阅读说明：本技术 一种轨道交通组合结构桥梁中栓钉疲劳损伤的长期监测方法 (Long-term monitoring method for fatigue damage of stud in rail transit composite structure bridge ) 是由 朱妍 朱毅 沈至毅 陈海华 于 2020-04-15 设计创作，主要内容包括：本发明公开了一种轨道交通组合结构桥梁中栓钉疲劳损伤的长期监测方法,其包括以下步骤：S1、利用有限元法确定最不利栓钉的截面位置；S2、在上翼缘板的底面标记最不利栓钉的位置；S3、在最不利栓钉的截面位置处,在腹板上布置多个应变片；S4：在组合结构桥梁上加载载荷,根据多个应变片的测量值确定应变花的布置位置；S5、在列车运行过程中,持续对应变片进行测量并计算出最不利栓钉的疲劳剪应力谱；S6、计算疲劳循环次数N,日均疲劳循环次数N-(d)和疲劳破坏需要的时间T,并最终确定检测间隔时间p；S7、隔p年后对最不利栓钉进行超声波探伤,确定是否发生损伤。利用本方法能够在保证栓钉安全的前提下降低了栓钉疲劳损伤的检测成本。(The invention discloses a long-term monitoring method for stud fatigue damage in a rail transit composite structure bridge, which comprises the following steps: s1, determining the section position of the most unfavorable stud by using a finite element method; s2, marking the position of the worst bolt on the bottom surface of the upper flange plate; s3, arranging a plurality of strain gauges on the web at the position of the cross section of the worst stud; s4: loading a load on the composite structure bridge, and determining the arrangement position of the strain rosette according to the measurement values of the plurality of strain gauges; s5, continuously measuring the strain gauge and calculating the fatigue shear stress spectrum of the most unfavorable stud in the running process of the train; s6, calculating the fatigue cycle number N and the daily average fatigue cycle number N d And the time T required for fatigue failure, and finally determining the detection interval time p; and S7, performing ultrasonic flaw detection on the worst stud after p years, and determining whether damage occurs. By using the method, the safety of the stud can be ensuredThe cost of detecting stud fatigue damage is reduced.)

1. The long-term monitoring method for the fatigue damage of the studs in the rail transit composite structure bridge is characterized by comprising the following steps of:

s1, after the design of the composite structure bridge is finished, determining the section position of the most unfavorable stud by using a finite element method;

s2, marking the position of the most unfavorable stud on the bottom surface of the upper flange plate before pouring the concrete layer;

s3, after the concrete layer is poured, arranging a plurality of strain gauges on the web plate along the vertical direction at the section position of the most unfavorable stud;

s4, loading a load on the composite structure bridge, and determining the arrangement position of the strain rosette according to the measurement values of the plurality of strain gauges;

s5, continuously measuring the strain gauge and calculating the shear stress borne by the worst bolt nail according to the measurement result of the strain gauge and obtaining the fatigue shear stress spectrum of the worst bolt nail in the process that the train runs on the composite structure bridge;

s6, calculating the fatigue cycle number N required by the worst stud fatigue crack propagation by adopting an iterative method, and calculating the daily average fatigue cycle number N according to the fatigue cycle number N and the fatigue shear stress spectrum_dCalculating the time T required by the least favorable bolt fatigue failure and finally determining the detection interval time p of the least favorable bolt;

s7, after p years, carrying out ultrasonic flaw detection on the worst bolt according to the mark at the bottom of the upper flange plate, and determining whether the worst bolt is damaged; if the worst peg is intact, repeating the steps S5, S6.

