• Structural Engineering and Mechanics
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• 제41권5호
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• pp.645-662
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• 2012

Deteriorative effects of steel corrosion on the structural response of reinforced concrete are simulated for varying degrees of corrosion. The simulation approach is based on a three-dimensional irregular lattice model of the bulk concrete, in which fracture is modeled using a crack band approach that conserves fracture energy. Frame elements and bond link elements represent the reinforcing steel and its interface with the concrete, respectively. Polylinear stress-slip properties of the link elements are determined, for several degrees of corrosion, through comparisons with direct pullout tests reported in the literature. The link properties are then used for the lattice modeling of reinforced concrete beams with similar degrees of corrosion of the main reinforcing steel. The model is successful in simulating several important effects of steel corrosion, including increased deflections, changes in flexural cracking behavior, and reduced yield load of the beam specimens.

• Coupled systems mechanics
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• 제7권6호
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• pp.669-690
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• 2018

This paper deals with numerical modeling of dynamic failure phenomena in rate-sensitive brittle and/or ductile materials. To this end, a two-dimensional continuum viscodamage-embedded discontinuity model, which is based on our previous work (see Do et al. 2017), is developed. More specifically, the pre-peak nonlinear and rate-sensitive hardening response of the material behavior, representing the fracture-process zone creation, is described by a rate-dependent continuum damage model. Meanwhile, an embedded displacement discontinuity model is used to formulate the post-peak response, involving the macro-crack creation accompanied by exponential softening. The numerical implementation in the context of the finite element method exploiting the second-order mid-point scheme is discussed in detail. In order to show the performance of the model several numerical examples are included.

• Advances in materials Research
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• 제13권2호
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• pp.87-102
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• 2024

This paper is focused on the delamination analysis of a multilayered beam structure loaded in torsion under strain-path control. The beam under consideration has a rectangular cross-section. The layers of the beam are made of different viscoelastic materials which exhibit continuous inhomogeneity in longitudinal direction. Since the delamination is located inside the beam structure, the torsion moments in the two crack arms are obtained by modeling the beam as an internally static undetermined structure. The strain energy stored in the beam is analyzed in order to derive the strain energy release rate (SERR). Since the delamination is located inside the beam, the delamination has two tips. Thus, solutions of the SERR are obtained for both tips. The solutions are verified by analyzing the beam compliance. Delamination analysis with bending-torsion coupling is also performed. The solutions derived are timedependent due to two factors. First, the beam has viscoelastic behavior and, second, the angle of twist of the beam-free end induced by the external torsion moment changes with time according to a law that is fixed in advance.

• Steel and Composite Structures
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• 제27권5호
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• pp.577-598
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• 2018

The imperfect steel-concrete interface bonding is an important deficiency of the concrete-filled double skin tubular (CFDST) columns that led to separating concrete and steel surfaces under lateral loads and triggering buckling failure of the columns. To improve this issue, it is proposed in this study to use longitudinal and transverse steel stiffeners in CFDST columns. CFDST columns with different patterns of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes were analyzed under constant axial force and reversed cyclic loading. In the finite element modeling, the confinement effects of both inner and outer tubes on the compressive strength of concrete as well as the effect of discrete crack for concrete fracture were incorporated which give a realistic prediction of the seismic behavior of CFDST columns. Lateral strength, stiffness, ductility and energy absorption are evaluated based on the hysteresis loops. The results indicated that the stiffeners had determinant role on improving pinching behavior resulting from the outer tube's local buckling and opening/closing of the major tensile crack of concrete. The lateral strength, initial stiffness and energy absorption capacity of longitudinally stiffened columns with fixed-free end condition were increased by as much as 17%, 20% and 70%, respectively. The energy dissipation was accentuated up to 107% for fixed-guided end condition. The use of transverse stiffeners at the base of columns increased energy dissipation up to 35%. Axial load ratio, hollow ratio and concrete strength affecting the initial stiffness and lateral strength, had negligible effect of the energy dissipation of the columns. It was also found that the longitudinal stiffeners and transverse stiffeners have, respectively, negative and positive effects on ductility of CFDST columns. The conclusions, drawn from this study, can in turn, lead to the suggestion of some guidelines for the design of CFDST columns.

