• 터널과지하공간
• /
• 제11권3호
• /
• pp.225-236
• /
• 2001

암반 절리면의 거칠기는 전단강도 및 변형거동에 가장 중요한 영향을 미치는 요소 중의 하나이다. 절리면은 전단변형이 발생하는 동안 손상을 받게 되고 이에 따라 거칠기각은 연속적으로 낮아진다. 절리면의 수직팽창성과 강도 경화 및 연화현상도 거칠기의 변화와 관련이 있는 것으로 이해되고 있다. 따라서 절리면의 거칠기의 변화를 효율적으로 반영시킬 수 있는 수치해석 모델의 개발이 중요하다. 이 연구에서는 탄소성이론을 바탕으로 거칠기 변화를 고려할 수 있는 탄소성 응력-변형 증분식을 유도하여 절리면 거질기 변화가 절리면 전단거동에 미치는 영향을 정량적으로 평가하는데 이용하였다. 유도된 탄소성 증분식을 검증하기 위하여 수치 주기전단시험을 실시하였다. 수치시험결과 개발된 탄소성 증분식은 거친 절리면의 주기전단시험에 나타나는 일반적인 현상들을 모사하는데 효과적임을 알 수 있었다.

• Computers and Concrete
• /
• 제25권1호
• /
• pp.67-73
• /
• 2020

Traditionally used analytical approach to predict the fatigue failure of reinforced concrete (RC) structure is generally conservative and has certain limitations. The nonlinear finite element method (FEM) offers less expensive solution for fatigue analysis with sufficient accuracy. However, the conventional implicit dynamic analysis is very expensive for high level computation. Whereas, an explicit dynamic analysis approach offers a computationally operative modelling to predict true responses of a structural element under periodic loading and might be perfectly matched to accomplish long life fatigue computations. Hence, this study simulates the fatigue behaviour of RC beams with finite element (FE) assemblage presenting a simplified explicit dynamic numerical solution to show computer aided fatigue behaviour of RC beam. A commercial FEM package, ABAQUS has been chosen for this complex modelling. The concrete has been modelled as a 8-node solid element providing competent compression hardening and tension stiffening. The steel reinforcements are simulated as two-node truss elements comprising elasto-plastic stress-strain behaviour. All the possible nonlinearities are duly incorporated. Time domain analysis has been adopted through an automatic Newmark-β time incremental technique. The program consists of twelve RC beams to visualize the real behaviour during fatigue process and to obtain the reliability of the study. Both the numerical and experimental results indicate a redistribution of stresses along the time and damage accumulation of beam which severely affect the serviceability and ultimate capacity of RC beam. The output of the FEM analysis demonstrates good match with the experimental consequences which affirm the efficacy of the computer aided model. The controlled fatigue damage evolution at service fatigue load limits makes the FE model an efficient tool in predicting high cycle fatigue behaviour of RC structures.

• 한국지반공학회지:지반
• /
• 제12권1호
• /
• pp.73-86
• /
• 1996

본 연구에서는 국내 8개 석탄화력발전소에서 발생하는 석탄회중 영월화력발전소에서 부산되는 석탄회를 주 대상으로 순수 비회(FA)와 저회(BA), 회사장에 투기되는 흔합회(FA:BA=8:2), 적정비로 혼합된 석탄회(FA:BA=5:5),그리고 일반도로성토재에 대하여 토질역학시험을 통해 공학적 특성이 비교, 분석되었으며 석탄회를 성토재 및 매립재로서 대규모로 이용할 경우의 변형해석을 위해 Hyperbolic Mode야 적용시 필요한 제반 변수를 산정하였다. 석탄회의 토공재로서의 활용 가능성을 검토한 결과 석탄회는 동일입도의 일반 홀에 비해 강도 정수 등 유리한 공학적 특성을 갖고 있으며,특히 연약지반상에 매립 또는 구조물 됫채움재로서 사용할 경우 자경성, 경량성 등 우수한 조건을 지니고 있다.

• 한국지진공학회논문집
• /
• 제12권5호
• /
• pp.23-29
• /
• 2008

강도한계 이선형 단자유도 시스템의 지진 하중 하에서의 동적 불안정에 대해 연구하였다. 강도한계 이선형 이력 모델은 철골 모멘트 골조의 이력거동을 가장 잘 모사한다. 단자유도 시스템의 동적 불안정을 판단하기 위해 붕괴 강도비를 사용하였고, 이것은 붕괴가 일어날 때의 항복강도 저감계수이다. 단단한 지반에서 측정된 240개의 지진을 이용하고 고유주기, 강성 경화 기울기, 음강성 기울기, 연성 그리고 $2{\sim}20%$의 감쇠비를 변수로 하여 강도한계 이선형 단자유도 시스템의 붕괴 강도비의 평균과 편차 값들을 구할 수 있도록 통계 분석을 하였다. 비선형 회귀분석을 통해 강도한계 이선형 단자유도 시스템의 붕괴 강도비의 평균과 표준편차를 계산할 수 있는 식을 구하였다. 제안한 식을 이용하여 붕괴 강도비의 확률적 분포를 구하였고, 실제 값과 비교하여 제안한 식의 정확성을 입증하였다.

