• Composites Research
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• 제15권3호
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• pp.11-17
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• 2002

본 연구에서는 분산형 강화복합재료에 균열이 발생하면 하중부하능력이 감소와 더불어 재료의 손상을 초래할 수 있어 재료의 완전한 게재물과 균열이 존재한 게재물이 있는 경우를 상정하여 하중부하능력과 탄성 음력분포를 평가한다. 무한체가 전단음력을 받을 때 완전한 게재물과 균열이 내재한 경우에 대하여 3차원 유한요소해석이 수행되어 완전한 게재물의 경우는 게재물의 영역의 음력은 동일하고 게재물의 계면은 다소 불균일하게 나타났다. 그리고 균열이 내재한 경우에는 균열주변에는 음력이 집중되는 경우를 볼수 있을 뿐만아니라 아주 복잡한 분포를 볼수 있었다. 불균질물의 평균응력은 하중부하능력으로 표현이 가능하였고 완전만 게재물과 균열의 경우도 균열손상에 의해 하중부하능력의 차이를 볼 수 있었다. 특히, 균열이 내재한 경우에 에스펙터비(aspect ratio)가 증가할수록 하중부하능력이 증가함을 알 수 있었다.

• 한국지반공학회지:지반
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• 제8권4호
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• pp.31-40
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• 1992

고대 석조아치교량의 아치부분은 암석블릭이 서로 맞물려 있는 불연속면의 특성을 지니고 있다. 이러한 석조아치교량의 내하력을 평가하기 위해서는 역학적으로 취약한 불연속면을 고려하는 것이 요구되나 기존의 해석방법은 아치를 연속된 하나의 일체부재로 보고 해석하였으므로 불연속면의 특성이 고려되지 않았다. 따라서 본 논문에서는 유한요소해석을 이용하여 불연속면을 고려하고 불연속면의 전단강성과 마찰각이 석조아치교량의 내하력에 미치는 영향을 분석함으로써 석조아치교량을 평가하고자 하 였다. 연구결과 고대 석조아치교량의 내하력은 아치블럭을 형성하고 있는 암석 자체의 압축강도보다는 불연속면의 마찰각과 전단강성에 의하여 좌우되며 화강암 교량일 경우에는 전단강성이 더 큰 영향을 미치는 것을 알 수 있었으며 해석대상인 흥국사 홍교는 현재 3등교수준의 내하력을 갖고 있는 것으로 추정된다.

• Structural Engineering and Mechanics
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• 제83권5호
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• pp.671-680
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• 2022

The shear capacity of beams is an essential parameter in designing beams carrying shear loads. Precise estimation of the ultimate shear capacity typically requires comprehensive calculation methods. For steel fiber reinforced concrete (SFRC) beams, traditional design methods may not accurately predict the interaction between different parameters affecting ultimate shear capacity. In this study, artificial neural network (ANN) modeling was utilized to predict the ultimate shear capacity of SFRC beams using ten input parameters. The results demonstrated that the ANN with 30 neurons had the best performance based on the values of root mean square error (RMSE) and coefficient of determination (R²) compared to other ANN models with different neurons. Analysis of the ANN model has shown that the clear shear span to depth ratio significantly affects the predicted ultimate shear capacity, followed by the reinforcement steel tensile strength and steel fiber tensile strength. Moreover, a Genetic Algorithm (GA) was used to optimize the ANN model's input parameters, resulting in the least cost for the SFRC beams. Results have shown that SFRC beams' cost increased with the clear span to depth ratio. Increasing the clear span to depth ratio has increased the depth, height, steel, and fiber ratio needed to support the SFRC beams against shear failures. This study approach is considered among the earliest in the field of SFRC.

• Earthquakes and Structures
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• 제8권3호
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• pp.665-679
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• 2015

