A method for assessing damage level of reinforced concrete building structures

Abstract

The present invention belongs to the field of building damage detection, and provides a method for assessing the damage level of reinforced concrete building structures. The method comprises the following steps: performing a modal test on the reinforced concrete building structure to be assessed, obtaining its modal parameters, which include at least natural frequency, damping ratio, and vibration mode; applying a dynamic load to the reinforced concrete building structure to be assessed, measuring its energy response, which includes at least input energy and dissipated energy, and calculating the energy loss rate; calculating the change in modal parameters before and after damage, which includes at least the change in natural frequency, the change in damping ratio, and the modal confidence factor; and using the change in modal parameters and the energy loss rate as input features, inputting them into a random forest classifier to generate an assessment result of the structural damage level. The above scheme can improve the accuracy of damage level assessment.

Description

Technical Field

[0001] The invention belongs to the field of building damage detection, and in particular relates to a method for assessing the damage level of a reinforced concrete building structure. Background Art

[0002] With the continuous development of modern society and the acceleration of urbanization, reinforced concrete building structures have been widely used as core components in the field of civil engineering. These structures play an irreplaceable supporting role in major projects such as high-rise buildings, bridges, tunnels and industrial facilities, and have become an important part of modern urban infrastructure. The reason why reinforced concrete structures are widely used is mainly due to their excellent mechanical properties, durability and relatively economical cost. However, with the increase of service life, reinforced concrete structures will inevitably be affected by various external factors during long-term service, which will cause structural damage.

[0003] In actual engineering, the traditional damage assessment method of reinforced concrete structures mainly relies on visual inspection and empirical judgment. Visual inspection is an intuitive and simple method that records cracks, peeling, deformation and other phenomena on the surface of the structure by naked eye observation or using simple tools. Although this method can detect obvious external damage at an early stage, it is often subjective and uncertain because it is highly dependent on the experience and judgment of the inspectors. At the same time, visual inspection is difficult to identify hidden damage inside the structure, especially the corrosion of steel bars inside the structure or fine cracks inside the concrete. These potential damages may be the root cause of future deterioration of structural performance.

[0004] In addition, empirical judgment, as a supplementary means, relies on the inspector's analysis of past experience with similar structures or problems. However, due to the different specific conditions and usage conditions of different structures, the accuracy of empirical judgment is also limited. In a complex structural system, it is difficult to form a comprehensive and scientific damage assessment conclusion by relying on a single empirical judgment.

[0005] In view of the limitations of the above traditional methods, there is an urgent need for a more scientific and accurate reinforced concrete structure damage assessment method to effectively identify, quantify and classify structural damage, thereby providing reliable data support for the maintenance, repair and reinforcement of building structures. Summary of the invention

[0006] In order to solve the problems in the prior art, the present invention provides a method for assessing the damage level of a reinforced concrete building structure, the method comprising the following steps: performing a modal test on the reinforced concrete building structure to be assessed to obtain its modal parameters, the modal parameters at least including natural frequency, damping ratio, and vibration mode; applying a dynamic load to the reinforced concrete building structure to be assessed to measure its energy response, the energy response at least including input energy and dissipated energy, and calculating the energy loss rate; calculating the change in modal parameters before and after damage, at least including the change in natural frequency, the change in damping ratio, and the modal confidence factor; using the change in modal parameters and the energy loss rate as input features, inputting them into a random forest classifier, and generating an assessment result of the structural damage level.

[0007] The present invention can produce the following beneficial effects through the above technical solution:

[0008] Accuracy: Using modal parameter changes and energy loss rates as input features can capture multi-dimensional information about structural damage and significantly improve the accuracy of the assessment results. The random forest classifier can effectively handle complex nonlinear relationships by integrating the results of multiple decision trees, thereby generating reliable damage level assessments.

[0009] Noise resistance: The random forest classifier has strong noise resistance. When processing actual engineering data, it can effectively filter out the noise introduced by measurement errors or environmental factors, thereby improving the robustness and stability of the evaluation.

[0010] Automation and efficiency: Using random forest classifiers to evaluate damage levels can automate structural health monitoring. Compared with traditional evaluation methods that rely on manual judgment, this method is not only faster and more efficient, but also can continuously monitor the structure and provide real-time evaluation results.

[0011] Strong adaptability: The random forest classifier can be continuously improved and optimized by adding new training data sets to adapt to the assessment needs of different types of structures and various damage modes. This flexibility makes the method applicable to a wide range of structural health monitoring scenarios.

