• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.399-404
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• 2000

This paper are the mechanical characteristics of eccentrically loaded normal strength and high strength reinforced concrete columns based on the test results. The columns are $120\times120$mmat the mid-section and are haunched at the ends to apply the eccentric loading and prevent premature failure. Variables are concrete strengths(361, 672, 974 kgf/$\textrm{cm}^2$), $\textrm{cm}^2$longitudinal reinforcement ratios (1.98, 3.54, 1 5.53%), spacing of lateral reinforcement (30, 60, 120mm), and eccentricities (24, 40mm). As a results, the main conclusions obtained from the comparison and analysis for the strength tendency, deformation and ductility of high strength reinforced concrete columns with variables are as follows; As the concrete compressive strength concrete and lateral reinforcement increases, the ductility index of high strength reinforced concrete columns decrease, but it increase with the increase of eccentricity and longitudinal reinforcement ratio. The confinement ratio must be greater than 20 percent in order for the level of ductility between high strength reinforced concrete columns and normal strength reinforced concrete columns to be almost equal.

• Structural Engineering and Mechanics
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• 제43권2호
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• pp.225-237
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• 2012

This paper presents an experimental investigation of the flexural behavior of square hollow steel section (HSS) beams subjected to pure bending. Totally six unfilled and nine ultra high performance concrete (UHPC)-filled HSS beams were tested under four-point bending until failure. The effects of the steel tube thickness, the yield strength of the steel tube and the strength of concrete on moment capacity, curvature, and ductility of UHPC-filled HSS beams were examined. The performance indices named relative ductility index (RDI) and strength increasing factor (SIF) were investigated with regard to different height-to-thickness ratio of the specimens. The flexural strengths obtained from the tests were compared with the values predicted by Eurocode 4, AISC-LRFD and CIDECT design codes. The results showed that the increase in the moment capacity and the corresponding curvature is much greater for thinner HSS beams than thicker ones. Eurocode 4 and AISC-LRFD predict the ultimate moment capacity of the all UHPC-filled HSS beams conservatively.

• Structural Engineering and Mechanics
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• 제52권3호
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• pp.559-572
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• 2014

This paper presents the results of an experimental investigation on the flexural behavior of doubly reinforced lightweight concrete (R.L.C.) beams tested under cyclic loading. A total of 20 beam specimens were tested. Test results are presented in terms of ductility index, the degradation of strength and stiffness, and energy dissipation. The flexural properties of R.L.C. beam were compared to those of normal concrete (R.C.) beams. Test results show that R.L.C. beam with low and medium concrete strength (20, 40MPa) performed displacement ductility similar to the R.C. beam. The ductility can be improved by enhancing the concrete strength or decreasing the tension reinforcement ratio. Using lightweight aggregate in concrete is advantageous to the dynamic stiffness of R.L.C. beam. Enhancement of concrete strength and increase of reinforcement ratio will lead to increase of the stiffness degradation of beam. The energy dissipation of R.L.C beam, similar to R.C. beam, increase with the increase of tension reinforcement ratio. The energy dissipation of unit load cycle for smaller tension reinforcement ratio is relatively less than that of beam with higher reinforcement ratio.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.593-596
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• 1999

Steel fibers are added to concrete to improve energy absorption, impact resistance and apparent ductility, and to provide crack resistance and crack control. This study is to investigate the toughness index and post-crack equivalent tensile strength of steel fiber reinforced concrete properties on the load-deflection behaviors of the steel fiber reinforced concrete beam model specimens.

