• Steel and Composite Structures
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• 제18권5호
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• pp.1083-1101
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• 2015

Previous theoretical equations for the shear capacity of steel beam to concrete filled steel tube (CFT) column connections vary in the assumptions for the shear deformation mechanisms and adopt different equations for calculating shear strength of each component (steel tube webs, steel tube flanges, diaphragms, and concrete etc.); thus result in different equations for calculating shear strength of the joint. Besides, shear force-deformation relations of the joint, needed for estimating building drift, are not well developed at the present. This paper compares previously proposed equations for joint shear capacity, discusses the shear deformation mechanism of the joint, and suggests recommendations for obtaining more accurate predictions. Finite element analyses of internal diaphragm connections to CFT columns were carried out in ABAQUS. ABAQUS results and theoretical estimations of the shear capacities were then used to calibrate rotational springs in joint elements in OpenSEES simulating the shear deformation behavior of the joint. The ABAQUS and OpenSEES results were validated with experimental results available. Results show that: (1) shear deformation of the steel tube dominates the deformation of the joint; while the thickness of the diaphragms has a negligible effect; (2) in OpenSEES simulation, the joint behavior is highly dependent on the yielding strength given to the rotational spring; and (3) axial force ratio has a significant effect on the joint deformation of the specimen analyzed. Finally, modified joint shear force-deformation relations are proposed based on previous theory.

• Steel and Composite Structures
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• 제9권2호
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• pp.131-158
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• 2009

This paper presents a modelling technique for the nonlinear analysis of composite steel-concrete beams with partial shear interaction. It extends the applicability of two stiffness elements previously derived by the authors using the direct stiffness method, i.e. the 6DOF and the 8DOF elements, to account for material nonlinearities. The freedoms are the vertical displacement, the rotation and the slip at both ends for the 6DOF stiffness element, as well as the axial displacement at the level of the reference axis for the 8DOF stiffness element. The solution iterative scheme is based on the secant method, with the convergence criteria relying on the ratios of the Euclidean norms of both forces and displacements. The advantage of the approach is that the displacement and force fields of the stiffness elements are extremely rich as they correspond to those required by the analytical solution of the elastic partial interaction problem, thereby producing a robust numerical technique. Experimental results available in the literature are used to validate the finite element proposed in the paper. For this purpose, those reported by Chapman and Balakrishnan (1964), Fabbrocino et al. (1998, 1999) and Ansourian (1981) are utilised; these consist of six simply supported beams with a point load applied at mid-span inducing positive bending moment in the beams, three simply supported beams with a point load applied at mid-span inducing negative bending moment in the beams, and six two-span continuous composite beams respectively. Based on these comparisons, a preferred degree of discretisation suitable for the proposed modelling technique expressed as a function of the ratio between the element length and depth is proposed, as is the number of Gauss stations needed. This allows for accurate prediction of the nonlinear response of composite beams.

• Geomechanics and Engineering
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• 제21권6호
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• pp.571-582
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• 2020

Aiming at the mechanical and structural characteristics of the contact zone composite rock, the uniaxial compression tests and numerical studies were carried out. The interaction forms and formation mechanisms at the contact interfaces of different materials were analyzed to reveal the effect of interaction on the mechanical behavior of composite samples. The research demonstrated that there are three types of interactions between the two materials at the contact interface: constraint parallel to the interface, squeezing perpendicular to the interface, and shear stress on the interface. The interaction is mainly affected by the differences in Poisson's ratio and elastic modulus of the two materials, stronger interface adhesion, and larger interface inclination. The interaction weakens the strength and stiffness of the composite sample, and the magnitude of weakening is positively correlated with the degree of difference in the mechanical properties of the materials. The tensile-shear stress derived from the interaction results in the axial tensile fracture perpendicular to the interface and the interfacial shear facture. Tensile cracks in stronger material will propagation into the weaker material through the bonded interface. The larger inclination angle of the interface enhances the effect of composite tensile/shear failure on the overall sample.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.675-684
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• 2020

An innovative retrofit method using pre-stressed steel strips and externally-bonded steel plates was presented in this paper. With the aim of exploring the seismic performance of the retrofitted RC interior joints, four 1/2-scale retrofitted joint specimens together with one control specimen were designed and subjected to constant axial compression and cyclic loading, with the main test parameters being the volume of steel strips and the existence of externally-bonded steel plates. The damage mechanism, force-displacement hysteretic response, force-displacement envelop curve, energy dissipation and displacement ductility ratio were analyzed to investigate the cyclic behavior of the retrofitted joints. The test results indicated that all the test specimens suffered a typical shear failure at the joint core, and the application of externally-bonded steel plates and that of pre-stressed steel strips could effectively increase the lateral capacity and deformability of the deficient RC interior joints, respectively. The best cyclic behavior could be found in the deficient RC interior joint retrofitted using both externally-bonded steel plates and pre-stressed steel strips due to the increased lateral capacity, displacement ductility and energy dissipation. Finally, based on the test results and the softened strut and tie model, a theoretical model for determining the shear capacity of the retrofitted specimens was proposed and validated.

