber calculation results, perform reverse cold bending or hot bending on the lower steel beams with a span of more than 30 meters to make the steel beams form an initial camber opposite to the theoretical deflection curve.

[0032] S40. Install the rigid positioning frame for the embedded part. Before pouring concrete, fix the embedded part on the rigid positioning frame. The rigid positioning frame is connected to the independent benchmark control network through three or more spatial constraints. During the pouring process, use a laser indicator to monitor the position deviation of the embedded part.

[0033] S50. Hoist the lower steel beam and perform hydraulic synchronous jacking and attitude adjustment. Install a hydraulic synchronous jacking device at the connection node between the steel beam and the steel grid frame. Adjust the jacking amount of each jacking point according to the coordinate data measured in real time by the total station, and perform 3 to 5 rounds of iterative adjustment.

[0034] S60. Apply prestressed tensioning to adjust the arch shape. Insert high-strength steel strands into the anchor holes reserved in the lower flange of the lower hanging steel beam. Use jacks to apply tension to the high-strength steel strands and adjust the tension of each high-strength steel strand to control the deflection curve shape of the steel beam.

[0035] S70. Perform cumulative error adjustment and allocation for the sections. Use the least squares adjustment technique to distribute the manufacturing and installation errors of 500 construction sections among the forced closed control points. Perform fine-tuning operations on the adjustable connection devices set at key nodes. Determine the error allocation path by solving the minimum spanning tree optimization problem.

[0036] In step S10, the forced closure control points are high-precision coordinate reference points artificially set within a large construction area to prevent the linear accumulation and transmission of errors. The independent reference control network is an independent measurement coordinate system not attached to the construction components themselves. It is established by embedding deep foundation measuring piers and installing highly stable measuring supports to avoid the impact of vibrations and deformations during construction on the measurement reference. The 3D laser scanner has a measurement accuracy of ±2mm and a scanning rate of 50,000 points per second, used to acquire 3D point cloud data of the construction area. The total station has an angle measurement accuracy of ±2 seconds and a distance measurement accuracy of ±1mm, used to accurately determine the spatial coordinates of the control points.

[0037] The semi-rigid connection characteristic of the nodes in step S20 refers to the fact that the steel structure connection nodes are neither ideal hinges nor ideal rigid connections, but rather a connection state with a certain rotational stiffness. In finite element analysis, spring elements are needed to simulate its rotational constraint effect. The incomplete constraint condition of the supports refers to the existence of small displacements and rotational degrees of freedom in actual engineering, which differs from the fixed constraints in theoretical calculations. Support stiffness parameters need to be introduced into the model for correction. The elastic deflection value is the recoverable deformation of the steel beam under load. The self-weight deflection of a 30-meter span steel beam is typically in the range of 50 to 80 mm. The pre-camber calculation uses a deflection prediction function, which calculates the maximum deflection value of the steel beam under its own weight. The inputs include the steel beam span, the moment of inertia of the steel beam section, and the steel beam line load; the output is the pre-camber setting value. The deflection prediction function is expressed as follows: the product of the fourth power of the steel beam span and the steel beam line load is divided by the product of the steel beam section moment of inertia and elastic modulus, and then multiplied by a span correction factor. The span correction factor is obtained through linear regression analysis of the ratio of measured deflection data from 30 sets of steel beams with different spans to theoretically calculated values. The coefficient of determination of the linear regression equation is 0.94, and the range of the span correction factor is 1.12 to 1.28. The parameters of the reverse precast bending curve include the location of the maximum arch height and the arch height distribution function coefficient. The location of the maximum arch height is taken as 0.48 to 0.52 times the steel beam span. The arch height distribution function coefficient is determined through goodness-of-fit analysis of measured arch data from 15 sets of steel beams and parabolic curves, with a goodness-of-fit range of 0.89 to 0.96.

[0038] The reverse pre-fabrication bending process in step S30 refers to artificially applying an initial curvature with the opposite direction to the deflection direction during the steel beam fabrication stage, so that the actual deformation of the steel beam after installation and loading matches the theoretical straight profile. Cold bending is suitable for steel beams with a cross-sectional height of less than 600mm. It involves using mechanical pressure at room temperature to induce plastic deformation in the steel, with the cold bending radius not less than 20 times the cross-sectional height of the steel beam. Hot bending is suitable for steel beams with a cross-sectional height greater than 600mm. It involves locally heating the steel to 820 to 920℃ to reduce its yield strength before applying a bending moment. The length of the heated area is 0.15 to 0.25 times the span of the steel beam. The initial camber setting value is equal to the pre-camber setting value output by the deflection prediction function in step S20 multiplied by a safety factor of 1.05 to 1.15.

[0039] The rigid positioning frame in step S40 is a space truss structure welded from H-beams. The H-beams have a cross-sectional height of 300 to 400 mm and a flange width of 200 to 300 mm. The rigid positioning frame's own deflection is less than 0.05 mm under a concentrated load of 1000 N. The "three-point or higher spatial constraint" refers to restricting the object's six degrees of freedom in three-dimensional space through at least three non-collinear constraint points, thus completely determining the embedded part's attitude. The laser indicator is an optical instrument that emits a 632.8 nm red laser beam with a diameter of 2 mm. The laser beam is aligned with a reflective marker on the embedded part's surface. When the embedded part shifts, the laser spot deviates from the center of the marker, allowing the operator to determine the direction and magnitude of the deviation. The embedded part's position deviation is monitored every 15 to 20 minutes. When the deviation exceeds 0.5 mm, concrete pouring is paused, and the embedded part's position is corrected using adjusting bolts on the rigid positioning frame. The 0.1 mm / meter embedded part machining accuracy control index requires that the surface flatness of the embedded part and the position accuracy of the mounting positioning hole should not deviate by more than 0.1 mm within the length range of one meter. The machining accuracy is achieved by CNC milling and inspection by a coordinate measuring machine.

[0040] The hydraulic synchronous lifting device in step S50 consists of hydraulic cylinders, pressure sensors, displacement sensors, and an electronic control unit. It coordinates the actions of 4 to 8 lifting points through a central control system. The rated thrust of the hydraulic cylinders is 50 to 200. The stroke is 100 to 300 mm, and the lifting speed is 0.5 to 2 mm / s. The pressure sensor has a range of 0 to 250 mm / s. The accuracy is ±0.5%FS, used to monitor the stress state of each jacking point. The displacement sensor has a range of 0 to 500 mm and an accuracy of ±0.01 mm, used to measure the displacement of the jacking point. The iterative adjustment refers to the cyclic process of repeatedly measuring the current coordinate deviation, adjusting the jacking amount, and re-measuring for verification. After each round of adjustment, the coordinate deviation gradually decreases, eventually positioning the three-dimensional coordinates of the steel beam within an accuracy range of ±2 mm. The coordinate deviation is calculated using a deviation evaluation function, which is used to evaluate the degree of deviation between the current position and the theoretical position of the steel beam. The input includes the measured coordinates of the measuring points, the theoretical coordinates of the measuring points, and the weight coefficient of the measuring points. The output is a comprehensive deviation index. The deviation evaluation function is expressed as follows: the sum of the squares of the differences between the measured coordinates and the theoretical coordinates of all measuring points is divided by the total number of measuring points, then divided by the square of the allowable deviation, and then multiplied by the normalized value of the weight coefficient of the measuring points. When the comprehensive deviation index is less than 1.0, it is judged as qualified. The weighting coefficient of the measuring point is determined according to the degree of influence of the location of the measuring point on the structural stress performance. The weighting coefficient of the measuring point in the critical stress part is 1.5 to 2.0, and the weighting coefficient of the measuring point in the general part is 1.0.

