• 한국강구조학회 논문집
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• 제14권1호
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• pp.23-29
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• 2002

거더와 가로보를 포함하는 많은 교량시스템과 콘크리트 상판은 특별직교이방성 판처럼 거동한다. 그런데 Navier나 Levy의 해로 해결할 수 없는 경계조건을 가졌거나, 불규칙 단면을 가진 경에에 해석해를 얻기 것이 매우 어렵다. 더구나 이러한 경우, 고유치 문제에 대한 수치해법은 너무 복잡하다. 그러나 불규칙 단면을 갖는 보와 탑에 대해, 첫 번째 진동모드에 해당하는 고유진동수를 계산하는 방법이 1974년 '김'에 의해 개발되어 발표되었다. 최근에 이 방법은 2차원 문제로 확장되었고 전단변형이 고려된 복합판에 적용되어 왔다. 본 연구에서는 이 방법을 다양한 경계조건을 갖는 특별직교이방성 복합적층판에 적용하여 타당성을 검토하고 그 해석결과를 제시한다.

• 한국강구조학회 논문집
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• 제23권5호
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• pp.607-614
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• 2011

본 연구는 복합신소재로 구성된 중앙 개구부를 갖는 적층 판구조의 비선형 동적 거동을 다룬다. 1차 전단 변형 판이론에 기반하여, 비선형 동적 방정식의 해는 Newmark 방법과 Newton-Raphson 반복법을 혼용하여 적용하여 산정하였다. 본 연구에서 개발한 유한요소 해석프로그램을 사용하여 개구부의 크기와 적층 배열의 변화가 판의 기하학적 비선형 거동에 미치는 영향을 상세 분석하였다. 몇 가지 수치해석 결과는 기존 연구자로부터 얻어진 결과와 잘 일치하는 것으로 나타났다. 본 연구의 새로운 결과는 경사 적층 구조의 중앙 개구부의 크기와 적층 배열과의 중요한 상호관계를 보여준다. 몇 가지 수치예제는 개구부를 갖는 적층 판구조를 설계하는데 필요한 가이드라인을 제시하였다.

• 한국강구조학회 논문집
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• 제28권4호
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• pp.231-242
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• 2016

대형기둥의 제작성과 시공성을 고려한 철근콘크리트기둥-강재보 접합부의 상세를 제안하였으며, 이를 적용한 접합부의 내진성능을 연구하였다. 접합부의 보강을 위하여, 교차보, 스터드, U형 타이 등의 상세를 고려하였다. 내진성능의 평가를 위해, 2/3 스케일의 대형내부접합부에 대하여 반복가력실험을 수행하였다. 실험체들은 층간변위비 4.0%를 넘는 우수한 변형능력을 발휘하였으며, 보의 항복과 접합부의 항복이 동시에 발생하였다. 최종적으로는, 접합부의 전단파괴로 하중이 감소하였다. 실험강도는 기존 설계모델과 비교되었다.

• Steel and Composite Structures
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• 제22권1호
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• pp.141-159
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• 2016

Commonly in steel frames, steel beam and concrete slab are connected together by shear keys to work as a unit member which is called composite beam. When a composite beam is subjected to positive bending, flexural strength and stiffness of the beam can be increased due to "composite action". At the same time despite these advantages, composite action increases the strain at the beam bottom flange and it might affect beam plastic rotation capacity. This paper presents results of study on the rotation capacity of composite beam connected to Rectangular Hollow Section (RHS) column in the steel moment resisting frame buildings. Due to out-of-plane deformation of column flange, moment transfer efficiency of web connection is reduced and this results in reduction of beam plastic rotation capacity. In order to investigate the effects of width-to-thickness ratio (B/t) of RHS column on the rotation capacity of composite beam, cyclic loading tests were conducted on three full scale beam-to-column subassemblies. Detailed study on the different steel beam damages and concrete slab damages are presented. Experimental data showed the importance of this parameter of RHS column on the seismic behavior of composite beams. It is found that occurrence of severe concrete bearing crush at the face of RHS column of specimen with smaller width-to-thickness ratio resulted in considerable reduction on the rate of strain increase in the bottom flange. This behavior resulted in considerable improvement of rotation capacity of this specimen compared with composite and even bare steel beam connected to the RHS column with larger width-to-thickness ratio.