2. The method for long-term monitoring of the fatigue damage of the stud in the rail transit composite structural bridge as claimed in claim 1, wherein the step S1 specifically includes the following processes:

establishing a finite element model of the composite structure bridge, wherein an I-shaped steel structure is modeled by a shell unit, and a concrete layer part is modeled by a solid unit;

establishing a measured value of steel adopted by the elastic modulus of the steel plate in the finite element model, and a design value provided by a specification adopted by the elastic modulus of the concrete;

loading the steel-concrete composite structure bridge central line with unit force, and recording the shear stress along the bridge direction on each steel-concrete common node; after each loading, moving the unit force by a unit distance, repeatedly calculating, recording the forward-bridge shear force of each common node, and processing the information to obtain the shear 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 process with the generated shear stress; then, converting the stress history 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 design specifications; the steel-concrete common node corresponding to the largest fatigue damage is located on the section with the most unfavorable shearing force of the steel-concrete combined structural beam, so that the position of the most unfavorable bolt is determined.

3. The method for long-term monitoring of bolt fatigue damage in a rail transit composite structural bridge of claim 2, wherein all bolts within 0.5m before and after the shear worst cross section are the worst bolts of the composite structural bridge.

4. The method for long-term monitoring of the fatigue damage of the stud in the rail transit composite structural bridge as claimed in claim 1, wherein the step S2 specifically includes the following processes: and drawing mutually perpendicular marking lines starting from the axis position of the worst stud 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 position of the marking lines is the axis position of the worst stud on the bottom surface of the upper flange plate.

5. The method for long-term monitoring of stud fatigue damage in a rail transit composite structural bridge of claim 4, wherein the marking lines are drawn at intervals, and the distance from the line end of the marking line to the edge of the least favorable stud is not less than 50 mm.

6. The method for long-term monitoring of stud fatigue damage in a rail transit composite structural bridge as claimed in claim 1, wherein in said step S3, said strain gauges should be arranged at equal intervals and at a distance of not less than 50mm from said upper flange plate and said lower flange plate.

7. The method for long-term monitoring of stud fatigue damage in a rail transit composite structural bridge as claimed in claim 1, wherein in said step S4, a positive stress measurement result is plotted based on the measured values of said strain gauge, and a neutral axis of said composite structural bridge is found from the measured data by least squares fitting, and the intersection point of said neutral axis and the cross-sectional position of said worst stud is said strain rosette position for shear force monitoring.

8. The method for monitoring the fatigue damage of the stud in the rail transit composite structural bridge as claimed in claim 1, wherein in step S5, the strain rosette is zeroed when the train arrives, the measurement is started, the measurement is stopped after the train leaves, and the measurement is repeated for 3 days.

9. The method for long-term monitoring of the fatigue damage of the stud in the rail transit composite structural bridge as claimed in claim 1, wherein in step S6, when determining the detection interval time p of the worst stud, a safety factor of 2.0 is considered, that is, the missing rate of ultrasonic flaw detection is considered to be 50%.

10. The method for long-term monitoring of the fatigue damage of the stud in the rail transit composite structural bridge as claimed in claim 1, wherein 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 indicates that the least favorable stud has fatigue crack and will fail.

Technical Field

The invention relates to a long-term monitoring method for fatigue damage of a stud in a rail transit composite structure bridge.

Background

The rail transit has economical efficiency, punctuality and environmental protection, which has become a main trip mode in cities, and once the rail transit is interrupted, huge economic and social losses are caused. The span of the simple beam with the stud combined structure is 30-60 m, the simple beam is suitable for crossing urban roads on a rail transit line, and the safety of the simple beam is of no great importance to the safe operation of rail transit.

At present, the fatigue problem of the steel-concrete composite beam has attracted attention, and many achievements are obtained in the research and calculation methods and corresponding specifications of the fatigue test of the steel-concrete composite beam at home and abroad. However, the detection method for the fracture of the stud in the bridge in use is not reported all the time, and potential safety hazards are left for the bridge in use.