[0041] The prestressed tensioning anti-arch shaping technique in step S60 refers to applying prestress to generate deformation opposite to the self-weight deflection, thereby offsetting or reducing the downward deflection of the steel beam. The standard value of the tensile strength of the high-strength steel strand is 1860. The tensile strength standard value was determined by uniaxial tensile tests on 120 groups of high-strength steel strand specimens. The test data were fitted with a Weber distribution function, and the strength value corresponding to the 95% guarantee rate was taken. The shape parameter of the Weber distribution was 15.6, and the scale parameter was 1912. The nominal diameter of the high-strength steel strand is 15.2 mm, and the modulus of elasticity is 195,000. The tension control stress of each high-strength steel strand is 1395. The corresponding tension is 252. The tension force is applied using a tension force distribution function to determine the magnitude of the tension force for each high-strength steel strand. This function determines the tension force at each anchorage point based on the steel beam deflection distribution. Inputs include the anchorage point location, target deflection curve parameters, and the elastic modulus of the high-strength steel strand; the output is the tension force value at each anchorage point. The tension force distribution function is expressed as follows: multiply the curvature value of the target deflection curve parameters at each anchorage point by the bending stiffness of the steel beam section, divide by the distance from the anchorage point to the neutral axis of the steel beam, and then multiply by the ratio of the elastic modulus of the high-strength steel strand to the effective area. After the steel beam is connected and fixed to the steel grid and the concrete top slab is poured, the stress state of the steel beam has changed. At this point, the prestress is gradually released and the high-strength steel strands are removed. The steel beam maintains its surface accuracy through its own stiffness and the constraints of the composite structure. The prestress release process is carried out in 4 to 6 stages, with 15% to 25% of the total prestress released in each stage. After each stage of release, a total station is used to measure the coordinate changes of the steel beam. When the single coordinate change exceeds 2mm, the release is paused and stress redistribution calculation is performed.

[0042] The least squares adjustment technique in step S70 is a mathematical method in surveying that optimally distributes the errors of observed values ​​according to a certain criterion, resulting in the highest overall accuracy of the adjusted coordinate system. The adjustable connection device is a mechanical device installed at the steel structure node that allows for minute three-dimensional displacement. It includes a long oval hole bolt connection, a wedge-shaped pad adjustment mechanism, and a screw fine-tuning device, used to absorb and disperse accumulated errors during assembly. The long oval hole bolt connection has a major axis adjustment range of ±8mm and a minor axis adjustment range of ±3mm. The wedge angle of the wedge-shaped pad is 3 to 5 degrees, and the thickness adjustment range is 0 to 10mm. Fine-tuning in the height direction is achieved by replacing wedge-shaped pads of different thicknesses. The screw diameter of the screw fine-tuning device is 16 to 24mm, the pitch is 2 to 3mm, and the single-turn rotation adjustment range is 2 to 3mm. The fine-tuning operation refers to a precise positioning action within the adjustment range of ±5mm, achieved by rotating the adjusting screw of the screw fine-tuning device or inserting wedge-shaped pads of different thicknesses.

[0043] The minimum spanning tree optimization problem is used to determine the optimal distribution path of the sectional cumulative error. The 500 construction sections and the forced closure control points are abstracted as nodes in graph theory, the connection relationship between adjacent sections is abstracted as edges, and the weight of the edge is defined as the stiffness ratio between the two sections. The minimum spanning tree is solved by the Prim algorithm or the Kruskal algorithm, so that the error distribution path is transmitted along the connection with larger stiffness, reducing the influence of structural deformation on error distribution. The stiffness ratio is obtained by calculating the relative displacement of adjacent sections under the action of unit force through finite element analysis. The connection path with a stiffness ratio greater than 2.0 is preferentially used for error transmission, and the connection path with a stiffness ratio less than 1.5 is set as an error absorption node. The Prim algorithm starts from any initial node and each time selects the edge with the smallest weight that is connected to the current tree and adds it to the tree until all nodes are connected. The Kruskal algorithm sorts all edges in ascending order of weight and successively selects the edge with the smallest weight that does not form a loop and adds it to the tree until a spanning tree is formed.

[0044] The implementation process of the adjustment and distribution of sectional cumulative error is as follows: First, measure the deviation vectors between the actual coordinates and the theoretical coordinates of each forced closure control point. Then, decompose the deviation amount according to the path determined by the minimum spanning tree and the sectional stiffness distribution weight. Finally, apply the corresponding adjustment amount at each adjustable connection device so that the overall coaxiality deviation is controlled within 15 mm. The coaxiality deviation refers to the spatial distance between the actual position of the central axis of the wind tunnel body structure and the position of the theoretical design axis, which has a direct impact on the air flow quality and test accuracy. The coaxiality deviation is calculated using an axis fitting function. The axis fitting function is used to fit the central axis of the tunnel body based on the coordinates of multiple measurement points and calculate the deviation. The input includes the three-dimensional coordinates of the measurement points on the inner wall of the tunnel, the number of measurement points, and the parameters of the theoretical axis equation, and the output is the maximum value of the coaxiality deviation. The axis fitting function uses the least squares method to minimize the sum of the squares of the distances from all measurement points to the fitted axis, solves the direction vector and position vector of the fitted axis by establishing an overdetermined system of equations, and then calculates the spatial distance between the fitted axis and the theoretical design axis as the coaxiality deviation.

[0045] The acceptance standard for the coordinate deviation between the steel beam and the theoretical profile to be less than ±5 mm is achieved through the following method: After the installation and adjustment of the steel beam are completed, use a three-dimensional laser scanner to perform a full-field scan of the steel beam surface with a scan point spacing of 50 mm. After obtaining the point cloud data, fit and compare it with the design model, and extract the normal deviation values of each measurement point. When the absolute value of the deviation of more than 95% of the measurement points is less than 5 mm and the maximum deviation does not exceed 8 mm, it is judged as qualified. The normal deviation value is the distance from the measurement point along the normal direction of the steel beam surface to the theoretical profile. A positive normal deviation value indicates that the measurement point is outside the theoretical profile, and a negative normal deviation value indicates that the measurement point is inside the theoretical profile.

[0046] The sandwich structure refers to a composite load-bearing system consisting of three layers: an upper concrete roof panel, a middle steel space frame, and a lower suspended concrete roof slab. The concrete roof panel has a thickness of 150 to 200 mm and a concrete strength grade of C40 to C50. The steel space frame members have a diameter of 60 to 120 mm, and the joint types are welded ball joints or bolted ball joints. The suspended concrete roof slab has a thickness of 100 to 150 mm and a concrete strength grade of C35 to C45. The suspended steel beam is a key force-transmitting component connecting the steel space frame and the suspended concrete roof slab. The suspended steel beam has a cross-sectional shape of H-beams or box-beams, a cross-sectional height of 400 to 800 mm, a flange width of 250 to 400 mm, a web thickness of 12 to 20 mm, a flange thickness of 16 to 28 mm, and uses steel grades of Q345B or Q390C.

