• Advances in concrete construction
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• v.13 no.3
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• pp.243-254
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• 2022

Reinforced concrete (RC) deep beams are critical structural elements used in offshore pile caps, rectangular cross-section water tanks, silo structures, transfer beams in high-rise buildings, and bent caps. As a result of the low shear span ratio to effective depth (a/d) in deep beams, arch action occurs, which leads to shear failure. Several studies have been carried out to improve the shear resistance of RC deep beams and avoid brittle fracture behavior in recent years. This study was performed to investigate the behavior of RC deep beams numerically and experimentally with different reinforcement arrangements. Deep beams with four different reinforcement arrangements were produced and tested under monotonic static loading in the study's scope. The horizontal and vertical shear reinforcement members were changed in the test specimens to obtain the effects of different reinforcement arrangements. However, the rebars used for tension and the vertical shear reinforcement ratio were constant. In addition, the behavior of each deep beam was obtained numerically with commercial finite element analysis (FEA) software ABAQUS, and the findings were compared with the experimental results. The results showed that the reinforcements placed diagonally significantly increased the load-carrying and energy absorption capacities of RC deep beams. Moreover, an apparent plastic plateau was seen in the load-displacement curves of these test specimens in question (DE-2 and DE-3). This finding also indicated that diagonally located reinforcements improve displacement ductility. Also, the numerical results showed that the FEM method could be used to accurately predict RC deep beams'behavior with different reinforcement arrangements.

• Structural Engineering and Mechanics
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• v.84 no.4
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• pp.531-546
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• 2022

Headed bars are often used when there is insufficient space for a straight or curved bar to be fully developed to ensure the transference of forces between steel and concrete in several types of connections between structural members. In such cases, the concrete breakout strength of the headed bars can be a critical point of the design and must be considered appropriately. This paper evaluates the tensile strength of headed bars embedded in reinforced concrete members, failing due to concrete breakout. Four experimental tests on headed bars embedded in slender concrete members are presented and discussed, showing that strength previsions from the design codes can be significantly conservative as they ignore the contribution from the flexural reinforcement. 3D finite element models were developed using Abaqus Unified FEA to simulate the tested specimens, and it was observed that they were able to reproduce the formation of the concrete cone accurately, besides the response and resistance observed in tests. Furthermore, the experimental, numerical, and design code resistances are compared and discussed. A new equation to evaluate the concrete cone strength of the tested headed bars is proposed, which takes into account parameters not explicitly considered in the current design equations.

• Structural Engineering and Mechanics
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• v.88 no.2
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• pp.129-140
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• 2023

To increase the stiffness and strength of a reinforced concrete shear wall, steel plates are bolted to the sides of the wall. The general behavior of a composite concrete-steel shear wall is dependent on the buckling of the steel plates that should be prevented. In this paper, the unilateral buckling of steel plates of a composite shear wall is studied using the Rayleigh-Ritz method. To model the unilateral buckling of steel plate, the restraining concrete wall is described as an elastic foundation with high stiffness in compression and zero stiffness in tension. To consider the effect of bolt connections on the plate's buckling, a constrained optimization problem is solved by using Lagrange multipliers method. This process is used to obtain the critical elastic local buckling coefficients of unilaterally-restrained steel plates with various numbers of bolts, subjected to pure compression, bending and shear loading, and the interaction between them. Using these results, the spacing between shear bolts in composite steel plate shear walls is estimated and compared with the results of the AISC seismic provisions (2016). The results show that the AISC seismic provisions(2016) are overly conservative in obtaining the spacing between shear bolts.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.401-409
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• 2013

In the present study, numerical analysis was performed for hydrodynamic motion and structural performance on four different concrete floating structures, which have same cross-section but different length. The hydrodynamic analysis of floating structures is carried out using ANSYS AQWA with the different 34 wave load on regular wave period from three seconds to ten seconds in 35 m water depth. In order to evaluate structural performance of floating structures under the critical wave load which obtained from hydrodynamic analysis. The integrated analysis is also carried out through the mapping method, which can directly connect the wave-induced hydraulic pressure obtained form ANSYS AQWA to Finite Element Model in ANSYS Mechanical. As a results of this study, the hydrodynamic motion of floating structures is decreased as the length of structure increased. It means that the effect of wave-structure interaction is strongly dependent on the relationship between a wave period and a length of structure. Moreover, it is found that tension stress on bottom slab of floating structure is occurred by the critical wave load, the sectional force is not influenced by length of a structure.

• Journal of the Korean Chemical Society
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• v.53 no.2
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• pp.125-132
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• 2009

The magnetized water is known to have a unique pattern of hydrogen bond between water molecules, thereby producing different physicochemical properties from the ordinary water. We have examined the effect of magnetized water on the change of critical micelle concentrations (CMC) of some surfactants. The CMC changes of SDS (sodium dodecyl sulfate) and CTAB (cetyltrimethylammonium bromide) dissolved in the magnetized water have been determined by the conductivity measurement at $25\;{^{\circ}C}$ and that of SDS, CTAB and Pluronic F-68 have also been examined by the surface tension method at $25\;{^{\circ}C}$. The CMC variation of SDS was examined by ITC (Isothermal Titration Calorimeter) at $25\;{^{\circ}C}$. The CMC of SDS, CTAB, and Pluronic F-68 are more decreased in the magnetized water, SDS is about $2.7{\sim}6.5$25 %, CTAB is about $2.3{\sim}3.0$%, and Pluronic F-68 is about 24.2 %, than in the control water.

