• Steel and Composite Structures
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• 제9권1호
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• pp.19-38
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• 2009

The present paper provides test data to evaluate the seismic performance of recycled aggregate concrete (RAC) filled steel square hollow section (SHS) beam-columns. Fifteen specimens, including 12 RAC filled steel tubular (RACFST) columns and 3 reference conventional concrete filled steel tubular (CFST) columns, were tested under reversed cyclic flexural loading while subjected to constant axially compressive load. The test parameters include: (1) axial load level (n), from 0.05 to 0.47; and (2) recycled coarse aggregate replacement ratio (r), from 0 to 50%. It was found that, generally, the seismic performance of RACFST columns was similar to that of the reference conventional CFST columns, and RACFST columns exhibited high levels of bearing capacity and ductility. Comparisons are made with predicted RACFST beam-column bearing capacities and flexural stiffness using current design codes. A theoretical model for conventional CFST beam-columns is employed in this paper for square RACFST beam-columns. The predicted load versus deformation hysteretic curves are found to exhibit satisfactory agreement with test results.

• Structural Engineering and Mechanics
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• 제50권6호
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• pp.741-754
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• 2014

The conventional PHC pile-footing connection is the weak part because the surface area and stiffness are sharply changed. The Composite PHC pile reinforced with the transverse shear reinforcing bars and infilled-concrete, hereafter ICP pile, has been developed for improving the flexural and shear performance. This paper investigates the cyclic behavior and performance of the ICP pile-footing connection. To investigate the behavior of the connection, one PHC and two ICP specimens were manufactured and then a series of cyclic loading tests were performed. From the test results, it was found that the ICP pile-footing connection exhibited higher cyclic behavior and connection performance compared to the conventional PHC pile-footing connection in terms of ductility ratio, stiffness degradation and energy dissipation capacity.

• 한국지반공학회논문집
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• 제28권12호
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• pp.53-64
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• 2012

본 논문에서는 주문진 표준사를 대상으로 개량된 반복삼축압축 시험장치를 이용하여 탄성계수와 감쇠비에 대한 변형특성을 분석하였다. 기존의 낮은 정밀도를 갖는 LVDT를 사용한 반복삼축시험기를 개량하여 정밀하고 넓은 영역의 동적변형특성을 얻기 위해서 전단변형률(${\gamma}$) $10^{-4}-10^{-1}%$ 범위의 측정을 제어하는 셀 외부 LDT와 내부의 시료에 LDT를 설치하여 사용하였다. 이러한 미소변형제어를 통하여 5가지의 재하속도 변화와 간극비를 구분하고 4가지의 구속응력 조건을 달리하여 반복삼축시험을 수행하였다. 시험결과를 바탕으로 전단탄성계수와 감쇠비를 여러 조건에 대하여 반복하중 및 변형률 크기의 영향을 비교하고 분석한 결과, 주문진 표준사의 기존(공진주 시험)의 동적변형특성 보다 넓은 구간에서 시험값들을 얻을 수 있었다. 또한, 공진주 시험에서 0.02% 이하의 미소변형률 구간에서 얻은 결과를 토대로 중간변형률 구간을 비선형 모델로 예측한 값들은 반복삼축시험으로 얻은 실험값들과 다른 변형특성을 나타내고 있음을 관찰할 수 있었다.

• Advances in concrete construction
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• 제4권3호
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• pp.161-172
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• 2016

An experimental investigation was carried out on the strength and behavior plain and fiber reinforced geopolymer concrete beam column joints and the results were compared with plain and steel fiber reinforced conventional concrete beam column joints. The volume fraction of fibers used was 0.5%. A total of six Geopolymer concrete joints and four conventional concrete joints were cast and tested under reversed cyclic loading to evaluate the performance of the joints. First crack load, ultimate load, energy absorption capacity, energy dissipation capacity stiffness degradation and moment-curvature relation were evaluated from the test results. The comparison of test results revealed that the strength and behavior of plain and fiber reinforced geopolymer concrete beam column joints are marginally better than corresponding conventional concrete beam column joints.

• Restorative Dentistry and Endodontics
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• 제38권1호
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• pp.31-35
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• 2013

Objectives: This study compared the cyclic fatigue resistance of nickel-titanium (NiTi) files obtained in a conventional test using a simulated canal with a newly developed method that allows the application of constant fatigue load conditions. Materials and Methods: ProFile and K3 files of #25/.06, #30/.06, and #40/.04 were selected. Two types of testing devices were built to test their fatigue performance. The first (conventional) device prescribed curvature inside a simulated canal (C-test), the second new device exerted a constant load (L-test) whilst allowing any resulting curvature. Ten new instruments of each size and brand were tested with each device. The files were rotated until fracture and the number of cycles to failure (NCF) was determined. The NCF were subjected to one-way ANOVA and Duncan's post-hoc test for each method. Spearman's rank correlation coefficient was computed to examine any association between methods. Results: Spearman's rank correlation coefficient (${\rho}$ = -0.905) showed a significant negative correlation between methods. Groups with significant difference after the L-test divided into 4 clusters, whilst the C-test gave just 2 clusters. From the L-test, considering the negative correlation of NCF, K3 gave a significantly lower fatigue resistance than ProFile as in the C-test. K3 #30/.06 showed a lower fatigue resistance than K3 #25/.06, which was not found by the C-test. Variation in fatigue test methodology resulted in different cyclic fatigue resistance rankings for various NiTi files. Conclusions: The new methodology standardized the load during fatigue testing, allowing determination fatigue behavior under constant load conditions.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.59-62
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• 2005

