• Structural Engineering and Mechanics
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• 제83권3호
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• pp.363-375
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• 2022

Flexural capacity prediction is a challenging problem for externally prestressed concrete beams (EPCBs) due to the unbonded phenomenon between the concrete beam and external tendons. Many prediction equations have been provided in previous research but typically ignored the differences in deformation mode between internal and external unbonded tendons. The availability of these equations for EPCBs is controversial due to the inconsistent deformation modes and ignored second-order effects. In this study, the deformation characteristics and collapse mechanism of EPCB are carefully considered, and the ultimate deflected shape curves are derived based on the simplified curvature distribution. With the compatible relation between external tendons and the concrete beam, the equations of tendon elongation and eccentricity loss at ultimate states are derived, and the geometric interpretation is clearly presented. Combined with the sectional equilibrium equations, a rational and simplified flexural capacity prediction method for EPCBs is proposed. The key parameter, plastic hinge length, is emphatically discussed and determined by the sensitivity analysis of 324 FE analysis results. With 94 collected laboratory-tested results, the effectiveness of the proposed method is confirmed, and comparisons with the previous formulas are made. The results show the better prediction accuracy of the proposed method for both stress increments and flexural capacity of EPCBs and the main reasons are discussed.

• Structural Engineering and Mechanics
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• 제84권6호
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• pp.707-722
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• 2022

In this study, a new refined hyperbolic shear deformation theory (RHSDT) is developed using an equivalent single-layer shell displacement model for the static bending and free vibration response of cross-ply laminated composite spherical shells. It is based on a new kinematic in which the transverse displacement is approximated as a sum of the bending and shear components, leading to a reduction of the number of unknown functions and governing equations. The proposed theory uses the hyperbolic shape function to account for an appropriate distribution of the transverse shear strains through the thickness and satisfies the boundary conditions on the shell surfaces without requiring any shear correction factors. The shell governing equations for this study are derived in terms of displacement from Hamilton's principle and solved via a Navier-type analytical procedure. The validity and high accuracy of the present theory are ascertained by comparing the obtained numerical results of displacements, stresses, and natural frequencies with their counterparts generated by some higher-order shear deformation theories. Further, a parametric study examines in detail the effect of both geometrical parameters (i.e., side-to-thickness ratio and curvature-radius-to-side ratio), on the bending and free vibration response of simply supported laminated spherical shells, which can be very useful for many modern engineering applications and their optimization design.

• Steel and Composite Structures
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• 제49권6호
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• pp.603-614
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• 2023

In this paper, frequency analysis of curved functionally graded (FG) nanobeam by consideration of deepness effect has been studied. Differential transform method (DTM) has been used to obtain frequency responses. The nonlocal theory of Eringen has been applied to consider nanoscales. Material properties are supposed to vary in radial direction according to power-law distribution. Differential equations and related boundary conditions have been derived using Hamilton's principle. Finally, by consideration of nonlocal theory, the governing equations have been derived. Natural frequencies have been obtained using semi analytical method (DTM) for different boundary conditions. In order to study the effect of deepness, the deepness term is considered in strain field. The effects of the gradient index, radius of curvature, the aspect ratio, the nonlocal parameter and interaction of aforementioned parameters on frequency value for different boundary conditions such as clamped-clamped (C-C), clamped-hinged (C-H), and clamped-free (C-F) have been investigated. In addition, the obtained results are compared with the results in previous literature in order to validate present study, a good agreement was observed in the present results.

• 복합신소재구조학회 논문집
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• 제1권3호
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• pp.24-34
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• 2010

