CN113533502B - Long-term monitoring method for stud fatigue damage in rail transit combined structure bridge - Google Patents
Long-term monitoring method for stud fatigue damage in rail transit combined structure bridge Download PDFInfo
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- 230000007774 longterm Effects 0.000 title claims abstract description 18
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- 230000002411 adverse Effects 0.000 claims abstract description 21
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- 229910000831 Steel Inorganic materials 0.000 claims description 12
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- 238000013461 design Methods 0.000 claims description 9
- 239000000523 sample Substances 0.000 claims description 7
- 238000010008 shearing Methods 0.000 claims description 7
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
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- G01N29/4409—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by comparison
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Abstract
The invention discloses a long-term monitoring method for fatigue damage of pegs in a rail transit combined structure bridge, which comprises the following steps: s1, determining the section position of the most unfavorable peg by using a finite element method; s2, marking the position of the least favorable bolt on the bottom surface of the upper flange plate; s3, arranging a plurality of strain gauges on the web at the section position of the most unfavorable stud; s4: loading a load on the bridge with the combined structure, and determining the arrangement position of the strain gauge according to the measured values of the strain gauges; s5, continuously measuring the strain gauge and calculating the fatigue shear stress spectrum of the least favorable bolt in the running process of the train; s6, calculating the fatigue cycle times N, the daily average fatigue cycle times N d and the time T required by fatigue failure, and finally determining the detection interval time p; and S7, carrying out ultrasonic flaw detection on the least adverse pin after p years, and determining whether damage occurs. By using the method, the detection cost of the fatigue damage of the peg can be reduced on the premise of ensuring the safety of the peg.
Description
Technical Field
The invention relates to a long-term monitoring method for fatigue damage of pegs in a bridge with a rail transit combined structure.
Background
Rail traffic has economical, punctual and environmental protection properties, which have become the main travel means in cities, and once rail traffic is interrupted, huge economic and social losses will be caused. The span of the simply supported beam with the bolt combined structure is 30-60 m, the simply supported beam is suitable for crossing urban roads by a rail transit line, and the safety of the simply supported beam is not important for the safe operation of the rail transit.
At present, the fatigue problem of the steel-concrete composite beam has been paid attention to, and various results are obtained by carrying out test research and calculation methods of Guan Gang-concrete composite beam fatigue and corresponding specifications at home and abroad. However, the detection method for the breakage of the peg in the bridge is not reported all the time, and potential safety hazards are left for the bridge.
The existing steel structure fatigue detection methods comprise an ultrasonic flaw detection method, a magnetic leakage method, a penetration method, an X-ray photography method and the like, wherein the magnetic leakage method and the penetration method can only detect surface cracks and can not detect buried cracks. X-ray radiography and ultrasonic flaw detection can detect internal injury, but the X-ray method has radiation danger and is not suitable for implementation in areas with dense urban population. In addition, the excessive thickness of the concrete slab of the composite girder bridge also has an influence on the detection accuracy. Ultrasonic flaw detection is the most feasible method at present, but due to the high discreteness of fatigue life, the ultrasonic flaw detection has high detection cost, cannot be continuously used for fatigue monitoring, and can be detected only once at intervals. At present, how to scientifically control the detection period of the damage of the bolt is an important problem of saving the detection cost and ensuring the safety of the rail transit under the condition of ensuring the fatigue life of the bolt.
Disclosure of Invention
The invention aims to overcome the defect that the detection period of the stud fatigue damage in the track traffic combined structure bridge in the prior art cannot be accurately determined, and provides a long-term monitoring method of the stud fatigue damage in the track traffic combined structure bridge.
