CN114297885A - In-service bridge bearing capacity evaluation method without resistance information - Google Patents
In-service bridge bearing capacity evaluation method without resistance information Download PDFInfo
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Abstract
The invention discloses a method for evaluating the bearing capacity of an in-service bridge without resistance information; the method comprises the steps of firstly carrying out necessary investigation and detection to accurately estimate the automobile load grade which can be achieved by a bridge, establishing a finite element model to calculate the dead load effect and the standard value of the automobile load effect, further obtaining corresponding statistical parameters and a probability density function to establish a structural failure probability formula, carrying out inverse calculation on a test load effect value meeting a target reliable index by the failure probability formula, and directly evaluating the automobile load grade meeting the bearing capacity according to a test result after implementing a test working condition without carrying out structural detection calculation. The invention does not need resistance information and check calculation, has the advantages of basically the same field implementation procedure and load test, has the same cost, is concise, efficient and reliable in result, can adjust the target reliable index corresponding to the bearing capacity and the continuous service life, meets different management requirements, and has strong practicability and high popularization value.
Description
Technical Field
The invention belongs to the field of bridge bearing capacity evaluation, and particularly relates to an in-service bridge bearing capacity evaluation method without resistance information.
Background
The bearing capacity of the bridge is measured by the probability that the bridge achieves the safety, applicability and durability of the structure in the design reference period under the conditions of normal design, normal construction and normal use, namely when the reliability probability is greater than the target probability, the bearing capacity meets the requirement, otherwise, the bearing capacity does not meet the requirement. At present, two methods for evaluating the bearing capacity of an in-service bridge mainly comprise a check calculation evaluation method and a load test evaluation method.
The 'detection and calculation evaluation method' is evaluated according to a detection and calculation method specified in 'road and bridge bearing capacity detection and evaluation regulation' (JTG/T J21-2011). the method is based on probability theory, introduces a subentry detection and calculation coefficient correction limit state design expression through a detection means, and judges whether the requirement of bearing capacity is met or not according to a resistance and action effect comparison result. Besides determining the correction coefficient, the detection needs to obtain the information about the resistance and the action effect to calculate the representative value. The detection and calculation evaluation method belongs to a probability limit state design method, but is not a direct probability analysis method, each subentry coefficient in an expression is not directly determined according to a target reliable index, and a calculated structure reliable index has deviation from the direct probability analysis method.
The load test evaluation method is a method for applying an external load equivalent to the design effect on the bridge, testing the actual response of the structure and comparing the actual response with the calculated response to evaluate the stress condition of the bridge. The method has higher field cost and certain influence on traffic, but compared with an evaluation method, only the action effect needs to be calculated, the resistance does not need to be analyzed, the calculation and detection difficulty is lower, and the method is a conventional method for evaluating the bearing capacity of the bridge by more detection units. However, the effect of the structure in the load test is a common variable generated by short-term fixed-value load, is not equal to a random variable of the design effect in a design reference period, is not equivalent in the probability sense, and cannot obtain a reliable probability from the test result, so that the load test cannot directly evaluate the bearing capacity of the bridge.
The only available inspection and calculation evaluation method uses the corrected design state as the existing state to evaluate the actual bearing capacity of the in-service bridge, so that design and construction data related to inspection and calculation are needed. Due to the reasons of longer construction period of the bridge, replacement of management and maintenance units, and no attention paid to file management, the conditions of missing and incomplete design and construction data of the in-service bridge are common. Although part of calculated information can be obtained through field detection, design parameters related to resistance, such as material parameters, arrangement of reinforcing steel bars or prestressed steel beams, effective prestress and the like, are difficult to accurately test according to the existing nondestructive or semi-destructive detection method, the damage detection difficulty is high, the risk is high, the limitation is more, the cost is high, structural damage caused during sampling has certain influence on the bearing capacity, the repair effect is difficult to guarantee, and a management and maintenance unit is often not allowed to use. When resistance information cannot be obtained through a detection means or the information is inaccurate, the structure detection calculation can only calculate the resistance by referring to assumed relevant parameters after similar years and similar bridge types. Because the deviation between the selected parameters and the design parameters is uncontrollable, the result of the bearing capacity evaluation is unreliable, the management and maintenance of the bridge cannot be correctly guided, and the operation safety of the bridge is threatened.
