Method and device for determining fatigue damage of corrugated steel web composite box girder

Abstract

This invention relates to the field of engineering life prediction technology, and particularly to a method and equipment for determining fatigue damage in corrugated steel web composite box girders. The invention acquires strain at local locations on the corrugated steel web using strain gauges, constructs strain response curves, determines the strain-transmitted damage characterization vector by comparing the vector directions of the crack propagation tendency characterization vector, and obtains several load output explicit cycle numbers by comparing and analyzing the strain response curves corresponding to local webs with each explicit tendency with a strain response reference curve. Finally, the maximum load-bearing cycle number of the test beam is determined and recorded. This invention implements the above steps by setting up a test bench, measurement module, feature analysis module, feature extraction module, and recording module. Furthermore, it achieves the correlation between the multi-directional geometric features of the corrugated steel web and the strain response differences in different damaged areas, accurately determining the maximum load-bearing cycle number and improving the accuracy of fatigue damage assessment.

Description

Technical Field

[0001] This invention relates to the field of engineering life prediction technology, and in particular to a method and equipment for determining fatigue damage of corrugated steel web composite box girders. Background Technology

[0002] Corrugated steel web composite box girders are widely used in highway and railway bridge engineering due to their lightweight structure and high load-bearing efficiency. The corrugated steel web, as the core load-bearing component, directly determines the overall structural safety and service life. However, the fatigue damage evolution of this type of structure under cyclic loading is significantly insidious and sudden. Cracks in the concrete slab and weld damage in the steel web often rapidly develop and expand without obvious warning signs. Failure to capture these damages in time can lead to missing experimental data or excessive structural failure. Relying on manual, periodic inspections and single-instrument monitoring methods makes it difficult to balance real-time performance and accuracy. Single strain response data cannot accurately correlate damage location and propagation state. Therefore, timely identification, location, and life prediction of fatigue damage have become core technical bottlenecks in the experimental research and engineering application of corrugated steel web composite box girders.

[0003] For example, Chinese Patent Publication No. CN114201808A discloses a method, device, equipment, and medium for predicting the service life of steel box girders, relating to the field of data processing. The method includes: determining multiple strain amplitude ranges based on multiple preset discrete strain amplitudes; determining multiple dynamic SN curves based on the multiple discrete strain amplitudes and the decay coefficient of each strain amplitude range, where the decay coefficient of each strain amplitude range represents the degree of degradation of the steel box girder material properties in each strain amplitude range relative to the material properties in the previous strain amplitude range; predicting the service life of the steel box girder based on the multiple dynamic SN curves, multiple monitored strain amplitudes of the steel box girder, and multiple monitoring cycle numbers corresponding one-to-one with the multiple monitored strain amplitudes, where the multiple monitored strain amplitudes fall within multiple strain amplitude ranges.

[0004] The following problems still exist in the existing technology:

[0005] Existing technologies do not consider the correlation between the multi-directional geometric features of corrugated steel webs and the differences in strain response in different damaged areas. They cannot dynamically match crack propagation characteristics with strain response curves, thus failing to capture key fatigue damage nodes in a timely manner and accurately determine the maximum number of load cycles, affecting the accuracy of fatigue damage assessment. Summary of the Invention

[0006] To address this issue, the present invention provides a method and equipment for determining fatigue damage in corrugated steel web composite box girders, thereby overcoming the problem that existing technologies fail to consider the correlation between the multi-directional geometric features of the corrugated steel web and the differences in strain response in different damaged areas, thus failing to capture key fatigue damage nodes in a timely manner and accurately determine the maximum number of load cycles.

[0007] To achieve the above objectives, the present invention provides a method for determining fatigue damage of corrugated steel web composite box girders, comprising:

[0008] During the cyclic load output to the test beam, the strain at local locations on the corrugated steel web is obtained by several strain gauges placed on the corrugated steel web of the test beam, and the strain response curve of each strain gauge changes with the number of load output cycles during the load test cycle is constructed.

[0009] In response to the result of satisfying the damage feature triggering condition, several crack propagation tendency characterization vectors of surface cracks in crack images are determined, and strain transfer damage characterization vectors are determined based on the vector direction comparison of the crack propagation tendency characterization vectors.

[0010] The damage feature triggering condition is the capture of a crack image on the surface of the test beam;

[0011] Based on the positional relationship between the strain transfer damage characterization vector and the corrugated steel web, the local corrugated steel web is divided into locally webs with obvious tendency and locally webs without obvious tendency. The strain response curves corresponding to each locally web with obvious tendency are compared and analyzed with the strain response reference curve to obtain the number of obvious load output cycles.

[0012] The strain response reference curve is determined by obtaining the strain response curves corresponding to the strain gauges on the non-obvious local web and fitting the strain response curves corresponding to several strain gauges on the non-obvious local web into a strain response reference curve.

