Friction type high-strength bolt connection bilateral friction coefficient evaluation method and system

Abstract

The invention discloses a friction-type high-strength bolt connection bilateral friction coefficient evaluation method and system, and relates to the technical field of steel structures, and the method comprises the steps: manufacturing a force measurement screw, and connecting the force measurement screw with a gusset plate to obtain a test piece; performing a tensile test on the test piece to obtain a tensile load-displacement curve and a tensile load-force measuring screw clamping force curve; based on the tensile load-displacement curve, determining initial slip loads on the two sides; according to the tensile load-force measuring screw clamping force curve, the sum of the force measuring screw clamping force on each side during initial sliding is determined, the friction coefficient is calculated by combining the number of contact surfaces of the test piece, and whether the friction coefficient meets the friction coefficient design value or not is judged. According to the invention, the precision and comprehensiveness of evaluation are improved, the force measuring screw can be reused, and the number of test pieces can be reduced.

Description

Technical Field

[0001] This invention relates to the field of steel structure technology, and in particular to a method and system for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection. Background Technology

[0002] In the design and construction of steel structures, high-strength bolts, due to their excellent connection performance, have become one of the main connection methods between various steel structural components. For friction-type high-strength bolt connections, the coefficient of friction of the contact surface at the connection node is a core indicator determining the reliability of the connection. Specifically, the coefficient of friction refers to the ratio of the maximum static friction force generated on the contact surface of a friction-type high-strength bolt connection node under external force to the sum of the bolt clamping force; it is a key parameter for measuring the anti-slip capability of the contact surface.

[0003] The current standard, "Technical Specification for High-Strength Bolt Connections of Steel Structures" (JGJ82-2011), stipulates that the method for determining the coefficient of friction is to first conduct a tensile test on the test specimen. After the test, the coefficient of friction is calculated based on the sum of the final tightening values ​​of the high-strength bolt clamping forces corresponding to the tensile load side of the test specimen. This method has significant drawbacks: firstly, it cannot obtain the true data of the bolt clamping force during the test, resulting in an inaccurate coefficient of friction assessed by the existing testing method; secondly, when the specimen slides, slippage occurs not only on the tensile load side but also on the other side. The current standard ignores the slippage data on the other side when determining the coefficient of friction, which further reduces the comprehensiveness and accuracy of the friction coefficient test. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method and system for evaluating the friction coefficient of friction-type high-strength bolt connections on both sides. This invention involves fabricating a test specimen with a force-measuring screw connection and conducting a tensile test on it to obtain the tensile load-displacement curve and the clamping force curve of the force-measuring screw. The friction coefficient is calculated based on the sum of the initial sliding loads on both sides and the measured values ​​of the clamping forces of all force-measuring screws on the corresponding sides, thereby improving the test accuracy and data comprehensiveness.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection, including: Fabricate a force-measuring screw and connect it to a node plate to obtain the test specimen; Tensile tests were performed on the test specimens to obtain tensile load-displacement curves and tensile load-force measuring screw clamping force curves. Based on the tensile load-displacement curve, the initial sliding load on both sides is determined; according to the tensile load-force measuring screw clamping force curve, the sum of the force measuring screw clamping forces on each side during the initial sliding is determined; combined with the number of contact surfaces of the specimen, the friction coefficient is calculated, and it is determined whether the friction coefficient meets the design value of the friction coefficient.

[0006] As a further technical solution, the method for manufacturing the force measuring screw is as follows: a blind hole is opened from the end of the screw along the rod axis towards the bolt head or from the bolt head along the rod axis towards the end of the screw. After cleaning the blind hole, glue is poured in and strain gauges are inserted. After the glue cures, wires are welded in.

[0007] As a further technical solution, two sets of force-measuring screws are made, and two through holes matching the force-measuring screws are opened on the node plate. The two sets of force-measuring screws pass through the two through holes respectively and are fastened with nuts to obtain the test specimen.

[0008] As a further technical solution, the tensile load-displacement curve includes four stages: friction overcoming stage, slippage stage, bearing stage, and failure stage.

[0009] As a further technical solution, the curve of the friction overcoming stage shows a standard linear growth; the curve of the bearing stage shows an increasing trend, and the slope is lower than that of the curve of the friction overcoming stage, while the displacement change is much greater than that of the slip stage; the tensile load of the failure stage remains unchanged with the increase of displacement.

