• Magazine of the Korea Concrete Institute
• /
• v.9 no.1
• /
• pp.115-121
• /
• 1997

This study deals with the suppressing characteristics of alkali-silica reaction by ground granulated blast-furnace slag(GGBS) in NaCl solution. NaCl contents used in the experiment ranges over 0%, 2.8% and 20%. Reactive aggregate used is Japanese andesite. Also, three GGBSs of about 4.000. 6, 000 and $8, 000cm^2/g$ were used in the experiment. The replacement proportions of portland cement by GGBSs were 40%. 60%, 70% and 80%. respectively. The specimens with GGBS were severely contracted according to the increasing replacement ratio in NaCl solution. The contraction rate increases according to the increasing in NaCl content. Also. it does with increasing the blaine fineness of GGRS. It is concluded that the suppression of alkali-silica reaction by GGBS in NaCl solution is complished by contraction of GGBS due to chloride ion induced chemical shrinkage.

• Journal of the Korea Concrete Institute
• /
• v.27 no.6
• /
• pp.625-632
• /
• 2015

In this study, a comparative analysis have been conducted to examine seismic reinforcement effect of a school building that is designed with a CBD (Channel Beam Damper) system supported by H-frame with existing non-seismic RC frame. As a result of experiment, seismic reinforcement specimen with CBD system showed hysteretic characteristics of a large ellipse with great energy dissipation ability and increased strength and stiffness, while non-seismic design specimen showed rapid reduction in strength and brittle shear failure at top and bottom of the left and right column. In addition, comparing the stiffness reduction between the two specimens, CBD system was effective in preventing the reduction of stiffness. Energy dissipation ability of specimen reinforced by CBD system was about 4.0 times higher than the non-reinforced specimen. Such enhancement in energy dissipation ability could be considered as the result of improved strength and deformation for further application in designing of seismic reinforcement.

• Journal of the Korea Concrete Institute
• /
• v.24 no.5
• /
• pp.525-533
• /
• 2012

In this study, bending tests were performed on beam specimens made of UHPCC with the fiber content range of 0~5 vol% to investigate the contribution of fiber content to first cracking strength and flexural tensile strength. Also, four-point bending tests for unnotched beam as well as three-point bending test for notched beam were performed to estimate the effect of the presence of notch on the strengths. The experiment result showed that the increase in fiber content made linear improvement in the flexural tensile strength; whereas first cracking strength was enhanced only when at least 1 vol% of fibers was incorporated. Comparison of the bending test results with and without notch showed that the notch effect varied with the fiber content. The increase in fiber content diminished the effect of stress concentration on the notch tip, reducing the difference in the strengths. With much higher fiber content, the effect of stress concentration almost disappeared and the defection on cracking plane or the size effect dominated the strengths, consequently resulting in higher strengths in the notched beams than the unnotched ones.

• Journal of the Korea Concrete Institute
• /
• v.25 no.5
• /
• pp.565-572
• /
• 2013

Hydration and physical characteristics of chemically-bonded phosphate ceramic (CBPC) binder based on dead-burned Mg-O with six different blends are investigated for efficient repair construction material by retarding set phase with $H_3BO_3$. The test specimen of the blender with silica fume shows higher compressive strength after 75 days. The CBPC with silica fume results in higher modulus of rupture that others. The test specimens of CBPC eludes lower calcium ion than that of OPC (Ordinay Portland Cement). The X-ray diffraction pattern shows that hydration results in the formation of magnesium hydroxide, M-S-H gel and $MgCO_3$ for the specimen with silica fumes. Combination with calcium for MgO is not desirable due to no formation of chemical bond between two components. Based on the experimental program, the mixture of MgO and silica fume shows efficient performance in strength and durability.

• Journal of the Korea Concrete Institute
• /
• v.25 no.6
• /
• pp.649-656
• /
• 2013

Coupled shear walls can provide an efficient structural system to resist lateral force. However, the reinforcement detail for diagonally reinforced coupling beams required by ACI-318 often causes the difficulties in construction due to the reinforcement congestion and interference among reinforcement. This paper is to evaluate cyclic behavior of High-Performance Fiber-Reinforced Cement Composite (HPFRCC) coupling beams having reduced transverse reinforcement around the beam perimeter. Experimental test was conducted using three specimens having a beam aspect ratio 2.0. Test results showed that HPFRCC coupling beams with half of transverse reinforcement required by ACI-318 provided similar energy dissipation capacities compared with the coupling beams having reinforcement satisfy the requirement of ACI-318.

