• 한국지진공학회논문집
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• 제28권4호
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• pp.171-181
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• 2024

For low-rise piloti-type buildings that suffered significant damage in the Pohang earthquake, the seismic performance of those designed by codes issued before and after the earthquake has been recently revised. This study started with the expectation that many of the requirements presented in the current codes may be excessive, and among them, the spacing of column stirrup could be relaxed. In particular, the recently revised design code of concrete structures for buildings, KDS 41 20 00, suggests that the column stirrup spacing is 1/2 of the minimum cross-sectional size or 200 mm, which is strengthened compared to KBC 2016, but relaxed than the current KDS, 41 17 00, which is 1/4 of the minimum size or 150 mm. As a result of the study, it was found that the target performance level was sufficiently satisfied by following the current standards and that it could be satisfied even if the relaxed spacing was followed. Therefore, the strict column stirrup spacing of KDS 41 17 00 could be relaxed if a wall other than core walls is recommended in the current guideline for the structural design of piloti-type buildings.

• Structural Engineering and Mechanics
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• 제91권3호
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• pp.263-277
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• 2024

The primary aim of this study is to introduce an innovative configuration for stirrup hooks in reinforced concrete beams and analyze the impact of factors such as stirrup spacing, placement, and hook lengths on the structural performance of reinforced concrete beam elements. A total of 18 specimens were produced and subjected to reversed cyclic loading, with two specimens serving as reference specimens and the remaining 16 specimens utilizing a specifically developed stirrup hook configuration. The experiment used reinforced concrete beams scaled down to half their original size. These beams were built with a shear span-to-depth ratio of 3 (a/d=3). The experimental samples were divided into two distinct groups. The first group comprises nine test specimens that consider the contribution of concrete to shear strength, while the second group consists of nine test specimens that do not consider this contribution. The preparation of reference beam specimens for both groups involved the utilization of standard hooks. The stirrup hooks in the test specimens are configured with a 90-degree angle positioned at the midpoint of the bottom section of the beam. The criteria considered in this study included the distance between hooks, hook angle, stirrup spacing, hook orientation, and hook length. In the experimental group examining the contribution of concrete on shear strength, it was noted that the stirrup hooks of both the R1 reference specimen and specific test specimens displayed indications of opening. However, when the contribution of concrete on shear strength was not considered, it was observed that none of the stirrup hooks proposed in the R0 reference specimen and test specimens showed any indications of opening. Neglecting the contribution of concrete in the assessment of shear strength yielded more favorable outcomes regarding structural robustness. The study found that the strength values obtained using the suggested alternative stirrup hook were similar to those of the reference specimens. Furthermore, all the test specimens successfully achieved the desired strengths.

• Steel and Composite Structures
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• 제49권2호
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• pp.245-255
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• 2023

The present paper summarizes the results of an experimental program on the influence of using waste lathe scraps in the concrete mixture on the shear behavior of RC beams with different amounts of shear reinforcement. Three different volumetric ratios (1, 2 and %3) for the scraps and three different stirrup spacings (160, 200 and 270 mm) were adopted in the tests. The shear span-to-depth ratios of the beams were 2.67 and the stirrup spacing exceeded the maximum spacing limit in the building codes to unfold the contribution of lathe scraps to the shear resistances of shear-deficient beams, subject to shear-dominated failure (shear-tension). The experiments depicted that the lathe scraps have a pronounced contribution to the shear strength and load-deflection behavior of RC beams with widely-spaced stirrups. Namely, with the addition of 1%, 2% and 3% waste lathe scraps, the load-bearing capacity escalated by 9.1%, 21.8% and 32.8%, respectively, compared to the reference beam. On the other hand, the contribution of the lathe scraps to the load capacity decreases with decreasing stirrup spacing, since the closely-spaced stirrups bear the shear stresses and render the contribution of the scraps to shear resistance insignificant. The load capacity, deformation ductility index (DDI) and modulus of toughness (MOT) values of the beams were shown to increase with the volumetric fraction of scraps if the stirrups are spaced at about two times the beam depth. For the specimens with a stirrup spacing of about the beam depth, the scraps were found to have no considerable contribution to the load capacity and the deformation capacity beyond the ultimate load. In other words, for lathe scrap contents of 1-3%, the DDI values increased by 5-23% and the MOT values by 63.5-165% with respect to the reference beam with a stirrup spacing of 270 mm. The influence of the lathe scraps to the DDI and MOT values were rather limited and even sometimes negative for the stirrup spacing values of 160 and 200 mm.

• 한국구조물진단유지관리공학회 논문집
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• 제27권3호
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• pp.47-57
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• 2023

본 연구에서는 스터럽 간격, 철근 직경 및 부식률이 이형철근의 부착강도에 미치는 영향을 파악하고자 인발실험이 수행되었다. 스터럽 간격, 철근 직경 및 부식률이 상이한 12개의 인발 실험체를 RILEM RC 6 기준에 따라 제작하였다. 스터럽이 보강된 실험체에 대하여, 부식률이 3% 미만인 경우에는 부착강도가 증가하였으나, 부식률이 3%를 초과한 경우에는 부착강도가 감소하였다. 반면, 스터럽이 보강되지 않은 실험체에 대해서는, 부식률이 증가함에 따라 부착강도가 감소하였다. 스터럽 간격 및 부식률 대비, 철근 직경이 부착강도에 미치는 영향은 적은 것으로 나타났다. 이에 따라 스터럽 비율 및 부식률을 변수로 사용하는 인발실험체의 부착강도 회귀모형이 제시되었으며, 제안모델은 선행 모델들에 비해 낮은 오차를 나타내었다.

