https://doi.org/10.4334/JKCI.2024.36.1.003

진수민(Su-Min Jin) ; 안효서(Hyoseo An) ; 나금옥(Geum-Ok Na) ; 유영종(Young-Jong Yoo) ; 김형근(Hyung Geun Kim) ; 이기학(Kihak Lee)

This study focuses on the experimental investigation of thermal heat bridge prevention systems in terms of the shear capacity resulting from bearing loadings supported by precast ultra-high-performance composite (UHPC) ribs with normal concrete PC cladding walls. Five specimens were tested under static loading conditions to examine both structural performance and the thermal behavior of UHPC ribs with and without shear keys. The test results showed that the specimens had excellent structural performance in terms of shear capacity, surpassing that developed by normal concrete by approximately threefold. When the experiment was conducted with various eccentric distances, the bearing load performance was the highest with the smallest eccentric distance provided. It was verified that the shear key presence contributed to enhancing the bearing load performance by about 5 %.

https://doi.org/10.4334/JKCI.2024.36.1.011

김예진(Ye-Jin Kim) ; 이순환(Soon-Hwan Lee) ; 김재규(Jae-Gyu Kim) ; 최명성(Myoung-Sung Choi)

There is significant domestic and international interest in the development of solar energy technology, particularly offshore solar technology, to overcome limitations in suitable installation sites. In marine solar technology, the structural integrity of the floating body is crucial for ensuring the safety of solar panels, in contrast to land-based solar systems. However, polyethylene (PE)-based floating bodies are susceptible to durability degradation from UV radiation and fatigue failure. Therefore, this work investigated a concrete floating body made of concrete that provides excellent durability, fire resistance, and ensures safety while floating. To achieve this, a comparative analysis of hydraulic model experiments and ANSYS AQWA simulations was conducted. The structural behavior of the concrete floating body under wave load conditions was evaluated by applying the validated analysis method to AQWA-structural coupled analysis of the actual structure.

https://doi.org/10.4334/JKCI.2024.36.1.023

최하진(Hajin Choi) ; 양승렬(Seung Yul Yang) ; 정시영(Siyoung Jung) ; 김병국(Byoung Kook Kim) ; 최완철(Oan Chul Choi)

Novel design criteria for the development length of reinforcing bars under tension are proposed, based on analytical expressions for bond strength derived from a bearing angle model. The development and lap splice lengths calculated using this approach are relatively shorter, averaging 10 % and 20 %, respectively, depending on factors such as bar diameter, concrete strength, and confinement, in contrast to calculations made according to the KDS 14 2022 Structural Design Code. The proposed provisions ensure a continuous progression in the development length, thus improving reliability and safety in bar anchorage details. Designers are encouraged to adopt the proposed method for development length calculation, benefiting from its short lengths, systematic approach, and broader applicability compared to current KDS provisions.

https://doi.org/10.4334/JKCI.2024.36.1.033

이균태(Kyun-Tae Lee) ; 박용명(Yong Myung Park) ; 성택룡(Taek Ryong Seong) ; 김진국(Jin-Kook Kim)

In this study, finite element analysis was conducted to examine the behavioral characteristics based on design variables for a proposed foundation connection using Concret filled steel tube (CFST) columns and socketed steel tubes in relation to socket-type column-foundation connections. The parameters considered for the analysis included column embedded depth, socket steel pipe diameter-to-thickness ratio, reinforcing bar diameter, socket concrete strength, and the presence or absence of an annular ring. The results were then compared with the plastic flexural strength of the column as per WSDOT (2021) standards. Additionally, the flexural strength of the socket component in the Japanese Design Standards for Railway Structures and Commentary (2016) was compared with the outcomes of the finite element analysis outcomes The primary influential factors of the proposed structure were found to be the column embedded depth and the socket steel pipe diameter-to-thickness ratio. By analyzing the effects of these parameters and the resulting behavioral characteristics, the feasibility of applying the CFST column-socket type foundation connection structure using socket steel pipes was determined, and design guidelines were presented accordingly.

