Advanced Nondestructive Evaluation I

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Authors: Hyung Choon Park, Dong Soo Kim
Abstract: The evaluation of soundness of pile is very important for safety of super structure. In this paper, the HWAW(Harmonic Wavelet Analysis of Wave) method is modified and applied to evaluate soundness of pile non-destructively. The proposed method can evaluate pile integrity such as pile length, material quality represented by wave velocity and pile end condition which are very important factors for pile behavior. To verify the applicability of proposed method, the numerical simulation test using ABAQUS was performed. A model pile was made and the proposed method was applied to evaluate soundness of model pile. Through numerical simulation and model tests, it is shown that the HWAW method has good potential of applying in the evaluation of pile integrity.
Authors: Bo Hwan Oh, Hong C. Rhim, Hyo Seon Park
Abstract: Better understanding of concrete behavior is beneficial to the determination of concrete strength and detection of cracking using nondestructive testing techniques such as ultrasonic and acoustic emission. For advanced nondestructive evaluation of high early strength concrete under triaxial compression loading, stress-strain relationship in axial as well as in radial directions needs to be described in explicit form. This paper presents empirical models developed for high early strength concrete under active confinement to explore the effect of confining pressure. Empirical model for axial stress-strain relationship is determined first. Transverse deformation model is automatically generated from the given axial stress-strain model using plastic strain rate. Parameters used in the model are identified and their recommended values are provided. Compressive strength of 24 MPa and 45 MPa concretes are considered along with four different levels of confining pressures.
Authors: Dong Soo Kim, Kwang Myong Lee, Nam Ryong Kim, Seok Woo Jin
Abstract: Non-destructive tests using impact echo (IE) and pulse velocity measurements (PVM) were conducted to evaluate degradation of elastic properties of cement-based materials during uniaxial compression. Prismatic specimens (100100200 mm) made of ECC (engineered cementitious composites) mixture, were used for the test. The specimens were subjected to monotonic axial loading until failure while resonance frequency and travel time were recorded. Changes in the amplitude, velocity, and frequency were correlated to the increasing damage levels and the feasibility of IE and PVM techniques to evaluate the damage level in ECC was preliminarily assessed.
Authors: Hong C. Rhim, Bo Hwan Oh, Hyo Seon Park
Abstract: An attempt has been made to measure existing steel stress using magnetoelasticity. A device has been developed and used for the measurement of magnetism in response to the deformation of a steel bar. The proposed technique can be used for the assessment of existing reinforced concrete structures by the measurements of steel stress embedded inside concrete. A traditional technique requires to break the existing steel bar to measure existing strain. However, the proposed technique is developed to measure the stress without damaging the steel bar. A successful application of magnetoelasticity depends on the establishment of relationship between elastic and magnetic response due to loading. To investigate the correlation between the two, steel bars are loaded in tension under uniaxial loading while the magnetic reading is recorded. Based on the test results, equations are suggested to predict stress for steel bars with different diameters.
Authors: Yi Ching Lin, Chun Kuei Yang, 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.
Authors: Jae Hyouk Choi, Kenichi Ohi
Abstract: It is important to estimate the structural safety of column base connection by calculating exact collapse loads. Column bases connection transfer reactions from the structure the foundation. In this paper, a simple mechanical model to predict their plastic resistance is proposed. An efficient linear-programming technique, which is called as Compact Procedure, is applied to column base connection model including multi-spring elements, where a column base is replaced by a set of plastic axial and bending springs. In Compact Procedure, it is not necessary to know the whole interaction surface of resistances at a plastic portion. A simple analytical model of column base connection to calculate its load-carrying capacity considering bi-axial loading effect is presented. In addition, efficiency of the proposed model is examined by comparing it with the past test results.
Authors: Hong C. Rhim, Sang Kyun Woo, Young Chul Song
Abstract: Microwave and ultrasonic methods have been used for the detection of debonding between concrete and fiber-reinforced plastic (FRP). To determine the capability of the microwave method in detecting thin delamination between two materials of concrete and FRP, concrete specimens are made with the dimensions of 600 mm (length) x 600 mm (width) x 50 mm (depth). Specimens have artificial delamination of 5 and 10 mm thick Styrofoam, which represent debonding in structures. Then, the specimens are partially covered with 1.5 mm thick FRP on the top of 3 mm thick epoxy. A horn antenna with a center frequency of 15 GHz and a frequency bandwidth of 10 GHz is used for the measurements. By transmitting and receiving microwave signals from the horn antenna, differences have been detected for the different types of the targets. Also, measurements using ultrasonic method at 5 kHz have been made on the same series of specimens. This work is directed toward a development of an effective and practical microwave based non-destructive evaluation methodology for the detection and quantification of damages in FRP-covered reinforced concrete members in bridges and buildings.
Authors: Philip Park, Yong Hak Huh, Dong Jin Kim, Byung Jik Son
Abstract: Effects of crack on static behavior in steel box girder were investigated to identify the possibility of crack detection and location using conventionally measured static data including deflection and inclination. Finite element analysis with finely meshed 3-D models and experiments were performed for steel box girder with crack. To eliminate the variation according to load magnitude, compliance technique was applied to analysis of the result. Through this study, the quantitative relationship between crack size and structural responses of deflection and inclination were obtained as a form of relation-curve. This relation-curve can be utilized to evaluate crack size in the steel box girder bridge. The results also demonstrated that the location of crack can be estimated by static measurement.
Authors: Young S. Cho, Han Seung Lee
Abstract: As most of the elementary, junior high, and high school buildings nationwide have been deteriorated since the quantitative increase of the buildings from 1985, many experts present the issues on the possibility of the structural instability of the building as well as the increase of the cost for maintenance of the building. So, it is necessary to examine the necessary structural information of the school buildings during the course of maintaining education facilities, and it is also necessary to establish some credible accessing procedures on the deteriorating school facilities so that the building structural engineers can propose the necessary standards for the proper maintenance and repairing works. To achieve the necessity, researches have been conducted to find out the ways of diagnosing the compressive strength and the durability of the concrete structures by measuring the compression wave velocity of concrete structures and the flaw detection inside the concrete specimens using the impact echo method, a non-destructive test to simulate the structures of school buildings. In this research, it was found that the impact echo method has great potentials in the application of the building structure maintenance and the repairing activities based on the accurate understanding of the existing school facilities that are being deteriorated. More over, school facilities has sometimes no structural design drawings available which NDT methods can contribute to detect the internal structural damages of existing building structures.
Authors: Jong Jae Lee, Masanobu Shinozuka, Soo Jin Cho
Abstract: In this study, an optical method of real-time displacement measurement of such bridges was carried out by means of digital image processing techniques. A commercially available digital video camera combined with a telescopic device takes a motion picture of the target panel with known geometry, which is installed on the measurement location of a bridge. The displacement of the target is calculated based on the captured images in real-time manner using image processing techniques, which require a texture recognition algorithm, projection of the captured image, and calculation of the actual displacement using target geometry and number of pixels moved. For the purpose of verification of the presented method, a laboratory test was made using shaking table test and the measured displacement by image processing techniques was compared with the data from a contact-type sensor, a linear variable differential transformer (LVDT). The proposed method gave close results to a conventional sensor. Field tests were carried out on a bridge with steel plate girders and a bridge with steel box girders. The test results gave sufficient dynamic resolution in frequency as well as the amplitude.

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