[0013] The maximum number of load cycles for the test beam is determined based on the number of recorded explicit load cycles, and this maximum number of load cycles is recorded.

[0014] Furthermore, the process of determining several crack propagation tendency characterization vectors of surface cracks in crack images includes:

[0015] On the surface crack, several characteristic trajectory points of cracking tendency are determined based on the trajectory slope;

[0016] The characteristic trajectory points of cracking tendency are numbered and sorted along the length direction of the surface cracks;

[0017] Two adjacent crack tendency feature trajectory points, numbered sequentially, are used as the starting and ending points of a vector, respectively, to determine several crack propagation tendency characterization vectors for surface cracks.

[0018] Furthermore, the cracking tendency characteristic trajectory points are trajectory points with a slope greater than a preset slope threshold.

[0019] Furthermore, the vector obtained by adding the crack propagation tendency characterization vectors is determined as the strain transfer damage characterization vector.

[0020] Furthermore, the process of dividing the local corrugated steel web into locally dipping and locally dipping webs includes:

[0021] Determine the directional angle between the plane containing the local corrugated steel web within the set of characteristic webs of each orientation and the strain transfer damage characterization vector;

[0022] The local corrugated steel webs within the set of oriented feature webs corresponding to the minimum directional angle are defined as dominant dip local webs, and all local corrugated steel webs other than the dominant dip local webs are defined as non-dominant dip local webs.

[0023] Furthermore, the process of determining the set of oriented feature webs includes:

[0024] The corrugated steel web is divided into several local corrugated steel webs based on the wave amplitude size;

[0025] Determine the angle between the plane containing the local corrugated steel web and the axis of the test beam;

[0026] Local corrugated steel webs with the same included angle are grouped into the same set of oriented characteristic webs to obtain several sets of oriented characteristic webs.

[0027] The web set with different orientations includes several local corrugated steel webs with the same included angle.

[0028] Furthermore, the process of comparing and analyzing the strain response curves corresponding to the local webs of each dominant tendency with the strain response reference curve includes:

[0029] The strain response curves corresponding to the local webs of each dominant tendency are compared with the strain response reference curves by segmentation based on their degree of overlap.

[0030] The curve segment with an overlap ratio less than the preset overlap ratio reference value is defined as the load output explicit curve segment.

[0031] Furthermore, the process of determining the number of dominant load output cycles includes:

[0032] The maximum value of the load output cycle number corresponding to the load output dominant curve segment on the horizontal axis is determined as the load output dominant curve segment's load output dominant cycle number.

[0033] Furthermore, the process of determining the maximum number of cycles required to bear the load of the test beam includes:

[0034] Obtain the number of load output explicit cycles for several recorded load output explicit curve segments;

[0035] The number of explicit cycles of the load output with the most recorded times is determined as the maximum number of cycles for the test beam to bear the load.

[0036] Furthermore, the present invention also provides a device for determining fatigue damage of corrugated steel web composite box girders, comprising:

[0037] A test bench is used to apply loads to a test beam for a number of cycles.

[0038] The measurement module includes an image acquisition unit set on the test bench to capture crack images, several strain gauges set on the corrugated steel web of the test beam to obtain the strain at local locations on the corrugated steel web, and a curve generation unit connected to the strain gauges to construct the strain response curve.

[0039] The feature analysis module, which is connected to the measurement module, is used to determine several crack propagation tendency characterization vectors of surface cracks in crack images, and to determine strain transfer damage characterization vectors based on the vector direction comparison of the crack propagation tendency characterization vectors.

[0040] The feature extraction module, which is connected to the feature analysis module, is used to divide the local waveform steel web into a local web with a visible dip and a local web without a visible dip. The strain response curves corresponding to each local web with a visible dip are compared and analyzed with the strain response curves corresponding to the strain gauges on the local web without a visible dip to obtain the number of visible load output cycles.

[0041] A recording module, which is connected to the feature extraction module, is used to determine the maximum number of load cycles of the test beam and record the maximum number of load cycles.

[0042] Compared with existing technologies, the advantages of this invention lie in that it acquires strain at local locations on the corrugated steel web of a test beam using strain gauges placed on the web. It constructs strain response curves for each strain gauge within the load test cycle, determines the strain-transfer damage characterization vector by comparing the vector directions of the crack propagation tendency characterization vector, and obtains several explicit load output cycles by comparing the strain response curves corresponding to local webs with explicit tendencies with strain response reference curves. Finally, it determines and records the maximum load-bearing cycle count of the test beam. This invention implements the above steps by setting up a test bench, measurement module, feature analysis module, feature extraction module, and recording module. Furthermore, it achieves the correlation between the multi-directional geometric features of the corrugated steel web and the strain response differences in different damaged areas, timely capturing key fatigue damage nodes, accurately determining the actual maximum load-bearing cycle count, and improving the accuracy of fatigue damage assessment.

