• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.3
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• pp.25-34
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• 1993

The long-term behavior, such as in excavation problems of weak medium, can be dealt with by the elasto-viscoplasticity models. In this paper, a combined formulation of elasto-viscoplasticity using boundary elements and finite elements without using internal cells is presented. The domain integral introduced due to the viscoplastic stresses is transformed into a boundary integral applying direct integration in cylindrical coordinates. The results of the developed boundary element analysis are compared with those from the explicit solution and from the finite element analysis. It is observed that the boundary element analysis without internal cells results in some error because of its deficiency in handling the nonlinearity in local stress concentration. Therefore, a coupled analysis of boundary elements and finite elements, in which finite elements are used in the area of stress concentration, is developed. The coupled method is applied to a time dependent inelastic problem with semi-infinite boundaries. It results in reasonable solution compared with other methods where relatively higher degree of freedoms are employed. Thus, it is concluded that the combined analysis may be used for such problems in the effective manner.

• Journal of the Korea Concrete Institute
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• v.24 no.6
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• pp.633-641
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• 2012

In this study, the effects of the inelastic shear behavior of beam-column joint on the response of RC OMRF are evaluated in the inelastic time history analysis. For an example, a 5-story structure for site class SB and seismic design category C was designed in accordance with KBC2009. Bending moment-curvature relationship for beam and column was evaluated using fiber model and bending moment-rotation relationship for beam-column joint was calculated using simple and unified joint shear behavior model and moment equilibrium relationship. The hysteretic behavior was simulated using three-parameter model suggested in IDARC program. The inelastic time history analysis with PGA for return period of 2400 years showed that the model with inelastic beam-column joint yielded smaller maximum base shear force but nearly equivalent maximum roof displacement and maximum story drift as those obtained from analysis using rigid joint. The maximum story drift satisfied the criteria of KBC2009. Therefore, the inelastic shear behavior of beam-column joint could be neglected in the structural design.

• Proceedings of the KAIS Fall Conference
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• 2007.11a
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• pp.382-385
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• 2007

본 연구에서는 기존 연구를 토대로 하여 비탄성 구간에 있는 계단식 I형보의 횡-비틀림 좌굴강도를 범용구조해석 프로그램 ABAQUS(2006)를 이용하여 산정하고, 간편한 설계식을 제안하고 있다. 본 연구 결과는 다양한 형식의 I형보가 사용되는 빌딩 및 교량의 경제적이고 합리적인 설계의 근간을 제공해 줄 것이며, 향후 다양한 하중 조건을 가지는 양단 또는 일단 계단식 단면 변화보의 비탄성 횡-비틀림 좌굴강도를 계산할 수 있는 설계식 개발에 적극 활용 될 수 있을 것이다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.123-134
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• 2019

This paper proposed a new design equation for the inelastic lateral torsional buckling (LTB) of singly symmetric stepped I-beams with non-compact flange sections. The proposed equation was generated using a finite element program, ABAQUS, and a statistical program, MINITAB. The parameters used were the stepped beams parameters; ${\alpha}$, ${\beta}$, and ${\gamma}$ and the length-to-height ratio ($L_b/h$) of the beam. The proposed equation was further validated by means of experimental test, where beams were subjected to four-point bending and supported by roller and lateral braces near the end supports. In addition, finite element models were simulated using the same parameters used in the experimental test to verify the results of the test conducted. It was proved that LTB capacity calculated from the proposed equation is accurate and conservative in comparison with the yielded values from the FEM and actual test, making it a reliable and safe approach in calculating the buckling capacities of singly symmetric stepped beams with non-compact flange sections.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.5A
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• pp.475-484
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• 2010

The purpose of this study is to investigate the inelastic behavior of precast concrete copings for precast segmental PSC bridge columns and to provide the details and reference data. Twelve one-fourth-scale precast concrete copings were tested under quasistatic monotonic loading. In this study, the computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), was used. A joint element is modified to predict the inelastic behaviors of segmental joints. This study documents the testing of precast concrete copings for precast segmental PSC bridge columns and presents conclusions based on the experimental and analytical findings.

