• Computers and Concrete
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• 제20권2호
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• pp.129-143
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• 2017

Seismic design of reinforced concrete (RC) structures requires a certain minimum level of flexural ductility. For example, Eurocode EN1998-1 directly specifies a minimum flexural ductility for RC beams, while Chinese code GB50011 limits the equivalent rectangular stress block depth ratio at peak resisting moment to achieve a certain nominal minimum flexural ductility indirectly. Although confinement is effective in improving the ductility of RC beams, most design codes do not provide any guidelines due to the lack of a suitable theory. In this study, the confinement for desirable flexural ductility performance of both normal- and high-strength concrete beams is evaluated based on a rigorous full-range moment-curvature analysis. An effective strategy is proposed for flexural ductility design of RC beams taking into account confinement. The key parameters considered include the maximum difference of tension and compression reinforcement ratios, and maximum neutral axis depth ratio at peak resisting moment. Empirical formulae and tables are then developed to provide guidelines accordingly.

• Steel and Composite Structures
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• 제39권4호
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• pp.367-381
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• 2021

Reinforced concrete (RC) columns can be strengthened by direct fastening of steel plates around a column, forming composite actions. This method can increase both the total load bearing area and the concrete confinement stress. To predict the axial load resistance of strengthened RC columns, the equivalent passive confinement stress of the stirrups and the steel jacket should be accurately quantified, which requires the stress in the stirrups and shear force in the connections to be first obtained. In this paper, parameters, i.e., the stress ratio of the stirrups and shear force ratio of steel plate connectors are utilized to quantify the stress of the stirrups and shear force in the connections. A mechanical model for determining the stress ratio of the stirrups and shear force ratio of steel plate connectors is proposed and validated using the experimental results in a previous study. The model is found to be robust. Subsequently, a parametric study is conducted and the optimum stress ratios of the stirrups and the optimum shear force ratios of connectors are proposed for engineering designs.

• 한국구조물진단유지관리공학회 논문집
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• 제4권4호
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• pp.141-148
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• 2000

Recently the Carbon Fiber Sheet(CFS) is widely used for strengthening damaged RC structures. Strengthening compression members such as column can increase ductility and strength due to the confinement effect. In this experiment, the behavior of concrete cylinders confined by CFS was examined. The confinement pressure is increased linearly as axial stress is increased in low axial stress, and the confinement effect of CFS was rapidly developed after near maximum axial stress, thus axial strength and ductility was improved. As the ratio of CPS is increased, concrete cylinders failed due to local fracture of CFS. The confinement effect of circular section is more efficient than that of rectangular section. And significant improvement of axial strength, axial strain, transverse strain at failure is observed in circular section. This is because in rectangular section the local fracture of CFS near corner may be occured, thus the strain efficiency ratio must be considered for RC structures with CFS.

• 콘크리트학회논문집
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• 제15권5호
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• pp.715-725
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• 2003

본 연구는 철근콘크리트 교각에 대한 새로운 내진설계법을 개발하기 위한 연구의 일환으로서, 지진하중을 받는 철근콘크리트 교각의 연성도와 심부구속철근량의 상관관계를 분석하고 설계식을 제시함을 목적으로 한다. 이를 위하여, 반복하중을 받는 철근콘크리트 기둥의 횡하중-변위 포락곡선 실험결과를 비교적 정확하게 예측하며, 특히 변형능력 및 연성도에 대하여는 실험결과에 비하여 안전측의 결과를 제공하는 비선형해석 프로그램 [NARCE]를 이용하였다. 해석의 대상 교각으로는, 단면지름, 형상비, 콘크리트 강도, 축방향철근 항복강도, 심부구속철근 항복강도, 축방향철근비, 축력비, 심부구속철근비 등을 주요변수로 하여 총 7,200개의 철근콘크리트 나선철근 기둥 모델을 채택하였다. 해석결과 자료를 대상으로 상관관계를 분석하여 소요연성도에 따른 심부구속철근량의 새로운 설계식을 제안하였으며, 이 식은 연성도에 기초한 철근콘크리트 교각의 새로운 내진설계법에 적용될 수 있을 것이다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 추계 학술발표회논문집
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• pp.271-279
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• 2003

The objective of this study is to evaluate the damage of the reinforced concrete bridge piers. For the purpose of this research, twelve reinforced concrete specimens were fabricated and experimented with quasi-static test method. The selected test parameters are lap splice, axial load ratio, confinement steel ratio and number of loading cycle. The method of evaluate of damage index is the model proposed by Park and Ang. In accordance with this research, the most effective test parameter is lap splice of longitudinal steel. Therefore, the retrofit scheme of reinforced concrete bridge piers with lap splice of longitudinal steel, which was constructed before 1992, must be settled without delay. Otherwise, the effect of axial force is trivial. The more confinement steel is less damage index and more loading cycle lead to raise damage. The damage statement proposed Park and Ang is the same with experimental results.

