• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.159-168
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• 2011

In the present study, an improved design method was developed for the punching shear strength of interior slabcolumn connections and column footings with and without shear reinforcement. In the evaluation of the punching shear strength, the possible failure mechanisms of the connections and column footings were considered. The considered failures modes were inclined tensile cracking of concrete, yielding of shear re-bars, and concrete crushing of compression zone/strut. The punching shear applied to the concrete critical section was assumed to be resisted mainly by the compression zone. The punching shear strength of the concrete compression zone was evaluated based on the material failure criteria of the concrete subjected to the compressive normal stress and shear stress. For verification of the proposed design method, its prediction was compared with the existing test results. The result showed that the proposed method predicted the strengths of the test specimens better than the current design methods of the KCI code for both the shear reinforced and unreinforced cases.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.67-74
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• 2007

We perform an experimental study of concrete beam with pultruded fiber reinforced polymer(FRP) plank using as a permanent formwork and the tensile reinforcement. A satisfactory bond at the interface between the smooth surface of the pultruded plank and the concrete must be developed for the FRP plank and the concrete to act as a composite structural member. Two kinds of aggregate were bonded to the FRP plank using a commercially available epoxy. No additional flexural or shear reinforcement was provided in the beams. For comparison we test two types of control specimen. One control did not have any aggregate bonded to the FRP plank and the other control had infernal steel reinforcing bars instead of the FRP plank. The beams were loaded by central patch load to their ultimate capacity. The experimental results were compared to current ACI 318 (2005) and ACI 440 (2006) code predictions. This study demonstrates that the FRP plank has the potential to serve as formwork and reinforcing for concrete structures.

• International Journal of Concrete Structures and Materials
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• v.7 no.1
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• pp.35-50
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• 2013

Rapid and effective repair methods are desired to enable quick reopening of damaged bridges after an earthquake occurs, especially for those bridges that are critical for emergency response and other essential functions. This paper presents results of tests conducted as a proof-of-concept in the effectiveness of a proposed method using externally bonded carbon fiber reinforced polymer (CFRP) composites to rapidly repair severely damaged RC columns with different damage conditions. The experimental work included five large-scale severely damaged square RC columns with the same geometry and material properties but with different damage conditions due to different loading combinations of bending, shear, and torsion in the previous tests. Over a three-day period, each column was repaired and retested under the same loading combination as the corresponding original column. Quickset repair mortar was used to replace the removed loose concrete. Without any treatment to damaged reinforcing bars, longitudinal and transverse CFRP sheets were externally bonded to the prepared surface to restore the column strength. Measured data were analyzed to investigate the performance of the repaired columns compared to the corresponding original column responses. It was concluded that the technique can be successful for severely damaged columns with damage to the concrete and transverse reinforcement. For severely damaged columns with damaged longitudinal reinforcement, the technique was found to be successful if the damaged longitudinal reinforcement is able to provide tensile resistance, or if the damage is located at a section where longitudinal CFRP strength can be developed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.8
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• pp.3745-3751
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• 2011

In this study flexural strength of damaged concrete beams reinforced by CFS is analysed. Nonlinear section analysis is used to include stress status of tension bars and compressive concrete under loads acting on the original member at the time of strengthening. Calculated flexural strength is compared with Sin-Hong formula which is frequently used in CFS reinforcement design. Nonlinear analysis with variation of the number of strengthening CFS, the ratio of tensile reinforcement, the ratio of section dimension shows that the flexural strength of CFS reinforced beams much depends on reinforcing stage. From the result of this analysis, the flexural strength of CFS reinforced concrete beam is reduced according to the magnitude of pre-loaded service loads.

• Steel and Composite Structures
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• v.29 no.1
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• pp.1-22
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• 2018

Multi-storey precast concrete skeletal structures are assembled from individual prefabricated components which are erected on-site using various types of connections. In the current design of these structures, beam-to-column connections are assumed to be pin jointed. Welded plate beam to-column connections have been used in the precast concrete industry for many years. They have many advantages over other jointing methods in component production, quality control, transportation and assembly. However, there is at present limited information concerning their detailed structural behaviour under bending and shear loadings. The experimental work has involved the determination of moment-rotation relationships for semi-rigid precast concrete connections in full scale connection tests. The study reported in this paper was undertaken to clarify the behaviour of such connections under symmetrical vertical loadings. A series of full-scale tests was performed on sample column for which the column geometry and weld arrangements conformed with successful commercial practice. Proprietary hollow core slabs were tied to the beams by tensile reinforcing bars, which also provide the in-plane continuity across the connections. The strength of the connections in the double sided tests was at least 0.84 times the predicted moment of resistance of the composite beam and slab. The secant stiffness of the connections ranged from 0.7 to 3.9 times the flexural stiffness of the attached beam. When the connections were tested without the floor slabs and tie steel, the reduced strength and stiffness were approximately a third and half respectively. This remarkable contribution of the floor strength and stiffness to the flexural capacity of the joint is currently neglected in the design process for precast concrete frames. In general, the double sided connections were found to be more suited to a semi-rigid design approach than the single sided ones. The behaviour of double sided welded plate connection test results are presented in this paper. The behaviour of single sided welded plate connection test results is the subject of another paper.