[0043] Furthermore, based on the geometric characteristics of crack propagation, the present invention finds that the area where the crack trajectory slope changes abruptly is often the region with the most significant cracking tendency. Crack propagation is dominated by the local strain field. When the crack tip encounters the weld seam of the corrugated steel web or a material defect, the strain state will change abruptly, causing the crack propagation direction to change, which is reflected in the abrupt change in the trajectory slope. By screening the cracking tendency characteristic trajectory points with abrupt slope changes, the direction of crack initiation and propagation can be accurately located.

[0044] Furthermore, this invention transforms the local crack propagation trend into a quantitative index of the overall strain transmission direction by vector superposition. Utilizing the correlation between geometric vectors and mechanical transmission paths, the strain source driving crack development is deduced in reverse. Those skilled in the art should understand that, from a mechanical perspective, the propagation direction of fatigue cracks is always consistent with the local strain transmission direction. Each crack propagation tendency characterization vector corresponds to a crack propagation trajectory under specific strain, and its direction directly reflects the dominant strain transmission direction in that region. By adding all crack propagation tendency characterization vectors, the essence is to determine the main strain signal based on the strain transmission in each local region, thereby obtaining the core strain transmission path driving the overall initiation and propagation of cracks and improving the data representativeness of the process analysis.

[0045] Furthermore, this invention establishes a correlation between the strain transmission direction and the stress sensitivity of the component. It quantifies the correlation between strain on the core strain path of the local web by using the directional angle. From the perspective of mechanical transmission laws, local areas, directly bearing the dominant strain, become the most sensitive areas to fatigue damage, exhibiting significant differences in strain response. In local areas with larger angles to the strain transmission direction, the fatigue damage effect on their strain response is more consistent with other areas. In corrugated steel web structures, local webs in different orientations have varying degrees of fit with the strain transmission damage characterization vector due to differences in geometric angles. By calculating the directional angle between the set of characteristic webs in each orientation and this vector, this fit can be intuitively quantified. That is, the smaller the angle, the closer the local web plane is to the core strain transmission direction, and the higher the degree of strain transmission influence. This achieves a correlation between the multi-directional geometric characteristics of the corrugated steel web and the differences in strain response in different damaged areas.

[0046] Furthermore, this invention extracts key cycle nodes from the explicit curve segment and statistically analyzes the number of frequently occurring load output cycles to ultimately determine a representative load-bearing limit index. From the perspective of fatigue damage evolution, the explicit load output curve segment corresponds to the load range where the strain anomaly occurs in the local web due to damage. The maximum value of the load output cycle number on the horizontal axis of this curve segment is the critical node where the strain in this region first shows a significant anomaly. Therefore, this value is determined as the explicit load output cycle number, which can accurately mark the specific load stage at which damage in this local area begins to dominate the strain response. When determining the maximum load-bearing cycle number of the test beam, considering that the damage sensitivity of different explicit web regions of the corrugated steel web may have slight differences, the explicit cycle number of a single region is difficult to represent the overall structure's load-bearing limit. By statistically analyzing the recorded frequency of all explicit load output cycle numbers, the value with the most frequent occurrence is defined as the maximum load-bearing cycle number. This value reflects the load cycle node where the sensitive areas affected by damage simultaneously enter a significant damage state under fatigue load, ensuring that the output results are more consistent with the actual load-bearing capacity of the structure and improving the accuracy of fatigue damage assessment. Attached Figure Description

[0047] Figure 1 This is a step diagram illustrating the method for determining fatigue damage in a corrugated steel web composite box girder according to an embodiment of the present invention.

[0048] Figure 2 This is a schematic diagram of a waveform steel web with a specific amplitude according to an embodiment of the present invention;

[0049] Figure 3 A schematic diagram illustrating the determination of the crack propagation tendency characterization vector in an embodiment of the present invention;

[0050] Figure 4This is a flowchart illustrating the steps of comparing and analyzing the strain response curve with a strain response reference curve in an embodiment of the present invention.

[0051] Figure 5 A schematic diagram illustrating the determination of the load output explicit curve segment in an embodiment of the present invention;

[0052] Figure 6 This is a simplified functional module diagram of the fatigue damage determination device for corrugated steel web composite box girder according to an embodiment of the present invention;

[0053] In the figure: 1-Wave steel web, 2-Strain gauge, 3-Surface crack, 4-First crack propagation tendency characterization vector, 5-Second crack propagation tendency characterization vector, 6-Third crack propagation tendency characterization vector, 7-Strain response curve, 8-Strain response reference curve. Detailed Implementation

[0054] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0055] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0056] It should be noted that in the description of this invention, the terms "upper," "lower," "inner," "outer," etc., which indicate the direction or positional relationship, are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0057] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0058] Please see Figure 1 as well as Figure 2 As shown, Figure 1 This is a step diagram illustrating the method for determining fatigue damage in a corrugated steel web composite box girder according to an embodiment of the present invention. Figure 2 This is a schematic diagram of a corrugated steel web with a specific amplitude according to an embodiment of the present invention. The method for determining fatigue damage of a composite box girder with a corrugated steel web according to the present invention includes:

[0059] Step S10: During the cyclic load output to the test beam, the strain at a local location on the corrugated steel web 1 is obtained by several strain gauges 2 arranged on the corrugated steel web 1 of the test beam, and the strain response curve of each strain gauge as a function of the number of load output cycles is constructed.

