• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.2
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• pp.71-82
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• 2013

Eight small scale circular reinforced concrete columns (4.5 aspect ratio) were tested under cyclic lateral load with constant axial load. The selected test variables are longitudinal steel ratio (2.017%, 3.161%), transverse steel ratio, and axial load ratio (0, 0.07, 0.15). Volumetric ratio of spirals of all the columns is 0.335~0.894% in the plastic hinge region. It corresponds to 39.7~122.3% of the minimum requirement of confining steel by Korean Bridge Design Specifications, which represent existing columns not designed by the current seismic design specifications or designed by seismic concept. The final objectives of this study are to provide quantitative reference data and tendency for performance or damage assessment based on the performance levels such as cracking, yielding, steel fracture, etc. In this paper, describes mainly failure behavior, strength degradation behaviour, displacement ductility of circular reinforced concrete bridge columns with respect to test variables.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.535-542
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• 2005

Two series of experiments on the performance of beam-column joints in High-Strength Reinforced concrete frames were carried out. Main experimental parameters were : concrete strength, column axial load and amount of joint hoop reinforcement. Test result showed that the ultimate shear strength of exterior joints increased of column axial compressive force and the amount of the joint hoop reinforcements. Through the regression analysis on the 24data, the following equation is obtained $jv_u=(2.935{\times}10-3\;{\rho}jw{\cdot}fy\;+\;0.365){\sqrt{f_{ck}}}$

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.4
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• pp.1-8
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• 2013

Constitutive modeling of constituent materials is very important for reinforced concrete (RC) frames. Cyclic constitutive behavior of unconfined concrete, confined concrete and reinforcing steel should be well defined in fiber-based discretization of RC sections. This study performs nonlinear dynamic analyses of RC frame structures to investigate the sensitivity of seismic behavior of such frames to different constitutive models of constituent materials. The study specifically attempts to examine confinement effects in concrete modeling and degrading effects in steel modeling, which substantially affects the monotonic, cyclic and seismic responses of RC members and frames. Based on the system level analysis, it is shown that the response of non-ductile frames is less sensitive to confined concrete models while the modeling of reinforcing steel is quite influential to the inelastic response of both non-ductile and ductile frames.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.5
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• pp.135-142
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• 2022

In this study, lap spliced ultra-high strength reinforced concrete beams were tested and the code criteria for calculating the lap splice length which was affected by the transverse reinforcement and concrete covering performance were reviewed. The main variables for test were set as fiber volume fraction and transverse reinforcing bar arrangement to improve the confining performance of the concrete cover. The change of the confining performance of concrete cover according to the increase in the fiber mixing amount at 1% and 2% volume ratio was examined, and D10 stirrups with a spacing of 100 mm were placed in the lap spliced region. As a result of the test, the specimens confined by the stirrups showed a sudden drop of load bearing capacity with horizontal cracking at the position of tensile longitudinal reinforcement. However, horizontal cracks were not appeared at the location of longitudinal reinforcement for the specimens with steel fiber. And these specimens showed gradual decrease of load bearing capacity after experiencing peak load. In particular, it was found that the strain at the position of the tensile longitudinal reinforcements of the specimens to which the mixing ratio of 2% was applied exceeds the yield strain. As a result of measuring the strain on the concrete surface, it was found that the fiber was more effective in preventing damage to the concrete surface than the stirrups for short lap spliced region.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.3 s.43
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• pp.69-75
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• 2005

In this paper, the comparative performance of repaired RC columns using steel and CFRP is presented. Also, the effect of transverse reinforcement ratio on the behavior of the steel and the CFRP repairing is investigated. Monotonic and cyclic load tests are conducted on nine RC column specimens with different repairing strategies and transverse reinforcement ratios to compare the load-displacement curves and the hysteretic behaviors. From the tests, it is observed that both steel and CFRP jacket repairings can significantly increase the displacement ductility and the ultimate load capacity of damaged columns.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.328-331
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• 2011

준정적 횡하중을 재하 받는 철근콘크리트 보-기둥 접합부의 전단강도에 대한 주요 영향요인을 Bayesian parameter estimation의 신뢰성 이론 접목을 통해 검토하였다. 이와 같은 연구 scope의 수행을 위해 철근콘크리트 보-기둥의 실험 database가 구축되었다. 실험 database는 일정한 criteria을 적용하여 구축되었으며, 포함된 시편들은 최종적으로 접합부 내의 전단파괴가 지배하는 경우들이다. 포함된 시편들의 상세는 ACI (American Concrete Institute) 352R-02를 기준으로 평가되어졌다. 보-기둥 접합부의 전단강도에 영향 요인을 편중되지 않게 평가하고자, Bayesian parameter estimation의 신뢰성 이론을 적용하였다. Bayesian parameter estimation의 적용을 통해 전단강도에 영향이 적은 변수 (not informative parameter)를 순차적으로 제거 (stepwise removal process)함으로 주요 영향요인의 우선 순위를 확인할 수 있었다. 검토된 8개의 변수들 중에서, 횡하중을 재하 받는 철근콘크리트 보-기둥의 전단강도는 주로 콘크리트 압축강도, in-plane geometry, 종방향 보의 주철근 그리고 접합부 내의 구속철근 순으로 영향을 줌을 알 수 있었다.

