(Special) PHM for Civil Engineering Applications - II
Chair: Prof. Young-Joo LEE (Ulsan National Institute of Science and Technology)
Assessment of Concrete Efflorescence based on Hyper-spectral Imaging Mr. Byunghyun KIM and Soojin CHO (University of Seoul)
Efflorescence is a phenomenon mostly made by carbonation process of concrete structures. It is one of the internal damages seriously considered in evaluating the durability of concrete bridges. In Korea, the guideline for the bridge safety inspection requests to assess crack, efflorescence, spalling and reinforcement exposure in prior for the slabs and girders of concrete bridges. Currently, the assessment is performed based on the visual inspection of expertized engineers, which may result in subjective inspection result. In this study, a novel method to assess concrete efflorescence is proposed based on hyper-spectral imaging (HSI) device. The HSI acquires the light intensity for a large number of continuous spectral bands of light for each pixel in an image, which makes the HSI provides more detailed information than a normal color camera that collects intensity for only three bands corresponding to the colors, RGB (red, green, and blue). A stepwise assessment algorithm is developed based on the spectral features developed to decompose efflorescence area from the inspected concrete area. The algorithm is verified in the laboratory testing using concrete specimens with the efflorescence, which shows high accuracy of the proposed HSI-based assessment
Computer Vision-based Displacement Measurement Method with Arbitrarily Positioned Camera Mr. Junhwa LEE, Kyong-Chan LEE, Soojin CHO and Sung-Han SIM (Ulsan National Institute of Science and Technology (UNIST), Korea Railroad Institute, University of Seoul)
Displacement is considered in structural health monitoring (SHM) as a meaningful indicator of structural status. Measuring the displacement of a structure using commonly used measuring equipment, such as LVDT, leads to the shortcomings of insufficient installation site, expensive equipment price, or lack of accuracy. Efforts have been made to measure the displacement of a structure through a camera by incorporating computer vision technology as a solution to overcome such drawbacks. The existing computer vision-based displacement measurement techniques show high accuracy in the indoor and outdoor test, however they still have issues in field testing such that the camera location is limited and light exposure often impairs accurate measurement. This study presents a computer vision-based displacement measurement system that shows accurate measurement results regardless of camera position or background light. Field experiments are conducted to verify that the developed approach performs robust and accurate displacement measurements even in adverse field condition allowing a wide range of camera locations and robustness to excessive light exposure.
Monitoring of tensile force of PSC girder by measuring iron loss variation using EM sensors Mr. Junkyeong KIM, Minsoo PARK, Byoung-Joon YU, Najeep ullah TAREEN and Seunghee PARK (Sungkyunkwan University)
The actual tensile force of pre-stressed (PS) tendons of a pre-stressed concrete (PSC) girder is one of the important factors for evaluating the performance of PSC girder bridges. To measure the tensile force of the PS tendon, this study proposed an iron loss variation based tensile force estimation method using embedded EM sensors. The iron loss of PS tendons are changed according to the applied tensile force. To measure the iron loss of PS tendon of PSC girder, the EM sensor should be embedded in the PSC girder because the PS tendons were located in inside of PSC girder. To verify the proposed method, the experimental tests were performed. The embedded EM sensors were embedded into PSC girder specimen and the iron loss changes due to the variations of tensile forces were measured using embedded EM sensors. According to the estimation results, the proposed method can be a one of the solution to estimate the tensile force of PS tendons.
Monitoring of the Hardening Process of Ultra High Performance Concrete (UHPC) based on Guided Wave Propagation Dr. Changgil LEE, Jooyoung PARK, Kassahun D. TOLA and Seunghee PARK (Sungkyunkwan University)
In this study, the hardening process of ultra high performance concrete (UHPC) was monitored non-destructively using a single embedded sensor system. The propagating characteristics of guided waves obtained from the sensing system were analyzed to estimate the setting time and the strength development of UHPC. Since the boundary conditions of the embedded sensor system continuously change during the hardening process of concrete materials, the hardening process can be monitored based on the measured characteristics of the propagating waves. To understand the variations in wave propagation, the modes for the guided waves were decomposed. The strength development of UHPC, with and without short-fiber reinforcement, was estimated using the variation of patterns of the decomposed wave modes. Based on the proposed methodology, which measures the propagation and variation of the guided waves, it is possible to estimate the time of phase transition and the strength development of UHPC.
Continuous-wave Laser Thermography for Concrete Crack Evaluation under Moving Conditions Mr. Keun-Young JANG, Soonkyu HWANG, Jiho PARK and Yun-Kyu AN (Sejong University, KAIST)
This paper presents a continuous-wave laser thermography (CLT) technique for concrete surface crack evaluation under moving conditions. The CLT technique is able to visualize and quantify surface cracks on moving concrete structures by generating a continuous-wave laser source and capturing infrared images at a fixed spatial point. Although the CLT system has spatially limited field of view, it can inspect the entire region of interest (ROI) of the moving target structure. To precisely quantify surface cracks, the data acquired from the entire ROI are integrated and subsequently processed by developing a crack evaluation algorithm. In this study, concrete specimens with various macro- and micro-cracks are specially prepared and used to validate the proposed CLT technique. The test results reveal that various cracks are successfully visualized and quantified within 3% error ratio.