A method for evaluating the bearing capacity of in-service bridges without requiring resistance information

Abstract

The present invention discloses a method for assessing the bearing capacity of an in-service bridge that does not require resistance information. The method first conducts necessary investigations and tests to correctly estimate the automobile load level that the bridge may reach, establishes a finite element model to calculate the standard values ​​of the dead load effect and the automobile load effect, further obtains corresponding statistical parameters and probability density functions to establish a structural failure probability formula, and reversely calculates the test load effect value that meets the target reliability index from the failure probability formula. After implementing the test conditions, the automobile load level that the bearing capacity meets is directly assessed according to the test results without the need for structural verification. The present invention does not require resistance information or verification, and the on-site implementation procedure is basically the same as that of the load test, with comparable costs. It has the advantages of simplicity, efficiency, and reliable results, and can adjust the target reliability index and the continued service life corresponding to the bearing capacity to meet different maintenance needs. It has strong practicality and high promotion value.

Description

Technical Field

[0001] The invention belongs to the field of bridge bearing capacity assessment, and in particular relates to a method for assessing the bearing capacity of an in-service bridge without requiring resistance information. Background Art

[0002] The bearing capacity of a bridge is measured by the probability that the bridge will achieve structural safety, serviceability, and durability under normal design, construction, and use conditions within the design reference period. When the reliability probability exceeds the target probability, the bearing capacity meets the requirements; otherwise, it fails to meet them. Currently, there are two main methods for assessing the bearing capacity of in-service bridges: calculation and load testing.

[0003] The "verification and evaluation method" is based on the verification methods specified in the "Regulations for the Inspection and Evaluation of the Bearing Capacity of Highway Bridges" (JTG / T J21-2011). This method is based on probability theory and uses testing methods to introduce sub-item verification coefficients to modify the limit state design expression. The comparison of resistance and action effects determines whether the bearing capacity requirements are met. In addition to determining the correction coefficient, the verification calculation also requires obtaining relevant information on resistance and action effects to calculate their representative values. The verification and evaluation method is a probabilistic limit state design method, but it is not a direct probability analysis method. The sub-item coefficients in the expression are not directly determined according to the target reliability index, and the calculated structural reliability index deviates from that of the direct probability analysis method.

[0004] The "load test assessment method" is a method of assessing the bridge's stress condition by applying an external load equivalent to the design action to the bridge, testing the actual response of the structure, and comparing it with the calculated response. This method has high on-site costs and has a certain impact on traffic. However, compared to the verification method, it only requires calculating the action effect and does not require analyzing the resistance. The calculation and testing are less difficult, and it is a common method used by many inspection units to assess the bearing capacity of bridges. However, because the structural action effect in the load test is an ordinary variable generated by a short-term constant load, it is not equivalent to the random variable of the design action effect within the design reference period. It is not "equivalent" in the probabilistic sense, and reliable probabilities cannot be derived from the test results. Therefore, load tests cannot directly assess the bearing capacity of bridges.

[0005] The only available verification and assessment method uses a revised design state as the current state to assess the actual load-bearing capacity of an in-service bridge. Therefore, relevant design and construction data are required for verification. Due to the age of bridges, changes in maintenance organizations, and a lack of attention to archival management, lost or incomplete design and construction data for in-service bridges is common. While some calculation information can be obtained through on-site testing, existing non-destructive or semi-destructive testing methods make it difficult to accurately measure design parameters related to load resistance, such as material parameters, reinforcement or prestressed tendon layout, and effective prestress. Destructive testing is difficult, risky, restrictive, and expensive. Structural damage caused during sampling can affect load-bearing capacity, and repair effectiveness is difficult to guarantee, leading maintenance organizations to often refuse to use it. When resistance information cannot be obtained through testing or is inaccurate, structural verification can only calculate resistance by assuming relevant parameters based on references to similar bridges of similar age and type. Uncontrollable deviations between the selected parameters and the design parameters render the load-bearing capacity assessment results unreliable, hindering accurate guidance for bridge maintenance and posing a threat to bridge operational safety.

