• Steel and Composite Structures
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• 제26권6호
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• pp.793-808
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• 2018

In this study, the seismic performance of the connections between L-shaped columns composed of concrete-filled steel tubes (L-CFST columns) and H-beams used in high-rise steel frame structures was investigated. Seven full-scale specimens were tested under quasi-static cyclic loading. The variables studied in the tests included the joint type, the axial compression ratio, the presence of concrete, the width-to-thickness ratio and the internal extension length of the side plates. The hysteretic response, strength degradation, stiffness degradation, ductility, plastic rotation capacity, energy dissipation capacity and the strain distribution were evaluated at different load cycles. The test results indicated that both the corner and exterior joint specimens failed due to local buckling and crack within the beam flange adjacent to the end of the side plates. However, the failure modes of the interior joint specimens primarily included local buckling and crack at the end plates and curved corners of the beam flange. A design method was proposed for the flexural capacity of the end plate connection in the interior joint. Good agreement was observed between the theoretical and test results of both the yield and ultimate flexural capacity of the end plate connection.

• Geomechanics and Engineering
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• 제20권5호
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• pp.461-474
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• 2020

Analysing the incompatible deformation and damage evolution around the tunnels in mixed strata is significant for evaluating the tunnel stability, as well as the interaction between the support system and the surrounding rock mass. To investigate this issue, confined compression tests were conducted on upper-soft and lower-hard strata specimens containing a circular hole using a rock testing system, the physical mechanical properties were then investigated. Then, the incompatible deformation and failure modes of the specimens were analysed based on the digital speckle correlation method (DSCM) and Acoustic Emission (AE) data. Finally, numerical simulations were conducted to explore the damage evolution of the mixed strata. The results indicate that at low inclination angles, the deformation and v-shaped notches inside the hole are controlled by the structure plane. Progressive spalling failure occurs at the sidewalls along the structure plane in soft rock. But the transmission of the loading force between the soft rock and hard rock are different in local. At high inclination angles, v-shaped notches are approximately perpendicular to the structure plane, and the soft and hard rock bear common loads. Incompatible deformation between the soft rock and hard rock controls the failure process. At inclination angles of 0°, 30° and 90°, incompatible deformations are closely related to rock damage. At 60°, incompatible deformations and rock damage are discordant due that the soft rock and hard rock alternately bears the major loads during the failure process. The failure trend and modes of the numerical results agree very well with those observed in the experimental results. As the inclination angles increase, the proportion of the shear or tensile damage exhibits a nonlinear increase or decrease, suggesting that the inclination angle of mixed strata may promote shear damage and restrain tensile damage.

• Advances in concrete construction
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• 제8권4호
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• pp.257-267
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• 2019

This paper presents the results of cyclic loading tests on new high-strength concrete (HC) short columns. The seismic performance and deformation capacity of three reinforced high-strength concrete filled Polyvinyl Chloride tube (RHC-PVCT) short columns and one reinforced high-strength concrete (RHC), under pseudo-static tests (PSTs) with vertical axial force was evaluated. The main design parameters of the columns in the tests were the axial compression ratio, confinement type, concrete strength, height-diameter ratio of PVCT. The failure modes, hysteretic curves, skeleton curves of short columns were presented and analyzed. Placing PVCT in the RHC column could be remarkably improved the ultimate strength and energy dissipation of columns. However, no fiber element models have been formulated for computing the seismic responses of RHC-PVCT columns with PVT tubes filled with high-strength concrete. Nonlinear finite element method (FEM) was conducted to predict seismic behaviors. Finite element models were verified through a comparison of FEM results with experimental results. A parametric study was then performed using validated FEM models to investigate the effect of several parameters on the mechanical properties of RHC-PVCT short columns. The parameters study indicated that the concrete strength and the ratio of diameter to height affected the seismic performance of RHC-PVCT short column significantly.

