Safety and durability evaluation method for I-steel-concrete composite continuous beam bridges

Abstract

The present invention discloses a safety and durability evaluation method for I-beam steel-concrete composite continuous beam bridges. The method comprises: evaluating the safety of the bridge under the ultimate bearing capacity limit state by the failure probability of the bridge system under the ultimate bearing capacity limit state; and evaluating the durability of the bridge under the ultimate bearing capacity limit state by the reliability degradation rate of the bridge system under the ultimate bearing capacity limit state. A lower failure probability indicates a higher safety of the bridge system, and a lower reliability degradation rate indicates a higher durability of the bridge system. The present invention provides a method that comprehensively considers the impact of multiple factors on construction quality, introduces relevant uncertainty parameters and qualitative parameters, and uses the calculated failure probability and reliability degradation rate values ​​to evaluate the safety and durability of the bridge. This method saves time and effort and is relatively objective and accurate.

Description

Technical Field

[0001] The present invention relates to the field of bridge system reliability evaluation, and more particularly to a method for evaluating the safety and durability of an I-beam-concrete composite continuous beam bridge. Background Art

[0002] Reliability refers to a product's ability to perform its intended function within a specified timeframe and under specified conditions. It encompasses both structural safety and durability. When measured probabilistically, this is called reliability. System safety can be expressed as the probability of failure. Currently, for I-beam-concrete composite continuous beam bridges, a target reliability value (converted from the probability of failure) is pre-determined before the construction plan is designed. This value is used to calculate the required construction parameters, such as the cross-sectional dimensions of the steel beam. After construction is completed, the safety and durability of these bridges need to be evaluated to assess project quality and provide guidance for subsequent construction and maintenance. However, in practice, hundreds of bridges may be constructed along the same highway project route. To determine which completed I-beam-concrete composite continuous beam bridge exhibits superior safety and durability, a safety evaluation is typically required for each completed bridge. Currently, methods for evaluating bridge safety include experimental testing and manual inspection and scoring. The experimental testing method typically involves arranging vehicles with certain loads to drive across a bridge before it opens to traffic, testing the bridge's stress and deformation, and comprehensively assessing its safety. Manual inspection and scoring methods typically involve manually inspecting and scoring completed bridges, and then comprehensively analyzing the scores to determine the bridge's safety and durability. However, both experimental testing and manual inspection and scoring methods are subject to limitations in objectivity, precision, time-consuming, labor-intensive, and resource-intensive, and are significantly influenced by the subjective experience of the scorers. Therefore, there is an urgent need for an objective, accurate, and intuitive evaluation method for the safety and durability of I-beam-concrete composite continuous beam bridges. This method would achieve a comprehensive measure of bridge safety and durability, screen out bridges of the same type with superior construction quality, and provide effective guidance for the subsequent construction and maintenance of these bridges. Summary of the Invention

[0003] One object of the present invention is to solve at least the above-mentioned problems and provide a safety and durability evaluation method for an I-beam-concrete composite continuous beam bridge, which can more accurately and intuitively characterize the safety and durability of the I-beam-concrete composite continuous beam bridge, and realize a comprehensive measurement of the safety and durability of the bridge. For multiple bridges of the same type, bridges with better construction quality can be screened out. The construction plans of the screened bridges with better quality are helpful for the learning of subsequent construction personnel, and also provide effective guidance for the subsequent construction of bridges of the same type.

[0004] In order to achieve these purposes and other advantages according to the present invention, a safety and durability evaluation method for an I-beam-concrete composite continuous beam bridge is provided, in which the safety of the bridge under the ultimate bearing capacity state is evaluated by the failure probability of the bridge system under the ultimate bearing capacity state, and the durability of the bridge under the ultimate bearing capacity state is evaluated by the reliability degradation rate of the bridge system under the ultimate bearing capacity state.

[0005] Preferably, the safety evaluation of the bridge under the ultimate bearing capacity state specifically includes the following steps:

[0006] S1. Determine the function:

[0007] The functional functions used to calculate the failure probability of the bridge system under the ultimate bearing capacity state include the bending bearing capacity formula Z1, the shear bearing capacity formula Z2, and the bending bearing capacity formula Z3 at the middle support position;

[0008] The specific formula Z1 is: Z1=M R -M S Among them, M R The calculation formula is: When the plastic neutral axis is within the concrete panel section, , when the plastic neutral axis is within the steel beam section, ;M S The calculation formula is: ;

[0009] The specific formula Z2 is: Z2=V R -V S ; Among them, V R The calculation formula is: ,

[0010] V S The calculation formula is: ;

[0011] Formula Z3 is specifically: ;in, The calculation formula is: , The calculation formula is: ;

[0012] In the formulas Z1 to Z3, the parameters involved are divided into nominal value parameters, design value parameters, random variable parameters, and qualitative parameters η c , the qualitative parameter η c Characterizes the closeness between the appearance quality of the bridge structure concrete and the acceptance standard. The closer to the acceptance standard, the better the η c The closer the value of is to 1;

[0013] The nominal value parameters are characterized as follows:

[0014] f cd is the compressive strength of concrete material, f d is the tensile strength of steel, f s is the tensile strength of the longitudinal reinforcement in the concrete panel, f vd is the shear strength of steel;

[0015] The design value parameters are specifically characterized as follows:

[0016] k is the fitting coefficient considering the slip effect; A c is the cross-sectional area of ​​the concrete bridge deck; y1 is the distance from the centroid of the concrete bridge deck in compression to the centroid of the steel beam in tension; A sc is the cross-sectional area of ​​the steel beam in compression; y2 is the distance from the centroid of the steel beam in compression to the centroid of the steel beam in tension; A r is the cross-sectional area of ​​the longitudinal reinforcement in the concrete bridge deck above the plastic neutral axis; y4 is the distance from the centroid of the cross section of the longitudinal reinforcement in the concrete bridge deck to the centroid of the cross section of the tensile zone of the steel beam; A cc is the area of ​​the concrete bridge deck above the plastic neutral axis; g is the dead load; L is the length of a single span of the bridge; 1+μ is the impact coefficient; h w is the web height of the steel beam; t w is the thickness of the steel beam web; A st is the tensile area of ​​the I-beam; h s is the height of the tension zone; h c is the height of the compression zone; x is the distance between the neutral axis of the cross section and the top surface of the I-beam;

[0017] The random variable parameters include structural uncertainty parameters and load parameters. The structural uncertainty parameters are characterized as follows:

[0018] γ cf Characterizes the degree of deviation between the compressive strength value of concrete material and the nominal value of the compressive strength of concrete material, γ cf =Concrete material compressive strength value / f cd ;

[0019] γ s Characterizes the deviation between the tensile strength of steel and the nominal value of the tensile strength of steel, γ s = tensile strength of steel / f d ;

[0020] γ ds Characterizes the degree of deviation between the cross-sectional dimension of the steel beam and the nominal value of the cross-sectional dimension of the steel beam, γ ds = Steel beam cross-section size value / design value of steel beam cross-section size;

[0021] γ dcCharacterizes the degree of deviation between the cross-sectional size of the bridge concrete panel and the design value of the cross-sectional size of the bridge concrete panel, γ dc =Bridge concrete panel cross-sectional dimension value / design value of bridge concrete panel cross-sectional dimension;

[0022] γ r Characterizes the degree of deviation between the tensile strength of steel bars and the nominal value of the tensile strength of steel bars, γ r = tensile strength of steel bar / f s ;

[0023] The load parameters are characterized as follows: q is the uniform lane load; P k For concentrated lane loads;

[0024] S2. Calculation of failure probability of bridge system under ultimate bearing capacity state:

[0025] The above random variable parameters are used as sampling objects, and formulas Z1, Z2, and Z3 are used as performance functions. The values ​​of each performance function are calculated. When any performance function value is less than or equal to 0, the bridge system fails. Otherwise, the bridge system is valid. Repeat the sampling N times, and count the number of failures n. The failure probability is n / N.

[0026] S3. Safety evaluation of bridge system under ultimate bearing capacity state:

[0027] Comparing the failure probabilities of any two I-beam-concrete composite continuous beam bridges under the ultimate bearing capacity state, the lower the failure probability, the higher the safety of the bridge under the ultimate bearing capacity state.

