• 한국도로학회논문집
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• 제11권4호
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• pp.87-94
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• 2009

콘크리트 슬래브는 타설 후 온도와 수분 변화를 통해 체적이 변화한다. 수분증발에 의하여 발생한 건조수축은 슬래브의 자중이나 하부층과의 마찰 등에 의하여 구속되어 슬래브 내부에 응력이 유발된다. 선행 연구에 의하면 건조수축에 의하여 발생된 실제 인장응력은 이론적으로 예측된 값보다 작은 것으로 보고되었다. 이는 부분적으로 구속된 슬래브에서 발생하는 초기 재령 콘크리트의 점탄성에 기인한 응력감소 현상이다. 본 연구에서는 재령에 따른 콘크리트의 응력감소 현상을 조사하기 위하여 구속된 원주형, 구속되지 않은 자유건조 원주형, 그리고 자유건조 각주형 콘크리트 시편의 변형률을 측정하였다. 재령 1, 3, 7, 14, 28일에 콘크리트의 탄성계수를 측정하였으며 관입저항 실험을 실시하였다. 실험결과를 기존 연구자들이 제안한 이론식에 대입하여 구속된 원주형 콘크리트 시편의 응력감소를 계산할 수 있었다. 향후 본 연구의 결과를 바탕으로 구속된 콘크리트 시편의 응력감소 현상을 콘크리트 포장의 설계에 적용할 예정이다.

• 한국구조물진단유지관리공학회 논문집
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• 제13권3호통권55호
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• pp.188-196
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• 2009

콘크리트는 초기재령에 있어서 수분의 증발 및 이동으로 소성 및 건조수축 등의 수축현상이 발생한 다. 국내에서는 아령형 구속건조수축몰드를 활용한 콘크리트의 건조수축 균열 평가방법을 KS에서 규격화하여 활용하고 있으나 이는 균열발생시점 및 구속수축응력을 평가하는 방법으로 균열발생량에 관한 정량적 평가는 어려운 실정이다. 이에 본 연구에서는 콘크리트의 수축변형거동 및 균열발생량에 대한 정량적 데이터를 확보하기 위하여 판상-링형 구속시험방법을 개발하고 시험체 치수가 콘크리트의 수축균열에 미치는 영향을 검토하여 판상-링형 구속시험방법의 최적 시험체 치수 도출 및 수축균열특성에 관한 정량적 평가방법을 제안하고 그 적용성을 검증하고자 한다.

• Steel and Composite Structures
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• 제34권4호
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• pp.561-580
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• 2020

Buckling restrained braces (BRBs) were developed as an enhanced alternative to conventional braces by restraining their global buckling, thus allowing development of a stable quasi-symmetric hysteretic response. A wider adoption of buckling restrained braced frames is precluded due to proprietary character of most BRBs and the code requirement for experimental qualification. To overcome these problems, BRBs with capacities corresponding to typical steel multi-storey buildings in Romania were developed and experimentally tested in view of prequalification. In the second part of this paper, a complex nonlinear numerical model for the tested BRBs was developed in the finite element environment Abaqus. The calibration of the numerical model was performed at both component (material models: steel, concrete, unbonding material) and member levels (loading, geometrical imperfections). Geometrically and materially nonlinear analyses including imperfections were performed on buckling restrained braces models under cyclic loading. The calibrated models were further used to perform a parametric study aiming at assessing the influence of the strength of the buckling restraining mechanism, concrete class of the infill material, mechanical properties of steel used for the core, self-weight loading, and frame effect on the cyclic response of buckling restrained braces.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 가을 학술발표회 논문집
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• pp.251-258
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• 2003

The early -age behavior of base restrained reinforced concrete (RC) walls is analyzed using a three-dimensional finite element method in this study. After calculating the temperature and internal relative humidity variations of an RC wall, determination of stresses due to thermal gradients, differential drying shrinkage, and average drying shrinkage is followed, and the relative contribution of these three stress components to the total stress is compared. The mechanical properties of early-age concrete, determined from many experimental studies, are taken into consideration, and a discrete reinforcing steel derived using the equivalent nodal force concept is also used to simulate the cracking behavior of RC walls. In advance, to Predict the crack spacing and maximum crack width in a base restrained RC wall, an analytical model which can simulate the post-cracking behavior of an RC tension member is introduced on the basis of the energy equilibrium before and after cracking of concrete.

• Structural Engineering and Mechanics
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• 제72권4호
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• pp.443-454
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• 2019

In order to reduce the residual drift of a structure in structural engineering field, a combined structural system (dual) consisting of steel buckling-restrained braced frame (BRBF) along with shear wall is proposed. In this paper, BRBFs are used with special reinforced concrete shear walls as combined systems. Some prototype models of the proposed combined systems as well as steel BRBF-only systems (without walls) are designed according to the code recommendations. Then, the nonlinear model of the systems is prepared using fiber elements for the reinforced concrete wall and appropriate elements for the BRBs. Seismic responses of the combined systems subjected to ground motions at maximum considered earthquake level are investigated and compared to those obtained from BRBFs. Results showed that the maximum residual inter-story drift from the combined systems is, on average, less than half of the corresponding value of the BRBFs. In this research, mean of absolute values of the maximum inter-story drift ratio demand obtained from combined systems is less than the 3% limitation, while this criterion has not been fulfilled by BRBF systems.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.781-784
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• 2005

