CN114036620A - Service life calculation method of steel-concrete composite structure under random pitting damage - Google Patents

Service life calculation method of steel-concrete composite structure under random pitting damage Download PDF

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CN114036620A
CN114036620A CN202111374180.6A CN202111374180A CN114036620A CN 114036620 A CN114036620 A CN 114036620A CN 202111374180 A CN202111374180 A CN 202111374180A CN 114036620 A CN114036620 A CN 114036620A
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steel
crack
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王达
谭本坤
向胜涛
赵鹏鑫
王谐
刘玉雄
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Changsha University of Science and Technology
Central South University of Forestry and Technology
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Abstract

The invention discloses a service life calculation method of a steel-concrete composite structure under random pitting damage, and relates to the technical field of bridge engineering. The method comprises the steps of selecting an area to be pitting-corroded from an original geometric model, randomly generating a pitting parameter set meeting requirements, simulating actual conditions as much as possible, carrying out parametric modeling on the parameter set, forming a steel-concrete combined structure model after pitting corrosion by a difference Boolean operation method, obtaining the position of the most unfavorable pit with the largest stress based on the steel-concrete combined structure model after pitting corrosion, inserting an initial crack into the most unfavorable pit to obtain a steel-concrete combined structure fracture mechanics model under pitting corrosion damage, carrying out fatigue crack propagation in the steel-concrete combined structure fracture mechanics model under pitting corrosion damage, obtaining fatigue action times corresponding to each fatigue crack propagation, and accumulating to obtain the residual fatigue life value of the steel-concrete combined structure under random pitting damage.

Description

Service life calculation method of steel-concrete composite structure under random pitting damage
Technical Field
The invention relates to the technical field of bridge engineering, in particular to a service life calculation method of a steel-concrete composite structure under random pitting damage.
Background
In recent years, steel-concrete composite structures (steel-concrete composite structures) are rapidly developed at home and abroad, are widely applied to the fields of bridges and civil buildings, and obtain remarkable economic benefits. Over time, due to the facts that a concrete bridge deck is cracked, a water drain pipe is damaged and the like, a steel structure is influenced by multiple factors such as rainwater, temperature, humidity and the like, a corrosion effect is generated, stress concentration caused by pitting corrosion caused by corrosion seriously damages the durability of the structure, the fatigue performance of the steel structure is greatly changed under the influence of the corrosion, the stress mode is complex, and the method is particularly important for effectively evaluating the fatigue performance under the condition of corrosion damage.
At present, the adverse effects of the pitting corrosion on ships, marine structural members and the like are widely concerned, but the corrosion aspect of steel structural bridges is not perfect, and the generation position of the pitting corrosion has obvious uncertainty due to the non-uniformity of materials in steel beams of the steel-concrete composite structure and the complex influence of the surrounding environment. Meanwhile, the fatigue damage caused by corrosion does not occur on the fatigue vulnerable details, but the pitting corrosion position generates fatigue cracks due to stress concentration to cause damage, the combined structure bridge generates new fatigue vulnerable details, and the fatigue failure mode under pitting damage migrates. And current research is generally only directed to fatigue failure of the structure due to defects at the weld site, while corrosion damage can greatly reduce the fatigue life of the structure.
With the development of other modern detection means such as bridge structure health monitoring, manual detection, nondestructive detection and the like, the steel beam corrosion form of the steel-concrete composite structure can be better identified, and the fatigue life evaluation under the corrosion damage of the steel-concrete composite structure is particularly important based on the detection information. For the performance evaluation of the steel-concrete combined structure, the fatigue performance of the steel-concrete combined structure under the pitting corrosion is researched by establishing a submodel and inserting the stress concentration part of the structure into the pitting corrosion pits which are distributed randomly under the consideration of corresponding factors, so that the method has practical significance and engineering application value. (Wangchunsen, Zhang Jingwen, Changlan, Tan Chenxin. Long-life high-performance weathering steel bridge research progress and engineering application [ J ]. traffic and transportation engineering newspaper)
The Chinese patent with publication number CN113378432A discloses a numerical simulation method for crack propagation on a pitting pit of an RPV (resilient packet metal) tube based on a propagation finite element, which considers the influence of pitting appearance and size on crack position initiation, and adopts a fixed and uniform stress for cracks. In reality, the position of the pitting area is not fixed, and the common and important fatigue problems faced by the bridge structure are mostly caused by vehicle load or wind load, and the pitting corrosion area is characterized in that the magnitude of the stress force is uncertain and is cyclically reciprocated until the structure is damaged.