• 터널과지하공간
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• 제19권5호
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• pp.440-449
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• 2009

LCM 시험은 TBM에서의 디스크 커터 설계와 굴진성능 예측을 위한 가장 신뢰성 있는 시험 중의 하나이다. 그러나 이는 실대형 암석시료의 채취, 운반 및 거치에 많은 비용이 소요되는 단점을 가지고 있으며, 절리가 포함된 시료에 대한 시험이 용이하지 않아 시험에서 예측된 모델을 설계에 활용하기 어려운 경우가 많다. 따라서 LCM 시험이 갖는 이러한 경제적 시간적 제약점들을 극복할 수 있는 현실성 있는 수치모델링이 고려된다면, 현장에서의 복잡한 검토과정 없이 현장에 직접 적용할 수 있는 적합한 형태의 TBM 절삭모델을 제시할 수 있을 것이다. 본 연구에서는 UDEC을 이용하여 단일절리를 포함한 암석시료에 대한 디스크 커터의 절삭 메커니즘 분석을 위해 디스크 커터의 가압지점의 위치와 절리의 방향성에 따른 균열전파양상을 분석하였으며, 이를 통하여 절리의 방향에 따른 적절한 디스크 커터의 가압지점 위치 및 디스크 커터의 적정 간격을 도출하였다.

• 비파괴검사학회지
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• 제20권2호
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• pp.130-137
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• 2000

대표적인 비파괴 평가 기술들 중의 하나인 초음파응용 기술은 각종 구조물에 존재하는 내부결함에 의한 산란신호를 통해 건전성을 평가하는 기법이므로 결함의 신뢰성 높은 정량적 평가를 위해서는 결함으로부터의 초음파 산란신호특성에 대한 기본적 이해가 필수적이며 따라서 이를 위한 모델링 수치해석 연구가 요구된다. 모델링 기법들은 비파괴 평가기술에 있어서 중요한 역할을 하고 있고 많은 모델링 기법들이 결함의 탄성파 산란문제를 해석하기 위하여 사용되어 오고 있다. 본 연구에서는 다양한 수치기법들 중 탄성파 산란문제 해석에 있어 많은 장점을 가지고 있는 동탄성 경계요소법에 대하여 자세히 소개하고, 응용 예로서 경계요소법을 이용한 기공결함의 수평횡파 산란장 해석과 표면균열의 표면파 산란장 해석을 소개한다.

• 한국전산구조공학회논문집
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• 제20권4호
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• pp.501-507
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• 2007

본 연구의 전편에서는 이동최소제곱 유한차분법을 이용한 고체역학문제의 정식화 과정이 소개되었다. 후편에서는 수치예제를 통해 이동최소제곱 유한차분법의 정확성, 강건성, 효율성을 검증했다. 탄성론 문제의 해석을 통해 개발된 해석기법의 우수한 수렴률을 확인했다. 탄성균열문제에 적용하여 간편한 불연속면 모델링이 가능하고, 적응적 절점배치를 통해 특이 응력해를 정확하고 효율적으로 계산할 수 있음을 보였다. 국소화 밴드문제 해석결과를 통해 변위나 응력이 급격하게 변화하는 특수문제에 대한 정확성과 효율성을 확인했으며, 본 해석기법이 다양한 특수 공학적 문제로 확장될 수 있을 것으로 기대된다.

• Structural Engineering and Mechanics
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• 제90권4호
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• pp.371-390
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• 2024

Investigating the impact of openings on the structural behavior of ferrocement I-beams with two distinct types of reinforcing metallic and non-metallic meshes is the primary goal of the current study. Up until failure, eight 250x200x2200 mm reinforced concrete I-beams were tested under flexural loadings. Depending on the kind of meshes used for reinforcement, the beams are split into two series. A control I-beam with no openings and three beams with one, two, and three openings, respectively, are found in each series. The two series are reinforced with three layers of welded steel meshes and two layers of tensar meshes, respectively, in order to maintain a constant reinforcement ratio. Structural parameters of investigated beams, including first crack, ultimate load, deflection, ductility index, energy absorption, strain characteristics, crack pattern, and failure mode were reported. The number of mesh layers, the volume fraction of reinforcement, and the kind of reinforcing materials are the primary factors that vary. This article presents the outcomes of a study that examined the experimental and numerical performance of ferrocement reinforced concrete I-beams with and without openings reinforced with welded steel mesh and tensar mesh separately. Utilizing ANSYS-16.0 software, nonlinear finite element analysis (NLFEA) was applied to illustrate how composite RC I-beams with openings behaved. In addition, a parametric study is conducted to explore the variables that can most significantly impact the mechanical behavior of the proposed model, such as the number of openings. The FE simulations produced an acceptable degree of experimental value estimation, as demonstrated by the obtained experimental and numerical results. It is also noteworthy to demonstrate that the strength gained by specimens without openings reinforced with tensar meshes was, on average, 22% less than that of specimens reinforced with welded steel meshes. For specimens with openings, this value is become on average 10%.