• 대한기계학회논문집A
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• 제28권5호
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• pp.524-531
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• 2004

To investigate relevance of the definition of the reference stress to estimate J and $C^{*}$ for surface crack problems, this paper compares FE J and $C^{*}$ results for surface cracked pipes with those estimated according to the reference stress approach using various definitions of the reference stress. Pipes with part circumferential inner surface crack and finite internal axial crack are considered, subject to internal pressure and global bending. The crack depth and aspect ratio are systematically varied. The reference stress is defined in four different ways using (i) the local limit load, (ii) the global limit load, (iii) the global limit load determined from the FE limit analysis, and (iv) the optimized reference load. It is found that the reference stress based on the local limit load gives overall excessively conservative estimates of J and $^{*}$. Use of the global limit load clearly reduces the conservatism, compared to that of the local limit load, although it can provide sometimes non-conservative estimates of J and $^{*}$. The use of the FE global limit load gives overall non-conservative estimates of J and $^{*}$. The reference stress based on the optimised reference load gives overall accurate estimates of J and $^{*}$, compared to other definitions of the reference stress. Based on the present finding, general guidance on the choice of the reference stress for surface crack problems is given.

• Journal of Advanced Marine Engineering and Technology
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• 제37권5호
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• pp.510-519
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• 2013

Urea-SCR시스템에 적용하기 위한 액막형 선회분사기의 분사압력변화에 따른 분무특성이 실험적으로 조사되었다. 실험에 사용된 노즐은 형상비 3.1을 갖는 단공 압력식 액막형 선회노즐이며, 노즐선단에 분사되는 유체에 선회류를 형성하기 위한 선회기가 설치되어 있다. 노즐의 분사량 조절은 PWM(pulse width modulation)기법에 의해 제어되었다. 분무의 발달과정은 2차원 PIV에 의해 가시화되었으며, 분무각 변화가 조사되었다. 분무액적의 속도 및 크기는 2차원 PDPA에 의해 상온 대기압 조건에서 측정되었다. 분무구조는 분사압력에 큰 영향을 받으며, SMD는 분사압력 증가에 따라 감소하며 선행연구자의 반실험적 결과와 유사한 경향을 보임을 알 수 있었다.

• 전자공학회논문지 IE
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• 제45권4호
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• pp.54-59
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• 2008

본 논문은 S-DMB 수신을 위한 2단 저잡음 증폭기를 결합한 능동형 원편파 패치안테나를 설계 및 제작하였다. 제작된 능동형 안테나의 크기는 $40{\times}40{\times}15\;[mm]$로서 유전상수가 2.2인 테플론 기판으로 제작하였다. 측정된 안테나의 입력 반사손실과 3 dB 축비의 대역폭은 각각 긴 MHz와 25 MHz로 양호한 특성을 나타내었다. 제작된 2단 LNA의 특성을 측정한 결과 입력 반사손실, 출력 반사손실, 이득과 잡음지수는 각각 $S_{11}$=-14 [dB], $S_{22}$=-18 [dB], $S_{21}$=26.8 [dB], NF=1.14 [dB]의 우수한 값을 가졌다. 중심주파수 f=2.642 [GHz]에서 제작된 능동형 안테나의 총 이득은 30.4 [dB]인 양호한 값을 갖는다.

• 전기전자학회논문지
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• 제16권2호
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• pp.69-75
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• 2012

본 논문에서는 자동차용 내비게이션(navigation) 단말기에 내장된 DSRC 방식의 5.8GHz 대역 무선통신을 위한 패치 안테나를 설계하고 제작하였다. 폭이 좁고 긴 구조적 특징을 갖는 내비게이션 단말기의 상단면에 장착될 수 있도록 기존에 사용되어왔던 단일 반파장 마이크로스트립 패치안테나를 소형화하였고 배열하였다. 또한 배열을 통해 주행차선 안쪽으로 빔폭을 제한하였고, 소형화에 따른 이득저하를 보상하였다. 제안된 안테나를 시뮬레이션 함으로써 타당성을 검증하였으며, 제작된 안테나는 $18{\times}40{\times}0.8mm^3$ 크기를 갖고, 4dB 축비대역폭이 40MHz인 원형편파특성을 나타낸다. 또한, 6.2dBi 이득과 자동차 진행차선의 횡단면 방향으로 약 70도의 빔 폭이 측정되었다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제34회 춘계학술대회논문집
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• pp.145-149
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• 2010

연료링의 위치 및 열차폐 코팅의 종류에 따른 연소기의 재생냉각 특성을 검토하였다. 연료링을 노즐의 중간 부분에 위치시키고 냉각채널을 분기시켜서 설계하는 방법이 열적으로 타당함을 확인하였다. 또한 복합재를 이용한 노즐확장부가 적용 가능한 기술적 상황이라면, 팽창비가 높고 열유속이 낮은 노즐 후류 부분은 이를 이용하는 것이 매우 적절하다고 판단된다. 적용 가능한 열차폐 코팅 중에서 30톤급 연소기 및 가스발생기 개발과정에서 사용했던 $Y_2O_3$ stabilized $ZrO_2$과 내산화성이 우수한 Ni/Cr을 고려하였다. 내산화성이 우수한 Ni/Cr에 비해 세라믹 코팅($Y_2O_3$ stabilized $ZrO_2$)이 열차폐 효과가 우수한 것으로 파악되었다.

• 해양환경안전학회지
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• 제17권3호
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• pp.295-300
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• 2011

선박은 상자형태 구조로 구성되어 있으며 선박의 선 수미, 선저만곡부, 갑판 등에 주로 사용하고 있다. 이런 구조는 박판구조이며 1차 지지부재로 사용된다. 평판구조와 비교하였을 때 상이한 거동을 보이며 일반적으로 압축하중을 받을 경우 곡률변화에 따라 다른 좌굴 및 최종 강도 경향을 나타냈다. 따라서 본 논문에서는 압축하중을 받고 있는 보강곡판인 1/2+1+1/2 bay 모델에 대하여 비선형유한요소해석을 수행하였으며 매개변수 영향은 곡률변화뿐만 아니라 세장비, 웨브높이/두께 등을 고려하여 해석모델에 대한 붕괴모드에 대해 검토하였다.