[0028] Preferably, the implementation of step S2 is specifically as follows: obtaining statistical characteristics of structural uncertainty parameters, sampling using a Monte Carlo method based on MATLAB, and calculating the system failure probability under the ultimate bearing capacity limit state of the bridge; wherein:

[0029] γ cf The specific acquisition of the statistical characteristics is as follows: taking multiple concrete material compressive strength values ​​measured on site as statistical objects, calculating the mean μ1 and standard deviation σ1 of the concrete material compressive strength, and then obtaining γ cf The normal distribution statistical characteristics N (μ1 / f cd ,σ1 / f cd );

[0030] γ ds The specific acquisition of the statistical characteristics is as follows: taking multiple steel beam cross-sectional dimensions measured on site as statistical objects, calculating the μ2 and standard deviation σ2 of the steel beam cross-sectional dimensions, and then obtaining γ ds The normal distribution statistical characteristics N (μ2 / design value of steel beam cross-section size, σ2 / design value of steel beam cross-section size);

[0031] γ dc The specific acquisition of the statistical characteristics is as follows: taking the cross-sectional dimensions of multiple bridge concrete panels measured on site as statistical objects, the cross-sectional dimensions μ3 and standard deviation σ3 of the bridge concrete panels are calculated, and then γ is obtained. dc Statistical characteristics of the normal distribution N (μ3 / design value of the cross-sectional size of the bridge concrete panel, σ3 / design value of the cross-sectional size of the bridge concrete panel);

[0032] γ s The statistical characteristics of γ are obtained specifically as follows: the tensile strength values ​​of multiple steels measured on site are used as statistical objects, the mean μ4 and standard deviation σ4 of the tensile strength of the steels are calculated, and then γ is obtained. s The normal distribution statistical characteristics of N (μ4 / f d ,σ4 / f d );

[0033] γ r The statistical characteristics of γ are obtained specifically as follows: the tensile strength values ​​of multiple steel bars measured on site are used as statistical objects, the mean μ5 and standard deviation σ5 of the tensile strength of steel bars are calculated, and then γ is obtained. r The normal distribution statistical characteristics N (μ5 / f s ,σ5 / f s ).

[0034] Preferably, the qualitative parameter η c The specific method of determining the value of is as follows: according to the qualitative description of the appearance of the bridge concrete structure in the design specification, the quantitative description of the bridge assessment standard is determined. The quantitative description includes five scales, as follows:

[0035] Scale 1: intact; under this scale, η c The value range is 0.95~1.0;

[0036] Scale 2: The cumulative area of ​​network cracks is ≤ 20% of the component area, and the area of ​​a single crack is ≤ 1.0m 2 , or the main beam crack length ≤ 1 / 3 of the cross-sectional size; under this scale, η c The value range is 0.9~0.95;

[0037] Scale 3: The cumulative area of ​​network cracks is ≤ 20% of the component area, and the area of ​​a single crack is > 1.0m 2 , or the main beam crack length is greater than 1 / 3 of the cross-sectional size and less than or equal to 2 / 3 of the cross-sectional size; under this scale, η c The value range is 0.85~0.90;

[0038] Scale 4: The length of the main beam crack is greater than 2 / 3 of the cross-sectional size, and the spacing is less than 20 cm. cThe value range is 0.80~0.850;

[0039] Scale 5: The width of the main beam crack is greater than 1.0 mm, and the spacing is ≤ 10 cm. c The value range is below 0.80.

[0040] Preferably, the safety of the bridge under the serviceability limit state is evaluated by the failure probability of the bridge system under the serviceability limit state, which specifically includes the following steps:

[0041] A1. Determine the function:

[0042] The functional functions used to calculate the failure probability of the bridge system under the normal serviceability limit state include the maximum crack width formula Z4 and the mid-span deflection formula Z5;

[0043] Formula Z4 is specifically: , ;

[0044] Formula Z5 is specifically: ; Among them, f1 is the short-term deflection, f2 is the long-term deflection; the calculation formula of f1 is: , , , ;in, , , , , , , ;

[0045] The calculation formula of f2 is: ,in, , ;

[0046] In formula Z4 and formula Z5, the parameters are represented as follows:

[0047] γ is the uncertainty coefficient of the calculation model; α cr is the stress characteristic coefficient of the component; f t is the tensile strength of steel fiber concrete; ρ te is the effective reinforcement ratio of the longitudinal tensile reinforcement; rs is the stress of the longitudinal tensile reinforcement at the crack section of the reinforced concrete member; l a is the average spacing of transverse reinforcement; f ry is the yield strength of the non-prestressed steel bars in the composite beam; f py is the yield strength of the prestressed steel bars in the composite beam; A s is the cross-sectional area of ​​the steel beam; fy is the yield strength of the steel beam; A P is the cross-sectional area of ​​the external prestressed tendons; f allow is the allowable deflection; B is the converted section stiffness of the composite beam; z1 is the distance from the centroid of the end prestressed tendon to the centroid of the converted section of the composite beam; l 1 is the projection length of the first section of prestressed tendons in the local coordinate system; θ1 is the angle between the first section of prestressed tendons and the horizontal line; θ2 is the angle between the second section of prestressed tendons and the horizontal line; B s is the converted section stiffness of the composite beam considering slip; m is the ratio of the distance from the beam end to the single point concentrated load loading point to the calculated span of the composite beam; r is the shear connection degree; K L is the shear stiffness of the shear connector per unit length; h sc E is the distance from the centroid of the steel beam section to the centroid of the concrete section; c is the elastic modulus of concrete; E s is the elastic modulus of steel; I c is the moment of inertia of the concrete section; I s is the moment of inertia of the steel beam section; A c is the cross-sectional area of ​​the concrete bridge deck; A s is the cross-sectional area of ​​the steel beam; n s is the number of rows of studs or perforated plate connectors; K is the shear stiffness of a single shear connector; p is the spacing between connectors; σ e is the effective prestressing force of the prestressed tendons; λ(t) is a coefficient related to time; k1 is a coefficient related to the average stress of the concrete bridge deck; is the average stress of the concrete bridge deck; T p is the effective prestressing force of the prestressed tendons; A0 is the cross-sectional area of ​​the composite beam after cross-sectional conversion; I0 is the moment of inertia of the composite beam after cross-sectional conversion; e is the eccentricity of the prestressing force;

[0048] A2. Calculation of failure probability of bridge system under serviceability limit state:

[0049] With ρ te 、f t 、A r 、f ry 、A P 、f py 、A s 、f y 、E s 、E c 、A c 、A s ,A0,q,P kThe sampling object is selected, and the function values ​​of formulas Z4 and Z5 are used to calculate each function. When any function value is less than or equal to 0, the bridge system fails. Otherwise, the bridge system is valid. Repeat the sampling M times, and count the number of failures m. The failure probability is m / M.

[0050] A3. Safety evaluation of bridge system under normal serviceability limit state:

[0051] Comparing the failure probabilities of any two I-beam-concrete composite continuous beam bridges under the serviceability limit state, the lower the failure probability, the higher the safety of the bridge under the serviceability limit state.

[0052] Preferably, the specific steps for evaluating the durability of a bridge system under the ultimate bearing capacity state are as follows:

[0053] B1. Determine the calculation formula: The calculation formula for the reliability degradation rate of a bridge under the ultimate bearing capacity state is: ;

[0054] The ultimate bearing capacity state is one of the ultimate bearing capacity state of bending, the ultimate bearing capacity state of shear, and the ultimate bearing capacity state of bending at the middle support position; α1 represents the reliability degradation rate of the bridge under the ultimate bearing capacity state, μ R01 Characterizes the mean resistance of the bridge structure at the initial moment under the ultimate bearing capacity state; σ R01 Characterizes the standard deviation of the resistance of the bridge structure at the initial moment under the ultimate bearing capacity state; σ S1 represents the standard deviation of the load effect of the bridge structure under the ultimate bearing capacity state; λ´ represents the corrosion rate of the steel web; γ0 represents the design thickness of the steel web;

[0055] B2. Calculation of the reliability degradation rate of bridges under the ultimate bearing capacity state:

[0056] Taking λ´ and γ0 as sampling objects, calculate the α1 value, repeat the sampling P times, calculate the mean of the α1 values ​​of the P sampling times, and obtain the reliability degradation rate under the corresponding bearing capacity limit state;

[0057] B3. Evaluation of bridge durability under the ultimate bearing capacity state:

[0058] Comparing the reliability degradation rates of any two I-beam-concrete composite continuous beam bridges under the corresponding ultimate bearing capacity state, the lower the reliability degradation rate, the higher the durability of the bridge under the ultimate bearing capacity state.

