Research On The Looseness Detection Of Reinforcing Bar’s Sleeve Connection Based On Guided Waves

The sleeve connection,with the advantages of low cost,no pollution and high strength,is a commonly used cold connection method and is widely used for the connection of reinforcing bars.The sleeve connection of the reinforcing bar may be loosened due to the reasons such as external vibration and bad processing quality,which affects the quality of the project.Therefore,it is necessary to detect the looseness.In this thesis,the looseness detection of the reinforcing bar’s sleeve connection(RBSC)based on magnetostrictive guided waves is studied,which provides a guarantee for the construction quality.Firstly,the propagation of the RBSC is studied using the semi-analytical finite element method.Based on the analysis of the cross-sectional characteristics of the RBSC,a semianalytical finite element model is established to calculate the dispersion curve of the RBSC and the dispersion curve is obtained.According to the obtained dispersion curve,the propagation characteristics of the RBSC are analyzed,the excitation frequency is determined and the vibration shapes at different frequencies are obtained.The dispersion curves are verified through the experiments.Secondly,the detection mechanism of the sleeve connection structure is studied based on the transmission and reflection characteristics of the elastic wave at the boundary of the medium.The RBSC can be regarded as the boundary when the guided wave propagates between the two reinforcing bars.The principle of the RBSC’s looseness detection based on the transmission and reflection of the guided waves is obtained.The looseness detection principle is verified through the experiments.The peak-to-peak value of the guided wave signal is extracted as the characteristic parameter for the looseness detection of the RBSC.Thirdly,the semi-open magnetostrictive sensor is developed in view of the limited installation space of on-site detection of the RBSC.From the perspective of the limit installation space,it is confirmed that the sensor has a semi-circular structure and can be installed on one side of the RBSC,and magnetostrictive transduction principle of the sensor is analyzed.The static magnetic field distribution of the semi-ring magnet and the alternating magnetic field distribution of the semi-circular coil are studied using finite element simulation.The semi-open sensor can generate guided waves with longitudinal mode as the main and flexural mode as the auxiliary.The sensor for the looseness detection of Φ20 RBSC is designed and manufactured,and the function of the sensor is tested.Finally,the application of the developed semi-circular sensor to detect the looseness of the RBSC is carried out.The decreasing relationship curve between the loosening angle of the RBSC and the peak-to-peak value of the guided wave signal is obtained by experiments.The convolutional neural network with multi-scale kernels is used as the signal processing method to realize the tiny looseness detection of the RBSC,whose accuracy can reach 5 °.The looseness detection of the RBSC is carried out on the construction site.