[0060] In practice, in the rectangular coordinate system containing the strain response curve, the horizontal axis represents the number of load output cycles (in cycles), and the vertical axis represents strain (in με × 10⁻⁶). -6 .

[0061] Step S20: In response to the result of satisfying the damage feature triggering condition, determine several crack propagation tendency characterization vectors of surface cracks in the crack image, so as to determine the strain transfer damage characterization vector based on the vector direction comparison of the crack propagation tendency characterization vectors.

[0062] The damage feature triggering condition is the capture of a crack image on the surface of the test beam;

[0063] Step S30: Based on the positional relationship between the strain transfer damage characterization vector and the corrugated steel web, the local corrugated steel web is divided into locally webs with obvious tendency and locally webs without obvious tendency. The strain response curves corresponding to each locally web with obvious tendency are compared and analyzed with the strain response reference curve to obtain the number of obvious load output cycles.

[0064] The strain response reference curve is determined by obtaining the strain response curves corresponding to the strain gauges on the non-obvious local web and fitting the strain response curves corresponding to several strain gauges on the non-obvious local web into a strain response reference curve.

[0065] Step S40: Determine the maximum number of load cycles for the test beam based on the number of recorded explicit load cycles, and record the maximum number of load cycles.

[0066] Specifically, this invention does not limit the specific method of fitting the strain response curves corresponding to several strain gauges on a non-obvious local web plate into a strain response reference curve. Fitting multiple curves into one curve is an existing technology and will not be described here.

[0067] In the fatigue damage test of corrugated steel web composite box girder, the core purpose of recording the maximum number of load cycles is to quantify the fatigue limit of the structure and provide key basis for engineering design, life assessment and safe operation and maintenance.

[0068] Specifically, the process of determining several crack propagation tendency characterization vectors of surface cracks in a crack image includes:

[0069] On the surface crack, several characteristic trajectory points of cracking tendency are determined based on the trajectory slope;

[0070] The characteristic trajectory points of cracking tendency are numbered and sorted along the length direction of the surface cracks;

[0071] Two adjacent crack tendency feature trajectory points, numbered sequentially, are used as the starting and ending points of a vector, respectively, to determine several crack propagation tendency characterization vectors for surface cracks.

[0072] Please see Figure 3 As shown, this is a schematic diagram of determining the crack propagation tendency characterization vector in an embodiment of the present invention. Crack tendency characteristic trajectory points m, n, p and q are determined on the surface crack 3. The crack tendency characteristic trajectory points m, n, p and q are numbered along the length direction of the surface crack. For example, crack tendency characteristic trajectory point m is numbered (1), crack tendency characteristic trajectory point n is numbered (2), crack tendency characteristic trajectory point p is numbered (3), and crack tendency characteristic trajectory point q is numbered (4). The crack tendency characteristic trajectory point m with adjacent numbering is taken as the starting point of the vector and the crack tendency characteristic trajectory point n is taken as the ending point of the vector. The first crack propagation tendency characterization vector 4 is determined. In this way, the second crack propagation tendency characterization vector 5 and the third crack propagation tendency characterization vector 6 are determined.

[0073] In this invention, two coordinate points can be taken on the surface crack. The slope of the trajectory segment between the two coordinate points is calculated to determine the slope of the midpoint between the two coordinate points relative to the crack length direction. This yields the trajectory slope at the midpoint. This is a common method for determining the slope of any point on a curve, and will not be elaborated here.

[0074] This invention extracts key feature points of cracks, establishes ordered associations, and finally generates direction vectors. It transforms the geometric morphology of surface cracks into quantifiable data on their expansion trends. It is understood that, based on the geometric characteristics of crack expansion, the areas where the crack trajectory slope abruptly changes are often the regions with the most significant cracking tendency. Crack expansion is dominated by the local strain field. When the crack tip encounters a weld seam in a corrugated steel web or a material defect, the strain state undergoes abrupt changes, leading to a change in the crack expansion direction, reflected in abrupt changes in the trajectory slope. By screening feature trajectory points with abrupt changes in slope, the essence is to accurately locate the direction of crack initiation and expansion. Feature trajectory points are numbered and sorted along the crack length, and vectors are constructed using adjacent numbered feature trajectory points as start and end points. The direction of each vector directly reflects the expansion direction of that crack segment.

