• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.351-357
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• 2022

In this study, offshore modular pier system using the ultra-high performance concrete was developed for the offshore construction environment. For the application of offshore modular pier system, the design, fabrication, and construction performance evaluation were performed using ultra-high performance concrete a compressive strength 120 MPa or more and a direct tensile strength 7 MPa or more. For offshore piers previously constructed with precast concrete, it was intended to verify the idea and possibility of solving errors due to position or vertical deformation during the driving of the foundation pile part during the construction stage. Furthermore, a offshore modular pier system was fabricated with ultra-high performance concrete for the construction performance evaluation. The results showed that a offshore modular pier system secured about 9 % of sectional performance of load bearing capacity under ultimate load conditions. If the offshore modular pier system developed through this study is utilized in the future, it is judged that competitiveness due to sufficient durability and constructability can be secured.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.4
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• pp.221-231
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• 2011

Thinner and lighter structural members can be designed by utilizing the high stiffness and toughness, and high compressive strength of UHPC(ultra high performance concrete), which reaches up to 200MPa. The punching shear capacity of UHPC was investigated in this paper aiming for the application of UHPC to bridge decks. Six square slabs were fabricated and punching shear test was performed under fixed boundary condition. Different thicknesses of test slabs, which were 40mm and 70mm, were selected. The shape ratio of loading plates were ranged between 1.0~2.5. 40mm thickness slabs showed longer softening region after the peak load and, on the other hand, 70mm thickness slabs revealed a more brittle shear failure. Experimental results were analyzed using various existing punching shear predicting equations. Ductal$^{(R)}$ equation and JSCE equation better predicted for 40mm slabs, and Harajli et al. equation and ACI-Ductal$^{(R)}$ equation better suited for 70mm slabs. Nevertheless generally they didn't well predict the test results. A new punching shear equation which was derived based on the actual failure mechanism was proposed. The proposed equation appeared to better predict the punching shear strength of UHPC than other available equations.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.566-577
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• 2002

As advanced earthquake analysis/design methods such as the nonlinear static analysis are developed, it is required to estimate precisely the cyclic behavior of reinforced concrete members that is characterized by strength, deformability, and capacity of energy dissipation. However, currently, estimation of energy dissipation depends on empirical equations that are not sufficiently accurate, or experiment and sophisticated numerical analysis which are difficult to use in practice.0 the present study, nonlinear finite element analysis was performed to investigate the behavioral characteristics of flexure-dominant RC members under cyclic load. The effects of axial force, arrangement of reinforcing bars, and reinforcement ratio on the cyclic behavior were studied. Based on the investigation, a simplified method to estimate the capacity of energy dissipation was proposed, and it was verified by the comparison with the finite element analyses and experiments. The proposed method can estimate the energy dissipation of RC members more precisely than currently used empirical equations, and it is easily applicable in practice.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.128-135
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• 2006

Steel slag (divided into electric arc furnace slag and convener slag) is being produced by millions of tons per every year in many industrial countries. About 6.5 million tonnes of steel slag is produced yearly as an industrial by-product in Korea. Generally natural aggregate is relatively stable and does not enter into complex chemical reactions with water. Unfortunately, however. steel slag aggregate contains a small amount of free lime. The hydration of free lime makes steel slag aggregate unstable and liable to expand. In this paper, firstly, several aging methods are used in order to decrease the volume expansion of electric arc furnace slag, that is stabilization. The volume expansion of electric arc furnace slag is formulated from the experiment. From the formula, the residual expansibility is predicted with immersion expansion. Compressive strength of concrete with electric arc furnace slag has relation with the residual expansibility in slag aggregate.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.4
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• pp.116-124
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• 2015

The objective of this study is to evaluate the effects of the replacement levels of grinded fly-ash on the repaired mortar based on a polymer. The main parameters are the curing temperature and replacement levels of grinded fly-ash. The curing temperature and the replacement levels of grinded fly-ash are varied at $40^{\circ}C$, $20^{\circ}C$ and $5^{\circ}C$, and between 0% and 35% of the total binder by weight, respectively. The flow in fresh mortar and compressive strengths according to ages, the relationship of stress-strain, elastic modulus and modulus rupture in hardened mortar, as well as scanning the electron microscopy and the X-ray diffraction of mortar, were measured, respectively. The test results showed that the flow, elastic modulus and modulus rupture are great in mortar specimens with 20~30% of the replacement levels of grinded fly-ash. In addition, compressive strengths according to ages were affected by the replacement levels of grinded fly-ash and the curing temperature indicated that the strength development ratio of mortar with 20% of the replacement levels of grinded fly-ash was greater than others. In the prediction of the compressive strength specified by the ACI 209 code, the strength development at an early and late age can be generalized by the functions of the replacement levels of grinded fly-ash and the curing temperature. In the analysis of scanning the electron microscopy and the X-ray diffraction, the number and intensity of peaks increased and the form of CSH gels on the surface of the particle of grinded fly-ash was observed.