[0059] Preferably, the evaluation of the durability of the bridge system under the serviceability limit state is also included, which specifically includes the following steps:

[0060] C1. Determine the calculation formula: The calculation formula for the reliability degradation rate of the bridge under the normal serviceability limit state is: ;

[0061] Wherein, the serviceability limit state is one of the concrete cracking limit state in the negative bending moment zone and the mid-span deflection limit state; α2 represents the reliability degradation rate of the bridge under the serviceability limit state;

[0062] When the serviceability limit state is the concrete cracking limit state in the negative moment zone, μ R02 Characterizes the maximum crack width limit, σ R02 is 0, σ S2 Characterizes the standard deviation of the maximum crack width;

[0063] When the serviceability limit state is the mid-span deflection limit state, μ R02 Characterizes the deflection limit of the bridge mid-span, σ R02 is 0, σ S2 Characterizes the standard deviation of the actual deflection of the bridge at mid-span;

[0064] C2. Calculation of the reliability degradation rate of bridges under the serviceability limit state:

[0065] Take λ´ and γ0 as sampling objects, calculate the α2 value, repeat the sampling Q times, calculate the mean of the α2 values ​​of Q samplings, and obtain the required reliability degradation rate;

[0066] C3. Evaluation of bridge durability under normal serviceability limit state:

[0067] Comparing the reliability degradation rates of any two I-beam-concrete composite continuous beam bridges under the corresponding serviceability limit state, the lower the reliability degradation rate, the higher the durability of the bridge under the serviceability limit state.

[0068] Preferably, the cross-sectional dimensions in the steel beam cross-sectional dimension values ​​are derived from any one of the thickness of the upper flange plate, the thickness of the lower flange plate, the web thickness, the web width, and the width of the steel beam; and the cross-sectional dimensions in the bridge concrete panel cross-sectional dimension values ​​are derived from any one of the length, width, and height of the concrete panel.

[0069] The present invention has at least the following beneficial effects:

[0070] For the safety evaluation of I-beam-concrete composite continuous beam bridges, uncertainty parameters and qualitative parameters reflecting construction influencing factors are introduced into the original formulas of the functional functions under each limit state. The functional functions under each limit state are sampled and calculated using a series model to obtain the failure probability. The lower the failure probability, the higher the safety of the bridge system. The functional functions under the bearing capacity limit state include the bending bearing capacity formula, the shear bearing capacity formula, and the bending bearing capacity formula at the center support position. The functional functions under the normal service limit state include the maximum crack width calculation formula and the mid-span underwinding formula.

[0071] For the durability evaluation of I-beam-concrete composite continuous beam bridges, the reliability degradation rate of the bridge is calculated based on the calculation formula after introducing uncertainty parameters and qualitative parameters. The lower the reliability degradation rate, the higher the durability of the bridge.

[0072] Overall, a safety and durability evaluation method for I-beam-concrete composite continuous beam bridges is provided, which can more accurately and intuitively characterize the safety and durability of I-beam-concrete composite continuous beam bridges, and realize the comprehensive measurement of bridge safety and durability. For multiple bridges of the same type, bridges with better construction quality can be screened out. The construction plans of the screened bridges with better quality are helpful for the learning of subsequent construction personnel, and also provide effective guidance for the subsequent construction of bridges of the same type.

[0073] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0074] The present invention is further described in detail below with reference to the embodiments so that those skilled in the art can implement the invention with reference to the description.

[0075] The present invention provides a safety and durability evaluation method for an I-beam-concrete composite continuous beam bridge, which is designed based on the following design principles:

[0076] Based on a large amount of research data and construction experience, the impact of various factors on the safety and durability of bridges during the construction process was considered. Based on the five principles of "leadership, representativeness, comparability, accessibility, and timeliness", the safety and durability of I-beam-concrete composite continuous beam bridges were considered in two dimensions. Starting from the multiple levels of bridge structure-related data-structural materials-component performance-structural system, a preliminary set of reliability evaluation indicators for the safety and durability of highway concrete beam bridges was formulated. Through expert survey and hierarchical analysis, some factors with relatively small influence were eliminated, and the final set of reliability evaluation indicators was obtained. Based on the final set of reliability evaluation indicators, a series of uncertainty factors (i.e., the structural level uncertainty parameters mentioned below) and qualitative parameters (concrete appearance quality) that characterize various influencing factors during the construction process were formed. Combining theoretical research and work practice, the above uncertainty factors and qualitative parameters were introduced into GB 50917-2013 The calculation formulas for bearing capacity and serviceability limit states in the steel-concrete composite bridge design specifications aim to characterize the impact of various factors on bridge construction quality during the construction process. Ultimately, the calculated failure probability and reliability degradation rate are used to characterize the safety and durability of the bridge. The failure probability is converted to a reliability value, which is then compared with the target reliability value set in the construction design plan to indicate the gap between construction quality and the target. See below for more details.

[0077] The present invention provides a safety and durability evaluation method for an I-beam-concrete composite continuous beam bridge. The safety of the bridge under the ultimate bearing capacity state is evaluated by the failure probability of the bridge system under the ultimate bearing capacity state, and the durability of the bridge under the ultimate bearing capacity state is evaluated by the reliability degradation rate of the bridge system under the ultimate bearing capacity state. The safety evaluation of the bridge under the ultimate bearing capacity state specifically includes the following steps:

[0078] S1. Determine the function:

[0079] The functional functions used to calculate the failure probability of the bridge system under the ultimate bearing capacity state include the bending bearing capacity formula Z1, the shear bearing capacity formula Z2, and the bending bearing capacity formula Z3 at the middle support position;

[0080] The specific formula Z1 is: Z1=M R -M S Among them, M R The calculation formula is: When the plastic neutral axis is within the concrete panel section, , when the plastic neutral axis is within the steel beam section, ;M S The calculation formula is: ;

[0081] The specific formula Z2 is: Z2=V R -V S ; Among them, V R The calculation formula is: ,

[0082] V S The calculation formula is: ;

[0083] Formula Z3 is specifically: ;in, The calculation formula is: , The calculation formula is: ;

[0084] In the formulas Z1 to Z3, the parameters involved are divided into nominal value parameters, design value parameters, random variable parameters, and qualitative parameters η c , the qualitative parameter η c Characterizes the closeness between the appearance quality of the bridge structure concrete and the acceptance standard. The closer to the acceptance standard, the better the η c The closer the value of η is to 1, the c It is a fixed constant obtained after scoring and has no unit.

[0085] The nominal value parameters are characterized as follows:

[0086] f cd is the compressive strength of concrete material, unit is MPa; f d is the tensile strength of steel, unit is MPa; f s is the tensile strength of the longitudinal reinforcement in the concrete panel, in MPa; f vd is the shear strength of steel, unit: MPa;

[0087] The design value parameters are specifically characterized as follows:

[0088] k is the fitting coefficient considering the slip effect, which has no unit; A c is the cross-sectional area of ​​the concrete bridge deck, in mm; y1 is the distance from the centroid of the concrete bridge deck in compression to the centroid of the steel beam in tension, in mm; A sc is the cross-sectional area of ​​the steel beam in compression zone, in mm; y2 is the distance from the centroid of the steel beam in compression zone to the centroid of the steel beam in tension zone, in mm; A r is the cross-sectional area of ​​the longitudinal reinforcement in the concrete bridge deck above the plastic neutral axis, in mm 2 ; y4 is the distance from the cross-sectional centroid of the longitudinal reinforcement in the concrete bridge deck to the cross-sectional centroid of the tensile zone of the steel beam, unit: mm; A cc is the area of ​​the concrete bridge deck above the plastic neutral axis, in mm 2; g is the constant load, unit is kN / m; L is the length of a single span of the bridge, unit is m; 1+μ is the impact coefficient, unitless; h w is the web height of the steel beam, in mm; t w A is the thickness of the steel beam web, in mm; st is the tensile area of ​​the I-beam, in mm 2 ;h s h is the height of the tensile zone, in mm; c is the height of the compression zone, in mm; x is the distance between the neutral axis of the cross section and the top surface of the I-beam, in mm;

[0089] The random variable parameters include structural uncertainty parameters and load parameters. The structural uncertainty parameters are characterized as follows:

