A method for in-situ stress detection of steel structure components in service based on structural axial force equivalent stiffness principle

Abstract

This invention discloses an in-situ stress detection method for in-service steel structural members based on the principle of equivalent stiffness of axial force. The method first determines the member to be tested and its support configuration. Displacement measuring devices are installed at both ends and the middle of the member to record the deflection increment under applied load. The rotational stiffness at the member's ends is calculated. Then, the flexural stiffness of the member is calculated based on the load applied at the measuring points and the obtained displacement. Finally, based on the equation derived from the relationship between the flexural stiffness and axial force (equivalent negative stiffness of axial force), the axial force and section stress on the member are calculated. This invention can directly detect the stress state of in-service steel structural members dominated by axial force without the need for interpolation using initial state results. This invention can greatly simplify the stress state of in-service structures and assess their safety, and can be widely applied to the stress state detection of in-service steel truss bridges, space frames, large trusses, and other members dominated by axial force.

Description

Technical Field

[0001] This invention relates to in-situ non-destructive testing technology in the field of civil engineering, and specifically to an in-situ stress detection method for in-service steel structural members based on the principle of equivalent stiffness of structural axial force. Background Technology

[0002] The in-situ non-destructive testing technology involved in this invention is mainly used to test the stress state of members primarily subjected to axial force under working conditions, in order to ensure the safety of the structure and its members. Currently, there are no specialized methods for detecting the stress state of steel structures under working conditions. In structures such as bridges, the vibration characteristics of the entire structure are usually monitored to infer the stiffness degradation, but this method cannot directly obtain the stress state of the structure and its members, and is greatly affected by environmental interference. Currently, strain sensors, such as strain gauges and vibrating wire sensors, are commonly used to test the stress of members. However, these methods can only measure stress changes during the testing phase. To obtain the stress value during service, the initial value under stress-free conditions is needed as a reference, which is difficult to achieve for structures under service conditions. Therefore, there is currently no technology that can easily perform non-destructive testing on the stress of steel structures under service conditions.

[0003] Steel structures contain numerous members primarily subjected to axial forces, such as space frame structures (e.g., roof structures of large stadiums, coal sheds), various truss structures (e.g., large-span roof structures), power transmission and communication towers, and various supporting structures. These structures experience complex stress states, and many members may exceed their load-bearing capacity, or even fracture due to overloading. Therefore, in-situ non-destructive testing is crucial for structural safety assessment. This invention effectively addresses these issues. Summary of the Invention

[0004] The purpose of this invention is to provide a non-destructive in-situ testing method for detecting the stress state of members under in-service conditions, primarily driven by axial force, based on the principle of equivalent stiffness of structural axial force. This method does not require unloading the original structure. By considering the influence of axial force on the lateral stiffness of the members, it quickly obtains the magnitude of the axial force experienced by the members under working conditions and calculates the member stress. This invention is mainly aimed at members that primarily bear axial force, such as members in truss structures, tower structures, space frame structures, and support members of various steel structures. The in-situ non-destructive testing technology involved in this invention does not require unloading the structure, avoiding the impact on the normal service state of the structure, and can directly calculate the magnitude of the axial force of the tested member under working conditions using the test structure.

[0005] The technical solution adopted in this invention is: A method for in-situ stress detection of in-service steel structural members based on the principle of equivalent stiffness of structural axial force is proposed. This method does not require unloading of the in-service structure to obtain the initial value of the stress-free state. It can directly detect the flexural stiffness of the members under stress and obtain the axial force of the members through calculation.

[0006] The method includes the following steps: 1) Preparation and calibration: Determine the parameters of the member to be measured, the type of support, and calibrate the displacement measuring equipment; 2) Measurement point layout: One or more measurement points are arranged at both ends and the middle of the rod to be measured, and a displacement sensor or laser measuring device is installed at each measurement point; 3) Data acquisition: Apply a load perpendicular to the axis of the rod to be tested to the middle position, and record the deflection increment at each measuring point under the applied load using the displacement sensor or laser measuring device. 4) End rotation stiffness calculation: Based on the connection between the member to be tested and the adjacent members in the in-service steel structure, calculate the end rotation stiffness of the members at both ends of the member to be tested in advance, or test the end rotation stiffness of the members at both ends of the member to be tested on site. 5) Solving for flexural stiffness and axial force: Using the applied load, deflection increment and end rotation stiffness, the flexural stiffness of the member is calculated; the current axial force and average stress of the section of the member under test are finally obtained from the flexural stiffness of the member. 6) Result evaluation: Compare the current axial force and cross-sectional stress of the test member with the design standard or safety threshold to determine whether the test member is overloaded or at risk of failure.