[0047] The specific implementation methods of the above steps are described in detail below.

[0048] The specific implementation of step S10 includes: First, deep foundation measuring piers are buried around the wind tunnel construction area. The piers are buried at a depth of not less than 2 meters to ensure they are not affected by surface vibration and temperature changes. A high-stability measuring bracket is installed on the top of the measuring pier as the physical carrier of an independent reference control network. Next, points are set up in the construction area according to the principle of setting one forced closure control point for every 50 construction sections. The forced closure control points are fixed to the measuring piers with stainless steel marker nails. The center coordinates of the marker nails are precisely measured using a total station, with an angle measurement accuracy of ±2 seconds and a distance measurement accuracy of ±1 mm. Then, a three-dimensional laser scanner is used to perform a full-area scan of the entire construction area. The scanner has a measurement accuracy of ±2 mm and a scanning rate of 50,000 points per second. The three-dimensional spatial information of the construction area is obtained through point cloud data. Finally, the coordinates of the control points measured by the total station are registered and fused with the point cloud data obtained by the laser scan to establish a unified spatial coordinate reference system. The registration process uses a least squares optimization algorithm to minimize the registration error. In step S10, a reference control network independent of the construction components was adopted, which avoids the influence of component deformation on the measurement reference during construction and brings about the technical effect of a long-term stable high-precision coordinate reference system.

[0049] The specific implementation of step S20 includes: First, establishing a finite element analysis model of the suspended steel beam. In the model, the steel beam is discretized into several beam elements. Spring elements are set at the connection nodes to simulate the semi-rigid connection characteristics of the nodes. The spring stiffness is determined by mechanical test data of the node connection form. Next, support stiffness parameters are introduced at the support positions to reflect the incomplete constraint conditions of the supports in actual engineering. The support stiffness parameters are obtained by the displacement response curve of the support loading test. Then, the self-weight load of the steel beam is applied to the finite element model. The self-weight load is calculated according to the cross-sectional dimensions and steel density of the steel beam to obtain the line load value. The elastic deflection distribution of the steel beam under self-weight is calculated. The self-weight deflection of a 30-meter span steel beam is usually in the range of 50 to 80 mm. Subsequently, the pre-camber setting value was calculated using a deflection prediction function. This function divides the product of the fourth power of the steel beam span and the line load by the product of the moment of inertia and the elastic modulus of the steel beam section, and then multiplies it by a span correction factor. The span correction factor was obtained through linear regression analysis of the ratio of measured deflection data of 30 sets of steel beams with different spans to theoretical calculation values. The coefficient of determination of the linear regression equation was 0.94, and the span correction factor ranged from 1.12 to 1.28. Finally, the parameters of the reverse prefabrication bending curve were determined, including the maximum arch height position being taken as 0.48 to 0.52 times the steel beam span. The arch height distribution function coefficient was determined through goodness-of-fit analysis of 15 sets of measured camber data of steel beams and parabolic curves, with a goodness-of-fit of 0.89 to 0.96. In this step S20, a finite element analysis method considering semi-rigid connections at nodes and incomplete constraints at supports was adopted, resulting in a significant improvement in the accuracy of pre-camber calculation.

[0050] The specific implementation of step S30 includes: First, determining the initial camber value by multiplying the pre-camber setting value calculated in step S20 by a safety factor of 1.05 to 1.15. The safety factor is introduced to compensate for processing errors and material property fluctuations. Next, selecting either cold bending or hot bending processes based on the steel beam section height. Steel beams with a section height less than 600mm are cold-bent, where mechanical pressure causes plastic deformation of the steel at room temperature. The cold bending radius is not less than 20 times the steel beam section height to prevent cracking. Steel beams with a section height greater than 600mm are hot-bent. The steel beam is locally heated to 820-920℃ using an oxyacetylene flame or induction heating method. The length of the heated area is 0.15-0.25 times the span of the steel beam. After heating, the yield strength of the steel decreases, making it easier to apply bending moment. Then, bending force is applied at the mid-span and symmetrical positions on both sides of the steel beam to form an initial camber curve opposite to the theoretical deflection curve. During the bending process, a level or laser displacement sensor is used to monitor the camber value in real time. Finally, after the steel beam cools or is unloaded, a coordinate measuring machine is used to check whether the camber curve meets the design requirements. Steel beams that do not meet the requirements undergo secondary adjustment and processing. In this step S30, a reverse pre-bending pre-deformation control method is adopted, resulting in the technical effect that the actual deformation of the steel beam after installation matches the theoretical profile.

[0051] The specific implementation of step S40 includes: First, fabricating a rigid positioning frame. The frame is a space truss structure welded from H-beams with a cross-sectional height of 300 to 400 mm and a flange width of 200 to 300 mm. The frame's deflection is less than 0.05 mm under a concentrated load of 1000 N to ensure positioning accuracy. Next, the embedded part is fixed to the rigid positioning frame with bolts, and reflective markings are attached to the surface of the embedded part as aiming targets for the laser pointer. Then, the rigid positioning frame is connected to an independent reference control network through three or more non-collinear spatial constraint points. The positions of the constraint points are accurately measured using a total station. The embedded part's orientation is fully determined by adjusting to the design coordinates. Then, before concrete pouring, a red laser pointer with a wavelength of 632.8 nm and a beam diameter of 2 mm is installed. The laser beam is aligned with the center of the reflective marker on the embedded part's surface. During pouring, the embedded part's position is measured every 15 to 20 minutes. When the laser spot deviates from the center of the marker by more than 0.5 mm, concrete pouring is paused, and the embedded part's position is corrected using adjusting bolts on the rigid positioning frame. Finally, after the concrete strength reaches more than 70% of the design strength, the rigid positioning frame is removed, and a total station is used to re-measure whether the final coordinate deviation of the embedded part is within ±1 mm. In step S40, the combination of a rigid positioning frame and real-time laser monitoring achieves the technical effect of maintaining the embedded part's position with high precision during concrete pouring.

