• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.2
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• pp.277-287
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• 2017

This paper describes the specifications on balanced steel ratio and maximum reinforcement for the design of RC flexural members by the Korean Highway Bridge Design Code based on limit states design. The Korean Highway Bridge Design Code (Limit States Design) is not provide for the balanced steel ratio specification for the calculation of required steel area of RC flexural members design. The maximum steel area limited the depth of the neutral axis at the ultimate limit states after redistribution of the moment, and also recommended the maximum steel area should not exceed 4 percent of the cross sectional area. However, from the maximum neutral axis depth provisions should increase the cross section is calculated to be less the maximum reinforcement area, and according to the 4% of the cross sectional area of the concrete, the tensile strain of the reinforcement is calculated to be greater than double the yielding strain, so can not guarantee a ductile behavior. This study developed a balanced reinforcement ratio that is basis for the required reinforcement calculation for tension-controlled RC flexural members design in the ultimate limit states verification provisons and material properties and applied the ultimate strain of the concrete compressive strength with a simple formular to be applied to design practice induced. And assumed the minimum allowable tensile strain of reinforcement double the yielding strain, and applying correction coefficient up to the ratio of maximum neutral axis depth, proposed maximum steel ratio that can be applied irrespective of the reinforcement yield strength and concrete compressive strength.

• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.7-12
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• 2016

In this paper, we have developed a simple, new and economical carbonation method to synthesize a pure form of aragonite needles using dolomite raw materials. The obtained aragonite Precipitated Calcium Carbonate (PCC) was characterized by XRD and SEM, for the measurement of morphology, particle size, and aspect ratio (ratio of length to diameter of the particles). The synthesis of aragonite PCC involves two steps. At first, after calcinated dolomite fine powder was dissolved in water for hydration, the hydrated solution was mixed with aqueous solution of magnesium chloride at $80^{\circ}C$, and then $CO_2$ was bubbled into the suspension for 3 h to produce aragonite PCC. Finally, aragonite type precipitated calcium carbonate can be synthesized from natural dolomite via a simple carbonation process, yielding product with average particle size of $30-40{\mu}m$.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.833-838
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• 2001

The objectives of this study are to investigate effective stiffness of circular reinforced bridge columns and to provide reasonable effective stiffness equations for seismic design to the current Korean Bridge Design Standard. The material nonlinear analysis was conducted for 5184 columns of which variables were the concrete compressive stress, the steel yielding stress, the longitudinal steel location parameter, the longitudinal steel ratio, the axial load level, and the diameter of section. The current Korean Bridge Design Standard generally used the gross section stiffness because of unclear provision, it may be non-conservative because of being evaluated greater design seismic force and less design displacement than those of the abroad provision. Therefore, the proposed effective stiffness equations include three variables such as : the longitudinal steel location parameter, the longitudinal steel ratio, and the axial load ratio. Two equations of effective stiffness are proposed which may be used for earthquake force estimation and for earthquake displacement estimation, respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.42-47
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• 1995

The flow properties of xoncrete depend on form of fine aggregate, the ratio of voides of fine aggregate and cement paste So, in this study, investigated for the improvement of rheology properties on mortar and paste replaced by Zeolite $\circled1$ The slump flow have to do with correlation on yielding value of mortar respectirely. $\circled2$The increase ratio of strength Mortar and paste 10% replaced by Zeolite was presented significently but the slump flow was decteased stiffly as the increase of plastic viscosity at the ratio of replacement over 10%

• Journal of the Korea Concrete Institute
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• v.12 no.3
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• pp.57-66
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• 2000

The ductility is an important consideration in the design of reinforced concrete structures. In the seismic design of reinforced concrete columns, it is necessary to allow for relatively large ductilities that the seismic energy be absorbed without shear failure of significant strength degradation after the reinforcement yielding in columns. Therefore, prediction of the ductility should be as accurate as possible. This research investigate the ductile behavior of rectangular reinforced high-strength concrete columns like as bridge piers with confinement steel. The effects on the ductility of axial load, lateral reinforcement ratio, longitudinal reinforcement ratio, shear span ratio, and compressive strength of concrete were investigated analytically using layered section analysis. as the results, it was proposed the proper relationship between ductility and variables and formulated into equations.