• Structural Engineering and Mechanics
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• 제26권2호
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• pp.127-150
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• 2007

The objective of this paper is to develop a finite element procedure for predicting the compressive strength and ultimate axial strain of Carbon Fiber Reinforced Plastics (CFRP) confined circular concrete columns and to study the effective parameters of confinement efficiency for helping design of CFRP retrofit technology. The behavior of concrete confined with CFRP is studied using the nonlinear finite element method. In this paper, effects of column size, CFRP volumetric ratio and plain concrete strength are studied. The confined concrete nonlinear constitutive relation, concrete failure criterion and stiffness reduction methodology after concrete cracking or crushing are adopted. First, the finite element model is verified by comparing the numerical solutions of confined concrete with experimental results. Then the effects of column size, CFRP volumetric ratio and plain concrete strength on the peak strength and ductility of the confined concrete are considered. The results of parametric study indicate that the normalized column axial strength increases with increasing CFRP volumetric ratio, but without size effect for columns with the same CFRP volumetric ratio. As the same, the increase in column ductility depends on CFRP volumetric ratio but without size effect for columns with the same CFRP volumetric ratio.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.403-408
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• 2003

The objective of this study is to understand the variables affected the confinement for the transverse reinforcement of the reinforced concrete structural walls with the T-shaped cross section subjected to cyclic lateral loads. The structural performance of T-shaped walls was advanced by the transverse reinforcement which restrained the concrete subjected to compressive stress. If the arrangement of transverse reinforcement was not suitable for the confinement, T-shaped walls happened the brittle failure by web crushing or bucking of vertical reinforcement at the compression zone. It is necessary to confine transverse reinforcement in order to prevent the these failure. But the location of neutral axis and the magnitude of ultimate strain vary according to the section shape, a ratio of axial load, a ratio of wall cross sectional area to the floor-plan area, an aspect ratio and the reinforcement ratio. Therefore, the objective of this research is to grasp the location of neutral axis and the range which needs for the confinement of transverse reinforcement through the results of the sectional analysis which varies the ratio of axial load and the ratio of vertical reinforcement.

• Steel and Composite Structures
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• 제31권1호
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• pp.13-25
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• 2019

Reactive powder concrete (RPC) is a type of ultra-high strength concrete that has a relatively high brittleness. However, its ductility can be improved by confinement, and the use of RPC in composite RPC filled steel tube columns has become an important subject of research in recent years. This paper aims to present an experimental study of axial capacity calculation of RPC filled circular steel tube columns. Twenty short columns under axial compression were tested and information on their failure patterns, deformation performance, confinement mechanism and load capacity were presented. The effects of load conditions, diameter-thickness ratio and compressive strength of RPC on the axial behavior were further discussed. The experimental results show that: (1) specimens display drum-shaped failure or shear failure respectively with different confinement coefficients, and the load capacity of most specimens increases after the peak load; (2) the steel tube only provides lateral confinement in the elastic-plastic stage for fully loaded specimens, while the confinement effect from steel tube initials at the set of loading for partially loaded specimens; (3) confinement increases the load capacity of specimens by 3% to 38%, and this increase is more pronounced as the confinement coefficient becomes larger; (4) the residual capacity-to-ultimate capacity ratio is larger than 0.75 for test specimens, thus identifying the composite columns have good ductility. The working mechanism and force model of the composite columns were analyzed, and based on the twin-shear unified strength theory, calculation methods of axial capacity for columns with two load conditions were established.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.89-92
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• 2005

Recently there have been occurred many loss of life and extensive damage to social infrastructures due to moderate and strong earthquakes all over the world. In this research, major design factors have been evaluated for the establishment of the rational seismic design code of rectangular RC bridge piers. It was concluded from this study that the axial force ratio and the longitudinal steel ratio should be the most important influencing design parameter for the seismic displacement ductility. However those parameters are not considered in the confinement steel ratio of the KHBDS. Thus, the objective of this study is to propose a rational design equation for transverse reinforcements of rectangular RC bridge piers. New confinement steel ratio is proposed by introducing the effect of the axial force and the longitudinal steel to the current KHBDS. It is thought that these new codes could release the rebar congestion problem in the plastic hinge region of RC bridge piers which contribute to the enhancement of constructibility and economization for RC bridge construction.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.191-196
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• 2001

The structural performance of a shear wall subjected to lateral loads is influenced by many factors, such as sectional shape, aspect ratio, vertical and horizontal reinforcement, lateral confinement and axial compression, etc. This experimental research is focusing to investigate the structural performance of T-shaped walls with different confining reinforcement. Experimental results show that all specimens finally failed by the crushing of the concrete in the compression zone. Although the location and content of the lateral confinement is different, the results are very similar during the negative loading direction where the flange is compressed. However, when flange is subjected to tension, the location and content of the lateral confinement results in a large difference in the structural performance of T-shaped walls. Therefore, selection of location and content of the lateral confinement would be important aspect in the design of the nonsymmetric structural walls.