• Advances in concrete construction
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• v.10 no.2
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• pp.151-159
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• 2020

An experimental study on the stress-strain relation of PVC-CFRP confined reinforced concrete columns subjected to eccentric compression was carried out. Two parameters, such as the CFRP strips spacing and eccentricity of axial load, were considered. The experimental results showed that all specimens failed by compressive yield of longitudinal steel bar and rupture of CFRP strips. The bearing capacity of specimen decreases as the eccentricity or the CFRP strips spacing increases. The stress-strain relation of specimens undergoes two stages: parabolic and linear stages. In the parabolic stage, the slope of stress-strain curve decreases gradually as the eccentricity of axial loading increases while the CFRP strips spacing has little effect on the slope of stress-strain curve. For the linear stage, the slope of stress-strain curve decreases as the eccentricity of axial load or the CFRP strips spacing increases. A model for predicting the stress-strain relation of columns under eccentric compression is proposed and it agrees well with various test data.

• Journal of the Korea Institute of Building Construction
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• v.3 no.3
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• pp.127-133
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• 2003

Carbonation and drying shrinkage are very important properties of concrete, that can cause concrete to lower its capacity and spall. But the research on them in high strength concrete is very poor. In this study, to estimate influences of W/B, the kind of admixture, the replacement ratio of admixture, fineness of blast furnace and etc. on drying shrinkage and carbonation, we make experiment with 3 levels(28, 35, 55%) of W/B, 3 kinds(blast-furnace slag, fly-ash, silica-fume) of admixture, 3 levels of the replacement ratio, 3 levels(4000, 6000, 8000cm2/g) of fineness of blast-furnace slag and 2 kinds of curing condition. As the results, compressive strength of concrete was decreased, as W/C was increased and the replacement ratio of admixture was increased. Drying shrinkage was increased, as W/B was higher, the replacement ratio of admixture was increased and fineness of blast-furnace slag was decreased. And carbonation was increased, as W/B ratio was higher, the replacement ratio of admixture was increased.

• Journal of the Korea Institute of Building Construction
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• v.8 no.5
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• pp.35-42
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• 2008

In this study, a sample was fabricated according to the recycled aggregate replacement level(0%, 30%, 60%), and the steel fiber mixing status in order to use recycled aggregate as a concrete alternative coarse aggregate, and then the materials and structural characteristics of recycled aggregate and steel fiber which impacted the reinforced concrete were analyzed. A conclusion was derived as follows. After considering the results of various material experiments and mock-up test, when a flexural strength and a ductility factor is increased and the replacement level is increased through mixing the steel fiber with the recycled aggregate concrete, the ductility and flexural strength reduction seems to be inhibited by adding the steel fiber. Also, it is indicated that the recycled aggregate has almost-similar compressive strength, tensile strength flexural strength and ductility capacity to the concrete which using the general gone even though the steel fiber is used and the replacement level is increased to 30%. Accordingly, the reinforced concrete frame using the steel fiber mixture and recycled aggregate seems to apply to the actual structure.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.113-117
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• 2009

Fly ash (called FA hereafter) that results from thermal power plants is a long-term strength improving substance with reactivity to pozzolan and has been used for long. However, large amount of FA shows many advantages such as reduction of hydratio energy, long-term improvement in strength and economic feasibility and also has difficulties from reduction in initial strength and durability. In a preceding study, fine particle cement was applied to test the effects on initial strength. Therefore in this study, the effects of fine particle cement on the quality of FA concrete were reviewed. The results can be summarized as follows. Liquidity was increased by the most at FC substitution ratio of 15%. Air capacity was reduced according to increasing substitution ratio of FA and FC. Compressive strength showed high strength expression at all ages when FC was substituted at 45%. Synthesizing the above results, appropriate mixing of FC in FA concrete can improve liquidity, reduce unit quantity and show improvement in strength. In particular, mixed use of FC seems effective in improving early quality of concrete.

• Nuclear Engineering and Technology
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• v.50 no.2
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• pp.292-296
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• 2018

Recent events in the nuclear industry have resulted in a movement towards increased seismic and LOCA excitations and requirements that challenge current fuel designs. AREVA NP's GAIA fuel design introduces unique and robust characteristics to resist the effects of seismic and LOCA excitations. For demanding seismic and LOCA scenarios, fuel assembly spacer grids can undergo plastic deformations. These plastic deformations must not prohibit the complete insertion of the control rod assemblies and the cooling of the fuel rods after the accident. The specific structure of the GAIA spacer grid produces a unique and stable compressive deformation mode which maintains the regular array of the fuel rods and guide tubes. The stability of the spacer grid allows it to absorb a significant amount of energy without a loss of load-carrying capacity. The GAIA-specific grid behavior is in contrast to the typical spacer grid, which is characterized by a buckling instability. The increased mechanical robustness of the GAIA spacer grid is advantageous in meeting the increased seismic and LOCA loadings and the associated safety requirements. The unique GAIA spacer grid behavior will be incorporated into AREVA NP's licensed methodologies to take full benefit of the increased mechanical robustness.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.253-260
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• 1999