본 논문은 전단변형효과를 고려한 복합신소재 적층 쉘을 해석하기 위하여, 일반 쉘의 지배방정식을 유도하고, 이 방정식을 풀기 위하여 수치해석 기법중 하나인 유한차분법을 수행하였다. 유한차분법을 미분방정식을 지배방정식으로 가지는 구조물 해석시 간편하게 사용될 수 있고, 오차의 범위를 선택적으로 정할수 있는 장점이 있다. 수치해석 결과의 타당성을 검증하기 위하여 수렴도 분석과 범용 구조해석 프로그램인 LUSAS의 해석결과와 비교하였다. 본 논문의 목적은 전단변형 효과를 고려한 일반 쉘의 거동 특징 및 분석, 복합재료로 구성되었을 경우 정확한 거동을 분석하고, 쉘 구조물이 보다 높은 강성을 가질 수 있도록 하는 적절한 화이버의 보강방안과 다양한 조건 변화를 통해서 최적의 쉘 구조물을 제시하는 것이다. 쉘의 곡률의 변화에 따른 거동과 합응력의 변화를 분석하고, 쉘의 높이-너비 비와 화이버 보강각도 변화에 따른 처짐 및 합응력의 변화를 비교, 분석하여 보다 유리한 쉘 구조물을 제시하였다. 또한 다양한 하중을 가하여 쉘의 형상 변화를 비교 분석함으로서 비등방성 재료로 이루어진 일반 쉘의 거동에 대하여 분석하였다.

• International Journal of Concrete Structures and Materials
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• 제18권3E호
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• pp.173-181
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• 2006

The objectives of this study are to evaluate the reliability of an existing nonlinear analysis program for predicting the inelastic behavior of reinforced concrete frame with seismic details and to observe the redistribution of the internal forces, which can not be easily measured by an experiment. In order to carry out this task, the nonlinear analysis program of IDARC 2D(3) was run on a 2-bay, 2-story moment-resisting reinforced concrete plane frame with seismic details. (1) The effort to obtain the results of the analysis similar to those of experiment was made by determining the appropriate values of model parameters. The comparison of the analysis results with those of experiment and the observation of the distribution of internal forces obtained through nonlinear analysis points to the following conclusions. (1) The overall relationship between lateral load and lateral displacement given by the analysis is similar to that of experiment. However, the values of initial stiffness and the amount of energy dissipation in the initial displacement steps given by the analysis show larger values than those of experiment. (2) The analysis provided detailed information on the distribution and redistribution of internal forces and proved useful in elucidating the crack pattern, the sequence of the occurrence of plastic hinges, and the failure or yielding mechanism for the whole structure. (3) In spite of the similarity in overall behavior of analysis and experiment, there exists a significant discrepancy in some local behaviors. Furthermore, the hysteresis in the relationship between moment and curvature in some column ends have shown sudden deteriorations in strength, which can not be interpreted satisfactorily at the present time. Therefore, it is necessary to develop a better analytical model to fill this knowledge gap.

• 폴리머
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• 제26권1호
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• pp.105-112
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• 2002

연구는 electro-active polymer(EAP)의 특성을 가지는 ion-exchange polymer metal composite(IPMC)을 이용하여 지능형 대장내시경 개발에 목적을 두고 있다. IPMC는 낮은 구동전압과 빠른 반응속도로 인하여 매우 매력적인 물질이다. 본 연구에서는 IPMC구동기의 전극을 무전의 도금 방법을 이용하여 용액함침-환원방법(impregnation-reduction method)으로 제조하였으며 코팅된 백금전극의 횟수에 따라 변위와 변화를 측정하였다. 구동특성을 알아보기 위하여 길이, 주파수에 대한 변위, 힘을 측정하였으며, 주파수 대역은 저주파 대역과 공명주파수 대역을 사용하는 것이 적합하다는 결론을 얻었다. 또한 다양한 구동적 특성과 수분의 함량에 따른 영향에 대해 고전적 적층 이론 (classical laminate theory, CLT)을 이용하여 이방성 IPMC의 응력분포와 수분이동에 따른 모멘트, 변형률, 곡률(cuvature)을 모델링 하였다.

