https://doi.org/10.11112/jksmi.2025.29.4.1

문광균(Kwang-Kyun Moon) ; 전낙현(Nak-Hyun Chun) ; 최현기(Hyun-Ki Choi) ; 권성준(Seung-Jun Kwon)

RC structures exposed to the harsh environment exhibit degradation in serviceability and structural safety due to that in durability performance. In the study, RC beams were prepared for investigating the relationship between the compressive zone characteristics with different crack widths/depths and the flexural behavior considering deterioration conditions. Only the compressive zone was exposed to chloride attack, carbonation, and sulfate ingress, respectively, and then flexural test was performed. Regarding the flexural load after chloride attack and carbonation, no significant difference was observed from control case. However, after the sulfate immersion conditions, the flexural and initial cracking load were greatly reduced, and this tendency was evaluated to be greater with increasing crack width and crack depth. Ductility ratio decreased significantly with increasing crack depth, which showed that when the crack width was over 0.3 mm and the crack depth was over 20 mm, it decreased only to the 35% level. Regarding ultimate load, no clear correlation was derived for crack width and crack depth, however in the case of sulfate immersion case, the flexural load decreased by more than 10%.

https://doi.org/10.11112/jksmi.2025.29.4.10

이규완(Kyu-Wan Lee) ; 김도균(Do-Kyun Kim) ; 박영식(Young-Sik Park)

This study proposes an improved non-contact sensor system for measuring structural displacement. While traditional contact-type sensors such as LVDTs offer high accuracy, they are difficult to install and may suffer from wear or deformation over long-term use. On the other hand, non-contact sensors like LDS can perform measurements without physical contact but often lack sufficient accuracy. To address these limitations, this research introduces a non-contact displacement measurement method utilizing a laser beam and a webcam. An economical multi-point bridge deflection measurement system was developed based on this approach. Furthermore, an AI-based high-precision measurement technique was implemented to enhance both the accuracy and efficiency of displacement estimation. The trained model achieved a maximum and minimum prediction error of 0.0484 mm and 0.0854 mm for the X-coordinate, and 0.0625 mm and 0.0596 mm for the Y-coordinate, respectively.

https://doi.org/10.11112/jksmi.2025.29.4.18

박우현(Woo-Hyun Park) ; 최지완(Ji-Woan Choi) ; 유성(Seong Yu) ; 권성준(Seung-Jun Kwon)

Cement-based construction materials essentially contain pores generated during hydration reactions, and pore characteristics (porosity, pore structure, and pore connectivity) are closely related to durability performance since they govern mass and moisture transport. In this study, carbonation behavior, gas permeability, and pore structure characteristics in cement mortar with changing w/c (water to cement ratio) were quantitatively evaluated and the relationships between them were analyzed. For the work, several tests like accelerated carbonation, permeability, porosity evaluation, and mechanical property evaluation were carried out on the test mortar with three w/c ratios (0.4, 0.5, and 0.6) with normalization. Through the test results, when w/c increased to 0.6, the porosity increased from 17.17% to 22.69%. Increasing ratio of 5.3 times and 1.77 times were evaluated for gas permeability and carbonation rate coefficient, respectively. In particular, gas permeability significantly and non-linearly increased in the 0.6 w/c case due to the poor pore structure the induced gas pressure. The normalized durability performance test results can provide basic engineering information as a durability index.

https://doi.org/10.11112/jksmi.2025.29.4.26

유석형(Suk-Hyeong Yoo) ; 김민준(Min-Jun Kim)

