Method for evaluating bearing capacity of reinforced concrete beam

Abstract

The invention relates to a reinforced concrete beam bearing capacity evaluation method applied to the technical field of civil engineering. Comprising the steps of performing finite element modeling on a to-be-evaluated beam, performing reduction of different degrees on the area of a tensile steel bar to represent uniform damage of the tensile steel bar, and calculating a bending moment displacement curve at a loading point under a non-destructive working condition and different damage working conditions based on a finite element model. And according to the bending moment displacement curve under each working condition, obtaining the corresponding tensile steel bar yield bending moment under each working condition and the slope of each bending moment displacement curve in the elastic stage, and the like. The bearing capacity of the reinforced concrete beam with uniform damage is quantitatively evaluated by combining simulation data and field actual measurement data, the method has the advantages of being clear in concept and simple and convenient to calculate, and technicians in the field can quickly and accurately evaluate the bearing capacity of the reinforced concrete beam conveniently; powerful support can be provided for bearing capacity evaluation of the in-service reinforced concrete bridge.

Description

Technical Field

[0001] The invention relates to a bearing capacity evaluation method, in particular to a reinforced concrete beam bearing capacity evaluation method applied in the technical field of civil engineering. Background Art

[0002] For civil engineering structures, especially bridge structures, their bearing capacity will continue to degrade under the influence of the environment and loads. When the load exceeds its bearing capacity, it will lead to the tragedy of bridge collapse, vehicle destruction and death. Accurately evaluating the bearing capacity of in-service bridges has important theoretical and practical significance. Therefore, a large number of scholars at home and abroad have conducted extensive research on the bearing capacity evaluation methods of reinforced concrete beams.

[0003] The invention patent with publication number CN110414580A discloses a method for evaluating the bearing capacity of reinforced concrete deep beams based on a random forest algorithm. The invention can directly give the shear strength of the node based on the input relevant parameters, avoiding the problems of high time consumption and high cost of traditional experimental methods, and also avoiding the problems of multiple assumptions, unclear mechanisms, and complex calculation processes brought about by the use of theoretical analysis methods.

[0004] The invention patent with publication number CN118194403A provides a method for calculating the bending bearing capacity of reinforced concrete beams under different cooling methods. The calculation method proposed in this invention can accurately predict the bending bearing capacity of reinforced concrete beams under two different cooling methods, namely water spray cooling and natural cooling, in actual fires, and can provide a theoretical basis for the repair and reinforcement of reinforced concrete beams after fire extinguishing by water spraying.

[0005] However, the current theoretical calculation methods have many parameters, inconvenient values, complex calculations, and insufficient accuracy of calculation results. On-site load tests have many loading conditions and can only qualitatively evaluate the bearing capacity but cannot quantify its specific value. Therefore, we propose a method for evaluating the bearing capacity of reinforced concrete beams. Summary of the invention

[0006] In view of the above-mentioned prior art, the technical problem to be solved by the present invention is that the current theoretical calculation method has the problems of a large number of parameters, inconvenient value selection, complex calculation, and insufficient accuracy of calculation results. The on-site load test also has the shortcomings of many loading conditions and can only qualitatively evaluate the bearing capacity but cannot quantify its specific value.

[0007] To solve the above problems, the present invention provides a method for evaluating the bearing capacity of a reinforced concrete beam, comprising the following steps:

[0008] S1. Perform finite element modeling on the beam to be evaluated to obtain a finite element model;

[0009] S2. In the finite element model, the tensile steel bar area is reduced to different degrees to characterize the uniform damage of the tensile steel bar, thereby obtaining different damage conditions D1, D2, D3...D n ;

[0010] S3. Calculate the non-destructive working condition D0 and different damage working conditions D1, D2, D3...D based on the finite element model n Moment displacement curve at the lower loading point;

[0011] S4. According to the moment displacement curves under various working conditions, the corresponding yield moments of the tensile reinforcement under various working conditions M0, M1, M2, M3...M n , and the slopes of the elastic stages of the moment-displacement curves K0, K1, K2, K3...K n ;

[0012] S5, for [K0, K1, K2, K3...K n ] and [M0, M1, M2, M3...M n ] to fit and get the equation of the straight line:

[0013] y=Kx+b (1)

[0014] In the formula, y is the dependent variable, x is the independent variable, K and b are constants;

[0015] S6. Carry out a load test on the beam to be evaluated and obtain the slope K of the elastic stage of the moment displacement curve at the loading point. p , K p Substituting it into formula (1) as the independent variable, the calculated y value is the section yield moment M at the loading point of the beam to be evaluated. p , the calculation formula is:

[0016] M p =K×K p +b (2).

[0017] In the above-mentioned reinforced concrete beam bearing capacity assessment method, the bearing capacity of reinforced concrete beams with uniform damage is quantitatively assessed by combining simulation data and field measured data, which has the advantages of clear concepts and simple calculations.

[0018] As a further improvement of the present application, in step S1, in order to ensure that the evaluation result is on the safe side, in the finite element model, the yield strength of the tensile steel bar is taken as the minimum value of the measured value, and the elastic modulus of the steel bar and concrete is taken as the maximum value of the measured value.