https://doi.org/10.4334/JKCI.2024.36.1.043

오서은(Seo-Eun Oh) ; 정상엽(Sang-Yeop Chung) ; 김동주(Dong Joo Kim)

IIn recent years, the aging of concrete structures has become a problem, prompting research into crack repair techniques. Notably, self-healing concrete is considered an effective solution due to its capacity to independently repair internal damages, such as cracks, without external intervention. Among the methods for achieving self-healing concrete, the use of bacterial biomineralization offers the advantage of having environmentally friendly and sustainable attributes within cement-based composites. In this study, the effect of bacterial biomineralization on micropores and cracks within mortar was investigated by considering various external curing conditions. A set of cement mortar specimens containing bacteria was exposed to different curing solutions to assess the influence of various external factors. The specimens cured in three different solutions were analyzed after 28 days using compressive strength tests, SEM, XRD, and micro-CT to ascertain changes in micropores and crack areas. The results showed that bacterial-generated calcium carbonate effectively filled micropores and cracks, exhibiting distinct calcium carbonate phases formed under varying culture water conditions.

https://doi.org/10.4334/JKCI.2024.36.1.051

문소현(So-Hyun Mun) ; 천성철(Sung-Chul Chun)

In the Concrete Design Code of Korea, bars spliced by noncontact lap splices should not be spaced transversely farther apart than the lesser of one-fifth the required lap splice length or 150 mm. The structural behavior of noncontact lap splices with D13 and D19, which are spaced transversely farther apart than the provisions of the Concrete Design Code of Korea, was tested in this work. The test results showed that the behavior of noncontact laps is similar to the behavior of contact laps within the transverse spacing of spliced bars of 225 mm. Regardless of the spacing between spliced bars, the flexural cracks on the sides were similar for all specimens. The load-deflection relationships of all specimens were similar to the deflection curves of flexural members determined according to KDS 14 20 30, implying that all specimens deformed like ideal flexural members. As the spacing between spliced bars increases, there is no significant difference in the load-deflection relationships. Comparisons of test results of noncontact laps with the predictions by the design code provision, Orangun et al. (1977)’s equation, and the ACI Committee 408 equation show that the test-to-prediction ratios of 1.27, 1.54, and 1.23, respectively, indicating that the noncontact laps had sufficient strength. Consequently, noncontact laps within a 225 mm transverse spacing have equivalent strength and behavior and can be safely designed using the previous equations.

https://doi.org/10.4334/JKCI.2024.36.1.061

이유정(Yu-Jeong Lee) ; 김인태(In-Tae Kim) ; 한동엽(Dong-Yeop Han)

This study involved developing a predictive model for concrete rheological parameters using a machine learning algorithm, based on conventional test results of concrete slump flow. To achieve this, the prediction model’s performance was assessed according to data preprocessing, data quality, and the quantity of training data. Analysis revealed that data preprocessing involving both data cleaning and normalization proved effective. Furthermore, the predictive model’s performance improved with higher quality and a larger volume of training data. This study can contribute to the development of a prediction model for rheology parameters based on fresh concrete slump flow data.

https://doi.org/10.4334/JKCI.2024.36.1.073

이재인(Jae-In Lee) ; 김채영(Chae-Young Kim) ; 윤주호(Joo-Ho Yoon) ; 최세진(Se-Jin Choi)

In this study, multi-walled carbon nanotubes (MWCNTs) and amorphous metallic fibers were combined to address the issue of quality deterioration in concrete structures caused by cracks and to improve the heating characteristics of cement composites with low electrical conductivity. For this purpose, the fluidity, micro-hydration heat, heating performance, compressive strength, split-tensile strength, flexural strength, ultrasonic pulse velocity, carbonation depth, and microstructure of mortar were compared and analyzed based on different mixing ratios of MWCNTs and amorphous metallic fibers. According to the measurement results, the sample containing 0.2 % MWCNTs and amorphous metallic fibers showed improved heat generation performance, mechanical properties, and durability compared to the control sample. On the other hand, the sample with an MWCNT mixing ratio of 0.4 % showed lower performance than the control sample across various parameters except for heating performance. However, when used with amorphous metallic fibers, there was similar or improved performance compared to the control sample.