https://doi.org/10.11112/jksmi.2025.29.1.1

홍석범(Seok-Bum Hong) ; 엄기영(Gi-Young Eum) ; 김자연(Ja-Yeon Kim) ; 임정현(Jeong-Hyeon Lim)

This study aims to optimize the wavelength expansion coefficient (C) using a genetic algorithm to minimize hunting motion in high-speed railways. Hunting motion, characterized by lateral oscillations during high-speed travel, was controlled by deriving an optimal C value. By considering train speed, wheel radius, and curve radius, a hunting motion-related accident risk function was constructed. The genetic algorithm determined an optimized C of 0.54, resulting in an 84.57% accident risk reduction compared to C=0 and a 79.35% reduction compared to C=1. Monte Carlo simulations further confirmed that the optimized C reduced accident risk by 82.25% compared to C=0, 15.44% compared to C=0.5, and 8.36% compared to C=1. These results highlight that excessive wavelength expansion may increase accident risk, underscoring the importance of balancing hunting suppression and accident risk minimization for improving railway operational stability.

https://doi.org/10.11112/jksmi.2025.29.1.11

윤현웅(Hyun-Woong Yoon) ; 박성현(Seong-Hyun Park) ; 박연준(Yeon-Jun Park) ; 김영환(Young-Hwan Kim) ; 오홍섭(Hong-Seob Oh)

This study investigated the effects of incorporating hydrophobic admixtures into mortar, replacing Ordinary Portland Cement (OPC) with Calcium Aluminate Cement (CAC), to enhance the durability of cement-based composites. Results showed that while the addition of hydrophobic admixtures significantly improved the hydrophobicity of the mortar, it also led to a decrease in mechanical strength. Regression analysis was conducted to quantitatively determine the correlation between the dosage of hydrophobic admixtures and the mechanical properties of the mortar, revealing a decreasing trend in strength with increasing admixture dosage. Although the relationship between surface roughness and hydrophobicity was explored, a clear correlation was not found. This study provides fundamental data for determining the optimal dosage and mix proportion of hydrophobic admixtures and can be used as a reference for improving the performance of mortar.

https://doi.org/10.11112/jksmi.2025.29.1.17

윤차영(Cha-Young Yun) ; 김재현(Jae-Hyun Kim) ; 김민준(Min-Jun Kim) ; 이득행(Deuck-Hang Lee) ; 김강수(Kang-Su Kim)

This study conducted an experimental investigation on the in-plane behavior of half PC (Precast Concrete) wall-type structure joints with various reinforcement details. Six full-scale specimens were fabricated, which varied in construction method, anchorage reinforcement type, and reinforcement ratio, followed by quasi-static cyclic loading tests. The test results allowed for a comparative analysis of each specimen’s structural performance, such as their strength, energy dissipation capacity, stiffness degradation, and slip. Additionally, the strength of the specimens was quantitatively evaluated in accordance with the current structural design codes. The results indicated that the Half PC wall-type structure joints exhibited slightly lower in-plane structural performance compared to RC (Reinforced Concrete) wall-type structure joints, but they sufficiently met the current structural design criteria regarding the diaphragm.

https://doi.org/10.11112/jksmi.2025.29.1.27

김준영(Jun-Yeong Kim) ; 백은림(Eun-Rim Baek) ; 이상호(Sang-Ho Lee)

Recently, collapses of RC slab occurred, and when the form-work shoring is removed early, compressive strength of concrete is not sufficiently developed, which can cause large deflection and/or crack in the slab. Therefore, it is important to determine form-work shoring period during construction of structure. In this study, it was designed the RC structure and analyzed using finite element method, to evaluate the form-work shoring period. The results of this study are as follows; (1) The form-work shoring period was showed different according to story and floor construction cycle, so it is unreasonable to classify simply into single and multi-structure. (2) Based on the deflection and/or crack shown in the finite element analysis result, the form-work shoring period was reviewed, and revealing that a high safety margin was applied to the structures of 2 and 3-story. (3) According to the effect of specified compressive strength of concrete, the form-work shoring period can be shortened, in the case of the high strength of concrete. (4) As the thickness of slab increased, the form-work shoring period increased due to initial weight. Therefore, the standards are needed considering the influence of slab thickness.

https://doi.org/10.11112/jksmi.2025.29.1.37

홍성욱(Seong-Uk Hong) ; 박준혁(Jun-Hyuk Park)

This paper is a basic study to evaluate the reinforcement performance and bonding force through joint design developed with Engineered Cementitious Composite to improve the seismic performance and bonding force of the pile structure. In order to examine the bonding force of the joint, an experiment was manufactured according to the variables of the joint on a pile wall reinforced with a Engineered Cementitious Concrete and the lateral force and displacement were measured. The joint experiments reinforced by variables showed an average effect of more than 1.5 times compared to the experiment that was a conventional bonding device, and all experiments except the experiment in which the mesh was bonded showed integration without lifting or separation of the bonding device, confirming that it is effective in bonding force.

https://doi.org/10.11112/jksmi.2025.29.1.43

박상아(Sang-Ah Park) ; 정민기(Min-Gi Jung) ; 김승훈(Seung-Hun Kim)

This study conducted shear tests to evaluate the mechanical anchorage performance of SD700 high-strength reinforcement at the ends of reinforced concrete (RC) and steel fiber-reinforced concrete (SFRC) beams. A total of eight specimens were fabricated, with variables including the anchorage method of the main reinforcement, development length, presence of shear reinforcement, and steel fiber content. The experimental results revealed that initial flexural cracks formed beneath the loading points in all specimens. Subsequently, diagonal cracks developed, and the final failure modes were identified as either anchorage failure or shear-compression failure. Compared to the S-series specimens with straight anchorage, the H-series specimens anchored with headed bars exhibited significantly higher anchorage stresses, ranging from 7.6% to 44.6%, indicating improved anchorage performance due to the headed bars. The theoretical nominal shear strength of specimens was evaluated using the strut-and-tie model. The failure mode of all specimens by the strut-and-tie model was the anchorage failure of the tensile reinforcements in the node region at beam ends. The experimental maximum shear strength to theoretical nominal shear strength ratio ranged from 1.9 to 4.37, suggesting that the development lengths specified in the current standards may be overestimated.

https://doi.org/10.11112/jksmi.2025.29.1.52

양성주(Sung-Ju Yang) ; 서창우(Chang-Woo Seo) ; 박해용(Hae-Yong Park) ; 김승훈(Seung-Hun Kim)

This study evaluated the bond performance of small L-shaped steel members with deformed bars welded as shear reinforcement in RC (reinforced concrete) and SFRC (steel fiber-reinforced concrete). Experimental results showed that most specimens exhibited splitting failure, with cracks forming along the flange edges of the L-shaped steel members. Furthermore, as the concrete cover thickness and bond area increased, the maximum load also increased. When the cover thickness was increased by approximately 1.7∼2.3 times, the bond stress improved by 55.4∼116.7%. However, when the bond area doubled, the bond stress decreased by approximately 17.0∼19.3%. Steel fiber reinforcement had a greater impact on preventing rapid stiffness degradation after the maximum load than on the bond stress itself. The lower 5% bond stress of all test specimens was evaluated as 1.75 MPa, which is 2.65 times higher than the bond stress specified in KDS 14 31 80. Based on the push-out tests, a nominal bond strength (Rn_k) design formula was proposed for small L-shaped steel members with deformed bar shear reinforcement details, considering the lower 5% bond stress.