• Computers and Concrete
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• v.28 no.6
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• pp.533-547
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• 2021

Calculating the shear capacity of slender reinforced concrete beams without shear reinforcement was the subject of numerous studies, where the eternal problem of developing a single relationship that will be able to predict the expected shear capacity is still present. Using experimental results to extrapolate formulae was so far the main approach for solving this problem, whereas in the last two decades different research studies attempted to use artificial intelligence algorithms and available data sets of experimentally tested beams to develop new models that would demonstrate improved prediction capabilities. Given the limited number of available experimental databases, these studies were numerically restrained, unable to holistically address this problem. In this manuscript, a new approach is proposed where a numerically generated database is used to train machine-learning algorithms and develop an improved model for predicting the shear capacity of slender concrete beams reinforced only with longitudinal rebars. Finally, the proposed predictive model was validated through the use of an available ACI database that was developed by using experimental results on physical reinforced concrete beam specimens without shear and compressive reinforcement. For the first time, a numerically generated database was used to train a model for computing the shear capacity of slender concrete beams without stirrups and was found to have improved predictive abilities compared to the corresponding ACI equations. According to the analysis performed in this research work, it is deemed necessary to further enrich the current numerically generated database with additional data to further improve the dataset used for training and extrapolation. Finally, future research work foresees the study of beams with stirrups and deep beams for the development of improved predictive models.

• Geomechanics and Engineering
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• v.30 no.5
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• pp.401-411
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• 2022

To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.

• Journal of the Korea Institute of Building Construction
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• v.22 no.4
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• pp.337-345
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• 2022

The foundation of high-rise concrete building in coastal areas generally must be installed in an integrated manner, not separately, in order to prevent defects caused by stress on the upper and lower parts of the mounting surface and to manage the process smoothly. However, when performing integrated punching, there is a concern that temperature stress cracks may occur due to hydration heat. Due to the large member size, it is difficult to make a sufficient commitment, so it is necessary to mix concrete with high self-charging properties to ensure workability. In this research, the amount of high-performance spray and admixture used was adjusted as experimental variables to satisfy this required performance. Through the analysis of the results for each blending variable, it was found that the unit quantity was 155kg/m³ and the cement ratio in the binder was 18%, and the target values of the pre-concrete properties and compressive strength were satisfied. A four-component binder(18% cement, 50% slag fine powder, 27% fly ash, 5% silica fume) was used.

• Journal of the Korean Geotechnical Society
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• v.39 no.2
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• pp.5-17
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• 2023

In this study, a classification and uniaxial compression test of soil was conducted on 15 collapsed sites to use ground improvement with excellent protection effect owing to the increase of localized heavy rain in Korea. The Casagrande method and fall cone test were performed on the field soil to derive an expression for comparing liquid limit and plastic limit values, soil classification, and correlation between each other. By deriving the optimal mixing ratio of the ground improvement agent using uniaxial compressive strength for each soil classification, the classification of the fine-grained soil was not clear owing to the proficiency difference and test error. However, after classifying using the fall cone test, it was possible to suggest a clear optimal mixing ratio.

• Journal of the Society of Disaster Information
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• v.18 no.4
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• pp.769-777
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• 2022

Purpose: This study analyzes and studies the characteristics of the Jeju area and uses them as basic data such as construction method design in the future development project. Method: Based on the ground survey data of the construction conducted in Jeju, the depth, relative density, N value, function state, color tone, groundwater level, and compressive strength were analyzed and studied. Result: Studies show that Jeju has columnar joints consisting of ancient volcanic activity and rapid cooling by nearby seawater, thick sand layers found on the coast, and clinker layers and Seogwipo layers formed by Mercury volcanic activity. Conclusion: It is hoped that it will be used as data for selecting basic design and basic construction method by understanding the special ground form of Jeju area and reflecting its characteristics well when designing construction.