[0010] As a further technical solution, the curve of the sliding stage shows a wave trend of first decreasing and then gradually increasing. The displacement of the sliding stage changes abruptly, the abrupt displacement is greater than the preset loading displacement, and the tensile load decreases abruptly. The sliding stage specifically includes two sliding stages, and the initial sliding load on both sides is determined through the two sliding stages.

[0011] As a further technical solution, the method for calculating the friction coefficient is as follows: ; in, This represents the design value of the friction coefficient. Indicates the initial slip load on one side. This indicates the initial slip load on the other side. Indicates the number of contact surfaces between the gusset plate and the force-measuring screw; express The sum of the measured clamping forces of all force-measuring screws on the corresponding side. express The sum of the measured clamping forces of all force-measuring screws on the corresponding side. and These represent the two sets of force-measuring screws on the corresponding sides.

[0012] Secondly, this invention provides a friction-type high-strength bolt connection double-sided friction coefficient evaluation system, comprising the following modules: The test specimen fabrication module is configured to: fabricate a force-measuring screw and connect the force-measuring screw to the node plate to obtain the test specimen; The test module is configured to perform a tensile test on the test specimen to obtain a tensile load-displacement curve and a tensile load-force measuring screw clamping force curve. The friction coefficient evaluation module is configured to: determine the initial sliding load on both sides based on the tensile load-displacement curve; determine the sum of the clamping forces of the force measuring screws on each side during the initial sliding based on the tensile load-force measuring screw clamping force curve; calculate the friction coefficient in combination with the number of contact surfaces of the specimen; and determine whether the friction coefficient meets the design value of the friction coefficient.

[0013] One or more technical solutions of the present invention have the following beneficial effects: 1. By fabricating a force-measuring screw (drilling blind holes along the axis at the end of the force-measuring screw or the head of the bolt, inserting strain gauges and curing them), and connecting it with a node plate, a bolt inspection specimen is obtained. With the help of a static strain acquisition instrument, the clamping force of the force-measuring screw corresponding to the initial slippage on both sides of the inspection specimen can be obtained in real time and accurately. This solves the problem that existing methods cannot obtain the clamping force corresponding to the slippage in real time, and improves the test accuracy.

[0014] 2. This invention calculates the friction coefficient by considering the initial sliding loads on both sides and the corresponding bolt clamping forces during the sliding phase, thus solving the problem of neglecting the influence of sliding on the other side in traditional methods and reducing data deviation. Comparative experiments show that the friction coefficient calculated using the testing method provided by this invention is more accurate and reliable, and the force-measuring screw can be reused, saving on test specimens.

[0015] 3. Through systematic improvements to the calculation formula, this invention achieves a more comprehensive evaluation of the friction performance of nodes and can automatically identify cases where the friction coefficient of any side does not meet the standard, thereby making a more reasonable judgment on the qualification of the connection pair and improving the reliability and applicability of engineering testing. Attached Figure Description

[0016] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0017] Figure 1 This is a structural diagram of the force-measuring screw in this invention; Figure 2 The diagram shows the top view, front view, and side sliding schematic diagram of the test specimen in this invention. Figure 3 This is a graph showing the tensile load-displacement relationship in this invention. Figure 4 The graph shows the relaxation change of the clamping force of the force measuring screw over time after final tightening. Figure 5 A simplified curve of tensile load versus clamping force of the force measuring screw. Detailed Implementation

[0018] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0019] Example 1 This embodiment provides a method for testing the anti-slip coefficient of the contact surface of a friction-type high-strength bolt connection. The specific steps are as follows: S1: Fabricate a force-measuring screw and connect the force-measuring screw to the node plate to obtain the test specimen.

[0020] In step S1, as Figure 1 As shown in the structural diagram of the force-measuring screw, a blind hole with a diameter of R and a depth of L is made from the end of the force-measuring screw along the rod axis towards the bolt head, or from the bolt head along the rod axis towards the end of the force-measuring screw. After cleaning the blind hole, glue is poured in, and strain gauges are inserted. After the glue cures, wires are soldered to complete the fabrication of the force-measuring screw. The fabricated force-measuring screw is then connected to the node plate to form a test specimen, such as... Figure 2 The front view of the force-measuring screw after it is connected to the node plate is shown.

[0021] During the tightening of the nut, a static strain gauge is used to collect the strain value displayed by the force-measuring screw to control the clamping force. Simultaneously, the clamping force data collected by the pressure ring is compared to verify the accuracy of the force-measuring screw.

