https://doi.org/10.11112/jksmi.2025.29.2.1

노병철(Byeong-Cheol Lho) ; 김진환(Jin-Hwan Kim)

The accuracy of tunnel displacement measurement is essential for evaluating structural stability and conducting maintenance effectively. Total Station (TS) is widely used for tunnel displacement monitoring; however, measurement errors caused by temperature variations and environmental factors remain a significant issue. In particular, optical distortion effects due to refractive index changes and air layer formation have not been sufficiently considered in previous studies, necessitating a more systematic approach. This study analyzes the impact of temperature fluctuations on displacement measurements in tunnels and develops a mathematical model for correction. The relationship between air density variations caused by temperature differences and subsequent light refraction phenomena is quantitatively evaluated. Based on this analysis, a refractive index-based correction model is applied to reduce measurement errors and improve accuracy. The results demonstrate that applying the proposed correction model improves the accuracy of tunnel displacement measurements by approximately 52.1% compared to conventional methods. Additionally, the study provides a more precise understanding of seasonal displacement variation patterns. The developed correction model is expected to enhance the reliability of existing TS-based automated measurement systems and could be applied to various underground structures such as subway tunnels and underground storage facilities.

https://doi.org/10.11112/jksmi.2025.29.2.10

서수연(Soo-Yeon Seo) ; 윤현도(Hyun-Do Yun) ; 최원창(Won-Chang Choi) ; 석승욱(Seung-Wook Seok)

In this study, the sensing capacity of FBG-FRP reinforcement, a Fiber Reinforced Polymer (FRP) reinforcement combined with a Fiber Bragg Grating (FBG) optical fiber (OF) sensor, was investigated through temperature test, simple tensile and repeated tensile test. FBG-FRP reinforcements were manufactured by debonding or fully bonding the surface of measuring part of optical fiber using epoxy between two CFRP plates, and the sensing capacity of each method was evaluated through the tests. As results, when an OF sensor is fully bonded to a CFRP plate using epoxy, a linear strain change relationship according to temperature changes was presented, and it was confirmed that the strain of the OF sensor showed almost the same value as the CFRP reinforcement with respect to monotonic increase and repetitive stress.

https://doi.org/10.11112/jksmi.2025.29.2.18

정종윤(Jong-Youn Jeong) ; 안효준(Hyo-Joon An) ; 조백순(Baik-Soon Cho) ; 이종한(Jong-Han Lee)

This study quantitatively evaluates the damage to road facility network caused by flooding and analyzes the resulting network performance degradation and recovery process. Terrain data resembling urban areas were generated, and flood simulations were conducted under various rainfall scenarios to analyze inundation depth and area within the road facility network. The analysis quantified the performance degradation of individual road facilities as well as the network-level performance loss. At the network level, a topological analysis was conducted to evaluate connectivity and importance, while an economic analysis and a resilience analysis quantified the extent of network performance degradation and recovery, respectively. The results revealed that damage to key links in the central region of the network had a significant impact on overall network performance. Furthermore, structural damage to bridges and road inundation were identified to contribute substantially to economic losses. This approach was adopted to comprehensively assess the degradation and recovery of road facility networks affected by flooding.

https://doi.org/10.11112/jksmi.2025.29.2.25

김종국(Jong-Guk Kim) ; 최우석(Woo-Suk Choi) ; 백승훈(Seung-Hoon Baek) ; 우욱용(Ukyong Woo) ; 최하진(Hajin Choi)

For displacement measurement of cultural properties and important structures, new technologies based on non-contact, non-attachment methods are required instead of traditional contact-based measurements. This study developed an image-based measurement algorithm with a resolution of less than 0.1 mm at a 1-meter distance. A laser-generated virtual grid system was designed to monitor structures through imaging, and the system was tested and operated over four years of data collection at various facilities. The measurement device was verified for resolution and accuracy through indoor testing, but field deployment faced challenges such as noise due to varying light conditions between day and night, as well as adverse weather conditions like rain and fog. To enhance I mage reading accuracy, an AI algorithm was applied. Specifically, the YOLO algorithm was utilized for automatic recognition of the virtual grid pattern, using a dataset consisting of a total of 6,512 images from field conditions, including normal and noisy samples, achieving an Intersection over Union (IoU) score of 0.9. The application of the developed algorithm demonstrated improved daily data variance, reducing from ±40 pixels (1.6mm) to ±20 pixels (0.8mm), thereby validating the noise reduction effectiveness through AI integration.

https://doi.org/10.11112/jksmi.2025.29.2.33

박동순(DongSoon Park) ; 신동훈(Dong-Hoon Shin)