Main objective of this study is to examine the hysteretic behaviors and to evaluate the capacity of precast concrete (PC) large panel structures simulated from the prototype of 15-story building, Two 1/2 scaled precast concrete wall specimens and one monolithic reinforced concrete specimen were designed and tested under the cyclic loading conditions. The main parameter of test specimens in PC large panel structure is the type of details for vertical continuity of vertical steel in horizontal joint. Also the behaviors of PC large panel structures are compared with that of monolithic reinforcement concrete wall structure. From the results, the stiffness and energy dissipation ratio of the precast concrete specimens are shown little bit lower than those of monolithic reinforced concrete specimen. In the PC large panel structures, the specimen connected vertically by welding (strong connection) showed higher strength than that of the specimen connected vertically by joint box. However the failure pattern of the former showed more brittle than that of the latter due to the diagonal compressive failure of wall panels.

• Journal of the Korea institute for structural maintenance and inspection
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• v.4 no.2
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• pp.113-129
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• 2000

This study evaluates the behavior and strength of an anchorage zone of the prestressed concrete box girder bridge on the Kyungboo highway railroad using the 2D SUB-3D STM approach and a linear elastic finite element analysis. The 2D SUB-3D STM approach utilizes several two-dimensional sub strut-tie models that represent the compressive and tensile stress flows of each projected plane of the three-dimensional structural concrete in the selection of a three dimensional strut-tie model, evaluation of the effective strengths of the concrete struts, and verification of the geometric compatibility condition and bearing capacity of the critical nodal zones in the selected three-dimensional strut-tie model. The finite element analysis uses an 8-node brick element and the longitudinal prestressing force is considered as the equivalent nodal force. Analysis results show that the 2D SUB-3D STM approach and linear elastic finite element method can be effectively applied to the analysis and design of three-dimensional structural concrete including a prestressed concrete box girder anchorage zone.

• Advances in concrete construction
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• v.8 no.2
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• pp.145-154
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• 2019

The present experimental study addresses the structural response of reinforced concrete (RC) beams strengthened in shear. Thirteen RC beams were divided into four different sets to investigate the effect of transverse and longitudinal steel reinforcement ratios, concrete compressive strength change and orientation for installing carbon fiber-reinforced polymer (CFRP) laminates. Then, we employed a shear strengthening solution through externally bonded reinforcement in grooves (EBRIG) and externally bonded reinforcement (EBR) techniques. In this regard, rectangular beams of $200{\times}300{\times}2000mm$ dimensions were subjected to the 4-point static loading condition and their load-displacement curves, load-carrying capacity and ductility changes were compared. The results revealed that using EBRIG method, the gain percentage augmented with the increase in the longitudinal reinforcement ratio. Also, in the RC beams with stirrups, the gain in shear strength decreased as transverse reinforcement ratio increased. The results also revealed that the shear resistance obtained by the experimental tests were in acceptable agreement with the design equations. Besides, the results of this research indicated that using the EBRIG system through vertical grooves in RC beams with and without stirrups caused the energy absorption to increase about 85% and 97%, respectively, relative to the control.

• Steel and Composite Structures
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• v.32 no.5
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• pp.583-594
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• 2019

In recent years, composite concrete-filled steel tubular (CFST) members have been widely utilized in framed building structures like beams, columns, and beam-columns since they have significant advantages such as reducing construction time, improving the seismic performance, and possessing high ductility, strength, and energy absorbing capacity. This paper presents a new composite joint - the composite CFST beam-column joint in which the CFST member is used as the beam. The main components of the proposed composite joint are steel H-beams, CFST beams welded with the steel H-column, and a reinforced concrete slab. The steel H-beams and CFST beams are connected with the concrete slab using shear connectors to ensure composite action between them. The structural performance of the proposed composite joint was evaluated through an experimental investigation. A three-dimensional (3D) finite element (FE) model was developed to simulate this composite joint using the ABAQUS/Explicit software, and the accuracy of the FE model was verified with the relevant experimental results. In addition, a number of parametric studies were made to examine the effects of the steel box beam thickness, concrete compressive strength, steel yield strength, and reinforcement ratio in the concrete slab on the proposed joint performance.

• Advances in concrete construction
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• v.7 no.1
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• pp.39-50
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• 2019

This study presents a comprehensive experimental investigation on mostly encountered types of Reinforced Concrete Haunched Beams (RCHBs) where three modes of RCHBs investigated; the diversity of studied beams makes it a pioneer in this topic. The experimental study consists of twenty RCHBs and four prismatic beams. Effects of important parameters including beam type, the inclination angle, flexure and compressive reinforcement, shear reinforcement on mechanical behavior and failure mode of each mode of RCHBs were examined in detail. Furthermore crack propagation at certain load levels were inspected and visualized for each RCHB mode. The results confirm that RCHBs have different behavior in shear as compared to the prismatic beams. At the same time, different mechanical behavior was observed between the modes of RCHBs. Therefore, RCHBs were classified into three modes according to the inclination shape and mode of failure (Modes A, B and C). However, it was observed that there is no significant difference between RCHBs and prismatic beams regarding flexural behavior. Moreover, a new and unified formula was proposed to predict the critical effective depth of all modes of RCHBs that is very useful to predict the critical section for failure.