• Steel and Composite Structures
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• 제16권4호
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• pp.417-436
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• 2014

During an earthquake, steel frame columns can be subjected to high axial forces combined with inelastic rotation demand resulting from story drift. Generally, the whole beam or component can be represented with one element. In elasto-plastic analysis, subdivision is necessary if the plastic deformation occurs within two ends of beams. If effects of the joint panel are necessarily considered in the analysis, the joint panel should be represented with an independent element. It is a special element to represent the shear deformation of the joint panel in the beam-column connection zone. Several analytical models for panel zone (PZ) behavior exist, in terms of shear force-shear distortion relationships. Among these models, the Krawinkler PZ model is the most popular one which is used in the AISC code. Some studies have pointed out that Krawinkler's model gives good results for the range of thin to medium column flanges thickness. This paper, introduces a new model to estimate the response of shear force-shear distortion for the PZ including column axial force. The model is applicable to both thin and thick column flange. To achieve an appropriate PZ mathematical model first, the effects of PZ strength and stiffness on connection response are parametrically studied using finite element models. More than one thousand and four-hundred beam-column connections are included in the parametric study, with varied parameters; then based on analytical results a simple mathematical model is presented. A comparison between the results of proposed method herein with FE analyses shows the average error especially in thick column flange is significantly reduced which demonstrates the accuracy, efficiency, and simplicity of the proposed model.

• 한국강구조학회 논문집
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• 제9권4호통권33호
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• pp.557-578
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• 1997

이 연구의 목적은 매우 큰 지진하에 휨 모멘트에 의해서만 항복하는 부재와 휨 모멘트와 축 방향력에 의하여 항복하는 부재를 모델 할 수 있는 보-기둥 요소를 개발하는데 있다. 이 요소는 직렬 힌지 모델 (one-component series hinge model)로 간주 될 수 있으며, 축 방향 강성도 변화와 축 방향 소성 변형을 고려 할 수 있고 또한 단조, 주기, 임의 하중 등을 적절히 모델 할 수 있는 경화 법칙 (hardening rules)을 고려한다. 일반적으로 이 요소는 실험 결과 및 화이버 모델 (fiber model)에 비교하여 볼 때 기존의 이직선 힌지 모델 (bilinear hinge model)보다 우수한 거동을 보였고 모멘트 저항 뼈대 구조물의 강 부재의 보-기둥 거동을 적절하게 모델 할 수 있었다. 개발된 보-기둥 요소는 지진 하중하에서 구조물의 전체적인 거동과 설계에 필요한 국부 변형량을 기존의 이직선 힌지 모델 보다 매우 정확하게 예측 할 수 있다.

• 한국강구조학회 논문집
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• 제15권6호통권67호
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• pp.701-709
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• 2003

이 논문은 모멘트 저항골조의 접합부에 이용하기 위한 T-스티프너로 보강된 접합부의 내진성능에 관해 나타냈다. 접합부는 보플랜지와 기둥플랜지에 T-스티프너의 수평 및 수직요소가 용접되어 보강되었다. T-스티프너 접합부의 거동을 명확히 파악하기 위해 유한요소해석과 실험이 수행되었다. 유한요소해석결과, T-스티프너의 수평요소의 길이가 길어짐에 따라 T-스티프너는 보플랜지와 수평요소사이의 응력집중을 줄이는데 효과적임을 나타냈다. 또한, 접합부의 이력 거동을 파악하기 위해 실대형 접합부 실험을 실시하였다. 주요 변수는 보에 대한 T-스티프너의 강도비와 수평요소의 형상이다. 수평요소의 길이가 길수록 접합부의 변형능력은 증가하였고, 모든 실험체는 방추형의 안정된 이력거동을 나타내었다.

• Structural Engineering and Mechanics
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• 제71권2호
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• pp.185-196
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• 2019

In this investigation, study of the static and dynamic behaviors of functionally graded beams (FGB) is presented using a hyperbolic shear deformation theory (HySDT). The simply supported FG-beam is resting on the elastic foundation (Winkler-Pasternak types). The properties of the FG-beam vary according to exponential (E-FGB) and power-law (P-FGB) distributions. The governing equations are determined via Hamilton's principle and solved by using Navier's method. To show the accuracy of this model (HySDT), the current results are compared with those available in the literature. Also, various numerical results are discussed to show the influence of the variation of the volume fraction of the materials, the power index, the slenderness ratio and the effect of Winkler spring constant on the fundamental frequency, center deflection, normal and shear stress of FG-beam.

• Structural Engineering and Mechanics
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• 제78권2호
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• pp.117-124
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• 2021

This work focused on the novel numerical tool for the bending responses of carbon nanotube reinforced composites (CNTRC) beams. The higher order shear deformation beam theory (HSDT) is used to determine strain-displacement relationships. A new exponential function was introduced into the carbon nanotube (CNT) volume fraction equation to show the effect of the CNT distribution on the CNTRC beams through displacements and stresses. To determine the mechanical properties of CNTRCs, the rule of the mixture was employed by assuming that the single-walled carbon nanotubes (SWCNTs)are aligned and distributed in the matrix. The governing equations were derived by Hamilton's principle, and the mathematical models presented in this work are numerically provided to verify the accuracy of the present theory. The effects of aspect ratio (l/d), CNT volume fraction (Vcnt), and the order of exponent (n) on the displacement and stresses are presented and discussed in detail. Based on the analytical results. It turns out that the increase of the exponent degree (n) makes the X-beam stiffer and the exponential CNTs distribution plays an indispensable role to improve the mechanical properties of the CNTRC beams.