[0090] γ cf Characterizes the degree of deviation between the compressive strength value of concrete material and the nominal value of the compressive strength of concrete material, γ cf =Concrete material compressive strength value / f cd ;

[0091] γ s Characterizes the deviation between the tensile strength of steel and the nominal value of the tensile strength of steel, γ s = tensile strength of steel / f d ;

[0092] γ ds Characterizes the degree of deviation between the cross-sectional dimension of the steel beam and the nominal value of the cross-sectional dimension of the steel beam, γ ds = Steel beam cross-section size value / design value of steel beam cross-section size;

[0093] γ dc Characterizes the degree of deviation between the cross-sectional size of the bridge concrete panel and the design value of the cross-sectional size of the bridge concrete panel, γ dc =Bridge concrete panel cross-sectional dimension value / design value of bridge concrete panel cross-sectional dimension;

[0094] γ r Characterizes the degree of deviation between the tensile strength of steel bars and the nominal value of the tensile strength of steel bars, γ r = tensile strength of steel bar / f s ;

[0095] The load parameters are characterized as follows: q is the uniform lane load, unit is kN / m; P k is the concentrated lane load, in kN / m;

[0096] S2. Calculation of failure probability of bridge system under ultimate bearing capacity state:

[0097] The above random variable parameters are used as sampling objects, and formulas Z1, Z2, and Z3 are used as performance functions. The values ​​of each performance function are calculated. When any performance function value is less than or equal to 0, the bridge system fails. Otherwise, the bridge system is valid. Repeat the sampling N times, and count the number of failures n. The failure probability is n / N.

[0098] S3. Safety evaluation of bridge system under ultimate bearing capacity state:

[0099] Compare the failure probabilities of any two I-beam-concrete composite continuous beam bridges under the ultimate bearing capacity state. The lower the failure probability, the higher the safety of the bridge under the ultimate bearing capacity state.

[0100] In the above technical solution, the ultimate bearing capacity state includes the ultimate bending bearing capacity state, the ultimate shear bearing capacity state, and the ultimate bending bearing capacity state at the middle support position. Among them, the function function under the ultimate bending bearing capacity state is Z1. In the formula Z1, M R is the bending moment that the bridge can bear, M S The mid-span bending moment occurs when the plastic neutral axis is within the concrete panel cross section and when the plastic neutral axis is within the steel beam cross section. These two states are the boundary positions between the tension zone and the compression zone in the composite beam under load. The calculation formulas vary depending on the position. In actual use, after the load is determined, it is possible to determine which of the two states the bridge is in. These are all existing technologies well known to those skilled in the art and will not be elaborated on here.

[0101] The function of the ultimate limit state of shear bearing capacity is Z2. In the formula Z2, V R is the shear bearing capacity of the bridge, V S is the maximum shear force; the function function of the ultimate bending bearing capacity of the middle support position is Z3. In formula Z3, is the bending moment that the bridge supports can bear, In equations Z1-Z3, the parameters involved are categorized as nominal parameters, design parameters, random variable parameters, and qualitative parameters. The nominal and design parameters are inherent in the original formulas in the Steel-Concrete Composite Continuous Beam Bridge Design Specification. Nominal parameters are typically mechanical property parameters, such as the compressive strength of concrete and steel, while design parameters are typically cross-sectional dimensions, coefficients, and other parameters. The representations and units of the design and nominal parameters are those specified in the existing GB 50917-2013 Steel-Concrete Composite Bridge Design Specification. For more details, please refer to that design specification and other existing materials.

[0102] Random variable parameters are divided into structural uncertainty parameters and load parameters, among which structural uncertainty parameters and qualitative parameters η cThese are parameters obtained through expert investigation, hierarchical analysis, theoretical research and practical experience. They characterize the impact of various factors such as construction materials, construction templates, and labor on the construction quality during the construction process. They can be regarded as influence coefficients, which comprehensively consider the degree of deviation between the overall quality of the bridge and the expected quality caused by various factors during the construction process. Among them, the qualitative parameter η c Characterizes the closeness between the appearance quality of the bridge structure concrete and the acceptance standard. The closer to the acceptance standard, the better the η c The closer the value is to 1, that is, the value of 1 is taken as the standard. The closer it is to the standard, the better the appearance of the concrete of the bridge structure. The acceptance standard can be set according to the relevant design specifications.

[0103] The structural uncertainty parameters include: γ, which characterizes the degree of deviation between the concrete material compressive strength value and the nominal value of the concrete material compressive strength; cf γ, which represents the deviation between the tensile strength of steel and the nominal value of the tensile strength of steel s γ, which represents the degree of deviation between the cross-sectional dimension of the steel beam and the nominal value of the cross-sectional dimension of the steel beam ds γ, which represents the degree of deviation between the cross-sectional size of the bridge concrete panel and the design value of the cross-sectional size of the bridge concrete panel dc , γ, which represents the degree of deviation between the tensile strength of steel bars and the nominal value of the tensile strength of steel bars r , where γ ds Characterizes the degree of deviation between the cross-sectional dimension of the steel beam and the nominal value of the cross-sectional dimension of the steel beam. Here, the cross-sectional dimension of the steel beam refers to any dimension of the cross-sectional dimension of the steel beam in the bridge, such as the thickness of the upper flange plate, the thickness of the lower flange plate, the thickness of the web plate, the width of the web plate, and the width of the steel beam. Similarly, γ dc Characterizes the degree of deviation between the cross-sectional dimension of the bridge concrete panel and the design value of the cross-sectional dimension of the bridge concrete panel. Here, the cross-sectional dimension of the concrete panel refers to any dimension of the cross-sectional dimension of the bridge concrete panel, such as the length, width, and height of the concrete panel. They reflect, to a certain extent, the construction factors that affect the most important aspects of the intrinsic safety level of the structure during the construction process. The load parameters are randomly varying loads known in the art, including uniform lane load q and concentrated lane load P. k ;

[0104] In this technical solution, when it is used specifically, the values ​​of the random variable parameters are first determined. The values ​​of the structural uncertainty parameters in the random variables can come from on-site measurements (such as the test results of different batches of raw materials of the construction unit or the test results of the compressive strength of concrete of the cast structure) or data records (such as those recorded in the design specifications, which can reduce the workload and greatly increase the value range of the parameter). The value of the load random variable can be obtained through data records or actual traffic tests. Multiple values ​​of the above-mentioned random variable parameters are taken to form a sampling sample, and then the above-mentioned functional function is used as the sampling functional function for sampling calculation. In the actual sampling process, sampling calculation is performed according to the series mode (that is, under the three limit states, the calculated value of the functional function of any limit state is less than or equal to 0, which indicates that the bridge system has failed. The series mode is a method well known in the art). The failure probability of the bridge system in the overall sampling is statistically analyzed. The lower the failure probability, the higher the safety of the bridge under the ultimate bearing capacity state.

[0105] The technical solution has the beneficial effect of providing a safety and durability evaluation method for I-beam-concrete composite continuous beam bridges, which can relatively accurately and intuitively characterize the safety and durability of I-beam-concrete composite continuous beam bridges and realize a comprehensive measurement of bridge safety and durability. By calculating the failure probability of the bridge, the failure probability is converted to a reliability value (the conversion method of failure probability and reliability value is shown in GB / T 50283 1999 Unified Standard for Reliability Design of Highway Engineering Structures). By comparing the reliability value with the target reliability value designed during bridge construction, the degree of deviation of the bridge from the design standard can be determined, and the construction quality can be evaluated. At the same time, for multiple bridges of the same type, by comparing the failure probability values, a bridge with a smaller failure probability value can be screened out, indicating that the construction quality of the bridge is better. The construction plan or construction process of the screened out bridge with better quality is helpful for the learning of subsequent construction personnel and also provides effective guidance for the subsequent construction of similar bridges.