[0006] In summary, given the widespread lack of resistance information or unreliable information on in-service bridges in my country, and the inability of existing bearing capacity assessment methods to effectively evaluate the bearing capacity of such bridges, it is necessary to develop a set of bridge bearing capacity assessment methods that do not require resistance information to ensure the safety of bridge operations, so as to achieve scientific management and maintenance of bridges that lack resistance information and provide a reliable basis for repair and reinforcement. Summary of the Invention

[0007] The present invention aims to provide a method for assessing the bearing capacity of in-service bridges without requiring resistance information. This method, based on structural reliability theory, eliminates the need for obtaining resistance distribution or performing load-bearing capacity calculations. Instead, it can rapidly assess the bearing capacity of bridges based directly on static load test results. This method is suitable for assessing the bearing capacity of in-service bridges where design and construction data are lacking and accurate resistance information cannot be obtained through testing. This method successfully addresses the lack of effective assessment methods for such bridges.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for evaluating the bearing capacity of an in-service bridge without requiring resistance information comprises the following steps:

[0010] 1) Measure bridge geometric parameters and investigate dead load conditions;

[0011] 2) Complete the appearance inspection of the bridge to understand the structural deterioration and damage; conduct an operation survey to understand the current load-bearing status of the bridge;

[0012] 3) Estimate the vehicle load level corresponding to the structure's current load-bearing capacity based on the bridge's construction year, route grade, dimensions of major load-bearing components, operational survey results, appearance inspection results, and inspection and maintenance data;

[0013] 4) Select the bridge target reliability index β f , and the target reliability index β f Calculate the maximum failure probability p fmax :

[0014] p fmax =1-Φ(β f ) (Formula 1)

[0015] 5) Establish a structural finite element model that conforms to the actual conditions of the bridge based on the investigation and test results, and select the control section or control part according to the most unfavorable stress principle;

[0016] 6) Calculate the standard value of the dead load effect S at the test control section or control position in the finite element model Gk and the standard value of vehicle load effect S Qik , where i = 1…n, i and n are both positive integers, n is the number of vehicle load levels corresponding to the estimated structure's existing bearing capacity (i in the following steps has the same meaning), S Qik Sort by smallest to largest;

[0017] 7) From S in step 6) Gk and S Qik Calculate the random variable dead load effect S G The average value μ SG and standard deviation σ SG , random variable vehicle load effect S Qi The average value μ SQi and standard deviation σ SQi :

[0018] μ SG =k SG S Gk ,σ SG =μ SG δ SG (Formula 2)

[0019] μ SQi =k SQ S Qik ,σ SQi =μ SQi δ SQ (Formula 3)

[0020] In Equations 2 and 3, k SG 、k SQ and δ SG , δ SQare the ratio of the average value to the standard value and the coefficient of variation of the dead load effect and vehicle load effect, respectively. Both are known constants and are selected according to Reliability and Probabilistic Limit State Design of Highway Bridge Structures (People's Communications Press, 1997);

[0021] 8) Random variable dead load effect S G Obeying the normal distribution, from S in step 7) G The average value μ SG and standard deviation σ SG Get S G The probability density function f SG (s G ):

[0022]

[0023] 9) Random variable vehicle load effect S Qi Obeying the extreme value type I distribution, from S in step 7) Qi The average value μ SQi and standard deviation σ SQi Get S Qi The probability density function f SQi (s Qi ):

[0024] f SQi (s Qi )=αexp[-α(s Qi -γ)]·exp{-exp[-α(s Qi -γ)]} (Equation 5)

[0025] In formula 5, α is the size function of extreme value type I distribution, according to Calculation; γ is the position parameter, according to Calculation; when the corresponding service life N' years is different from the design reference period N years, use γ N' Instead of γ, γ N' according to calculate;

[0026] 10) Through iterative and numerical calculation methods, calculate p according to the structural failure probability formula f =p fmax The test load at the time of calculation of the effect S on the control section Si ; The formula for the probability of structural failure is:

[0027]

[0028] 11) Design the load test conditions in the finite element model so that the calculated effect of the test load on the control section or control part is not less than S Si ;

[0029] 12) Repeat steps 7) to 11) to calculate the test load effect S on the control section corresponding to each estimated vehicle load level. Si ;

[0030] 13) Select the control section, control part or the position that can effectively reflect its response to arrange the displacement and strain measurement points. When the stress crack appears near the control section or control part, the crack observation point should also be arranged; according to the estimated vehicle load level corresponding to the S Si The working conditions should be implemented from small to large. Each working condition should be loaded in stages, and the number of stages should be appropriately increased compared to conventional load tests, generally not less than 3 to 5 stages. After each stage of loading, check whether the response of the main measuring points exceeds the calculated value, whether the cracks have obvious expansion or other abnormal conditions, and stop loading in time to ensure test safety.

