(Special) PHM for Civil Engineering Applications - I
Chair: Prof. Sung-Han Sim (Ulsan National Institute of Science and Technology)
Probabilistic Fatigue Life Prognosis for Steel Railway Bridges after Local Inspection and Repair Dr. Young-Joo LEE (Ulsan National Institute of Science and Technology (UNIST))
Steel railway bridges are exposed to repeated train loads which often cause fatigue failure. To guarantee the target fatigue life, bridge maintenance such as local inspection and repair should be properly provided based on accurate fatigue life prognosis, but it is a challenging task because there are various sources of uncertainty associated with bridges, train loads, environment, and maintenance work. For the optimal risk-based maintenance, it is thus essential to predict the probabilistic fatigue life of a steel railway bridge and update the life prognosis information based on the results of local inspection and repair. In this research, a probabilistic approach is proposed to estimate the fatigue failure risk of steel railway bridges and update the prior information of fatigue life prognosis after bridges are inspected and repaired. The proposed method is applied to a generic steel railway bridge, and the effects of local inspection and repair on the probabilistic fatigue life prognosis is discussed through parametric studies.
Line Laser Scanning Thermography System for Paint Thickness Estimation Mr. Soonkyu HWANG, Jiho PARK, Yun-Kyu AN and Hoon SOHN (KAIST, Sejong University)
In this study, a novel paint-thickness visualizing (PTV) system is proposed using a line laser thermography and image processing algorithms. The prior paint-thickness techniques have a high accuracy for estimating paint-thickness on steel structures, but the technical hurdles exist for using real structures such as contact type and single point inspection. The proposed PTV system offers advantage of non-contact and non-invasive paint-thickness inspection over the existing techniques. Once the proposed PTV system generates thermal waves on the steel structure surface using line laser beam scanning, the corresponding thermal responses are measured using an infrared (IR) camera. According to the paint thickness, the thermal wave reflecting phenomena alters at the layer between paint and steel structure. By using this phenomena, the newly proposed image processing algorithm quantifies the amount of the altered thermal wave reflection and visualize the paint-thickness distribution. The performance of the proposed PTV system was verified through lab scale tests with painted steel structure. Six types of paints which are used for a real steel-box girder bridges were used for the verification and 40 μm of the paint thickness difference was successfully visualized.
Computer Vision-based Stsress Estimation of Concrete Structures Ms. Eun-Jin KIM, Seongwoo GWON, Soojin CHO, Myoungsu SHIN and Sung-Han SIM (Ulsan National Institute of Science and Technology (UNIST), University of Seoul)
Losing tension forces of tendons is a critical issue in pre- and post-tensioned structures. The decreasing tension force can be considered as an initial step of structural damage, as it can further cause concrete cracks, reduced load carrying capacity, and even structural instability. Indeed, it is a serious threat to structural soundness while difficult to identify. Several approaches for estimating current tension forces have been developed, including ultrasonic wave-based methods, vibration-based methods, and impedance of the piezoelectric material. Although these methods in the literature have made certain progress in this field, practical use is still limited. Instead of measuring the tension force, this study presents a method that can directly measures the static stress level of concrete by combining the stress relaxation method (SRM) and digital image correlation (DIC). By drilling a small hole, a part of the current static stress can be released, inducing stress field change around the hole. DIC can identify the deformation due to the stress field change using two images taken before and after drilling the hold. This deformation is subsequently compared to one that is calculated using finite element model to finally estimate the current static stress level in concrete. An optimization approach is developed to obtain the best estimate of the static stress. The proposed strategy is validated using concrete specimen loaded by the universal testing machine.