• Journal of the Korea Society of Computer and Information
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• v.27 no.10
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• pp.123-130
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• 2022

In this paper is one of the measures to prevent concrete collapse accidents at construction sites in advance. Analyzed based on accumulated Meteorological Agency data. It is a reliable model that confirms the prediction of the decrease rate occurrence interval, and the verification items such as p_value is 0.5 or less and ecof appears in one direction through the SARIMA model, which is suitable for regular and clear time series data models, ensure reliability. Significant results were obtained. As a result of analyzing the temperature change by time zone and the water reduce ratio by section using the data secured based on such trust, the water reduce ratio is the highest in the 29-31 ℃ section from 12:00 to 13:00 from July to August. found to show. If a factor in the research result interval occurs using the research results, it is expected that the batch plant will produce Ready-mixed concrete that reflects the water reduce ratio at the time of designing the water-cement mixture, and prevent the decrease in concrete compressive strength due to the water reduce ratio.

• Journal of Korean Society of Steel Construction
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• v.24 no.5
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• pp.535-547
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• 2012

PSRC column is a concrete encased steel angle column. In the PSRC column, the steel angles placed at the corner of the cross-section resists bending moment and compression load. The lateral re-bars welded to steel angles resist the column shear and the bond between the steel angle and concrete. In the present study, current design procedures in KBC 2009 were applied to the flexure-compression, shear, and bond design of the PSRC composite column. To verify the validity of the design method and failure mode, simply supported 2/3 scaled PSRC and correlated SRC beams were tested under two point loading. The test parameters were the steel angle ratio and lateral bar spacing. The test results showed that the bending, shear, and bond strengths predicted by KBC 2009 correlated well with the test results. The flexural strength of the PSRC specimens was much greater than that of the SRC specimen with the same steel ratio because the steel angles were placed at the corner of the column section. However, when the bond resistance between the steel angle and concrete was not sufficient, brittle failures such as bond failure of the angle, spalling of cover concrete, and the tensile fracture of lateral re-bar occurred before the development of the yield strength of PSRC composite section. Further, if the weldability and toughness of the steel angle were insufficient, the specimen was failed by the fracture of the steel angle at the weld joint between the angle and lateral bars.

• Composites Research
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• v.23 no.4
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• pp.44-51
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• 2010

Recently, to solve the problems associated with the neutralization and corrosion of reinforced concrete compression members, the structural configurations such as CFFT (Concrete Filled GFRP Tube) and RCFFT (Reinforced Concrete Filled GFRR Tube) have been developed and applied to main members of civil engineering structure. These members can increase structural performance in terms of structural stability, ductility as well as chemical resistance compared with conventional concrete structural members. Many researches in numerous institutions to predict the load carrying capacity of the concrete compression member strengthened with FRP materials have been conducted and they have been suggested an equation for the prediction of the load carrying capacity of the members. Through the review of the research results, it was found that their results are similar each other. Moreover, it was also found that the results are not directly applicable to our specimens since the results are largely depended upon the member configurations. Also, since the accurate design criteria for the RC members strengthened with FRP such as RCFFT have not been established properly, relevant theoretical and experimental investigations must be conducted for the application to the practical structures. In this study, structural behavior of RCFFT was evaluated through compressive and quasi-static flexural tests in order to formulate design criteria for the structural design. In addition, the RCFFT members were also investigated to examine their confinement effect and the equations capable of estimating the compressive ultimate strength and flexural stiffness of the RCFFT members were proposed.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.06a
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• pp.58-59
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• 2020

The change of temperature and humidity in early-age concrete has a great influence on the durability of the structure. In this study, a reliable wireless sensor network system and a concrete embedded type Compressive strength prediction sensor were designed using the Arduino platform. The accuracy of the compressive strength prediction sensor was verified through a mock-up experiment, and it was confirmed that the experiment had sufficient accuracy to be used in the field environment.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.101-102
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• 2021

The compressive strength of concrete is greatly affected by the temperature inside the concrete at the initial age immediately after pouring. The apparent activation energy of cement and the setting time of concrete are major factors influencing the development of compressive strength of concrete. This study measured the apparent activation energy and setting time according to the change in W/B for each mixing rate of Ground Granulated Blast-Furnace Slag (GGBFS). And after calculating the compressive strength prediction model, the accuracy of the prediction model was evaluated by comparing the predicted compressive strength and the compressive strength.