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CONTENTS
Volume 17, Number 2, February 2016
 

Abstract
This paper presents a Strut-and-Tie Model for reinforced concrete (RC) columns subject to lateral loading. The proposed model is based on the loading path for the post-yield state, and the geometries of struts and tie are determined by the stress field of post-yield state. The analysis procedure of the Strut-and-Tie Model is that 1) the shear force and displacement at the initial yield state are calculated and 2) the relationship between the additional shear force and the deformation is determined by modifying the geometry of the longitudinal strut until the ultimate limit state. To validate the developed model, the ultimate strength and associated deformation obtained by experimental results are compared with the values predicted by the model. Good agreements between the proposed model and the experimental data are observed.

Key Words
deformation; lateral loading; reinforced concrete column; strut-and-time model; ultimate strength

Address
Sung-Gul Hong, Seongwon Hong and Thomas H.K. Kang: 1Department of Architecture and Architectural Engineering, Seoul National University,1 Gwanak-ro, Gwanak-gu, Seoul 08826, Korea
Soo-Gon Lee: Samsung C&T, 14 Seocho-daero 74-gil, Seocho-gu, Seoul 06620, Korea

Abstract
Generally, thermal stress induced by hydration heat causes cracking in mass concrete structures, requiring a thorough control during the construction. The prediction of the thermal stress is currently undertaken by means of numerical analysis despite its lack of reliability due to the properties of concrete varying over time. In this paper, a method for the prediction of thermal stress in concrete structures by adjusting thermal stress measured by a thermal stress device according to the degree of restraint is proposed to improve the prediction accuracy. The ratio of stress in concrete structures to stress under complete restraint is used as the degree of restraint. To consider the history of the degree of restraint, incremental stress is predicted by comparing the degree of restraint and the incremental stress obtained by the thermal stress device. Furthermore, the thermal stresses of wall and foundation predicted by the proposed method are compared to those obtained by numerical analysis. The thermal stresses obtained by the proposed method are similar to those obtained by the analysis for structures with internally as well as externally strong restraint. It is therefore concluded that the prediction of thermal stress for concrete structures with various boundary conditions using the proposed method is suggested to be accurate.

Key Words
mass concrete; thermal stress; hydration heat; thermal stress device; degree of restraint

Address
Sang Lyul Cha, Gyeong Hee An and Jin Keun Kim: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology,291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea
Yun Lee: Department of Civil Engineering, Daejeon University,
96-3 Yongun-dong, Dong-gu, Daejeon 300-716, Republic of Korea

Abstract
Chloride penetration is considered as a most crucial factor for the determination of the service life of concrete. A lot of experimental tools for the chloride penetration into concrete have been developed, however, the mechanism was based on only diffusion, although permeability is also main driving forces for the chloride penetration. Permeation reacts on submerged concrete impacting for short to long term durability while capillary suction occurs on only dried concrete for very early time. Furthermore, hydrostatic pressure increases in proportional to measured depth from the surface of water because of the increasing weight of water exerting downward force from above. It is thought, therefore, that the water pressure has a great influence on the chloride penetration and thereby on the service life of marine concrete.In this study, new experiment is designed to examine the effect of water pressure on chloride penetration in concrete quantitatively. As an experiment result, pressure leaded a quick chlorides penetration by a certain depth, while diffusion induced chlorides to penetrate inward slowly. Therefore, it was concluded that chloride should penetrates significantly by water pressure and the phenomena should be accelerated for concrete exposed to deep sea. The research is expected as a framework to define the service life of submerged concrete with water pressure and compute water permeability coefficient of cementitious materials.

Key Words
chloride penetration; permeation; water pressure; service life; chloride profile

Address
In-Seok Yoon: Department of Construction Information Engineering, Induk University, Choansanro12, Nowon-gu,Seoul 01880, Republic of Korea
Jin-Won Nam: Baytech Korea Inc., 8F, 464 Dunchon-Daero, Jungwon-gu, Seongnam-si, Gyeonggi-do, 13229, Republic of Korea