• 한국음향학회지
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• 제42권5호
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• pp.452-459
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• 2023

음파의 힘을 이용하는 음향집게는 나노 단위의 세포외소포에서 밀리미터 단위의 대규모 다세포생 물체까지 다양한 생체 입자를 조작하는 데 사용되는 매우 유용한 도구이다. 해당 분야는 수십년간 점진적인 개발이 이루어지고 있으며, 단일 초음파 빔을 사용하는 단일 빔 음향 집게(Single Beam Acoustic Tweezers, SBAT)기술 또한 세포 및 생물체 정밀 이동 및 분석이 가능한 플랫폼으로 발전했다. 최근 혁신적인 발전으로 SBAT를 이용하여 입자/세포 분리, 단일 세포 변형 기술이 개발되었으며 이로 인해 의공학 분야에서 학문적인 관심을 모으고 있다. 본 종설에서 SBAT기술의 기초 원리와 작동 방법에 대해서 설명하며 그간의 연구를 요약하고 이를 바탕으로 향후 연구에 대해서 전망한다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2008년도 International Symposium on Remote Sensing
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• pp.422-425
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• 2008

TerraSAR-X is new radar satellite operated at X-band, multi polarization, and multi beam mode. Compared with C-band or L-band SAR, the X-band system inherently suffers from more temporal decorrelation, but is more sensitive to surface deformation monitoring due to short wavelength (3.1 cm) and high spatial resolution (1m-3m). It is generally expected that sensitivity to estimate surface movement using TerraSAR-X will be increased by the factor of 10, compared to current C-band system with low spatial resolution such as ERS-2, Envisat. Many urban areas are experiencing land subsidence due to water, oil and natural gas withdrawal, underground excavation, sediment compaction, and so on. Monitoring of surface deformation is valuable for effectively limiting damage areas. In addition high accuracy and spatially dense subsidence map can be achieved by X-band InSAR observation, promoting identification and separation of various subsidence processes and leading to enhanced understanding via mechanical modeling. In this study we will introduce some initial InSAR results using new TerraSAR-X SAR data for surface deformation monitoring.

• Smart Structures and Systems
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• 제18권6호
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• pp.1125-1143
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• 2016

Forced vibration analysis of a simple supported viscoelastic nanobeam is studied based on modified couple stress theory (MCST). The nanobeam is excited by a transverse triangular force impulse modulated by a harmonic motion. The elastic medium is considered as Winkler-Pasternak elastic foundation.The damping effect is considered by using the Kelvin-Voigt viscoelastic model. The inclusion of an additional material parameter enables the new beam model to capture the size effect. The new non-classical beam model reduces to the classical beam model when the length scale parameter is set to zero. The considered problem is investigated within the Timoshenko beam theory by using finite element method. The effects of the transverse shear deformation and rotary inertia are included according to the Timoshenko beam theory. The obtained system of differential equations is reduced to a linear algebraic equation system and solved in the time domain by using Newmark average acceleration method. Numerical results are presented to investigate the influences the material length scale parameter, the parameter of the elastic medium and aspect ratio on the dynamic response of the nanobeam. Also, the difference between the classical beam theory (CBT) and modified couple stress theory is investigated for forced vibration responses of nanobeams.

• Steel and Composite Structures
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• 제21권5호
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• pp.1045-1067
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• 2016

Concrete bridges with corrugated steel webs and prestressed by both internal and external tendons have emerged as one of the promising bridge forms. In view of the different behaviour of components and the large shear deformation of webs with negligible flexural stiffness, the assumption that plane sections remain plane may no longer be valid, and therefore the classical Euler-Bernoulli and Timoshenko beam models may not be applicable. In the design of this type of bridges, both the ultimate load and ductility should be examined, which requires the estimation of full-range behaviour. An analytical sandwich beam model and its corresponding beam finite element model for geometric and material nonlinear analysis are developed for this type of bridges considering the diaphragm effects. Different rotations are assigned to the flanges and corrugated steel webs to describe the displacements. The model accounts for the interaction between the axial and flexural deformations of the beam, and uses the actual stress-strain curves of materials considering their stress path-dependence. With a nonlinear kinematical theory, complete description of the nonlinear interaction between the external tendons and the beam is obtained. The numerical model proposed is verified by experiments.

• Structural Engineering and Mechanics
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• 제56권1호
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• pp.67-83
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• 2015

The load transfer mechanism and load-bearing capacity of cast steel joints for H-shaped beam to square tube column connection are studied based on the deformation compatibility theory. Then the monotonic tensile experiments are conducted for 12 specimens about the cast steel joints for H-shaped beam to square tube column connection. The findings are that the tensile bearing capacity of the cast steel joints for beam-column connection depends on the ring of cast steel stiffener. The tensile fracture happens at the ring of the cast steel stiffener when the joint fails. The thickness of square tube column has little influence on the bearing capacity of the joint. The square tube column buckles while the joint without concrete filled, but the strength failure happens for the joint with concrete filled column. And the length of welding connection between square tube column and cast steel stiffener has little influence on the load-bearing capacity of the cast steel joint. Finally it is shown that the load-bearing capacity of the joints for H-shaped beam to concrete filled square tube column connection is larger than that of the joints for H-shaped beam to square tube column connection by 10% to 15%.