• Steel and Composite Structures
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• v.42 no.3
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• pp.325-351
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• 2022

This paper studies the lateral impact behavior of ultra-high performance fiber-reinforced concrete (UHPFRC) filled double-skin steel tubular (UHPFRCFDST) columns. The impact force, midspan deflection, and strain histories were recorded. Based on the test results, the influences of drop height, axial load, concrete type, and steel tube wall thickness on the impact resistance of UHPFRCFDST members were analyzed. LS-DYNA software was used to establish a finite element (FE) model of UHPFRC filled steel tubular members. The failure modes and histories of impact force and midspan deflection of specimens were obtained. The simulation results were compared to the test results, which demonstrated the accuracy of the finite element analysis (FEA) model. Finally, the effects of the steel tube thickness, impact energy, type of concrete and impact indenter shape, and void ratio on the lateral impact performances of the UHPFRCFDST columns were analyzed.

• Earthquakes and Structures
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• v.23 no.6
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• pp.527-534
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• 2022

EDCC (Eco-Friendly Ductile Cementitious Composites) is a recently created class of engineered cementitious composites that exhibit extremely high ductility and elastoplastic behavior under pure tension. EDCC contains reduced amounts of cement and very large volumes of fly ash. Due to these properties, EDCC has become one of the solutions to use in seismic upgrading. This paper discloses previous studies and research that discussed the seismic upgrading of unreinforced, non-grouted, unconfined, and non-load bearing masonry walls which are called URM infill walls using the EDCC technique. URM infill wall is one of the weak links in the building structure to withstand the earthquake waves, as the brittle behavior of the URM infill walls behaves poorly during seismic events. The purpose of this study is to fill a knowledge gap about the theoretical and experimental ways to use the EDCC in URM infill walls. The findings reflect the ability of the EDCC to change the behavior from brittle to ductile to a certain percentage behavior, increasing the overall drift before collapse as it increases the energy dissipation, and resists significant shaking under extensive levels with various types and intensities.

• Steel and Composite Structures
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• v.42 no.1
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• pp.123-137
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• 2022

The fundamental period (FP) is one of the most critical parameters for the seismic design of structures. In the reinforced concrete (RC) infilled frame, the infill walls significantly affect the FP because they change the stiffness and mass of the structure. Although several formulas have been proposed for estimating the FP of the RC infilled frame, they are often associated with high bias and variance. In this study, an efficient soft computing model, namely the group method of data handling (GMDH), is proposed to predict the FP of regular RC infilled frames. For this purpose, 4026 data sets are obtained from the open literature, and the quality of the database is examined and evaluated in detail. Based on the cleaning database, several GMDH models are constructed and the best prediction model, which considers the height of the building, the span length, the opening percentage, and the infill wall stiffness as the input variables for predicting the FP of regular RC infilled frames, is chosen. The performance of the proposed GMDH model is further underscored through comparison of its FP predictions with those of existing design codes and empirical models. The accuracy of the proposed GMDH model is proven to be superior to others. Finally, explicit formulas and a graphical user-friendly interface (GUI) tool are developed to apply the GMDH model for practical use. They can provide a rapid prediction and design for the FP of regular RC infilled frames.

• Structural Engineering and Mechanics
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• v.88 no.5
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• pp.501-519
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• 2023

This paper introduces a new hybrid structural connection joint that combines shear walls with section steel beams, fundamentally resolving the construction complexity issue of requiring pre-embedded connectors in the connection between shear walls and steel beams. Initially, a quasi-static loading scheme with load-deformation dual control was employed to conduct low-cycle repeated loading experiments on five new connection joints. Data was acquired using displacement and strain gauges to compare the energy dissipation coefficients of each specimen. The destruction process of the new connection joints was meticulously observed and recorded, delineating it into three stages. Hysteresis curves and skeleton curves of the joint specimens were plotted based on experimental results, summarizing the energy dissipation performance of the joints. It's noteworthy that the addition of shear walls led to an approximate 17% increase in the energy dissipation coefficient. The energy dissipation coefficients of dog-bone-shaped connection joints with shear walls and cover plates reached 2.043 and 2.059, respectively, exhibiting the most comprehensive hysteresis curves. Additionally, the impact of laminated steel plates covering composite concrete floors on the stiffness of semi-rigid joint ends under excessive stretching should not be disregarded. A comparison with finite element analysis results yielded an error of merely 2.2%, offering substantial evidence for the wide-ranging application prospects of this innovative joint in seismic performance.

• Nuclear Engineering and Technology
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• v.55 no.10
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• pp.3860-3865
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• 2023

A metallic microcell UO₂ pellet has a microstructure where a metal wall is connected to overcome the low thermal conductivity of the UO₂ fuel pellet. It has been verified that metallic microcell fuel pellets provide an impressive reduction of the fuel centerline temperature through a Halden irradiation test. However, it is difficult to predict the effective thermal conductivity of these pellets and researchers have had to rely on measurement and use of the finite element method. In this study, we designed a unit microcell model using a thermal resistance circuit to calculate the effective thermal conductivity on the basis of the microstructure characteristics by using the aspect ratio and compared the results with those of reported metallic UO₂ microcell pellets. In particular, using the thermal conductivity calculated by our model, the fuel centerline temperature of Cr microcell pellets on the 5th day of the Halden irradiation test was predicted within 6% error from the measured value.