• Computers and Concrete
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• 제25권5호
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• pp.383-400
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• 2020

Due to higher stiffness to weight, higher corrosion resistance, higher strength to weight ratios and good durability, concrete composite structures provide many advantages as compared with conventional materials. Thus, they have wide applications in the field of concrete construction. This research focuses on the structural behavior of steel-tube CFRP confined concrete (STCCC) columns under axial concentric loading. A nonlinear finite element analysis (NLFEA) model of STCCC columns was simulated using ABAQUS which was then, calibrated for different material and geometric models of concrete, steel tube and CFRP material using the experimental results from the literature. The comparative study of the NLFEA predictions and the experimental results indicated that the proposed constitutive NLFEA model can accurately predict the structural performance of STCCC columns. After the calibration of NLFEA model, an extensive parametric study was performed to examine the effects of different critical parameters of composite columns such as; (i) unconfined concrete strength, (ii) number of CFRP layers, (iii) thickness of steel tube and (iv) concrete core diameter, on the axial load capacity. Furthermore, a large database of axial strength of 700 confined concrete compression members was developed from the previous researches to give an analytical model that predicts the ultimate axial strength of composite columns accurately. The comparison of the predictions of the proposed analytical model was done with the predictions of 216 NLFEA models from the parametric study. A close agreement was represented by the predictions of the proposed constitutive NLFEA model and the analytical model.

• 한국재료학회지
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• 제30권10호
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• pp.550-557
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• 2020

Used in the ceramic tile market as a representative building material, relief ceramic tile is showing increased demand recently. Since ceramic tiles are manufactured through a sintering process at over 1,000 ℃ after uniaxial compression molding by loading granule powders into a mold, it is very important to secure the flowability of granular powders in a mold having a relief pattern. In this study, kaolin, silica, and feldspar are used as starting materials to prepare granule powders by a spray dryer process; the surface of the granule powders is subject to hydrophobic treatment with various concentrations of stearic acid. The effect on the flowability of the granular powder according to the change of stearic acid concentration is confirmed by measuring the angle of repose, tap density, and compressibility, and the occurrence of cracks in the green body produced in the mold with the relief pattern is observed. Then, the green body is sintered by a fast firing process, and the water absorption, flexural strength, and durability are evaluated. The surface treatment of the granule powders with stearic acid improves the flowability of the granule powders, leading to a dense microstructure of the sintered body. Finally, the hydrophobic treatment of the granule powders makes it possible to manufacture relief ceramic tiles having a flexural strength of 292 N/cm, a water absorption of 0.91 %, and excellent mechanical durability.

• 콘크리트학회지
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• 제11권1호
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• pp.231-242
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• 1999

면외 바닥하중과 토압과 수압에 의한 면내 압축력을 받는, 깊은 지하구조에 사용되는 플랫플레이트 슬래브에 대한 수치해석연구를 실시하였다. 비선형 유한요서해석을 위하여 재료와 기하학적 비선형효과를 고려한 수치해석프로그램을 개발하였으며, 이 수치해석방법은 4 변이 단순지지된 플레이트에 대한 실험결과와 비교에 의하여 검증되었다. 해석모델로서 국내 콘크리트계산규준의 직접설계법에 의하여 설계된 플랫플레이트 슬래브가 사용되었다. 하중조합과 하중순서에 대한 연구를 통하여 플랫플레이트 슬래브의 강도를 지배하는 하중조건을 연구하였으며, 이 지배하중을 받는 슬래브에 대한 변수연구를 통하여 철근비, 형상비, 콘크리트강도, 세장비에 따를 슬래브의 강도변화를 연구하였다. 이 연구결과를 바탕으로 바닥하중증대법을 제시하였다.

• 터널과지하공간
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• 제19권2호
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• pp.158-166
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• 2009