[0007] In step 1), the displacement measuring device is one or more of the following: a laser rangefinder, a mechanical dial gauge, and a resistance strain gauge.

[0008] In step 3), the load is applied in a graded loading manner. After each loading stage is completed, the displacement changes at both ends and the middle of the test member are recorded. The displacement changes are deflection increments.

[0009] In step 4), the calculation of the rotational stiffness includes the following steps: The dimensions of adjacent members to the member under test are measured and the connection method is determined to establish the rotational stiffness of the support. The rotational stiffness parameters of the support connection are obtained by applying torque and corresponding rotation angle at the support. The formula for calculating the end stiffness of the member under test using the following formula is employed: ; ; Where A and B represent the endpoints of one end of the rod to be measured.K 1 and K 2 represents the end stiffness of member A and the end stiffness of member B, respectively. i Let be the linear stiffness of the adjacent members of the member under test. k The number of the member. and These are the two ends of the rod. A and B Linear stiffness of all connected members i sum.

[0010] In step 5), the formula for calculating the flexural stiffness of the rod is as follows: ; in, K The flexural stiffness of the rod under test is given by [the value of the ... F Load applied to the measuring point at the middle of the member under test ， Apply a load to the measuring point at the middle of the member to be tested. F The deformation value corresponding to the time.

[0011] In step 5), based on structural stability theory and the principle of equivalent stiffness of axial force in rods, the following calculation formula can be obtained, that is, the axial force calculation formula of the rod to be tested is as follows: ; ; ; in, β It is a stiffness parameter. K 0 represents the initial flexural stiffness of the rod under test. L The length of the rod to be measured is... EI The bending stiffness of the cross section of the rod under test is given by [reference to a specific parameter]. P Let P be the axial force of the rod to be measured, with tension being positive, i.e., the sign is defined as positive or negative.

[0012] The formula for calculating the current cross-sectional stress of the member under test based on the axial force is as follows: ; in, A The cross-sectional area of ​​the rod to be tested is... The stress is the cross-sectional stress of the rod under test.

[0013] The present invention has the following beneficial effects: 1) Minimal environmental interference: By installing displacement sensors at specific locations on the members (the distance from the nodes and the cross-sectional shape can be flexibly adjusted) and applying small out-of-plane loads, the deformation can be measured by combining the deformation and rotational stiffness boundary conditions of the structure itself. The axial stress of the members can then be calculated.

[0014] 2) Wide range of applications: This invention is applicable to members with axial force as the main force, such as space frame and truss structures of large stadium roof structures, support structures in various steel structures, truss steel bridges, etc.

[0015] 3) Strong applicability: This invention can take into account different boundary conditions of the rod, as well as factors such as the initial bending and deformation of the rod.

[0016] 4) Simple construction: The testing device can use general displacement gauges, laser rangefinders or mechanical measuring instruments, all of which are commonly used testing equipment; the equipment and instruments used are all portable instruments, which are convenient for on-site testing. Attached Figure Description

[0017] Figure 1 This is a diagram illustrating the rod detection process. Figure 2 This is a schematic diagram illustrating actual steel truss detection practices in engineering projects. Figure 3 This is a schematic diagram of the detection process. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] A method for in-situ stress detection of in-service steel structural members based on the principle of equivalent stiffness of structural axial force is also a method for in-situ detection of axial stress in steel structural members. This method does not require unloading the in-service structure to obtain initial values ​​in a stress-free state. It can directly detect the flexural stiffness of members under stress and calculate the axial force of the members. The method includes the following steps: 1) Preparation and calibration: Based on the design drawings or site survey, determine the member to be measured and the support type of the member to be measured, and calibrate the displacement measuring equipment; 2) Measurement point layout: One or more measurement points are arranged at both ends and the middle of the rod to be measured, and a displacement sensor or laser measuring device is installed at each measurement point; 3) Data acquisition: Apply a load perpendicular to the axis of the member to be measured to the middle position, and record the deflection increment at each measuring point under the applied load using a displacement sensor or laser measuring device. 4) End rotation stiffness calculation: Based on the connection between the member to be tested and the adjacent members in the in-service steel structure, i.e. the surrounding members, the required data are obtained through the design drawings to pre-calculate the end rotation stiffness of the members at both ends of the member to be tested, or the end rotation stiffness of the members at both ends of the member to be tested is tested on site. 5) Solving for flexural stiffness and axial force: The flexural stiffness of the member is calculated using the applied load, the deflection increment corresponding to each load level, and the end rotation stiffness. The flexural stiffness of the member is substituted into the calculation formula, and the current axial force and section stress of the member under test are finally obtained from the flexural stiffness of the member. 6) Result evaluation: Compare the current axial force and cross-sectional stress of the test member with the design standard or safety threshold to determine whether the test member is overloaded or at risk of failure.