[0012] Comprehensive decision-making ability: The random forest classifier reduces the risk of misjudgment of a single model by integrating the results of multiple decision trees, making the damage level assessment results more robust and reliable. This feature is particularly suitable for damage assessment of complex structures, and can still give accurate assessment results under multiple possible damage modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0015] Below, the invention is preferably described in conjunction with the accompanying drawings and specific implementation methods.

[0016] This embodiment solves the above problem through the following steps:

[0017] In one embodiment, reference Figure 1 The present invention provides a method for assessing the damage level of reinforced concrete building structures. The method aims to identify, quantify and classify the damage that may occur to reinforced concrete building structures during service through scientific means and techniques, so as to accurately assess their damage level.

[0018] Reinforced concrete building structure is a widely used building form in modern civil engineering. It is a structural form composed of two main materials, steel bars and concrete. The steel bars provide tensile strength, while the concrete provides compressive strength. This composite material combines the advantages of both steel bars and concrete, making the building structure have higher strength and durability. It is widely used in important projects such as high-rise buildings, bridges, tunnels, and airport runways.

[0019] In reinforced concrete structures, damage refers to the phenomenon that the performance of structural materials or components deteriorates due to external factors such as load, environmental erosion, natural aging, etc. Damage may manifest as steel corrosion, concrete cracking, spalling, structural deformation, etc. These damages not only affect the appearance of the structure, but also weaken its bearing capacity and stability.

[0020] Damage level is a quantitative description of the degree of structural damage, which is divided into different levels (such as minor damage, moderate damage, severe damage, etc.). Damage level assessment helps engineers judge the safety and service life of the structure and provides a basis for decision-making on maintenance, repair or reinforcement of the structure. Different damage levels correspond to different repair measures and urgency.

[0021] Specifically, the reinforced concrete building structure damage level assessment method includes the following steps:

[0022] Step S1, performing a modal test on a reinforced concrete building structure to be evaluated to obtain its modal parameters, wherein the modal parameters at least include natural frequency, damping ratio, and vibration mode.

[0023] Modal testing is a method used to analyze and determine the dynamic characteristics of a structure, and is particularly suitable for identifying the natural vibration characteristics of a structure, such as natural frequency, damping ratio, and mode shape. In modal testing, a certain form of excitation (such as an impact hammer or vibrator) is applied to the structure to excite the free vibration of the structure, and then the response of the structure is measured by sensors installed on the surface of the structure (such as accelerometers, velocimeters, or displacement sensors). After signal processing, these response data can be extracted to obtain modal parameters that reflect the dynamic behavior of the structure.

[0024] The core of modal testing is its non-destructive nature, that is, key information about the health status of the structure can be obtained without damaging the structure. This testing method is widely used in health monitoring and damage detection of complex engineering structures such as bridges, large buildings, aircraft, and automobiles.

[0025] Modal parameters are important characteristics that describe the behavior of a structure under vibration. In the present invention, modal parameters include at least the following three main parts:

[0026] The natural frequency is the frequency at which a structure vibrates freely without external excitation. For reinforced concrete building structures, the natural frequency is closely related to the mass and stiffness of the structure. When the structure is in good condition, its natural frequency remains stable; but when the structure is damaged (such as cracks, material deterioration, etc.), the structural stiffness will decrease, resulting in a decrease in the natural frequency. Therefore, changes in the natural frequency are an important indicator of the health of the structure. Through modal testing, any slight changes in the natural frequency can be detected, thereby identifying potential damage in the structure.

[0027] Damping ratio is a key parameter that describes the energy dissipation capacity of a structure during vibration. It reflects the ratio of the energy lost by the structure in one vibration cycle to its total energy. The damping of the structure comes from factors such as friction inside the material, friction on the contact surfaces between the parts of the structure, and air resistance. The larger the damping ratio, the faster the structural vibration decays, indicating more energy dissipation. For reinforced concrete structures, changes in the damping ratio are often related to the occurrence of damage. For example, the formation of microcracks inside the material will increase friction, resulting in an increase in the damping ratio. By analyzing the changes in the damping ratio, it is possible to further determine whether the structure is damaged and its severity.

[0028] A mode shape is a deformation or vibration mode that describes a structure at a specific natural frequency. Each mode shape corresponds to a pattern in which different parts of the structure vibrate in different ways. For complex reinforced concrete structures, mode shapes can reveal the local and overall dynamic behavior of the structure. When the structure is in good condition, the mode shape has a specific shape; when the structure is partially damaged, such as a decrease in the stiffness of a certain part, the shape of the mode shape will change, especially the vibration shape at the damaged part may be significantly different from that when it is not damaged. Mode shape analysis is an important tool for locating the damage location because it can directly reflect the impact of the damage on the vibration characteristics of the structure.