[0031] 14) After the test, the bearing capacity of the bridge is evaluated based on the test results.

[0032] The present invention further illustrates that the derivation process of the structural failure probability formula is as follows:

[0033] Reliability of bridge structure and resistance R, dead load effect S G and vehicle load effect S Qi So the function Z is:

[0034] Z=RS G -S Qi (Equation 7)

[0035] Since the load test is to impose a certain load on the bridge structure, there is a risk of damage to the structure during the test. When the bridge produces the calculated effect S under the test load Si , the structure does not show any damage or cumulative damage, the test is considered successful, and the resistance R of the structure is not less than the actual dead load effect S G0 With S Si Sum; S G0 It is a common fixed value variable. Since the variability of the dead load is very small, S G0 =μ SG , and because k SG =1.0148, from formula 2 we can know that S G0 =1.0148S Gk ≈S Gk ; It is conservative to assume that the resistance R is equal to the actual dead load effect S G0 With S Si The sum of R=S G0 +S Si =S Gk +S Si , substituting into formula 7, we get:

[0036] Z=SGk +S Si -S G -S Qi (Equation 8)

[0037] According to the performance function and reliability theory, the failure probability p is established. f The analytical expression of :

[0038]

[0039] The probability density function of the dead load effect obtained in step 8) is SG (s G ) and the vehicle load effect probability density function f obtained in step 9) SQi (s Qi ) into Equation 9 to obtain Equation 6.

[0040] The present invention further illustrates that step 14) is specifically as follows: after completing the working condition corresponding to the i-th estimated vehicle load level, when the measured deflection or strain is linearly related to its theoretical value, the relative residual deflection or strain is not greater than 20%, and the crack width does not exceed the requirements of the "Highway Bridge Bearing Capacity Testing and Assessment Procedure" (JTG / T J21), the test is considered successful, and the bridge bearing capacity is assessed to be able to meet the i-th estimated vehicle load level requirements within the continued service life of N' years; otherwise, it is assessed as failing to meet the requirements; for test conditions that are not completed, they are directly assessed as failing to meet the corresponding vehicle load level requirements.

[0041] The present invention further illustrates that the step 1) includes measuring the bridge deck alignment, arch ring alignment, main cable alignment, overall bridge dimensions, component dimensions, bridge deck pavement and arch filler thickness, bridge additional load investigation, and arch filler weight determination.

[0042] The present invention further illustrates that step 2) specifically comprises: conducting a detailed appearance defect inspection of the entire bridge, including the superstructure, substructure, and bridge deck system, focusing on inspecting the main load-bearing components, understanding the structural deterioration and damage, and analyzing the impact of the defects on the bearing capacity; investigating the operation of the bridge, including on-site investigation and data review, analyzing the current load-bearing status of the bridge, and using this as a basis for defect analysis to provide basic data for estimating the level of automobile load that can be sustained.

[0043] The present invention further illustrates that the vehicle load level corresponding to the estimated existing load-bearing capacity of the structure in step 3) includes multiple levels, and the load-bearing capacity is evaluated from low to high.

[0044] The present invention further illustrates that the bridge target reliability index β in step 4) fThe selection is based on the provisions of the Unified Standard for Reliability Design of Highway Engineering Structures (JTG2120). At the same time, the indicators of existing bridges in operation are adjusted according to the maintenance conditions and needs.

[0045] Compared with the existing technology, the present invention has the following outstanding advantages:

[0046] 1. Based on reliability theory and load test results, this invention analyzes the probability of bridge failure, effectively evaluating the bridge's bearing capacity and structural safety, and resolving the challenge of accurately assessing the bearing capacity of bridges lacking resistance information. The method combines the simplicity and directness of load testing, with essentially the same on-site implementation procedures and direct costs as load testing, while overcoming its inherent inability to directly assess bearing capacity. It meets the need for probabilistic analysis of bearing capacity, enabling assessment of bearing capacity solely from load test results without the need for verification. This method possesses strong practicality and high promotional value.