This study investigates the nonlinear seismic response characteristics of slender reinforced concrete walls exhibiting double-curvature behavior, which typically occurs in the front elevation of wall-type structures with deep coupling beams. To assess the modeling accuracy and practical applicability of analysis techniques, two numerical models the Fiber Element Model (FIBEM) and the Concentrated Plastic Hinge Model (CPHM) were applied. The influence of the coupling beam-to-wall stiffness ratio on wall behavior was analyzed, with particular focus on the curvature reversal mechanism.The FIBEM enables detailed simulation of distributed plasticity and material nonlinearity through sectional discretization, whereas the CPHM facilitates efficient modeling by idealizing structural components using rigid connections and plastic hinges based on the Equivalent Frame Model(EFM). Compared to the benchmark FIBEM, the CPHM tended to somewhat overestimate energy dissipation while accurately reproducing initial stiffness, peak strength, and the shape of the hysteretic envelope. However, for models with stiffness ratios greater than 7, the CPHM underpredicted both energy dissipation and ultimate strength relative to the FIBEM, indicating limitations in capturing nonlinear cyclic behavior at higher stiffness ratios. Analysis results as a function of the stiffness ratio, for both models, the sum of top and bottom rotations increased with higher stiffness ratios, consistent with the formation of curvature reversal in the mid-height region. While the FIBEM resulted in greater absolute rotation values and wider dispersion, the CPHM showed more consistent responses concentrated near the trend line, with narrower 95% confidence intervals. Therefore, the CPHM is considered a useful approach for predicting the double-curvature behavior of walls under cyclic loading in terms of both analytical reliability and practical applicability.

https://doi.org/10.11112/jksmi.2025.29.4.36

서유재(Yujae Seo) ; 주현진(Hyunjin Ju)

Fabric-Reinforced Cementitious Matrix (FRCM), a method for strengthening reinforced concrete (RC) structures, involves embedding fabric within a cementitious matrix as an external reinforcement system. To ensure the effectiveness of FRCM strengthening, the interface between the RC substrate and the FRCM must remain stable. This study applies a bond behavior evaluation model that accounts for failure mechanisms at the interface between the cement matrix and the fabric to sectional analysis for assessing the flexural strength of FRCM-strengthened members. A total of 59 test results from FRCM-strengthened beams and one-way slabs were collected from existing literature. The flexural strength of these specimens was evaluated under four different conditions: without considering FRCM reinforcement, considering only fabric properties, applying a bond behavior evaluation model, and applying a proposed bond behavior evaluation model that additionally accounts for spacing between fabrics and bearing stress. Among these, the model incorporating additional fabric characteristics demonstrated superior accuracy in predicting flexural strength with a mean, standard deviation, and coefficient of variation of 1.216, 0.185, and 0.152, respectively.

https://doi.org/10.11112/jksmi.2025.29.4.43

박원주(Won-Joo Park) ; 이덕근(Deok-Keun Lee)

In this study, an artificial ground motion was generated by scaling the magnitude 4.8 earthquake that occurred on June 12, 2024, in Buan-gun, Jeollabuk-do, to the design-level spectrum. Using the artificial ground motion reflecting the frequency characteristics of the Buan earthquake, response spectrum analysis (RSA) and time history analysis (THA) were conducted on an in-service offshore steel-concrete composite cable-stayed bridge. Seismic responses of the pylon, stiffening girder, and stay cables were investigated. For validation of the numerical model used in dynamic seismic analysis, measured natural frequencies of the bridge were compared, and the average error up to the sixth vertical mode was 3.72 %, confirming the adequacy of the model. Nonlinear time history analysis was performed to evaluate the variation in cable tension and stress, as well as safety factors for individual cables, and the optimal locations for installing cable force sensors were discussed.

https://doi.org/10.11112/jksmi.2025.29.4.54

박성호(Sung-Ho Park) ; 이기세(Kee-Sei Lee) ; 김종찬(Jong-Chan Kim)

With full-time on-site supervision throughout the entire duration fo dismantlement, a method has been introduced to allow the use of the cost-plus-fixed-fee method in addition to the previously used percentage-of-construction-cost method for calculating supervision fees. Unlike the percentage-of-construction-cost method, which applies rate depending on cost of dismantlement works, the cost-plus-fixed-fee method permits variations in supervision fees through consultations among stakeholders, with such variations reflecting building scale, dismantlement plan, etc. Therefore, this study perform the correlation analysis between supervision fees and variables by utilizing dismantlement supervision contract data from Seoul over the past four years. Based on these main variables with high correlation to supervision fees, a simplified estimation formula is proposed to statistically evaluate appropriate supervision fee levels, and its predictive performance is evaluated.