The strain rate of reinforced concrete (RC) structures stimulated by earthquake action has been generally recognized as in the range from $10^{-4}/s$ to $10^{-1}/s$. Because both concrete and steel reinforcement are rate-sensitive materials, the RC beam-column joints are bound to behave differently under different strain rates. This paper describes an investigation of seismic behavior of RC beam-column joints which are subjected to large cyclic displacements on the beam ends with three loading velocities, i.e., 0.4 mm/s, 4 mm/s and 40 mm/s respectively. The levels of strain rate on the joint core region are correspondingly estimated to be $10^{-5}/s$, $10^{-4}/s$, and $10^{-2}/s$. It is aimed to better understand the effect of strain rates on seismic behavior of beam-column joints, such as the carrying capacity and failure modes as well as the energy dissipation. From the experiments, it is observed that with the increase of loading velocity or strain rate, damage in the joint core region decreases but damage in the plastic hinge regions of adjacent beams increases. The energy absorbed in the hysteresis loops under higher loading velocity is larger than that under quasi-static loading. It is also found that the yielding load of the joint is almost independent of the loading velocity, and there is a marginal increase of the ultimate carrying capacity when the loading velocity is increased for the ranges studied in this work. However, under higher loading velocity the residual carrying capacity after peak load drops more rapidly. Additionally, the axial compression ratio has little effect on the shear carrying capacity of the beam-column joints, but with the increase of loading velocity, the crack width of concrete in the joint zone becomes narrower. The shear carrying capacity of the joint at higher loading velocity is higher than that calculated with the quasi-static method proposed by the design code. When the dynamic strengths of materials, i.e., concrete and reinforcement, are directly substituted into the design model of current code, it tends to be insufficiently safe.

• 콘크리트학회논문집
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• 제22권4호
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• pp.585-593
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• 2010

선행연구에서 제안된 변형률기반 전단강도모델에 근거하여, 슬래브-기둥 내부 및 외부접합부의 직접뚫림전단강도와 불균형휨모멘트강도를 정확하게 평가할 수 있는 강도모델을 개발하였다. 슬래브-기둥 접합부는 뚫림전단파괴에 앞서서 휨균열에 의해서 손상을 받으므로, 이 연구에서는 위험단면의 압축대에서 대부분의 전단저항이 발휘된다고 가정하였다. 슬래브 휨모멘트에 의해서 유발되는 압축수직응력이 콘크리트 압축대의 전단강도에 미치는 영향을 고려하기 위하여, 다축응력 상태에 대한 콘크리트 재료파괴기준을 이용하였다. 그 결과 위험단면의 전단성능이 휨손상의 정도에 따라서 정의되었다. 외부접합부는 비대칭적인 위험단면을 가지고 있으므로 하중재하방향을 고려하여 휨모멘트강도를 정의하였다. 실험 결과와 비교 결과, 제안된 강도모델은 현행 설계기준 보다 실험체의 강도를 더 정확하게 추정하는 것으로 밝혀졌다.

• 대한건축학회논문집:구조계
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• 제34권11호
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• pp.19-26
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• 2018

This paper presents the shear strengthening effect of externally post-tensioning (EPT) method using high-strength steel rod in pre-cracked reinforced concrete (RC) beams. Three- and four-point bending tests were performed on a total of 8 specimens by adjusting the strengthening depths in the deviator position of EPT. The effective strengthening depths were 435, 535, and 610 mm. The pre-loading up to about 2/3 of ultimate load capacity measured in unstrengthened RC beam were applied in the beam to be post-tensioned. The EPT method was then applied to the pre-damaged RC beams and re-loading was added until the end of the test. EPT restored deflections of 3 mm or more, which account for about 40% of deflection when the pre-loading was applied. The shear strengthening increases more than 3 times and 36~107% in terms of the stiffness and load-carrying capacity compared to unstrengthening RC beams. The increased load-carrying capacities of the post-tensioned beam with strengthening depths of 435 and 535 mm are almost the same as 36~61%, and those of 610 mm are 84~107%, which shows the greatest shear strengthening effect.

• Computers and Concrete
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• 제24권1호
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• pp.37-49
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• 2019

In this study, the shear behaviour of reinforced concrete (RC) beams that were retrofitted using precast panels of ultra-high performance fiber reinforced concrete (UHPFRC) is presented. The precast UHPFRC panels were glued to the side surfaces of RC beams using epoxy adhesive in two different configurations: (i) retrofitting two sides, and (ii) retrofitting three sides. Experimental tests on the adhesive bond were conducted to estimate the bond capacity between the UHPFRC and normal concrete. All the specimens were tested in shear under varying levels of shear span-to-depth ratio (a/d=1.0; 1.5). For both types of configuration, the retrofitted specimens exhibited a significant improvement in terms of stiffness, load carrying capacity and failure mode. In addition, the UHPFRC retrofitting panels glued in three-sides shifted the failure from brittle shear to a more ductile flexural failure with enhancing the shear capacity up to 70%. This was more noticeable in beams that were tested with a/d=1.5. An approach for the approximation of the failure capacity of the retrofitted RC beams was evolved using a multi-level regression of the data obtained from the experimental work. The predicted values of strength have been validated by comparing them with the available test data. In addition, a 3-D finite element model (FEM) was developed to estimate the failure load and overall behaviour of the retrofitted beams. The FEM of the retrofitted beams was conducted using the non-linear finite element software ABAQUS.