In summary, aiming at the current situations that the existing bridge in service has no resistance information or unreliable information in China, and the existing bearing capacity evaluation method cannot effectively evaluate the bearing capacity of the bridge, in order to guarantee the operation safety of the bridge, a set of bridge bearing capacity evaluation method without resistance information is needed to be formed, so that the scientific management and maintenance of the bridge lacking resistance information are realized, and a reliable basis is provided for maintenance and reinforcement.
Disclosure of Invention
The invention aims to provide an in-service bridge bearing capacity evaluation method without resistance information. The method is based on the structural reliability theory, resistance distribution does not need to be obtained, bearing capacity detection calculation is not needed, the bearing capacity of the bridge can be rapidly evaluated directly according to the static load test result, the method is suitable for evaluating the bearing capacity of the in-service bridge which lacks design construction data and is difficult to obtain accurate resistance information through a detection means, and the problem that the bridge is not effectively evaluated is successfully solved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for evaluating the bearing capacity of an in-service bridge without resistance information comprises the following steps:
1) measuring geometric form parameters of the bridge and investigating the constant load condition;
2) finishing bridge appearance inspection, and mastering the structure deterioration and damage conditions; carrying out operation condition investigation to know the current bearing situation of the bridge;
3) integrating the construction age of the bridge, the route grade, the size of a main bearing component, the operation investigation condition, the appearance inspection result and the detection management information, and estimating the automobile load grade corresponding to the existing bearing capacity of the structure;
4) selecting a reliable index beta of a bridge targetfAnd from the target reliability indicator betafCalculating the maximum failure probability pfmax：
pfmax＝1-Φ(βf) (formula 1)
5) Establishing a structural finite element model according with the actual conditions of the bridge according to the investigation and detection results, and selecting a control section or a control part according to the most unfavorable stress principle;
6) respectively calculating the constant load effect standard value S at the test control section or the control part in the finite element modelGkAnd standard value S of automobile load effectQikWherein i is 1 … n, i and n are positive integers, n is the number of automobile load grades corresponding to the estimated existing bearing capacity of the structure (i in the subsequent step is the same), and S isQikSorting according to the sequence from small to large;
7) from S in step 6)GkAnd SQikCalculating random variable constant load effect SGAverage value of (d)SGAnd standard deviation σSGRandom variable automobile load effect SQiAverage value of (d)SQiAnd standard deviation σSQi：
μSG＝kSGSGk,σSG＝μSGδSG(formula 2)
μSQi＝kSQSQik,σSQi＝μSQiδSQ(formula 3)
In formula 2 and formula 3, kSG、kSQAnd deltaSG、δSQThe ratio and the variation coefficient of the average value and the standard value of the constant load effect and the automobile load effect are known constants respectively, and are selected according to the design of the reliability and the probability limit state of the highway bridge structure (people's traffic press, 1997);
8) random variable dead load effect SGFollowing a normal distribution, from S in step 7)GAverage value of (d)SGAnd standard deviation σSGTo obtain SGProbability density function fSG(sG)：
9) Random variable automobile load effect SQiObeying the extreme value type I distribution, from S in step 7)QiAverage value of (d)SQiAnd standard deviation σSQiTo obtain SQiProbability density function fSQi(sQi)：
fSQi(sQi)＝αexp[-α(sQi-γ)]·exp{-exp[-α(sQi-γ)]} (formula 5)
In formula 5, alpha is the size function of the distribution of the extreme type I according to
Calculating; gamma is a position parameter, in
Calculating; when the evaluation corresponds to the difference between the N' years of the continued service life and the N years of the design benchmark period, using gammaN'Instead of gamma, gammaN'Push button
Calculating;
10) back-computing p according to structural failure probability formula by iteration and numerical computation methodf＝pfmaxTime test load calculation effect S on control sectionSi(ii) a The structural failure probability formula is as follows:
11) carrying out load test working condition design in a finite element model to ensure that the calculation effect of the test load on a control section or a control part is not less than SSi；
12) Repeating the steps 7) to 11), and calculating the test load calculation effect S on the control section corresponding to each estimated automobile load gradeSi；
13) Selecting a control section, a control part or a position capable of effectively showing the response of the control section and the control part to arrange displacement and strain measuring points, and arranging crack observation points when stress cracks appear near the control section or the control part; s corresponding to the estimated automobile load gradeSiImplementing the working condition from small to large; grading loading is carried out on each working condition, and the grading number is properly increased compared with that of a conventional load test, and is generally not less than 3-5 grades; after each stage of loading is tested, whether the response of the main measuring point exceeds a calculated value or not and whether cracks are obviously expanded or other abnormal conditions exist or not are checked, and the loading is stopped in time to ensure the safety of the test;
14) and after the test is finished, evaluating the bearing capacity of the bridge according to the test result.