[0020] In step 1), the displacement measuring device is one or more of the following displacement detection devices: laser rangefinder, mechanical dial gauge, resistance strain gauge, etc.

[0021] In step 3), the load is applied in stages, generally 3 to 5 stages, with the same load applied at each stage. The applied load can be determined based on the stress-free stiffness, the yield strength of the steel, and the range of the measuring instrument. After each stage of loading is completed, the displacement changes at both ends and the middle of the member under test are recorded. The displacement changes are the deflection increments to improve measurement accuracy and facilitate correction of nonlinear errors.

[0022] Step 4) involves the following steps in calculating the rotational stiffness: Measure the dimensions of adjacent members, such as columns and beams, to determine the rotational stiffness of the support based on site conditions or design drawings and the connection method. If site conditions permit, obtain the rotational stiffness parameters of the support connection by applying torque and corresponding rotation angle at the support. The formula for calculating the end stiffness of the member under test using the following formula is applied: ; ; Where A and B represent the endpoints of one end of the rod to be measured. K 1 and K 2 represents the dimensionless rotational constraint stiffness at the end of member A and the end of member B, respectively. i Let be the linear stiffness of the adjacent members of the member under test. k The number of the member. and These are the two ends of the rod. A and B Linear stiffness of all connected members i sum.

[0023] In step 5), the formula for calculating the flexural stiffness of the member is as follows: ; in, K Let F be the flexural stiffness of the member under test, and F be the load applied at the measuring point in the middle of the member under test. ， Load applied to the measuring point at the middle of the member under test F The corresponding deformation value, that is, the displacement value measured in the middle member after the external force is applied.

[0024] In step 5), based on structural stability theory and the principle of equivalent stiffness of axial force in members, the following calculation formula can be obtained, that is, the formula for calculating the axial force of the member under test is as follows: ; ; ; in, β It is a stiffness parameter. K 0 represents the initial flexural stiffness of the rod under test. L The length of the rod to be measured is... EI The bending stiffness of the cross section of the rod under test is given. P P represents the axial force of the rod under test, with tension being a positive value.

[0025] The formula for calculating the current cross-sectional stress of the member under test based on the axial force is as follows: ; in, A Let be the cross-sectional area of ​​the member to be measured. The stress is the cross-sectional stress of the member to be tested.

[0026] The method is applicable to structural members such as trusses (chords, web members), space frame members, power transmission and communication towers, and supports that are mainly subjected to axial forces. It does not require unloading of the structure and enables in-situ non-destructive testing of the structure.

[0027] This invention relates to an in-situ stress detection method for in-service steel structure (trusses, space frames, steel roof trusses, transmission towers, bridges) components based on the principle of equivalent stiffness of structural axial force. This method is applicable to detecting stress in members subjected to axial compression or tension. First, displacement measuring devices are installed at both ends and the middle of the member to record the change in deflection under small external or environmental loads. Then, the flexural stiffness of the member is calculated based on the applied load and the obtained displacement at the measuring points. Finally, the axial force and section stress of the member are calculated using an equation derived from the relationship between the flexural stiffness and axial force based on the equivalent negative stiffness of axial force.

[0028] Compared to traditional strain testing methods (such as strain gauges and vibrating wire strain gauges), this invention can directly detect the stress state of in-service steel structural members dominated by axial force, without the need for subtraction based on initial state results. Traditional strain testing methods require readings under both unloaded and loaded conditions, and then subtract the readings to obtain the strain under loaded conditions. This necessitates unloading the in-service structure to obtain accurate results. Therefore, this invention significantly simplifies the stress state assessment of in-service structures and can be widely applied to stress state detection in in-service steel truss bridges, space frames, large trusses, and other members dominated by axial force.

[0029] like Figure 1 , Figure 2 As shown, based on the above principles, the overall process of our detection of a certain truss system is as follows. A simplified flowchart of the main process can be found here. Figure 3 : Step S1, Preparation and Calibration: Determine the parameters of the member to be measured and the support type based on the design drawings or site survey; plan the measuring points according to the actual situation.

[0030] Step S2, Equipment Installation: Arrange load application equipment (such as hydraulic jacks) and displacement measurement equipment (such as laser rangefinders, displacement gauges, dial gauges), ensuring that the probes are perpendicular to the surface of the rod.