Abstract
The outer tank of a liquefied natural gas (LNG) storage tank is a longitudinally and meridianally pre-stressed concrete (PSC) wall structure. Because of the current trend of constructing larger LNG storage tanks, the pre-stressing forces required to increase wall strength must be significantly increased. Because of the increase in tank sizes and pre-stressing forces, an extreme loading scenario such as a bomb blast or an airplane crash needs to be investigated. Therefore, in this study, the blast resistance performance of LNG storage tanks was analyzed by conducting a blast simulation to investigate the safety of larger LNG storage tanks. Test data validation for a blast simulation of reinforced concrete panels was performed using a specific FEM code, LS-DYNA, prior to a full-scale blast simulation of the outer tank of a 270,000-kL LNG storage tank. Another objective of this study was to evaluate the safety and serviceability of an LNG storage tank with respect to varying amounts of explosive charge. The results of this study can be used as basic data for the design and safety evaluation of PSC LNG storage tanks.

Key Words
LNG storage tank; blast analysis; LS-DYNA; protective design; pre-stressed concrete

Address
Sang Won Lee, Seung Jai Choi and Jang-Ho Jay Kim: Department of Civil and Environmental Engineering, Yonsei University,
50 Yonsei-ro, Seodaemun-gu, Seoul 120-749, Republic of Korea

Abstract
High performance materials such as Fiber Reinforced Plastic (FRP) are often used for retrofitting structures against blast loads due to its ductility and strength. The effectiveness of retrofit materials needs to be precisely evaluated for the retrofitting design based on the dynamic material responses under blast loads. In this study, the blast resistance of Carbon Fiber Reinforced Plastic (CFRP) and Kevlar/Glass hybrid fabric (K/G) retrofitted reinforced concrete (RC) wall is analyzed by using the explicit analysis code LS-DYNA, which accommodates the high-strain rate dependent material models. Also, the retrofit effectiveness of FRP fabrics is evaluated by comparing the analysis results for non-retrofitted and retrofitted walls. The verification of the analysis is performed through comparisons with the previous experimental results.

Key Words
HFPB analysis; blast resistance; FRP Composite; strain rate; LS-DYNA

Address
Jin-Won Nam: Baytech Korea Inc., 8F, 464 Dunchon-Daero, Jungwon-gu, Seongnam-si, Gyeonggi-do, 13229, Korea
In-Seok Yoon:Department of Construction Information Engineering, Induk University, 12 Choansan-ro, Nowon-gu,Seoul, 01880, Korea
Seong-Tae Yi: Department of Civil & Environmental Engineering, Inha College, 100 Inha-Ro, Nam-Gu,Incheon, 22212, Korea

Abstract
An analytical study was conducted to investigate the effect of the shape and spacing of modified inclined studs used as shear connector between concrete and steel plate on the cyclic behavior of steel plate concrete (SC) shear wall. 9 different analysis cases were adopted to determine the optimized shape and spacing of stud. As the results, the skeleton curves were obtained from the load-displacement hysteresis curves, and the ultimate and yielding strengths were increased as the spacing of studs decrease. In addition,the strength of inclined studs is shown to be bigger compared to that of conventional studs. The damping ratios increased as the decrease of stiffness ratio. Finally, with decreasing the spacing distance of studs, the cumulative dissipated energy was increased and the seismic performance was improved.

Key Words
modified inclined stud, steel plate concrete, shape, spacing, cumulative dissipated energy, seismic performance

Address
Jin-Sun Lim: Department of Civil Engineering, Inha University, Incheon 22212, Korea
Young-Do Jeong: R&D Center, POSCO E&C, Incheon 22009, Korea
Jin-Won Nam: Baytech Korea Inc., 8F, 464 Dunchon-Daero, Jungwon-gu, Seongnam-si, Gyeonggi-do, 13229, Korea
Chun-Ho Kim: Department of Civil Engineering, Joongbu University, Gyeonggi 10279, Korea
Seong-Tae Yi: Department of Civil and Environmental Engineering, Inha Technical College, Incheon 22212, Korea

Abstract
Depending on the researcher, the effect of prestressing on the natural frequency of a PSC (prestressed concrete) structure appear to have been interpreted differently. Most laboratory tests on PSC beams available showed that the natural frequency is increased appreciably by prestressing. On the other hand, some other references based on field experience argued that the dynamic response of a PSC structure does not change regardless of the prestressing applied. Therefore, the deduced conclusions are inconsistent. Because an experiment with and without prestressing is a difficult task on a full size PSC bridge, the change in natural frequency of a PSC bridge due to prestressing may not be examined through field measurements. The study examined analytically the effects of prestressing on the natural frequency of PSC bridges. A finite element program for an undamped dynamic motion of a beamtendon system was developed with additional geometric stiffness. The analytical results confirm that a key parameter in changing the natural frequency due to prestressing is the relative ratio of prestressing to the total weight of the structure rather than the prestressing itself.