• Corrosion Science and Technology
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• v.23 no.2
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• pp.139-144
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• 2024

Recently, due to the rapid spread and continuation of COVID-19, customer demand for health and hygiene has increased, requiring the development of new products that express antiviral and antibacterial properties. In particular, viruses are much smaller in size than bacteria and have a fast propagation speed, making it difficult to kill. POSCO has developed eco-friendly PCM color coated steel sheets with excellent antiviral properties by introducing inorganic composite materials to the color coating layer on the surface of Zn-Al-Mg alloy plated steels. The virus is not only destroyed by adsorption of metal ions released from the surface of the coating film, but is also further promoted by the generation of reactive oxygen species by the reaction of metal ions and moisture. As a result of evaluating the developed products under the International Standard Evaluation Act, the microbicidal activity was 99.9% for viruses, and 99.99% for bacteria and 0% fungi. In particular, excellent results were also shown in the durability evaluation for life cycle of the product. The developed product was applied as a wall of school classrooms and toilets and ducts for building air conditioning, resulting in excellent results. Developed products are being applied for construction and home appliances to practice POSCO's corporate citizenship.

• Journal of the Korea Concrete Institute
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• v.27 no.5
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• pp.541-549
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• 2015

This study was conducted to experimentally investigate the seismic retrofitting performance of non-ductile reinforced concrete (RC) frames by introducing engineered cementitious composite (ECC) wing panel elements. Non-ductile RC frame tested in this study were designed and detailed for gravity loads with insufficient or no consideration to lateral loads. Therefore, Non-ductile RC frame were not satisfied on present seismic code requirements. The precast ECC wing panels were used to improve the seismic structural performance of existing non-ductile RC frame. A series of experiments were carried out to evaluate the structural performance of ECC wing panel elements alone a non-ductile RC frame strengthened by adding ECC panel elements. Failure pattern, strength, stiffness and energy dissipation characteristics of specimens were evaluated based on the test results. The test results show that both lateral strength and stiffness were significantly improved in specimen strengthened than non-ductile RC frame. It is noted that ECC wing wall elements application on non-ductile RC frame can be effective alternative on seismic retrofit of non-ductile building.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.3
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• pp.180-201
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• 2020

It has been widely known that the effect of diffracted waves at the tip of composite breakwater with finite length causes the change of standing wave height along the length of breakwater, the spatial change of wave pressure on caisson, and the occurrence of meandering damage on the different sliding distance in sequence. It is hard to deal with the spatial change of wave force on trunk of breakwater through the two-dimensional experiment and/or numerical analysis. In this study, two and three-dimensional numerical techniques with olaFlow model are used to approach the spatial change of wave force including the impulsive breaking wave pressure applied to trunk of breakwater, the effect of rear region, and the occurrence of diffracted waves at the tip of caisson located on the high crested rubble mound. In addition, it is thoroughly studied the mean wave height, mean horizontal velocity, and mean turbulent kinetic energy through the numerical analysis. In conclusion, it is confirmed that the larger wave pressure occurs at the front wall of caisson around the still water level than the original design conditions when it generates the shock-crushing wave pressure checked by not two-dimensional analysis, but three-dimensional analysis through the change of wave pressure applied to the caisson along the length of breakwater.

• Korean Chemical Engineering Research
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• v.55 no.4
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• pp.456-466
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• 2017

This work investigated the particle morphology change to difference in milling media in a metal based composite fabrication process using a stirred ball mill with ball behavior of DEM simulation. A simulation of the three dimensional motion of grinding media in the stirred ball mill for the research of grinding mechanism to clarify the force, kinetic energy, and medium velocity of grinding media were calculated. In addition, the rotational speed of the stirred ball mill was changed to the experimental conditions for the composite fabrication, and change of the input energy was also calculated while changing the ball material, the flow velocity, and the friction coefficient under the same conditions. As the rotating speed of the stirred ball mill increased, the impact energy between the grinding media to media, media to wall, and media and the stirrer increased quantitatively. Also, we could clearly analyze the change of the particle morphology under the same experimental conditions, and it was found that the ball behavior greatly influences in the particle morphology changes.

• Restorative Dentistry and Endodontics
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• v.22 no.1
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• pp.428-446
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• 1997

Restorative procedures can lead to weakening tooth due to reduction and alteration of tooth structure. It is essential to prevent fractures to conserve tooth. The resistance to fracture of the restored tooth may be influenced by many factors, among these are the cavity dimension and the physical properties of the restorative material. The placement of direct composite resin restorations has generally been found to have a strengthening effect on the prepared teeth. It is the purpose of this investigation to study the relationship between the cavity isthmus and the fracture resistance of a tooth in composite resin restorations. In this study, MO cavity was prepared on maxillary first premolar. Three dimensional finite element models were made by serial photographic method and isthmus(1/4, 1/3, 1/2 of intercuspal distance) were varied. Two types of model(B and R model) were developed. B model was assumed perfect bonding between the restoration and cavity wall and R model was left unfilled. A load of 500N was applied vertically at the first node from the lingual slope of the buccal cusp tip. This study analysed the displacement, 1 and 2 direction normal stress and strain with FEM software ABAQUS Version 5.2 and hardware IRIS 4D/310 VGX Work-station. The results were as follows : 1. Displacement of buccal cusp in R model occurred and increased as widening of the cavity, and displacement in B model was little and not influenced by cavity width. 2. There was a significant decrease of stress resulting in increase of fracture resistance in B model when compared with R model. 3. With the increase of the isthmus width, B model showed no change in the stress and strain. In R model, the stress and strain increased both in the area of buccal-pulpal line angle and the buccal side of marginal ridge, therefore the possibility of crack increased. 4. The stress and strain were distributed evenly on the tooth in B model, but in R model, were concentrated on the buccal side of the distal marginal ridge and buccal-pulpal line angle, therefore the possibility of fracture increased.