• Journal of Pharmaceutical Investigation
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• v.27 no.4
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• pp.287-293
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• 1997

To make a stable o/w emulsion, the effects of egg lecithin as an emulsifier and polyvinylpyrrolidone (PVP) as an auxiliary emulsifier on the physical stability of emulsion were investigated. The oil-in-water emulsion system was manufactured by microfluidizer and evaluated the physical stability. Average particle size and size distribution of emulsion was measured by dynamic light scattering analyzer and interfacial tension was measured. From the interfacial tension tested, critical micelle concentration of the egg lecithin was 0.1 %w/v and optimal concentration for the preparation of emulsion was 1.0 %w/v. The mean particle size was about $0.2\;{\mu}m$ which was suitable for injections. The short-term accelerated stability studies were conducted by centrifugation, freeze-thaw method and shaking of the emulsion samples. The addition of PVP was caused the reduction in the particle size and improved the physical stability of emulsion. These results suggested that a mixed interfacial film comprising the egg lecithin and PVP was formed at the o/w interface and it was effective in preventing phase separation under thermic or mechanical stress. We used antineoplaston A10 (A10) as a model drug which is peptide and amino acid derivative having a action to the living organism against the development of neoplastic growth by a nonimmunological progress. It has a poor solubility in water and there may be a difficulty in formulation of A10. Emulsion formulation study about A10 was performed. Solubility of A10 in emulsion was about five times as high as that in water. From the results of solubility and partition coefficient, almost A10 molecules in o/w emulsion exist in the interface between oil and water.

• Korean Journal of Social Welfare
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• v.63 no.2
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• pp.155-177
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• 2011

This paper attempts to explore the universal foundation on which the discourses on the validity criteria in qualitative research should be based, and further discuss in depth the scope and direction of an adequate validity criterion in qualitative research by critical examination of previous discourses. To establish the foundation for qualitative research, first of all, the concept of quality and qualitative paradigm were examined in terms of ontology and epistemology, especially focused on the works carried out by Aristotle, Kenneth and Boyd. Secondly, the earlier studies on the validity of qualitative research were critically reviewed in terms of the theoretical findings on the concept of quality and qualitative paradigm. The major results include the following: First, the true content of quality is defined as the 'what-ness' or essence of things perceived by subjects, and qualitative paradigm as adequate framework for qualitative research is comprised of two intrinsic modes: one is the mode of awareness and the other is that of expression. Second, qualitative researchers are able to reach to the higher level of validity by considering not only the subjectivity and the originality but also the sociality in drawing a conclusion through qualitative perception. Third, the trend of previous validity discourses can be firmly summarized as the effort to overcome the effect of quantitative research and acquire the true identity for qualitative research, which is subjectivity, and as the quest to compromise the tension between subjectivity and sociality. Finally, based on the findings, several research topics are suggested. For example, the more attention should be paid to the area of the expression of qualitative awareness as a way of overcome the tension between subjectivity and publicness.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.579-588
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• 2006

In recent years, the availability of high-strength reinforcing and prestressing steels leads us to build economically and efficiently designed concrete structural members. One of critical problems faced to the structural engineers dealing with these types of structural member is controls of crack width that is used as a criterion for the serviceability in the limit state design. Especially, flexural cracking must be controlled to secure the structural safety and to improve the durability as well as serviceability of the load carving members. The proposed method utilizes the results of pure tension test in which tensile loads are applied both side of specimen, done by Ikki. The bond characteristics of deformed reinforcing bar under pure tension is considered by the area of concrete and rib area. The results of proposed method are compared with the test data and the results show that the proposed method can take into account the dimensions, variation of sectional properties, and direction of reinforcing and gives more accurate maximum bond stress and corresponding relative slip than the existing methods. the characteristics of bonding is considered by using dimensionless slip magnitude and effective reinforcement ratio. The validity of the proposed equation is verified by test experimental data.

• Korean Chemical Engineering Research
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• v.50 no.6
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• pp.960-968
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• 2012

In this study, the measurement of physical properties of 3 different ethylene oxide adducted zwitterionic surfactants were measured such as critical micelle concentration, surface tension, interfacial tension, contact angle, viscosity and foam stability. Also, the dual function characteristics of the zwitterionic surfactants were investigated by determining an isoelectric point, which were obtained using zeta potential measurement and QCM (quartz crystal microbalance) experiments. The isoelectric point of the synthesized zwitterionic surfactant determined by zeta potential measurement was close to that obtained by QCM experiment and both results have shown almost the same trend as that determined by the frictional property measured using an automated mildness tester. In particular, it has been observed that all three surfactants used during this study provide better softening effect at a pH of neutral condition than at an acidic or an alkaline condition. This result indicates that the synthesized surfactants act as a cationic surfactant at a pH of neutral condition and thus provide good softening effect during a rinsing cycle in the detergency process.

• Applied Chemistry for Engineering
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• v.20 no.1
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• pp.9-14
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• 2009

A zwitterionic surfactant shows not only detergency but also softening effect since it shows characteristics of a nonionic or an anionic surfactant above an isoelectric point, while showing characteristics of a cationic surfactant below an isoelectric point. Therefore, a zwitterionic surfactant can serve as a dual function surfactant by a single molecule through the interconversion of cleaning and softening effects depending on pH of the aqueous solution. In this study, the dual function characteristics of an amine oxide zwitterionic surfactant were investigated by measuring the zeta potential and the isoelectric point using quartz crystal microbalance (QCM). In addition, the physical properties of an amine oxide surfactant such as critical micelle concentration, surface tension, interfacial tension, contact angle and viscosity were measured and phase behavior study was also performed. The isoelectric point of an amine oxide surfactant determined by zeta potential measurement was near 7.35 and that obtained by QCM experiment was about 7.4, where both results were found to be close to the value reported in the literature.