• Structural Engineering and Mechanics
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• 제87권4호
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• pp.333-346
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• 2023

This paper presents findings from an experimental study that was focused on evaluating the use of Forta-Ferro (FF) and Polyvinyl Alcohol (PVA) fibers on the response of moderate and special ductility beams under load cycles. For this reason, eight full-scale specimens, identical in geometry, were subjected to gradual cyclic loading. The specimens included two plain concrete beams with medium and special ductility, three beams with medium ductility and stirrup spacing of one-quarter the effective depth (d/4) and three beams with special ductility, and stirrup spacing of one-half the effective depth (d/2), strengthened with FF and PVA fibers separately. The use of fibers was aimed at reducing the amount of shear reinforcement in flexural members. Here, the variation of parameters including the maximum strength, ultimate strength, stiffness, ductility, damage index, energy dissipation, and equivalent damping was studied. Utilizing FF and PVA fibers improved the performance in beams with moderate ductility when compared to those beams with special ductility. Therefore, in special ductility beams, fibers can be used instead of crossties and in moderate ductility beams, fibers can be added to reduce the ratio of shear reinforcement. Furthermore, increasing the stirrup spacing in the moderate ductility beams from d/4 to d/2 and adding 0.6% FF or 1.5% PVA fibers resulted in behavior similar to those of the moderate ductility beam.

• Earthquakes and Structures
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• 제24권3호
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• pp.183-192
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• 2023

It is essential to properly understand the seismic behavior of reinforced concrete (RC) columns confined by stirrups that experience different corrosion rates. The current study investigated the effect of seismic performance indicators such as strength loss, energy dissipation rate, ductility and hysteresis damping on specimens and models for different stirrup corrosion rates. Analysis revealed the adverse effects of corrosion on the bond performance between the concrete and steel bars which affected the seismic performance of the columns. It was found that with increasing corrosion rate, ductility and energy dissipation of the specimens decreased. Compared with the uncorroded specimen, the ductility factor and energy dissipation decreased observably, by 22.89% and 60.64%, respectively. An attenuation relationship is proposed for the corrosion rate of the stirrups for different stirrup yield strengths, concrete compressive strengths, concrete covers and stirrup spacing.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.263-266
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• 2005

Recently, many researches for high-strength and high-durability concrete structure have remarkably been studied by adopting new construction material, fiber reinforced polymer (FRP). In connection with these research trend, the shearing capacity of concrete beams reinforced by GFRP stirrup which is developed in this study was evaluated. Experimental variables are span to depth ratio and spacing of shear reinforcement for test. In the result of test, the crack pattern, failure mode and shear load between shear steel reinforcement specimen and GFRP stirrup reinforcement specimen showed similar structural tendency. Therefore, it was investigated that the adaptability of shear-reinforced concrete structure with GFRP stirrup will be improved with further researches of shear design variables.

• Structural Engineering and Mechanics
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• 제28권3호
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• pp.317-334
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• 2008

Seismic performance of coupling beams not designed for ductility is examined. Eight 1:4 scale coupling beam specimens, with seven reinforced concrete sections and one composite section, were tested under cycles of push-pull action. Characteristics of the specimens include moderate shear span ratio in the range of 2.5-3.5, high main reinforcement ratio at 3-4% and small to large stirrup spacing with 90- degree hooks. All the reinforced concrete specimens failed in a brittle manner. Displacement ductility of specimens with large stirrup spacing (${\geq}$140 mm) is in the range of 3 to 5. Seismic performance of the specimens is also examined using the ultimate drift angle and the amount of energy dissipated. Correlating the test data, an empirical relationship is proposed to estimate the ultimate drift angle of a class of coupling beams considered in the study not designed for ductility.

• 한국강구조학회 논문집
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• 제30권2호
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• pp.67-76
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• 2018

스터럽 보강 선설치 앵커의 동적 전단하중 하의 파열파괴강도를 평가하기 위한 실험 연구를 수행하였다. 전단 하중은 ACI 355.2 및 ETAG 001에 제시된 지진모의실험 방식으로 재하하였다. 시험체는 M36 앵커(연단거리 180mm)를 D10 스터럽(간격 100mm)으로 보강하였다. 이들 시험체는 거의 극한 파열파괴 강도에 도달한 후 앵커의 파단이 발생하였다. 이에 M42 앵커(연단거리 160mm)를 D6 스터럽(간격 100mm)으로 보강한 시험체에 대한 실험을 추가로 수행하였다. 실험 결과, 동적 전단강도는 정적 강도에 비해 낮은 값을 보이지 않았다. 또한, ACI 318 및 ETAG 001 기준은 스터럽 보강이 많을수록 파열파괴강도를 안전측으로 평가하는 것으로 나타났다.

• 한국전산구조공학회논문집
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• 제28권3호
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• pp.259-266
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• 2015

본 논문에서는 유공형 강판의 횡방향 보강간격에 따른 넓은 보의 전단성능을 실험적으로 평가하기 위하여 횡방향 전단보강 간격과 넓은 보의 유효깊이를 변수로 고려하였다. 시험체는 총 8개로 유공형 강판으로 전단보강한 시험체가 5개, 무보강 시험체가 3개이다. 균열 및 파괴유형, 변형률과 하중-변위 곡선을 분석하였다. 유공형 전단보강재의 전단강도 기여분을 분석하고, 횡방향 전단보강의 최대간격을 제안하였다. 횡방향 전단보강 개수가 2개인 시험체에 비해 3개인 시험체에서 전단강도가 크게 나타났으며 유효깊이가 증가할수록 전단강도가 크게 나타났다.