[0047] 2. Compared with the verification and evaluation method, the method of the present invention belongs to the direct probability analysis method, which directly evaluates the carrying capacity based on the target reliability index, can comprehensively and accurately consider the variability of each basic variable, and has relatively high calculation accuracy.

[0048] 3. When calculating the vehicle load effect, the method of the present invention takes into account the impact of the continued service life of the in-service bridge and the design reference period on the probability distribution, so that the bearing capacity can be assessed for different planned service lives. At the same time, the target reliability index can be adjusted according to maintenance needs, providing a more accurate basis for maintenance decisions of in-service bridges. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram of the control beam piece of an application example of the present invention.

[0050] Figure 2 This is a finite element model diagram of a bridge as an application example of the present invention.

[0051] Figure 1 The numbers in the figures are: 1-side beam control beam piece, 2-center beam control beam piece. DETAILED DESCRIPTION

[0052] The specific embodiments of the present invention are described in detail below with reference to examples, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0053] Currently, the only effective method for assessing the bearing capacity of in-service bridges is verification and assessment. However, this method requires sufficient resistance design parameters. Given the lack of design and construction data for many in-service bridges, and the difficulty of accurately measuring verification and assessment parameters using existing testing methods, a new method for assessing the bearing capacity of in-service bridges that does not require resistance information is proposed. This method first conducts necessary investigations and testing to accurately estimate the potential vehicle load levels that the bridge will experience. A finite element model is then established to calculate standard values ​​for the dead load and vehicle load effects. Corresponding statistical parameters and probability density functions are then derived to establish a structural failure probability formula. This formula is then used to inversely calculate the test load effect value that meets the target reliability index. After conducting test conditions, the vehicle load level required for bearing capacity assessment is directly assessed based on the test results, eliminating the need for structural verification. This failure probability formula uses the load effect that the bridge can withstand during the load test as the lower resistance limit, replacing the resistance variable with this lower resistance limit. Therefore, it can calculate the failure probability of bridges with unknown resistance distributions, effectively assessing the bearing capacity of in-service bridges lacking resistance information.

[0054] Example:

[0055] A method for evaluating the bearing capacity of an in-service bridge without requiring resistance information, comprising the following steps:

[0056] S1. To accurately calculate the dead load effects and establish a realistic structural finite element model, it is necessary to measure bridge geometry and investigate the dead load conditions. This includes measuring the bridge deck alignment, arch ring alignment, and main cable alignment; measuring the overall bridge dimensions, component dimensions, deck pavement, and arch fill thickness; investigating the bridge's additional loads; and determining the weight of the arch fill.

[0057] S2: Conduct a detailed visual inspection of the entire bridge, including the superstructure, substructure, and deck system, with a focus on major load-bearing components, assess structural deterioration and damage, and analyze the impact of defects on the bridge's load-bearing capacity. Conduct an investigation into the bridge's operations, including on-site investigations and data review, to analyze the bridge's current load-bearing capacity. This analysis serves as the basis for defect analysis and provides basic data for estimating the level of vehicle loads it can withstand.

[0058] S3: Based on the data from S1 and S2, and in combination with the bridge's construction year, route grade, and inspection and maintenance data, the original design standards used in the bridge design and the bridge's actual load capacity are estimated to produce an estimated vehicle load level. If the estimated level is not the lowest level in the corresponding standard, multiple levels may be included to assess the load capacity from low to high.

[0059] S4, bridge target reliability index β fThe selection can be made according to the provisions of the Unified Standard for Reliability Design of Highway Engineering Structures (JTG2120). However, this standard specifies the target reliability index of the proposed bridge. It may not be appropriate to use the same index for the bridge in operation. Therefore, the maintenance unit can adjust the index according to the maintenance conditions and needs. After the reliability index is determined, the target reliability index β f Calculate the maximum failure probability p fmax :

[0060] p fmax =1-Φ(β f ) (Formula 1)

[0061] S5. Based on the investigation and test results, a structural finite element model that conforms to the actual conditions of the bridge is established, the unfavorable stress positions of the structure are analyzed, and the control sections or control parts of the test conditions are determined in combination with the appearance inspection.