[0052] The specific implementation of step S50 includes: firstly, installing a hydraulic synchronous jacking device at the connection node between the lower steel beam and the steel space frame; the device has a rated thrust of 50 to 200. The system consists of hydraulic cylinders with a stroke of 100 to 300 mm and a lifting speed of 0.5 to 2 mm / s, along with pressure and displacement sensors. Four to eight lifting points coordinate their movements through a central control system. Next, a total station is used to measure the current coordinates of key measuring points on the steel beam. These measuring points are located at the mid-span and quarter-span positions of the beam, with a measurement frequency of once per lifting cycle. Then, the deviation vector between the measured and theoretical coordinates of the measuring points is calculated. A deviation evaluation function is used to assess the comprehensive deviation index. This function is calculated by dividing the sum of the squares of the differences between the measured and theoretical coordinates of all measuring points by the total number of measuring points, then dividing by the square of the allowable deviation, and finally multiplying by the normalized value of the measuring point weight coefficient. The weight coefficient for measuring points in critical stress areas is 1.5 to 2.0, and for general areas, it is 1.0. Subsequently... The required lifting amount for each lifting point is calculated based on the deviation vector and the positional relationship of each lifting point. A linear relationship between the lifting amount and coordinate deviation is established using the Jacobian matrix method. The adjustment amount for each lifting point is obtained by solving a system of linear equations. Next, the central control system sends commands to each hydraulic cylinder to execute the lifting action. During the lifting process, pressure and displacement sensors monitor the force and displacement state of each lifting point in real time. When the pressure at a certain lifting point exceeds 90% of the rated value, the system automatically stops lifting at that point. Finally, the cycle of measuring, calculating the deviation, and adjusting the lifting amount is repeated for 3 to 5 rounds of iterative adjustment. After each round of adjustment, the comprehensive deviation index gradually decreases. When the comprehensive deviation index is less than 1.0, it is considered qualified. At this point, the three-dimensional coordinate positioning accuracy of the steel beam reaches within ±2mm. In this step S50, a combination of hydraulic synchronous lifting and iterative feedback adjustment is used, resulting in precise control of the multi-degree-of-freedom spatial attitude.

[0053] The specific implementation of step S60 includes: firstly, inserting a nominal diameter of 15.2 mm and a tensile strength standard value of 1860 into the anchoring hole reserved in the lower flange of the lower hanging steel beam. The elastic modulus is 195,000. High-strength steel strands were used, with anchor holes arranged along the span of the steel beam at intervals of 1 to 2 meters. A tension distribution function was then used to determine the tension force at each anchor point. This function calculates the tension force at each anchor point by multiplying the curvature value of the target deflection curve parameters at each anchor point by the bending stiffness of the steel beam section, dividing by the distance from the anchor point to the neutral axis of the steel beam, and then multiplying by the ratio of the elastic modulus of the high-strength steel strand to its effective area. The tension control stress for a single high-strength steel strand was 1395. The corresponding tension is 252. Then, using jacks, tension is applied to each high-strength steel strand in stages. First, 25% of the design tension is applied, and after holding the load for 5 minutes, the anchorage and steel strands are checked for any abnormalities. Then, the tension is applied to 50%, 75%, and 100% of the design tension, with each stage held for at least 3 minutes. Subsequently, a total station is used to measure the coordinate changes of each measuring point on the steel beam. The tension of each high-strength steel strand is adjusted according to the deviation between the measured deflection curve and the target deflection curve. The tension of the corresponding anchorage point is increased or decreased at locations with larger deviations. Finally, after the steel beam is connected and fixed to the steel grid and the concrete top slab is poured, the stress state of the steel beam changes. The prestress is gradually released in 4 to 6 stages, releasing 15% to 25% of the total prestress in each stage. After each stage of release, the coordinate changes of the steel beam are measured. When the single coordinate change exceeds 2 mm, the release is paused and stress redistribution calculation is performed. After all the prestress is released, the high-strength steel strands are removed. In this step S60, an active deformation control method of prestressed tensioning and anti-arch shaping is adopted, which brings about the technical effect that the deflection curve of the steel beam can be precisely adjusted.

[0054] The specific implementation of step S70 includes: First, using a total station to measure the actual coordinates between each forced closure control point, comparing the actual coordinates with the theoretical coordinates to obtain the deviation vector, which includes components in the X, Y, and Z directions; then, abstracting the 500 construction sections and forced closure control points as nodes in graph theory, and abstracting the connection relationship between adjacent sections as edges, calculating the relative displacement of adjacent sections under unit force through finite element analysis, and determining the edge weight as the stiffness ratio between the two sections, with connection paths having a stiffness ratio greater than 2.0 preferentially used for error transmission. First, connection paths with a stiffness ratio less than 1.5 are set as error absorption nodes. Then, Prim's algorithm or Kruskal's algorithm is used to solve for the minimum spanning tree. Prim's algorithm starts from any initial node and selects the edge with the smallest weight connected to the current tree and adds it to the tree until all nodes are connected. Kruskal's algorithm sorts all edges by weight from smallest to largest and selects the edge with the smallest weight that does not form a cycle and adds it to the tree until a spanning tree is formed. The minimum spanning tree determines the optimal path for error distribution. Then, the least squares adjustment technique is used to adjust the deviation according to the path determined by the minimum spanning tree and... The stiffness distribution weights of each section are decomposed, and the least squares method is used to solve for the adjustment amount by establishing a set of error equations and minimizing the sum of squares of the observed residuals, thus maximizing the overall accuracy of the adjusted coordinate system. Next, corresponding adjustment amounts are applied to the adjustable connection devices in each section. These adjustable connection devices include elongated hole bolt connections, wedge-shaped pad adjustment mechanisms, and screw fine-tuning devices. The major axis adjustment of the elongated hole bolt connections is ±8mm, and the minor axis adjustment is ±3mm. The wedge angle of the wedge-shaped pads is 3 to 5 degrees, and the thickness adjustment range is 0 to 10mm. The screw of the screw fine-tuning device... With a diameter of 16 to 24 mm, a pitch of 2 to 3 mm, and a single-turn adjustment of 2 to 3 mm, precise positioning within a range of ±5 mm is achieved by rotating the screw or replacing wedge-shaped pads of different thicknesses. Finally, an axis fitting function is used to verify the coaxiality deviation of the tunnel's central axis. This function minimizes the sum of the squares of the distances from all measuring points to the fitted axis using the least squares method. An overdetermined system of equations is established to solve for the direction and position vectors of the fitted axis. The spatial distance between the fitted axis and the theoretically designed axis is calculated as the coaxiality deviation, requiring the overall coaxiality deviation to be controlled within 15 mm. In step S70, an error allocation method based on minimum spanning tree optimization and least squares adjustment techniques are employed, resulting in effective control of cumulative errors in large-scale construction sections.

[0055] It should be noted that the key technical ideas of this invention include the following aspects. First, the segmented control strategy of independent benchmark control network and forced closed control points, by establishing independent measurement benchmarks outside the construction area that are not attached to the component itself, blocks the linear cumulative transmission of errors along the construction sequence. Compared with the traditional attached measurement method, this avoids the influence of component deformation on the measurement benchmark, fundamentally solving the problem of cumulative error control for long-distance, large-span structures. Second, the pre-camber calculation and reverse prefabrication bending pre-deformation control technology, by establishing a refined finite element model considering the semi-rigidity of nodes and the incomplete constraints of supports, accurately predicts the actual deflection behavior of the steel beam, and applies reverse prefabrication bending during the fabrication stage. Compared with the traditional passive adjustment method after installation, this achieves active control of deformation, significantly reducing the workload and difficulty of on-site adjustment. Third, the multi-degree-of-freedom iterative adjustment mechanism of hydraulic synchronous jacking, by establishing the Jacobian matrix relationship between the jacking amount and the coordinate deviation, adopts closed-loop feedback control to achieve precise positioning of the spatial attitude of the steel beam, significantly improving adjustment efficiency and accuracy stability compared with the traditional manual adjustment method. Fourth, error distribution path planning based on minimum spanning tree optimization introduces graph theory algorithms into the measurement adjustment process, allowing errors to propagate along paths with higher stiffness. Compared to traditional uniform distribution methods, this reduces the impact of structural deformation on error distribution and improves the overall coordinate system's consistency. The synergistic effect of these key technological approaches lies in constructing a comprehensive precision control system encompassing measurement benchmark establishment, component pre-deformation control, installation attitude adjustment, and cumulative error distribution. Each stage supports the others, forming a closed-loop control chain. Compared to traditional single-stage control methods, this achieves hierarchical error control and multi-level mitigation, ultimately ensuring the high-precision positioning requirements of the steel beams suspended under the sandwich composite structure.