[0019] As a further improvement of the present application, the bending moment displacement curve in step S3 includes an elastic stage and a yield stage.

[0020] As a further improvement of the present application, step S3 also includes the following content: comparing the elastic stage of the moment-displacement curve under the lossless working condition calculated based on the finite element model with the elastic stage of the measured moment-displacement curve of the lossless beam to ensure the accuracy of parameters and calculations in the finite element model.

[0021] As a further improvement of the present application, when calculating the moment-displacement curve at the loading point based on the finite element model in step S3, the loading method can adopt single-point or multi-point vertical loading, and the loading point and the displacement measurement point can be the same cross-sectional position or different cross-sectional positions.

[0022] As a further improvement of the present application, the method is applicable to the bearing capacity assessment of reinforced concrete beams under the condition of uniform damage to the tensile reinforcement.

[0023] In summary, the reinforced concrete beam bearing capacity assessment method in the present application, by combining simulation data and field measured data to perform quantitative assessment of the bearing capacity of reinforced concrete beams with uniform damage, has the advantages of clear concepts and simple calculations, which facilitates technical personnel in the field to quickly and accurately assess the bearing capacity of reinforced concrete beams, and can provide strong support for the bearing capacity assessment of reinforced concrete bridges in service. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a method flow chart of a method for evaluating the bearing capacity of reinforced concrete beams in the first embodiment of the present application;

[0025] Figure 2 This is a schematic diagram of the cross-sectional structure of a simply supported T-beam in the second embodiment of the present application;

[0026] Figure 3 The bending moment displacement curve at the loading point under different damage conditions obtained by finite element model simulation in the second embodiment of the present application;

[0027] Figure 4 This is a fitting effect diagram of the elastic phase slope of the moment-displacement curve and the yield moment at the loading point under different damage conditions in the second embodiment of the present application;

[0028] Figure 5 This is a graph of the bending moment displacement at the measured loading point of the simply supported T-beam in the second embodiment of the present application. DETAILED DESCRIPTION

[0029] Two implementation modes of the present application are described in detail below with reference to the accompanying drawings.

[0030] The first implementation method:

[0031] Figure 1 A method for evaluating the bearing capacity of a reinforced concrete beam is shown, comprising the following steps:

[0032] S1. Conduct finite element modeling on the beam to be evaluated to obtain a finite element model. To ensure that the evaluation result is on the safe side, in the finite element model, the yield strength of the tensile steel bar is taken as the minimum value of the measured value, and the elastic modulus of the steel bar and concrete is taken as the maximum value of the measured value;

[0033] S2. In the finite element model, the tensile steel bar area is reduced to different degrees to characterize the uniform damage of the tensile steel bar, thereby obtaining different damage conditions D1, D2, D3...D n ;

[0034] S3. Calculate the non-destructive working condition D0 and different damage working conditions D1, D2, D3...D based on the finite element model n The moment displacement curve at the lower loading point includes the elastic stage and the yield stage. The loading method can be single-point or multi-point vertical loading. The loading point and the displacement measurement point can be at the same cross-sectional position or at different cross-sectional positions. The moment displacement curve under the non-destructive working condition calculated based on the finite element model is compared with the measured moment displacement curve of the non-destructive beam (only the elastic stage is compared) to ensure the accuracy of the parameters and calculations in the finite element model;

[0035] S4. According to the moment displacement curves under various working conditions, the corresponding yield moments of the tensile reinforcement under various working conditions M0, M1, M2, M3...M n , and the slopes of the elastic stages of the moment-displacement curves K0, K1, K2, K3...K n ;

[0036] S5, for [K0, K1, K2, K3...K n ] and [M0, M1, M2, M3...M n ] to fit and get the equation of the straight line:

[0037] y=Kx+b (1)

[0038] In the formula, y is the dependent variable, x is the independent variable, K and b are constants;

[0039] S6. Carry out a load test on the beam to be evaluated and obtain the slope K of the elastic stage of the moment displacement curve at the loading point. p , K p Substituting it into formula (1) as the independent variable, the calculated y value is the section yield moment M at the loading point of the beam to be evaluated. p , the calculation formula is:

[0040] M p =K×K p +b (2).

[0041] The reinforced concrete beam bearing capacity assessment method in the present application performs a quantitative assessment of the bearing capacity of reinforced concrete beams with uniform damage by combining simulation data and field measured data. It has the advantages of clear concepts and simple calculations, and is convenient for technical personnel in this field to quickly and accurately assess the bearing capacity of reinforced concrete beams, and can provide strong support for the bearing capacity assessment of reinforced concrete bridges in service.

[0042] It should be noted that the bearing capacity assessment method in this application is mainly applicable to the bearing capacity assessment when the tensile steel bars in reinforced concrete beams are uniformly damaged (such as uniformly corroded).