The invention solves the technical problems by the following technical scheme:
The long-term monitoring method for the stud fatigue damage in the rail transit combined structure bridge comprises an I-shaped steel structure with an upper flange plate, a lower flange plate and a web plate, wherein the stud is fixed on the top surface of the upper flange plate, a concrete layer is poured above the upper flange plate, and the stud is positioned in the concrete layer, and the long-term monitoring method for the stud fatigue damage in the rail transit combined structure bridge is characterized by comprising the following steps:
S1, after the design of the bridge with the combined structure is completed, determining the section position of the least favorable stud by using a finite element method;
s2, marking the position of the most adverse peg on the bottom surface of the upper flange plate before pouring the concrete layer;
S3, after the concrete layer pouring is completed, arranging a plurality of strain gauges on the web plate along the vertical direction at the section positions of the least favorable pegs;
S4, loading a load on the bridge with the combined structure, and determining the arrangement position of the strain gauge according to the measured values of the strain gauges;
S5, continuously measuring the strain gauge and calculating the shear stress born by the least favorable bolt according to the measurement result of the strain gauge and obtaining the fatigue shear stress spectrum of the least favorable bolt in the running process of the train on the bridge with the combined structure;
S6, calculating the fatigue cycle number N required by the fatigue crack expansion of the most unfavorable stud by adopting an iteration method, calculating the time T required by the fatigue damage of the most unfavorable stud according to the fatigue cycle number N and the daily average fatigue cycle number N d calculated by a fatigue shear stress spectrum, and finally determining the detection interval time p of the most unfavorable stud;
S7, after p years, carrying out ultrasonic flaw detection on the least favorable pin according to the mark at the bottom of the upper flange plate, and determining whether the least favorable pin is damaged or not; and if the least favorable peg is intact, repeating the steps S5 and S6.
Preferably, the step S1 specifically includes the following steps:
Establishing a finite element model of the composite structure bridge, wherein the I-shaped steel structure is modeled by a shell unit, and the concrete layer part is modeled by a solid unit;
establishing a practical measurement value of steel materials for the elastic modulus of the steel plate in the finite element model, and adopting a design value provided by a standard for the elastic modulus of the concrete;
loading the unit force on the central line of the bridge of the combined structure, and recording the shear stress of each steel-concrete common node along the bridge direction; after each loading, moving the unit force by the unit distance, repeatedly calculating, recording the forward-bridge shearing force of each common node, and processing the information to obtain the shearing force influence line of each common node;
Establishing a simulated train load, moving a carriage model along the shear force influence line of each node, and calculating a stress course of the generated shear stress; then adopting a rain flow counting method to convert the stress history of the shear stress into fatigue stress spectrums of the shear stress, and calculating fatigue damage caused by each stress spectrum according to design specifications; the section of the steel-concrete shared node corresponding to the greatest fatigue damage is the section of the steel-concrete combined structural beam with the least favorable shearing force, so that the position of the least favorable stud is determined.
Preferably, all studs within 0.5m before and after the shear force most adverse cross-section are the most adverse studs of the composite structure bridge.
Preferably, the step S2 specifically includes the following steps: and drawing mutually perpendicular marking lines from the axle center positions of the least favorable bolts on the top surface of the upper flange plate and extending the marking lines to the bottom surface of the upper flange plate, wherein the crossing positions of the marking lines are the axle center positions of the least favorable bolts on the bottom surface of the upper flange plate.
Preferably, the marker lines are drawn at intervals, the line ends of which are not less than 50mm from the edge of the most adverse peg.
Preferably, in the step S3, the strain gauges should be arranged at equal intervals, and the distance from the upper flange plate and the lower flange plate is not less than 50mm.
Preferably, in the step S4, a positive stress measurement result is plotted according to the measurement value of the strain gauge, and a neutral axis of the composite structural bridge is found from measurement data by least square fitting, and an intersection point of the neutral axis and the section position of the most adverse pin is the strain relief position for shear monitoring.
Preferably, in step S5, the strain gauge is zeroed when the train arrives, and measurement is started, and measurement is stopped after the train leaves, and measurement is repeatedly continued for 3 days.
Preferably, in step S6, the detection interval time p of the most adverse pin is determined, taking into account a safety factor of 2.0, i.e. taking into account that the leak rate of the ultrasonic flaw detection is 50%.
Preferably, in step S7, when a defect signal is displayed on the ultrasonic flaw detector and the distance from the defect to the probe is approximately equal to the plate thickness of the upper flange plate, it is indicated that the most adverse peg has fatigue crack, i.e. will fail.
On the basis of conforming to the common knowledge in the field, the above preferred conditions can be arbitrarily combined to obtain the preferred examples of the invention.
The invention has the positive progress effects that: the method can accurately calculate the detection period of the stud fatigue damage in the rail transit combined structure bridge, thereby reducing the detection cost of the stud fatigue damage on the premise of ensuring the safety of the stud.
Drawings
FIG. 1 is a schematic view of the bottom surface of an upper flange plate in a preferred embodiment of the present invention.
Fig. 2 is a schematic structural view of a bridge with a combined structure according to a preferred embodiment of the present invention.