[0106] In another technical solution, step S2 is implemented as follows: obtaining statistical characteristics of structural uncertainty parameters, sampling using the Monte Carlo method based on MATLAB, and calculating the system failure probability under the ultimate bearing capacity state of the bridge; wherein:

[0107] γ cf The specific acquisition of the statistical characteristics is as follows: taking multiple concrete material compressive strength values ​​measured on site as statistical objects, calculating the mean μ1 and standard deviation σ1 of the concrete material compressive strength, and then obtaining γ cf The normal distribution statistical characteristics N (μ1 / f cd ,σ1 / f cd );

[0108] γds The specific acquisition of the statistical characteristics is as follows: taking multiple steel beam cross-sectional dimensions measured on site as statistical objects, calculating the μ2 and standard deviation σ2 of the steel beam cross-sectional dimensions, and then obtaining γ ds The normal distribution statistical characteristics N (μ2 / design value of steel beam cross-section size, σ2 / design value of steel beam cross-section size);

[0109] γ dc The specific acquisition of the statistical characteristics is as follows: taking the cross-sectional dimensions of multiple bridge concrete panels measured on site as statistical objects, the cross-sectional dimensions μ3 and standard deviation σ3 of the bridge concrete panels are calculated, and then γ is obtained. dc Statistical characteristics of the normal distribution N (μ3 / design value of the cross-sectional size of the bridge concrete panel, σ3 / design value of the cross-sectional size of the bridge concrete panel);

[0110] γ s The statistical characteristics of γ are obtained specifically as follows: the tensile strength values ​​of multiple steels measured on site are used as statistical objects, the mean μ4 and standard deviation σ4 of the tensile strength of the steels are calculated, and then γ is obtained. s The normal distribution statistical characteristics of N (μ4 / f d ,σ4 / f d );

[0111] γ r The statistical characteristics of γ are obtained specifically as follows: the tensile strength values ​​of multiple steel bars measured on site are used as statistical objects, the mean μ5 and standard deviation σ5 of the tensile strength of steel bars are calculated, and then γ is obtained. r The normal distribution statistical characteristics N (μ5 / f s ,σ5 / f s );

[0112] In the above technical solution, on-site measurements can be the test results of different batches of raw materials of the construction unit or the test results of relevant components on the constructed bridge (poured concrete / constructed steel beam components). The Monte Carlo method based on MATLAB is a very existing sampling calculation method and will not be elaborated on here. The beneficial effect of adopting this technical solution is that by obtaining the statistical characteristics of the uncertainty parameters at the structural level and combining them with the Monte Carlo method based on MATLAB for sampling calculation, the failure probability can be quickly obtained, which greatly improves the efficiency of the calculation work.

[0113] In another technical solution, the qualitative parameter η c The specific method of determining the value of is as follows: according to the qualitative description of the appearance of the bridge concrete structure in the design specification, the quantitative description of the bridge assessment standard is determined. The quantitative description includes five scales, as follows:

[0114] Scale 1: intact; under this scale, ηc The value range is 0.95~1.0;

[0115] Scale 2: The cumulative area of ​​network cracks is ≤ 20% of the component area, and the area of ​​a single crack is ≤ 1.0m 2 , or the main beam crack length ≤ 1 / 3 of the cross-sectional size; under this scale, η c The value range is 0.9~0.95;

[0116] Scale 3: The cumulative area of ​​network cracks is ≤ 20% of the component area, and the area of ​​a single crack is > 1.0m 2 , or the main beam crack length is greater than 1 / 3 of the cross-sectional size and less than or equal to 2 / 3 of the cross-sectional size; under this scale, η c The value range is 0.85~0.90;

[0117] Scale 4: The length of the main beam crack is greater than 2 / 3 of the cross-sectional size, and the spacing is less than 20 cm. c The value range is 0.80~0.850;

[0118] Scale 5: The width of the main beam crack is greater than 1.0 mm, and the spacing is ≤ 10 cm. c The value range is below 0.80.

[0119] In the above technical solution, scales 1 to 5 are used to score and evaluate the appearance quality of the constructed bridge concrete panels. The design content of scales 1 to 5 is designed with reference to existing standards. The "intact" in scale 1 indicates that the concrete panel is intact and has no defects such as cracks. The "components" in scales 2 to 3 refer to the bridge concrete panels. The spacing in scales 4 to 5 refers to the width of the cracks in the main beam. When used, construction workers score the appearance quality of the bridge concrete panel structure according to these five scales. After taking the average of the scores of multiple construction workers, the final qualitative parameter η can be obtained. c The value of represents objectivity and accuracy.

[0120] Another technical solution also includes evaluating the safety of the bridge under the serviceability limit state by using the failure probability of the bridge system under the serviceability limit state, which specifically includes the following steps:

[0121] A1. Determine the function:

[0122] The functional functions used to calculate the failure probability of the bridge system under the normal serviceability limit state include the maximum crack width formula Z4 and the mid-span deflection formula Z5;

[0123] Formula Z4 is specifically: , ;

[0124] Formula Z5 is specifically: ; Among them, f1 is the short-term deflection, which is positive when it is downward, and f2 is the long-term deflection; the calculation formula of f1 is: , , , ;in, , , , , , , ;

[0125] The calculation formula of f2 is: ,in, , ;

[0126] In formula Z4 and formula Z5, the parameters involved are represented as follows:

[0127] γ is the uncertainty coefficient of the calculation model, which has no unit and can be taken as 1.0 in actual calculation; α cr is the stress characteristic coefficient of the component, unitless; f t is the tensile strength of steel fiber concrete, unit: MPa; ρ te is the effective reinforcement ratio of the longitudinal tensile reinforcement, unitless; is the stress of the longitudinal tensile reinforcement at the crack section of the reinforced concrete member, unit MPa; l a is the average spacing of transverse reinforcement, in mm; f ry A is the yield strength of the non-prestressed steel bars in the composite beam, in MPa; r The representation of is as mentioned above, that is, the cross-sectional area of ​​the longitudinal reinforcement in the concrete bridge deck on the upper side of the plastic neutral axis, in mm 2 ;f py A is the yield strength of the prestressed steel bars in the composite beam, in MPa; s is the cross-sectional area of ​​the steel beam, in mm; f y A is the yield strength of the steel beam, unit: MPa; P is the cross-sectional area of ​​the external prestressed tendons, in mm 2 ;f allow is the allowable deflection, unit is mm; B is the converted section stiffness of the composite beam, unit is N·mm 2 ; z1 is the distance from the centroid of the end prestressed tendon to the centroid of the converted cross section of the composite beam, in mm. The centroid of the prestressed tendon is positive when it is above the converted centroid; l 1 is the projection length of the first section of prestressed tendons in the local coordinate system, in mm; θ1 is the angle between the first section of prestressed tendons and the horizontal line, in degrees; θ2 is the angle between the second section of prestressed tendons and the horizontal line, in degrees; B sConverted section stiffness of composite beam considering slip, unit: N·mm 2 ; m is the ratio of the distance from the beam end to the single point concentrated load loading point to the calculated span of the composite beam, unitless; r is the shear connection degree, unitless; K L h is the shear stiffness of the shear connector per unit length, in MPa; sc E is the distance from the centroid of the steel beam section to the centroid of the concrete section, in mm; c is the elastic modulus of concrete, unit: MPa; E s is the elastic modulus of steel, unit: MPa; I c is the moment of inertia of the concrete section, in mm 4 ;I s is the moment of inertia of the steel beam section, in mm 4 ; A c is the cross-sectional area of ​​the concrete bridge deck, in mm 2 ; A s is the cross-sectional area of ​​the steel beam, in mm 2 ;n s is the number of rows of studs or perforated plate connectors, unitless; K is the shear stiffness of a single shear connector, unit N / mm, using stud connectors; p is the spacing between connectors, unit mm; σ e is the effective prestressing force of the prestressed tendons, in MPa; is a coefficient related to time, unitless, t is the calculation time, unit d; k1 is a coefficient related to the average stress of the concrete bridge deck, unitless; is the average stress of the concrete bridge deck, unit MPa, which takes a negative value for compression and 0 for tension; T p is the effective prestressing force of the prestressed tendons, in N; A0 is the cross-sectional area of ​​the composite beam after cross-sectional conversion, in mm 2 ; I0 is the moment of inertia of the composite beam after cross-section conversion, unit: mm 4 ;e is the prestress eccentricity, unit is mm;

[0128] A2. Calculation of failure probability of bridge system under serviceability limit state:

[0129] With ρ te 、f t 、A r 、f ry 、A P 、f py 、A s 、f y 、E s 、E c 、A c 、A s ,A0,q,P kThe sampling object is selected, and the function values ​​of formulas Z4 and Z5 are used to calculate each function. When any function value is less than or equal to 0, the bridge system fails. Otherwise, the bridge system is valid. Repeat the sampling M times, and count the number of failures m. The failure probability is m / M.

