A prestressed concrete bridge rapid evaluation method based on elastic modulus

Abstract

The application discloses a prestressed concrete bridge rapid evaluation method based on elastic modulus, and belongs to the technical field of bridge engineering nondestructive testing and health monitoring. The method first selects a key test area and a load working condition according to bridge stress characteristics; subsequently, adopts an impact elastic wave technology to test a tangent elastic modulus of concrete on site; further, inverses actual stress levels of the structure through elastic modulus changes based on a concrete constitutive model, and identifies damage states in combination with wave speed analysis; finally, compares measured stress levels with design values, and comprehensively considers damage conditions, so that rapid grading evaluation of bridge bearing capacity and safety conditions is realized. The application realizes rapid, nondestructive and quantitative evaluation of the prestressed concrete bridge, overcomes the limitations of high cost, long cycle or difficulty in reflecting overall stress states of traditional methods, and is suitable for conventional screening, emergency evaluation and on-site calibration of a health monitoring system of the bridge.

Description

Technical Field

[0001] This invention relates to the field of bridge engineering structural testing and health monitoring technology, and in particular to a rapid evaluation method for prestressed concrete bridges based on the elastic modulus. Background Technology

[0002] Prestressed concrete bridges are widely used in infrastructure such as highways and railways due to their excellent mechanical properties and economic efficiency. However, with increasing service life, the structural performance of these bridges deteriorates under the combined effects of environmental erosion, material aging, fatigue loads, and prestress loss, posing a potential threat to their operational safety. Therefore, regular and effective performance evaluation and safety diagnosis of in-service prestressed concrete bridges are crucial to ensuring their service life and public safety.

[0003] Currently, the conventional testing and evaluation methods for prestressed concrete bridges mainly include the following categories:

[0004] Manual visual inspection relies on the inspector's experience and mainly discovers obvious defects on the surface of the structure (such as cracks and peeling). However, it is difficult to effectively identify and quantify internal structural damage, material performance degradation, and changes in the overall stress state, resulting in a high rate of missed detections.

[0005] Specialized non-destructive testing methods include ultrasonic rebound testing, steel corrosion potential detection, and crack depth detection. These techniques typically target specific performance characteristics or localized defects in a structure. While they can provide quantitative data, they are mostly localized information in the form of "points" or "lines," making it difficult to comprehensively and holistically reflect the overall performance and remaining load-bearing capacity of the bridge structure under current loads.

[0006] Load testing, including static and dynamic load tests, is currently the most direct and authoritative method for evaluating the actual working condition and load-bearing capacity of bridges. This method involves applying equivalent loads to the bridge and measuring the structure's displacement, strain, and dynamic characteristics to comprehensively assess its performance. However, load testing is typically costly, time-consuming, requires traffic interruption or control, and the loading process itself may pose additional risks to already damaged or aging bridge structures. Therefore, it is difficult to use as a routine testing method for large-scale, frequent testing.

[0007] Long-term structural health monitoring systems acquire real-time environmental and structural response data by deploying sensor networks at key locations on bridges. These systems are primarily used for extra-long span and important landmark bridges, enabling continuous monitoring. However, the system's construction and maintenance costs are extremely high, data analysis is complex, and sensors suffer from drift and failure issues. Therefore, its economic viability and applicability are insufficient for the vast number of ordinary small- and medium-span prestressed concrete bridges.

[0008] In summary, existing technologies suffer from limitations such as strong subjectivity, incomplete assessment, high cost, low efficiency, and inconvenient implementation. There is an urgent need in this field to develop a rapid, non-destructive, and quantitatively assessable on-site testing and evaluation method for the overall stress state and load-bearing capacity of prestressed concrete bridges. This method would compensate for the shortcomings of existing technologies and enable efficient and economical screening and early warning of bridge safety conditions. Summary of the Invention

[0009] This invention aims to address the shortcomings of existing conventional testing methods (such as manual visual inspection and localized specialized testing) in rapidly and quantitatively assessing the overall stress state and load-bearing capacity of bridge structures. Furthermore, while traditional load testing methods provide authoritative results, they suffer from high costs, long cycles, traffic disruptions, and potential additional risks to the structure, making them unsuitable for large-scale, frequent routine inspections. Additionally, the current technological system lacks a non-destructive testing method that can directly and efficiently correlate the microscopic mechanical properties of materials with the macroscopic load-bearing capacity of the structure, thus hindering convenient diagnosis and early warning of bridge safety conditions. Therefore, this invention provides a rapid evaluation method for prestressed concrete bridges based on the elastic modulus.