• Earthquakes and Structures
• /
• v.18 no.1
• /
• pp.113-127
• /
• 2020

In this study, the behavior of external beam-column joints reinforced by plain and deformed bars with non-seismic reinforcement details is investigated and compared. The beam-column joints represented in this study include a benchmark specimen by seismic details in accordance with ACI 318M-11 requirements and four other deficient specimens. The main defects of the non-seismic beam-column joints included use of plain bar, absence of transverse steel hoops, and the anchorage condition of longitudinal reinforcements. The experimental results indicate that using of plain bars in non-seismic beam-column joints has significantly affected the failure modes. The main failure mode of the non-seismic beam-column joints reinforced by deformed bars was the accumulation of shear cracks in the joint region, while the failure mode of the non-seismic beam-column joints reinforced by plain bars was deep cracks at the joint face and intersection of beam and column and there was only miner diagonal shear cracking at the joint region. In the other way, use of plain bars for reinforcing concrete can cause the behavior of the substructure to be controlled by slip of the beam longitudinal bars. The experimental results show that the ductility of non-seismic beam-column joints reinforced by plain bars has not decreased compared to the beam-column joints reinforced by deformed bars due to lack of mechanical interlock between plain bars and concrete. Also it can be seen a little increase in ductility of substructure due to existence of hooks at the end of the development length of the bars.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.3
• /
• pp.103-110
• /
• 2018

The long-term flexural behavior of reinforced concrete (RC) beams strengthened with an iron based-shape memory alloys (Fe-SMAs) by a near-surface mounted (NSM) method was evaluated. The pre-strained values of 2% and 4% and introduced prestressing force by an activation of a shape memory effect of the Fe-SMA strengthening material were considered as experimental variables. Deflections at the center of the RC beams were measured for six months after the 1 tonf concrete weight was loaded on the beam. Experimental results show that the deflections decreased because of the increased flexural stiffness of beams strengthened with the Fe-SMA strips. On the contrary, with increased pre-strained values, the deflection increased due to stiffness reduction of the strengthening material. It was confirmed that the specimens incorporating the prestressed force showed the deflection reduction of about 30%, compared to the ones without the prestressed force.

• Journal of Korean Society of Steel Construction
• /
• v.16 no.5 s.72
• /
• pp.587-598
• /
• 2004

In this study, an experiment was conducted on the Slim Floor system, using a hollow core PC slab, which could reduce the over-all depth of a composite beam. The Slim Floor system is a method used in steel frame multi-story building construction, in which the structural depth of each floor is minimized after incorporating the steel floor beams within the depth of the concrete floor slab. This experimental study focused on the flexural behavior of the partially connected Slim Floor system with asymmetric steel beams encased in hollow core PC slabs. Ten full-scale specimens were constructed and tested in this study, with different steel beam heights, hollow core PC slabs, slab widths, and PC slab bearings. Observations made in line with the experiments indicated that the degree of shear connection without additional shear connection was 0.48-0.98 times more than that of the full shear connection, due to inherent mechanical and chemical bond stress.

• Smart Structures and Systems
• /
• v.26 no.4
• /
• pp.403-418
• /
• 2020

In recent years, the use of Fiber Reinforced Polymers (FRPs) as one of the most common ways to increase the strength of concrete samples, has been introduced. Evaluation of the final strength of these specimens is performed with different experimental methods. In this research, due to the variety of models, the low accuracy and impact of different parameters, the use of new intelligence methods is considered. Therefore, using artificial intelligent-based models, a new solution for evaluating the bond strength of FRP is presented in this paper. 150 experimental samples were collected from previous studies, and then two new hybrid models of Imperialist Competitive Algorithm (ICA)-Artificial Neural Network (ANN) and Artificial Bee Colony (ABC)-ANN were developed. These models were evaluated using different performance indices and then, a comparison was made between the developed models. The results showed that the ICA-ANN model's ability to predict the bond strength of FRP is higher than the ABC-ANN model. Finally, to demonstrate the capabilities of this new model, a comparison was made between the five experimental models and the results were presented for all data. This comparison showed that the new model could offer better performance. It is concluded that the proposed hybrid models can be utilized in the field of this study as a suitable substitute for empirical models.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.16 no.5
• /
• pp.88-97
• /
• 2012

The objective of this research is to investigate the seismic performance and flexure-shear behavior of square reinforced concrete bridge piers with solid and hollow cross section. Test specimens were nonseismically designed with the aspect ratio 4.5 Two reinforced concrete columns were tested under constant axial load while subjected to lateral load reversals with increasing drift levels. Longitudinal steel ratio was 2.217 percent. The transverse reinforcement ratio As/($s{\cdot}h$), corresponding to 58 percent of the minimum lateral reinforcement required by Korean Bridge Design Specifications for seismic detailing, which represent existing columns not designed by the current seismic design specifications or designed by limited ductility concept. This study are to provide quantitative reference data for the limited ductility design concept and tendency for performance or damage assessment based on the performance levels such as cracking, yielding, collapse, etc. Failure behavior, ultimate displacement/drift ratio, displacement ductility, response modification factor, equivalent viscous damping ratio, residual deformation, effective stiffness, plastic hinge length, strain of reinforcements and nonlinear analysis are investigated and discussed in this paper.