• 한국도로학회논문집
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• 제20권1호
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• pp.9-18
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• 2018

PURPOSES : In this research, the initiation and development of corrugation on a gravel road with certain wheel and boundary conditions were evaluated using a coupled discrete-element method (DEM) with multibody dynamics (MBD). METHODS : In this study, 665,534 particles with a 4-mm diameter were generated and compacted to build a circular roadbed track, with a depth and width of 42 mm and 50 mm, respectively. A single wheel with a 100-mm diameter, 40-mm width, and 0.157-kg mass was considered for the track. The single wheel was set to run slowly on the track with a speed of 2.5 rad/s so that the corrugation was gradually initiated and developed without losing contact between the wheel and the roadbed. Then, the shape of the track surface was monitored, and the movement of the particles in the roadbed was tracked at certain wheel-pass numbers to evaluate the overall corrugation initiation and development mechanism. RESULTS : Two types of corrugation, long wave-length and short wave-length, were observed in the circular track. It seems that the long wave-length corrugation was developed by the longitudinal movement of surface particles in the entire track, while the short wave-length corrugation was developed by shear deformation in a local section. Properties such as particle coefficients, track bulk density, and wheel mass, have significant effects on the initiation and development of long-wave corrugation. CONCLUSIONS : It was concluded that the coupled numerical method applied in this research could be effectively used to simulate the corrugation of a gravel road and to understand the mechanism that initiates and develops corrugation. To derive a comprehensive conclusion for the corrugation development under various conditions, the driver's acceleration and deceleration with various particle gradations and wheel-configuration models should be considered in the simulation.

• Structural Engineering and Mechanics
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• 제59권3호
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• pp.503-526
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• 2016

In-plane and out-of-plane free vibration analysis of Timoshenko curved beams is addressed based on the isogeometric method, and an effective scheme to avoid numerical locking in both of the two patterns is proposed in this paper. The isogeometric computational model takes into account the effects of shear deformation, rotary inertia and axis extensibility of curved beams, and is applicable for uniform circular beams, and more complicated variable curvature and cross-section beams as illustrated by numerical examples. Meanwhile, it is shown that, the $C^{p-1}$-continuous NURBS elements remarkably have higher accuracy than the finite elements with the same number of degrees of freedom. Nevertheless, for in-plane or out-of-plane vibration analysis of Timoshenko curved beams, the NURBS-based isogeometric method also exhibits locking effect to some extent. To eliminate numerical locking, the selective reduced one-point integration and $\bar{B}$ projection element based on stiffness ratio is devised to achieve locking free analysis for in-plane and out-of-plane models, respectively. The suggested integral schemes for moderately slender models obtain accurate results in both dominated and non-dominated regions of locking effect. Moreover, this strategy is effective for beam structures with different slenderness. Finally, the influence factors of structural parameters of curved beams on their natural frequency are scrutinized.

• Structural Engineering and Mechanics
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• 제37권2호
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• pp.149-162
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• 2011

The aim of this research is a comprehensive review and evaluation of beam theories resting on elastic foundations that used to model mode-I delamination in multidirectional laminated composite by DCB specimen. A compliance based approach is used to calculate critical strain energy release rate (SERR). Two well-known beam theories, i.e. Euler-Bernoulli (EB) and Timoshenko beams (TB), on Winkler and Pasternak elastic foundations (WEF and PEF) are considered. In each case, a closed-form solution is presented for compliance versus crack length, effective material properties and geometrical dimensions. Effective flexural modulus ($E_{fx}$) and out-of-plane extensional stiffness ($E_z$) are used in all models instead of transversely isotropic assumption in composite laminates. Eventually, the analytical solutions are compared with experimental results available in the literature for unidirectional ($[0^{\circ}]_6$) and antisymmetric angle-ply ($[{\pm}30^{\circ}]_5$, and $[{\pm}45^{\circ}]_5$) lay-ups. TB on WEF is a simple model that predicts more accurate results for compliance and SERR in unidirectional laminates in comparison to other models. TB on PEF, in accordance with Williams (1989) assumptions, is too stiff for unidirectional DCB specimens, whereas in angle-ply DCB specimens it gives more reliable results. That it shows the effects of transverse shear deformation and root rotation on SERR value in composite DCB specimens.