The invention further illustrates that the derivation process of the structural failure probability formula is as follows:
reliability and resistance R of bridge structure, and constant load effect SGAnd the effect of the vehicle load SQiIn this regard, the function Z is therefore:
Z＝R-SG-SQi(formula 7)
Because the load test is to apply determined load to the bridge structure, the structure has the risk of damage during the test, and when the bridge generates the calculation effect S under the test load effectSiThe structure is not damaged or accumulated and damaged, the test is considered to be successful, and the resistance R of the structure is not less than the actual constant load effect SG0And SSiSumming; sG0Is a common constant value variable, can be taken as S because of small constant load variabilityG0＝μSGAnd due to kSG1.0148, formula 2 indicates SG0＝1.0148SGk≈SGk(ii) a Conservatively, the resistance R is considered equal to the actual dead load effect SG0And SSiSum, i.e. R ═ SG0+SSi＝SGk+SSiSubstituting equation 7 yields:
Z＝SGk+SSi-SG-SQi(formula 8)
Establishing failure probability p according to function and reliability theoryfThe analytical formula (2):
carrying out constant load effect probability density function f obtained in the step 8)SG(sG) And the probability density function f of the automobile load effect obtained in the step 9)SQi(sQi) Formula 6 can be obtained by substituting formula 9.
The invention further explains that the step 14) is specifically as follows: after the working condition corresponding to the ith estimated automobile load grade is finished, when the actually measured deflection or strain and the theoretical value thereof are in a linear relationship, the relative residual deflection or strain is not more than 20 percent, and the crack width does not exceed the specification of the road bridge bearing capacity detection evaluation regulation (JTG/T J21), the test is considered to be successful, the estimated bridge bearing capacity can meet the ith estimated automobile load grade requirement within N' years of continuous service life, otherwise, the estimated bridge bearing capacity cannot meet the requirement; and directly evaluating the unfinished test working condition that the corresponding automobile load grade requirement cannot be met.
The invention further explains that the step 1) comprises bridge deck line shape, arch ring line shape and main cable line shape measurement, bridge overall size, component size, bridge deck pavement and arch filler thickness measurement, bridge additional load survey, arch filler gravity measurement and the like.
The invention further illustrates that the step 2) is specifically as follows: carrying out detailed appearance disease inspection on the full bridge, wherein the inspection comprises an upper structure, a lower structure and a bridge deck system, mainly inspecting main bearing components, grasping the degradation and damage conditions of the structure, and analyzing the influence of diseases on the bearing capacity; and (4) surveying the operation condition of the bridge, including field survey and data lookup, analyzing the current bearing situation of the bridge, and providing basic data for predicting the grade of the bearable automobile load as a basis for disease analysis.
The invention further explains that the automobile load grade corresponding to the estimated existing bearing capacity of the structure in the step 3) comprises a plurality of grades, and the bearing capacity is estimated from low to high.
The invention further illustrates that the reliability index beta of the bridge target in the step 4)fSelecting according to the provision of unified design for reliability of highway engineering structure standard (JTG2120), and adjusting indexes of operated bridges in service according to management conditions and requirements.
Compared with the prior art, the invention has the following outstanding advantages:
1. the method is based on the reliability theory, analyzes the failure probability of the bridge according to the load test result, effectively evaluates the bearing capacity and the structural safety of the bridge, and solves the problem that the bridge lacking resistance information cannot accurately evaluate the bearing capacity. The method has the advantages of simplicity and convenience and directness of the load test, the field implementation procedure and the direct cost are basically the same as the load test, the congenital defect that the bearing capacity cannot be directly evaluated is overcome, the requirement of probability analysis on the bearing capacity is met, the bearing capacity can be evaluated only by the load test result without checking and calculating, and the method has strong practicability and high popularization value.
2. Compared with a detection and evaluation method, the method disclosed by the invention belongs to a direct probability analysis method, the bearing capacity is directly evaluated according to the target reliable index, the variability of each basic variable can be comprehensively and accurately considered, and the calculation precision is relatively high.