[0010] On the one hand, this invention provides a rapid evaluation method for prestressed concrete bridges based on the elastic modulus, including: According to the present invention, a rapid evaluation method for prestressed concrete bridges based on the elastic modulus is provided. A rapid evaluation method for prestressed concrete bridges based on the elastic modulus provided by the present invention includes the following steps: Step S1: Selection of test area and working conditions: Based on the bridge design drawings and stress analysis, determine the key test parts of the beam and select at least two load conditions for testing. The load conditions include the bridge's self-weight state and the state of self-weight and external load acting together. Step S2: On-site test of elastic modulus: The impact elastic wave method is used to test the selected location to obtain the elastic wave velocity, and the on-site tangential elastic modulus of the concrete is calculated based on the theoretical relationship between wave velocity and elastic modulus. Step S3: Stress Level and Damage State Analysis: Based on the tangential elastic modulus measured in Step S2, combined with the constitutive model of concrete, the current stress level of the concrete is inverted; and through elastic wave signal analysis, the potential damage state of the structure is identified. Step S4: Evaluation of bridge bearing capacity and safety status: Compare the stress level obtained from the inversion in step S3 with the bridge design stress level and calculate the stress level ratio; at the same time, in conjunction with the damage status identified in step S3, classify and evaluate the bridge's bearing capacity and overall safety status.

[0011] In some embodiments of the present application, in step S1, the key test parts include at least two of the compression zone, the tension zone or the potential tension zone of the beam body, and the area near the neutral axis.

[0012] In some embodiments of the present application, in step S2, the impact elastic wave method is the transmission method or the surface single-sided propagation method; when calculating the in-situ tangent elastic modulus (Et), the formula used is: Or Or

[0013] Where ρ is the concrete density, Vp is the wave velocity of the longitudinal elastic wave (P wave), and μ is the Poisson's ratio of the concrete.

[0014] In some embodiments of the present application, in step S3, the constitutive relation model of the concrete includes the hyperbolic model recommended by the code or the Guo Zhenhai power function model.

[0015] In some embodiments of the present application, in step S3, the identification of the damage state through elastic wave signal analysis specifically includes: qualitatively judging the existence and development status of cracks by comparing and analyzing the propagation speed differences between the tensile wave and the compressive wave.

[0016] In some embodiments of the present application, in step S4, the calculation formula of the stress level ratio (Rσ) is:

[0017] Where σ / f C Is the measured stress level, and σd / f Cd Is the design stress level.

[0018] In some embodiments of the present application, the hierarchical evaluation is specifically: When Rσ ≤ 0.8, it is evaluated that the bearing capacity is sufficient; When 0.8 < Rσ ≤ 1.0, it is evaluated that the bearing capacity meets the requirements; When 1.0 < Rσ ≤ 1.2, it is evaluated that the bearing capacity is close to the critical value; When Rσ > 1.2, it is evaluated that the bearing capacity is insufficient.

[0019] In some embodiments of the present application, the method is applicable to the rapid and safe assessment of prestressed concrete beam, slab or pier structures, or as an in-situ calibration method for a long-term health monitoring system.

[0020] Compared with the prior art, the beneficial effects of the present application are as follows: By obtaining the elastic modulus, which reflects the microscopic mechanical state of a material, through impact elastic wave technology and correlating it with the macroscopic stress state of the structure, this method overcomes the subjectivity of manual visual inspection and the one-sidedness of localized specialized testing. This method eliminates the need for large-scale load tests, can be implemented rapidly without disrupting traffic or under temporary control, and directly outputs quantitative evaluation indicators such as stress level and bearing capacity ratio, providing objective and comprehensive decision-making basis for bridge safety management. Furthermore, by utilizing the sensitivity of the tangential elastic modulus of concrete to stress state, and employing a technical approach of multi-condition elastic modulus testing, constitutive model stress inversion, and bearing capacity comparison evaluation, it indirectly achieves the assessment of bridge bearing capacity. This avoids the high economic cost, long time cycle, and potential additional damage risks to the structure associated with traditional load tests, making it particularly suitable for a large number of small-to-medium span bridges. Routine screening of bridges; by comparing and analyzing the variation of elastic modulus of key parts (compression, tension, and neutral zone) under different load conditions, and combining the wave velocity difference analysis of tensile and compressive waves, this invention can not only quantitatively invert stress levels, but also qualitatively identify the development of cracks and the accumulation of damage. This method, which combines stress state analysis with damage identification, enhances the early warning capability for potential structural safety hazards. The testing equipment of this method is lightweight and the process is standardized, making it easy to deploy and implement quickly on-site. At the same time, the on-site elastic modulus benchmark value obtained by this method can provide on-site calibration and verification of key parameters for existing long-term structural health monitoring systems, effectively solving the drift problem in long-term sensor monitoring, improving the data reliability and evaluation accuracy of the entire monitoring system, and achieving complementary advantages of rapid detection and long-term monitoring.

