• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.903-910
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• 2005

In recent years, fiber reinforced polymer(FRP) plates have shown a great promise as an alternative to steel plates for reinforced concrete beam rehabilitation. Reinforced concrete beams strengthened with externally bonded FRP sheets to the tension face can exhibit ultimate flexural strengths several times greater than their original strength if their bond strength is enough. Debonding failure, however, may occur before the strengthened beam can achieve its enhanced flexural strength. The purpose of this paper is to investigate the debonding failure strength of FRP-strengthened reinforced concrete beams. An analytical procedure for calculating debonding load between concrete and strengthening FRP is presented. Based on the local bond stress-slip relationship in the previous studies, uniform bond stress is assumed on the effective bond length. The analytical expressions are developed from linear elastic theory and statistical analyses of experimantal results reported in the literature. The proposed method is verified by comparisons with experimental results reported in the previous researches.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.731-740
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• 2011

Provisions for the redistribution of negative moments in KCI 2007 and ACI 318-08 use a method for continuous flexural members subjected to uniformly-distributed gravity load. Moment redistributions and plastic rotations in beams of reinforced concrete moment frames subjected to lateral load differ from those in continuous flexural members due to gravity load. In the present study, a quantitative relationship between the moment redistribution and plastic rotation is established for beams subjected to both lateral and gravity loads. Based on the relationship, a design method for the redistribution of negative moments is proposed based on a plastic rotation capacity. The percentage change in negative moments in the beam was defined as a function of the tensile strain of re-bars at the section of maximum negative moment, which is determined by a section analysis at an ultimate state using KCI 2007 and ACI 318-08. Span, reinforcement ratio, cracked section stiffness, and strain-hardening behavior substantially affected the moment redistribution. Design guidelines and examples for the redistribution of the factored negative moments determined by elastic theory for beams under lateral load are presented.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.511-521
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• 2002

A simple numerical modelling technique is proposed for estimating the shear stress distribution in beams of framed tube structures with multiple internal tubes. The structures arc analysed using a continuum approach in which each tube is individually modelled by a tube beam that accounts for the flexural and shear deformations, as well as the shear lag effects. The numerical analysis of shear stress is based on the mathematical analogy in conjunction with the elastic theory By simplifying assumptions regarding the form of strain distributions in external and internal tubes, the shear stress distributions are expressed in terms of a series of lineal functions of the second moments of area of the structures and the corresponding geometric and material properties, as well as the applied loads. Previous studies for axial stresses and shear lag phenomenon are further developed lot the numerical analysis of shear stresses in the tubes. The simplicity and accuracy of the proposed method are demonstrated through the solutions of throe numerical examples.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.4
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• pp.133-138
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• 1987

The precise methods applied to adjust plane trilateration nets employ least squares techniques. The observations or the condition equations in these known methods are, without exception, nonlinear. The coefficients of the corrections in the conditions equations methods are lengthy and complicated. This paper presents a new method in which the coefficiets of the corrections of the conditions are simple and can be easily calculated and checked. In this method the measured distances in trilateration nets are considered as elastic members in an internally redundant framework. If the redundant members have measuring errors, axial forces must be applied to fit them in the framework. As a result axial forces will develop in all other members causing changes in their lengths. By applying minimum work techniques one can determine these changes in length which are in fact the required corrections of the measured distances. The result of this study presents that the closing ratio is about 1/145000 and it is improved that this method is useful in analysis plane trilateration nets.

• Advanced Composite Materials
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• v.17 no.1
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• pp.57-73
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• 2008

The present paper focuses on experimental verification of the ply-by-ply basis inelastic analysis of multidirectional laminates. First of all, rate dependence of the tensile behavior of balanced symmetric cross-ply T800H/epoxy laminates with a $[0/90]_{3S}$ lay-up under off-axis loading conditions at $100^{\circ}C$ is examined. Uniaxial tension tests are performed on plain coupon specimens with various fiber orientations $[{\theta}/(90-{\theta})]_{3S}$ ($\theta$ = 0, 5, 15, 45 and $90^{\circ}C$) at two different strain rates (1.0 and 0.01%/min). The off-axis stress.strain curves exhibit marked nonlinearity for all the off-axis fiber orientations except for the on-axis fiber orientations $\theta$ = 0 and $90^{\circ}$, regardless of the strain rates. Strain rate has significant influences not only on the off-axis flow stress in the regime of nonlinear response but also on the apparent off-axis elastic modulus in the regime of initial linear response. A macromechanical constitutive model based on a ply viscoplasticity model and the classical laminated plate theory is applied to predictions of the rate-dependent off-axis nonlinear behavior of the cross-ply CFRP laminate. The material constants involved by the ply viscoplasticity model are identified on the basis of the experimental results on the unidirectional laminate of the same carbon/epoxy system. It is demonstrated that good agreements between the predicted and observed results are obtained by taking account of the fiber rotation induced by deformation as well as the rate dependence of the initial Young's moduli.