Reference numerals illustrate:
Upper flange plate 10
Lower flange plate 20
Web 30
Concrete layer 40
Least favorable peg 50
Marking line 60
Strain gage 70
Strain gauge 80
Positive stress measurement result graph 90
Neutral axis 100
Shear force most unfavorable section 110
Detailed Description
The invention is further illustrated by means of the following examples, which are not intended to limit the scope of the invention.
In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention.
The method comprises the following steps:
1. After the design of the combined structure bridge is completed, the position of the most adverse pin 50 measuring point is determined, and the method comprises the following steps:
(1) A finite element model of a composite structural bridge is built in which the i-section steel structure is modeled with shell elements and the concrete layer 40 is modeled in part with solid elements.
(2) The elastic modulus of the steel plate in the finite element model is established by adopting an actual measurement value of steel materials, and the elastic modulus of the concrete adopts a design value provided by a standard. And setting constraint on the finite element model according to the actual position of the support.
(3) Loading the unit force on the central line of the bridge of the combined structure, and recording the shear stress of each steel-concrete common node along the bridge direction; after each loading, moving the unit force by a unit distance, repeatedly calculating, and recording the forward-bridge shearing force of each common node; and processing the information to obtain the shear force influence lines of the common nodes.
(4) And (3) building a simulated train load, moving the train model along the shear influence line of each node, and calculating the stress history of the generated shear stress. And then converting the stress course of the shear stress into a fatigue stress spectrum of the shear stress by adopting a rain flow counting method. And calculating fatigue damage caused by each stress spectrum according to the design specification. The section of the steel-concrete common node corresponding to the greatest fatigue damage is the shear force most unfavorable section 110 of the composite structure bridge. Considering the uncertainty of fatigue damage, the fatigue problem of some pegs needs to be considered more, so that the pegs of two rows before and after the most unfavorable position need to be taken into consideration. In this embodiment, all of the studs within 0.5m of the shear force most unfavorable cross section 110 are the most unfavorable studs 50 on the composite bridge.
2. As shown in fig. 1, the bottom surface of upper flange plate 10 is marked with marking lines 60 to locate the most adverse peg 50 prior to casting concrete layer 40. Starting from the axial center position of the most adverse peg 50 on the top surface of the upper flange plate 10, drawing mutually perpendicular marking lines 60 and extending the marking lines 60 to the bottom surface of the upper flange plate 10, wherein the crossing position of the marking lines 60 is the axial center position of the most adverse peg 50 on the bottom surface of the upper flange plate 10. In this embodiment, a black finish paint is used to draw the mark line 60, and the thickness of the line is 1mm. The distance from the end of the marker wire 60 to the edge of the least favored peg 50 (at the dashed line) must not be less than 50mm. The marks are drawn at intervals and do not intersect, so that the probe position can be vacated for subsequent ultrasonic detection, the probe can directly contact the bottom surface of the lower flange plate 20, and the paint of the mark line 60 does not need to be polished. The clearance of 50mm is a diameter of a straight probe that allows for detection of a pin crack.
3. After the concrete is poured and curing of the concrete is completed, 5 strain gages 70 are arranged on the web 30 in the vertical direction at the cross-sectional position of the most disadvantageous peg 50, the strain gages 70 are arranged at equal intervals, and the distance from the upper flange plate 10 and the lower flange plate 20 is not less than 50mm, as shown in fig. 2. The clearance of 50mm is considered that the thickness of the web 30 is generally 14-20 mm, and the web is kept at a certain distance from the upper flange plate 10 and the lower flange plate 20, so that on one hand, the strain gauge 70 is easy to attach (the operation cannot be blocked by space), and on the other hand, the interference of stress concentration caused by welding seams between the web 30 and the upper flange plate 10 and the lower flange plate 20 can be avoided.
The load is applied to the midspan of the composite bridge, the readings of the 5 strain gauges 70 are measured, and a positive stress measurement result diagram 90 is drawn. The neutral axis 100 of the composite bridge is found from the measured data by least squares fitting. The intersection of the neutral axis 100 and the cross section of the most adverse peg 50 is the attachment location of the strain gauge 80 for shear monitoring.
In this embodiment, the benefits of placing the strain gauge 80 in the neutral axis 100 are two: firstly, the shear stress on the neutral axis 100 is the largest, and under the condition that the error of the strain gauge 70 is the same, the measurement result is the most accurate; second, the derivative of the shear stress on the height coordinate at the neutral axis 100 is minimal, and even if the strain gauge 70 is offset by 1cm, the relative measurement error is not greater than 0.5%.