[0021] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of force analysis provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the tangential elastic modulus ~x relationship when different grades of concrete are eccentrically tensioned, provided by an embodiment of the present invention. Detailed Implementation

[0024] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0025] Example 1 This invention provides a rapid evaluation method for prestressed concrete bridges based on the elastic modulus. Please refer to [link to relevant documentation]. Figures 1-2 As shown, it includes: A rapid evaluation method for prestressed concrete bridges based on the modulus of elasticity, characterized by the following steps: Step 1: Selection of Test Area and Operating Conditions Based on the bridge design drawings and stress analysis, the key test locations for the beam were determined, including: The pressure zone (such as the upper edge); Tension zone or potential tension zone (below the lower edge); The region near the neutral axis.

[0026] Select at least two load conditions for testing, including: bridge self-weight condition; and condition where self-weight and typical traffic load act together.

[0027] Step 2: On-site testing of elastic modulus The impact elastic wave method is employed, with excitation points and sensors arranged at selected test locations. Impact elastic waves (P-waves) are excited and received, wave velocities are measured, and the in-situ tangential elastic modulus (Et) of the concrete is calculated based on the theoretical relationship between wave velocity and elastic modulus (considering corrections for the influence of reinforcing steel). Testing methods can employ transmission or surface single-sided propagation, and signal noise reduction processing (such as EMD) can be performed to improve accuracy.

[0028] This method uses impact elastic waves as the test medium. By measuring the wave velocity of the elastic waves, the dynamic tangential elastic modulus Et of the material is calculated, and the corresponding elastic modulus Ec of concrete is estimated. For a one-dimensional homogeneous elastic body, its dynamic elastic modulus is Compared with elastic wave P-wave velocity The relationship can be represented as: ,

[0029] in, For concrete, the density of the material is... The typical value is around 2400 kg / m³. However, the P-wave velocity varies slightly when the test object is 2D or 3D. 2D: ,

[0030] 3D: ,

[0031] For surface waves (Rayleigh waves), the relationship can be expressed as: Rayleigh wave: ,

[0032] There are many empirical formulas relating the dynamic and static elastic moduli of concrete, with the Lydon and Balendran formulas being a typical example:

[0033] However, this correlation only applies to medium- and low-strength concrete. More generally, the following can be used (unit: GPa):

[0034] Step 3: Stress Level and Damage State Analysis Establish benchmark: Under its own weight, test the initial elastic modulus of each part.

[0035] Load response analysis: After applying traffic load, the change in elastic modulus (ΔEt) is measured.

[0036] Stress inversion: Based on the constitutive model of concrete (such as the hyperbolic model recommended by the code or the power function model of the Zhenhai standard), a mathematical relationship is established between the tangent elastic modulus (Et) of concrete and the stress level (σ / fc). Substituting the measured Et into this relationship, the current stress level of the concrete is inverted.

[0037] The relationship between the elastic modulus and the stress level can be obtained by differentiating the stress-strain curve of concrete, which yields the tangential elastic modulus at each point.

[0038] Hyperbolic model of the compression zone (standard model) The pressure-strain relationship of concrete under compression can be rewritten as follows:

[0039] Pair the left and right sides of the above equation respectively. Differentiating and rearranging, we get:

[0040] It can also be rewritten as

[0041] in, In a certain , The tangential elastic modulus of concrete can be obtained from the elastic wave velocity. To correspond to the concrete compressive stress reaching Secant modulus of elasticity at time,

[0042] for , for a certain stress ( , The stress level of concrete under the condition of ).