• Steel and Composite Structures
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• 제21권2호
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• pp.267-287
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• 2016

The seismic performance of the ordinary steel reinforced concrete (SRC) columns has no significant improvement compared to the reinforced concrete (RC) columns mainly because I, H or core cross-shaped steel cannot provide sufficient confinement for core concrete. Two improved SRC columns by constructing with new-type shaped steel were put forward on this background, and they were named as enlarging cross-shaped steel and diagonal cross-shaped steel for short. The seismic behavior and carrying capacity of new-type SRC columns have been researched theoretically and experimentally, while the shear behavior remains unclear when the new-type columns are joined onto SRC beams. This paper presents an experimental study to investigate the shear capacity of new-type SRC joints. For this purpose, four new-type and one ordinary SRC joints under low reversed cyclic loading were tested, and the failure patterns, load-displacement hysteretic curves, joint shear deformation and steel strain were also observed. The ultimate shear force of joint specimens was calculated according to the beam-end counterforce, and effects of steel shape, load angel and structural measures on shear capacity of joints were analyzed. The test results indicate that: (1) the new-type SRC joints display shear failure pattern and has higher shear capacity than the ordinary one; (2) the oblique specimens have good bearing capacity if designed reasonably; and (3) the two proposed construction measures have little effect on the shear capacity of SRC joints embedded with diagonal cross-shaped steel. Based on the mechanism observed from the test, the formulas for calculating ultimate shear capacity considering the main factors (steel web, stirrup and axial compression ratio) were derived, and the calculated results agreed well with the experimental and simulated data.

• 한국강구조학회 논문집
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• 제17권6호통권79호
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• pp.737-747
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• 2005

강재 보와 콘크리트 슬래브로 구성되어 지는 합성보에서 두 부재는 일반적으로 전단연결재에 의해 서로 합성되어져 일체적인 구조거동을 하게 된다. 현재까지 전단연결재로서는 스터드(stud)가 널리 사용되어지고 있다. 합성보의 구조적 거동은 사용된 부재의 재료적 특성 외에도 스터드에 의한 전단합성작용에 의해 많은 영향을 받게 된다. 합성보 전단연결부에서의 전단합성거동은 합성보에서가 아닌 단순화된 Push-Out 시험체(Push-Out Test Specimen)에 의해 실험적으로 결정되고 있다. 최근의 연구결과에 따르면, Push-Out 실험에서 얻은 전단 스터드의 합성거동과 실제 합성보에서의 전단합성거동에는 분명한 차이점이 존재하며, 특히 부분합성된 합성보에서는 그 차이가 매우 크다는 것이 밝혀지고 있다. 본 연구에서는 표준 Push-Out 시험체 및 합성보의 구조거동 해석을 위해, Push-Out 실험으로부터 결정되는 스터드에 대한 하중-상대변위 곡선의 도입이 필요 없는 3차원 유한요소모델을 개발하였다. 해석결과의 비교 분석으로부터 합성보 전단연결부에서의 합성거동을 평가할 수 있었고, 이를 Push-Out 실험결과와 비교하여 보았으며 전단합성거동의 차이점에 대한 구체적 원인을 찾을 수 있었다.

• 대한건축학회논문집:구조계
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• 제34권1호
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• pp.3-10
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• 2018

This experimental investigation was conducted to observe the shear strengthening behavior of pre-damaged reinforced concrete (RC) beams strengthened with externally post-tensioning steel rods. A total of six simply supported beams - two control beams and four post-tensioned beams using external steel rods - were tested to failure in shear. The external steel rods of 18 mm or 28 mm diameter were respectively employed as post-tensioning material. The four post-tensioned beams have a V-shaped profile with a deviator (or saddle pin) located at mid-span, and the post-tensioning system increased the low load-carrying capacity and overcame a little bit of deflection caused by damage. Concretely, the load-carrying capacity and flexural stiffness were respectively increased by about 25~57% and 263~387% due to the post-tensioning when compared with the unstrengthened control beams.