• Structural Engineering and Mechanics
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• 제82권1호
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• pp.121-131
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• 2022

The main goal of this study is to prepare a program for analyzing High Strength Steel Fibrous Reinforced Concrete (HSSFRC) slabs and predict the response and strength of the slab instead of preparing a prototype and testing it in the laboratory. For this purpose, new equations are proposed to represent the material properties of High Strength Steel Fibrous Reinforced Concrete. The proposed equations obtained from performing regression analysis on many experimental results using statistical programs. The finite element method is adopted for non-linear analysis of the slabs. The eight-node "Serendipity element" (3 DoF) is chosen to represent the concrete. The layered approach is adopted for concrete elements and the steel reinforcement is represented by a smeared layer. The compression properties of the concrete are modeled by a work hardening plasticity approach and the yield condition is determined depending on the first two stress invariants. A tensile strength criterion is adopted in order to estimate the cracks propagation. many experimental results for testing slabs are compared with the numerical results of the present study and a good agreement is achieved regarding load-deflection curves and crack pattern. The response of the load deflection curve is slightly stiff at the beginning because the creep effect is not considered in this study and for assuming perfect bond between the steel reinforcement and the concrete, however, a great agreement is achieved between the ultimate load from the present study and experimental results. For the models of the tension stiffening and cracked shear modulus, the value of Bg and Bt (Where Bg and Bt are the curvature factor for the cracked shear modulus and tension stiffening models respectively) equal to 0.005 give good results compared with experimental result.

• Steel and Composite Structures
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• 제47권6호
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• pp.709-728
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• 2023

Experimental and analytical studies were conducted to clarify the influencing mechanisms of the longitudinal reinforcement on performance of axially loaded Reinforced Concrete-Filled Steel Tube (R-CFST) short columns. The longitudinal reinforcement ratio was set as parameter, and 10 R-CFST specimens with five different ratios and three Concrete-Filled Steel Tube (CFST) specimens for comparison were prepared and tested. Based on the test results, the failure modes, load transfer responses, peak load, stiffness, yield to strength ratio, ductility, fracture toughness, composite efficiency and stress state of steel tube were theoretically analyzed. To further examine, analytical investigations were then performed, material model for concrete core was proposed and verified against the test, and thereafter 36 model specimens with four different wall-thickness of steel tube, coupling with nine reinforcement ratios, were simulated. Finally, considering the experimental and analytical results, the prediction equations for ultimate load bearing capacity of R-CFSTs were modified from the equations of CFSTs given in codes, and a new equation which embeds the effect of reinforcement was proposed, and equations were validated against experimental data. The results indicate that longitudinal reinforcement significantly impacts the behavior of R-CFST as steel tube does; the proposed analytical model is effective and reasonable; proper ratios of longitudinal reinforcement enable the R-CFSTs obtain better balance between the performance and the construction cost, and the range for the proper ratios is recommended between 1.0% and 3.0%, regardless of wall-thickness of steel tube; the proposed equation is recommended for more accurate and stable prediction of the strength of R-CFSTs.

• 한국터널지하공간학회 논문집
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• 제12권2호
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• pp.165-175
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• 2010

최근에 물류비 절감, 교통 편의성 개선, 지역발전 등 정치, 경제, 사회적 요구에 따라 장대 해저터널 건설의 필요성이 증가하고 있다. 또한, 도심지에 건설되는 도로 및 철도터널에서도 터널의 장대화에 따라 공사용 및 환기용 수직구의 설치가 필수적이다. 수직구 굴착 후 설치되는 콘크리트 라이닝의 설계시 결정해야할 요소는 직경, 단면두께, 소요철근량 등이다. 이러한 수직구 직경, 하중조건, 지반조건을 고려하여 최적의 라이닝 단면설계를 위해서는 많은 구조검토가 필요하다. 본 연구에서는 이러한 다양한 조건에 대하여 구조해석을 수행하여 라이닝 단면설계도표를 제시하였다. 제안된 도표를 이용하여 간편하게 규모 및 하중조건에 따른 라이닝 단면두께 및 소요철근량 산정이 가능하다.