• Structural Engineering and Mechanics
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• v.87 no.5
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• pp.499-516
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• 2023

To defend against harmful gamma radiation, new types of materials for use in the construction of heavyweight concrete (HWC) are still needed to be developed. This research introduces new materials to be employed as a partial replacement for fine aggregate (FA) to manufacture high-performance heavyweight concrete (HPHWC). These materials include hematite, black sand, ilmenite, and magnetite, with substitution ratios of 50% and 100% of FA. In this research, the hardening and fresh characteristics of HPHWC were obtained. Concrete samples' Gamma-ray linear attenuation coefficient was evaluated utilizing a gamma source of Co-60 through the thicknesses of 2.5, 5, 7.5, 10, 12.5, and 15 cm. High temperatures were studied for HPHWC samples, which were exposed to up to 700℃ for two hours. Energy-dispersive x-rays and a scanning electron microscope carried out microstructure analyses. Magnetite as an FA attained the lowest compressive strength of 87.1 MPa, but the best radiation protection characteristics and the highest density of 3100 kg/m³ were achieved. After 28 days, the attenuation efficiency of concrete mixtures was increased by 6.5% when fine sand was replaced with black sand at a ratio of 50%. HPHWC, which contains hematite, black sand, ilmenite, and magnetite, is designed to reduce environmental and health dangers and be used in medicinal, military, and civil applications.

• Journal of the Korea Institute of Building Construction
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• v.23 no.2
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• pp.197-207
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• 2023

Concrete is a widely used material due to its excellent compressive strength and durability. However, depending on the surrounding environment and the characteristics of the materials used in the construction, various defects may occur, such as cracks on the surface and subsidence of the structure. The detects on the surface of the concrete structure occur after completion or over time. Neglecting these cracks may lead to severe structural damage, necessitating regular safety inspections. Traditional visual inspections of concrete walls are labor-intensive and expensive. This research presents a deep learning-based semantic segmentation model designed to detect cracks in concrete walls. The model addresses surface defects that arise from aging, and an image augmentation technique is employed to enhance feature extraction and generalization performance. A dataset for semantic segmentation was created by combining publicly available and self-generated datasets, and notable semantic segmentation models were evaluated and tested. The model, specifically trained for concrete wall fracture detection, achieved an extraction performance of 81.4%. Moreover, a 3% performance improvement was observed when applying the developed augmentation technique.

• Journal of the Korean Geotechnical Society
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• v.24 no.1
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• pp.25-35
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• 2008

It has been recognized that the behaviour of unsaturated soil plays an important role in geomechanics. However, up to now, only a few experimental data are available for the technical difficulties related to both volume changes and suction measurements. In this study, the volume changes of unsaturated compacted silty soil were monitored with proximeter during various triaxial compression tests, which gave a realistic estimation in the volume changes of unsaturated soil sample. From the test results, the behaviours of wetting-induced collapses are observed during the drainage/water absorption tests. Under exhausted-drained conditions during shearing, the shear strength increases with an increasing initial suction. On the other hand, the volume changes become small with an increase in the initial suction. And, the volumetric strain during shearing is independent of the confining pressure.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.25-32
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• 2008

Based on recent studies, the side resistance of rock socketed drilled shafts was affected by unconfined compressive strength of rock, socket roughness, rock types and joints, and initial normal stress. Especially, the socket roughness was affected by rock types and joints, drilling methods, and diameters of pile. In this study, a new roughness measurement system (BKS-LRPS, Backyoung-KyungSung Laser Roughness Profiling System) usable in water was developed. Based on the laboratory model tests, an EMD (Effective Measurement Distances) according to various turbidity was proposed as $EMD=1149.2{\times}T_{b}^{-0.64}$.

• Journal of the Korean Geotechnical Society
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• v.24 no.4
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• pp.47-55
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• 2008

This study was carried out to investigate and analyse the influence of maximum size of coarse aggregate and quality control of aggregate on the properties of shotcrete through the laboratory and field test. From the results of the test, as the maximum size of coarse aggregate decreased from 13 mm to 8 mm, plasticity property declined and compressive strength and dynamic modulus of elasticity of hardened concrete increased remarkably, so it was found that the aggregate size 8 mm was superior to 13, 10 mm in fluidity, constructability and durability. Therefore, it was advisable for well maximum size of coarse aggregate to apply to the 8mm aggregates through the Ready-mixed Method for quality control and minimum segregation.