[0056] It should be noted that this invention also solves the following technical problem: During wind tunnel construction, suspended steel beams with spans exceeding 30 meters will experience elastic deflection of 50 to 80 mm under their own weight. Traditional construction methods, which only involve jacking and adjusting after installation, cannot completely eliminate the deflection effect. This invention addresses this by performing reverse pre-fabrication bending based on finite element analysis results during the steel beam fabrication stage. This allows the steel beam to pre-form an initial camber opposite to the direction of its own weight deflection, automatically springing back to its theoretical straight profile after installation and loading. The finite element model, considering the semi-rigid connection characteristics of nodes and the incomplete constraint conditions of supports, can accurately predict the actual deflection value, avoiding deviations in pre-camber settings caused by calculations based on ideal rigid or hinged connections. After the steel beam is installed, the deflection curve is further refined using prestressed tensioning and reverse camber adjustment technology. The tension force at each anchorage point is determined based on the tension force distribution function, achieving precise control of the steel beam profile.

[0057] Specifically, the principle of this invention is as follows: The invention solves the problem of accumulated errors in the construction of large-span, multi-section projects by employing an error blocking and dispersion control strategy. In traditional methods, errors are linearly transmitted and superimposed along the construction sequence, leading to excessive errors at the end. This invention establishes an independent coordinate reference benchmark by setting forced closure control points, thus breaking the error transmission chain. A minimum spanning tree optimization algorithm is used to determine the error distribution path, and the accumulated errors are reasonably distributed to each adjustable connection device according to the structural stiffness characteristics, avoiding localized error concentration. Addressing the large self-weight deflection of large-span steel beams, the deflection value is predicted through finite element analysis and reverse pre-fabrication bending is performed, allowing the steel beam to automatically spring back to its theoretical position after being loaded. Combined with iterative adjustments using hydraulic synchronous jacking and fine-tuning of prestressed tensioning, a comprehensive precision control system is formed from fabrication to installation, and from coarse to fine adjustments, ensuring that the coordinate accuracy of the steel beam meets the stringent requirements of the wind tunnel.

[0058] The following provides a specific embodiment 1 of the present invention, and the specific implementation of each step in this embodiment 1 is described in detail below.

[0059] The specific implementation methods of steps S10 and S40 are the same as those described above, and will not be repeated in detail here.

[0060] The specific implementation of step S20 involves using a deflection prediction function to calculate the precamber setting value of the steel beam under its own weight. The formula for the deflection prediction function is as follows:

[0061] ;

[0062] In the formula, Set the pre-camber value in mm; The span of the steel beam is in meters (m). For steel beam line loads, the unit is . ; The elastic modulus of the steel beam is expressed in units of 1. ; The moment of inertia of the steel beam section is expressed in units of 1000 m / s. ; This is the span correction factor, which is dimensionless.

[0063] The parameter acquisition method is as follows: Obtained directly from design drawings; Calculated based on the self-weight density and cross-sectional area of ​​the steel beam; For Q345B steel, take 206000. ; The moment of inertia of the steel beam is obtained according to the cross-sectional dimensions using the formula. The regression was obtained using linear regression, and the regression equation is expressed as follows:

[0064] ;

[0065] In the formula, This is a span correction factor, dimensionless; The regression slope coefficient is taken as 0.0053, with units of... ; The span of the steel beam is in meters (m). Let be the regression intercept constant, taken as 1.003, dimensionless. The coefficient of determination of the regression equation is 0.94. Within the range of 20 to 40 meters The value ranges from 1.12 to 1.28. The location of the maximum arch height in the parameters of the reverse precast bending curve. The arch height distribution function is expressed in parabolic form as follows: 0.48 to 0.52 times the span of the steel beam, typically 0.5 times. The unit is meters.

[0066] ;

[0067] In the formula, The distance from the left end of the steel beam is The arch height at the location is expressed in mm. This is the maximum arch height, in mm; This is the distance from the left end of the steel beam, in meters. This represents the span of the steel beam, in meters (m). Calculate using the following formula:

[0068] ;

[0069] In the formula, This is the maximum arch height, in mm; Set the pre-camber value in mm; The safety factor ranges from 1.05 to 1.15, but is typically set to 1.10. It is dimensionless.

[0070] In a specific implementation of step S30, the initial camber setting value is calculated according to the following formula:

[0071] ;

[0072] In the formula, Set the initial camber value in mm; Set the precamber value for the output of the deflection prediction function in step S20, in mm; For safety factors, the value ranges from 1.05 to 1.15, but is typically 1.10; it is dimensionless. Cold bending radius. The constraint condition is not less than 20 times the height of the steel beam section, as stated below:

[0073] ;

[0074] In the formula, The radius of cold bending is in mm. This represents the cross-sectional height of the steel beam, in mm. The length of the heated zone during hot bending is also shown. Determine according to the following formula:

[0075] ;

[0076] In the formula, The length of the heating zone is in meters (m). This is the heating length coefficient, ranging from 0.15 to 0.25, typically 0.20, and is dimensionless. The span of the steel beam is in meters (m).

[0077] The specific implementation of step S50 involves using a deviation evaluation function to calculate the degree of deviation between the current position and the theoretical position of the steel beam. The formula for the deviation evaluation function is as follows:

[0078] ;

[0079] In the formula, This is a comprehensive deviation index, dimensionless. The total number of measurement points is dimensionless. For the first Actual measurements at each measuring point Coordinates, in mm; For the first Actual measurements at each measuring point Coordinates, in mm; For the first Actual measurements at each measuring point Coordinates, in mm; For the first Theory of individual measurement points Coordinates, in mm; For the first Theory of individual measurement points Coordinates, in mm; For the first Theory of individual measurement points Coordinates, in mm; To allow for a tolerance of 2mm; For the first The weighting coefficients for each measurement point are dimensionless.

[0080] The parameter acquisition method is as follows: Data was obtained in real time using a total station. Extracted from the design model; The weighting coefficient for measuring points is determined based on their location and its impact on the structural stress performance. For measuring points in critical stress areas, the weighting coefficient is 1.5 to 2.0, while for those in general areas, it is 1.0. Measurements are taken after each round of iterative adjustments. Value, when It was deemed qualified at that time.