3. The method of the invention considers the influence on the probability distribution when the service life of the in-service bridge is different from the design reference period when calculating the automobile load effect, so that the bearing capacity can be evaluated according to different planned service lives, and simultaneously, the target reliable index can be adjusted according to the management and maintenance requirement, thereby providing more accurate basis for the management and maintenance decision of the in-service bridge.
Drawings
FIG. 1 is a schematic view of a control beam of an embodiment of the present invention.
FIG. 2 is a diagram of a bridge finite element model according to an embodiment of the present invention.
The reference numerals in fig. 1 are: 1-boundary beam control beam piece, 2-middle beam control beam piece.
Detailed Description
The following detailed description of specific embodiments of the present invention is provided by way of example, and it should be understood that the scope of the present invention is not limited to the specific embodiments.
The current effective method for evaluating the bearing capacity of the existing bridge in service only comprises a check calculation evaluation method, but the method requires to obtain enough resistance design parameters, and provides a method for evaluating the bearing capacity of the existing bridge in service without resistance information aiming at the current situation that more design construction data of the existing bridge in service are lost and the existing detection means are difficult to accurately test the check calculation parameters. The method comprises the steps of firstly carrying out necessary investigation and detection to accurately estimate the automobile load grade which can be achieved by a bridge, establishing a finite element model to calculate the dead load effect and the standard value of the automobile load effect, further obtaining corresponding statistical parameters and a probability density function to establish a structural failure probability formula, carrying out inverse calculation on a test load effect value meeting a target reliable index by the failure probability formula, and directly evaluating the automobile load grade meeting the bearing capacity according to a test result after implementing a test working condition without carrying out structural detection calculation. The failure probability formula is established on the basis of replacing resistance variables with resistance lower limits which are load effects borne by the bridge in a load test, so that the failure probability of the bridge with unknown resistance distribution can be calculated, and the effective evaluation of the bearing capacity of the bridge in service lacking resistance information is completed.
Example (b):
a method for evaluating the bearing capacity of an in-service bridge without resistance information comprises the following specific steps:
s1, in order to correctly calculate the dead load effect and establish a structure finite element model which is consistent with the actual condition, the geometric form parameters of the bridge are measured and the dead load condition is investigated. The method specifically comprises bridge deck line shape, arch ring line shape and main cable line shape measurement, bridge overall size, component size, bridge deck pavement and arch filler thickness measurement, bridge additional load investigation, arch filler gravity measurement and the like.
S2, carrying out detailed appearance defect inspection on the full bridge, wherein the inspection comprises an upper structure, a lower structure and a bridge deck system, mainly inspecting main bearing components, grasping the structure deterioration and damage conditions, and analyzing the influence of the defects on the bearing capacity; and (4) surveying the operation condition of the bridge, including field survey and data lookup, analyzing the current bearing situation of the bridge, and providing basic data for predicting the grade of the bearable automobile load as a basis for disease analysis.
And S3, conjecturing the design standard adopted by the original design of the bridge and the actual bearing capacity of the bridge according to the data of S1 and S2 and by combining the construction age of the bridge, the route grade and the detection management and maintenance data, and obtaining the estimated automobile load grade. If the estimated grade is not the lowest grade in the corresponding standard, the estimated grade can comprise a plurality of grades, and the bearing capacity is estimated from low to high.
S4, bridge target reliability index betafThe method can be selected according to the provision of unified design for reliability of highway engineering (JTG2120), but the provision of the standard is a target reliability index of a proposed bridge, and the same index is still adopted for an operated bridge in service possibly to be inappropriate, so that a management and maintenance unit can adjust the index according to management and maintenance conditions and requirements. After determining the reliability index, the target reliability index betafCalculating the maximum failure probability pfmax：
pfmax＝1-Φ(βf) (formula 1)
And S5, establishing a structure finite element model according with the actual conditions of the bridge according to the investigation and detection results, analyzing the stress unfavorable position of the structure, and determining the control section or the control part of the test working condition by combining the appearance inspection condition.
S6, respectively calculating the constant load effect standard value S at the test control section or the control part in the finite element modelGkAnd standard value S of automobile load effectQikWherein i is 1 … n, i and n are positive integers, n is the number of the estimated bearing capacity corresponding to the automobile load grade (i in the subsequent step is the same), and S isQikIn order from small to large.