Hoek-Brown 암석에서 응력에 의해 발생되는 균열의 전파특성을 수치해석적으로 분석하기 위한 기초연구로서 탄성균열의 균질화 기법이 제안되었다. 균열의 개시조건으로 Hoek-Brown 경험식이 이용되었고, 균열의 방향 탐색을 위해 임계면법이 이용되었다. 균열물질과 무결암으로 구성된 대표체적에 대해 체적평균 응력 및 변형률 개념을 적용하여 균열과 신선암의 역학적 특성을 균질화시킴으로써 등가 이방성매질의 구성관계식을 유도하였다. 제안된 균질화모델을 포트란 코드로 작성하여 상업유한요소 코드인 COSMOSM에 이식하였다. 제안된 수치해석모델의 적합성을 검증하기 위하여 2차원 평면변형률조건에서 수치 일축압축시험을 실시하였다. 모델 상하부 가압면의 구속조건을 달리한 2가지 해석모델을 선정하여 구속조건이 일축압축시험편의 변형 및 파단면 형성형태에 미치는 영향이 분석되었다. 균열의 균질화를 고려한 수치 일축압축시험 결과는 실제 실험에서 발생되는 형태와 유사한 변형거동 및 파단면 형성 특성을 잘 나타내었다.

• 터널과지하공간
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• 제29권6호
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• pp.523-531
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• 2019

암석역학이나 암반공학의 여러 활용 분야 중 발파, 천공 및 기계굴착의 경우에는 파괴인성이 중요한 요소이며, 암석의 파괴인성을 측정하기 위한 여러 가지 방법들이 제안되었다. 본 연구에서는 간단히 시험편을 제작할 수 있고, 압축 하중으로 암석의 모드 I 파괴인성을 구할 수 있도록 쐐기 분열 시험편(Wedge Splitting Test Specimen)을 이용하였다. 쐐기의 작용하는 연직하중에 의한 수직 및 수평하중 모두를 고려한 균열선단의 응력상태로부터 수치해석을 통한 응력확대계수의 식을 제안하였다. 쐐기 분열 시험편에 의해 구해진 모드 I 파괴인성값을 GD와 SENB 시험편의 시험 결과와 비교하여 시험법의 타당성을 확인하였다.

• 한국운동역학회지
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• 제19권3호
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• pp.603-610
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• 2009

본 연구의 목적은 드롭 착지 동작 시 탄성 섬유 바지 착용이 충격력과 근육 활동에 어떠한 영향을 미치는가를 분석하는데 있다. 10명의 피험자를 대상으로 7쌍의 표면전극을 대퇴직근, 내측광근, 외측광근, 대퇴이두근, 전경골근, 내측비복근, 외측비복근에 부착하고 탄성 바지와 일반 바지를 무작위로 착용한 상태로 플랫폼에서 드롭 랜딩하였고 각 변인에 대해 대응표본 t-검증을 실시하여 통계적 유의차를 밝혔다(p< .05). 착지 구간 동안 전경골근, 대퇴이두근, 내측비복근의 평균적분 근전도치가 일반바지 착용 시 유의하게 감소되었다. 대퇴직근을 제외한 모든 근육에서 최대적분 근전도가 탄성바지 착용 집단이 높게 나타났다. 탄성바지 착용 시 신체 하지분절의 감속과 안정을 유지하기 위한 근육 동원 능력이 높아져 이러한 현상이 발생되어진 것으로 사료된다. 탄성바지 착용이 충격력과 부하율의 감소에 통계적으로 유의한 결과를 발생시키지 못하였다. 본 연구에서 사용된 탄성바지는 피험자의 하지 둘레에 적합하게 제작되어진 바지가 아니기 때문에 탄성과 압축력이 이상적으로 발생되지 못한 것으로 판단된다.

• 대한조선학회논문집
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• 제48권3호
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• pp.275-280
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• 2011

In the present study, a unified viscoplastic-damage model has been applied in order to describe the mechanical characteristics of fresh water ice such as nonlinear material behavior and volume fraction. The strain softening phenomenon of fresh water ice under quasi-static compressive loading has been evaluated based on unified viscoplastic model. The material degradation such as growth of slip/fraction has quite close relation with material inside damage. The volume fraction phenomenon of fresh water ice has been identified based on volume fraction (nucleation and growth of damage) model. The viscoplastic-damage model has been transformed to the fully implicit formulation and the discretized formulation has been implemented to ABAQUS user defined subroutine (User MATerial: UMAT) for the benefit of application of commercial finite element program. The proposed computational analysis method has been compared to uni-axial compression test of fresh water ice in order to validate the compatibilities, clarities and usefulness.