[0075] Specifically, the cracking tendency characteristic trajectory points are trajectory points with a slope greater than a preset slope threshold.

[0076] In this invention, the preset slope threshold is set by those skilled in the art based on the monitoring sensitivity requirements. If the slope threshold is too small, a large number of crack tendency feature trajectory points will be selected, resulting in redundant data calculation. If the slope threshold is too large, the number of crack tendency feature trajectory points selected will be insufficient, affecting the accuracy of the output results. Therefore, the slope threshold range is [0.17, 0, 21], and preferably, the slope threshold is 0.18.

[0077] Specifically, the vector obtained by adding the crack propagation tendency characterization vectors is determined as the strain transfer damage characterization vector.

[0078] In this invention, each crack propagation tendency characterization vector can be decomposed into vector components in the x-direction and vector components in the y-direction under the same coordinate system. The vector components are then superimposed, and finally the vector synthesized by the superimposed vector components in the x-direction and the superimposed vector components in the y-direction is determined as the strain transfer damage characterization vector. The superposition of vectors is a common calculation method in mathematics, which will not be elaborated here.

[0079] For example: Given three crack propagation tendency characterization vectors, V1=(0.8,0.3), V2=(1.2,0.5), and V3=(0.9,0.4), calculate ∑Vx=0.8+1.2+0.9=2.9 in the x-direction and ∑Vy=0.3+0.5+0.4=1.2 in the y-direction to obtain the strain transfer damage characterization vector V. , =(2.9,1.2).

[0080] It is understood that this invention transforms the local crack propagation trend into a quantitative index of the overall strain transmission direction by vector superposition. By utilizing the correlation between geometric vectors and mechanical transmission paths, the strain source driving crack development is deduced in reverse. Those skilled in the art should understand that, from a mechanical perspective, the propagation direction of fatigue cracks is always consistent with the local strain transmission direction. Each crack propagation tendency characterization vector corresponds to a crack propagation trajectory under specific strain, and its direction directly reflects the dominant strain transmission direction in that region. By adding all crack propagation tendency characterization vectors, the essence is to determine the main strain signal based on the strain transmission in each local region, thereby obtaining the core strain transmission path that drives the overall initiation and propagation of cracks and improving the data representativeness of process analysis.

[0081] Specifically, the process of dividing a local corrugated steel web into a locally inclined web and a locally inclined web includes:

[0082] Determine the directional angle between the plane containing the local corrugated steel web within the set of characteristic webs of each orientation and the strain transfer damage characterization vector;

[0083] The local corrugated steel webs within the set of oriented feature webs corresponding to the minimum directional angle are defined as dominant dip local webs, and all local corrugated steel webs other than the dominant dip local webs are defined as non-dominant dip local webs.

[0084] Understandably, this invention links the strain transmission direction with the stress sensitivity of a component, quantifying the correlation between strain on the core strain path of a local web by using the directional angle. From the perspective of mechanical transmission laws, local areas, directly bearing the dominant strain, become the most sensitive areas to fatigue damage, manifesting as significant differences in strain response. Local areas with larger angles to the strain transmission direction show more consistent synchronicity with other areas in their strain response to fatigue damage. In corrugated steel web structures, local webs in different orientations have varying degrees of fit with the strain transmission damage characterization vector due to differences in geometric angles. By calculating the directional angle between the set of characteristic webs in each orientation and this vector, this fit can be intuitively quantified; that is, the smaller the angle, the closer the local web plane is to the core strain transmission direction, and the higher the degree of strain transmission influence.

[0085] Specifically, the process of determining the set of oriented feature webs includes:

[0086] The corrugated steel web is divided into several local corrugated steel webs based on the wave amplitude size;

[0087] In practice, each wave amplitude corresponds to a local corrugated steel web;

[0088] Determine the angle between the plane containing the local corrugated steel web and the axis of the test beam;

[0089] Local corrugated steel webs with the same included angle are grouped into the same set of oriented characteristic webs to obtain several sets of oriented characteristic webs.

[0090] The web set with different orientations includes several local corrugated steel webs with the same included angle.

[0091] Please continue reading. Figure 2As shown, this is a schematic diagram of a waveform steel web of one amplitude size according to an embodiment of the present invention. A waveform steel web of one amplitude size includes a local waveform steel web (a), a local waveform steel web (b), a local waveform steel web (c), a local waveform steel web (d), and a local waveform steel web (e). That is, (a)-(e) are five local waveform steel webs within a waveform steel web of one amplitude size. According to the angle between the plane containing the local waveform steel webs (a), (b), (c), (d), and (e) and the axis of the test beam, the local waveform steel webs (a), (c), and (e) within each waveform steel web of one amplitude size are assigned to the same set of characteristic webs of the same orientation. The local waveform steel web (b) within each waveform steel web of one amplitude size is assigned to the same set of characteristic webs of the same orientation. The local waveform steel web (d) within each waveform steel web of one amplitude size is assigned to the same set of characteristic webs of the same orientation, resulting in three sets of characteristic webs of the same orientation.