• Magazine of the Korea Concrete Institute
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• v.7 no.1
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• pp.117-125
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• 1995

Bond test was carried out to assess the effect of several variables on bond characteristics between reinforcing bar and concrete. Key variables are concrete compressive strength($f_c$'=340, 460, 6513, 904kg/$cm^2$), concrete cover (25, 38, 51, 105, IlOmm), and bar diameter(Dl3 and D22). Confining effect and bar spacing are not taken into account. Thirty-two specimens subjected to uniaxial tension were tested under hypothesis uniform bond stress distribution along the reinforcing bar embeded in concrete. Failure mode was examined and local bond stress versus slip relationship diagrams were represented to show effect of the above variables, also test results(u1timate bond stress) were compared with bond and development provisions of the ACI Building Code(AC1 318-89) and proposed equations from previous research. According to analysis, borld stress and ultimate bond stress increased although compressive strength increased beyond the ACI Building Code upper limit. Therefore in calculating development length. compressive strength effect(exceeding 700kg /$cm^2$) should be accounted.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.467-473
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• 2002

The purpose of this study is to investigate the inelastic behavior and ductility capacity of reinforced concrete frame subjected to cyclic lateral load and to provide result for developing improved seismic design criteria. A computer program named RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology) for the analysis of reinforced concrete structures was used. Material nonlinearity is taken into account by comprising tensile, compressive and shear models of cracked concrete and a model of reinforcing steel. The smeared crack approach is incorporated. The strength increase of concrete due to the lateral confining reinforcement has been taken into account to model the confined concrete. In boundary plane at which each member with different thickness is connected local discontinuous deformation due to the abrupt change in their stiffness can be taken into account by introducing interface element. The effect of number of load reversals with the same displacement amplitude has been also taken into account to model the reinforcing steel. The proposed numerical method for the inelastic behavior and ductility capacity of reinforced concrete frame subjected to cyclic lateral load is verified by comparison with reliable experimental results.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.1
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• pp.1-7
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• 2003

The carbon composite tube can play an important role in replacing or complementing longitudinal and transverse reinforcing steels by providing ductility and strength for conventional columns. In this study, both the experimental and analytical investigations of axial behavior of large-scale square concrete columns confined by carbon composite tube are presented. The specimens are filament-wound carbon composite with 90$^{\circ}$+30$^{\circ}$, 90$^{\circ}$+45$^{\circ}$ winding angle respect to longitudinal axis of tube. The instrumented large-scale concrete-filled composite tubes(CFCT) are subjected to monotonic axial loads exerted by 10,000kN UTM. The influence of winding angle, thickness of tube on stress-strain relationships of the confined columns is identified and discussed. Proposed equations to predict both the strength and ductility of confined columns by carbon composite tube demonstrate good correlation with test data obtained from large-scale specimens.

• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.705-714
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• 2003

Even though Korean peninsula is located in regions of moderate seismic risks, current seismic design provisions of the roadway bridge design code have adopted the AASHTO code which is based on the requirements for high seismic regions. The objective of this research is to investigate the seismic performance of circular reinforced concrete (RC) bridge piers with limited ductility, which may be desirable in low or moderate seismic regions, such as in Korea. Four test specimens were designed and constructed. The reference specimen was designed with longitudinal steel ratio as 1.01% and the confinement reinforcement ratio as 0.13% without considering earthquake, and three other test specimens were designed in accordance with a limited-ductility concept as 0.3% for the confinement steel ratio. This confinement ratio is 0.32 times of minimum lateral reinforcement specified in current seismic design provisions, and 2.3 times of lateral reinforcement required in nonseismic design provisions. The pseudo-dynamic test was carried out to evaluate the seismic performance of full-scale specimens in size of 1.2m diameter and 4.8m height. Judging from the experiment, the reference specimen was not satisfactory for the demand displacement ductility ${\mu}$=5.0, but three limited-ductility specimens appeared to have the displacement ductility of more than 5.