Advanced Nondestructive Evaluation I

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Authors: Sung Woo Shin, Chung Bang Yun
Abstract: A modified one-sided Rayleigh wave (R-wave) velocity measurement technique is applied to monitor the strength gain of early-age concrete. A series of experiments were performed on early-age concrete specimens with various curing conditions. The results show that the R-wave velocity and strength gain has a strong relationship and that the R-wave velocity can be effectively used to monitor the strength development of the early-age concrete.
Authors: Soo Ho Chang, Soon Wook Choi, Gyu Jin Bae
Abstract: To protect underground structures and passengers from fire, it is essential to characterize fire-induced damage on the construction materials for underground structures. However, it is almost impossible and uneconomical to carry out full-scale fire tests in tunnels that are under public usage. In this study, a high temperature furnace capable of simulating RABT (Richtlinien für die Ausstattung und den Betrieb von Straßentunneln) fire curve was newly designed and manufactured. In the fire tests, furnace temperature is set to reach 1,200 within five minutes after ignition. The temperature of 1,200 was maintained for one hour, and the fire was extinguished after two hours had elapsed. From the temperature measurement by thermocouples embedded in test specimens, the depth of lost concrete was estimated to reach approximately 20 cm from the surface that was exposed to fire. In addition, the alteration of physico-mechanical properties and microstructures of concrete segments after fire tests were investigated from core specimens. The results show that the deterioration of material properties was up to 10 cm from the surface of the remaining concrete block
Authors: Yong Seok Seo, Chang Yong Kim, Kwang Yeom Kim, Kyoung Mi Lee
Abstract: A faulted rock usually shows the swelling behavior because of clay minerals which consist of the fault gouges. It makes rock mass unstable and threatens the safety of structures built in rock mass. This study was aimed at clarifying characteristics of physical and mechanical properties of faulted rock materials. At first, microstructures and mineralogical composition associated with faulting in the fault gouge zones were analyzed by using X-ray diffractometry (XRD) and SEM microphotographs. Physical properties of the faulted rock materials from fields were measured in the laboratory. It is well known that the mechanical properties are sensitive to the mineralogical assemblage and are affected by the shapes, distribution and preferred crystallographic orientation of the components. Material and direct shear tests were also conducted on faulted rock materials under saturated and unsaturated conditions. The mechanical results were analyzed together with the analyzed result of XRD and SEM.
Authors: Hyo Seon Park, W.H. Lee, K.S. Yun, Hong C. Rhim
Abstract: A wide variety of residual stress measurement methods can be used to measure the axial stress in a column. One of the most widely used techniques for measuring residual stress is slotting method since it is relatively simple and cost-effective to implement at vertical columns in field. However, the slotting method is considered to be semi-destructive or destructive method depending on the amount of material to be removed. Therefore, in this paper, optimal depth of slots for measuring actual stress is presented to minimize the amount of material to be removed. Finite element method is used to estimate the minimum depth of the slot in H-shaped steel column. By performing actual saw cutting, optimality of the simulated depth of the slot is investigated.
Authors: Mi Ra Cho, Ki Bong Kim, Sung Ho Joh, Tae Ho Kang
Abstract: The impact-echo method, which is to evaluate the integrity of concrete and masonry structures nondestructively, is an excellent method in practical applications, and provides a high quality of structural integrity assessment. However, in the case of multi-layered systems in which each layer has different stiffness, the impact-echo method may lack reliability in thickness evaluation, which demands improvement of the impact-echo method. This study was first dedicated to the understanding of stress-wave propagation in the impact-echo test, and secondly, the reliability of the impact-echo method was investigated through the numerical simulation of the impact-echo test. The investigation included the research on influencing factors such as stiffness contrast between layers and receiver location. Finally, the research in this paper led to the development of the phase-difference response (PDR) method, based on the frequency response between two receivers deployed in a line with an impact source.
Authors: Jiunn Ren Lai, Chih Peng Yu, Shu Tao Liao
Abstract: The objective of this paper is to investigate the capabilities of the Impedance Log method in profiling the geometry of a pile along its length. The main idea of this method is to introduce a transient stress wave into the pile and then utilize the reflected signals to obtain the impedance profile of the pile. Any anomaly, which results in changes in impedance, would be detected by this method. In this study, four model piles with plan defects of weak zone or neck were constructed and tested using Seismic Echo, Impulse Response, and Impedance Log pile integrity nondestructive testing methods. Results of these tests show that interpretation of signals using the Impedance Log method is more straightforward than the other two methods. It is concluded that the Impedance Log technique is a tool with high potential for evaluating the integrity of piles.
Authors: Chun Ho Kim
Abstract: Despite being an important element to connect the major building materials in a steel bridge, bolt joints have not been sufficiently studied in terms of each defect generated in them. Among defects in bolt joints of steel bridges currently in public use, the most frequently occurring problem is the insufficient axial bolt clamping force. To measure sliding load caused by change in axial bolt clamping force, a test sample of H-beam applied with pure bending was created and static tests were administered. Based on the axial bolt clamping force of the test sample where the designed axial bolt clamping force is 100%, tests were carried out with different axial bolt clamping forces of 75%, 50% and 25%. Then, the sliding load caused by change in the axial bolt clamping force was analyzed.
Authors: Chia Chi Cheng, Kuang Chih Pei, Jiunn Hong Wu
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.
Authors: Kyung Seok Song, Jae Yeol Kim, You Hong Kim
Abstract: Contact type detection, one of UT for the detection of defects in welding area, has several weak-points. Proximity type ultrasonic inspection using laser is being studied these days to make up for the weak points of contact type ultrasonic inspection. In this paper, automatic inspection system of the welding area of spiral welding pipe has been developed, of which mechanical characteristic is better than that of circular directional pipes, and executed the proximity ultrasonic inspections using laser. The usefulness of proximity ultrasonic inspection using laser will be verified in this paper through the analysis of the inspection results.
Authors: Chih Peng Yu, Chia Chi Cheng, Chih Hung Chiang
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.

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