This study investigates five major earth-cored embankment dam incidents in Korea, focusing on core material degradation and seepage-related issues. Each dam exhibited unique symptoms?sinkholes, fluidized cores, wet downstream surfaces, and slope failures?yet shared a common issue: compromised impermeability of the clay core. Geotechnical and geophysical investigations revealed that this degradation was largely inhomogeneous and anisotropic, primarily due to insufficient compaction, material deficiencies, and complex geotechnical interactions. Electrical resistivity surveys identified significant heterogeneity, with critically low resistivity values indicating potential seepage paths. A key finding is that the severity of consequences varied depending on the extent and distribution of core material defects. When critical indicators of seepage failures emerged, swift and multi-tiered investigations were essential. Electrical resistivity surveys provided an effective preliminary assessment, necessitating targeted drilling for further verification. Older dams, often lacking design records, required proactive and direct investigations to preempt potential failures. The study underscores the necessity of a government-led Incident Management System (IMS) for dam safety, integrating real-time data collection, predictive analytics, and structured response protocols. For remediation, a low-pressure permeation grouting method was implemented to restore the core layer's water barrier function. The study proposes a tiered response framework based on incident severity: preventive drainage and localized grouting for minor anomalies, targeted low-pressure grouting for moderate seepage zones, and emergency measures?such as controlled reservoir drawdowns and rapid embankment reinforcements?for severe cases. The empirical case studies and insights presented in this study serve as critical references for hazard mitigation in aging dam rehabilitation projects.

https://doi.org/10.11112/jksmi.2025.29.2.43

하성준(Seong Jun Ha) ; 방진수(Jin Soo Bang) ; 임홍재(Hong Jae Yim)

3D concrete printing is a construction method that fabricates structures by depositing layer by layer of concrete, which requires considerations for quality control compared to conventional mold-cast concrete. In particular, 3D printed concrete can be highly sensitive to setting and hardening depending on the surface area exposed to the curing environment due to the absence of formwork. This study proposed monitoring methods using non-destructive evaluation to assess the setting time of 3D printed concrete. The obtained results from proposed monitoring methods were compared with results of penetration resistance test to analyze the setting time. In addition, compressive and flexural strength tests were conducted on concrete samples with large and small surface areas to the curing environment after 24 hours of curing to evaluate the effect of exposed surface area on the hardening of concrete. The compared results showed that as the exposed surface area increased, the setting time of conventionally placed concrete accelerated, while its compressive and flexural strength decreased by approximately 23%. With the same exposed surface area, 3D printed concrete and conventionally placed concrete exhibited similar setting times.

https://doi.org/10.11112/jksmi.2025.29.2.52

김성완(Sung-Wan Kim) ; 윤다운(Da-Woon Yun) ; 박동욱(Dong-Uk Park) ; 장성진(Sung-Jin Chang) ; 전법규(Bub-Gyu Jeon)

The piping system of a nuclear power plant is composed of straight pipes and pipe elbows sequentially connected to transport fluids. Pipe elbows are an important component for absorbing the deformation and energy in a piping system. Pipe elbows are vulnerable elements in the piping system of nuclear power plants because of their low bending stiffness compared with that of straight pipes of the same material and cross-section, thus resulting in relatively large deformations. Therefore, pipe elbows require high structural integrity against seismic loads because they are important components in the piping system of nuclear power plants. Under repetitive loading conditions such as earthquakes, pipe elbows can experience significant cross-sectional plastic deformation associated with strain beyond the elastic limit of the material, which can cause the pipe elbow to failure. The most fundamental factor affecting the limit state of a pipe elbow is the structural dimensions, such as the thickness, diameter, and length of the pipe. In this study, low-cycle fatigue tests are conducted on 4-inch steel pipe elbows of schedules 40 and 80 to determine the difference in limit states due to changes in their thicknesses. The low-cycle fatigue test is conducted until leakage occurs because of fatigue cracks, which signifies the limit state of the steel pipe elbow. The limit state of the steel pipe elbow with respect to thickness change is quantitatively expressed using the damage index, which can account for cumulative damage.

https://doi.org/10.11112/jksmi.2025.29.2.63

김현식(Hyun-Sik Kim) ; 이은경(Eun-Kyung Lee) ; 이강석(Kang-Seok Lee)

This research proposed a V-bracing system incorporating a non-buckled horizontal friction damper (NHFD) to address the limitations of conventional vibration control systems, with the aim of applying it to existing reinforced concrete buildings. To assess the damper's material properties and energy dissipation, a dedicated performance test was conducted. Two full-scale, two-story reinforced concrete frame specimens, modeled after a domestic building lacking seismic detailing, were prepared: one as an unstrengthened control, and the other retrofitted with the proposed NHFD V-bracing system. A pseudo dynamic testing was performed to investigate the effectiveness of the seismic retrofit, focusing on key response parameters such as maximum shear strength, maximum displacement, and earthquake damage degree. The results demonstrated that the NHFD V-bracing system significantly improved lateral load resisting capacity and reduced story deformation, even under severe seismic intensities including 400 and 500 cm/s2.