S7, step S6GkAnd SQikCalculating random variable constant load effect SGAverage value of (d)SGAnd standard deviation σSGRandom variable automobile load effect SQiAverage value of (d)SQiAnd standard deviation σSQi：
μSG＝kSGSGk,σSG＝μSGδSG(formula 2)
μSQi＝kSQSQik,σSQi＝μSQiδSQ(formula 3)
In formula 2-formula 3, kSG、kSQAnd deltaSG、δSQThe ratio and the variation coefficient of the average value and the standard value of the constant load effect and the automobile load effect are known constants and are selected according to the design of the reliability and the probability limit state of the highway bridge structure (people's traffic press, 1997).
S8, constant load effect SGSubject to a normal distribution, represented by S in step S7GAverage value of (d)SGAnd standard deviation σSGTo obtain SGProbability density function fSG(sG)：
S9, vehicle load effect SQiSubject to extreme value type I distribution, by S in step S7QiMean value of μSQiAnd standard deviation σSQiTo obtain SQiProbability density function fSQi(sQi)：
fSQi(sQi)＝αexp[-α(sQi-γ)]·exp{-exp[-α(sQi-γ)]} (formula 5)
In formula 5, alpha is the size function of the distribution of the extreme type I according to
Calculating; gamma is a position parameter, in
And (4) calculating. When the evaluation corresponds to the difference between the N' years of the continued service life and the N years of the design benchmark period, using gammaN'Instead of gamma, gammaN'Push button
And (4) calculating.
S10, when the test is successful, it can be considered that the resistance R is equal to the actual constant load effect SG0And the test load effect SSiSum of, and sum of k is small in the variation of dead loadSGObtaining S by approximating 1G0≈SGkThe function Z of the derived structure is SGk+SSi-SG-SQiAnd then establishing a failure probability analytic expression, substituting the random variable probability density function expression obtained in the steps S8-S9 into the failure probability analytic expression, and deriving a structural failure probability formula. Back-computing p by structural failure probability expression through iteration and numerical computation methodf＝pfmaxTime test load calculation effect S on control sectionSi. The failure probability formula is:
s11, adjusting the position and size of the test load in the finite element model to make the calculation effect of the test load on the control section or the control part not less than SSi。
S12, heavyRepeating the steps S7-S11, and calculating the effect S of the test load corresponding to the n estimated automobile load grades on the control sectionSi。
And S13, arranging the test section at the control section or the control part, and selecting a position capable of effectively reflecting the measured response when the test section is not arranged conveniently. The test contents mainly include displacement and strain, and the cable force is also tested for a guy cable, a suspender and the like. In addition, structural cracks need to be observed in a key point, important typical cracks are carefully selected, the number of measuring points is sufficient, and the early warning purpose is achieved. Test condition according to SSiThe step of loading is carried out from small to large in a grading mode, grading quantity is properly increased compared with a common load test, each working condition is generally not less than 3-5 grades, and the effect increment is smaller when the grade is higher. After each stage of loading is tested, whether the response of the main measuring point exceeds a calculated value or not and whether cracks are obviously expanded or other abnormal conditions exist or not are checked, and the loading is stopped in time to ensure the safety of the test.
And S14, after the test is finished, evaluating the bearing capacity of the bridge according to the test result. After the working condition corresponding to the ith estimated automobile load grade is finished, when the actually measured deflection or strain and the theoretical value thereof are in a linear relationship, the relative residual deflection or strain is not more than 20 percent, and the crack width does not exceed the specification of the road bridge bearing capacity detection evaluation regulation (JTG/TJ21), the test is considered to be successful, the estimated bridge bearing capacity can meet the ith estimated automobile load grade requirement within N' years of continuous service life, and otherwise the estimated bridge bearing capacity does not meet the requirement. And directly evaluating the unfinished test working condition that the bearing capacity can not meet the corresponding automobile load grade requirement.
To further illustrate how the present invention may be carried out, the following description is provided by way of examples of applications which are made with reference to the above-described steps and equations.
Application example:
the upper structure of a certain bridge adopts a prefabricated reinforced concrete simply-supported hollow slab beam which is arranged in a single-width mode, the span combination is 1 multiplied by 13m, 11 hollow slabs are transversely arranged, and a slab rubber support is arranged below. The lower structure adopts a U-shaped gravity type bridge abutment to enlarge the foundation. The bridge deck pavement is a concrete pavement layer, and the guardrail is a reinforced concrete wall type guardrail. The bridge is built in 2005 and is positioned on a secondary highway, the full length is 31.30m, the full width is 11.76m, and no sidewalk is arranged.
