• 한국지반공학회논문집
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• 제39권11호
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• pp.7-22
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• 2023

최근 지하안전에 관한 특별법이 시행(2022년 1월)되었으며, 지하안전영향평가를 통해 계획단계부터 지하안전에 관한 사전검토가 실시되고 있다. 지하굴착을 위해서는 가설 흙막이의 구조 안전성을 확보하는 것이 중요하므로 지하안전 검토는 더욱 강화되고 있다. 본 연구에서는 토사지반에서 Soil-Cement 흙막이의 벽체 두께를 확대하고 H-pile의 선택과 설치간격을 자유롭게 할 수 있는 MFS(Multi-axis Flat Continuous Soil Cement Earth Retaining Wall) 흙막이 벽체 공법의 거동 특성을 분석하였다. 실내모형실험을 통해 MFS 공법의 H-pile 설치간격에 따른 벽체에 작용하는 하중-변위 거동을 확인하였으며, MFS 흙막이 벽체의 두께별 H-pile 설치간격 및 크기 변화에 따른 하중-변위를 3차원 수치해석으로 분석하여 벽체에 작용하는 아칭효과 높이를 산정하였다. MFS 공법에서 산정한 최대 아칭높이를 기존의 부재력 검토 방법에 적용하여 벽체에 작용하는 축력, 전단력을 정량적으로 분석하는 설계방법을 제시하였다. 그 결과 MFS 흙막이 벽체에 적용되는 H-pile 설치 간격 및 크기에 따른 축력 및 전단력이 24.6~62.9%가 저감하는 것을 확인하였다.

• Steel and Composite Structures
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• 제51권6호
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• pp.661-678
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• 2024

The utilization of geopolymer recycled aggregate concrete (GRAC) as the infilled core of the concrete-filled steel tubular (CFST) columns provides superior economic and environmental benefits. However, limited research exists within the field of geopolymer recycled aggregate concrete considered a green and sustainable material, in addition to the limitation of the design guidelines to predict the behavior of such an innovative new material combination. Moreover, the behavior of high-strength concrete is different from the normal-strength one, especially when there is another material of high-strength properties, such as the steel tube. This paper aims to investigate the behavior of the axially loaded square high-strength GRACFST columns through the nonlinear finite element analysis (NLFEA). A total of thirty-two specimens were simulated using ABAQUS/Standard software with three main variables: recycled aggregate replacement ratio (0, 30, and 50) %, width-to-thickness ratios (52.0, 32.0, 23.4, and 18.7), and length-to-width ratio (3, 5, 9, and 12). During the analysis, the response in terms of the axial load versus the longitudinal strain was recorded and plotted. In addition, various mechanical properties were calculated and analyzed. In view of the results, it has been demonstrated that the mechanical properties of high-strength GRACFST columns such as ultimate load-bearing capacity, compressive stiffness, energy absorption capacity, and ductility increase with the increase of the steel tube thickness owing to the improvement of the confinement effect of the steel tube. In contrast, the incorporation of the recycled aggregate adversely affected the mentioned properties except the ductility, while the increase of the recycled aggregate replacement ratio improved the column's ductility. Moreover, it has been found that the increase in the length-to-width ratio significantly reduced both the failure strain and the energy absorption capacity. Finally, the obtained NLFEA results of the ultimate load-bearing capacity were compared with the corresponding predicted capacities by numerous codes. It has been concluded that AISC, ACI, and EC give conservative predictions for the ultimate load-bearing capacity since the confinement effect was not considered by these codes.

• 한국항해항만학회지
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• 제31권3호
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• pp.271-279
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• 2007