[0029] Step S2, applying dynamic load to the reinforced concrete building structure to be evaluated, measuring its energy response, wherein the energy response at least includes input energy and dissipated energy, and calculating the energy loss rate.

[0030] Dynamic loads refer to external forces or pressures that vary with time and have a certain frequency and amplitude. When acting on a building structure, they will cause vibration or dynamic response of the structure. Common dynamic loads include earthquake loads, wind loads, traffic loads (such as vehicles driving on bridges), and vibration loads generated by the operation of machinery and equipment. These loads are instantaneous and variable, and can stimulate the vibration characteristics of the structure, thereby revealing the dynamic behavior of the structure. When evaluating the health of reinforced concrete building structures, applying dynamic loads is an important step in modal testing and energy response measurement. By analyzing the response of the structure to dynamic loads, key information about the structural state and potential damage can be obtained.

[0031] Energy response refers to the energy change of a structure under dynamic loads, including input energy and dissipated energy. It describes how a structure absorbs, stores, and dissipates energy under external loads. The analysis of energy response can help understand the dynamic behavior of a structure, especially when evaluating the stability and health of a structure. Energy response provides a direct quantitative indicator. For reinforced concrete structures, energy response can reflect important properties of the material, such as elasticity, plasticity, and damping characteristics.

[0032] Input energy refers to the total energy input into the structure by externally applied dynamic loads. It reflects the work done by external forces on the structure and is determined by the intensity, duration and mode of action of the dynamic load. During the vibration of the structure, part of the input energy will be absorbed by the structure, resulting in displacement and stress changes in the structure, and the other part will be dissipated. The size and distribution of the input energy are crucial for analyzing the dynamic response and damage state of the structure.

[0033] Dissipated energy refers to the energy consumed during structural vibration through internal friction, plastic deformation within the material, damping and other mechanisms. This part of energy no longer participates in vibration, but is dissipated in the form of heat, sound energy, etc. The dissipated energy of reinforced concrete structures mainly comes from the internal friction of concrete, the slip of steel bars, interface friction and the damping effect of the entire structure. The presence of damage will increase the dissipated energy of the structure because the damaged area may cause more internal friction and nonlinear deformation. By measuring the dissipated energy, the health status and degree of damage of the structure can be evaluated.

[0034] The energy loss rate is the ratio of dissipated energy to input energy, and is used to quantify the efficiency of energy dissipation of a structure under dynamic loads. It indicates how much energy is consumed by the structure during vibration rather than stored or recovered. The higher the energy loss rate, the more energy the structure loses during vibration, which means that the structure has more serious damage or nonlinear behavior. The energy loss rate is an important parameter for assessing the degree of structural damage. By calculating the energy loss rate, engineers can determine whether the structure needs to be repaired or reinforced.

[0035] Specific examples:

[0036] We are conducting a structural health assessment on a 20-story reinforced concrete high-rise residential building. This building is 20 years old and is located in an earthquake-prone area. It has been subjected to wind loads and seismic loads for a long time. In order to ensure its safety, we need to conduct a comprehensive assessment of its structure, especially to detect potential damage and assess its damage level.

[0037] Choose to apply dynamic loads to the building through artificial excitation method. The specific steps are as follows:

[0038] Excitation device: An exciter is installed on the top floor (20th floor) of the building. The exciter can generate periodic vibrations, which propagate downward through the structure of the building and stimulate the dynamic response of the entire building.

[0039] Excitation parameters: Set the frequency and amplitude of the shaker to excite vibration modes within the natural frequency range of the building. This helps to detect the dynamic characteristics of the structure, especially the vibration modes that are prone to damage. Assume that the frequency of the shaker is set between 1 Hz and 10 Hz, and gradually sweep this frequency range to find the resonant frequency of the structure.

[0040] During the application of dynamic loads, the dynamic response of the structure is measured by accelerometers installed on each floor of the building. The measured response data is used to calculate the energy response. The specific steps are as follows:

[0041] The input energy is the total energy applied to the structure by the shaker. This can be calculated by recording the shaker power (i.e. the product of the force applied by the shaker and the velocity) and integrating it. Assuming the shaker power varies with time, the input energy It can be expressed as:

[0042]

[0043] in, is the force applied by the exciter, is the corresponding speed, is the total time the load is applied.

[0044] Dissipated energy is the energy consumed by the building structure during vibration due to damping and internal friction of the material. This energy can be estimated by measuring the acceleration response of each floor, calculating the corresponding velocity and displacement, and then using the following formula:

[0045]

[0046] in, represents the dissipated energy, is the damping coefficient of the building structure, is the velocity response of each floor.