[0022] In this embodiment, as Figure 2 The top view after the force measuring screw is connected to the node plate is shown. Two sets of force measuring screws are made, and two through holes matching the force measuring screws are opened on the node plate. The two sets of force measuring screws pass through the two through holes respectively and are fastened with nuts to obtain the test specimen.

[0023] S2: Perform a tensile test on the test specimen to obtain the tensile load-displacement curve and the tensile load-force measuring screw clamping force curve.

[0024] In step S2, during the tensile test, multiple sets of relationship curves are simultaneously collected and established, including: tensile load-displacement curve, tensile load-force measuring screw clamping force curve (e.g., ... Figure 5 ) and the relaxation graph of clamping force over time after final tightening (e.g.) Figure 4This is to comprehensively analyze and examine the mechanical response of the test specimen.

[0025] Using a tensile testing machine, a clamping force is applied to the tensile force-measuring screw. A regression equation is established between the strain value and the clamping force of the force-measuring screw, and its expression is: y =a x +b, y Indicates the strain value. x The clamping force is represented by , and a and b represent the regression coefficients of the equation. Table 1 shows the strain values ​​corresponding to the regression analysis after the force-measuring screw is calibrated. Table 2 compares the test results of the force-measuring screw and the pressure ring. The absolute error ranges from 0.00% to 2.91%, with an average value of 1.49%, demonstrating high accuracy and reliability, and can be used for experimental verification.

[0026] Table 1. Strain values ​​corresponding to regression analysis after force-measuring screw calibration.

[0027] Table 2 Comparison of test results for force-measuring screw and pressure ring

[0028] Tensile tests on test specimens can yield their tensile load-displacement curves, which consist of four stages: friction overcoming stage, slippage stage, bearing stage, and failure stage.

[0029] In this embodiment, as Figure 3 As shown in the tensile load-displacement curve, during the friction-overcoming stage, the curve exhibits a standard linear increase, indicating that the connection is in the elastic stage. In this stage, the shear load is transmitted through the friction between the cover and the core plate.

[0030] During the slip phase, the curve exhibits a wave-like trend of first decreasing and then gradually increasing. A sudden displacement occurs during this phase, exceeding the preset loading displacement, and the tensile load decreases abruptly. In this stage, the force-measuring screw gradually contacts the bore wall, beginning to resist the external tensile load through the interaction between the screw and the bore wall. The slip phase specifically includes two side slip phases; in practice, the component slips on both sides as follows... Figure 2 As shown.

[0031] During the bearing stage, the curve shows an increasing trend, and its slope is lower than that of the curve during the friction overcoming stage. In this stage, the tensile load is transmitted through the constraint process of the hole wall, and the displacement change is much greater than that during the slip stage. Due to stress concentration caused by the extrusion of the force-measuring screw, the steel around the hole in the plate begins to yield, and significant deformation occurs around the hole in the core plate.

[0032] When the tensile load increases to the ultimate load of the test specimen, it enters the failure stage. In the failure stage, the tensile load remains constant with the increase of displacement. For the test specimen in this embodiment, necking phenomenon was observed at the plate hole, and the bolt rod broke and failed.

[0033] S3: Based on the tensile load-displacement curve, determine the initial sliding load on both sides; according to the tensile load-force measuring screw clamping force curve, determine the sum of the force measuring screw clamping forces on each side during the initial sliding; combined with the number of contact surfaces of the specimen, calculate the friction coefficient, and determine whether the friction coefficient meets the design value of the friction coefficient.

[0034] In step S3, as Figure 4 As shown, JC-1 and JC-2 are the component codes used in this embodiment. Bolt1 and 2 are the two force-measuring screws on the test specimen corresponding to JC-1, and Bolt3 and 4 are the two force-measuring screws on the test specimen corresponding to JC-2. Figure 5 As shown and These represent the sum of the bolt clamping forces corresponding to the initial slippage on both sides of the node.

[0035] In this embodiment, the friction coefficient is calculated as follows: ; in, This represents the design value of the friction coefficient. Indicates the initial slip load on one side. This indicates the initial slip load on the other side. Indicates the number of contact surfaces between the gusset plate and the force-measuring screw; express The sum of the measured clamping forces of all force-measuring screws on the corresponding side. express The sum of the measured clamping forces of all force-measuring screws on the corresponding side. and These represent the two sets of force-measuring screws on the corresponding sides.