Key Words
prestressing; natural frequency; PSC bridge; laboratory test; geometric stiffness; total weight

Address
Soobong Shin and Yuhee Kim: Department of Civil Engineering, INHA University, 100 Inha-ro, Nam-gu, Incheon 22212, Korea
Hokyoung Lee: Korea Bridge Institute Co., 252 Gilju-ro,Wonmi-gu, Bucheon-si, Gyeonggi-do 14548, Korea

Abstract
The waste glass sludge is a waste produced in the glass industry. It is in a dust form and disposed with water. In the disposal process, various cohesive agents are incorporated in order to precipitate the glass particles efficiently. In this paper, we investigate the pozzolanic reaction of the waste glass sludge incorporating precipitation additives experimentally. The consumption of calcium hydroxide, the setting time and the compressive strength and the pore structure were tested for two different types of the waste glass sludge depending on whether precipitation additives were used. It was found that the waste glass sludge incorporating the precipitation additives had a higher pozzolanic potential than the reference waste glass sludge without precipitation additives.

Key Words
waste glass sludge; precipitation additives; cohesive agent; coagulant aid; caustic soda; alkali activation; pozzolanic reaction

Address
Ilhwan You and Goangseup Zi: School of Civil, Environmental & Architectural Engineering, Korea University, 145 An-Am Ro, Sung-Buk Gu, Seoul, 136-713, Republic of Korea
Jisun Choi: Hyundai Engineering & Construction, Yongin-Si, Gyeonggi-Do 446-716, Republic of Korea
David A. Lange: Department of Civil Engineering, University of Illinois at Urbana-Champaign, 2122 Newmark CE Lab, MC-250, 205 North Mathews, Urbana, IL 61801-2352, USA


Abstract
This study examined the mechanical properties and adiabatic temperature rise of low-heat concrete developed based on ternary blended cement using ASTM type IV (LHC) cement, ground fly ash (GFA) and limestone powder (LSP). To enhance reactivity of fly ash, especially at an early age, the grassy membrane was scratched through the additional vibrator milling process. The targeted 28-day strength of concrete was selected to be 42 MPa for application to high-strength mass concrete including nuclear plant structures. The concrete mixes prepared were cured under the isothermal conditions of 5

Key Words
mass concrete; ternary blended concrete; mechanical properties; adiabatic temperature rise

Address
Si-Jun Kim and Keun-Hyeok Yang: Department of Plant Architectural Engineering, Kyonggi University, Suwon, Kyonggi-do, Korea
Kyung-Ho Lee: Department of Architectural Engineering, Kyonggi University, Suwon, Kyonggi-do, Korea
Seong-Tae Yi: Department of Civil & Environmental Engineering, Inha Technical College, Incheon, Korea

Abstract
The increased awareness of electromagnetic wave hazards has prompted studies on electromagnetic shielding using conductive materials in the construction industry. Previous studies have explored the effects of the types of conductive materials and their mix proportions on the electromagnetic shielding performance; however, there has been insufficient research on the effect of the geometry of the conductive materials on the electromagnetic shielding performance. Therefore, in this study, the dependence of the electromagnetic shielding performance on the cross-sectional geometry, diameter and length of fibers was investigated. The results showed that the electromagnetic shielding performance improved when the fiber length increased or the diameter decreased, but the effect of the cross-sectional geometry of the fibers was smaller than the effect of the fiber spacing factor.

Key Words
electromagnetic wave; shielding effectiveness; metal fiber; geometry; spacing factor

Address
Young Jun Kim, Dinberu M. Yemam, Baek-Joong Kim and Chongku Yi:School of Civil, Environmental and Architectural Engineering, Korea University 145 Anam-ro, Seongbuk-gu, Seoul 02841, Republic of Korea


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