The existing steel structure fatigue detection methods comprise an ultrasonic flaw detection method, a magnetic flux leakage method, a penetration method, an X-ray photography method and the like, wherein the magnetic flux leakage method and the penetration method can only detect surface cracks and can not detect buried cracks. The X-ray photography method and the ultrasonic flaw detection method can detect internal damage, but the X-ray method has radiation danger and is not suitable for being implemented in a region with dense urban population. In addition, the concrete slab of the composite girder bridge is too thick, which also affects the detection accuracy. The ultrasonic flaw detection method is the most feasible method at present, but due to the high dispersion of the fatigue life, the detection cost of the ultrasonic flaw detection is high, the ultrasonic flaw detection method cannot be continuously used for fatigue monitoring, and the ultrasonic flaw detection method can only detect once at intervals. At present, how to scientifically control the detection period of stud damage is an important problem of saving detection cost and ensuring the safety of rail transit under the condition of ensuring the fatigue life of the stud.

Disclosure of Invention

The invention aims to overcome the defect that the detection period of the stud fatigue damage in the rail transit composite structure bridge in the prior art cannot be accurately determined, and provides a long-term monitoring method for the stud fatigue damage in the rail transit composite structure bridge.

The invention solves the technical problems through the following technical scheme:

the long-term monitoring method for the fatigue damage of the studs in the rail transit composite structure bridge is characterized by comprising the following steps of:

s1, after the design of the composite structure bridge is finished, determining the section position of the most unfavorable stud by using a finite element method;

s2, marking the position of the most unfavorable stud on the bottom surface of the upper flange plate before pouring the concrete layer;

s3, after the concrete layer is poured, arranging a plurality of strain gauges on the web plate along the vertical direction at the section position of the most unfavorable stud;

s4, loading a load on the composite structure bridge, and determining the arrangement position of the strain rosette according to the measurement values of the plurality of strain gauges;

s5, continuously measuring the strain gauge and calculating the shear stress borne by the worst bolt nail according to the measurement result of the strain gauge and obtaining the fatigue shear stress spectrum of the worst bolt nail in the process that the train runs on the composite structure bridge;

s6, calculating the fatigue cycle number N required by the worst stud fatigue crack propagation by adopting an iterative method, and calculating the daily average fatigue cycle number N according to the fatigue cycle number N and the fatigue shear stress spectrum_dCalculating the time T required by the least favorable bolt fatigue failure and finally determining the detection interval time p of the least favorable bolt;

s7, after p years, carrying out ultrasonic flaw detection on the worst bolt according to the mark at the bottom of the upper flange plate, and determining whether the worst bolt is damaged; if the worst peg is intact, repeating the steps S5, S6.

Preferably, the step S1 specifically includes the following steps:

establishing a finite element model of the composite structure bridge, wherein an I-shaped steel structure is modeled by a shell unit, and a concrete layer part is modeled by a solid unit;

establishing a measured value of steel adopted by the elastic modulus of the steel plate in the finite element model, and a design value provided by a specification adopted by the elastic modulus of the concrete;

loading the steel-concrete composite structure bridge central line with unit force, and recording the shear stress along the bridge direction on each steel-concrete common node; after each loading, moving the unit force by a unit distance, repeatedly calculating, recording the forward-bridge shear force of each common node, and processing the information to obtain the shear 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 process with the generated shear stress; then, converting the stress history 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 design specifications; the steel-concrete common node corresponding to the largest fatigue damage is located on the section with the most unfavorable shearing force of the steel-concrete combined structural beam, so that the position of the most unfavorable bolt is determined.

Preferably, all pegs within 0.5m forward and aft of the shear worst cross section are the worst pegs of the composite structural bridge.

Preferably, the step S2 specifically includes the following steps: and drawing mutually perpendicular marking lines starting from the axis position of the worst stud 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 position of the marking lines is the axis position of the worst stud on the bottom surface of the upper flange plate.

Preferably, the marking lines are drawn at intervals, and the distance from the line end of the marking line to the edge of the worst peg must not be less than 50 mm.

Preferably, in the step S3, the strain gauges should be arranged at equal intervals, and the distance from the upper flange plate to the lower flange plate is not less than 50 mm.