선체구조는 기본적으로 판부재의 조합으로 이루어져 있으며, 이러한 판부재의 하중분담 능력 혹은 최종강도 평가는 선체구조의 합리적인 설계 및 구조의 안정성 평가에 있어서는 아주 중요하다. 또한, 선체구조를 구성하고 있는 구조요소들은 작용외력에 대하여 개별적으로 작용하지 않으며 전체적으로 연속거동을 하게 된다. 실제 선박에서의 붕괴형태 중 한가지는 종방향 굽휨에 의해서 갑판 혹은 선저부에 좌굴 및 소성붕괴이다. 그래서, 합리적인 설계에서는 이러한 급작스런 붕괴형태를 방지하기 위하여 좌굴 및 소성붕괴 거동을 파악하는 것이 아주 중요하며, 실제 선박에서는 갑판부와 선저부에서는 하중분담 능력을 증가시키기 위하여 여러개의 종보강재를 가진 보강판 구조의 설계를 하게 된다. 본 연구에서는 선체 판넬구조의 모델링 방법에 따른 최종강도 거동의 차이를 분석하여, 합리적인 모델링영역을 규명하고자 한다. 사용된 해석 모델은 실제 상선의 이중저구조에서 사용되는 판넬에서 채택하였으며 유한요소해석 모델링 시 3가지 단면형상에 대해 각각 6가지 서로 다른 해석모델을 적용하였으며, 이때 보강재의 단면형상을 변화하였다. 본 연구의 목적은 압축하중이 작용하는 선체 보강판구조에서 해석영역에 대한 좌굴 및 최종강도 거동의 특성을 분석하였다.

• 콘크리트학회논문집
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• 제25권6호
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• pp.631-639
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• 2013

이 연구에서는 기존에 수행된 시공성과 경제성이 향상되고 중진 지역에서 사용 가능한 새로운 프리캐스트 콘크리트 보-기둥 접합상세의 비선형 유한요소해석이 수행되었다. 해당 상세는 복합구조를 기반으로 함으로써 기둥 내에는 각관을 보유하고 있으며 보에는 강판이 매입되어 있는 복잡한 단면을 보유하고 있다. 또한 콘크리트와 강재뿐만 아니라 ECC라는 새로운 재료를 사용함에 따라 요소의 선택 및 재료모델의 결정에 대한 방법론을 제시하였다. 비선형 유한요소해석은 상용 유한요소해석 프로그램인 ABAQUS를 통해 수행되었으며 요소 및 재료 모델은 ABAQUS에서 제공하는 모델들을 사용하였다. 비선형 유한요소해석 결과 기 수행되었던 실험 결과에 유사하거나 보수적으로 평가함으로써 변수분석에 사용할 수 있을 것으로 판단하였다. 구축된 유한요소해석 모델을 통해 해당 상세의 성능에 대한 압축력의 영향, 휨강도비의 영향에 대해 분석하였다. 압축력의 경우 기둥 압축강도의 10~20%에서 가장 좋은 성능을 발휘할 수 있었으며, 휨강도비 1.2 이상에서 기둥의 항복 없이 보의 소성힌지를 유도할 수 있음을 확인하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.909-914
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• 2001

It is important to consider an effect of concrete member sizes when estimating the ACI rectangular stress block of a reinforced concrete flexural member. However, the experimental data and analytical analyses are still not available for a proper evaluation. For all types of loading conditions, the trend is that the size of an ACI rectangular stress block tends to change when the member sizes change. In this paper, the size variations of strength coefficients for ACI rectangular stress block and actual stress distribution have been studied. Results of a series of C-shaped specimens subjected to axial compressive load and bending moment were adopted from references 1 and 2. The analysis results show that the effect of specimen sizes on strength coefficients for ACI rectangular stress block and actual stress distribution of concrete member was apparent. Thus, the results suggest that the current strength criteria based design practice should be reviewed.

• Steel and Composite Structures
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• 제22권5호
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• pp.1141-1162
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• 2016

Concrete-filled double skin steel tube (CFDST) beam-columns are widely used in industrial plants, subways, high-rise buildings and arch bridges. The CFDST columns have the same advantages as traditional CFT members. Moreover, they have lighter weight, higher bending stiffness, better cyclic performance, and have higher fire resistance capacities than their CFT counterparts. The scope of this study is to develop finite element models that can predict accepted capacities of double skin concrete-filled tube columns under the combined effect of axial and bending actions. The analysis results were studied to determine the distribution of stresses among the different components and the effect of the concrete core on the outer and inner steel tube. The developed models are first verified against the available experimental data. Accordingly, an extensive parametric study was performed considering different key factors including load eccentricity, slenderness ratio, concrete compressive strength, and steel tube yield strength. The results of the performed parametric study are intended to supplement the experimental research and examine the accuracy of the available design formulas.