4. After the bridge of the combined structure is formally operated and the train operation is stabilized, stress monitoring is carried out on the strain gauge 80 for three days. In this solution, considering the drift problem of the strain gauge 80 (when the strain gauge 80 is used for long-term measurement, the measurement error becomes large due to chemical variation or physical relaxation of the glue adhering to the strain gauge 80, which leads to gradual deviation of the measurement result in a certain direction), it is actually found that the strain gauge 80 is zeroed when coming, and measurement is started, and the measurement is stopped after the vehicle leaves.
5. Since the magnitude of the shear stress at different heights on the same cross-section is only related to the cross-sectional shape, the shear stress experienced by the most adverse peg 50 can be calculated from the measurement of the strain gauge 80 at the neutral axis 100, in combination with the theory of material mechanics.
6. The shear stress of the least favorable peg 50 for three days can be obtained from the strain-gauge 80 measurements for three days. The fatigue shear stress spectrum of the most adverse peg 50 can be obtained by treating these measured shear stresses with a rain flow method.
7. The number of fatigue cycles N required for fatigue crack propagation of the least favorable peg 50 is calculated using an iterative method based on the following formula.
The calculation of the parameters in the formula is as follows.
TABLE 1 calculation parameters for fatigue cycle number N
8. The time T required for fatigue failure of the least favorable pin 50 (i.e., the fatigue life of the least favorable pin 50 in days) is calculated from the number of fatigue cycles N and the number of daily average fatigue cycles N d calculated from the stress spectrum.
The detection interval p (units: years) of the most adverse pin 50 was determined in consideration of a safety factor of 2.0 (i.e., in consideration of the leak rate of ultrasonic flaw detection of 50%).
9. The least favorable pegs 50 should be ultrasonically inspected at intervals of p years based on the markings on the bottom surface of the upper flange plate 10. The flaw detection adopts a straight probe. When a defect signal is displayed on the ultrasonic flaw detector and the defect-to-probe distance is approximately equal to the plate thickness of the upper flange plate 10, it is indicated that fatigue cracks are present in the least favorable peg 50, i.e., will fail.
10. If the least favorable pin 50 is intact, after inspection, the process should revert to step 4. (in view of the problem of drift of the strain relief 80, the strain relief 80 should be removed and then re-attached in situ to form the strain relief 80.)
The monitoring method of the steps can infer the residual service life of the least favorable peg 50, and set the time interval for the next monitoring of the least favorable peg 50 under a certain guarantee rate according to the residual service life, thereby avoiding the related cost caused by frequently detecting the least favorable peg 50 and also avoiding the economic loss and social influence caused by occupying the road under the bridge in the detection process.
While specific embodiments of the invention have been described above, it will be appreciated by those skilled in the art that this is by way of example only, and the scope of the invention is defined by the appended claims. Various changes and modifications to these embodiments may be made by those skilled in the art without departing from the principles and spirit of the invention, but such changes and modifications fall within the scope of the invention.
Claims (10)
1. The long-term monitoring method for the fatigue damage of the stud in the rail transit combined structure bridge comprises an I-shaped steel structure with an upper flange plate, a lower flange plate and a web plate, the stud is fixed on the top surface of the upper flange plate, a concrete layer is poured above the upper flange plate, and the stud is positioned in the concrete layer, and the long-term monitoring method for the fatigue damage of the stud in the rail transit combined structure bridge is characterized by comprising the following steps:
S1, after the design of the bridge with the combined structure is completed, determining the section position of the least favorable stud by using a finite element method;
s2, marking the position of the most adverse peg on the bottom surface of the upper flange plate before pouring the concrete layer;
S3, after the concrete layer pouring is completed, arranging a plurality of strain gauges on the web plate along the vertical direction at the section positions of the least favorable pegs;
S4, loading a load on the bridge with the combined structure, and determining the arrangement position of the strain gauge according to the measured values of the strain gauges;
S5, continuously measuring the strain gauge and calculating the shear stress born by the least favorable bolt according to the measurement result of the strain gauge and obtaining the fatigue shear stress spectrum of the least favorable bolt in the running process of the train on the bridge with the combined structure;
S6, calculating the fatigue cycle number N required by the fatigue crack expansion of the most unfavorable stud by adopting an iteration method, calculating the time T required by the fatigue damage of the most unfavorable stud according to the fatigue cycle number N and the daily average fatigue cycle number N d calculated by a fatigue shear stress spectrum, and finally determining the detection interval time p of the most unfavorable stud;
S7, after p years, carrying out ultrasonic flaw detection on the least favorable pin according to the mark at the bottom of the upper flange plate, and determining whether the least favorable pin is damaged or not; and if the least favorable peg is intact, repeating the steps S5 and S6.