• 콘크리트학회지
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• 제6권5호
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• pp.140-148
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• 1994

R/C 라멘골조에 있어서 수직부재(기둥, 벽등)에 수평부재(보, 슬라브등)의 콘크리트 강도보다 1.4배가 넘는 강도의 콘크리트를 분리타설할 경우 ACI 318R-89 R10.13.1은 수직부재에 타설한 콘크리트가 수평부재로 2ft(60cm)이상의 내민길이를 확보하도록 규정하고 있다. 이에 따라 본 연구는 이규정을 그대로 적용하기에 앞서 실험적인 검증을 통한 구조적인 안전성을 확보하기 위하여 고강도 콘크리트 내민길이, 콘크리트 압축강도 등을 주요변수로 하여 총 6개의 실험체를 제작하여 실험 및 분석하였다. 실험결과 압축강도 및 내민 길이의 증가에 따라 각 실험체의 연성능력은 증가하는 것으로 나타났으며 R/C 라멘골조에 고강도 콘크리트와 보통강도 콘크리트를 분리타설할 경우 균열발생상황, 접합부에서의 거동 등을 고려할 때 고강도 콘크리트의 내민길이는 2h(h=보의 전체춤) 정도를 확보하여야 할 것으로 보여진다.

• Advances in concrete construction
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• 제9권5호
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• pp.511-527
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• 2020

The main aim of the current research is to investigate the flexural behavior of the reinforced concrete (RC) slabs strengthened with strain hardening cementitious composites (SHCC) experimentally and numerically. Seven RC slabs were prepared and tested under four-points loading test. One un-strengthened slab considered as control specimen while six RC slabs were strengthened with reinforced SHCC layers. The SHCC layers had different reinforcement ratios and different thicknesses. The results showed that the proposed strengthening techniques significantly increased the ultimate failure load and the ductility index up to 25% and 22%, respectively, compared to the control RC slab. Moreover, a three dimensional (3D) finite element model was proposed to analyze the strengthened RC slabs. It was found that the results of the proposed numerical model well agreed with the experimental responses. The validated numerical model used to study many parameters of the SHCC layer such as the reinforcement ratios and the different thicknesses. In addition, steel connectors were suggested to adjoin the concrete/SHCC interface to enhance the flexural performance of the strengthened RC slabs. It was noticed that using the SHCC layer with thickness over 40 mm changed the failure mode from the concrete cover separation to the SHCC layer debonding. Also, the steel connectors prevented the debonding failure pattern and enhanced both the ultimate failure load and the ductility index. Furthermore, a theoretical equation was proposed to predict the ultimate load of the tested RC slabs. The theoretical and experimental ultimate loads are seen to be in fairly good agreement.

• Architectural research
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• 제20권1호
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• pp.17-25
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• 2018

Countermeasures against earthquake disasters such as the seismic capacity evaluation and/or retrofit schemes of buildings, especially existing low-rise reinforced concrete buildings, have not been fully performed since Korea had not experienced many destructive earthquakes in the past. However, due to more than 1200 earthquakes with low or moderate intensity in the off-coastal and inland of Korea during the past 20 years, and due to the recent moderate earthquakes in Korea, such as the 2016 Gyeongju Earthquake with M=5.8 and the 2017 Pohang Earthquake with M=5.4, the importance of the future earthquake preparedness measures is highly recognized in Korea. The main objective of this study is to provide the basic information regarding seismic capacities of existing low-rise reinforced concrete buildings in Korea. In this paper, seismic capacities of 14 existing low-rise reinforced concrete public buildings in Korea are evaluated based on the Japanese Standard for Evaluation of Seismic Capacity of Existing Reinforced Concrete Buildings. Seismic capacities between existing buildings in Korea and those in Japan is compared, and the relationship of seismic vulnerability of Korean buildings and Japanese buildings damaged due to severe earthquakes are also discussed. Results indicated that Korean existing low-rise reinforced concrete buildings have a narrow distribution of seismic capacities and they are relatively lower than Japanese buildings, and are also expected to have severe damage under the earthquake intensity level experienced in Japan. It should be noted from the research results that the high ductility in Korean existing low-rise buildings obtained from the Japanese Standard may be overestimated, because most buildings investigated herein have the hoop spacing wider than 30 cm. In the future, the modification of strength and ductility indices in the Japanese Standard to propose the seismic capacity evaluation method of Korean buildings is most needed.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.643-657
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• 2020