Disclosure of Invention
The invention aims to solve the technical problem that the prior art is insufficient, and provides a service life calculation method of a steel-concrete combined structure under random pitting damage.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a service life calculation method of a steel-concrete combined structure under random pitting damage comprises the following steps:
s1, establishing an initial geometric model of the steel-concrete composite structure in finite element software, selecting a part to be pitting in the model, generating a parameter set of random pitting pits, assembling the parameter set to the area to be pitting etched, and acquiring a steel-concrete composite structure model after pitting etching; the method for generating the parameter group of the random pitting pits comprises the following steps:
s101, acquiring a radius range of a pitting pit and a first distribution function obeyed by the radius, and a depth range of the pitting pit and a second distribution function obeyed by the depth based on actual pitting statistical data;
s102, randomly generating random radius data which obeys the first distribution function every time, and judging whether the random radius data are within the radius range of the pit; randomly generating random depth data which obeys the first distribution function every time, and judging whether the random depth data is in the depth range of the pit; randomly generating a pitting coordinate each time;
s103, repeating the step S102 until n random radius data in the radius range and n random depth data in the depth range are obtained; n point erosion coordinates;
s104, randomly selecting 1 coordinate of pitting, 1 random radius data in a radius range and 1 random depth data in a depth range to form a parameter group of 1 random pitting pit; acquiring parameter sets of n random pitting pits;
s2, performing static calculation on the steel-concrete combined structure model after pitting to obtain the most unfavorable pit position with the largest stress, and inserting an initial crack into the most unfavorable pit to obtain a steel-concrete combined structure fracture mechanical model under pitting damage;
s3, calculating the initial crack stress intensity factor and fatigue crack propagation parameter in the pitting pit, and performing fatigue crack propagation;
and S4, acquiring the fatigue action times corresponding to each fatigue crack propagation, and accumulating to obtain the residual fatigue life value of the steel-concrete composite structure under the random pitting damage.
In the scheme, n can be set according to the characteristics of the material and the actual scene. The actual pitting statistical data can be obtained according to tests or actual measurement, the test method can refer to a method recorded in 'wilson wave, pitting evolution process and influence on rusty steel fatigue performance research [ D ]. Western-Ann building science and technology university, 2016', and the actual measurement method can refer to a method recorded in 'replacement wave, pitting deterioration effect of riveting component fatigue performance under hot riveting residual stress [ D ]. southwest traffic university, 2020'.
Specifically, in step S1, the implementation of assembling and configuring the parameters of the random pitting pits in the to-be-pitting area includes: the initial geometric model is divided into a first residual model and a first submodel, the area to be pitting etched corresponds to the first submodel, parametric modeling is carried out based on the parameter group of the random pitting pits to generate a geometric pitting body, the geometric pitting body and the first submodel are subjected to difference set Boolean operation to obtain a first pitting submodel, and the first pitting submodel and the first residual model are combined into a steel-mixed combined structure model after pitting etching.
Specifically, the specific implementation manner of step S2 includes: performing static calculation on the steel-concrete combined structure model after pitting corrosion to obtain the most unfavorable pit position with the maximum stress of the whole steel-concrete combined structure model after pitting corrosion, inserting an initial crack in the most unfavorable pit position to form a second pitting corrosion sub model, meshing the second pitting corrosion sub model again, and combining the second pitting corrosion sub model with the first residual model to obtain the steel-concrete combined structure fracture mechanical model under pitting corrosion damage.
Specifically, the method for inserting the initial crack comprises the following steps: and introducing a first point etching model by using Franc3D software, selecting a semielliptical initial crack, setting the length of a major semi-axis, the length of a minor semi-axis and the size of a tip of the semielliptical initial crack, then carrying out grid division, and generating two unit rings at the tip of the initial crack, wherein the two unit rings are an inner ring of a 15-node singular wedge-shaped unit and an outer ring of a 20-node hexahedral unit respectively.