The bridge has no design and construction data, and the structure size is measured on site. And (4) investigating or detecting the constant load condition, the operation condition and the appearance disease on site.
Before and after the construction of the bridge is implemented in general road and bridge design Specifications (JTG D60-2004), the design load grade can still be selected according to the general road and bridge Specifications (JTJ 021-89), and the estimated design load grade is road-II grade specified in the general road and bridge design Specifications (JTG D60-2004) and steam-20 grade specified in the general road and bridge Specifications (JTJ 021-89) in combination with the route grade. Considering that the bridge deck has fewer heavy vehicles, but more through transverse cracks appear in the hollow slab, and a plurality of the through transverse cracks are wider than the limit, and increasing the steam-15 grade in the general Specification for highways and culverts (JTJ 021-89) as the estimated design load grade. Therefore, 3 estimated automobile load grades are set at this time, namely a steam-15 grade, a steam-20 grade and a highway-II grade.
A highway newly built in 5 years by the local government plans to shunt more than 30% of traffic of the bridge, and a management and maintenance unit plans to reduce a target reliable index so as to reduce maintenance cost, so that the determined target reliable index is reduced by one level compared with 4.2 of the newly built bridge, namely the target reliable index is 3.7. Corresponding maximum probability of failure pfmax＝1.078×10-4. The continuous service life N' is calculated by deducting the operating time from the design reference period and is 85 years.
Establishing a finite element model by detection and investigation data, respectively selecting an edge beam and a middle beam as control beam pieces, calculating the constant load standard value S of the edge beam and the middle beam at the control section by taking the midspan section as the control section according to the stress characteristics of the simply supported beamGAnd the standard value S of the automobile load under different estimated automobile load gradesQi(i ═ 1, 2, 3). After establishing the failure probability expression according to the methods of the steps S7-S12, compiling a reverse iterative program of a JC method (namely, an improved one-time second-order moment method) by matlab software to solve the failure probability pf＝pfmaxTime test load calculation effect S on control sectionSi(i-1, 2, 3) and the results are shown in the table1。
TABLE 1 Cross section test calculation results table (unit: kN. m)
Due to SS1And SS2The numerical values are very close, the test is combined into a test working condition during test implementation, the working conditions of the corresponding side beam and the middle beam are respectively working condition 1 and working condition 2, and the loading is divided into 3 levels; and verifying that the working conditions of the corresponding boundary beam and the middle beam are respectively called working condition 3 and working condition 4 when the automobile is at the-20 level, and the loading is carried out by 5 levels, wherein the first 3 levels are 3 levels of the working conditions 1 (2). In order to obtain the residual strain and deflection of each stage, the actually measured elastic response of each stage is calculated, and a mode of loading one stage and unloading one stage is adopted during the test. The test section is the same as the control section, a midspan section is taken, and strain and deflection measuring points are arranged on the bottom surface of each hollow slab; and 3 crack width change measuring points are arranged on the bottom surface near the span of the control beam in an overlimit width transverse crack arrangement mode, and the width change of the crack in the test process is tested. Applying test load according to the size of the working condition serial number, comparing the actual measurement response and the theoretical calculation size of the structure in real time by a detector during the test, observing the linear relation between the actual measurement response and the theoretical calculation size, checking whether the residual strain or deflection exceeds 20 percent after each stage of unloading, checking the expansion condition of cracks near a control section, and ensuring that the abnormal change of the structure can be found in time.
Under the working conditions 1 and 2, the actually measured deflection and strain are in a linear relation with theoretical values thereof, the relative residual deflection or strain is not more than 20%, cracks are not expanded, the test is considered to be successful, and the evaluation of the bearing capacity of the bridge can reach the requirements of grade-15 and grade-II of the highway within 85 years of continuous service life. When the load is loaded to the 4 th level of the working condition 3, the width of a crack measuring point at one position of the boundary beam is increased from 0.22mm to 0.26mm, the width is 0.24mm after the load is unloaded, the crack is not completely recovered, and the crack is found to extend from the bottom surface to the outer side surface. As the cracks of the hollow slab are expanded, the original cracks are more, the appearance condition is poor, the test is stopped, and the bearing capacity of the bridge cannot meet the requirement of steam-20 grade within 85 years of the continuous service life.