[0036] Compared with JGJ82-2011, this technical solution improves the formula for calculating the coefficient of friction: The current standard JGJ82-2011 calculates the friction coefficient using the initial sliding load and the final tightening force of the bolt on either side, without considering the effects of bolt relaxation and tensile load after final tightening, or the combined effect of slippage on the other side. This invention uses the measured value of the bolt clamping force during slippage and incorporates the initial sliding loads from both sides, significantly improving the accuracy of friction coefficient calculation and the comprehensiveness of the assessment.

[0037] The clamping force of the force-measuring screw exhibits significant relaxation within 24 hours after final tightening, and further loss of clamping force occurs during the tensile testing process when the specimen slips. This invention effectively avoids friction coefficient errors caused by estimation deviations in the clamping force of the force-measuring screw by monitoring the clamping force in real time, thereby reducing the inaccuracy of friction coefficient assessment.

[0038] This method incorporates initial sliding loads on both sides of the test specimen for comprehensive calculation of the friction coefficient. The current standard JGJ82-2011 calculates the friction coefficient based only on the initial sliding load on one side, failing to reflect the overall friction coefficient of the joint. This improved formula considers both initial sliding loads and the measured clamping force of the force-measuring screw, providing a more comprehensive assessment of the friction coefficient of the test specimen's connection surface. Test data shows that some test specimens have a friction coefficient that meets design requirements on one side but is significantly lower on the other. This improved method can effectively identify such non-compliance.

[0039] To demonstrate the advantages and accuracy of the friction coefficient evaluation method and system for high-strength friction-type bolt connections provided in this embodiment compared to previous calculation methods, this study examines the improved friction coefficient calculation method. In the JGJ82-2011 standard, the clamping force after final tightening of the bolt is used as the benchmark. However, in practical applications, the clamping force gradually decreases within 24 hours after final tightening, and additional clamping force loss occurs during tensile testing, leading to systematic deviations in the original formula's calculation results. The improved friction coefficient calculation method directly uses the measured clamping force at the point of slippage. This method is verified using measured data. First, record the quantitative change in clamping force over time after final tightening; Secondly, the influence data of the tensile test specimen on the clamping force was analyzed, and the changes in clamping force were monitored and recorded in real time by a component connection strain acquisition instrument. To demonstrate the advantages and accuracy of the improved method and system for evaluating the bilateral friction coefficient of friction-type high-strength bolt connections provided in this embodiment compared to the calculation method in JGJ82-2011, a verification test was conducted. Under tensile load, the coefficient can be determined using the equations in the "Technical Specification for High-Strength Bolt Connections of Steel Structures" (JGJ82-2011). = Calculate the coefficient of friction. Wherein, This indicates the initial slip load on the side that slips first. This represents the sum of the final tightening values ​​of the clamping forces of all force measuring screws on the sliding side of the test specimen.

[0040] Twelve test specimens were tested according to the JGJ82-2011 test method, and their friction coefficients were calculated. As shown in Table 3: Table 3 Test results according to the method specified in JGJ82-2011

[0041] In this embodiment, the sum of the clamping forces of the force-measuring screw after relaxation can be measured. The sum of the clamping forces of the force-measuring screw during stretching and sliding . , This represents the slip coefficient on both sides of the specimen. Using the calculation method provided in this embodiment, twice the amount of data can be obtained, as shown in Tables 4 and 5.

[0042] Table 4 This method μ 1 Calculation Results

[0043] Table 5 This method μ 2 Calculation Results

[0044] Compared with the calculation results in JGJ82-2011 (Table 3), the calculation results in Table 4 are higher. This is because the new method considers the relaxation of clamping force over time after final tightening and the reduction of clamping force of the force-measuring screw during tensile testing, making the calculation results more convincing. The friction coefficient calculation formula in JGJ82-2011 is limited by relying solely on unilateral slip data. Compared with the calculation results of the new method (Tables 4 and 5), the amount of friction coefficient data calculated in the JGJ82-2011 standard is reduced by half, resulting in a less comprehensive evaluation.

[0045] This embodiment proposes an improved method for evaluating the friction coefficient on both sides of friction-type high-strength bolt connections. By collecting data on the changes in the clamping force of the force-measuring bolt after final tightening and during relaxation and tensile testing, and calculating the friction coefficient on the other slipping side of the test specimen, the friction characteristics of the joint contact surface can be accurately and comprehensively evaluated. To verify its superiority, the calculation results of the improved formula were compared with those of the standard method. Measured data show that in joints deemed acceptable by the standard method, there are cases where the friction coefficient on the other side is significantly lower than the design value, while the method of this invention can effectively identify such hidden risks. Therefore, this invention provides a more comprehensive and accurate evaluation of the anti-slip performance of joints, significantly improving the accuracy of structural safety assessment.