Specifically, the specific implementation manner of step S3 includes:
s301, formula
Figure BDA0003363234590000031
Calculating stress intensity factor value K of open type crackIStress intensity factor value K of slip-type crackIIStress intensity factor value K with tearing crackIIIG is a shear elastic modulus, r and theta are two coordinate components in a local cylindrical coordinate system of the crack tip, and u, v and omega are radial displacement, normal displacement and tangential displacement of any point of the crack tip respectively;
s302, setting a first fatigue crack propagation rate parameter m and a propagation step length delta a of a crack front end central pointmedianAccording to the formula
Figure BDA0003363234590000032
Calculating the expansion step length delta a of other points of the front end of the cracki，ΔKeq,iThe effective stress intensity factor amplitude of the crack tip point is calculated by the formula
Figure BDA0003363234590000041
Figure BDA0003363234590000042
The effective stress intensity factor amplitude of the central point of the crack tip; v. of*Is the Poisson's ratio of the material;
by the formula
Figure BDA0003363234590000043
Calculating the angle theta of crack tip point propagationiI is the number of propagation steps, i is 1,2, …, and t is the number of propagation steps until the crack propagates through the substrate or forms a macroscopic crack;
s303, setting a fatigue load ratio R based on the expansion step length delta aiAngle theta of crack tip propagationiAnd carrying out fatigue crack propagation on the steel-concrete combined structure fracture mechanical model under the pitting damage in Franc 3D.
Specifically, the specific implementation manner of step S4 includes: setting a second fatigue crack propagation rate parameter C according to the formula
Figure BDA0003363234590000044
Calculating the residual fatigue life N of the steel-concrete composite structure under the pitting damageiWhile obtaining the final propagation form of the fatigue crack, given N0＝0。
Compared with the prior art, the invention has the beneficial effects that: the method comprises the steps of selecting an area to be pitting-corroded from an original geometric model, randomly generating a pitting parameter set meeting requirements, simulating actual conditions as much as possible, carrying out parametric modeling on the parameter set, forming a steel-concrete combined structure model after pitting corrosion by a difference Boolean operation method, obtaining the position of the most unfavorable pit with the largest stress based on the steel-concrete combined structure model after pitting corrosion, inserting an initial crack into the most unfavorable pit to obtain a steel-concrete combined structure fracture mechanics model under pitting corrosion damage, carrying out fatigue crack propagation in the steel-concrete combined structure fracture mechanics model under pitting corrosion damage, obtaining fatigue action times corresponding to each fatigue crack propagation, and accumulating to obtain the residual fatigue life value of the steel-concrete combined structure under random pitting damage. The first sub-model and the first point erosion sub-model have the same structure, so that the time for dividing the grid is saved, and the calculation efficiency is improved.
Drawings
FIG. 1 is a flow chart of a modeling method according to an embodiment of the invention.
FIG. 2 is a diagram of an initial geometric model and a first sub-model according to an embodiment of the invention.
FIG. 3 is an elevation of a mesh partition after parametric modeling of a first point erosion model according to an embodiment of the invention.
FIG. 4 is a top view of the meshing after parametric modeling of the first point erosion model of FIG. 3.
FIG. 5 is a top view of a second pitting sub-model and its initial crack in accordance with an embodiment of the invention.
FIG. 6 is a top view of the initial crack of FIG. 5.
FIG. 7 is an elevational view of the initial crack of FIG. 5.
Fig. 8 is a schematic elevation view showing the propagation pattern of fatigue cracks in the second pitting submodel according to the embodiment of the present invention.
Fig. 9 is a side view showing a state of fatigue crack propagation in the second pitting submodel according to the embodiment of the present invention.
FIG. 10 is a residual fatigue life versus crack depth curve for a second pitting sub-model in accordance with an embodiment of the invention.
Wherein, A1 is the initial geometric model, and B1 is the first submodel.