[0062] S6, calculate the standard value of the dead load effect S at the test control section or control position in the finite element model Gk and the standard value of vehicle load effect S Qik , where i = 1…n, i and n are both positive integers, n is the number of vehicle load levels corresponding to the estimated carrying capacity (i in the subsequent steps has the same meaning), S Qik Sort by smallest to largest.

[0063] S7, by S in step S6 Gk and S Qik Calculate the random variable dead load effect S G The average value μ SG and standard deviation σ SG , random variable vehicle load effect S Qi The average value μ SQi and standard deviation σ SQi :

[0064] μ SG =k SG S Gk ,σ SG =μ SG δ SG (Formula 2)

[0065] μ SQi =k SQ S Qik ,σ SQi =μ SQi δ SQ (Formula 3)

[0066] In formula 2-3, k SG 、k SQ and δ SG , δ SQare the ratio of the average value to the standard value and the coefficient of variation of the dead load effect and vehicle load effect, respectively. Both are known constants and are selected according to Reliability and Probabilistic Limit State Design of Highway Bridge Structures (People's Communications Press, 1997).

[0067] S8, dead load effect S G Obeying the normal distribution, the S in step S7 G The average value μ SG and standard deviation σ SG Get S G The probability density function f SG (s G ):

[0068]

[0069] S9, vehicle load effect S Qi Obeying the extreme value type I distribution, the S in step S7 Qi Average value μ SQi and standard deviation σ SQi Get S Qi The probability density function f SQi (s Qi ):

[0070] f SQi (s Qi )=αexp[-α(s Qi -γ)]·exp{-exp[-α(s Qi -γ)]} (Equation 5)

[0071] In formula 5, α is the size function of extreme value type I distribution, according to Calculation; γ is the position parameter, according to When the corresponding service life N' years is different from the design reference period N years, use γ N' Instead of γ, γ N' according to calculate.

[0072] S10, when the test is successful, it can be conservatively assumed that the resistance R is equal to the actual dead load effect S G0 and test load effect S Si The sum of the constant load variability and k SG Close to 1 to get S G0 ≈S Gk , the structure function Z = S Gk +S Si -S G -S QiThen, the failure probability analytical formula is established, and the random variable probability density function expression obtained from steps S8-S9 is substituted into the failure probability analytical formula to derive the structural failure probability formula. The structural failure probability expression is inverted and calculated by iterative and numerical calculation methods. f =p fmax The test load at the time of calculation of the effect S on the control section Si The failure probability formula is:

[0073]

[0074] S11, adjust the test load position and size in the finite element model so that the calculated effect of the test load on the control section or control part is not less than S Si .

[0075] S12, repeat steps S7 to S11 to calculate the test load corresponding to n estimated vehicle load levels on the control section calculation effect S Si .

[0076] S13, the test section is generally arranged at the control section or control part. When it is inconvenient to arrange it, a location that can effectively reflect the measured response should be selected. The test content is mainly displacement and strain. For cables, hangers, etc., cable force should also be tested. In addition, the focus should be on observing structural cracks. Important typical cracks should be carefully selected, and the number of measurement points should be sufficient to achieve the purpose of early warning. The test conditions are as follows S Si The test is carried out from small to large, with graded loading. The number of grades should be appropriately increased compared to ordinary load tests. Each working condition should generally be no less than 3 to 5 grades. The higher the grade, the smaller the effect increment should be. After each loading stage, check whether the response of the main measuring points exceeds the calculated value, whether there is obvious crack expansion or other abnormal conditions, and stop loading in time to ensure test safety.

[0077] S14. After the test is completed, the bridge's bearing capacity is evaluated based on the test results. After completing the working condition corresponding to the i-th estimated vehicle load level, if the measured deflection or strain is linearly related to its theoretical value, the relative residual deflection or strain is no more than 20%, and the crack width does not exceed the requirements of the "Highway Bridge Bearing Capacity Testing and Assessment Procedure" (JTG / TJ21), the test is considered successful. The bridge's bearing capacity is assessed to meet the i-th estimated vehicle load level requirements within a continued service life of N' years. Otherwise, it is assessed as not meeting the requirements. For test conditions that fail to be completed, the bearing capacity is directly assessed as not meeting the corresponding vehicle load level requirements.