• 척추신경추나의학회지
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• 제4권1호
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• pp.65-73
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• 2009

Objectives : The propose of this study is to analyze characteristics with sex, age, motivation, symptom, Impression, treatment effect about temporomandibular disorder patients. Method : We performed a retrospective study of 52 patients who visited the Jaseng Hospital of Oriental Medicine, from August 2008 to October 2008. Result : Women occupied the most part. And 27 persons in the 20th are the most distribution of age. The majority of patients occured the symptom for no reason. In the distribution of symptoms, TMD pain(88.46%), Click sound(82.69%), neck pain(52.92%), headache(38.46%), lumbago(21.15%) happened. In the impression through radiological diagnoses, The majority of patients diagnosed Straightening of cervical lordotic curvature. Oriental medical treatment showed a very valuable effect on improvement of TMD symptom. Conclusion : The results showed a valuable treatment effect of temporotandibular disorders on Oriental medical treatment. Therefore this work have the necessity of continuous study and observation and will help us to understand the features of patients who visiting the TMD clinic of Jaseng Hospital of Oriental medicine.

• 대한기계학회논문집A
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• 제20권12호
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• pp.3792-3803
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• 1996

Since the skew beam element has two curvatures which are a curvature and a torsion, spatial behavior of curved beam which cannot be included in one plane can be anlayzed by emploting the skew beam element. The $C^{0}$-continuous skew beam element shows the stiffness locking phenomenon when full integration is employed. The locking phenomenpn is characterized by two typical phenomena ; one is the much smaller displacement thant the exact one and theother is the undelation phenomenon is stress distribution. In this paper, we examine how unmatched coefficient in the constrained energy brings about the locking by Reduced Minimization theory. We perform the numerical ones. These comparisons show that uniformly full integration(UFI), which employs full integration for the constrained energy, entails the locking phenomenon. But the use of uniformly reduced integration(URI) of selectively reduced integration(SRI), which employs reduced integration for constrained energy, does not produce the significant errors of displacements of the undulation phenomenon in stress distribution since they do not entails the locking, Additionally, the error due to the approximated parameters for describing the geometry of skew beam is examined.d.

• 한국전산구조공학회논문집
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• 제23권1호
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• pp.95-110
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• 2010

본 논문에서는 합성보의 부착슬립 효과를 고려할 수 있는 유한요소 수치모델을 제안하고자 한다. 전단연결재가 설치된 슬래브와 거더 경계에서 선형 전단력-슬립 관계를 가정하여, 부착슬립 거동을 해석할 수 있는 수치모델이 구현되었다. 본 수치모델을 통하여 축 방향의 자유도를 부가하지 않고 2절점의 보 요소를 적용하여 합성보 경계에서의 슬립 거동을 고려하는 것이 가능하다. 선형 부분전단 연결이론을 토대로 한 슬립 거동의 지배방정식은 슬래브와 거더 경계에서 힘의 평형상태와 단면 내에서 상수로 가정된 곡률을 바탕으로 결정된다. 또한, 지배방정식 구성에 있어서 요소 양 절점에서의 휨 모멘트 값을 필요로 하기 때문에 유한요소 해석으로 도출되는 상수 모멘트를 요소 내에서 선형으로 분포시켰다. 제안된 수치모델을 적용한 해석결과를 기존 연구의 수치해석 결과 및 실험결과와 비교하였으며, 하중-처짐 곡선의 비교를 통하여 본 모델의 성능을 검증하였다.

• 한국광학회지
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• 제17권2호
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• pp.149-158
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• 2006

가우스 괄호법을 이용한 굴절능 배치 방법과 등가렌즈 설계법으로 기존에 설계한 반도체와이어 본딩 검사용 다중배치 현미경 광학계에 대한 공차 분석을 하였다. 축상 대칭 공차인 곡률과 두께에 대한 공차는 회절 한계에 의한 초점심도 내에서 후방초점거리(BFL)가 변하도록 결정하였고, 축 비대칭 공차인 decenter와 tilt에 대한 공차는 0.7 field에서 공간주파수 50 lp/mm에서의 MTF(Modulation Transfer Function) 변화가 5% 이내가 되도록 시행착오 방법으로 정하였다. 이 결과 공차분포확률에 관계없이 MTF의 감소율이 5% 미만 되는 곳에 가장 많은 확률로 공차가 분포하므로 위와 같은 방법으로 공차를 부여하면 원하는 본 광학계의 결상 성능을 만족시킬 수 있음을 확인하였다.