[0092] Understandably, this invention, based on the geometric characteristics of the multi-segment corrugated steel web, decomposes the complex overall structure into comparable local units. From the construction of the corrugated steel web, it consists of multiple repeating flat plate segments and inclined plate segments with fixed wave amplitude dimensions. Local webs with different orientations have different strain transmission paths and load-bearing characteristics due to their different angles with the axis of the test beam. Local webs with the same angle have highly consistent stress directions and strain distribution patterns; while local webs with different angles have significantly different stress states. Therefore, by calculating the angle between each local web and the axis, the geometric orientation can be transformed into a quantifiable numerical index; finally, local webs with the same angle are grouped into a set of characteristic webs with the same orientation.

[0093] Specifically, please refer to Figure 4 The diagram illustrates the steps of comparing and analyzing the strain response curve with the strain response reference curve in an embodiment of the present invention. The process of comparing and analyzing the strain response curve corresponding to each dominant local web with the strain response reference curve includes:

[0094] Step S31: Compare the overlap ratio of the strain response curves corresponding to the local webs of each dominant tendency with the strain response reference curve.

[0095] In this invention, the strain response curve and the strain response reference curve can be divided into several curve segments according to the interval of the number of load output cycles. Preferably, the interval can be 500. That is, on the strain response curve and the strain response reference curve, the curve segments with the number of load output cycles between [0, 500) are compared for overlap, and the curve segments with the number of load output cycles between [500, 1000) are compared for overlap, and so on.

[0096] Specifically, the present invention does not limit the specific method of segmented comparison of the degree of overlap. Preferably, the degree of overlap can be determined by the Euclidean distance between the corresponding sampling points of the two curves within the segmented interval. Using the Euclidean distance to determine the degree of overlap of two curves is a common technical means, which will not be elaborated here.

[0097] Step S32: The curve segment with an overlap ratio less than the preset overlap ratio reference value is determined as the load output explicit curve segment.

[0098] Please see Figure 5 As shown, this is a schematic diagram of determining the load output explicit curve segment in an embodiment of the present invention. The strain response curve 7 corresponding to the local web with explicit tendency is compared with the strain response reference curve 8 by segmenting the overlap. For example, the strain response curve 7 and the strain response reference curve 8 are divided into several curve segments along the horizontal axis, including curve segments s1-s15. The overlap of the strain response curve 7 and the strain response reference curve 8 in each curve segment is calculated. For example, if the overlap in curve segment s14 is less than the preset overlap reference value, then curve segment s14 is determined as the load output explicit curve segment.

[0099] In this invention, the overlap reference value can be obtained through pre-calculation. The average overlap of several curve segments is pre-calculated, and the calculated average overlap is determined as the overlap reference value. Preferably, a value of 0.85 is provided here for the overlap reference value.

[0100] Understandably, this invention establishes a benchmark reference by leveraging the insensitivity of damage to the non-indicative local web. By comparing the strain response differences with those of the indicative local web, it accurately captures the load application stage associated with damage. From the perspective of structural stress characteristics, the strain response curve of the non-indicative local web, due to its larger angle with the core strain transmission direction, stably reflects the normal law of strain variation with the number of load cycles under no-damage or micro-damage conditions. The indicative local web, as a sensitive area of ​​strain concentration, will deviate from the normal law once fatigue damage occurs, manifested as a deviation between the strain response curve and the benchmark curve. When the overlap is lower than a preset value, it indicates that the strain distribution in the indicative region has changed abnormally due to damage at the corresponding load cycle number of the curve segment, meaning that the load application at this stage has affected the strain transmission of the structure.

[0101] Specifically, the process of determining the number of dominant cycles for load output includes:

[0102] The maximum value of the load output cycle number corresponding to the load output dominant curve segment on the horizontal axis is determined as the load output dominant curve segment's load output dominant cycle number.

[0103] Specifically, the process of determining the maximum number of load cycles for the test beam includes:

[0104] Obtain the number of load output explicit cycles for several recorded load output explicit curve segments;

[0105] The number of explicit cycles of the load output with the most recorded times is determined as the maximum number of cycles for the test beam to bear the load.

[0106] For example, the number of explicit cycles corresponding to the eight load output explicit curve segments of a certain test beam are 2.2 million, 2.2 million, 2.3 million, 2.2 million, 2.4 million, 2.2 million, 2.3 million, and 2.2 million, respectively.