Concrete structures often present volumetrical changes particularly due to thermal and moisture related shrinkages. Volumetric instability is detrimental to the performance and durability of concrete structures because structural elements are usually restrained. These restrained shrinkages develope tensile stresses which often results in cracking in combination with the low fracture resistance of concrete. Early-age defects in high-performance concrete due to thermal and autogenous deformation shorten the life cycle of concrete structures. Thus, it is necessary to examine the behavior .of early-age concrete at the stages of design and construction. The purpose of this study was to propose a shrinkage models of VES-LMC (very-early strength latex-modified concrete) at early-age considering thermal deformation and autogenous shrinkage.

• International Journal of Concrete Structures and Materials
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• 제1권1호
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• pp.3-9
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• 2007

Fiber-reinforced self-compacting concrete (FRSCC) is a new type of concrete mix that can mitigate two opposing weaknesses: poor workability in fiber-reinforced concrete and cracking resistance in plain SCC concrete. This study focused on early-age cracking of FRSCC due to restrained drying shrinkage, one of the most common causes of cracking. In order to investigate the effect of fiber on shrinkage cracking of FRSCC, ring shrinkage tests were performed for polypropylene and steel fiber-reinforced SCC. In addition, finite element analyses for those specimens were carried out considering drying shrinkage based on moisture diffusion, creep, cracking resistance of concrete, and the effect of fiber. The analysis results were verified via a comparison between the measured and calculated crack width. From the test and analysis results, the effectiveness of fiber with respect to reducing cracking was confirmed and some salient features on the shrinkage cracking of FRSCC were obtained.

• Structural Engineering and Mechanics
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• 제63권4호
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• pp.521-536
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• 2017

Reinforced concrete core-wall structures with buckling-restrained brace outriggers are interesting systems which have the ability to absorb and dissipate energy during strong earthquakes. Outriggers can change the energy demand in a tall building. In this paper, the energy demand was studied by using the nonlinear time history analysis for the mentioned systems. First, the structures were designed according to the prescriptive codes. In the dynamic analysis, three approaches for the core-wall were investigated: single plastic hinge (SPH), three plastic hinge (TPH) and extended plastic hinge (EPH). For SPH approach, only one plastic hinge is allowed at the core-wall base. For TPH approach, three plastic hinges are allowed, one at the base and two others at the upper levels. For EPH approach, the plasticity can extend anywhere in the wall. The kinetic, elastic strain, inelastic and damping energy demand subjected to forward directivity near-fault and ordinary far-fault earthquakes were studied. In SPH approach for all near-fault and far-fault events, on average, more than 65 percent of inelastic energy is absorbed by buckling-restrained braces in outrigger. While in TPH and EPH approaches, outrigger contribution to inelastic energy demand is reduced. The contribution of outrigger to inelastic energy absorption for the TPH and EPH approaches does not differ significantly. The values are approximately 25 and 30 percent, respectively.

• Computers and Concrete
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• 제3권6호
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• pp.439-454
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• 2006

This paper develops an artificial neural network (ANN) model for uniformly loaded restrained reinforced concrete (RC) slabs incorporating membrane action. The development of membrane action in RC slabs restrained against lateral displacements at the edges in buildings and bridge structures significantly increases their load carrying capacity. The benefits of compressive membrane action are usually not taken into account in currently available design methods based on yield-line theory. By extending the existing knowledge of compressive membrane action, it is possible to design slabs in building and bridge decks economically with less than normal reinforcement. The processes involved in the development of ANN model such as the creation of a database of test results from previous research studies, the selection of architecture of the network from extensive trial and error procedure, and the training and performance validation of the model are presented. The ANN model was found to predict accurately the ultimate strength of fully restrained RC slabs. The model also was able to incorporate strength enhancement of RC slabs due to membrane action as confirmed from a comparative study of experimental and yield line-based predictions. Practical applications of the developed ANN model in the design process of RC slabs are also highlighted.

• 한국도로학회논문집
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• 제15권5호
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• pp.101-110
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• 2013

PURPOSES : The purpose of this study is to evaluate the durability of ternary blended concrete mixtures adding ultra fine admixture. METHODS : From the literature review, crack was considered as the main distress failure criterion on concrete bridge deck pavement. To reduce the initial crack development due to drying shrinkage, CSA expansion agent and shrink reduction agent were used to ternary blended concrete mixtures as a admixture. Laboratory tests including chloride ion penetration test, surface scaling test, rapid freeze & thaw resistance test, non restrained drying shrinkage and restrained drying shrinkage test were conducted to verify the durability of ternary blended concrete mixtures. RESULTS : Based on the test results, proposed mixtures were verified as high qualified durable materials. Expecially initial drying shrinkage crack was not occurred in ternary blended concrete mixtures with CSA expansion agent. CONCLUSIONS : It is concluded that the durability of proposed ternary blend concrete mixture was acceptable to apply for the concrete bridge deck pavement.