Evaluating Grouting Quality Of Tendon Ducts Using The Impact-echo Method And Support Vector Machines

Since1980, the post-tensioned prestressed concrete structure was widely used inbridge engineering. However, the poor grouting quality of tendon ducts results in thecorrosion of the steel tendons and even causes the collapse of bridge structure. Hence,it is necessary to develop effective and reliable methods to identify the grou tingquality of tendon ducts. The impact-echo method is a nondestructive testing methodbased on the transient impact theory. In this paper, the method is employed to detectthe grouting quality of tendon ducts. The study is summarized as follow:1. The history of the impact-echo method and its application to the engineeringfield are introduced firstly, and then, the basic principle of the proposed method usedto the slab structure is given a brief introduction. The simplified calculation methodof transient response of concrete plate under impact load is introduced to provide afundamental basis for the present research.2. Numerous simulation analyses are conducted to investigate the influence ofthe model parameters and test environment on the characteri stics of theamplitude-frequency curves when there is no grouting to the ducts. It concludes that:(1) When the ratio of duct diameter to plate thickness is greater than to0.4, thefrequency peak indicating the defect depth can be identified from theamplitude-frequency curves, whereas the larger ratios may cause the severedecreasing of the resonance frequency due to the interference of Rayleigh wave andreflected P-wave.(2) When the impact point slowly moves away from the center lineof the duct, three typical response characteristics of the thickness frequency peaks canbe identified in different offset range.(3) The offset rate of the thickness frequencypeak is a function of the ratio of diameter to thickness.3. Five typical defect cases indicating the different grouting quality of the ductsare extracted and the support vector machine technology is then employed to conducta pattern classification.4. The laboratory study is presented to verify the effectiveness of the FEM-basedsimulation analysis and the classification model. A comprehensive summary oftheoretical and experimental study on the application of impact-echo method isconducted, and a preliminary discussion is finally made for the further study.