[0107] The frequency of each occurrence was as follows: 5 occurrences in 2.2 million occurrences, 2 occurrences in 2.3 million occurrences, and 1 occurrence in 2.4 million occurrences. The 2.2 million occurrences, which had the highest frequency, were determined as the maximum number of cycles that could be carried.

[0108] Understandably, this invention extracts key cycle nodes from the explicit curve segment and statistically analyzes the number of frequently occurring load output cycles to ultimately determine a representative load-bearing limit index. From the perspective of fatigue damage evolution, the explicit load output curve segment corresponds to the load range where the strain anomaly occurs in the local web due to damage. The maximum value of the load output cycle count on the horizontal axis of this curve segment is the critical node where the strain in this region first shows a significant anomaly. Therefore, this value is determined as the explicit load output cycle count, which can accurately mark the specific load stage at which damage in this local area begins to dominate the strain response. When determining the maximum load-bearing cycle count for the test beam, considering that the damage sensitivity of different explicit web regions of the corrugated steel web may have slight differences, the explicit cycle count of a single region is difficult to represent the overall structure's load-bearing limit. By statistically analyzing the recorded frequency of all explicit load output cycle counts, the value with the most frequent occurrence is defined as the maximum load-bearing cycle count. This value reflects the load cycle node where the sensitive areas affected by damage simultaneously enter a significant damage state under fatigue load, ensuring that the output results are more consistent with the actual load-bearing capacity of the structure and improving the accuracy of fatigue damage assessment.

[0109] Specifically, please refer to Figure 6 The diagram shown is a simplified functional module diagram of the fatigue damage determination device for corrugated steel web composite box girder according to an embodiment of the present invention. The present invention also provides a fatigue damage determination device for corrugated steel web composite box girder, comprising:

[0110] A test bench is used to apply loads to a test beam for a number of cycles.

[0111] Specifically, the test bench in this invention is an electro-hydraulic servo test bench. In order to avoid resonance between the test beam and the test bench, the load output frequency of the cyclic output is generally below 10Hz. In the implementation of this invention, the load output frequency is 5Hz.

[0112] The measurement module includes an image acquisition unit set on the test bench to capture crack images, several strain gauges set on the corrugated steel web of the test beam to obtain the strain at local locations on the corrugated steel web, and a curve generation unit connected to the strain gauges to construct the strain response curve.

[0113] In practice, the image acquisition unit captures a crack image once every 300 load output cycles.

[0114] Specifically, the present invention does not limit the specific structure of the image capturing unit. The image capturing unit in the implementation can be a high-definition camera, which will not be described in detail here.

[0115] Specifically, this invention does not limit the specific structure of the strain gauge. The strain gauge in the implementation can be a steel strain gauge. The technology of using strain gauges to collect strain is widely used in engineering test monitoring, which will not be elaborated here.

[0116] Specifically, this invention does not limit the specific structure of the curve generation unit. The curve generation unit in the implementation can be a strain gauge with a variable sampling frequency connected to the strain gauge. The use of strain gauges and strain gauges in engineering test monitoring is a conventional technical means, and will not be elaborated here.

[0117] The feature analysis module, which is connected to the measurement module, is used to determine several crack propagation tendency characterization vectors of surface cracks in crack images, and to determine strain transfer damage characterization vectors based on the vector direction comparison of the crack propagation tendency characterization vectors.

[0118] The feature extraction module, which is connected to the feature analysis module, is used to divide the local waveform steel web into a local web with a visible dip and a local web without a visible dip. The strain response curves corresponding to each local web with a visible dip are compared and analyzed with the strain response curves corresponding to the strain gauges on the local web without a visible dip to obtain the number of visible load output cycles.

[0119] A recording module, which is connected to the feature extraction module, is used to determine the maximum number of load cycles of the test beam and record the maximum number of load cycles.

[0120] Specifically, the present invention does not limit the feature analysis module, feature extraction module, and recording module. They can be computer-readable storage media that stores computer program code. When the computer program code is run on a computer, it can perform related functions, which will not be elaborated here.

[0121] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0122] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining fatigue damage in a corrugated steel web composite box girder, characterized in that, The method comprises the following steps: During the load output cycle of the test beam, the strain at a local position on the corrugated steel web is obtained through a plurality of strain gauges arranged on the corrugated steel web of the test beam, and a strain response curve of each strain gauge with respect to the number of load output cycles in the load test period is constructed; In response to the result of meeting the damage feature trigger condition, a plurality of crack propagation tendency characteristic vectors of surface cracks in the crack image are determined to determine a strain transfer damage characteristic vector according to the vector direction comparison of the crack propagation tendency characteristic vectors; The damage feature trigger condition is that a crack image is captured on the surface of the test beam; According to the positional relationship between the strain transfer damage characteristic vector and the corrugated steel web, the local corrugated steel web is divided into dominant tendency local webs and non-dominant tendency local webs, and the strain response curves corresponding to each dominant tendency local web are compared with the strain response reference curve to obtain a plurality of load output dominant cycle numbers; The determination method of the strain response reference curve is to obtain the strain response curves corresponding to the strain gauges on the non-dominant tendency local web, and to fit the strain response curves corresponding to the plurality of strain gauges on the non-dominant tendency local web into a strain response reference curve; The load maximum cycle number of the test beam is determined according to the recorded number of load output dominant cycle numbers, and the load maximum cycle number is recorded.

