Study On Influencing Factors Of Defects Detection In Concrete-filled Steel Tubular Members Based On Guided Wave Method

Due to the rational use of the properties of steel, concrete material and quick, easy construction, steel concrete structure is more concerned about its mechanical performance boosts and widely use. However, when construction is poor, defects such as crack and void appear in its component, which will affect the performance and mechanical properties of engineering structures. Therefore, how to quickly and effectively find defective steel concrete members and determine the size and location of defects is a key point of detection methods. Current detection methods for concrete-filled steel tubular members(CFST)mainly include artificial percussion method, fiber optic monitoring method. Meantime, trouble detecting, measuring leaky or other shortcomings exist in these methods. Starting from the overall component, the guided wave method can fully detect the status of every member. Therefore, through analyzing the guided wave propagation characteristics in a CFST member, using theoretical analysis and finite element numerical simulation method, influence factors and the guided wave response of a CFST member are presented based on guided wave defect detection techniques.Firstly, the main mode of guided waves transmission in a CFST member and its factors member is analyzed in this paper. The genesis waveguide will be described. According to the dynamic theory, equivalent area, equivalent stiffness, equivalent density and equivalent damping coefficient of this CFST member can be obtained during the process of guided wave detection. Meanwhile, the dynamic response equation of this CFST member in the elastic range is derived. In this process, the influence of bottom boundary condition on the echo phase is analyzed and factors such as stiffness, density, member cross-sectional area and member length will be calculated. These jobs can provide some futural directions of the following researches. Then the theoretical solution will be compared with the finite element simulation results, and the rationality of the modeling method is verified, which provides a theoretical basis for the study of numerical simulation in the later stage.Secondly, dispersion of guided waves in CFST members and complexity of the interaction between the guided wave and the characteristic of the component should be considered. Based on Abaqus and Matlab, the frequency dispersion theory and the wave propagation effect of CFST members are studied. Then, frequency dispersion equation, propagation velocity and the method of determining the type of excitation head wave will be determined. And the finite element simulation system for the guided wave detection of CFST members is established to analyze the change of signal excitation region and signal extraction region and determine the reasonable range of the excitation region and signal extraction region of the guided wave signal. At the same time, influence analysis of the stiffness, Poisson’s ratio and density variations of this member on guided wave propagation is presented, and the relationship between the velocity and the amplitude is simplified.Finally, in the condition of concrete phase, concrete cracks and steel and concrete pavement, the complex change of the echo signal should be analyzed. In this paper, a three-dimensional multi-dimensional random aggregate model based on the principle of Monte Carlo meso aggregate model is built to study the influence of multi phase on the propagation of guided waves in CFST members. Axial defect in CFST members is established to analyze the relation between its size and echo. With the increase of the defect length, its size will increase first but then decrease. And the specific defect size should be further defined by the decomposition of the waveform. Changing the position of the defect in the CFST member, the relationship between position and echo of the defect will be studied. When the defect is located at the end of the component, the echo signal is almost coincident with the echo of the bottom of the component, and the detection effect is not good.