Papers by Author: Chia Chi Cheng

Abstract: The objective of this paper is to introduce an impact device made by embedding a piezoelectric sensor into a steel sphere and to develop a calibration method for measuring the impact force. The force-time function of impact can be used to normalize the spectrum obtained from an impact-echo test. Furthermore, an approach was proposed to make the normalized spectrum dimensionless. A new technique based on the dimensionless normalized spectrum is developed to quantitatively evaluate the difference in acoustic impedance at the interface between two dissimilar materials. The impact-echo test results show that the dimensionless normalized spectrum is capable of identifying the degree of the difference in acoustic impedance at the interface between two dissimilar materials.

Abstract: In this paper, a newly developed approach for the determination of characteristics associated with local defects of a beam is briefly introduced. From the numerical studies carried out in this study, the complex ratio between two transfer functions associated with an imaginary intact beam and a damaged beam can provide such information. Based on the numerical studies, the rules in determining degree of damages and locations of defects were first briefly outlined. These idealized rules were then verified by experimental data obtained from dynamic tests of realistic specimens of simply-supported reinforced concrete beams. The preliminary results indicate that the defined ratio of transfer functions can potentially serve as an exaggerated indication for the degree of changes in certain modal responses. Thus, the proposed ratio of transfer functions can be used to assist system identification, while the nature of high sensitivity also restricts its direct application to certain complicated data associated with field tests. A variety of test setup for both receivers and impact sources were studied and the test results appear to agree with designated conditions of the specimens.

Abstract: The paper introduces a newly developed imaging technique for evaluating the integrity of concrete structures. The image of normalized amplitude spectra is obtained from B-scan of impact-echo tests. The normalizing process was carried out by obtaining the simulated transfer functions, in which the displacement of R-wave waveform of the impact-echo response multiplying a correcting factor is used as the simulated force-time function. Two specimens, one reinforced and the other unreinforced concrete plates, containing naturally delaminated cracks with crack widths 1 mm, 3 mm and 5 mm were constructed and repaired by injected epoxy into the delaminated cracks. The NDT method was performed on the specimens before and after the repairing work for comparison. The spectral image shows consistent high intensity at the crack-depth-frequency for specimens at crack stages and less in intensity for the ones at repaired stage.