• International Journal of Highway Engineering
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• v.11 no.1
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• pp.165-175
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• 2009

With the current move towards adopting mechanistic-empirical concepts in the design of pavement structures, state-of-the-art mechanistic analysis methodologies are needed to determine accurate pavement responses, such as stress, strain, and deformation. Previous laboratory studies of pavement foundation geomaterials, i.e., unbound granular materials used in base/subbase layers and fine-grained soils of a prepared subgrade, have shown that the resilient responses followed by nonlinear, stress-dependent behavior under repeated wheel loading. This nonlinear behavior is commonly characterized by stress-dependent resilient modulus material models that need to be incorporated into finite element (FE) based mechanistic pavement analysis methods to predict more realistically predict pavement responses for a mechanistic pavement analysis. Developed user material subroutine using aforementioned resilient model with nonlinear solution technique and convergence scheme with proven performance were successfully employed in general-purpose FE program, ABAQUS. This numerical analysis was investigated in predicted critical responses and domain selection with specific mesh generation was implemented to evaluate better prediction of pavement responses. Results obtained from both axisymmetric and three-dimensional (3D) nonlinear FE analyses were compared and remarkable findings were described for nonlinear FE analysis. The UMAT subroutine performance was also validated with the instrumented full scale pavement test section study results from the Federal Aviation Administration's National Airport Pavement Test Facility (FAA's NAPTF).

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.11-20
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• 1993

Nonlinear inelastic behavior of an HP saddle shell has been examined by a finite element computer program developed on a Cray Y-MP. The mesh convergence is studied using three progressively refined finite element mesh models, $16{\times}16$, $32{\times}32$ and $64{\times}64$, for the elastic and inelastic analyses. It is shown that the $32{\times}32$ mesh model gives a solution that is very close to that given by the $64{\times}64$ mesh model, thus, showing a convergence. The inelastic analysis shows that the shell has a tremendous capacity to redistribute the stresses. At the ultimate, the concrete cracks and the reinforcement yieldings are spread out all over the shell, indicating that the stress distribution in the shell is approaching that given by the classical membrane theory. The present computer program provides a very useful tool for evaluating the nonlinear ultimate behavior of concrete shells during the design process.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.3
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• pp.191-198
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• 2013

In this paper, the effects of uncertain material constant on the nonlinear behavior of steel frames with semi-rigid joints are examined. As to the probabilistic model, a normal distribution is assumed to simulate the uncertain elastic modulus of steel material. A nonlinear structural analysis program, which can consider both semi-rigidity in joints of the steel frames and uncertainty in the material constant, is developed. Including the geometric, material and connection nonlinearites which are the parameters of nonlinear behavior of steel frames, probabilistic analysis is conducted based on the Monte-Carlo simulation. In the probabilistic analyses, we consider the three different cases for random variables. The deterministic analysis results are shown to be in good agreement with those of the previous research results in the literature. As to the probabilistic analyses, it is observed that the coefficient of variation(COV) of displacements increases as the loading increases, and that the values of COV are dependent on the structural features of the frames.

• Magazine of the Korea Concrete Institute
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• v.9 no.6
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• pp.129-137
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• 1997

본 논문의목적은 단조증가하중을 받는 강판 및 탄소섬유 sheet 로 보강된 철근콘크리트 단순보의 역학적 거동특성을 규명하기 위한 것이다. 본 연구의 목적을 달성하기 위하여 단부응력해석이 고려된 비선형 해석프로그램을 개발하였으며, 적용된 재료비선형모델은 콘크리트인 경우 tensile strain softening이 고려된 응력-변형율선도, 철근과 강판에 대해서는 bilinear 모델, 그리고 탄소섬유 sheet에 대해서는 완전탄성체의 모델이 적용되었다. Debonding 에 대해서는 보강재 단부의 전단응력에 의한 콘크리트박리하중을 Roberts의 해석적방법을 수정하여 계산하였다. 또한 개발된 프로그램은 실험결과 및 ADINA에 의한 해석결과와 비교하였으며, 보강단면 등에 따른 거동을 잘 예측하는 것으로 나타났다.

• Magazine of the Korea Concrete Institute
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• v.5 no.2
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• pp.162-170
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• 1993

축력과 횡력을 받는 전단벽의 휨과 전단 거동을 분리산정하기 위하여 R/C 전단벽에 관한 실험 결과에 대해 System Identification을 행한다. 이를 토대로, 전단벽의 강도 저하 계수 'R'과 극한 회전능력을 구하는 실험식을 제안한다. R/C뼈대구조-전단벽에 대한 비탄성 해석 유한요소 컴퓨터 프로그램(IDARC)을 이용하여 전단벽의 지진 이력 거동을 재현한다. Identification 결과를 Digitize한 실험 결과와의 비교에 의해 검증하고, 총변형으로부터 휨과 전단에 의한 변형요소를 해석적으로 분리 함으로서 비탄성 전단 거동과 강도 저하 계수 'R'의 산정이 가능해진다. 또한 실험 결과에 대한 회귀 분석을 통하여 전단벽의 극한 회전 능력에 대한 실험식이 얻어진다.