TABLE 2 Cross-section deflection result table under working condition 1 and working condition 2
TABLE 3 Cross-section strain results table for working condition 1 and working condition 2
The bearing capacity of the in-service bridge is successfully evaluated according to the load test result under the condition of no resistance information by the method, the structural check calculation is not needed, the resistance parameter acquisition deviation caused by design and construction data loss is avoided, the target reliable index and the continuous service life can be adjusted according to the management and maintenance requirement, and the management and maintenance requirement is well met. Therefore, the method has good application effect on engineering and has high popularization value.
The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.
Claims (7)
1. A method for evaluating the bearing capacity of an in-service bridge without resistance information is characterized by comprising the following steps:
1) measuring geometric form parameters of the bridge and investigating the constant load condition;
2) finishing bridge appearance inspection, and mastering the structure deterioration and damage conditions; carrying out operation condition investigation to know the current bearing situation of the bridge;
3) integrating the construction age of the bridge, the route grade, the size of a main bearing component, the operation investigation condition, the appearance inspection result and the detection management information, and estimating the automobile load grade corresponding to the existing bearing capacity of the structure;
4) selecting a reliable index beta of a bridge targetfAnd from the target reliability indicator betafCalculating the maximum failure probability pfmax：
pfmax＝1-Φ(βf) (formula 1)
5) Establishing a structural finite element model according with the actual conditions of the bridge according to the investigation and detection results, and selecting a control section or a control part according to the most unfavorable stress principle;
6) respectively calculating the constant load effect standard value S at the test control section or the control part in the finite element modelGkAnd standard value S of automobile load effectQikWherein i is 1 … n, i and n are positive integers, n is the number of automobile load grades corresponding to the estimated existing bearing capacity of the structure, and SQikSorting according to the sequence from small to large;
7) from S in step 6)GkAnd SQikCalculating random variable constant load effect SGAverage value of (d)SGAnd standard deviation σSGRandom variable automobile load effect SQiAverage value of (d)SQiAnd standard deviation σSQi：
μSG＝kSGSGk,σSG＝μSGδSG(formula 2)
μSQi＝kSQSQik,σSQi＝μSQiδSQ(formula 3)
In formula 2 and formula 3, kSG、kSQAnd deltaSG、δSQThe ratio and the variation coefficient of the average value and the standard value of the constant load effect and the automobile load effect are known constants respectively, and are selected according to the design of the reliability and the probability limit state of the highway bridge structure (people's traffic press, 1997);
8) random variable dead load effect SGFollowing a normal distribution, from S in step 7)GAverage value of (d)SGAnd standard deviation σSGTo obtain SGProbability density function fSG(sG)：
9) Random variable automobile load effect SQiObeying the extreme value type I distribution, from S in step 7)QiAverage value of (d)SQiAnd standard deviation σSQiTo obtain SQiProbability density function fSQi(sQi)：
fSQi(sQi)＝αexp[-α(sQi-γ)]·exp{-exp[-α(sQi-γ)]} (formula 5)
In formula 5, alpha is the size function of the distribution of the extreme type I according to
Calculating; gamma is a position parameter, in
Calculating; when the evaluation corresponds to the difference between the N' years of the continued service life and the N years of the design benchmark period, using gammaN'Instead of gamma, gammaN'Push button
Calculating;
10) back-computing p according to structural failure probability formula by iteration and numerical computation methodf＝pfmaxTime test load calculation effect S on control sectionSi(ii) a The structural failure probability formula is as follows:
11) carrying out load test working condition design in a finite element model to ensure that the calculation effect of the test load on a control section or a control part is not less than SSi；
12) Repeating the steps 7) to 11), and calculating the test corresponding to each estimated automobile load gradeCalculation of the effect S of the load on the control sectionSi；
13) Selecting a control section, a control part or a position capable of effectively showing the response of the control section and the control part to arrange displacement and strain measuring points, and arranging crack observation points when stress cracks appear near the control section or the control part; s corresponding to the estimated automobile load gradeSiImplementing the working condition from small to large; grading loading is carried out on each working condition, and the grading number is properly increased compared with that of a conventional load test, and is generally not less than 3-5 grades; after each stage of loading is tested, whether the response of the main measuring point exceeds a calculated value or not and whether cracks are obviously expanded or other abnormal conditions exist or not are checked, and the loading is stopped in time to ensure the safety of the test;
14) and after the test is finished, evaluating the bearing capacity of the bridge according to the test result.