• Structural Engineering and Mechanics
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• 제36권4호
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• pp.421-445
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• 2010

In this paper the formulation of an efficient frame element applicable for nonlinear analysis of 3D reinforced concrete (RC) frames is outlined. Interaction between axial force and bending moment is considered by using the fibre element approach. Further, section warping, effect of normal and tangential forces on the torsional stiffness of section and second order geometrical nonlinearities are included in the model. The developed computer code is employed for nonlinear static analysis of RC sub-assemblages and a simple approach for extending the formulation to dynamic cases is presented. Dynamic progressive collapse assessment of RC space frames based on the alternate path method is undertaken and dynamic load factor (DLF) is estimated. Further, it is concluded that the torsional behaviour of reinforced concrete elements satisfying minimum standard requirements is not significant for the framed structures studied.

• Earthquakes and Structures
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• 제12권6호
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• pp.603-617
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• 2017

This paper presents investigation into the behavior of beam-column joints, with the joint region concrete being replaced by steel fiber reinforced concrete (SFRC) and by ultra-high performance concrete (UHPC). A total of ten beam-column joint specimens (BCJ) were tested experimentally to failure under monotonic and cyclic loading, with the beam section being subjected to flexural loading and the column to combined flexural and axial loading. The joint region essentially transferred shear and axial stresses as received from the column. Steel fiber reinforced concrete (SFRC) and ultra-high performance concrete (UHPC) were used as an innovative construction and/or strengthening scheme for some of the BCJ specimens. The reinforced concrete specimens were reinforced with longitudinal steel rebar, 18 mm, and some specimens were reinforced with an additional two ties in the joint region. The results showed that using SFRC and UHPC as a replacement concrete for the BCJ improved the joint shear strength and the load carrying capacity of the hybrid specimens. The mode of failure was also converted from a non-desirable joint shear failure to a preferred beam flexural failure. The effect of the ties in the SFRC and UHPC joint regions could not be observed due to the beam flexural failure. Several models were used in estimating the joint shear strength for different BCJ specimens. The results showed that the existing models yielded wide-ranging values. A new concept to take into account the influence of column axial load on the shear strength of beam-column joints is also presented, which demonstrates that the recommended values for concrete tensile strength for determination of joint shear strength need to be amended for joints subject to moderate to high axial loads. Furthermore, finite element model (FEM) simulation to predict the behaviour of the hybrid BCJ specimens was also carried out in an ABAQUS environment. The result of the FEM modelling showed good agreement with experimental results.

• Steel and Composite Structures
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• 제23권5호
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• pp.585-596
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• 2017

Tubular joints have been widely used in offshore platforms and space structures due to their merits such as easy fabrication, aesthetic appearance and better static strength. For existing tubular joints, a grouted sleeve reinforced method was proposed in this paper. Experimental tests on five tubular T-joints reinforced with the grouted sleeve and two conventional tubular T-joints were conducted to investigate their mechanical behaviour. A constant axial compressive force was applied to the chord end to simulate the compressive state of the chord member during the tests. Then an axial compressive force was applied to the top end of the brace member until the collapse of the joint specimens occurred. The parameters investigated herein were the grout thickness, the sleeve length coefficient and the sleeve construction method. The failure mode, ultimate load, initial stiffness and deformability of these joint specimens were discussed. It was found that: (1) The grouted sleeve could change the failure mode of tubular T-joints. (2) The grouted sleeve was observed to provide strength enhancement up to 154.3%~172.7% for the corresponding un-reinforced joint. (3) The initial stiffness and deformability were also greatly improved by the grouted sleeve. (4) The sleeve length coefficient was a key parameter for the improved effect of the grouted sleeve reinforced method.

• Structural Engineering and Mechanics
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• 제21권1호
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• pp.35-52
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• 2005

This paper proposes a realistic approach to pushover analyses of reinforced concrete (RC) structures with single column type and frame type. The characteristic of plastic hinge of a single RC column subjected to fixed axial load was determined first according to column's three distinct failure modes which were often observed in the experiments or earthquakes. By using the determined characteristic of plastic hinge, the pushover analyses of single RC columns were performed and the analytical results were investigated to be significantly consistent with those of cyclic loading tests. Furthermore, a simplified methodology considering the effect of the variation of axial force for each RC column of the frame structure during pushover process is proposed for the first time. It would be helpful in performing pushover analysis for the structures examined in this study with efficiency as well as accuracy.