• Journal of the Korea Concrete Institute
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• v.21 no.3
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• pp.311-318
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• 2009

An experimental investigation was conducted to examine the hysteretic behaviors of ultra-high strength concrete tied columns. The purpose of this study is to propose the volumetric ratio of transverse reinforcement for ultra-high strength concrete tied columns with 100 MPa compressive strength. Nineteen 1/3 scaled columns were fabricated to simulate an 1/2 story of actual structural members with the main variables of axial load ratio, configurations and volumetric ratios of transverse reinforcement. The results show that the deformability of columns are affected by the configurations and volumetric ratios of transverse reinforcement. Especially, it has been found that the behavior of columns are affected by axial load ratio rather than the amounts and the configurations of transverse reinforcement. To improve the ductility behavior of RC column using ultra high strength concrete in a seismic region, We suggested the amount of transverse reinforcement for all data that satisfy the required displacement ductility ratio over 4. It is means that the lateral confining reduction factor (${\lambda}^c$) considering the effective legs, configuration and spacing of transverse reinforcement and axial load ratio was reflected for the volumetric ratio of transverse reinforcement.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.169-178
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• 2009

An equation for calculating confining reinforcement amount of RC bridge columns, specified in the current bridge design codes, has been made to provide additional load-carrying strength for concentrically loaded columns. The additional load-carrying strength will be equal to or slightly greater than the resistant strength of a column against axial load, which is lost because the cover concrete spalls off. The equation considers concrete compressive strength, yield strength of transverse reinforcement, and the section area ratio as major variables. Among those variables, the section area ratio between the gross section and the core section, varying by cover thickness, is a variable which considers the strength in the compression-controlled region. Therefore, the cross section ratio does not have a large effect in the aspect of ductile behavior of the tension-controlled region, which is governed by bending moment rather than axial force. However, the equation of the design codes for calculating confining reinforcement amount does not directly consider ductile behavior, which is an important factor for the seismic behavior of bridge columns. Consequently, if the size of section is relatively small or if the section area ratio becomes excessively large due to the cover thickness increased for durability, too large an amount of confining reinforcement will be required possibly deteriorating the constructability and economy. Against this backdrop, in this study, comparison and analysis were performed to understand how the cover thickness influences the equation for calculating the amount of confining reinforcement. An equation for calculating the amount of confining reinforcement was also modified for reasonable seismic design and the safety. In addition, appropriateness of the modified equation was examined based on the results of various test results performed at home and abroad.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.399-406
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• 2012

Beam-column joints are generally recognized as the critical regions in the moment resisting reinforced concrete (RC) frames subjected to both lateral and vertical loads. As a result of severe lateral load such as seismic loading, the joint region is subjected to horizontal and vertical shear forces whose magnitudes are many times higher than in column and adjacent beam. Consequently, much larger bond and shear stresses are required to sustain these magnified forces. The critical deterioration of potential shear strength in the joint area should not occur until ductile capacity of adjacent beams reach the design demand. In this study, a method was provided to predict the deformability of reinforced concrete beam-column joints failing in shear after the plastic hinges developed at both ends of the adjacent beams. In order to verify the deformability estimated by the proposed method, an experimental study consisting of three joint specimens with varying tensile reinforcement ratios was carried out. The result between the observed and predicted behavior of the joints showed reasonably good agreement.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.357-367
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• 2004

In this paper, the effect of cumulative damage for reinforced concrete bridge piers subjected to both single and multiple earthquakes is investigated. For this purpose, selected are three set of accelerograms one of which represents the real successive input ground motions, recorded at the same station with three months time interval. The analytical predictions indicate that piers are in general subjected to a large number of inelastic cycles and increased ductility demand due to multiple earthquakes, and hence more damage in terms of stiffness degradation is expected to occur. In addition, displacement ductility demand demonstrates that inelastic seismic response of piers can significantly be affected by the applied input ground motion characteristics. Also evaluated is the effect of multiple earthquakes on the response with shear. Comparative studies between the cases with and without shear indicate that stiffness degradation and hence reduction in energy dissipation capacity of piers are pronounced due to the multiple earthquakes combined with shear. It is thus concluded that the effect of multiple earthquakes should be taken into account for the stability assessment of reinforced concrete bridge piers.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.303-311
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• 1998