• 대한토목학회논문집
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• 제28권4A호
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• pp.457-463
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• 2008

종방향 보강재는 압축플랜지를 단순지지함으로써 국부좌굴강도를 증가시키는 역할을 수행한다. 최근 연구에 의하면, 종방향으로 적절한 간격을 두고 점지지 되었을 경우 그 선을 따라서 단순 지지된 경우와 동일한 좌굴강도를 보이는 것으로 밝혀졌다. 이 같은 연구결과로부터, 하부콘크리트에 부착된 전단연결재가 압축플랜지의 좌굴시 점지지 조건을 만족할 수 있다면 전단연결재가 단순지지의 역할도 수행할 수 있을 것이라는 예측이 가능하다. 이와 같은 사실이 입증이 된다면, 강박스거더 제작비에서 매우 큰 부분을 차지하는 종방향보강재를 생략할 수 있기 때문에 보다 경제적인 설계가 가능해 질 것이다. 본 연구에서는 하부압축플랜지에 종방향보강재를 대체할 전단연결재의 종방향 배치 시 최소간격 결정과 동시에 하부 콘크리트와 합성거동을 하기 위해 소요되는 전단연결재 소요 개수와 간격을 결정하기 위한 연구를 수행하였다.

• Computers and Concrete
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• 제32권2호
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• pp.217-232
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• 2023

Numerous studies have been performed on the behavior of pile foundations in cold regions. This study first attempted to employ artificial neural networks (ANN) to predict pile-bearing capacity focusing on pile data recorded primarily on cold regions. As the ANN technique has disadvantages such as finding global minima or slower convergence rates, this study in the second phase deals with the development of an ANN-based predictive model improved with an Elephant herding optimizer (EHO), Dragonfly Algorithm (DA), Genetic Algorithm (GA), and Evolution Strategy (ES) methods for predicting the piles' bearing capacity. The network inputs included the pile geometrical features, pile area (m²), pile length (m), internal friction angle along the pile body and pile tip (Ø°), and effective vertical stress. The MLP model pile's output was the ultimate bearing capacity. A sensitivity analysis was performed to determine the optimum parameters to select the best predictive model. A trial-and-error technique was also used to find the optimum network architecture and the number of hidden nodes. According to the results, there is a good consistency between the pile-bearing DA-MLP-predicted capacities and the measured bearing capacities. Based on the R2 and determination coefficient as 0.90364 and 0.8643 for testing and training datasets, respectively, it is suggested that the DA-MLP model can be effectively implemented with higher reliability, efficiency, and practicability to predict the bearing capacity of piles.

• Structural Engineering and Mechanics
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• 제84권4호
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• pp.547-560
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• 2022

By presetting various reinforcement diameters in topology optimization with the discrete model finite element analysis, an algorithm of bidirectional evolutionary structural optimization of multi-level reinforcement diameter is presented to obtain the optimal reinforcement topologies which describe the degree of stress of different parts. The results of a comparative study on different reinforcement feasible domain demonstrate that the more angle types of reinforcement are arranged in the initial domain, the higher utilization rate of reinforcement of the optimal topology becomes. According to the nonlinear finite element analysis of some deep beam examples, the ones designed with the optimization results have a certain advantage in ultimate bearing capacity, although their failure modes are greatly affected by the reinforcement feasible domain. Furthermore, the bearing capacity can be improved when constructional reinforcements are added in the subsequent design. However the adding would change the relative magnitude of the bearing capacity between the normal and inclined section, or the relative magnitude between the flexural and shear capacity within the inclined section, which affects the failure modes of components. Meanwhile, the adding would reduce the deformation capacity of the components as well. It is suggested that the inclined reinforcement and the constructional reinforcement should be added properly to ensure a desired ductile failure mode for components.

• Computers and Concrete
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• 제34권1호
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• pp.1-14
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• 2024