[0130] A3. Safety evaluation of bridge system under normal serviceability limit state:

[0131] Comparing the failure probabilities of any two I-beam-concrete composite continuous beam bridges under the serviceability limit state, the lower the failure probability, the higher the safety of the bridge under the serviceability limit state.

[0132] In the above technical solution, the representations of the above parameters are existing, and can be specifically referred to GB 50917-2013 Code for Design of Steel-Concrete Composite Bridges (hereinafter referred to as the design code), wherein the random variable parameters in each parameter include: ρ te ,ft,f ry 、 f py 、 A s 、f y 、A P 、E c 、E s 、A c 、A s ,A0,q,P k , the rest are fixed-value parameters. Among the fixed-value parameters, those involving mechanical properties are nominal value parameters, and the others are design value parameters. Both nominal value parameters and design value parameters are common knowledge in this field and will not be elaborated here. The value of random variables can be obtained by on-site measurement or from existing data, preferably from on-site measurement; the normal service limit state mainly tests whether the maximum crack width and mid-span deflection generated during the use of the bridge are within the normal range. If they are beyond the range, the system fails. The normal service limit state specifically includes the mid-span deflection limit state (the corresponding function function is formula Z5) and the negative bending moment zone concrete cracking limit state (the corresponding function function is formula Z4). In the actual sampling calculation process, these two limit states are sampled and calculated in series mode to obtain the failure probability. The lower the failure probability, the higher the safety of the bridge under the normal service limit state;

[0133] The beneficial effect of adopting this technical solution is that it provides a method for evaluating the safety of bridges under the limit state of normal use. It can simultaneously evaluate the safety of I-beam-concrete composite continuous beam bridges under the ultimate state of bearing capacity and the limit state of normal use. The evaluation is comprehensive and has wider applicability.

[0134] In another technical solution, the specific steps for evaluating the durability of a bridge system under the ultimate bearing capacity state are as follows:

[0135] B1. Determine the calculation formula: The calculation formula for the reliability degradation rate of a bridge under the ultimate bearing capacity state is:

[0136] ;

[0137] The ultimate bearing capacity state is one of the ultimate bearing capacity state of bending, the ultimate bearing capacity state of shear, and the ultimate bearing capacity state of bending at the middle support position; α1 represents the reliability degradation rate of the bridge under the ultimate bearing capacity state, μ R01 Characterizes the mean resistance of the bridge structure at the initial moment under the ultimate bearing capacity state; σ R01 Characterizes the standard deviation of the resistance of the bridge structure at the initial moment under the ultimate bearing capacity state; σ S1 represents the standard deviation of the load effect of the bridge structure under the ultimate bearing capacity state; λ´ represents the corrosion rate of the steel web; γ0 represents the design thickness of the steel web;

[0138] B2. Calculation of the reliability degradation rate of bridges under the ultimate bearing capacity state:

[0139] Taking λ´ and γ0 as sampling objects, calculate the α1 value, repeat the sampling P times, calculate the mean of the α1 values ​​of the P sampling times, and obtain the reliability degradation rate under the corresponding bearing capacity limit state;

[0140] B3. Evaluation of bridge durability under the ultimate bearing capacity state:

[0141] Comparing the reliability degradation rates of any two I-beam-concrete composite continuous beam bridges under the corresponding ultimate bearing capacity state, the lower the reliability degradation rate, the higher the durability of the bridge under the ultimate bearing capacity state.

[0142] In the above technical solution, the calculation formula of the reliability degradation rate is specifically based on GB 50917-2013, Code for Design of Steel-Concrete Composite Bridges, where the ultimate bearing capacity state is one of the ultimate bearing capacity state of bending, the ultimate bearing capacity state of shear, and the ultimate bearing capacity state of bending at the center support. In actual calculation, the reliability degradation rate values ​​under the ultimate bearing capacity state of bending, the ultimate bearing capacity state of shear, and the ultimate bearing capacity state of bending at the center support are calculated respectively. The reliability degradation rate values ​​of the two bridges under the corresponding ultimate bearing capacity state are compared to obtain the durability evaluation of the bridge under the corresponding ultimate bearing capacity state.

[0143] μ R01 , σ R01 , σ S1The specific method of obtaining the value is as follows:

[0144] Under the ultimate bending bearing capacity state: μ R01 is M in the above formula Z1 R The mean of M in Z1 R The formula is used to perform multiple sampling calculations, and the mean is μ R01 The standard deviation is σ R01 value; σ S1 Characterizes the standard deviation of the load effect of the bridge structure under the ultimate bearing capacity state, which is expressed by M in the above Z1. S Formula, multiple sampling calculations are performed, and the standard deviation is σ S1 value;

[0145] Under the ultimate shear capacity state: μ R01 V in the above formula Z2 R The mean value of V in Z2 R The formula is used to perform multiple sampling calculations, and the mean is μ R01 The standard deviation is σ R01 value; σ S1 Characterizes the standard deviation of the load effect of the bridge structure under the ultimate bearing capacity state, which is expressed by V in the above Z2 formula S The calculation formula is to perform multiple sampling calculations and take the standard deviation as σ S1 value;

[0146] Under the ultimate bending bearing capacity of the middle support position: μ R01 is M in the above formula Z3 R,0 The mean of M in Z3 R,0 The formula is used to perform multiple sampling calculations, and the mean is μ R01 The standard deviation is σ R01 value; σ S1 Characterizes the standard deviation of the load effect of the bridge structure under the ultimate bearing capacity state, which is expressed by M in the above Z3 formula S,0 Formula, multiple sampling calculations are performed, and the standard deviation is σ S1 value;

[0147] It should be noted that the above-mentioned multiple sampling calculations can be directly performed using the sampling samples used to calculate the failure probability under the ultimate bearing capacity state as the sampling samples;

[0148] The values ​​of λ´ and γ0 can be information recorded in existing research literature;

[0149] In this technical solution, when used, the ultimate bearing capacity state to be evaluated is first determined, and then the mean resistance value of the bridge structure at the initial moment under the corresponding ultimate bearing capacity state, the standard deviation of the resistance of the bridge structure at the initial moment, and the standard deviation of the load effect of the bridge structure are calculated to obtain the calculation formula of the reliability degradation rate. Then, the values ​​of the random variables (λ´, γ0) are designed and a sampling sample is formed. With this sampling sample as the sample library, multiple samplings are performed and the reliability degradation rate value is calculated. The average value is the reliability degradation rate under the corresponding ultimate bearing capacity state. The lower the reliability degradation rate, the higher the durability of the bridge.

[0150] The beneficial effect of adopting this technical solution is that it provides a method for evaluating the durability of bridge systems under the ultimate bearing capacity state. It can intuitively, accurately and quickly judge the durability of bridges, and then screen out bridges with better durability, providing meaningful guidance for the subsequent construction of similar bridges.

[0151] Another technical solution also includes evaluating the durability of the bridge system under the serviceability limit state, which specifically includes the following steps:

[0152] C1. Determine the calculation formula: The calculation formula for the reliability degradation rate of the bridge under the normal serviceability limit state is: ;

[0153] Wherein, the serviceability limit state is one of the concrete cracking limit state in the negative bending moment zone and the mid-span deflection limit state; α2 represents the reliability degradation rate of the bridge under the serviceability limit state;

[0154] When the serviceability limit state is the concrete cracking limit state in the negative moment zone, μ R02 Characterizes the maximum crack width limit, σ R02 is 0, σ S2 Characterizes the standard deviation of the maximum crack width;

[0155] When the serviceability limit state is the mid-span deflection limit state, μ R02 Characterizes the deflection limit of the bridge mid-span, σ R02 is 0, σ S2 Characterizes the standard deviation of the actual deflection of the bridge at mid-span;

[0156] C2. Calculation of the reliability degradation rate of bridges under the serviceability limit state:

[0157] Take λ´ and γ0 as sampling objects, calculate the α2 value, repeat the sampling Q times, calculate the mean of the α2 values ​​of Q samplings, and obtain the required reliability degradation rate;

[0158] C3. Evaluation of bridge durability under normal serviceability limit state:

[0159] Compare the reliability degradation rates of any two I-beam-concrete composite continuous beam bridges under the corresponding serviceability limit state. The lower the reliability degradation rate, the higher the durability of the bridge under the serviceability limit state.