Ten reinforced concrete rigid frames and infilled shear wall frames were tested under both vertical and cyclic loadings. Experiments were carried out to evaluate the structural performance of such test specimens, such as the hysteretic behavior, the maximum horizontal strength, crack propagation, and ductility etc. under load reversals. All the specimens were modeledin one-third scale size. Based on the test results reported in this study, the follwing conclusions can be made. For the rigid frame type and the fully rigid babel type shear wall specimens, the hysteresis diagrams indicate that the degradations of their strength were developed slowly beyond maximum carrying capacity. It was shown that when the hoop reinforcement ratio became higher, the energy dissipation capacity became larger and the failure mode became ductile. The specimens designed by the less hoop reinforcement for the fully rigid babel type shear wall, were mainly failed due to diagonal crack in comparison with the specimens designed by the larger hoop reinforcement ratio. Maximum horizontal resisting moment capacity of speciment designed by the fully rigid babel shear wall were increased by 5.47~7.95 times in comparison with the rigid frame type.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.1-10
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• 2012

This paper presents an experimental result and suggests the confinement effect of headed cross tie in reinforced concrete(RC) columns subjected to cycling horizontal loads under constant axial load. Five RC columns specimens were manufactured, taking confined type of transverse reinforcement, whether or not using cross tie, end detail of cross tie (hooked or headed), and axial stress in column as major variables, Cyclic horizontal load applied to the columns under constant axial stress and the effect of cross tie to structural capacity of column was evaluated from the test. The column without cross tie failed showing bending deformation of hoop with crack in core concrete at low horizontal load while the column with cross tie showed quite improved strength and ductility by suppressing bending deformation of hoop as well as buckling of longitudinal bar at once even after crack in core concrete. At high lateral displacement, the column with hooked cross tie showed the failure pattern loosing the confining force of cross tie since the $90^{\circ}$ hooked part of cross tie was stretched out and the cracked core concrete lumps were came off. However, the column with headed cross tie showed very stable behavior since the head of cross tie effectively confined the hoop and longitudinal bars even at high lateral displacement.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.251-260
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• 2001

It is required to evaluate the axial strain of reinforced concrete beams in order to predict the ductility of reinforced concrete beams subjected to reversed cyclic loading. A model was proposed to determine the axial strains In reinforced concrete beams by analysing the behavior of reinforced concrete sections and comparing with published test results. The proposed axial strain model inclusively reflected four kinds of paths : Path 1-steel bar in an elastic stage or a unloading region; Path 2-after flexural yielding; Path 3-a slip region; and Path 4-a reversing loading region. The equations to predict the axial strains of each path were proposed. The proposed equations took into account the effects of the loading program. Comparison of axial strains between experimental results and the results from proposed equations showed to be in a good agreement with experimental results.

• Journal of the Korea Concrete Institute
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• v.26 no.1
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• pp.35-46
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• 2014

Two types of cast-in-place concrete-filled hollow PC (HPC1, HPC2) columns were developed to reduce lifting load of heavy-weight PC columns and to improve the structural integrity of joints. To form the hollow PC columns, a couple of prefabricated PC panels was used for HPC1, and special hoops were used for HPC2. Lateral pressure of wet concrete on PC faces was measured while placing the concrete inside the columns. To evaluate the seismic resistance, full scale specimens of two HPC columns and a conventional RC column were tested under combined axial compression and lateral cyclic loading. The test results showed that the structural performance of the proposed HPC columns such as intial stiffness, maximum strength, and displacement ductility was comparable to that of the conventional RC column, but the energy dissipation of HPC2 slightly decreased after rebar-buckling. However, all the test specimens satisfied the energy dissipation requirement specified in ACI 374.

• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.499-509
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• 2014

This study focuses on mixing steel fiber in the concrete to improve the ductility and toughness of the columns. The purpose of the study is to evaluate the load capacity and deformation capacity associated with the amount of steel fiber and loading condition and to analyze the interplay between the steel fiber reinforced concrete and the welding built-up square tube in terms of structure and fire resistance performance. Reinforcement of concrete with steel fiber(Vf=0.375%), when cross-section shape and boundary condition (load ratio) remained unchanged, improved fire resistance performance by 1.1~1.3 times. It is deemed that the area resisting thermal load increased and fire resistance performance was improved since the concrete reinforced with steel fiber restrained cracking. In addition, the fact that the cross-sections of the concrete were barely damaged indicates that load share capacity was greatly improved.

• Journal of Korean Society of Steel Construction
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• v.15 no.5 s.66
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• pp.561-570
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• 2003

This study evaluate the characteristics of stainless steel for the use of stainless steel tubes as structural members. The strength of stainless steel tube was compared with that of steel tube stub-columns through tensile experiment and compressed experiment. The selected experimental parameters were diameter (width)-thickness and section shape. The results of tests showed that stainless steel tubes could be predicted as superior to steel tubes in terms of tensile strength, yield ratio, elongation percentage, and absorption ability of energy. The yield strength of stainless steel tubes were found to be higher than the Korean Standards ($Fy=2.1tf/cm^2$) and the design strength of SIJ-ASD($Fy=2.4tf/cm^2$). It was also higher then the yield strength of steel tubes. The plastic deformation of stainless steel tubes was found to beto that of steel tubes.