2. The method for determining fatigue damage of a corrugated steel web group box girder according to claim 1, characterized in that, The process of determining a plurality of crack propagation tendency characteristic vectors of surface cracks in the crack image comprises: According to the trajectory slope, a plurality of cracking tendency feature trajectory points are determined on the surface cracks; The cracking tendency feature trajectory points are numbered and sorted along the length direction of the surface cracks; The two cracking tendency feature trajectory points adjacent in the number sorting are respectively taken as the starting point and the ending point of the vector to determine a plurality of crack propagation tendency characteristic vectors of the surface cracks.

3. The method for fatigue damage determination of corrugated steel web group box girder according to claim 2, characterized in that, The cracking tendency feature trajectory point is a trajectory point with a slope greater than a preset slope threshold.

4. The method for fatigue damage determination of corrugated steel web group box girder according to claim 2, characterized in that, The sum of the crack propagation tendency characteristic vectors is taken as the strain transfer damage characteristic vector.

5. The method for fatigue damage determination of corrugated steel web group box girder according to claim 4, characterized in that, The process of dividing the local corrugated steel web into dominant tendency local webs and non-dominant tendency local webs comprises: The direction angle between the plane where each orientation feature web set is located and the strain transfer damage characteristic vector is determined; The local corrugated steel web in the orientation feature web set corresponding to the minimum direction angle is determined as the dominant tendency local web, and all local corrugated steel webs other than the dominant tendency local web are determined as the non-dominant tendency local web.

6. The method for fatigue damage determination of corrugated steel web group box girder according to claim 5, characterized in that, The process of determining the orientation feature web set comprises: The corrugated steel web is divided into a plurality of local corrugated steel webs based on the wave amplitude size; The angle between the plane where the local corrugated steel web is located and the axis direction of the test beam is determined; The local corrugated steel webs with the same angle are divided into the same orientation feature web set to obtain a plurality of orientation feature web sets; Each orientation feature web set comprises a plurality of local corrugated steel webs with the same angle.

7. The method for fatigue damage determination of corrugated steel web group box girder according to claim 5, characterized in that, The process of comparing and analyzing the strain response curves corresponding to each dominant tendency local web with the strain response reference curve comprises: The strain response curve corresponding to each dominant tendency local web plate is compared with the strain response reference curve in a sectional coincidence manner; The curve segment with a coincidence degree less than a preset coincidence reference value is determined as a load output dominant curve segment.

8. The method for fatigue damage determination of corrugated steel web group box girder of claim 7, wherein, The process of determining the load output dominant cycle number comprises: The maximum value of the load output cycle number on the horizontal axis corresponding to the load output dominant curve segment is determined as the load output dominant cycle number of the load output dominant curve segment.

9. The method for fatigue damage determination of corrugated steel web group box girder of claim 8, wherein, The process of determining the load-carrying maximum cycle number of the test beam comprises: The load output dominant cycle numbers of the recorded load output dominant curve segments are obtained; The load output dominant cycle number with the most recorded times is determined as the load-carrying maximum cycle number of the test beam.

10. A device for determining fatigue damage of a corrugated steel web composite box girder, for performing the method for determining fatigue damage of a corrugated steel web composite box girder according to any one of claims 1 to 9, characterized in that, It comprises: A test bench for the test beam to output a load for a number of cycles; A measurement module comprising an image capturing unit arranged on the test bench to capture crack images, a number of strain gauges arranged on the corrugated steel web plate to obtain strains at local positions on the corrugated steel web plate, and a curve generation unit connected to the strain gauges to construct strain response curves; A feature analysis module connected to the measurement module to determine a number of crack propagation tendency feature vectors of surface cracks in the crack images, and to determine a strain transfer damage feature vector according to the vector direction comparison of the crack propagation tendency feature vectors; A feature extraction module connected to the feature analysis module to divide the local corrugated steel web plate into dominant tendency local web plates and non-dominant tendency local web plates, and to compare and analyze the strain response curves corresponding to each dominant tendency local web plate with the strain response curves corresponding to the strain gauges on the non-dominant tendency local web plates to obtain a number of load output dominant cycle numbers; A recording module connected to the feature extraction module to determine the load-carrying maximum cycle number of the test beam and record the load-carrying maximum cycle number.

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