[0160] In the above technical solution, the calculation formula for the reliability degradation rate is specifically based on GB 50917-2013, Code for Design of Steel-Concrete Composite Bridges. The serviceability limit states include the mid-span deflection limit state (corresponding to the function function of mid-span deflection) and the maximum crack width limit state (i.e., the concrete cracking limit state in the negative bending moment zone, corresponding to the function function of the maximum crack width).

[0161] μ R02 , σ R02 , σ S2 The specific method of obtaining the value is as follows:

[0162] Under the ultimate limit state of concrete cracking in the negative bending moment zone: μ R02 Characterizes the maximum crack width limit, which is a default value in this field and is taken as 0.2 in the above formula Z4, that is, μ R02 =0.2;σ R02 Characterizes the standard deviation of the maximum crack width limit. Since the maximum crack width limit is a default value in this field, σ R02 The value is 0; S2 Characterizes the standard deviation of the maximum crack width, where the calculation formula for the maximum crack width is the part after "0.2-" in the above formula Z4, that is, the maximum crack width = , calculated according to the formula, σ S2 The value of is: the random variable involved in the formula (ρ te 、f t 、A r 、f ry 、A P 、f py 、A s 、f y 、E s ) is a sampling sample, and the maximum crack width is calculated according to the maximum crack width formula to obtain multiple maximum crack width calculation values. The multiple maximum crack width calculation values ​​are used as statistical objects, and the standard deviation of the maximum crack width is calculated, which is σ S2 The value of

[0163] Under the mid-span deflection limit state: μ R02 Characterizes the deflection limit of the bridge mid-span deflection, which is also the aforementioned allowable deflection (f allow ), σ R02Characterizes the standard deviation of the deflection limit of the bridge mid-span deflection, where the deflection limit is an exact fixed value. The deflection limit is calculated by multiplying the deflection-span ratio limit by the bridge span. The deflection-span ratio limit is determined by consulting the design specifications. In actual application, due to μ R02 is an exact constant, so σ R02 is 0; S2 The standard deviation of the actual deflection of the bridge mid-span is obtained by performing multiple sampling calculations on the deflection calculation formula. Specifically, the calculation formulas for short-term deflection (f1) and long-term deflection (f2) in formula Z5 are used as the calculation formulas. The random variables involved in these two formulas are used to construct sampling samples, and the actual deflection of each sampling is calculated (in each sampling, the short-term deflection and the long-term deflection are calculated at the same time, and the largest calculation result is selected as the calculation result of this sampling). After multiple samplings, multiple actual deflection values ​​are obtained, and the mean and standard deviation of the actual deflection of the multiple samples are calculated, where the standard deviation is σ S2 The above formulas and parameter representations are inherent in the design specifications, and more specific references can be made to the design specifications;

[0164] The beneficial effect of adopting this technical solution is that it provides a method for evaluating the durability of bridge systems under normal use limit states. It can comprehensively evaluate the durability of bridge systems under major limit states, facilitate the screening of bridges with better durability, and provide guidance for the subsequent construction of similar bridges.

[0165] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A safety and durability evaluation method for I-beam-concrete composite continuous beam bridges is characterized by: The safety of bridges under the ultimate load-bearing capacity state is evaluated by the failure probability of the bridge system under the ultimate load-bearing capacity state; The durability of bridges under the ultimate bearing capacity state is evaluated by the reliability degradation rate of the bridge system under the ultimate bearing capacity state; The safety evaluation of bridges under the ultimate bearing capacity state specifically includes the following steps: S1. Determine the function: Bending bearing capacity formula: Z1=M R -M S ; When the plastic neutral axis is within the concrete panel section, , When the plastic neutral axis is within the steel beam section, ; ; Shear bearing capacity formula: Z2=V R -V S ; , ； The formula for the bending bearing capacity at the middle support position is: ; , ; In the formulas Z1 to Z3, the qualitative parameter η c Characterizes the closeness between the appearance quality of the bridge structure concrete and the acceptance standard. The closer to the acceptance standard, the better the η c The closer the value of is to 1; The nominal value parameters are characterized as follows: f cd is the compressive strength of concrete material, f d is the tensile strength of steel, f s is the tensile strength of the longitudinal reinforcement in the concrete panel, f vd is the shear strength of steel; The design value parameters are specifically characterized as follows: k is the fitting coefficient considering the slip effect; A c is the cross-sectional area of ​​the concrete bridge deck; y1 is the distance from the centroid of the concrete bridge deck in compression to the centroid of the steel beam in tension; A sc is the cross-sectional area of ​​the steel beam in compression; y2 is the distance from the centroid of the steel beam in compression to the centroid of the steel beam in tension; A r is the cross-sectional area of ​​the longitudinal reinforcement in the concrete bridge deck above the plastic neutral axis; y4 is the distance from the centroid of the cross section of the longitudinal reinforcement in the concrete bridge deck to the centroid of the cross section of the tensile zone of the steel beam; A cc is the area of ​​the concrete bridge deck above the plastic neutral axis; g is the dead load; L is the length of a single span of the bridge; 1+μ is the impact coefficient; h w is the web height of the steel beam; t w is the thickness of the steel beam web; A st is the tensile area of ​​the I-beam; h s is the height of the tension zone; h c is the height of the compression zone; x is the distance between the neutral axis of the cross section and the top surface of the I-beam; The parameters of random variables are characterized as follows: γ cf =Concrete material compressive strength value / f cd ; γ s = tensile strength of steel / f d ; γ ds = Steel beam cross-section size value / design value of steel beam cross-section size; γ dc =Bridge concrete panel cross-sectional dimension value / design value of bridge concrete panel cross-sectional dimension; γ r = tensile strength of steel bar / f s ; q is the uniform lane load; P k For concentrated lane loads; S2. Using the above random variable parameters as sampling objects and formulas Z1, Z2, and Z3 as performance functions, calculate the values ​​of each performance function. When any performance function value is less than or equal to 0, the bridge system fails; otherwise, the bridge system is valid. Repeat the sampling N times, and count the number of failures n. The failure probability is n / N. S3. Compare the failure probabilities of any two I-beam-concrete composite continuous beam bridges under the ultimate bearing capacity state. The lower the failure probability, the higher the safety of the bridge under the ultimate bearing capacity state.

2. The safety and durability evaluation method for an I-beam-concrete composite continuous beam bridge according to claim 1, wherein: The implementation of step S2 is as follows: obtaining the statistical characteristics of the structural uncertainty parameters, sampling using the Monte Carlo method based on MATLAB, and calculating the system failure probability under the ultimate bearing capacity state of the bridge; where: γ cf The specific acquisition of the statistical characteristics is as follows: taking multiple concrete material compressive strength values ​​measured on site as statistical objects, calculating the mean μ1 and standard deviation σ1 of the concrete material compressive strength, and then obtaining γ cf The normal distribution statistical characteristics N (μ1 / f cd ,σ1 / f cd ); γ ds The specific acquisition of the statistical characteristics is as follows: taking multiple steel beam cross-sectional dimensions measured on site as statistical objects, calculating the μ2 and standard deviation σ2 of the steel beam cross-sectional dimensions, and then obtaining γ ds The normal distribution statistical characteristics N (μ2 / design value of steel beam cross-section size, σ2 / design value of steel beam cross-section size); γ dc The specific acquisition of the statistical characteristics is as follows: taking the cross-sectional dimensions of multiple bridge concrete panels measured on site as statistical objects, the cross-sectional dimensions μ3 and standard deviation σ3 of the bridge concrete panels are calculated, and then γ is obtained. dc The normal distribution statistical characteristics N (μ3 / design value of the cross-sectional size of the bridge concrete panel, σ3 / design value of the cross-sectional size of the bridge concrete panel); γ s The statistical characteristics of γ are obtained specifically as follows: the tensile strength values ​​of multiple steels measured on site are used as statistical objects, the mean μ4 and standard deviation σ4 of the tensile strength of the steels are calculated, and then γ is obtained. s The normal distribution statistical characteristics of N (μ4 / f d ,σ4 / f d ); γ r The statistical characteristics of γ are obtained specifically as follows: the tensile strength values ​​of multiple steel bars measured on site are used as statistical objects, the mean μ5 and standard deviation σ5 of the tensile strength of steel bars are calculated, and then γ is obtained. r The statistical characteristics of the normal distribution N (μ5 / f s ,σ5 / f s ).

