Guided Wave In Concrete-filled Steel Tubes And Its Simulation

The concrete-filled steel tube (CFST) has been applied widely in many civilengineering structures because of its advantages of good mechanical properties andrapid construction. However, CFST is prone to cavity defects because of negligencein construction, poor management of the technology and material properties of steeltube and concrete. The cavity defects pose negative influence on the integrity andmechanical properties of the structures. Therefore, detection of defects in CFST isrequired.At present, detection of defects in CFST often makes use of the ultrasonictechnique, which inspects targets point by point, and it is time and labor consuming.While the guided wave detection features fast, efficient and wide-coverage, and hasbeen widely used in the metal structures. Based on guided wave theory, guidedwaves in CFST (with and without defects) are studied in this paper by theoreticalanalysis and numerical simulations. The main contents are as follows:Firstly, the guided wave’s frequency dispersion equation of the longitudinalsymmetric mode in CFST is derived. The frequency dispersion curves are obtainedby solving the equation numerically with MATLAB. Guided waves mode L(0,1) isidentified for detecting defects in CFST. The influences of four factors, i.e., steeltube’s outside diameter, wall thickness, strength of concrete and poisson’s ratio tothe frequency dispersion curve are analyzed in details.Secondly, the basic procedure for numerical simulation of guided waves inCFST by finite element software ABAQUS is introduced, which includes: the basicsteps of finite element simulation, the procedure of model set-up, the choice ofelement types and the principles of mesh size. The guided waves in defect-freeCFST are simulated, and two-dimensional Fourier transformation is employed toanalyze the data. The numerical simulation is validated by the theoretical results inchapter2.Finally, numerical simulations of guided waves in CFST with defects areconducted. The numerical results show that within a certain size range of CFST,guided waves mode L(0,1) is good for detecting defects in it. The relationships ofreflection coefficients with the area loss of section, the radial depth of defect, the longitudinal length of defect and the circumferential length of defect are studied,and they shade some lights on defect quantization.