https://doi.org/10.11112/jksmi.2025.29.4.60

박경규(Kyung-Kyu Park) ; 최원준(Won-Jun Choi) ; 이상현(Sang-Hyun Lee) ; 허석재(Seok-Jae Heo)

This study proposes a novel methodology for automatically generating structural drawings by leveraging large language models (LLMs) in architectural structural design. To apply LLMs to the highly repetitive process of structural drafting, a Structured Prompt (S-Prompt) technique was developed. The S-Prompt explicitly incorporates regulations from the Korean Building Code (KBC) into the prompt, hierarchically organizes parameters, and utilizes numerical constraints to minimize hallucinations by the LLM. To validate the effectiveness of the proposed method, experiments were conducted using two LLMs?OpenAI’s GPT-4o and Anthropic's Claude 3.7 Sonnet?for generating reinforced concrete structural member drawings. The results showed that the Claude 3.7 Sonnet model achieved an average drawing accuracy of 92.8%, significantly outperforming GPT-4o’s 49.0%. Furthermore, the structured prompt technique notably reduced interference errors between drawing elements and the omission of critical information. This study demonstrates the feasibility of LLM-based automation in structural drawing generation and highlights the high practicality and scalability of the proposed S-Prompt technique for future applications in automated architectural design.

https://doi.org/10.11112/jksmi.2025.29.4.69

박성현(Seong-Hyun Park) ; 박연준(Yeon-Jun Park) ; 윤현웅(Hyun-Woong Yoon) ; 장낙섭(Nak-Seop Jang) ; 오홍섭(Hong-Seob Oh)

This study aims to elucidate the tension-stiffening effect of concrete members reinforced with grid-type CFRP under direct tensile loading. For this purpose, direct tensile tests were performed on specimens with two parameters: concrete compressive strength (30 MPa, 60 MPa) and transverse grid spacing (0 mm, 100 mm). Furthermore, a three-dimensional finite element analysis model featuring a cohesive-zone formulation was developed using the ABAQUS/Explicit solver to simulate the bond response at the interface between the CFRP grid and concrete. All specimens exhibited a typical three-stage response: an elastic phase, a crack-development phase, and a residual-tension phase. The transverse grid ribs reduced the average crack spacing and produced a more dispersed crack pattern, while higher concrete strength delayed the onset of cracking. The tension-stiffening model in Eurocode 2 reproduced the overall stress-strain trend but consistently overestimated the initial cracking strain. In contrast, the finite element analysis model accurately simulated crack initiation, propagation, and internal stress redistribution, predicting crack patterns and average crack spacing in close agreement with the experimental results. These findings quantify the crack-control performance and validate the design applicability of grid-type CFRP reinforcement and provide a basis for durability-focused design guidelines for concrete structures.

https://doi.org/10.11112/jksmi.2025.29.4.79

이강연(Kang-Yeon Lee) ; 양우정(Woo-Jung Yang) ; 박준서(Junseo Park) ; 안진희(Jin-Hee Ahn)

In this study, regional temperature variations were quantitatively analyzed utilizing long-term meteorological data collected nationwide and from 68 selected regions in Korea over the past five decades, spanning from 1973 to 2024. The analysis employed both national and regional datasets provided by the Korea Meteorological Administration. Subsequently, the temperature design loads required for the design of bridge bearings and expansion joints were compared with the current bridge temperature design standards, with the aim of assessing appropriate temperature design loads that duly consider the effects of climate change. The analysis of long-term temperature records revealed a general upward trend in the annual mean, maximum, and minimum temperatures across the country, with the increase in minimum temperatures being particularly pronounced. Extreme temperature values were estimated for 30-, 50-, and 100-year return periods using probabilistic models. In certain regions, the predicted extreme temperatures for the 100-year return period exceeded the current design standards for Normal-climate steel bridges by 1.4% when temperature loads were not applied. When temperature loads were considered, the exceedance amounted to 1.4% for Normal-climate composite bridges and 2.4% for cold-climate composite bridges. These findings underscore the necessity for a more refined and regionally differentiated approach to bridge temperature design standards, one that reflects both local characteristics and anticipated future temperature variability. Such revisions are expected to contribute significantly to ensuring the structural safety and durability of bridges in the era of climate change.