Detailed Description
The method for calculating the service life of the steel-concrete composite structure under the random pitting damage comprises the following steps:
as shown in fig. 2, an initial geometric model a1 of a steel-concrete composite structure was created in the Abaqus software, consisting of a concrete slab, a stud connector and a steel beam thereunder, the total length of the steel beam being 3200mm and the length of the concrete slab being 3000 mm. Wherein the width and the thickness of the concrete plate are respectively 300mm and 80mm, the thickness of the I-shaped steel beam plate is 10mm, the widths of the top plate and the bottom plate are respectively 120mm and 160mm, and the height of the web plate is 150 mm. And (3) simulating the cross-middle bottom plate corrosion condition in the model, dividing a to-be-pitting region, and dividing the initial geometric model A1 into a first residual model D1 and a first sub-model B1 corresponding to the to-be-pitting region. And simultaneously generating a parameter group of the random pitting pits:
s101, based on tests, the experimental method refers to an evolution process of an anyhow wave pit and an influence study on fatigue performance of rusted steel [ D ]. Sieman building science and technology university, 2016 ], simulates a working state of a steel-concrete combined structure in an approximate atmospheric corrosion environment, and by taking midspan bottom plate corrosion as an example, obtains a radius r average value of the pitting pit of 5mm, a radius r range of 1.5 mm-6 mm, and the radius r obeys normal distribution; obtaining the average value of the depth h of the pitting pits to be 3mm, wherein the range of the depth h is 1.5 mm-6 mm, and the depth h obeys normal distribution;
s102, setting the number n of the etching pits to be 50; using Python statements, with 5mm as the mean, 0.5 as the standard deviation, using the function random. Randomly generating random radius data which obeys normal distribution every time, judging whether the random radius data is within the radius range of 1.5-6 mm of the pitting pits, if so, rejecting the value, regenerating the random radius data, and if so, keeping the value; meanwhile, random depth data which obeys normal distribution is randomly generated every time, whether the random depth data is within the depth range of the pitting pits of 1.5-6 mm or not is judged, the value is removed when the random depth data exceeds the range, the random depth data is regenerated, and the value is reserved if the random depth data is within the range; randomly generating a pitting coordinate each time, judging whether the two pitting coordinates are overlapped or intersected according to the sum of the distance and the radius between the two pitting coordinates, if so, rejecting data, regenerating the random pitting coordinates, and if not, keeping the random pitting coordinates;
s103, repeating the step S102 until 50 random radius data in the radius range, 50 random depth data in the depth range and 50 pitting coordinates are obtained;
s104, randomly selecting 1 coordinate of pitting, 1 random radius data in a radius range and 1 random depth data in a depth range to form a parameter group of 1 random pitting pit; a set of 50 random pit parameters was obtained.
As shown in fig. 3 and 4, in the Abaqus software, the parameter set of the pitting pits is stretched into a cylinder, the cylinder is assembled with the first submodel B1, and then difference boolean operations are performed to obtain a first pitting submodel B2, and the first pitting submodel B2 and the first residual model D1 are combined into a pitting steel-concrete combined structure model a 2.
Performing static calculation on a steel-concrete combined structure model A2 after pitting, wherein concrete material is C50, steel material is Q235B, defining model material parameters, boundary conditions and loading positions, and the stud connecting piece can be simulated by a solid unit or a spring unit, and can also be simplified and simulated by setting binding constraint between concrete and a steel beam for simplifying the model.
And acquiring the most unfavorable pit position with the maximum stress of the whole pitting steel-concrete combined structure model A2, and cutting the first pitting submodel B2 with the most unfavorable pit position through Franc3D software, wherein an initial crack is inserted into the most unfavorable pit position as shown in FIG. 5. As shown in fig. 6 and 7, the initial crack is a semiellipse, the length of the major axis and the minor axis of the semiellipse is set to be 0.5 and 0.2, two unit rings are generated at the tip of the initial crack, the two unit rings are respectively an inner ring of a 15-node singular wedge-shaped unit and an outer ring of a 20-node hexahedral unit, and then grid division is performed to form a second pitting submodel B3.
And merging the second pitting submodel B3 after being re-meshed with the first residual model D1 to obtain a steel-concrete combined structure fracture mechanics model A3 under pitting damage.