• Steel and Composite Structures
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• v.17 no.6
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• pp.891-906
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• 2014

This study aims to present a three dimensional finite element model to investigate the wave propagation in a concrete filled steel tubular column (CFSC) due to transient impact load. Both the concrete and steel are regarded as linear elastic material. The impact load is simulated by a semi sinusoidal impulse. Besides the CFSC models, a concrete column (CC) model is established for comparing under the same loading condition. The propagation characteristics of the transient waves in CFSC are analyzed in detail. The results show that at the intial stage of the wave propagation, the velocity waves in CFSC are almost the same as those in CC before they arrive at the steel tube. When the waves reach the column side, the velocity responses of CFSC are different from those of CC and the difference is more and more obvious as the waves travel down along the column shaft. The travel distance of the wave front in CFSC is farther than that in CC at the same time. For different wave speeds in steel and concrete material, the wave front in CFSC presents an arch shape, the apex of which locates at the center of the column. Differently, the wave front in CC presents a plane surface. Three dimensional effects on top of CFSC are obvious, therefore, the peak value and arrival time of incident wave crests have great difference at different locations in the radial direction. High-frequency waves on the waveforms are observed. The time difference between incident and reflected wave peaks decreases significantly with r/R when r/R < 0.6, however, it almost keeps constant when $r/R{\geq}0.6$. The time duration between incident and reflected waves calculated by 3D FEM is approximately equal to that calculated by 1D wave theory when r/R is about 2/3.

• Smart Structures and Systems
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• v.26 no.3
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• pp.331-343
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• 2020

In this paper, based on the CPT, motion equations for a sandwich plate containing a core and two integrated face-sheets have derived. The structure rests on the Visco-Pasternak foundation, which includes normal and shear modules. The piezo-magnetic core is made of CoFe₂O₄ and also is subjected to 3D magnetic potential. Two face sheets at top and bottom of the core are under electrical fields. Also, in order to obtain more accuracy, the effect of flexoelectricity has took into account at face sheets' relations in this work. Flexoelectricity is a property of all insulators whereby they polarize when subject to an inhomogeneous deformation. This property plays a crucial role in small-scale rather than macro scale. Employing CPT, Hamilton's principle, flexoelectricity considerations, the governing equations are derived and then solved analytically. By present work a detailed numerical study is obtained based on Piezoelectricity, Flexoelectricity and modified couple stress theories to indicate the significant effect of length scale parameter, shear correction factor, aspect and thickness ratios and boundary conditions on natural frequency of sandwich plates. Also, the figures show that there is an excellent agreement between present study and previous researches. These finding can be used for automotive industries, aircrafts, marine vessels and building industries.

• The Journal of the Acoustical Society of Korea
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• v.24 no.5
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• pp.282-293
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• 2005

Sonoelastography is an ultrasound-based technique that visualizes the elastic properties of soft tissues by measuring the tissue motion generated by an externally applied vibration. In this paper. the characteristics of wave generation in soft tissues due to an acoustic vibrator are studied. The effects of modal patterns on the detectability of lesions such as tumors in senoelastography are also investigated These are accomplished by analyzing the vibration patterns calculated using theoretical equations and finite element methods in halt space, infinite plate. and finite-sized tissue. A finite-width source generates shear waves with large amplitude Propagating in specific directions. and the generation characteristics depend both on the width and frequency of the vibrator. as well as the distance from it. It is shown in a finite-sized tissue that the lesion detection in displacement images is quit dependent on the modal patterns inside tissue. In contrast it Is also found that the lesion detectability in strain images is less dependent on the modal Patterns and is much better than that in displacement images.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.4 no.4
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• pp.236-241
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• 2011

Mechanical properties of cancellous bone with a high porosity and cortical bone with a high fraction of solid are estimated by the measurement of ultrasonic wave propagation. The speed of sound (SOS) in ultrasonic waves is usually measured by two equations, bulk wave equation and bar wave equation. Bulk wave speed has almost same as the fast wave of Biot's theory. In this study, we examine whether the bulk wave speed is influenced by the anisotropy of bone matrix. The SOS when the bone matrix is isotropy is 0.69% faster than that when the bone matrix is transversely isotropy. We also examine if the use of bar equation is adequate for a cortical bone. In the previous paper, the bar wave speed is a function of Young's modulus or elastic coefficient tensor. In the same manner, the effect of bar wave speed to isotropic and anisotropic bone is estimated.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.246-255
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• 2016

When spring of the suspension is exerted by an external load, a car should be designed to prevent predictable damages and designed for a ride comfort. We used experiments design to design VON-MISES STRESS and K, a constant, of spring of suspension which is installed in a car as a goal level. We analyzed the result from Edison's Elastic - Plastic Analysis SW(CSD_EPLAST) by setting D, d, n as external diameter of coil, internal diameter of coil, the number of total coil respectively. The experiment design let the outcome be as Full-second order by using Box-Behnken which is one of response surface methods. Experimented and analyzed results based on the established experiments design, We found out design parameter which has desired VON-MISES STRESS and the constant K. Additionally, we predicted life time of when the external load was exerted by repeated load by using fatigue equation, and verification of plastic deformation has also been made. Additionally we interpreted a model, which is formed by optimized design parameter, with linear analysis and non-linear analysis, at the same time we also analyzed plastic deformation with the values from the both models. Finally, we predicted fatigue life of optimized model by using fatigue estimation theory and also evaluated a ride comfort with oscillation analysis.