[0043] Power function model of the compressed region (Zhenhai model) right Taking the derivative directly, we get:

[0044] Furthermore, when it is known At that time, by

[0045] By taking a positive value, we can obtain the stress and stress level.

[0046] However, it should be noted that in the actual testing process, due to factors such as concrete strength, peak strain, and... Since the values ​​are all unknowns, a comprehensive analysis of other parameters is required.

[0047] The quadratic function model (canonical model) in the tension region right Taking the derivative directly, we get:

[0048]

[0049] To correspond to the tensile stress of concrete reaching secant modulus of elasticity at time

[0050] Furthermore, when the test results At that time, we can obtain:

[0051] Tangential elastic modulus of concrete near the neutral axis In concrete beams, there exists a neutral axis where the normal stress is close to zero. On the other hand, in the prestressed compression zone (such as the lower edge of a simply supported beam), due to the loss of prestress, the compressive stress in the concrete gradually decreases and transforms into a tensile stress zone. Therefore, it is meaningful to study the change in the tangential modulus of elasticity of concrete near the neutral axis.

[0052] Near the neutral axis, x 0. The tangential elastic moduli obtained from different models are shown in the table below: Table 5-1 Elastic modulus Et near the neutral axis (standard value)

[0053] It can be seen that the tangential elastic modulus near the neutral axis has the following characteristics: The moduli are basically the same; The eccentric tensile modulus is slightly lower; Damage identification: If the elastic modulus of the tension zone decreases significantly when the load increases, it may indicate the presence of tensile stress or microcracks in that area. If the elastic modulus of the compression zone first increases and then decreases with the load, it may reflect changes in stress state or accumulation of micro-damage. By comparing the differences in wave velocities between tensile and compressive waves, the existence and development of cracks can be qualitatively determined.

[0054] Step 4: Evaluation of Bridge Load-Bearing Capacity and Safety Status The concrete stress level (σ / fc) and the identified crack conditions are derived from the measured elastic modulus and combined with the theoretical calculations from the bridge design stage (including the design stress level σd / fcd and the allowable crack conditions) to directly assess the bridge's load-bearing capacity and overall safety.

[0055] 1) Bearing capacity evaluation based on stress level comparison design By comparing the measured stress level with the design stress level, the bearing capacity state can be directly assessed. (1) Determination of design reference values Extract the design stress level (σ) of key sections from bridge design drawings and calculation sheets. d / f cd ), typically includes: Allowable stress level under normal serviceability limit state (e.g., σ) d / f cd ≤ 0.6); Design stress level under ultimate limit state of bearing capacity (e.g., σ) d / f cd ≤ 0.85); (2) Stress level comparison evaluation criteria Define the stress level ratio (R) σ As a core evaluation indicator:

[0056] According to R σ Values ​​are used to classify bearing capacity: Table 5-2 Stress Level-Bearing Capacity Evaluation Table

[0057] 2) Safety evaluation combining crack condition and design allowable conditions (1) Design crack control standards According to design specifications, prestressed concrete bridges under normal service conditions are generally fully prestressed or Class A prestressed components, requiring: Under short-term load combinations: tensile stress (σ) is not allowed. st ≤ 0); Under long-term load combinations: tensile stress should be controlled within a certain range; If cracks are permitted in the design, there should be a clear limit on the crack width (e.g., ≤0.2mm).

[0058] (2) Evaluation of crack condition compared with design No cracks: Meets the expectations of the fully prestressed design and is in good safety condition.

[0059] The appearance of cracks indicates that the actual stress state may have exceeded the design expectations, and a risk assessment should be conducted in conjunction with the stress level.

[0060] Crack development degree: The crack activity is qualitatively assessed by the difference in elastic wave velocity and compared with the design allowable crack state.

[0061] (3) Comprehensive safety status evaluation matrix Combined stress level ratio (R) σ Based on the degree to which the crack condition conforms to the design expectations, a rapid safety evaluation matrix is ​​established: Table 5-3 Bridge Safety Status Evaluation Table

[0062] Technical problems solved and advantages Evaluation principle based on elastic modulus stress sensitivity: For the first time, the micro-mechanical properties of concrete elastic modulus changing with stress state are systematically applied to the rapid load-bearing capacity evaluation of macro-bridge structures, and a quantitative evaluation chain of "elastic modulus change, stress level / structural damage, and load-bearing capacity" is established.