[0078] To further illustrate how to implement the present invention, an application example is given below for specific explanation. The application example is performed with reference to the above steps and formulas.

[0079] Application examples:

[0080] The superstructure of a certain bridge utilizes precast reinforced concrete simply supported hollow slab beams, arranged in a single span with a combined span of 1 x 13 meters. Eleven hollow slabs are arranged transversely, supported by plate-type rubber bearings. The substructure features U-shaped gravity abutments and expanded foundations. The bridge deck is paved with concrete, and the guardrails are reinforced concrete wall-type guardrails. The bridge, built in 2005, is located on a secondary highway. It is 31.30 meters long and 11.76 meters wide, with no sidewalks.

[0081] There is no design or construction documentation for this bridge, and all structural dimensions were measured on-site. On-site investigations or inspections were conducted on the dead load conditions, operational status, and external defects.

[0082] Since the bridge was built before or after the implementation of the "General Specification for the Design of Highway Bridges and Culverts" (JTG D60-2004), the design load level may still be selected according to the "General Specification for the Design of Highway Bridges and Culverts" (JTJ 021-89). Taking into account the route classification, the estimated design load level is "Highway-II" as specified in the "General Specification for the Design of Highway Bridges and Culverts" (JTG D60-2004) and "Automobile-20" as specified in the "General Specification for the Design of Highway Bridges and Culverts" (JTJ 021-89). Considering the low traffic volume on the bridge deck, but the presence of numerous transverse cracks in the hollow slab and several excessive widths, the "Automobile-15" level specified in the "General Specification for the Design of Highway Bridges and Culverts" (JTJ 021-89) has been added as an estimated design load level. Therefore, a total of three estimated vehicle load levels have been set: Automobile-15, Automobile-20, and Highway-II.

[0083] The local government plans to build a new expressway within five years, which will divert more than 30% of the bridge's traffic. The management and maintenance unit intends to lower the target reliability index to reduce maintenance costs. Therefore, the target reliability index is set one level lower than the 4.2 for the new bridge, that is, the target reliability index is 3.7. The corresponding maximum failure probability p fmax =1.078×10 -4 The continued service life N' is calculated by deducting the operating time from the design reference period, which is 85 years.

[0084] The finite element model was established based on the test and investigation data. One edge beam and one center beam were selected as the control beams. Based on the stress characteristics of the simply supported beam, the mid-span section was used as the control section. The standard value of the dead load S of the edge beam and the center beam at the control section was calculated. G and the standard value of vehicle load S under different estimated vehicle load levels Qi (i=1, 2, 3). After establishing the failure probability expression according to the method of steps S7 to S12, use MATLAB software to compile the reverse iteration program of the JC method (i.e., the improved first-order second-moment method) to solve the failure probability p f =p fmax The test load at the time of calculation of the effect S on the control section Si((i=1, 2, 3), the calculation results are shown in Table 1.

[0085] Table 1 Mid-span section test calculation effect results (unit: kN.m)

[0086]

[0087] Because S S1 and S S2 The values ​​are very close. They are combined into one test condition during the test. The conditions corresponding to the side beams and the center beams are condition 1 and condition 2 respectively, with three levels of loading. When verifying the car-20 level, the conditions corresponding to the side beams and the center beams are called condition 3 and condition 4 respectively, with five levels of loading. The first three levels are the three levels of condition 1 (2). In order to obtain the residual strain and deflection of each level and calculate the measured elastic response of each level, the test adopts the method of loading one level and unloading one level. The test section is the same as the control section. The mid-span section is taken, and strain and deflection measuring points are arranged on the bottom surface of each hollow slab. Three excessive width transverse cracks on the bottom surface near the mid-span of the control beam are selected to arrange crack width change measuring points to test the width change of the cracks during the test. The test load is applied according to the size of the condition number. During the test, the inspection personnel compare the measured response of the structure with the theoretical calculation size in real time and observe the linear relationship between the two. After each level of unloading, the residual strain or deflection is checked to see if it exceeds 20%, and the expansion of the cracks near the control section is checked to ensure that abnormal changes in the structure can be discovered in time.