The design of disturbed regions in reinforced concrete structures usually applies the well known Strut and Tie Method (STM). As an alternative, the Stringer-Panel Method (SPM), an intermediate model between STM and the Finite Element Method (FEM), consists in dividing a structure into two distinct elements: the stringers (which carry axial forces) and panels (which carry shear forces). SPM has already showed good applicability in manual calculations and computer implementations, and its most known application was SPanCAD, an AutoCAD plugin for linear and nonlinear analysis by SPM. Unfortunately, SPanCAD was discontinued by the developers, and it's not compatible with the most recent versions of AutoCAD. So, this paper aims to present a computer program that was developed as an upgrade to the latter: the Stringer Panel Modelling Tool (SPMTool), which is intended to be an auxiliary design tool and it presents improvements, in comparison to SPanCAD. It is possible to execute linear and nonlinear analysis by three distinct formulations: Modified Compression Field Theory (MCFT), Disturbed Stress Field Model (DSFM) and Softened Membrane Model (SMM). The nonlinear results were compared to experimental data of reinforced concrete elements that were not designed by SPM; these elements were also analyzed in SPanCAD. On overall, SPMTool made more realistic predictions to the behavior of the analyzed structures than SPanCAD. Except for DSFM predictions for corbels (1.24), in overall average, the ultimate load predictions were conservative (0.85 to 0.98), which is a good aspect for a design tool. On the other hand, the cracking load predictions presented overestimations (1.06 to 1.47) and higher variations (25.59% to 34.25%) and the post-cracking behavior could not be accurately predicted; for this use case, a more robust finite element software is recommended.

• 한국구조물진단유지관리공학회 논문집
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• 제11권3호
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• pp.77-86
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• 2007

건축물의 증가와 자원의 효율적인 활용의 목적으로 기존 건축물에 대한 리모델링이 주목을 받고 있다. 리모델링 공사로 인해 세대간 병합을 위해 기존 벽에 개구부를 설치하는 경우 개구부의 영향을 파악 하는 것을 목적으로 철근콘크리트 전단벽의 정적가력 실험을 실시했다. 그 결과 개구부 유무에 따른 파괴현상은 벽판에 형성된 압축지주의 단면적이 감소함으로써 다르게 나타났다. 특히 최대 내력은 개구부 설치에 따라 약 35%정도 감소되는 특성을 보였다. 이러한 경향은 강성 및 에너지 소산능력에서도 유사하게 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제12권4호
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• pp.98-106
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• 2008

인양홀을 이용한 정착장치는 손상된 구조물에 내하력을 증가시키기 위해 사용되어지며, 시공이 간편하고 보강효율이 좋은 경제적인 방법이다. 본 논문에서는 구조물에 손상을 입히지 않으면서 충분한 보강효과를 가져 올 수 있는 인양홀 이용 정착장치를 선정하여 그에 대한 적용 가능성을 연구하였다. 실무에서 시공빈도가 높은 인양홀 이용 단부 정착 장치가 적용된 3개의 실험체를 제작하였고, 이에 대한 휨 실험을 수행하여 처짐, 변형률 및 파괴양상을 분석하였다. 인양홀 이용 정착장치가 구비된 철근 콘크리트 보의 보강 성능을 실험적으로 규명하기 위하여 각 실험체의 균열하중, 항복하중, 극한하중, 강선의 응력 증가량, 처짐 및 연성 등을 비교 분석하였다.

• 구강회복응용과학지
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• 제18권3호
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• pp.145-155
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• 2002

본 연구에서는 knitted glass fabric 강화 레진에 대한 치과보철소재로서의 적용가능성을 평가하기 위한 목적으로, 가장 높은 수준의 교합하중이 작용하게 되는 구치부 3본 고정성국소의치에 이 재료를 사용하는 경우에 대해 해석을 수행하였다. 우선 구치부3본 고정성국소의치에 대해 knitted glass fabric 강화 레진을 적용한 두 가지 설계 개념을 상정하였고, 각 설계형상에 대한 유한요소해석을 하였다. 강도 평가를 위해서75N의 생리적인 반복 수직 교합 하중 조건을 부여, 보철물에 유도되는 국소응력을 피로강도측면에서 고찰하였다. 각각의 설계에는 knitted glass fabric을 모재로 하고 보강재로 unidirectional 형의 glass 복합재가 사용되었다. 본 연구에서 개념설계 된 두 가지의 3본 고정성국소의치는 수직 교합 하중 75N 에 대해 충분한 강성과 강도를 가진 것으로 분석되었다. 가공치와 knitted caps사이의 연결 부위에서 국소적인 응력 집중이 관찰되었으나 그 크기는 재료의 피로강도 범위 이내였으며 국소적인 설계변경을 통하여 응력분포를 더욱 개선할 수 있을 것으로 추정하였다. 본 연구를 통해 knitted glass fabric 은 새로운 치과 보철 소재로서의 그 가능성이 기대된다.