3. The safety and durability evaluation method for an I-beam-concrete composite continuous beam bridge according to claim 1, wherein: Qualitative parameter η c The specific method of determining the value of is as follows: according to the qualitative description of the appearance of the bridge concrete structure in the design specification, the quantitative description of the bridge assessment standard is determined. The quantitative description includes five scales, as follows: Scale 1: intact; under this scale, η c The value range is 0.95~1.0; Scale 2: The cumulative area of ​​network cracks is ≤ 20% of the component area, and the area of ​​a single crack is ≤ 1.0m 2 , or the main beam crack length ≤ 1 / 3 of the cross-sectional size; under this scale, η c The value range is 0.9~0.95; Scale 3: The cumulative area of ​​network cracks is ≤ 20% of the component area, and the area of ​​a single crack is > 1.0m 2 , or the main beam crack length is greater than 1 / 3 of the cross-sectional size and less than or equal to 2 / 3 of the cross-sectional size; under this scale, η c The value range is 0.85~0.90; Scale 4: The length of the main beam crack is greater than 2 / 3 of the cross-sectional size, and the spacing is less than 20 cm. c The value range is 0.80~0.850; Scale 5: The width of the main beam crack is greater than 1.0 mm, and the spacing is ≤ 10 cm. c The value range is below 0.

80.

4. The safety and durability evaluation method for an I-beam-concrete composite continuous beam bridge according to claim 1, wherein: It also includes evaluating the safety of the bridge under the serviceability limit state by using the failure probability of the bridge system under the serviceability limit state, which specifically includes the following steps: A1. Determine the function: The functional functions used to calculate the failure probability of the bridge system under the normal serviceability limit state include the maximum crack width formula Z4 and the mid-span deflection formula Z5; Formula Z4 is specifically: , ; Formula Z5 is specifically: ; Among them, f1 is the short-term deflection, f2 is the long-term deflection; the calculation formula of f1 is: , , , ;in, , , , , , , ; The calculation formula of f2 is: ,in, , ; In formula Z4 and formula Z5, the parameters are represented as follows: γ is the uncertainty coefficient of the calculation model; α cr is the stress characteristic coefficient of the component; f t is the tensile strength of steel fiber concrete; ρ te is the effective reinforcement ratio of the longitudinal tensile reinforcement; rs is the stress of the longitudinal tensile reinforcement at the crack section of the reinforced concrete member; l a is the average spacing of transverse reinforcement; f ry is the yield strength of the non-prestressed steel bars in the composite beam; f py is the yield strength of the prestressed steel bars in the composite beam; A s is the cross-sectional area of ​​the steel beam; f y is the yield strength of the steel beam; A P is the cross-sectional area of ​​the external prestressed tendons; f allow is the allowable deflection; B is the converted section stiffness of the composite beam; z1 is the distance from the centroid of the end prestressed tendon to the centroid of the converted section of the composite beam; l 1 is the projection length of the first section of prestressed tendons in the local coordinate system; θ1 is the angle between the first section of prestressed tendons and the horizontal line; θ2 is the angle between the second section of prestressed tendons and the horizontal line; B s is the converted section stiffness of the composite beam considering slip; m is the ratio of the distance from the beam end to the single point concentrated load loading point to the calculated span of the composite beam; r is the shear connection degree; K L is the shear stiffness of the shear connector per unit length; h sc E is the distance from the centroid of the steel beam section to the centroid of the concrete section; c is the elastic modulus of concrete; E s is the elastic modulus of steel; I c is the moment of inertia of the concrete section; I s is the moment of inertia of the steel beam section; A c is the cross-sectional area of ​​the concrete bridge deck; n s is the number of rows of studs or perforated plate connectors; K is the shear stiffness of a single shear connector; p is the spacing between connectors; σ e is the effective prestressing force of the prestressed tendons; λ(t) is a coefficient related to time; k1 is a coefficient related to the average stress of the concrete bridge deck; is the average stress of the concrete bridge deck; T p is the effective prestressing force of the prestressed tendons; A0 is the cross-sectional area of ​​the composite beam after cross-sectional conversion; I0 is the moment of inertia of the composite beam after cross-sectional conversion; e is the eccentricity of the prestressing force; A2. Calculation of failure probability of bridge system under serviceability limit state: With ρ te 、f t 、A r 、f ry 、A P 、f py 、A s 、f y 、E s 、E c 、A c ,A0,q,P k The sampling object is selected, and the function values ​​of formulas Z4 and Z5 are used to calculate each function. When any function value is less than or equal to 0, the bridge system fails. Otherwise, the bridge system is valid. Repeat the sampling M times, and count the number of failures m. The failure probability is m / M. A3. Safety evaluation of bridge system under normal serviceability limit state: Comparing the failure probabilities of any two I-beam-concrete composite continuous beam bridges under the serviceability limit state, the lower the failure probability, the higher the safety of the bridge under the serviceability limit state.

5. The safety and durability evaluation method for an I-beam-concrete composite continuous beam bridge according to claim 1, wherein: The specific steps for evaluating the durability of a bridge system under the ultimate bearing capacity state are as follows: B1. Determine the calculation formula: The calculation formula for the reliability degradation rate of a bridge under the ultimate bearing capacity state is: ; The ultimate bearing capacity state is one of the ultimate bearing capacity state of bending, the ultimate bearing capacity state of shear, and the ultimate bearing capacity state of bending at the middle support position; α1 represents the reliability degradation rate of the bridge under the ultimate bearing capacity state, μ R01 Characterizes the mean resistance of the bridge structure at the initial moment under the ultimate bearing capacity state; σ R01 Characterizes the standard deviation of the resistance of the bridge structure at the initial moment under the ultimate bearing capacity state; σ S1 represents the standard deviation of the load effect of the bridge structure under the ultimate bearing capacity state; λ´ represents the corrosion rate of the steel web; γ0 represents the design thickness of the steel web; B2. Calculation of the reliability degradation rate of bridges under the ultimate bearing capacity state: Taking λ´ and γ0 as sampling objects, calculate the α1 value, repeat the sampling P times, calculate the mean of the α1 values ​​of the P sampling times, and obtain the reliability degradation rate under the corresponding bearing capacity limit state; B3. Evaluation of bridge durability under the ultimate bearing capacity state: Comparing the reliability degradation rates of any two I-beam-concrete composite continuous beam bridges under the corresponding ultimate bearing capacity state, the lower the reliability degradation rate, the higher the durability of the bridge under the ultimate bearing capacity state.

6. The safety and durability evaluation method for an I-beam-concrete composite continuous beam bridge according to claim 5, characterized in that: It also includes the evaluation of the durability of the bridge system under the normal serviceability limit state, which includes the following steps: C1. Determine the calculation formula: The calculation formula for the reliability degradation rate of the bridge under the normal serviceability limit state is: ; Wherein, the serviceability limit state is one of the concrete cracking limit state in the negative bending moment zone and the mid-span deflection limit state; α2 represents the reliability degradation rate of the bridge under the serviceability limit state; When the serviceability limit state is the concrete cracking limit state in the negative moment zone, μ R02 Characterizes the maximum crack width limit, σ R02 is 0, σ S2 Characterizes the standard deviation of the maximum crack width; When the serviceability limit state is the mid-span deflection limit state, μ R02 Characterizes the deflection limit of the bridge mid-span, σ R02 is 0, σ S2 Characterizes the standard deviation of the actual deflection of the bridge at mid-span; C2. Calculation of the reliability degradation rate of bridges under the serviceability limit state: Take λ´ and γ0 as sampling objects, calculate the α2 value, repeat the sampling Q times, calculate the mean of the α2 values ​​of Q samplings, and obtain the required reliability degradation rate; C3. Evaluation of bridge durability under normal serviceability limit state: Comparing the reliability degradation rates of any two I-beam-concrete composite continuous beam bridges under the corresponding serviceability limit state, the lower the reliability degradation rate, the higher the durability of the bridge under the serviceability limit state.

7. The safety and durability evaluation method for an I-beam-concrete composite continuous beam bridge according to claim 1, wherein: The cross-sectional dimensions in the steel beam cross-sectional dimension value are derived from any one of the thickness of the upper flange plate, the thickness of the lower flange plate, the web thickness, the web width, and the width of the steel beam; the cross-sectional dimensions in the bridge concrete panel cross-sectional dimension value are derived from any one of the length, width, and height of the concrete panel.

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