[0088] Under Conditions 1 and 2, the measured deflections and strains showed a linear relationship with their theoretical values, the relative residual deflection or strain was no greater than 20%, and the cracks did not expand. The test was considered successful, and the bridge's bearing capacity was assessed to meet the requirements of Class 15 for Automotive and Class II for Highway within 85 years of continued service. During loading at Level 4 of Condition 3, the width of a crack at a measured point in the edge beam increased from 0.22mm to 0.26mm. After unloading, the width was 0.24mm, indicating incomplete recovery. The crack was also observed to have extended from the bottom to the outer side. Due to the expansion of the hollow slab crack, the large number of existing cracks, and the poor appearance, the test was terminated. The bridge's bearing capacity was assessed to be unable to meet the requirements of Class 20 for Automotive within 85 years of continued service.

[0089] Table 2 Deflection results of mid-span section for working conditions 1 and 2

[0090]

[0091] Table 3 Strain results of mid-span sections for working conditions 1 and 2

[0092]

[0093] In the above example, the method of the present invention successfully assessed the bearing capacity of an in-service bridge using load test results in the absence of resistance information. This method eliminates the need for structural calculations and avoids errors in resistance parameter acquisition caused by missing design and construction data. Furthermore, the method can adjust the target reliability index and service life based on maintenance requirements, effectively adapting to maintenance needs. Therefore, this method has proven effective in engineering applications and has high potential for widespread adoption.

[0094] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for evaluating the bearing capacity of an in-service bridge without requiring resistance information, characterized in that The following steps are involved: 1) Measure bridge geometric parameters and investigate dead load conditions; 2) Complete the appearance inspection of the bridge to understand the structural deterioration and damage; conduct an operation survey to understand the current load-bearing status of the bridge; 3) Estimate the vehicle load level corresponding to the structure's current load-bearing capacity based on the bridge's construction year, route grade, dimensions of major load-bearing components, operational survey results, appearance inspection results, and inspection and maintenance data; 4) Select the bridge target reliability index β f , and the target reliability index β f Calculate the maximum failure probability p fmax : p fmax = 1 - Φ(β f ) (Equation 1) 5) Establish a structural finite element model that conforms to the actual conditions of the bridge based on the investigation and test results, and select the control section or control part according to the most unfavorable stress principle; 6) Calculate the standard value of the dead load effect S at the test control section or control position in the finite element model Gk and the standard value of vehicle load effect S Qik , where i = 1…n, i and n are both positive integers, n is the number of vehicle load levels corresponding to the estimated structure's existing bearing capacity, S Qik Sort by smallest to largest; 7) From S in step 6) Gk and S Qik Calculate the random variable dead load effect S G The average value μ SG and standard deviation σ SG , random variable vehicle load effect S Qi The average value μ SQi and standard deviation σ SQi : m SG =k SG S Gk ,s SG =μ SG d SG (formula 2) m SQi =k SQ S Qik ,s SQi =μ SQi d SQ (formula 3) In Equations 2 and 3, k SG 、k SQ and δ SG , δ SQ are the ratio of the average value to the standard value and the coefficient of variation of the dead load effect and vehicle load effect, respectively. Both are known constants and are selected according to Chapter 6, Section 2, "Analysis of Reliability Indicators under the Ultimate Limit State of Bearing Capacity," in "Reliability and Probabilistic Limit State Design of Highway Bridge Structures" (People's Communications Press, 1997); 8) Random variable dead load effect S G Obeying the normal distribution, from S in step 7) G The average value μ SG and standard deviation σ SG Get S G The probability density function f SG (s G ): 9) Random variable vehicle load effect S Qi Obeying the extreme value type I distribution, from S in step 7) Qi The average value μ SQi and standard deviation σ SQi Get S Qi The probability density function f SQi (s Qi ): f SQi (s Qi ) = α exp[-α(s Qi - γ)]·exp{-exp[-α(s Qi - γ)]} (Equation 5) In formula 5, α is the size function of extreme value type I distribution, according to Calculation; γ is the position parameter, according to Calculation; when the corresponding service life N' years is different from the design reference period N years, use γ N' Instead of γ, γ N' according to calculate; 10) Through iterative and numerical calculation methods, calculate p according to the structural failure probability formula f =p fmax The test load at the time of calculation of the effect S on the control section Si ; The formula for structural failure probability is: The derivation process of the structural failure probability formula is as follows: Reliability of bridge structure and resistance R, dead load effect S G and vehicle load effect S Qi So the function Z is: Z=RS G -S Qi (Equation 7) Since the load test is to impose a certain load on the bridge structure, there is a risk of damage to the structure during the test. When the bridge produces the calculated effect S under the test load Si , the structure does not show any damage or cumulative damage, the test is considered successful, and the resistance R of the structure is not less than the actual dead load effect S G0 With S Si Sum; S G0 It is a common fixed value variable. Since the variability of the dead load is very small, S G0 =μ SG , and because k SG =1.0148, from formula 2 we can know that S G0 =1.0148S Gk ≈S Gk ; It is conservative to assume that the resistance R is equal to the actual dead load effect S G0 With S Si The sum of R=S G0 +S Si =S Gk +S Si , substituting into formula 7, we get: Z=S Gk +S Si -S G -S Qi (Equation 8) According to the performance function and reliability theory, the failure probability p is established. f The analytical expression of : The probability density function of the dead load effect obtained in step 8) is SG (s G ) and the vehicle load effect probability density function f obtained in step 9) SQi (s Qi ) into formula 9 to obtain formula 6; 11) Design the load test conditions in the finite element model so that the calculated effect of the test load on the control section or control part is not less than S Si ; 12) Repeat steps 7) to 11) to calculate the test load effect S on the control section corresponding to each estimated vehicle load level. Si ; 13) Select the control section, control part or the position that can effectively reflect its response to arrange the displacement and strain measurement points. When the stress crack appears near the control section or control part, the crack observation point should also be arranged; according to the estimated vehicle load level corresponding to the S Si The working conditions should be implemented from small to large. Each working condition should be loaded in stages, and the number of stages should be appropriately increased compared to conventional load tests, not less than 3 stages. After each stage of loading, check whether the response of the main measuring points exceeds the calculated value, whether the cracks have obvious expansion or other abnormal conditions, and stop loading in time to ensure test safety. 14) After the test, the bearing capacity of the bridge is evaluated based on the test results.