[0081] The specific implementation of step S60 involves using a tension force distribution function to determine the magnitude of the tension force at each anchorage point, and the standard value of the tensile strength of the high-strength steel strand. The tensile strength data of 120 groups of high-strength steel strand specimens were determined by uniaxial tensile tests using the following method. The data were fitted using the Weiber distribution function, and the cumulative distribution function of the Weiber distribution is expressed as follows:

[0082] ;

[0083] In the formula, For tensile strength less than or equal to The cumulative probability is dimensionless. The tensile strength value measured in the experiment, in units of ; Let be the scaling parameter of the Weiber distribution, taken as 1912. ; The shape parameter of the Weber distribution is taken as 15.6, which is dimensionless. Standard value of tensile strength. The strength value corresponding to a 95% guarantee rate, that is, satisfying Calculations yielded The formula for the tension distribution function is as follows:

[0084] ;

[0085] In the formula, For the first The tension value at each anchorage point, in units of ; For the target deflection curve at the th The curvature values ​​at each anchorage point, in units of ; The elastic modulus of high-strength steel strand is taken as 195,000. ; The effective area of ​​high-strength steel strand is expressed in units of... ; For the first The distance from each anchor point to the neutral axis of the steel beam, in meters.

[0086] The parameter acquisition method is as follows: According to the second derivative of the target deflection curve at the th... The values ​​for each anchor point location are calculated. According to the The distance between each anchor hole and the neutral axis of the steel beam was measured. Based on the nominal diameter of the high-strength steel strand being 15.2mm, the following is taken: Tension control stress of high-strength steel strand 1395 The corresponding tension Calculate using the following formula:

[0087] ;

[0088] In the formula, For the corresponding tension, take 252. ; To determine the tension control stress, we take 1395. ; The effective area of ​​the high-strength steel strand is taken as 181.5. The prestress release process is carried out in 4 to 6 stages, with each stage releasing 15% to 25% of the total prestress. Release is paused when the single coordinate change exceeds 2 mm.

[0089] The specific implementation of step S70 involves using minimum spanning tree optimization to determine the distribution path of the cumulative error in the segment, and the stiffness ratio. The relative displacement of adjacent sections under a unit force is obtained through finite element analysis. The calculation formula is as follows:

[0090] ;

[0091] In the formula, For section and section The ratio of stiffness between them is dimensionless; For section Displacement under a unit force, expressed in mm; For section The displacement under a unit force, expressed in mm.

[0092] The parameter acquisition method is as follows: and Apply 1 using finite element analysis software Obtained by calculating the unit force. The connection path with a stiffness ratio greater than 2.0 is preferentially used for error transmission, and the connection path with a stiffness ratio less than 1.5 is set as an error absorption node. Prim's algorithm starts from the initial node and each time selects the edge with the smallest weight that is connected to the current tree and adds it to the tree until all nodes are connected. Kruskal's algorithm sorts all edges in ascending order of weight and successively selects the edge with the smallest weight that does not form a loop and adds it to the tree until a spanning tree is formed. After the error distribution is completed, the coaxiality deviation is calculated using the axis fitting function. The axis fitting function uses the least squares method to minimize the sum of the squares of the distances from all measurement points to the fitted axis. The calculation formula is expressed as follows:

[0093] ;

[0094] In the formula, is the distance from the -th measurement point to the fitted axis, with the unit of mm; is the number of measurement points, dimensionless; is the three-dimensional coordinate vector of the -th measurement point, expressed as , with the unit of mm; is the three-dimensional coordinate vector of any point on the fitted axis, expressed as , with the unit of mm; is the unit direction vector of the fitted axis, expressed as , satisfying , dimensionless; represents the vector dot product operation; represents the Euclidean norm of the vector.

[0095] Among them, the parameter acquisition method is: in are the three-dimensional coordinate components of the -th measurement point, respectively, obtained by scanning the inner wall of the tunnel with a three-dimensional laser scanner; and are obtained by solving the overdetermined equations of the above minimization problem, and the Lagrange multiplier method or the singular value decomposition method is used for solving. The coaxiality deviation is the spatial distance between the fitted axis and the theoretical design axis, with the unit of mm. The calculation method is to obtain the shortest distance from any point on the fitted axis to the theoretical design axis. When the overall coaxiality deviation is controlled within 15 mm, it is determined to be qualified. The normal deviation value of the measurement point on the steel beam surface is the distance from the measurement point along the normal direction of the steel beam surface to the theoretical surface, with the unit of mm. When the absolute value of the deviation of more than 95% of the measurement points is less than 5 mm and the maximum deviation does not exceed 8 mm, it is determined to be qualified.

[0096] It should be noted that the detailed explanations of the variables involved in the present invention are shown in Table 1.

[0097] Table 1. Variable Explanation Table

[0098]

[0099] To better understand and implement this invention, the following is a specific application scenario of the invention, Example 2: A wind tunnel test section adopts a sandwich composite structure, such as... Figure 2 As shown, the structure includes an upper concrete roof slab, a middle steel space frame, and a lower suspended concrete roof slab. The test section is divided into 500 construction sections, including 256 suspended steel beams. Each beam has a span of 32 meters, an H-section, a section height of 650 mm, a flange width of 350 mm, a web thickness of 16 mm, a flange thickness of 22 mm, and is made of Q345B steel. The coaxiality of the tunnel's central axis must be controlled within 15 mm, and the deviation between the steel beams and the theoretical surface coordinates must be less than ±5 mm, requiring extremely high construction precision.

[0100] The technical team first established an independent benchmark control network within the wind tunnel construction area. Twelve deep-foundation measuring piers, each 4.5 meters deep, were embedded around the perimeter of the construction area, with high-stability measuring supports mounted on top, each 2.8 meters high. Ten forced-closure control points were established, one for every 50 sections out of 500 construction segments. These control points were marked with stainless steel markers embedded in the concrete structure, each marked with a crosshair, achieving a positioning accuracy of ±0.5mm. The team then used a 3D laser scanner and a total station to establish a spatial coordinate benchmark system. The 3D laser scanner had a measurement accuracy of ±2mm and a scanning rate of 50,000 points per second, while the total station had an angle measurement accuracy of ±2 seconds and a distance measurement accuracy of ±1mm. Through scanning and measuring the entire construction area, initial 3D point cloud data was obtained. A spatial coordinate reference system independent of the construction components was established at each point.

[0101] The technical team performed pre-camber calculations on the 32-meter span suspended steel beam, establishing a finite element analysis model that considers the semi-rigid connection characteristics of the nodes and the incomplete constraint conditions of the supports. In the model, the node connections are simulated using spring elements, and the rotational stiffness is set to a value of [value missing]. The support stiffness parameter is taken as: The steel beam line load is 12.8. The moment of inertia of the steel beam section is The elastic modulus is 206000. Based on the deflection prediction function, the fourth power of the steel beam span of 32 meters is calculated and the line load is 12.8. The product of the two values ​​is divided by the product of the section moment of inertia and the elastic modulus, and then multiplied by the span correction factor of 1.24 to obtain a pre-camber setting value of 68mm. The technical team conducted parabolic fitting analysis using measured camber data from 15 sets of steel beams with similar spans, determining the camber height distribution function coefficient to be 0.0132, with a goodness of fit of 0.92. The maximum camber height was set at 0.50 times the span of the steel beam, i.e., at 16 meters.