[0063] Multi-condition comparative testing and stress inversion technology: By comparing the self-weight and loading states, the change in elastic modulus caused by the load is separated, and the stress of the actual bridge is inverted using the concrete constitutive model, realizing indirect testing of bearing capacity without large-scale loading.

[0064] Integration of rapid on-site testing technology for impact elastic waves: This technology combines high-precision impact elastic wave modulus testing with the stress characteristics of bridge structures to form a standardized rapid testing scheme for different regions of the beam (compression, tension, and neutral zones).

[0065] The method of this invention can be used independently for rapid detection, or as a means of on-site calibration for long-term health monitoring systems, solving the problem of sensor drift and improving the reliability and accuracy of the monitoring system.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A rapid evaluation method for prestressed concrete bridges based on the modulus of elasticity, characterized in that, It includes the following steps: Step S1: Selection of test area and working conditions: According to the bridge design drawings and stress analysis, determine the key test parts of the beam body, and select at least two load working conditions for testing. The load working conditions include the self-weight state of the bridge and the state of the combined action of self-weight and external loads; Step S2: In-situ test of elastic modulus: Use the impact elastic wave method to test at the selected parts to obtain the elastic wave velocity, and calculate the in-situ tangent elastic modulus of concrete according to the theoretical relationship between the wave velocity and the elastic modulus; Step S3: Analysis of stress level and damage state: Based on the tangent elastic modulus measured in Step S2, combined with the constitutive relationship model of concrete, invert the current stress level of concrete; and identify the potential damage state of the structure through elastic wave signal analysis; Step S4: Evaluation of bridge bearing capacity and safety condition: Compare the stress level inverted in Step S3 with the bridge design stress level, and calculate the stress level ratio; at the same time, combined with the damage state identified in Step S3, conduct a hierarchical evaluation of the bearing capacity and overall safety condition of the bridge.

2. The rapid evaluation method for prestressed concrete bridges based on elastic modulus according to claim 1, characterized in that, In Step S1, the key test parts include at least two of the compression zone, tension zone or potential tension zone of the beam body, and the area near the neutral axis.

3. The rapid evaluation method for prestressed concrete bridges based on elastic modulus according to claim 1, characterized in that, In Step S2, the impact elastic wave method is the transmission method or the surface single-sided propagation method; when calculating the in-situ tangent elastic modulus (Et), the formula used is: or or where ρ is the concrete density, Vp is the elastic longitudinal wave (P-wave) velocity, and μ is the concrete Poisson's ratio.

4. The rapid evaluation method for prestressed concrete bridges based on elastic modulus according to claim 1, characterized in that, In Step S3, the constitutive relationship model of concrete includes the hyperbolic model recommended by the code or the Guo Zhenhai power function model.

5. The rapid evaluation method for prestressed concrete bridges based on elastic modulus according to claim 1, characterized in that, In Step S3, the identification of the damage state through elastic wave signal analysis specifically includes: qualitatively judging the existence and development status of cracks by comparing and analyzing the propagation velocity differences between tensile waves and compressive waves.

6. The rapid evaluation method for prestressed concrete bridges based on elastic modulus according to claim 1, characterized in that, In step S4, the formula for calculating the stress level ratio (Rσ) is: Where, σ / f C For the measured stress level, σd / f Cd To design the stress level.

7. The rapid evaluation method for prestressed concrete bridges based on elastic modulus according to claim 6, characterized in that, The hierarchical evaluation is specifically: When Rσ ≤ 0.8, it is evaluated that the bearing capacity is sufficient; When 0.8 < Rσ ≤ 1.0, it is evaluated that the bearing capacity meets the requirements; When 1.0 < Rσ ≤ 1.2, it is evaluated that the bearing capacity is close to the critical value; When Rσ > 1.2, it is evaluated that the bearing capacity is insufficient.

8. The rapid evaluation method for prestressed concrete bridges based on the modulus of elasticity according to any one of claims 1 to 7, characterized in that, The method is applicable to the rapid safety assessment of prestressed concrete beams, slabs or pier structures, or as an in-situ calibration method for long-term health monitoring systems.

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