• 대한조선학회논문집
• /
• 제34권1호
• /
• pp.77-86
• /
• 1997

최근들어 안전하고 합리적인 구조를 설계하기 위하여 구조물의 내충돌 또는 내충격에 대한 요구와 관심이 높아지고 있는데, 이러한 문제들은 아주 짧은 시간동안에 대변형이 일어나는 비선형문제라는 특징이 있다. 구조재료는 변형속도가 빨라짐에 따라 정적인 범주에서 보이는 거동과는 달리 변형률 의존적인 거동을 보인다. 따라서 대변형 소성문제인 충돌해석 등에는 종래 사용하여 온 변형률 비의존 재료구성방정식으로는 한계가 있다. 이 논문에서는 이러한 점을 개선하기 위하여 연강의 소성거동을 잘 나타낼 수 있는 소성슬립모델을 채용하고, 비선형경화를 도입하여 변형도 적용범위를 확장한 대변형 탄소성 변형률의존 재료구성방정식을 제시하였다. 본 구성방정식의 특징으로 항복조건과 하중조건이 필요없기 때문에 계산이 간편하며, 전위밀도와 속도로써 소성을 표현하기 때문에 보다 물리적인 의미를 가지고 금속재료의 소성현상을 나타낼 수 있다.

• 대한조선학회논문집
• /
• 제53권2호
• /
• pp.85-91
• /
• 2016

The most important factor in the structural design of ships and offshore structures operating in arctic region is ice load, which results from ice-structure interaction during the ice collision process. The mechanical properties of ice related to strength and failure, however, show very complicated aspect varying with temperature, volume fraction of brine, grain size, strain rate and etc. So it is nearly impossible to establish a perfect material model of ice satisfying all the mechanical characteristics completely. Therefore, in general, ice collision analysis was carried out by relatively simple material models considering only specific aspects of mechanical characteristics of ice and it would be the most significant cause of inevitable errors in the analysis. Especially, it is well-known that the most distinctive mechanical property of ice is high dependency on strain rate. Ice shows brittle attribute in higher strain rate while it becomes ductile in lower strain rate range. In this study, the simulation method of ice collision to ship hull using the nonlinear dynamic FE analysis was dealt with. To consider the strain rate effects of ice during ice-structural interaction, strain rate dependent constitutive model in which yield stress and hardening behaviors vary with strain rate was adopted. To reduce the huge amount of computing time, the modeling range of ice and ship structure were restricted to the confined region of interest. Under the various scenario of ice-ship hull collision, the structural behavior of hull panels and failure modes of ice were examined by nonlinear FE analysis technique.

• Advances in nano research
• /
• 제10권2호
• /
• pp.151-163
• /
• 2021

The main target of this study is to investigate nonlinear transient responses of moving polymer nano-size plates fortified by means of Graphene Platelets (GPLs) and resting on a Winkler-Pasternak foundation under a transverse pressure force and a temperature variation. Two graphene spreading forms dispersed through the plate thickness are studied, and the Halpin-Tsai micro-mechanics model is used to obtain the effective Young's modulus. Furthermore, the rule of mixture is employed to calculate the effective mass density and Poisson's ratio. In accordance with the first order shear deformation and von Karman theory for nonlinear systems, the kinematic equations are derived, and then nonlocal strain gradient scheme is used to reflect the effects of nonlocal and strain gradient parameters on small-size objects. Afterwards, a combined approach, kinetic dynamic relaxation method accompanied by Newmark technique, is hired for solving the time-varying equation sets, and Fortran program is developed to generate the numerical results. The accuracy of the current model is verified by comparative studies with available results in the literature. Finally, a parametric study is carried out to explore the effects of GPL's weight fractions and dispersion patterns, edge conditions, softening and hardening factors, the temperature change, the velocity of moving nanoplate and elastic foundation stiffness on the dynamic response of the structure. The result illustrates that the effects of nonlocality and strain gradient parameters are more remarkable in the higher magnitudes of the nanoplate speed.

• Geomechanics and Engineering
• /
• 제27권5호
• /
• pp.465-479
• /
• 2021

One of the important causes of building and infrastructure failure, such as bridges on pile foundations, is the placement of the piles in liquefiable soil that can become unstable under seismic loads. Therefore, the overarching aim of this study is to investigate the seismic behavior of a soil-pile system in liquefiable soil using three-dimensional numerical FEM analysis, including soil-pile interaction. Effective parameters on concrete pile response, involving the pile diameter, pile length, soil type, and base acceleration, were considered in the framework of finite element non-linear dynamic analysis. The constitutive model of soil was considered as elasto-plastic kinematic-isotropic hardening. First, the finite element model was verified by comparing the variations on the pile response with the measured data from the centrifuge tests, and there was a strong agreement between the numerical and experimental results. Totally 64 non-linear time-history analyses were conducted, and the responses were investigated in terms of the lateral displacement of the pile, the effect of the base acceleration in the pile behavior, the bending moment distribution in the pile body, and the pore pressure. The numerical analysis results demonstrated that the relationship between the pile lateral displacement and the maximum base acceleration is non-linear. Furthermore, increasing the pile diameter results in an increase in the passive pressure of the soil. Also, piles with small and big diameters are subjected to yielding under bending and shear states, respectively. It is concluded that an effective stress-based ground response analysis should be conducted when there is a liquefaction condition in order to determine the maximum bending moment and shear force generated within the pile.