[0102] The technical team implemented reverse prefabrication bending of the steel beam. Since the beam's cross-sectional height was 650mm, which is greater than 600mm, a hot bending process was employed. Local heating was carried out within a 6.4-meter radius on both sides of the beam's mid-span, with the heating temperature controlled at 870℃. The total length of the heated area was 12.8 meters, representing 0.40 times the beam's span. After heating, a bending moment was applied using hydraulic jacks, causing the beam to form an initial camber opposite to the theoretical deflection curve. The initial camber setting was equal to the pre-camber setting of 68mm multiplied by a safety factor of 1.10, ultimately set at 75mm. After hot bending, the beam cooled to room temperature. The measured maximum camber height was 73mm, located 0.3 meters to the left of the mid-span, deviating from the design value by 2mm, meeting the processing accuracy requirements.

[0103] Before concrete pouring, the technical team installed a rigid positioning frame for the embedded parts. This frame was welded from H-beams, with a cross-sectional height of 350mm, a flange width of 250mm, a web thickness of 10mm, and a flange thickness of 14mm. The rigid positioning frame was connected to an independent reference control network via four spatial constraint points arranged in a rectangle, with a long side of 2.4 meters and a short side of 1.8 meters. The embedded parts, measuring 600mm × 400mm × 30mm, were fixed to the rigid positioning frame using a CNC milling machine, achieving a surface flatness of 0.08. The positioning accuracy of the mounting holes is 0.09. The concrete was inspected and approved by a coordinate measuring machine. During the pouring process, a laser pointer was used to monitor the positional deviation of the embedded parts. The laser pointer emitted a red laser beam with a wavelength of 632.8 nanometers and a diameter of 2 mm, which was aligned with the reflective marking plate on the surface of the embedded parts. The technical team measured the position of the embedded parts every 18 minutes. During the pouring process, it was found that the offset of embedded part No. 3 reached 0.6 mm when the pouring height reached 2.3 meters, exceeding the control limit of 0.5 mm. Concrete pouring was immediately suspended, and the position of the embedded part was corrected to 0.2 mm offset using the adjusting bolts on the rigid positioning frame before pouring continued.

[0104] The technical team hoisted and lowered the steel beams and performed hydraulic synchronous jacking and attitude adjustment. Hydraulic synchronous jacking devices were installed at eight connection points between the steel beams and the steel space frame. The hydraulic cylinders have a rated thrust of 120 kN, a stroke of 200 mm, and a jacking speed of 1.2 seconds. The pressure sensor has a range of 0 to 250. The accuracy is ±0.5%FS, and the displacement sensor range is 0 to 500 mm with an accuracy of ±0.01 mm. The technical team used a total station to measure the three-dimensional coordinates of 24 measuring points on the steel beam in real time. The measuring points are distributed on the upper flange, web, and lower flange of the steel beam. Before the first round of adjustments, the technical team measured the coordinates of each measuring point and calculated the comprehensive deviation index to be 3.8, which is much greater than the qualified standard of 1.0. The weight coefficient of the 8 measuring points in the key stress-bearing parts was set to 1.8, and the weight coefficient of the 16 measuring points in the general parts was set to 1.0. Based on the calculation results of the deviation evaluation function, the adjustment amount of the 8 jacking points was determined, as shown in Table 2.

[0105] Table 2 Adjustment Amount for the First Round of Hydraulic Synchronous Lifting

[0106]

[0107] After the first round of adjustments, the overall deviation index decreased to 2.1. The technical team continued with the second, third, and fourth rounds of adjustments. After four rounds of iterative adjustments, the overall deviation index decreased to 0.87, and the three-dimensional coordinate positioning accuracy of the steel beam reached ±1.8mm, meeting the accuracy requirement of ±2mm. The trends of the overall deviation index after each round of adjustments are as follows: Figure 3 As shown, the synchronous jacking device during construction is as follows: Figure 4 As shown.

[0108] The technical team inserted high-strength steel strands into the 12 pre-drilled anchoring holes on the lower flange of the suspended steel beam. The standard tensile strength of the high-strength steel strands is 1860 Nm. The nominal diameter is 15.2 mm, and the elastic modulus is 195,000. Based on the target deflection curve parameters, the tension force values ​​at each anchorage point were calculated using a tension force distribution function. The tension forces at the 12 anchorage points were 198 kN, 216 kN, 235 kN, 248 kN, 252 kN, 252 kN, 252 kN, 248 kN, 235 kN, 216 kN, and 198 kN, respectively. Jacks were used to apply tension to each high-strength steel strand. During the tensioning process, a total station was used to monitor the deflection changes of the steel beam. After all 12 high-strength steel strands were tensioned, the steel beam exhibited an upward camber of 42 mm at the mid-span, effectively offsetting 62% of the self-weight deflection. After the steel beam was connected and fixed to the steel grid and the lower concrete slab was poured, the technical team gradually released the prestress in five stages, releasing 20% ​​of the total prestress in each stage. After the third stage of prestressing release, the measured change in the mid-span coordinates of the steel beam was 2.3 mm, exceeding the control limit of 2 mm. The technical team paused the release and performed stress redistribution calculations before resuming the release. After complete prestressing release, the high-strength steel strands were removed. The steel beam maintained its surface accuracy through its own stiffness and the constraints of the composite structure. The measured deviation between the actual and theoretical surface coordinates of the steel beam was ±3.8 mm.

[0109] The technical team conducted cumulative error adjustment and allocation for the 500 construction sections, using the least squares adjustment technique to distribute the manufacturing and installation errors among 10 mandatory closed control points. The team first measured the deviation vector between the actual and theoretical coordinates of the 10 mandatory closed control points. The X component of the deviation vector ranged from -8.6mm to +9.2mm, the Y component from -7.8mm to +8.5mm, and the Z component from -6.3mm to +7.1mm. The 500 construction sections and 10 mandatory closed control points were abstracted into 510 nodes in graph theory, and the connections between adjacent sections were abstracted into 762 edges. Finite element analysis was used to calculate the relative displacement of adjacent sections under a unit force, obtaining the stiffness ratio of each edge. A total of 486 connection paths with a stiffness ratio greater than 2.0 were prioritized for error propagation, while 89 connection paths with a stiffness ratio less than 1.5 were designated as error absorption nodes. The Kruskal algorithm is used to solve the minimum spanning tree. All 762 edges are sorted in descending order of stiffness ratio. The edges with the largest stiffness ratio that do not form a cycle are added to the tree in turn, and finally a spanning tree with 510 nodes and 509 edges is formed. The error distribution path is propagated along the connection with the larger stiffness.