This study presents experimental and numerical investigations on circular steel tube confined ultra high performance concrete (UHPC) columns under axial compression. The plain UHPC without fibers was designed to achieve a compressive strength ranged between 150 MPa and 200 MPa. Test results revealed that loading on only the UHPC core can generate a significant confinement effect for the UHPC core, thus leading to an increase in both strength and ductility of columns, and restricting the inherent brittleness of unconfined UHPC. All tested columns failed by shear plane failure of the UHPC core, this causes a softening stage in the axial load versus axial strain curves. In addition, an increase in the steel tube thickness or the confinement index was found to increase the strength and ductility enhancement and to reduce the magnitude of the loss of load capacity. Besides, steel tube with higher yield strength can improve the post-peak behavior. Based on the test results, the load contribution of the steel tube and the concrete core to the total load was examined. It was found that no significant confinement effect can be developed before the peak load, while the ductility of post-peak stage is mainly affected by the degree of the confinement effect. A finite element model (FEM) was also constructed in ABAQUS software to validate the test results. The effect of bond strength between the steel tube and the UHPC core was also investigated through the change of friction coefficient in FEM. Furthermore, the mechanism of circular steel tube confined UHPC columns was examined using the established FEM. Based on the results of FEM, the confining pressures along the height of each modeled column were shown. Furthermore, the interaction between the steel tube and the UHPC core was displayed through the slip length and shear stresses between two surfaces of two materials.

• 한국구조물진단유지관리공학회 논문집
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• 제12권4호
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• pp.98-106
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• 2008

인양홀을 이용한 정착장치는 손상된 구조물에 내하력을 증가시키기 위해 사용되어지며, 시공이 간편하고 보강효율이 좋은 경제적인 방법이다. 본 논문에서는 구조물에 손상을 입히지 않으면서 충분한 보강효과를 가져 올 수 있는 인양홀 이용 정착장치를 선정하여 그에 대한 적용 가능성을 연구하였다. 실무에서 시공빈도가 높은 인양홀 이용 단부 정착 장치가 적용된 3개의 실험체를 제작하였고, 이에 대한 휨 실험을 수행하여 처짐, 변형률 및 파괴양상을 분석하였다. 인양홀 이용 정착장치가 구비된 철근 콘크리트 보의 보강 성능을 실험적으로 규명하기 위하여 각 실험체의 균열하중, 항복하중, 극한하중, 강선의 응력 증가량, 처짐 및 연성 등을 비교 분석하였다.

• Computers and Concrete
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• 제30권3호
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• pp.165-173
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• 2022

The effect of basalt and polypropylene fibers on the flexural behavior of reinforced concrete (RC) beams is investigated in this paper. The compressive and tensile behaviors of the basalt concrete and polypropylene concrete cylinders are also investigated. Eight beams and 28 cylinders were made with different percentages of basalt and polypropylene fibers. The dosages of fiber were selected as 0.6%, 1.3%, and 2.5% of the total cement weight. Each type of fiber was mixed solely with the concrete mix. Basalt and polypropylene fibers are modern and cheap materials that can be used to improve the structural behavior of RC members. This research is designed to find the optimum percentage of basalt and polypropylene fibers for enhancing the flexural behavior of RC beams. Test results showed that the addition of basalt and polypropylene fibers in any dosage (0.6%, 1.3%, and 2.5%) can increase the flexural strength and displacement ductility index of the beams where the maximum enhancement was measured with 1.3% fibers. The maximum increments in the flexural strength and the displacement ductility index were 30.39% and 260% for the basalt fiber case, while the maximum improvement for the polypropylene fibers case was 55.5% and 230% compared to the control specimen. Finite element (FE) models were then developed in ABAQUS to predict the numerical behaviour of the tested beams. The FE models were able to predict the experimental behaviour with reasonable accuracy. This research confirms the efficiency of basalt and polypropylene fibers in enhancing the flexural behavior of RC beams, and it also suggests the optimum dosage of fibers.