• International Journal of Concrete Structures and Materials
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• v.2 no.2
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• pp.115-122
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• 2008

Ductility is important in the design of reinforced concrete structures. In seismic design of reinforced concrete members, it is necessary to allow for relatively large ductility so that the seismic energy is absorbed to avoid shear failure or significant degradation of strength even after yielding of reinforcing steels in the concrete member occurs. Therefore, prediction of the ductility should be as accurate as possible. The principal aim of this paper is to present the basic data for the ductility evaluation of reinforced high-strength concrete beams. Accordingly, 23 flexural tests were conducted on full-scale structural concrete beam specimens having concrete compressive strength of 40, 60, and 70MPa. The test results were then reviewed in terms of flexural capacity and ductility. The effect of concrete compressive strength, web reinforcement ratio, tension steel ratio, and shear span to beam depth ratio on ductility were investigated experimentally.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.2
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• pp.119-127
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• 2023

In this paper, seismic performance evaluation was carried out for eight circular reinforced concrete columns designed seismically by KRTA[1]and KCI[8]. Primary design parameters for such columns included many longitudinal reinforcements, yield strength of reinforcements, the vertical spacing of spirals, aspect ratio, and axial force ratio. The test results showed that all the columns exhibited stable hysteretic and inelastic responses. Based on the test results, drift ratios corresponding to each damage state, such as initial yielding, initial cover spalling, initial core concrete crushing, buckling, and fracture of longitudinal reinforcement and final spalled region, were evaluated. Then, those ratios were compared with widely accepted damage limit states. The comparison revealed that the existing damage states were considerably conservative. This implies that additional research is required for the damage limit states of such columns designed seismically by current Korean design codes.

• Journal of Korean Society of Steel Construction
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• v.25 no.2
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• pp.131-139
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• 2013

The object of this paper is to perform the experiments to investigate the relationship of the resistance forces and the failure temperatures on the failure behaviors of H-shaped steel compressive members. H-shaped members(SS400) were used for the test models and the tests for the elevated temperatures were performed by ISO 834 in FILK(Fire Insurers Laboratories of Korea). The local, overall buckling stresses and a yielding stresses for the failure temperatures were compared with the compressive stresses for the loading forces of test models, the yielding strength and elastic modulus reduction factor of the steel at a high temperature were based on the criteria of the EC3(Eurocode 3) Part1.2(1993). The slenderness ratio was fixed by 45.4 and the compressive forces corresponded with 50%, 70% and 80% of the yielding forces at the normal temperatures were chosen for the loading forces of the test models. The failure temperatures of the test models were investigated under three kinds of loading conditions. It was known that the resistance forces have come close to the yielding forces, not the elastic buckling loads evaluated by EC3 at the failure temperatures obtained from the tests which are related to the failure temperatures and the loading stresses.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.04a
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• pp.1.1-4
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• 1999

The toughening mechanism and fracture behavior of rubber/polymer composites were investigated with respect to two factors; (1) the composition ratio of polymers(PPO and PS which have a different chain flexibility) and (ii) the rubber particle size in PPO/PS blend system Izod impact test and fractographic observation of the fracture surface using scanning electron microscope were conducted, Finite element analysis were carried out to gain understanding of plastic deformation(shear yielding and crazing) of these materials.

• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.187-197
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• 2010

The longitudinal reinforcement ratio for the performance-based design of columns was studied. Unlike the existing design codes using uniform minimum reinforcement ratio and effective stiffness for all columns, the longitudinal reinforcement ratio of columns was defined as the function of various design parameters. To evaluate the minimum reinforcement ratio, two conditions were considered: 1) prevention of passive yielding of compression re-bars due to the creep and shrinkage of concrete under sustained service loads; and 2) ultimate flexural strength greater than the cracking moment capacity to maintain the ductility of columns for earthquake design. In addition, the effective flexural stiffness of columns for structural analysis was determined according to the longitudinal reinforcement ratio. The design method addressing the three criteria was proposed. The proposed method was applied to a design example.