• Membrane and Water Treatment
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• v.2 no.1
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• pp.25-37
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• 2011

PES UF membranes containing silver were prepared to impart antibacterial properties for waste water treatment. Asymmetric membranes for antibacterial application were prepared from polyethersulfone (PES) and silver nitrate ($AgNO_3$) (PES/$AgNO_3$=15/2 by weight) solution in N-Methyl-2-pyrrolidone (NMP) via simple wet phase inversion technique. These membranes were characterized by polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) of different molecular weights (1000 ppm in water) at room temperature and on operating pressure of 5 bars. It was observed that the water flux of PES-$AgNO_3$ membrane is slightly lower than virgin PES but still increased linearly with the increment of pressure applied. The morphology of the resulting membranes was examined using Field-Emission Scanning Electron Microscope (FESEM) coupled with Energy Dispersive Spectroscopy (EDS). Elemental analysis using EDS proved that silver is successfully loaded on the membrane surfaces. Due to the success of loading silver on membrane surfaces, antibacterial activities were evaluated via agar diffusion method against Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) culture. By incorporating 2 wt% of silver nitrate, PES-$AgNO_3$ showed significant inhibition ring on both E.coli and S.aureus. Filtration of E.coli solution (OD 0.31) showed satisfactory rejection data with ~100% inhibition growth after 24 hours incubation at $37^{\circ}C$. Resultant membranes also exhibit better tensile strength (compared to virgin PES) up to 71% may be due to the suggested interactions. The residual silver during fabrication was measured using ICP-MS and result showed that the residual silver content of PES-$AgNO_3$ membrane was only ~1% of the original silver added in the polymer solution. These studies have shown that PES-$AgNO_3$ UF membranes are potential in improving the filtration in water treatment.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.801-804
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• 2008

Fiber reinforced plastics (FRP) are light in weight, non-corrosive and exhibits high tensile strength. FRPs having superior material properties to corrosive steels have been widely replacing steel bars or tendons used in concrete structures as flexural reinforcements. Although current design guidelines for estimating shear strength of FRP concrete beam follow the format of conventional reinforced concrete design method, there are noticeable differences among the existing formulas in calculating the contributions of concrete to shear resistance. In this paper, the artificial neural network (ANN) technique is employed as an analytical alternative to existing methods for predicting shear capacity of FRP concrete beams. Influential factors on shear strength were identified through literature review and input in ANN and the ANN was trained for the target ultimate shear obtained from database. The results from ANN were compared with existing formulas for its accuracy. It was found that the developed ANN were more closely predicting the test data than those of the currently available predictive equations.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.811-819
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• 2003

The corrosion of steel reinforcing bar(re-bar) has been the major cause of the reinforced concrete deterioration. FRP(Fiber-reinforced polymer) reinforcing bar has emerged as one of the most promising and affordable solutions to the corrosion problems of steel reinforcement in structural concrete. However, FRP re-bar is pone to deteriorate due to other degradation mechanisms than those for steel. The high alkalinity of concrete, for instance, is a possible degradation source. Other potentially FRP re-bar aggressive environments are sea water, acid solution and fresh water/moisture. In this study long-term durability performance of FRP re-bar were evaluated. The mechanical and durability properties of two type of CFRP-, GFRP re-bar and one type of AFRP re-bar were investigated; the FRP re-bars were subjected to alkaline solution acid solution, salt solution and deionized water. The mechanical and durability properties were investigated by performing tensile, compressive and short beam tests. Experimental results confirmed the desirable resistance of FRP re-bar to aggressive chemical environment.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.279-288
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• 2016

The present study simplified the moment-curvature relationship to straightforwardly determine the flexural behavior of reinforced concrete (RC) columns. For the idealized column section, moments and neutral axis depths at different stages(first flexural crack, yielding of tensile reinforcing bar, maximum strength, and 80% of the maximum strength at the descending branch) were derived on the basis of the equilibrium condition of forces and compatibility condition. Concrete strains at the extreme compression fiber beyond the maximum strength were determined using the stress-strain relationship of confined concrete, proposed by Kim et al. The lateral load-displacement curves converted from the simplified moment-curvature relationship of columns are well consistent with test results obtained from column specimens under various parameters. The moments and the corresponding neutral axis depth at different stages were formulated as a function of longitudinal reinforcement and transverse reinforcement indices and/or applied axial load index. Overall, curvature ductility of columns was significantly affected by the axial load level as well as concrete compressive strength and the amount of longitudinal and transverse reinforcing bars.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.3
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• pp.149-155
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• 2006

This paper presents a torsional micromirror detached from PZT actuators (TMD), whose rotational motion is achieved by push bars in the PZT actuators detached from the micromirror. The push bar mechanism is intended to reduce the bending, tensile and torsional constraints generated by the conventional bending bar mechanism, where the torsional micromirror is attached to the PZT actuators (TMA). We have designed, fabricated and tested prototypes of TMDs for single-axis and dual-axis rotation, respectively. The single-axis TMD generates the static rotational angle of $6.1^{\circ}$ at 16 VDC, which is 6 times larger than that of single-axis TMA, $0.9^{\circ}$. However, the rotational response curve of TMD shows hysteresis due to the static friction between the cover and the push bar in the PZT actuator. We have shown that 63.2% of the hysteresis is due to the static friction caused by the initial contact force of the PZT actuaor. Without the initial contact force, the rotational response curve of TMD shows linear voltage-angle characteristics. The dual-axis TMD generates the static rotational angles of $5.5^{\circ}$ and $4.7^{\circ}$ in x-axis and y-axis, respectively at 16 VDC. The measured resonant frequencies of dual-axis TMD are $2.1\pm0.1$ kHz in x-axis and $1.7\pm0.1$ kHz in y-axis. The dual-axis TMD shows stable operation without severe wear for 21.6 million cycles driven by 16 Vp-p sinusoidal wave signal at room temperature.