• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.6
• /
• pp.226-234
• /
• 2021

The objective of this study is to establish the fundamental design data for axial load-displacement relationship under axial monotonic or cyclic responses of seismic damping·isolation (SDI) units developed for ceiling structures. The main parameters include the installation of a spring, the number of rubber layer, prestress stress of bolts for connector between the spring and rubbers, and loading type. Test results showed that SDI units with a spring in the core and higher prestress stress of bolts tended to be higher stiffness at the ascending branch and more ductile behavior at the descending branch. This trends more notable for the specimens under monotonic load rather than cyclic loads. Consequently, the energy dissipation of SDI unit can be optimally designed with the following conditions: installation of a spring within 3-layer rubbers and prestress applied to the bolts at 10% of their yielding strength . When compared with the experimental tension capacity of the developed SDI units, the predictions by JIS B 2704-1 and KDS 31 00 are conservative under monotonic loading but higher by approximately 10% under cyclic loading.

• Journal of Korean Association for Spatial Structures
• /
• v.5 no.3 s.17
• /
• pp.109-115
• /
• 2005

The experimental work was performed to investigate the effect influenced to the hystresis and the flexural strength improvement of RC beam using carbon fiber plates. Major parameters of this experimental program were the section size of carbon fiber plates and the damage level of RC beam before reinforcement. Particularly, the damage level of beam is for the cases damaged by overloads. The damage level is for 30%, 60%, and 100% of flexural strength, and no damaged beams were also tested for comparison with the damaged one. from the test results, it showed that the beams reinforced by carbon fiber plates had the higher strength and lower deformation capacity than the general beams and that it had the same ductility ratio of the general beams.

• The Journal of the Korea Contents Association
• /
• v.15 no.9
• /
• pp.576-587
• /
• 2015

This paper presents a quantitative evaluation of water permeability in concrete with cold joint considering mineral admixture and loading conditions. Concrete samples with OPC (Ordinary Portland Cement) and GGBFS(Ground Granulated Blast Furnace Slag) are prepared considering 0.6 of W/C ratio and 40% of replacement. 30% and 60% loading levels for compression and 60% loading level for tension are induced to concrete samples. In compression conditions, the permeability in control case shows $2.41{\times}10^{-11}m/s$ in OPC concrete, and it changes to $2.07{\times}10^{-11}m/s$ (30% of peak) and $2.36{\times}10^{-11}m/s$ (60% of peak). The results in GGBFS concrete shows the same trend, which yields $2.17{\times}10^{-11}m/s$ (control), $1.65{\times}10^{-11}m/s$ (30% of peak), and $1.96{\times}10^{-11}m/s$ (60% of peak), respectively. In tensile conditions, the permeability increases from $2.37{\times}10^{-11}m/s$ (control) to $2.67{\times}10^{-11}m/s$ (60% of peak) while that in GGBFS concrete increases from $2.17{\times}10^{-11}m/s$ (control) to $2.24{\times}10^{-11}m/s$ (60% of peak). Permeability coefficients decreases in 30% of compressive level but increases in 60% level, while results in tensile level increases rapidly. This shows pore structure in concrete is condensed and with loading and permeability increases due to micro-cracking. Permeability evaluation considering the effects of loading conditions, cold joint, and GGBFS is verified to be important since water permeability greatly changes due to their effects.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.13 no.5
• /
• pp.61-71
• /
• 2009

This paper presents the results of an experiment comparing the current circular CFT columns and circular CFT columns that were additionally confined by carbon fiber sheets (CFS) under axial loading. The main experimental parameters are the numbers of CFS layers and the diameter-to-thickness ratio. 10 specimens were prepared according to the experimental parameter plans, and axial compression tests were conducted. From the tests, the failure procedure, load-axial deformation curve, maximum axial strength, and deformation capacity of the CFT columns and confined CFT columns were compared. The test results showed that the maximum axial strengths of CFT columns additionally confined by CFS are increased higher than those of the current CFT columns, and that local buckling can be delayed due to the confinement effect of CFS.

• 한국방재학회:학술대회논문집
• /
• 2011.02a
• /
• pp.160-160
• /
• 2011

현대의 건설기술은 자원절약과 환경보전이라는 시대적 흐름 속에, 자원순환과 지속 가능한 친환경 건설기술 개발은 차세대 연구분야로써, 연구가 시급한 분야가 되었다. 최근에는 골재 수급불균형 문제를 해결하고 동시에 자원순환을 위한 방안으로서 건설폐기물로부터 생산된 순환골재를 콘크리트용 천연골재의 대체재로 활용하기 위한 연구개발이 이루어지고 있다. 지속가능형 건설기술을 국내 독자 기술로 확립하고 건설현장에서 발생하는 폐기물의 순환시스템을 확고하게 구축하여 순환자원에 의한 국가경쟁력 강화를 기대할 수 있다. 본 연구의 목적은 순환골재 콘크리트의 역학적 특성을 개선하기 위해 순환골재 콘크리트 공시체를 제작하여 강도 및 강성을 검증하는 것이다. 실험방법으로 순환굵은골재의 치환 비율을 0%에서 100%까지 변화시킨 공시체를 제작하고 각 공시체의 정적 극한강도 거동을 비교 분석하였다. 하중은 공시체가 파괴가 발생 할 때까지 변위제어 방식으로 재하 하였으며 이 때 공시체의 파괴거동은 설치된 계측센서들을 이용하여 계측 및 분석하였다. 실험결과 공시체의 압축강도는 순환굵은골재 치환률이 25% 미만일 경우 일반 콘크리트 압축강도의 95% 이상의 구조성능을 갖지만, 순환굵은골재 치환률이 100%인 경우, 일반콘크리트 압축강도의 85% 수준의 구조성능을 나타냈다. 강성은 FRP 부재의 순환골재 치환률에 따라 최대 14%의 강성차이를 보였다. 이를 통해 순환골재 치환률이 높을수록 순환골재 표면의 폐모르타르와 이물질의 영향으로 재료간의 부착강도가 감소되어 강도와 강성이 저하되었음을 확인하였다.