[0043] The second implementation method:

[0044] Please refer to Figure 2-Figure 5 , taking a beam in a reinforced concrete simply supported T-beam bridge as an example, the reinforced concrete beam bearing capacity evaluation method in the first implementation mode is explained. The simply supported T-beam is 19.96m long, with a calculated span of 19.50m and a cross-sectional size of Figure 2 As shown in the figure, the concrete strength grade of the beam is C30, and the main reinforcement is HRB335 steel bar. The tensile reinforcement of the beam has a certain degree of uniform corrosion damage. It is necessary to quantitatively evaluate the bearing capacity of the beam. The evaluation method is as follows:

[0045] 1. The load-displacement response of the beam under different damage degrees D0, D1, D2, and D3 is calculated by the finite element model. The damage is achieved by reducing the area of ​​the tensile reinforcement. The loading method is three-point loading, and the displacement measurement point is the loading point. When calculating by the finite element model, the yield strength of the tensile reinforcement takes the minimum value of the measured value, and the elastic modulus of the reinforcement and concrete takes the maximum value of the measured value. The moment displacement curves at the loading point under different damage degrees calculated by the finite element model are as follows: Figure 3 As shown;

[0046] 2. According to the bending moment displacement curves under different damage degrees D0, D1, D2, and D3, the corresponding elastic stage curve slopes K0 = 36.64 kN.m / mm, K1 = 33.52 kN.m / mm, K2 = 29.84 kN.m / mm, K3 = 25.07 kN.m / mm and the yield bending moments at the loading point M0 = 2384 kN.m, M1 = 2107 kN.m, M2 = 1830 kN.m, and M3 = 1467 kN.m are fitted. The fitting effect is as follows: Figure 4 As shown, the coefficient of determination (R-square) = 0.9987, and the linear equation is: M p =78.67K p -513;

[0047] 3. Carry out a load test on the beam and obtain the moment displacement curve at the loading point as shown in Figure 5 As shown, according to the graph, the slope K of the elastic stage of the moment displacement curve is obtained p =31.75 kN.m / mm, substituting it into the above linear equation, we can get the yield moment M at the loading point of the beam. p =1984.8kN.m.

[0048] The yield moment evaluated by this method is 1984.8 kN.m, and the measured value is 1961 kN.m, with an error of 1.21%.

[0049] In view of current practical needs, the above-mentioned implementation mode adopted in this application is not limited to the scope of protection. Various changes made within the knowledge scope of technical personnel in this field without departing from the concept of this application still fall within the scope of protection of the present invention.

Claims

1. A method for evaluating the bearing capacity of a reinforced concrete beam, characterized in that: The following steps are involved: S1. Perform finite element modeling on the beam to be evaluated to obtain a finite element model; S2. In the finite element model, the tensile steel bar area is reduced to different degrees to characterize the uniform damage of the tensile steel bar, thereby obtaining different damage conditions D1, D2, D3...D n ; S3. Calculate the non-destructive working condition D0 and different damage working conditions D1, D2, D3...D based on the finite element model n Moment displacement curve at the lower loading point; S4. According to the moment displacement curves under various working conditions, the corresponding yield moments of the tensile reinforcement under various working conditions M0, M1, M2, M3...M n , and the slopes of the elastic stages of the moment-displacement curves K0, K1, K2, K3...K n ; S5. Use the equation of the straight line to calculate [K0, K1, K2, K3...K n ] and [M0, M1, M2, M3...M n ] to fit, the straight line equation is: y=Kx+b (1) In the formula, y is the dependent variable, x is the independent variable, K and b are coefficients, and K and b are determined by fitting; S6. Carry out a load test on the beam to be evaluated and obtain the slope K of the elastic stage of the moment displacement curve at the loading point. p , K p Substituting it into formula (1) as the independent variable, the calculated y value is the section yield moment M at the loading point of the beam to be evaluated. p , the calculation formula is: M p =K×K p +b (2)。 2. A reinforced concrete beam bearing capacity evaluation method according to claim 1, characterized in that: In step S1, in order to ensure that the evaluation result is on the safe side, in the finite element model, the yield strength of the tensile steel bar is taken as the minimum value of the measured value, and the elastic modulus of the steel bar and concrete is taken as the maximum value of the measured value.

3. A reinforced concrete beam bearing capacity evaluation method according to claim 1, characterized in that: The moment displacement curve in step S3 includes an elastic stage and a yield stage.

4. A reinforced concrete beam bearing capacity evaluation method according to claim 3, characterized in that: The step S3 also includes the following contents: comparing the elastic phase of the moment displacement curve under the lossless working condition calculated based on the finite element model with the elastic phase of the measured moment displacement curve of the lossless beam to ensure the accuracy of the parameters and calculations in the finite element model.

5. A reinforced concrete beam bearing capacity evaluation method according to claim 1, characterized in that: When calculating the moment displacement curve at the loading point based on the finite element model in step S3, the loading method may be single-point or multi-point vertical loading, and the loading point and the displacement measurement point may be at the same cross-sectional position or at different cross-sectional positions.

6. A reinforced concrete beam bearing capacity evaluation method according to claim 1, characterized in that: This method is suitable for the bearing capacity assessment of reinforced concrete beams with uniformly damaged tensile reinforcement.

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