Preferably, in step S4, a positive stress measurement result is plotted according to the measured values of the strain gauge, and a neutral axis of the composite structural bridge is found from the measured data by least squares fitting, and an intersection point of the neutral axis and the cross-sectional position of the worst stud is the strain flower position for shear force monitoring.

Preferably, in step S5, the train starts to zero the strain gauge and starts to measure, and stops measuring after the train leaves, and the measurement is repeated for 3 days.

Preferably, in step S6, when determining the detection interval time p of the worst peg, a safety factor of 2.0 is considered, that is, the missing rate of ultrasonic flaw detection is considered to be 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 thickness of the upper flange plate, it indicates that the worst stud has fatigue cracks, i.e., will fail.

On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.

The positive progress effects of the invention are as follows: by the method, the detection period of the stud fatigue damage in the rail transit composite structure bridge can be accurately calculated, so that the detection cost of the stud fatigue damage is reduced on the premise of ensuring the stud safety.

Drawings

FIG. 1 is a schematic view of the underside of the upper flange plate in a preferred embodiment of the invention.

Fig. 2 is a schematic structural view of a composite structural bridge according to a preferred embodiment of the present invention.

Description of reference numerals:

upper flange plate 10

Lower flange plate 20

Web 30

Concrete layer 40

Worst case peg 50

Marking line 60

Strain gage 70

Strain flower 80

Normal stress measurement result graph 90

Neutral axis 100

Worst shear cross section 110

Detailed Description

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.

In the description of the present invention, it is to 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 those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.

The method comprises the following steps:

1. after the design of the combined structure bridge is finished, the position of the measuring point of the most unfavorable stud 50 is determined, and the method comprises the following steps:

(1) and 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 40 part is modeled by a solid unit.

(2) And (3) establishing a finite element model, wherein the elastic modulus of the steel plate adopts the measured value of steel, and the elastic modulus of the concrete adopts the design value provided by the specification. And setting constraints on the finite element model according to the actual position of the support.

(3) Loading unit force on the central line of the composite structure bridge, and recording the shear stress along the bridge direction on each steel-concrete common node; after each loading, moving the unit force by a unit distance, repeatedly calculating, and recording the forward-bridge shear force of each common node; and processing the information to obtain the shear influence lines of the shared nodes.

(4) And establishing a simulated train load, moving the train model along the shear influence line of each node, and calculating the stress course with the generated shear stress. And then, converting the stress history of the shear stress into a fatigue stress spectrum of the shear stress by adopting a rain flow counting method. And calculating the fatigue damage caused by each stress spectrum according to the design specification. The section where the steel-concrete common node corresponding to the largest fatigue damage is located is the section 110 where the shear force of the composite structural bridge is the worst. Considering the uncertainty of fatigue damage, the fatigue problem of some pegs needs to be considered more, so that the pegs in two rows in front of and behind the most unfavorable position need to be considered. In this embodiment, all studs in the range of 0.5m forward and aft of the worst shear cross section 110 are the worst studs 50 on the composite structural bridge.

2. As shown in fig. 1, the locations of the worst studs 50 are marked with a marking line 60 on the bottom surface of the upper flange plate 10 before the concrete layer 40 is poured. From the axial center position of the least favorable stud 50 on the top surface of the upper flange plate 10, the mutually perpendicular marking lines 60 are drawn and the marking lines 60 are extended to the bottom surface of the upper flange plate 10, and the crossing position of the marking lines 60 is the axial center position of the least favorable stud 50 on the bottom surface of the upper flange plate 10. In the scheme, black finish paint is adopted to draw a marking line 60, and the thickness of the line is 1 mm. The distance from the end of the marking line 60 to the edge of the worst peg 50 (in dashed line) must not be less than 50 mm. The marked parts are drawn at intervals and do not intersect, the position of the probe 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 marking line 60 does not need to be polished. The gap is 50mm and is the diameter of the straight probe that allows for detection of a pin crack.