2. The method for evaluating the bearing capacity of an in-service bridge without requiring resistance information according to claim 1, characterized in that: The step 14) is specifically as follows: after completing the working condition corresponding to the i-th estimated vehicle load level, when the measured deflection or strain is linearly related to its theoretical value, the relative residual deflection or strain is not greater than 20%, and the crack width does not exceed the requirements of the "Highway Bridge Bearing Capacity Testing and Assessment Procedure" (JTG / T J21-2011), the test is considered successful, and the bridge bearing capacity is assessed to be able to meet the i-th estimated vehicle load level requirements within the continued service life of N' years; otherwise, it is assessed as failing to meet the requirements; for test conditions that are not completed, they are directly assessed as failing to meet the corresponding vehicle load level requirements.

3. The method for evaluating the bearing capacity of an in-service bridge without requiring resistance information according to claim 1, characterized in that: The step 1) includes measuring the bridge deck alignment, arch ring alignment, main cable alignment, overall bridge dimensions, component dimensions, bridge deck pavement and arch filler thickness, bridge additional load investigation, and arch filler weight determination.

4. The method for evaluating the bearing capacity of an in-service bridge without requiring resistance information according to claim 1, characterized in that: Step 2) specifically includes: conducting a detailed visual inspection of the entire bridge, including the superstructure, substructure, and deck system, with a focus on inspecting the main load-bearing components, understanding structural deterioration and damage, and analyzing the impact of the defects on the load-bearing capacity; investigating the bridge's operating conditions, including on-site investigations and data review, analyzing the bridge's current load-bearing status, and using this as a basis for defect analysis to provide basic data for estimating the level of vehicle load that can be sustained.

5. The method for evaluating the bearing capacity of an in-service bridge without requiring resistance information according to claim 1, characterized in that: The vehicle load level corresponding to the estimated existing load-bearing capacity of the structure in step 3) includes multiple levels, and the load-bearing capacity is evaluated from low to high.

6. The method for evaluating the bearing capacity of an in-service bridge without requiring resistance information according to claim 1, characterized in that: The bridge target reliability index β in step 4) f The selection is based on the provisions of the Unified Standard for Reliability Design of Highway Engineering Structures (JTG 2120-2020). At the same time, the indicators of existing bridges in operation are adjusted according to maintenance conditions and needs.

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