[0031] Step S3, Data Acquisition: Record the initial readings of the loading and testing equipment; apply a lateral force perpendicular to the axis of the rod. F Record the displacements of each measuring point and the support at the end of the rod, and calculate the net displacement of the measuring points. The lateral stiffness at the measuring point location was calculated. K = F / Multiple stages of loading and multiple displacement measurement points can be used to calculate the displacement of each measurement point separately, so as to obtain more accurate results.

[0032] Step S4, Calculate the boundary rotational stiffness: Based on the on-site beam and column section parameters, support connection stiffness, etc., derive the boundary rotational stiffness condition. K 1 and K 2 The estimated value.

[0033] Step S5, Solve for the axial force of the member: Calculate the lateral stiffness based on the displacement of each measuring point. K Substituting the corrected stiffness into the formula, the current axial force of the member is finally obtained. P .

[0034] Step S6, Judgment and Analysis: Compare with the design value or specification limit to determine whether the member is at risk of overload or failure.

[0035] Those skilled in the art can readily make various changes and modifications based on the provided textual description, drawings, and claims, without departing from the spirit and scope of the invention as defined by the claims. Any modifications or equivalent variations made to the above embodiments based on the technical concept and essence of the invention fall within the protection scope defined by the claims of this invention.

Claims

1. A method for in-situ stress detection of in-service steel structural members based on the principle of equivalent stiffness of structural axial force, characterized in that, The method includes the following steps: 1) Preparation and calibration: Determine the parameters of the member to be measured, the type of support, and calibrate the displacement measuring equipment; 2) Measurement point layout: One or more measurement points are arranged at both ends and the middle of the rod to be measured, and a displacement sensor or laser measuring device is installed at each measurement point; 3) Data acquisition: Apply a load perpendicular to the axis of the rod to be tested to the middle position, and record the deflection increment at each measuring point under the applied load using the displacement sensor or laser measuring device. 4) End rotation stiffness calculation: Based on the connection between the member to be tested and the adjacent members in the in-service steel structure, calculate the end rotation stiffness of the members at both ends of the member to be tested in advance, or test the end rotation stiffness of the members at both ends of the member to be tested on site. 5) Solving for flexural stiffness and axial force: Using the applied load, deflection increment and end rotation stiffness, the flexural stiffness of the member is calculated; the current axial force and average stress of the section of the member under test are finally obtained from the flexural stiffness of the member. 6) Result evaluation: Compare the current axial force and cross-sectional stress of the test member with the design standard or safety threshold to determine whether the test member is overloaded or at risk of failure. In step 5), the formula for calculating the flexural stiffness of the rod is as follows: ； Wherein, K is the flexural stiffness of the member under test, F is the load applied to the measuring point in the middle of the member under test, and Δ is the deformation value corresponding to the load F applied to the measuring point in the middle of the member under test. In step 5), the formula for calculating the axial force of the rod to be tested is as follows: ； ； ； Wherein, β is the stiffness parameter, K0 is the initial flexural stiffness of the rod under test, L is the length of the rod under test, EI is the bending stiffness of the cross section of the rod under test, P is the axial force of the rod under test, and K1 and K2 are the end stiffness of the rod at end A and end stiffness of the rod at end B, respectively. The formula for calculating the current cross-sectional stress of the member under test based on the axial force is as follows: ； Where A is the cross-sectional area of ​​the rod under test. The stress is the cross-sectional stress of the rod under test.

2. The in-situ stress detection method for in-service steel structural members based on the principle of equivalent stiffness of structural axial force as described in claim 1, characterized in that, In step 1), the displacement measuring device is one or more of the following: a laser rangefinder, a mechanical dial gauge, and a resistance strain gauge.

3. The in-situ stress detection method for in-service steel structural members based on the principle of equivalent stiffness of structural axial force as described in claim 1, characterized in that, In step 3), the load is applied in a graded loading manner. After each loading stage is completed, the displacement changes at both ends and the middle of the test member are recorded. The displacement changes are deflection increments.

4. A method for in-situ stress detection of in-service steel structural members based on the principle of equivalent stiffness of structural axial force, as described in claim 1 or 2, characterized in that... In step 4), the calculation of the rotational stiffness includes the following steps: The dimensions of adjacent members to the member under test are measured and the connection method is determined to establish the rotational stiffness of the support. The rotational stiffness parameters of the support connection are obtained by applying torque and corresponding rotation angle at the support. The formula for calculating the end stiffness of the member under test using the following formula is employed: ； ； Where A and B represent the endpoints of the member under test, K1 and K2 are the end stiffnesses of the member at endpoint A and endpoint B, respectively, i is the linear stiffness of the adjacent member of the member under test, and k is the member number. and These are the sums of the linear stiffnesses i of all members connected to the two endpoints A and B of the member.

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