[0110] The technical team performed fine-tuning operations on 128 adjustable connection devices set up at key nodes. These devices included elongated hole bolt connections, wedge-shaped pad adjustment mechanisms, and screw fine-tuning devices. The elongated hole bolt connections had a major axis adjustment range of ±8mm and a minor axis adjustment range of ±3mm. The wedge-shaped pads had a wedge angle of 4 degrees and a thickness adjustment range of 0 to 10mm; height adjustments were achieved by replacing wedge-shaped pads of different thicknesses. The screw fine-tuning device had a screw diameter of 20mm, a pitch of 2.5mm, and a single-turn adjustment of 2.5mm. Based on the path determined by the minimum spanning tree and the weight allocation of segment stiffness, the deviation was decomposed to each adjustable connection device. The adjustment range for the 128 devices was -4.8mm to +5.2mm, with an average adjustment of 1.6mm. After the fine-tuning operations were completed, the technical team used a 3D laser scanner to scan the entire inner wall of the tunnel, with a scan point spacing of 50mm, obtaining a total of [data missing]. The coaxiality deviation of the tunnel's central axis was calculated using an axis fitting function. By minimizing the sum of the squares of the distances from all measuring points to the fitted axis using the least squares method, an overdetermined system of equations was established to solve for the direction and position vectors of the fitted axis. The spatial distance between the fitted axis and the theoretically designed axis was calculated, and the maximum coaxiality deviation was found to be 12.6 mm, which is less than the design requirement of 15 mm.

[0111] The technical team conducted final acceptance measurements on 256 suspended steel beams. A 3D laser scanner was used to perform a full-area scan of the surface of each beam, with a scan point spacing of 50mm, yielding approximately 700,000 point cloud data points for each beam. The point cloud data was fitted and compared with the design model, and the normal deviation values ​​of each measuring point were extracted. Statistical results showed that 97.3% of the measuring points had an absolute normal deviation of less than 5mm, with the maximum deviation of 7.2mm occurring at the end of beam number 127. This meets the acceptance standard that over 95% of the measuring points have an absolute deviation of less than 5mm and a maximum deviation of no more than 8mm. After the entire wind tunnel structure was completed, airflow quality tests showed that the airflow uniformity in the test section reached 0.3%, and the turbulence intensity was 0.08%, meeting the requirements for transonic wind tunnel testing.

[0112] The technological advancements of this invention compared to traditional construction methods lie in its ability to prevent the linear accumulation and propagation of errors across 500 construction sections by establishing an independent benchmark control network and setting forced closure control points. This avoids the problem of excessive end-point deviation caused by the segment-by-segment accumulation of errors in traditional dependent measurement methods. The pre-camber calculation considers the semi-rigid connection characteristics of nodes and the incomplete constraint conditions of supports, making the precast bending curve more consistent with the actual stress state and overcoming the inaccurate pre-camber setting problem caused by traditional simplified calculation models. The combined application of hydraulic synchronous jacking and posture adjustment and prestressed tension anti-camber adjustment technology achieves dual precise control of the steel beam's spatial position and surface shape, resolving the contradiction that traditional single adjustment methods cannot simultaneously meet the requirements of coordinate accuracy and surface accuracy. The minimum spanning tree optimization algorithm determines the error distribution path, allowing errors to propagate along connections with higher stiffness and be absorbed at nodes with lower stiffness. Compared to traditional uniform distribution methods, this reduces the impact of structural deformation on error distribution and improves the overall coaxiality control level. Related embedded rigid positioning frames and prestressed tension anti-camber adjustment devices, such as… Figure 5 and 6 As shown, the systematic implementation of multi-round iterative adjustments and segment cumulative error adjustment allocation integrates discrete local precision control measures into a closed-loop feedback global precision control system, achieving the high-precision construction goal of large-span complex structures.

[0113] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling the coordinate accuracy of a steel beam suspended from a sandwich composite structure, applied to the construction of a wind tunnel structure, characterized in that... include: Establish an independent benchmark control network, set up forced closure control points within the wind tunnel construction area, and establish a spatial coordinate benchmark system using a 3D laser scanner and total station; The pre-camber of the lower steel beam is calculated, and a finite element analysis model considering the semi-rigid connection characteristics of the nodes and the incomplete constraint conditions of the supports is established. The elastic deflection value of the steel beam under its own weight is calculated, and the parameters of the reverse prefabrication bending curve are determined. The reverse prefabrication bending process of the steel beam is carried out, and the lower steel beam is subjected to reverse cold bending or hot bending treatment. The rigid positioning frame for embedded parts is installed. Before concrete pouring, the embedded parts are fixed to the rigid positioning frame. The rigid positioning frame is connected to the independent benchmark control network through three or more spatial constraints. The lower steel beam is hoisted and hydraulic synchronous jacking and posture adjustment are performed at the connection nodes between the steel beam and the steel grid. A hydraulic synchronous jacking device was installed at the site, and the jacking amount of each jacking point was adjusted according to the coordinate data measured in real time by the total station, and iterative adjustments were made. Prestressed tensioning was applied to adjust the arch shape, and high-strength steel strands were inserted into the anchoring holes reserved in the lower flange of the hanging steel beam. Jacks were used to apply tension to the high-strength steel strands. The cumulative error adjustment of the section was carried out. The least squares adjustment technique was used to distribute the manufacturing error and installation error of the construction section among the forced closed control points. Fine-tuning operations were carried out on the adjustable connection device set at the key nodes. The error distribution path was determined by solving the minimum spanning tree optimization problem.

2. The method according to claim 1, characterized in that, The forced closure control point is a high-precision coordinate reference point artificially set within a large construction area to prevent the linear accumulation and transmission of errors.

3. The method according to claim 2, characterized in that, The independent reference control network is an independent measurement coordinate system that is not attached to the construction components themselves. It is established by burying deep foundation measurement piers and installing highly stable measurement supports.

4. The method according to claim 3, characterized in that, The pre-camber calculation uses a deflection prediction function. The inputs include the steel beam span, the steel beam section moment of inertia, and the steel beam line load. The output is the pre-camber setting value.

5. The method according to claim 4, characterized in that, The deflection prediction function is expressed as follows: the product of the fourth power of the steel beam span and the steel beam line load is divided by the product of the moment of inertia and the elastic modulus of the steel beam section, and then multiplied by the span correction factor.

6. The method according to claim 5, characterized in that, The parameters of the reverse precast bending curve include the location of the maximum arch height and the arch height distribution function coefficient, with the location of the maximum arch height taken at the span of the steel beam.

7. The method according to claim 6, characterized in that, The reverse prefabrication bending process refers to artificially applying an initial curvature in the steel beam manufacturing stage that is opposite to the deflection direction in the service stage, so that the actual deformation of the steel beam after installation and loading matches the theoretical straight surface.

8. The method according to claim 7, characterized in that, The rigid positioning frame is a spatial truss structure welded from H-beams and is connected to an independent reference control network through three or more spatial constraints.

9. The method according to claim 8, characterized in that, The hydraulic synchronous lifting device consists of a hydraulic cylinder, a pressure sensor, a displacement sensor, and an electrical control unit. It achieves coordinated action of multiple lifting points through a central control system.

10. The method according to claim 9, characterized in that, The iterative adjustment refers to the cyclical process of repeatedly measuring the current coordinate deviation, adjusting the lifting amount, and measuring and verifying again. After each round of adjustment, the coordinate deviation gradually decreases.

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