• 대한조선학회논문집
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• 제29권1호
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• pp.158-172
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• 1992

대형구조물의 국부구조계를 구성하는 후판, 선체이중저구조와 같은 복판팬널등의 진동문제에 있어서 전단변형 및 회전관성효과가 매우 크므로 정확한 진동해석을 위해서는 이들 구조계를 상기 효과를 고려한 Mindlin판유추 구조계로 취급하여야 한다. 또한, 이들 구조계의 실제 경계조건은 일반적으로 단순지지와 고정의 중간상태이므로 경계조건을 회전에 대한 탄성구속으로 다룰 필요가 있다. 그러나 4변모두 단순지지 경계조건을 갖는 Mindlin판을 제외하고는 엄밀해를 구하기 어려워 근사적 방법의 사용이 불가피한데, 한 방법으로 Rayleigh-Ritz 방법이 널리 이용된다. Rayleigh-Ritz 방법에 의한 Mindlin판유추 구조계의 진동해석에 있어서 진동파형가정함수로서 통상 Timoshenko보함수가 이용된다. 이 경우 전단변형의 효과가 고려되어야 하므로 횡방향처짐 및 굽힘회전각에 대한 2개의 함수계가 도입되어야 하므로 실제 연산이 Euler보함수를 이용한 박판유추 구조계의 진동해석 때 보다도 훨씬 더 복잡하다. 따라서, 본 논문에서는 이러한 연산의 복잡성을 줄이기 위해 진동파형가정함수로서 Timoshenko보함수 성질을 갖는 다항식 도출방안을 제시하였고, 이를 이용하여 주변경계조건이 회전에 대해 탄성구속된 Mindlin판유추 구조계의 진동해석 및 감도해석을 정식화하여, 등방성 후판 및 실선이중저구조의 1/8축척 모델을 대상으로 일련의 수치계산을 수행하여 이의 정확도 및 효율성을 검증하였다.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제13권3호
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• pp.252-264
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• 1991

The purpose of this study was to compare the response of adjacent tissue and new bone formation after implantation by different methods of subperiosteal using using Proplast I and II in rabbit mandible. Microstructure of Proplast I and II was observed by scanning electron microscope. And the implantation procedure was carried out by dividing into tow groups, A and B. a group consisted of subperiosteal graft on the cortex, and the other B group was made up onlay graft following artificial decortication in the madibular body of rabbit. The experimental animals were sacrificed on the 1st, 2nd, 4th and 8th week after grafting for macroscopic and histopathologic examination. The samples extracted at the 6th postgrafting week were also used for biometric test. The result ere as follows : 1. By scanning electron microscopic observation, pore size was $50{\sim}180{\mu}m$ in the Proplast I and $100{\sim}220{\mu}m$ in Proplast II. 2. Macroscopically, infection of the graft site, deformation and displacement of the implanted materials were not observed in all experimental groups. 3. In the tissue response, infiltration of inflammatory cells and multinucleated giant cells were observed from the 2nd to the 8th week in Proplast I. Inflammatory cells decreased in number from the 2nd week in Proplast II suggesting that Proplast II is better than Proplast I. 4. Bone formation was not observed until the 8th week in the group A, but new bone formation from the surrounding graft bed and the periostium was appeared from the 4th week in the group B. 5. The maximum mean values of shear stress mere serially $65.5gf/mm^2$ in Proplast II of group B, $32.9gf/mm^2$ in Proplast I of group B, $17.0gf/mm^2$ in Proplast II of group A, and $15.7gf/mm^2$ in Proplast I. of group A.

• 대한토목학회논문집
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• 제32권3C호
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• pp.85-94
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• 2012

본 논문은 액상화 지반에서의 지반-지하 중공구조물 상호작용에 따른 구조물의 rocking현상을 조사하기 위해서 수행한 원심모형실험에 관하여 서술하고 있다. 지진이 발생하였을 때 지반이 강한 진동에 노출되면 상대밀도가 낮은 느슨한 모래지반에서는 액상화가 발생하며, 액상화된 지반보다 작은 단위중량을 가진 지하 중공구조물은 부상한다. 지하 중공구조물이 부상하는 동안에 구조물의 동적 거동과 구조물의 부상량에 대한 원지반의 영향을 평가하기 위하여 원지반의 상대밀도를 다르게 모델지반을 제작하였고, 아크릴 박스를 이용하여 트랜치를 제작하여 모형실험을 수행하였다. 실험결과, 액상화된 원지반의 측방유동 및 주변지반의 전단변형에 의해 야기되는 지하 중공구조물의 rocking현상이 지하 중공구조물의 부상량의 규모에 크게 기여하는 것으로 나타났다.