• Steel and Composite Structures
• /
• 제44권2호
• /
• pp.155-169
• /
• 2022

In the present paper an analytical model was developed to study the non-linear vibrations of Functionally Graded Carbon Nanotube (FG-CNT) reinforced doubly-curved shallow shells using the Multiple Scales Method (MSM). The nonlinear partial differential equations of motion are based on the FGM shallow shell hypothesis, the non-linear geometric Von-Karman relationships, and the Galerkin method to reduce the partial differential equations associated with simply supported boundary conditions. The novelty of the present model is the simultaneous prediction of the natural frequencies and their mode shapes versus different curvatures (cylindrical, spherical, conical, and plate) and the different types of FG-CNTs. In addition to combining the vibration analysis with optimization algorithms based on the genetic algorithm, a design optimization methode was developed to maximize the natural frequencies. By considering the expression of the non-dimensional frequency as an objective optimization function, a genetic algorithm program was developed by valuing the mechanical properties, the geometric properties and the FG-CNT configuration of shallow double curvature shells. The results obtained show that the curvature, the volume fraction and the types of NTC distribution have considerable effects on the variation of the Dimensionless Fundamental Linear Frequency (DFLF). The frequency response of the shallow shells of the FG-CNTRC showed two types of nonlinear hardening and softening which are strongly influenced by the change in the fundamental vibration mode. In GA optimization, the mechanical properties and geometric properties in the transverse direction, the volume fraction, and types of distribution of CNTs have a considerable effect on the fundamental frequencies of shallow double-curvature shells. Where the difference between optimized and not optimized DFLF can reach 13.26%.

• 농업과학연구
• /
• 제13권2호
• /
• pp.255-264
• /
• 1986

수확시기(收穫時期)의 벼줄기에 대(對)한 역학적(力學的), 점탄성적(粘彈性的) 특성(特性)을 구명(究明)하기 위(爲)해 압축시(壓縮時) 최대압축하중(最大壓縮荷重), 이력현상(履歷現象), 가공경화현상(加工硬化現象) 및 점탄성(粘彈性) 거동(粘彈性)에 대(對)한 변형속도(變形速度), 초기하중(初期荷重)이 영향을 분석(分析)하며, 도해법(圖解法) 및 computer에 의(依)한 수치해법(數値解法)으로 하중이완(荷重弛緩)의 rheological model 을 제시(提示)코져 시험(試驗)한 결과(結果)는 다음과 같다. 1. 압축시험시(壓縮試驗時) 벼줄기의 최대압축하중(最大壓縮荷重)은 다수계(多收系) 품종(品種)보다 일반계(一般系)에서 큰 경향(傾向)이었다. 2. 동진벼의 부위별(部位別) 최대압축하중(最大壓縮荷重)은 4절간이 가장 컷고, 3절간, 1절간 하부(下部), 2절간, 1절간 상부(上部)의 순(順)으로 작았다. 3. 비례한도내(比例限度內)의 하중(荷重)으로 loading-unloading 할 때 일부의 잔유변형이 발생(發生)하여 탄소성(彈塑性) 변형(變形)을 일으켜 이력손실(履歷損失)을 가져왔다. 4. Loading-unloading cycle을 반부(反復)하면 소성변형(塑性變形)이 감소(減少)하여 가공경화현상(加工硬化現象)을 보였다. 5. 하중이완거동(荷重弛緩擧動)은 변형속도(變形速度)의 증가(增加)에 따라 이완속도(弛緩速度)가 빨라졌다. 6. Computer에 의(依)한 수치해법(數値解法)과 도해법(圖解法)으로 이완거동(弛緩擧動)을 분석(分析)한 결과(結果) 3개지수항(個指數項)으로 표시(表示)되고 일반화(一般化) Maxwell model로 나타내었다. 이 model의 rheology 방정식(方程式)은 다음과 같다. $$F(t)=C_1e^{{-t/{\tau}}_1}+C_2e^{{-t/{\tau}}_2}+C_3e^{{-t/{\tau}}_3}$$ 동진벼줄기의 함수율(含水率) 71.9%(w.b.), 초기하중(初期荷重) 45.5 N, 변형속도(變形速度) 38mm/min 일 때 하중이완(荷重弛緩) 방정식(方程式)은 다음과 같았다. $$F(t)=24.3e^{-t/1006}+7.6e^{-t/12.7}+13.6e^{-t/1.8}$$ 7. 초기변형(初期變形)이 클수록 하중이완(荷重弛緩)은 크게 일어났다.