[0046] Example 2 This embodiment provides a friction-type high-strength bolt connection double-sided friction coefficient evaluation system, including the following modules: The test specimen fabrication module is configured to: fabricate a force-measuring screw and connect the force-measuring screw to the node plate to obtain the test specimen; The test module is configured to perform a tensile test on the test specimen to obtain a tensile load-displacement curve and a tensile load-force measuring screw clamping force curve. The friction coefficient evaluation module is configured to: determine the initial sliding load on both sides based on the tensile load-displacement curve; determine the sum of the clamping forces of the force measuring screws on each side during the initial sliding based on the tensile load-force measuring screw clamping force curve; calculate the friction coefficient in combination with the number of contact surfaces of the specimen; and determine whether the friction coefficient meets the design value of the friction coefficient.

[0047] Various modifications and variations of this invention will be apparent to those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection, characterized in that, include: Fabricate a force-measuring screw and connect it to a node plate to obtain the test specimen; Tensile tests were performed on the test specimens to obtain tensile load-displacement curves and tensile load-force measuring screw clamping force curves. Based on the tensile load-displacement curve, the initial sliding load on both sides is determined; according to the tensile load-force measuring screw clamping force curve, the sum of the force measuring screw clamping forces on each side during the initial sliding is determined; combined with the number of contact surfaces of the specimen, the friction coefficient is calculated, and it is determined whether the friction coefficient meets the design value of the friction coefficient.

2. The method for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection as described in claim 1, characterized in that, The method for manufacturing the force-measuring screw is as follows: a blind hole is made from the end of the screw along the rod axis towards the bolt head or from the bolt head along the rod axis towards the end of the screw. After cleaning the blind hole, glue is poured in and strain gauges are inserted. After the glue has cured, wires are welded in.

3. The method for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection as described in claim 1, characterized in that, Two sets of force-measuring screws are made, and two through holes matching the force-measuring screws are opened on the node plate. The two sets of force-measuring screws pass through the two through holes respectively and are fastened with nuts to obtain the test specimen.

4. The method for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection as described in claim 1, characterized in that, The tensile load-displacement curve includes four stages: friction overcoming stage, slippage stage, bearing stage, and failure stage.

5. The method for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection as described in claim 4, characterized in that, The curve of the friction overcoming stage shows a standard linear growth; the curve of the bearing stage shows an increasing trend, and the slope is lower than that of the curve of the friction overcoming stage, while the displacement change is much greater than that of the slip stage; the tensile load of the failure stage remains unchanged with the increase of displacement.

6. The method for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection as described in claim 4, characterized in that, The curve of the slip phase shows a wave trend of first decreasing and then gradually increasing. The displacement changes abruptly during the slip phase. The abrupt displacement is greater than the preset loading displacement, and the tensile load decreases abruptly. The slip phase specifically includes two slip phases, and the initial slip load on both sides is determined through the two slip phases.

7. The method for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection as described in claim 1, characterized in that, The method for calculating the friction coefficient is as follows: ； in, This represents the design value of the friction coefficient. Indicates the initial slip load on one side. This indicates the initial slip load on the other side. Indicates the number of contact surfaces between the gusset plate and the force-measuring screw; express The sum of the measured clamping forces of all force-measuring screws on the corresponding side. express The sum of the measured clamping forces of all force-measuring screws on the corresponding side. and These represent the two sets of force-measuring screws on the corresponding sides.

8. A friction-type high-strength bolt connection double-sided friction coefficient evaluation system, characterized in that, Includes the following modules: The test specimen fabrication module is configured to: fabricate a force-measuring screw and connect the force-measuring screw to the node plate to obtain the test specimen; The test module is configured to perform a tensile test on the test specimen to obtain a tensile load-displacement curve and a tensile load-force measuring screw clamping force curve. The friction coefficient evaluation module is configured to: determine the initial sliding load on both sides based on the tensile load-displacement curve; determine the sum of the clamping forces of the force measuring screws on each side during the initial sliding based on the tensile load-force measuring screw clamping force curve; calculate the friction coefficient in combination with the number of contact surfaces of the specimen; and determine whether the friction coefficient meets the design value of the friction coefficient.

9. A computer-readable storage medium having a program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in the method for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection as described in any one of claims 1-7.

10. An electronic device comprising a memory, a processor, and a program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the method for evaluating the coefficient of friction on both sides of a friction-type high-strength bolt connection as described in any one of claims 1-7.

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