• Elastomers and Composites
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• 제48권2호
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• pp.172-179
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• 2013

고분자 소재의 충격강도 증대를 위해 충격보강제를 이용하는 경우가 많다. 본 연구에서는 충격보강제가 함유된 나일론6에 대해서 충격보강 원리를 분석하고자 충격시험을 모사하였다. 이를 위해 나일론6에 포함된 충격보강제인 고무 첨가제의 모델링을 시도하였다. 모델링을 토대로 충격시험을 모사하고 충격시편 단면에서의 응력 분포 및 방향을 통해 충격강도 증대 원리를 관찰하였다. 시편 단면에서 충격보강제 유무에 따른 해석을 하여 비교하였고, 충격보강을 위해 사용되는 고무첨가제의 표면처리 여부에 따른 해석도 수행하여 응력을 비교하였다. 해석결과 노치에서 발생한 응력이 내부로 전파되면서 충격보강제 주변으로 경로가 바뀌면서 응력이 감소되는 현상이 나타났다. 특히 충격보강제를 함유한 시편에서 노치부 표면의 응력이 낮았다. 또한, 크랙이 발생하는 방향과 직각인 방향의 주 응력 크기도 충격보강제를 포함한 시편에서 낮게 나타났다. 이로 인해 크랙의 전파가 감소되고 충격강도가 증대되었다고 분석된다. 이러한 컴퓨터모사 방법은 복합재료의 물성 증대 원인을 파악하는데 활용할 수 있다고 판단된다.

• Interaction and multiscale mechanics
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• 제2권1호
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• pp.69-89
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• 2009

Reinforced and prestressed concrete (RC and PC) thin walls are crucial to the safety and serviceability of structures subjected to shear. The shear strengths of elements in walls depend strongly on the softening of concrete struts in the principal compression direction due to the principal tension in the perpendicular direction. The past three decades have seen a rapid development of knowledge in shear of reinforced concrete structures. Various rational models have been proposed that are based on the smeared-crack concept and can satisfy Navier's three principles of mechanics of materials (i.e., stress equilibrium, strain compatibility and constitutive laws). The Cyclic Softened Membrane Model (CSMM) is one such rational model developed at the University of Houston, which is being efficiently used to predict the behavior of RC/PC structures critical in shear. CSMM for RC has already been implemented into finite element framework of OpenSees (Fenves 2005) to come up with a finite element program called Simulation of Reinforced Concrete Structures (SRCS) (Zhong 2005, Mo et al. 2008). CSMM for PC is being currently implemented into SRCS to make the program applicable to reinforced as well as prestressed concrete. The generalized program is called Simulation of Concrete Structures (SCS). In this paper, the CSMM for RC/PC in material scale is first introduced. Basically, the constitutive relationships of the materials, including uniaxial constitutive relationship of concrete, uniaxial constitutive relationships of reinforcements embedded in concrete and constitutive relationship of concrete in shear, are determined by testing RC/PC full-scale panels in a Universal Panel Tester available at the University of Houston. The formulation in element scale is then derived, including equilibrium and compatibility equations, relationship between biaxial strains and uniaxial strains, material stiffness matrix and RC plane stress element. Finally the formulated results with RC/PC plane stress elements are implemented in structure scale into a finite element program based on the framework of OpenSees to predict the structural behavior of RC/PC thin-walled structures subjected to earthquake-type loading. The accuracy of the multiscale modeling technique is validated by comparing the simulated responses of RC shear walls subjected to reversed cyclic loading and shake table excitations with test data. The response of a post tensioned precast column under reversed cyclic loads has also been simulated to check the accuracy of SCS which is currently under development. This multiscale modeling technique greatly improves the simulation capability of RC thin-walled structures available to researchers and engineers.