3. After the concrete is poured and the curing of the concrete is completed, as shown in fig. 2, 5 strain gauges 70 are arranged on the web 30 in the vertical direction at the cross-sectional position of the most unfavorable stud 50, the strain gauges 70 are arranged at equal intervals, and the distance from the upper flange plate 10 to the lower flange plate 20 is not less than 50 mm. The empty opening of 50mm is to consider that the thickness of the web 30 is generally 14-20 mm, a certain distance is kept between the web 30 and the upper flange plate 10 and the lower flange plate 20, the strain gauge 70 is easy to attach (operation cannot be blocked by space), and the interference of stress concentration caused by welding seams among the web 30, the upper flange plate 10 and the lower flange plate 20 can be avoided.

And loading load in the span of the composite structure bridge, measuring the reading values of the 5 strain gauges 70, and drawing a normal stress measurement result graph 90. The neutral axis 100 of the composite structural bridge is found from the measured data by least squares fitting. The intersection of the neutral axis 100 and the cross-section of the worst peg 50 is the location of attachment of the strain rosette 80 for shear monitoring.

In this embodiment, the benefits of placing the strain gage 80 on the neutral axis 100 are two-fold: firstly, the shear stress on the neutral axis 100 is the largest, and the measurement result at the position is the most accurate under the condition that the errors of the strain gauges 70 are the same; secondly, the derivative of the shear stress to the height coordinate at the position of the neutral axis 100 is the minimum, and even if the strain gauge 70 is attached and dislocated by 1cm, the relative measurement error is not larger than 0.5%.

4. And after the composite structure bridge is formally operated and the train operation is stable, stress monitoring is carried out on the strain gauge 80 for three days. In the scheme, the problem of drift of the strain rosette 80 is considered (when the strain rosette 80 is used for long-term measurement, due to the fact that the glue sticking to the strain rosette 80 is subjected to chemical variation or physical relaxation, the measurement error is increased, and the measurement result gradually deviates to a certain direction), the strain rosette 80 is set to zero when the vehicle comes from the vehicle, the 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 shape of the cross section, the shear stress that the most unfavorable stud 50 is subjected to can be calculated from the measurement results of the strain gauge 80 at the neutral axis 100 in combination with the material mechanics theory.

6. The shear stress of the worst peg 50 for three days can be obtained from the strain rosette 80 measurements for three days. These measured shear stresses are processed by the rain flow method to obtain the fatigue shear stress spectrum of the least favorable stud 50.

7. The number of fatigue cycles N required for the worst stud 50 to fatigue crack propagate is calculated iteratively based on the following formula.

The parameters in the formula are calculated as follows.

TABLE 1 calculation parameters for fatigue cycle number N

8. The daily average fatigue cycle number N calculated from the fatigue cycle number N and the stress spectrum_dThe time T required for the worst bolt 50 to fail in fatigue is calculated (i.e., the fatigue life of the worst bolt 50 in days).

The detection interval p (unit: year) of the least favorable peg 50 is determined taking into account a safety factor of 2.0 (i.e., taking into account a missing rate of 50% for ultrasonic flaw detection).

9. Every p years the worst peg 50 should be ultrasonically inspected according to the markings on the underside 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 distance from the defect to the probe is approximately equal to the thickness of the upper flange plate 10, it is indicated that fatigue cracks occur in the worst stud 50, i.e., it will fail.

10. If the worst stud 50 is intact, the procedure should be returned to step 4 after inspection. (in consideration of the problem of the strain flower 80 drifting, the strain flower 80 should be formed by re-attaching the original strain flower 80 in situ)

The monitoring method of the steps can conjecture the residual service life of the worst bolt 50, and set the time interval of the next monitoring of the worst bolt 50 according to the residual service life under a certain guarantee rate, thereby avoiding the related cost caused by frequent detection of the worst bolt 50 and 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 that 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 spirit and scope of the invention, and these changes and modifications are within the scope of the invention.