Seven columns laterally reinforced with either mechanically anchored crossties or conventional crossties under cyclic loading are tested. 4 columns are specimens for flexural strength and 3 columns are for shear strength. Main variable is anchorage types of crossties. Conventional hooks, 180$^{\circ}$ standard hook-mechanical anchorage and all mechanical anchorage type are used. The specimens are tested under 10$\%$ axial load of nominal axial capacity of the columns combined with increasing lateral load. From the flexure test, it is found that columns with mechanical anchorages exhibit superior performance in terms of ductility and energy dissipation. The crossties with mechanical anchorages reduce buckling length of longitudinal rebar. From the shear test, it is found that. 3 specimens exhibit almost the same strength, displacement, and shear failure mode at ductility factor =2.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 봄 학술발표회 논문집
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• pp.431-438
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• 1999

An assessment of liquefaction potential is made in principle by comparing the shear stress induced by earthquake to the liquefaction strength of the soil. In this study, a modified method based on Seed and Idriss theory is developed for evaluating liquefaction potential. The shear stress in the ground can be evaluated with seismic response analysis and the liquefaction strength of the soil can be investigated by using cyclic triaxial tests. The cyclic triaxial tests are conducted in two different conditions in order to investigate the factors affecting liquefaction strength such as cyclic shear stress amplitude and relative density. And performance of the modified method in practical examples is demonstrated by applying it to liquefaction analysis of artificial zones with dimensions and material properties similar to those in a typical field. From the result, the modified method for assessing liquefaction potential can successfully evaluate the safety factor under moderate magnitude(M=6.5) of earthquake.

• 한국철도학회논문집
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• 제9권3호
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• pp.305-312
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• 2006

Gravel ballasted tracks are used as a basic structure for the domestic railway tracks. However, such kind of tracks has few disadvantages with service life of the structure, such as rapid deterioration of the tracks. Due to this reason, there is a need to develop low maintenance track to improve the service life of the conventional line tracks. CMP paved tacks are one of the kind of concrete tracks those were manufactured by using the prepacked concrete techniques. The purpose to develop paved tracks is to reduce the maintenance cost. The most important controlling factors to design the paved tracks are surrounding environmental condition and repeated train loading. In this study, in order to investigate the deformation characteristics such as displacement, earth pressure, strain ratio, and crack along the repeated loading cycle, cyclic loading test through real scale model was carried out.

• 한국구조물진단유지관리공학회 논문집
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• 제19권4호
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• pp.75-82
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• 2015

이 논문에서는 철근으로 보강한 고인성 섬유복합체(ECC) 기둥의 반복이력거동을 연구하였다. ECC를 제조하기 위하여 1종 보통 포틀랜드 시멘트(OPC)를 기본 결합재로 하고, 플라이애시를 다량 치환하여 결합재와 충전재로 사용하는 배합을 적용하였다. 철근 보강한 ECC 기둥의 반복이력거동을 평가하기 위하여 일반 철근콘크리트 기둥 실험체를 제작하여 실험을 수행하였다. 반복하중에 의한 실험의 결과, 일반 철근콘크리트 기둥에 비하여 철근 보강한 ECC 기둥은 높은 연성비와 함께 안정적인 이력거동을 나타내었고, 우수한 휨 균열 제어 특성을 나타내었다. 또한 횡방향 하중에 대한 기둥의 내력 증진효과와 함께 에너지 소산능력의 향상을 나타내었다.

• Steel and Composite Structures
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• 제44권2호
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• pp.283-294
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• 2022

In this study, a new seismic retrofit scheme of building structures is developed by combining a steel moment frame and steel slit plates to be installed inside of an existing reinforced concrete frame. This device has the energy dissipation capability of slit dampers with slight loss of stiffness compared to the conventional steel frame reinforcement method. In order to investigate the seismic performance of the retrofit system, it was installed inside of a reinforced concrete frame and tested under cyclic loading. Finite element analysis was carried out for validation of the test results, and it was observed that the analysis and the test results match well. An analytical model was developed to apply the retrofit system to a commercial software to be used for seismic retrofit design of an example structure. The effectiveness of the retrofit scheme was investigated through nonlinear time-history response analysis (NLTHA). The cyclic loading test showed that the steel frame with slit dampers provides significant increase in strength and ductility to the bare structure. According to the analysis results of a case study building, the proposed system turned out to be effective in decreasing the seismic response of the model structure below the given target limit state.