Quantitative Monitoring And Health Status Evaluation Of Concrete Structural Cracks Using Piezoelectric Active Method

It can be found from the practice of civil engineering that cracks are one of the most important diseases of concrete structures.The appearance of cracks will adversely affect the main structure,such as causing the surface concrete to peel off,accelerating the corrosion of steel bars,reducing the bearing capacity,etc.,and then threatening the safety and durability of the structure.If the development of cracks in the structure is not grasped in time,it will not only influence its normal use,but also have safety risks.Once an accident occurs,the irreversible major losses may be caused.However,it can only qualitatively identify the presence of cracks in the structure under the existing monitoring methods,and it is difficult to realize the quantitative monitoring and health status evaluation.Under this background,this topic will conduct the following research:(1)An ideal test for three-point bending conditions is designed based on the concrete standard specimen beam.Through the loading system established,the evolution form of cracks and the failure process of the specimen are studied.It is found that the specimen finally shows two types of cracks,namely the vertical cracks at midspan area and oblique cracks at the support area.At the same time,the corresponding numerical analysis model is built using the finite element software ABAQUS,and the element damage determining criterion is proposed as well.Based on above work,the crack damage situations of the model in the same working conditions are analyzed.It is discovered that the two forms of cracks in the test and simulation are highly consistent,which indicates that the simulation method adopted can effectively simulate the working conditions set in the test,and thus artificial cracks in subsequent studies can be set by referring to the comparative analysis results.(2)Different sizes of vertical cracks at the mid-span area and diagonal cracks at the support area are respectively preset in the batch concrete standard specimens.According to the designed piezoelectric active sensing monitoring system for concrete cracks,time-history signals of stress waves in different working conditions are collected.The principle of crack monitoring by this method is proved by analyzing the changes in the signal amplitude and wavelet packet energy values.The quantitative interval of crack parameters are extracted from the interval characteristics of signal energy attenuation,and the intrinsic relationship between them is established,which provides an exploratory idea for a certain degree of quantitative monitoring of cracks.(3)A crack monitoring simulation method based on piezoelectric active sensing is developed.By establishing numerical models of piezoelectric-concrete beam electromechanical coupling and setting the same crack conditions as the above test in the models,a series of processes such as stress wave excitation,propagation,and reception in the piezoelectric active sensing method are simulated.The attenuation mechanism of cracks on stress wave is analyzed,and it is proved that the proposed method can effectively identify cracks.In addition,the simulation results of various crack conditions are compared with the test results,and it is found that the trend of the interval energy attenuation in the test is more obvious than simulation.(4)On the basis of the above research,a damage degree evaluation method based on energy attenuation is established according to the proposed damage index.Combining the interval characteristics of the signal when it evolved with the crack evolution in the experiment and simulation,a damage degree evaluation method based on the quantitative interval of crack parameters is built.The methods are used to evaluate the health status of concrete specimen beam in the experiment which studies the forms of crack.