• Composites Research
• /
• v.25 no.1
• /
• pp.19-25
• /
• 2012

The study investigated the buckling behavior of sandwich composite columns with different hole sizes and hole positions when they were applied to a compressive load. The columns consisted of 1.7mm thick faces of glass fabric/epoxy and 23mm, 37mm, 48mm, and 61mm thick cores of urethane-foam. Different hole sizes with the diameter of 25mm and 38mm were considered in this experiment. To evaluate the effect of hole position on the buckling behavior, we considered three types of hole position: 25mm diameter hole located at the center, 25mm diameter hole at 1/4 position from the center to the end of the column, and 25mm diameter hole at 1/2 position from the center to the end of the column. According to the results, buckling and maximum loads of the column having 25mm diameter hole were lower by 10% compared to those of the column without hole, whereas the loads for the column having 38mm diameter hole were 30% less than those of the column without hole. Hole position appeared to have no effect on buckling and maximum loads. Major failure modes were observed as follows: the core shear failure for the thin columns having 23mm and 37mm thick cores, and the face-core debonding for the thick columns having 48mm and 61mm thick cores.

• Journal of the Korea Concrete Institute
• /
• v.17 no.2 s.86
• /
• pp.255-261
• /
• 2005

Immense quantities of coal combustion by-products are produced every year, and only a small fraction of them are currently utilized. The purpose of this study is to investigate reused techniques of coal ash in the construction field, which may contribute to the savings of building materials and conservation of environment. From the results of the compressive strength test, the elastic modulus was experimentally proposed. Also, based on the three- point-bending test, the fracture parameters - notch sensitivity, fracture energy, and initial compliance were experimentally proposed. As a result, the strength and fracture characteristics were lower than those of concrete or mortar. Also, the study showed that the deflection at a fracture decreased as the age increased and as the notch depth rate decreased. However, it was judged that its use as a building material could be expected if further research is carried out.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.11 no.5
• /
• pp.135-143
• /
• 2007

This paper presents results of an experimental study designed to investigate the effect of sustained load on the flexural performance of reinforced recycled aggregate concrete beams. In this experimental program, three beams with recycled aggregate replacement percentages(natural 100%, recycled coarse aggregate 100%, recycled fine aggregate 50%) were tested up to failure after sustained loading($0.5M_n$) for one year. The experimental results showed that reinforced concrete beams using recycled aggregate(water absorption : 1.86~3.64%) concrete showed the same flexural performance as that of natural aggregate concrete beam. Current the ACI code underestimated experimental obtained ultimate flexural strength of beams irrespective of usage of recycled aggregates.

• Journal of Korean Society of Steel Construction
• /
• v.14 no.5 s.60
• /
• pp.567-576
• /
• 2002

Maximum-strength concrete-ailed steel square tubular columns were tested under concentric and biaxial eccentric load. Buckling length-section depth ratio $L_k/D$, magnitude of eccentricity e, and angle of eccentric load ${\theta}$ were selected as experimental parameters. Strength and behavior were also examined. Test results showed that the maximum strength of columns under biaxial eccentric load could be predicted using the previously proposed strength formula of columns under uniaxial eccentric load. Likewise, the behavior and maximum strength of columns could be predicted using the analysis.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.35 no.1
• /
• pp.57-64
• /
• 2022

This study investigated the structural performance of the RC boundary beam-wall system subjected to axial loads that required lesser construction quantity and smaller floor height in comparison with the conventional RC transfer girder system. Four specimens of 1/2 scale were constructed, and their peak strengths under axial loads and failure characteristics were compared and analyzed. Test parameters included the ratio of the lower to the upper wall length, lower wall thickness, and stirrup details of the lower wall. In addition, three-dimensional nonlinear finite element analysis was performed to verify the effectiveness of the boundary beam-wall system. The peak strength of each specimen was similar to the nominal axial strength of the lower wall, indicating that the axial load was transferred smoothly from the upper to the lower wall. The contribution of the lower wall cross-section was high if the ratio of the lower to the upper wall length was small; the contribution was low if the out-of-plane eccentricity existed in the lower wall. The specimen with smaller stirrup distance and cross-ties in the lower wall showed higher initial stiffness and peak load than other specimens.