[0047] According to the above measured data, the energy loss rate It can be calculated as follows:

[0048]

[0049] The energy loss rate reflects the energy dissipation efficiency of a building under dynamic loads. A higher energy loss rate means that the building structure may have a certain degree of damage, such as loose connections between floors, aging of materials, or the appearance of local cracks.

[0050] Step S3, calculating the changes of modal parameters before and after damage, including at least the changes of natural frequency, damping ratio and modal confidence factor.

[0051] When a structure is damaged, such as cracks, material degradation, or loose connections, the stiffness of the structure decreases, resulting in a decrease in the natural frequency. The change in natural frequency can be calculated by comparing the natural frequencies before and after damage. Assume that the i-th natural frequency of the structure before and after damage is and , then the change in natural frequency It can be expressed as:

[0052]

[0053] Natural frequency The absolute change of reflects the influence of structural damage on the natural frequency. The larger it is, the more serious the structural damage is.

[0054] When a structure is damaged, such as cracks inside the material or loose interfaces, the damping ratio will increase because the damage will cause more energy dissipation. The change in damping ratio can be calculated by comparing the damping ratio before and after damage. Assume that the damping ratio of the i-th mode of the structure before and after damage is and , then the damping ratio change is expressed as:

[0055]

[0056] in, is the absolute change in damping ratio. It indicates that the damping ratio increases, which means that there is damage to the structure.

[0057] Modal Assurance Criterion (MAC) is an indicator used to quantify the similarity of two modal vibration modes. It measures the degree of change in the structural mode by calculating the similarity between the corresponding vibration mode vectors before and after damage. The value range of MAC is between 0 and 1, where 1 means that the two vibration modes are exactly the same and 0 means that they are completely unrelated.

[0058] The MAC value can be calculated using the following formula:

[0059]

[0060] in, and are the i-th order vibration mode vectors of the structure before and after damage, respectively. A MAC value close to 1 indicates that the vibration mode before and after damage is highly similar and the vibration mode does not change much; while a MAC value significantly lower than 1 indicates that the vibration mode has changed significantly, which may mean that the structure has been damaged locally or as a whole. The larger the MAC value, the more serious the damage.

[0061] In step S4, the change amount of the modal parameters and the energy loss rate are used as input features and input into the random forest classifier to generate an assessment result of the structural damage level.

[0062] The random forest classifier is a machine learning algorithm that belongs to the ensemble learning method. It performs classification or regression analysis by constructing multiple decision trees and combining the prediction results of these trees. Each decision tree is generated based on a different feature subset and training data, and the final classification result is determined by the votes of all trees. Random forest has the advantages of processing high-dimensional data, strong noise resistance, and preventing overfitting, and is very suitable for classification tasks of complex data sets.

[0063] In step S4, we use the changes in the modal parameters and the energy loss rate calculated in the previous steps as input features and input them into the random forest classifier to generate an assessment result of the structural damage level.

[0064] The change in modal parameters and the energy loss rate represent the changes in the dynamic characteristics and energy response of the structure, respectively. These features complement each other and provide comprehensive structural damage information for the machine learning model. The change in modal parameters can reveal the changes in the stiffness, damping characteristics and vibration mode of the structure, while the energy loss rate quantifies the energy dissipation of the structure during vibration. By fusing these features into one input vector, the model can capture multi-dimensional information of structural damage, thereby improving the accuracy of the evaluation results.

[0065] As an integrated learning method, the random forest classifier has powerful capabilities in processing high-dimensional data and resisting noise. It constructs multiple decision trees and integrates the output results of these trees to obtain the final classification result. In structural damage assessment, random forest can effectively handle the complex nonlinear relationship between the change in modal parameters and the energy loss rate, and identify the subtle differences between different damage modes. In addition, since random forest can avoid the overfitting problem of a single decision tree, it can maintain high prediction accuracy on complex data sets.

[0066] By inputting the modal parameter changes and energy loss rates into the random forest classifier, the model can automatically generate assessment results of the structural damage level. These results are expressed in discrete levels, such as level 1 for slight damage, level 2 for moderate damage, and level 3 for severe damage. The random forest classifier matches the characteristics of the current structure with the known damage patterns based on historical damage cases in the training data to predict the current damage level of the structure.

[0067] The calculated natural frequency change , Damping ratio change , modal confidence factor MAC and energy loss rate;

[0068] 𝜂 is used as the input feature and fed into the trained random forest classifier.

[0069] The random forest model is trained based on historical damage data and can identify different damage patterns and characteristics. The model generates damage level assessment results for building structures by integrating the prediction results of multiple decision trees. The assessment results may be divided into the following levels:

[0070] Level 1 (minor damage): The building can still be used normally, and regular monitoring is recommended.

