| Currently, the primary methods of detecting the quality of cofferdam metal buffer rod are the drawing method and coring method, but these two methods all belong to damage detection, which can’t meet the requirements of Engineering practice. This paper, through analyzing the conducting characteristics of guided waves, by applying, the combination of theoretical calculation and finite element simulation test, analyzes the application of detective technique based on ultrasonic guided wave in metal buffer rod bonding quality of cofferdam system.The thesis explains how guided waves are formed, introduces the phase velocity, group velocity dispersion curves and cutoff frequency of it, discusses the dispersion and multi-modal properties of guided wave, and puts forward that it is best to choose single modal and weaker dispersion of ultrasonic guided wave to detect the structure.Then the thesis deduces the theoretical model of free metal rod and cofferdam metal rod, brings forward three different boundary conditions of the response equations such as the top free, bottom free and fixed. Validated by finite element simulation conduction results, it is clear that the theoretical model well explains the conducting principles and rules of the guided waves in the metal rod and the cofferdam metal rod.Based on ultrasonic guided wave theory, the thesis analyses the factors influencing the cofferdam metal rod and its bonding quality, conducts high and low frequency simulation experiments with different bonding areas. It shows that the low-frequency of75KHz can clearly identify the interface reflection wave in fixed end, so the length of effective bond can be worked out; High-frequency of2MHz can clearly identify the bottom reflection wave, therefore, the attenuation coefficient of overall length can be worked out, according to which the bonding quality of the cofferdam metal rod can be quantified.Internal damping of the metal rod makes the material creep and relax, so the numerical value of free metal rod damping x reflects the value of internal damping, that is, the larger the numerical value of τ is, the larger internal damping is and the worse amplitude attenuation will be. The figure of cofferdam metal rod bonded segment τ1reflects the degree of metal rods and cofferdam bonded, that is, the larger τ1, the better bonded and the worse amplitude attenuation, which signifies that damping results in the energy decay of the cofferdam metal rod within the low frequency.This paper also analyses axial flow distribution and attenuation of the specific frequency guided waves L (0,1) and L (0,2) of cement mortar metal rod in rod section. Studies axial, radial displacement, axial How of energy distribution and attenuation of the specific frequency guided wave I,(0,1) of the resin cofferdam metal rod in rod section; It can be concluded that the specific frequency guided wave is sensitive to surface defects and inner defects.Besides, the paper analyses principles of the guided wave when conducting in the cofferdam interface, states the causes of guided wave velocity change(decrease) and the widened waveform in time domain response curve, makes an idea clear that in the cofferdam interface, it is the coupled wave group(low-frequency) that conducts most, which consists of interface wave and Love wave.According to the attenuation amplitude’s difference of the same frequency guided wave conducting in free metal rod and cofferdam metal rod, the bonding quality of cofferdam metal rod has been qualitatively analyzed. Using the time’s difference in reflection waves and excitation waves in solid upper interface, the way of resin metal buffer rod ioad has been put forward. Through the testing of time difference of the reflection waves of metal rod low side and solid upper interface, a way to determine the bonding density of cement mortar cofferdam metal rod has been proposed. According to the debond delect echo time and the velocity of longitudinal guided wave, which is the best to test frequency, when conducting in the cofferdam metal bumper bar, the rod body debond delect has been located. With the increasing of concrete solidification period, the quality of cofferdam metal rod’s bonding gradually gets better, and the amplitude value of reflection wave in upper interlace becomes bigger, by which the rod’s bonding quality can be assessed and judged.Field test shows that the quality of detection instrument can accurately collect the ultrasonic guided wave’s reflection wave in the cofferdam system and detect the effective bonding length of cofferdam metal rod. According to the bond strength of medium, the cofferdam metal rod’s curing grip can be obtained, so it is an effective and feasible way to detect the quality. |
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