Based on the steel-concrete combined structure fracture mechanics model A3 under the pitting damage, the fatigue crack propagation method specifically comprises the following steps:
s301, integrating by M, using formula
Figure BDA0003363234590000061
Calculating stress intensity factor value K of open type crackIStress intensity factor value K of slip-type crackIIStress intensity factor value K with tearing crackIIIG is a shear elastic modulus, r and theta are two coordinate components in a local cylindrical coordinate system of the crack tip, and u, v and omega are radial displacement, normal displacement and tangential displacement of any point of the crack tip respectively;
s302, performing test fitting data by GB/T6398-2000 fatigue crack growth rate test method for metal materials to obtain a first fatigue crack growth rate parameter m, setting the recommended value m of BS7910(2005) for Q235B steel to be 3, and setting the growth step length delta a of the center point of the front end of the crackmedianAccording to the formula
Figure BDA0003363234590000071
Calculating the expansion step length delta a of other points of the front end of the cracki；
ΔKeq,iThe effective stress intensity factor amplitude of the crack tip point is calculated by the formula
Figure BDA0003363234590000072
Figure BDA0003363234590000073
The effective stress intensity factor amplitude of the central point of the crack tip;
v*is the Poisson's ratio of the material;
by the formula
Figure BDA0003363234590000074
Calculating the angle theta of crack tip point propagationi；
i is the number of propagation steps, i is 1,2, …, T, T is the number of propagation steps until the crack propagates through the floor or forms a macroscopic crack, and T is set by the method reported in "Fisher J W, Albrecht P, Yen B T, et al.
S303, set the fatigue load ratio R to 0.2 based on the extension step Δ aiAngle theta of crack tip propagationiAnd carrying out fatigue crack propagation on the steel-concrete combined structure fracture mechanical model under the pitting damage in Franc 3D.
The second fatigue crack growth rate parameter C is obtained by performing test fitting data according to GB/T6398-2000 'fatigue crack growth rate test method for metal materials', and the recommended value of BS7910(2005) for Q235B steel is C-5.21 multiplied by 10-13According to Paris's formula
Figure BDA0003363234590000075
a is the crack propagation step length, N is the fatigue propagation number, and
Figure BDA0003363234590000076
calculating the residual fatigue life N of the steel-concrete composite structure under the pitting damageiGiven N0＝0。
Finally, the residual fatigue life N of the steel-concrete composite structure under the pitting damage shown in FIG. 10 is obtainediA curve with fatigue crack propagation depth, the abscissa in fig. 10 represents the fatigue life in units of times; the ordinate is the crack depth in mm. At the same time, the fatigue crack propagation patterns shown in fig. 8 and 9 were obtained.

Claims (6)

1. A service life calculation method of a steel-concrete composite structure under random pitting damage is characterized by comprising the following steps:
s1, establishing an initial geometric model of the steel-concrete composite structure in finite element software, selecting a part to be pitting in the model, generating a parameter set of random pitting pits, assembling the parameter set to the area to be pitting etched, and acquiring a steel-concrete composite structure model after pitting etching; the method for generating the parameter group of the random pitting pits comprises the following steps:
s101, acquiring a radius range of a pitting pit and a first distribution function obeyed by the radius, and a depth range of the pitting pit and a second distribution function obeyed by the depth based on actual pitting statistical data;
s102, randomly generating random radius data which obeys the first distribution function every time, and judging whether the random radius data are within the radius range of the pit; randomly generating random depth data which obeys the first distribution function every time, and judging whether the random depth data is in the depth range of the pit; randomly generating a pitting coordinate each time;
s103, repeating the step S102 until n random radius data in the radius range and n random depth data in the depth range are obtained; n point erosion coordinates;
s104, randomly selecting 1 coordinate of pitting, 1 random radius data in a radius range and 1 random depth data in a depth range to form a parameter group of 1 random pitting pit; acquiring parameter sets of n random pitting pits;
s2, performing static calculation on the steel-concrete combined structure model after pitting to obtain the most unfavorable pit position with the largest stress, and inserting an initial crack into the most unfavorable pit to obtain a steel-concrete combined structure fracture mechanical model under pitting damage;
s3, calculating the initial crack stress intensity factor and fatigue crack propagation parameter in the pitting pit, and performing fatigue crack propagation;
and S4, acquiring the fatigue action times corresponding to each fatigue crack propagation, and accumulating to obtain the residual fatigue life value of the steel-concrete composite structure under the random pitting damage.