[0071] Level 2 (moderate damage): Some repair is required to prevent further deterioration of the damage.

[0072] Level 3 (Severe Damage): Immediate reinforcement measures are required to ensure the safety of the building.

[0073] Through the above scheme, the modal parameter change and energy loss rate are used as input features to capture the multi-dimensional information of structural damage and significantly improve the accuracy of the assessment results. The random forest classifier can effectively handle complex nonlinear relationships by integrating the results of multiple decision trees, thereby generating reliable damage level assessments.

[0074] The random forest classifier has strong noise resistance. When processing actual engineering data, it can effectively filter out the noise introduced by measurement errors or environmental factors, thereby improving the robustness and stability of the evaluation.

[0075] Using random forest classifiers to assess damage levels can automate structural health monitoring. Compared with traditional assessment methods that rely on manual judgment, this method is not only faster and more efficient, but can also continuously monitor the structure and provide real-time assessment results.

[0076] The random forest classifier can be continuously improved and optimized by adding new training data sets to adapt to the assessment needs of different types of structures and various damage modes. This flexibility makes the method applicable to a wide range of structural health monitoring scenarios.

[0077] The random forest classifier reduces the risk of misjudgment by a single model by combining the results of multiple decision trees, making the damage level assessment results more robust and reliable. This feature is particularly suitable for damage assessment of complex structures, and can still give accurate assessment results under multiple possible damage modes.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

[0079] The present invention does not particularly specify the structure of some modules, which shall be subject to the contents recorded in the prior art. The prior art mentioned in the above background technology section and the specific embodiment section of the present invention can be used as part of the present invention to understand the meaning of some technical features or parameters. The scope of protection of the present invention shall be subject to the contents actually recorded in the claims.

Claims

1. A method for assessing the damage level of reinforced concrete building structures, characterized in that The method comprises the following steps: Performing modal testing on the reinforced concrete building structure to be evaluated to obtain its modal parameters, wherein the modal parameters at least include natural frequency, damping ratio, and vibration mode; By applying dynamic loads to the reinforced concrete building structure to be evaluated, measuring its energy response, the energy response at least including input energy and dissipated energy, and calculating the energy loss rate; Calculate the changes in modal parameters before and after damage, including at least the changes in natural frequency, damping ratio and modal confidence factor; The modal parameter changes and energy loss rates are used as input features and fed into the random forest classifier to generate structural damage level assessment results; Apply dynamic loads to the building through artificial excitation method to measure its energy response; The input energy Ein is expressed as: Where F(t) is the force applied by the exciter, v(t) is the corresponding velocity, and T is the total time of applying the load; The dissipated energy is estimated by the following formula: Where c is the damping coefficient of the building structure, is the velocity response of each floor; The energy loss rate η is calculated as follows: The random forest model is trained based on historical damage data and can identify different damage patterns and features. The model generates damage level assessment results for building structures by integrating the prediction results of multiple decision trees. The assessment results are divided into the following levels: Level 1: The building can still be used normally, and regular monitoring is recommended; Level 2: Repair is required to prevent further deterioration of the damage; Level 3: Immediate reinforcement measures are required to ensure the safety of the building.

2. A reinforced concrete building structure damage level assessment method according to claim 1, characterized in that: By applying an impact hammer or vibrator to the structure, the free vibration of the structure is excited, and then the response of the structure is measured by sensors installed on the surface of the structure. After signal processing, the response data is extracted to obtain the modal parameters reflecting the dynamic behavior of the structure.

3. A reinforced concrete building structure damage level assessment method according to claim 1, characterized in that: Assume that the i-th order natural frequency of the structure before and after damage is f i 0 and f i , then the natural frequency change Δf i It is expressed as: Δf i =f i 0 -f i Natural frequency Δf i The absolute change of reflects the influence of structural damage on the natural frequency, Δf i The larger it is, the more serious the structural damage is.

4. A reinforced concrete building structure damage level assessment method according to claim 3, characterized in that: Assume that the damping ratio of the i-th mode of the structure before and after damage is and i , then the damping ratio change is expressed as: Among them, Δζ i is the absolute change in damping ratio, the positive value of Δζ i It indicates that the damping ratio increases, which means that there is damage to the structure.

5. A reinforced concrete building structure damage level assessment method according to claim 4, characterized in that: The MAC value is calculated using the following formula: in, and φ i They are the i-th order vibration mode vectors of the structure before and after damage, respectively. The MAC value is less than or equal to 1. The larger the MAC value, the more serious the damage.

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