2. The in-service bridge bearing capacity evaluation method without resistance information according to claim 1, characterized in that: the derivation process of the structural failure probability formula is as follows:
reliability and resistance R of bridge structure, and constant load effect SGAnd the effect of the vehicle load SQiIn this regard, the function Z is therefore:
Z＝R-SG-SQi(formula 7)
Because the load test is to apply determined load to the bridge structure, the structure has the risk of damage during the test, and when the bridge generates the calculation effect S under the test load effectSiThe structure is not damaged or accumulated and damaged, the test is considered to be successful, and the resistance R of the structure is not less than the actual constant load effect SG0And SSiSumming; sG0Is a common constant value variable, can be taken as S because of small constant load variabilityG0＝μSGAnd due to kSG1.0148, formula 2 indicates SG0＝1.0148SGk≈SGk(ii) a Conservatively, the resistance R is considered equal to the actual dead load effect SG0And SSiSum, i.e. R ═ SG0+SSi＝SGk+SSiSubstituting equation 7 yields:
Z＝SGk+SSi-SG-SQi(formula 8)
Establishing failure probability p according to function and reliability theoryfThe analytical formula (2):
carrying out constant load effect probability density function f obtained in the step 8)SG(sG) And the probability density function f of the automobile load effect obtained in the step 9)SQi(sQi) Formula 6 can be obtained by substituting formula 9.
3. The in-service bridge bearing capacity evaluation method without resistance information according to claim 1, characterized in that: the step 14) is specifically as follows: after the working condition corresponding to the ith estimated automobile load grade is finished, when the actually measured deflection or strain and the theoretical value thereof are in a linear relationship, the relative residual deflection or strain is not more than 20 percent, and the crack width does not exceed the specification of the road bridge bearing capacity detection evaluation regulation (JTG/T J21), the test is considered to be successful, the estimated bridge bearing capacity can meet the ith estimated automobile load grade requirement within N' years of continuous service life, otherwise, the estimated bridge bearing capacity cannot meet the requirement; and directly evaluating the unfinished test working condition that the corresponding automobile load grade requirement cannot be met.
4. The in-service bridge bearing capacity evaluation method without resistance information according to claim 1, characterized in that: the step 1) comprises bridge deck line shape, arch ring line shape and main cable line shape measurement, bridge overall size, component size, bridge deck pavement and arch filler thickness measurement, bridge additional load survey and arch filler gravity measurement.
5. The in-service bridge bearing capacity evaluation method without resistance information according to claim 1, characterized in that: the step 2) is specifically as follows: carrying out detailed appearance disease inspection on the full bridge, wherein the inspection comprises an upper structure, a lower structure and a bridge deck system, mainly inspecting main bearing components, grasping the degradation and damage conditions of the structure, and analyzing the influence of diseases on the bearing capacity; and (4) surveying the operation condition of the bridge, including field survey and data lookup, analyzing the current bearing situation of the bridge, and providing basic data for predicting the grade of the bearable automobile load as a basis for disease analysis.
6. The in-service bridge bearing capacity evaluation method without resistance information according to claim 1, characterized in that: and 3) estimating the automobile load grade corresponding to the existing bearing capacity of the structure in the step 3), wherein the automobile load grade comprises a plurality of grades, and the bearing capacity is estimated from low to high.
7. The in-service bridge bearing capacity evaluation method without resistance information according to claim 1, characterized in that: the reliability index beta of the bridge target in the step 4)fSelecting according to the provision of unified design for reliability of highway engineering structure standard (JTG2120), and adjusting indexes of operated bridges in service according to management conditions and requirements.
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| CN118278093A (en) * | 2024-05-31 | 2024-07-02 | 华东交通大学 | Method, system and equipment for determining target reliability of old road bridge bearing capacity |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114925440A (en) * | 2022-07-22 | 2022-08-19 | 交通运输部公路科学研究所 | Evaluation method and device for performance of waveform beam guardrail, storage medium and electronic equipment |
| CN114925440B (en) * | 2022-07-22 | 2022-10-21 | 交通运输部公路科学研究所 | Evaluation method and device for performance of waveform beam guardrail, storage medium and electronic equipment |
| CN118278093A (en) * | 2024-05-31 | 2024-07-02 | 华东交通大学 | Method, system and equipment for determining target reliability of old road bridge bearing capacity |
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