2. The method for calculating the service life of the steel-concrete composite structure under the random pitting damage according to claim 1, wherein the step S1 of assembling and configuring the parameters of the random pitting pits in the area to be pitted includes: the initial geometric model is divided into a first residual model and a first submodel, the area to be pitting etched corresponds to the first submodel, parametric modeling is carried out based on the parameter group of the random pitting pits to generate a geometric pitting body, the geometric pitting body and the first submodel are subjected to difference set Boolean operation to obtain a first pitting submodel, and the first pitting submodel and the first residual model are combined into a steel-mixed combined structure model after pitting etching.
3. The method for calculating the service life of the steel-concrete composite structure under the random pitting damage according to claim 2, wherein the concrete implementation manner of the step S2 includes: performing static calculation on the steel-concrete combined structure model after pitting corrosion to obtain the most unfavorable pit position with the maximum stress of the whole steel-concrete combined structure model after pitting corrosion, cutting out the first pitting submodel with the most unfavorable pit position, inserting an initial crack in the most unfavorable pit position to form a second pitting submodel, dividing the second pitting submodel into grids again, and then combining the grids with the first residual model to obtain the steel-concrete combined structure fracture mechanics model under pitting corrosion damage.
4. The method for calculating the service life of a steel-concrete composite structure under random pitting damage according to claim 3, wherein the method for inserting the initial crack comprises: and introducing a first point etching sub model by using Franc3D software, selecting a semielliptical initial crack, setting the length of a major semi-axis and the length of a minor semi-axis of the semielliptical initial crack, and generating two unit rings at the tip of the initial crack, wherein the two unit rings are an inner ring of a 15-node singular wedge-shaped unit and an outer ring of a 20-node hexahedron unit respectively.
5. The method for calculating the service life of the steel-concrete composite structure under the random pitting damage according to claim 3, wherein the concrete implementation manner of the step S3 includes:
s301, formula
Figure FDA0003363234580000021
Calculating stress intensity factor value K of open type crackIStress intensity factor value K of slip-type crackIIStress intensity factor value K with tearing crackIIIG is a shear elastic modulus, r and theta are two coordinate components in a local cylindrical coordinate system of the crack tip, and u, v and omega are radial displacement, normal displacement and tangential displacement of any point of the crack tip respectively;
s302, setting a first fatigue crack propagation rate parameter m and a propagation step length delta a of a crack front end central pointmedianAccording to the formula
Figure FDA0003363234580000022
Calculating the expansion step length delta a of other points of the front end of the cracki；
ΔKeq,iThe effective stress intensity factor amplitude of the crack tip point is calculated by the formula
Figure FDA0003363234580000023
Figure FDA0003363234580000024
The effective stress intensity factor amplitude of the central point of the crack tip;
v*is the Poisson's ratio of the material;
by the formula
Figure FDA0003363234580000031
Calculating the angle theta of crack tip point propagationi；
i is the number of propagation steps, i is 1,2, …, t, t is the number of propagation steps until the crack propagates through the base plate or forms a macroscopic crack;
s303, setting a fatigue load ratio R based on the expansion step length delta aiAngle theta of crack tip propagationiAnd carrying out fatigue crack propagation on the steel-concrete combined structure fracture mechanical model under the pitting damage in Franc 3D.
6. The method for calculating the service life of the steel-concrete composite structure under the random pitting damage according to claim 5, wherein the concrete implementation manner of the step S4 includes: setting a second fatigue crack propagation rate parameter C according to the formula
Figure FDA0003363234580000032
Calculating the residual fatigue life N of the steel-concrete composite structure under the pitting damageiWhile obtaining the final propagation form of the fatigue crack, given N0＝0。
CN202111374180.6A 2021-11-19 2021-11-19 Service life calculation method of steel-concrete composite structure under random pitting damage Pending CN114036620A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116306153A (en) * 2023-03-24 2023-06-23 同济大学 Three-dimensional point cloud-based method for calculating fatigue life of post-rust steel plate

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116306153A (en) * 2023-03-24 2023-06-23 同济大学 Three-dimensional point cloud-based method for calculating fatigue life of post-rust steel plate
CN116306153B (en) * 2023-03-24 2024-02-02 同济大学 Three-dimensional point cloud-based method for calculating fatigue life of post-rust steel plate

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