2. The method for long-term monitoring of stud fatigue damage in a rail transit composite structural bridge according to claim 1, wherein the step S1 specifically comprises the following steps:
Establishing a finite element model of the composite structure bridge, wherein the I-shaped steel structure is modeled by a shell unit, and the concrete layer part is modeled by a solid unit;
establishing a practical measurement value of steel materials for the elastic modulus of the steel plate in the finite element model, and adopting a design value provided by a standard for the elastic modulus of the concrete;
loading the unit force on the central line of the bridge of the combined structure, and recording the shear stress of each steel-concrete common node along the bridge direction; after each loading, moving the unit force by the unit distance, repeatedly calculating, recording the forward-bridge shearing force of each common node, and processing the information to obtain the shearing force influence line of each common node;
Establishing a simulated train load, moving a carriage model along the shear force influence line of each node, and calculating a stress course of the generated shear stress; then adopting a rain flow counting method to convert the stress history of the shear stress into fatigue stress spectrums of the shear stress, and calculating fatigue damage caused by each stress spectrum according to design specifications; the section of the steel-concrete shared node corresponding to the greatest fatigue damage is the section of the steel-concrete combined structural beam with the least favorable shearing force, so that the position of the least favorable stud is determined.
3. A method of long term monitoring of stud fatigue damage in a rail transit composite structural bridge according to claim 2, wherein all studs within 0.5m before and after the shear force most adverse cross-section are the most adverse studs of the composite structural bridge.
4. The method for long-term monitoring of stud fatigue damage in a rail transit composite structural bridge according to claim 1, wherein the step S2 specifically comprises the following steps: and drawing mutually perpendicular marking lines from the axle center positions of the least favorable bolts on the top surface of the upper flange plate and extending the marking lines to the bottom surface of the upper flange plate, wherein the crossing positions of the marking lines are the axle center positions of the least favorable bolts on the bottom surface of the upper flange plate.
5. The method for long-term monitoring of peg fatigue damage in a rail transit composite structure bridge according to claim 4, wherein the marker lines are drawn at intervals, and the line ends of the marker lines are not less than 50mm from the edge of the least favorable peg.
6. The method for long-term monitoring of stud fatigue damage in a rail transit composite structural bridge according to claim 1, wherein in the step S3, the strain gauges are arranged at equal intervals, and the distance from the upper flange plate and the lower flange plate is not less than 50mm.
7. The method according to claim 1, wherein in the step S4, a positive stress measurement result is plotted according to the measured value of the strain gauge, and a neutral axis of the composite structural bridge is found from the measured data by least square fitting, and an intersection point of the neutral axis and the cross-sectional position of the most adverse stud is the strain relief position for shear monitoring.
8. The method for long-term monitoring of stud fatigue damage in a rail transit composite structure bridge according to claim 1, wherein in step S5, the strain gauge is zeroed and measurement is started when the train comes, measurement is stopped after the train leaves, and measurement is repeatedly continued for 3 days.
9. The method for long-term monitoring of stud fatigue damage in a rail transit composite structural bridge according to claim 1, wherein in step S6, when determining the detection interval time p of the most unfavorable stud, a safety factor of 2.0 is considered, namely, a leak detection rate of ultrasonic flaw detection is considered to be 50%.
10. A method for long term monitoring of stud fatigue damage in a rail transit composite structural bridge according to claim 1, wherein in step S7, when a defect signal is displayed on an ultrasonic flaw detector and the defect to probe distance is approximately equal to the plate thickness of the upper flange plate, it is indicated that the most adverse stud has fatigue crack, i.e. will fail.
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| WO2003038295A1 (en) * | 2001-10-31 | 2003-05-08 | Nsk Ltd. | Rolling bearings |
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| CN106012806A (en) * | 2016-06-17 | 2016-10-12 | 中建三局集团有限公司 | Hollow slab hinge joint shear connection structure and construction process |
| CN106767667A (en) * | 2017-01-24 | 2017-05-31 | 广西交通科学研究院有限公司 | Using the appraisal procedure of the steel-concrete combination beam fatigue additional deformation of Welded-Stud Conectors |
| CN106768996A (en) * | 2017-04-01 | 2017-05-31 | 西南交通大学 | A kind of loading device for peg non-proportional loading model test |
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