• Steel and Composite Structures
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• v.37 no.5
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• pp.589-603
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• 2020

This paper presents an investigation of the thermal performance of composite floor slabs with profiled steel decking exposed to fire effects from floor. A detailed finite-element model has been developed by representing the concrete slab with steel decking under of it and steel beam both steel parts protected by intumescent coating. Although this type of floor systems offers a better fire resistance, passive fire protection materials should be applied when a higher fire resistance is desired. Moreover, fire exposed side is so crucial for composite slab systems as the total fire behaviour of the floor system changes dramatically. When the fire attack from steel parts, the temperature rises rapidly resulting in a sudden decrease on the strength of the beam and decking. Herein this paper, the fire attack side is assumed from the face of the concrete floor (top of the concrete assembly). Therefore, the heat is transferred through concrete to the steel decking and reaching finally to the steel beam both protected by intumescent coating. In this work, the numerical model has been established to predict the heat transfer performance including material properties such as thermal conductivity, specific heat and dry film thickness of intumescent coating. The developed numerical model has been divided into different layers to understand the sensitivity of steel temperature to the number of layers of intumescent coating. Results show that the protected composite floors offer a higher fire resistance as the temperature of the steel section remains below 60℃ even after 60-minute Standard (ISO) fire and Fast fire exposure. Obtaining lower temperatures in steel due to the great fire performance of the concrete itself results in lesser reductions of strength and stiffness hence, lesser deflections.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2350-2355
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• 2015

A tool was developed in this research for automation of one-dimensional finite element analysis (1D FEA) for design of a machine tool spindle system composed mainly of a shaft and bearings. As it is based on object-oriented programing, it uses the objects of a CAD system. It requires minimum data to be input to define the spindle system such as shaft cross-sections and bearing stiffness. Then, it automatically generates the geometric model based on the data and then, converts it into the FE model of 1D beams and springs. The graphic user interfaces developed allow a user to interact with the tool. This tool can be applied to identification of a near optimal design of the spindle system in minimum time and efforts by automating the FEA process with numerous design changes.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.3
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• pp.66-80
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• 1996

Recently, HT steel has been widely used in structure, and this enables to reduce the plate thickness. To use the HT steel effectively for a ship hull, the plate thickness becomes thin so that plate buckling may take place. Therefore, precise assessment of the behaviour of plat above primary buckling load is important. The plate under the load, that is called, secondary buckling load may undergo abrupt changes in wave form after primary buckling. This is very important when the collapse strength of the whole structures is considered. From this point of view, this paper discusses secondary buckling behaviour of thin plate under inplane compressive loading. A elastic large deflection analysis of plates with initial imperfection is performed assuming uniaxial compression, respectively, and the influence of secondary buckling is investigated. It is known that square plate is not influenced by non-symmetrical deflection coefficient but influenced by symmetrical deflection coefficient. Also, it has been found that rectangular plate($\alpha$=a/b) is influenced by all deflection coefficient, and the reduction of inplane stiffness of the plate after primary buckling is continued.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.375-387
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• 2006

Different from the previous studies which investigated seismic P-$\Delta$ effect in slender columns though comparison of response spectra according to stability coefficients obtained from the analyses based on the assumed moment-curvature relationship, the axial force and P-$\Delta$ effect in RC columns are investigated on the basis of the layered section method which can effectively consider the changes of stiffness and yield strength due to the application of axial force in RC members. Practical ranges of slenderness and stability coefficient are assumed, and sixty sets of horizontal/vertical earthquake inputs are used in the analysis. From the parametric study, it is noted that the maximum deformation of the slender RC column is hardly affected by P-$\Delta$ effect or vortical earthquake but dominantly affected by the applied axial force. Therefore, it can be concluded that no additional consideration for the P-$\Delta$ effect and vortical earthquake is required in the seismic design of a slender RC column if the axial force effect is taken into account in the analysis and design procedures.

• Composites Research
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• v.16 no.6
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• pp.41-47
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• 2003

Composites are widely used for aircraft, satellite and other structures due to its good mechanical and thermal characteristics such as low coefficient of thermal expansion(CTE), heat-resistance, high specific stiffness and specific strength. In order to use composites under condition of high temperature, however, material properties of composites at high temperatures must be measured and verified. In this paper, material properties of T700/Epoxy were measured through tension tests of composite specimens with an embedded FBG sensor in the thermal chamber at the temperatures of RT, $100^{\circ}$, $200^{\circ}$, $300^{\circ}$, $300^{\circ}$. Through the pre-test of an embedded optical fiber, we confirmed the embedding effects of an optical fiber on material properties of the composites. Two kinds of specimens of which stacking sequences are [0/｛0｝/0]$_{T}$. and [$90_2$/｛0｝/$90_2$]. were fabricated. From the experimental results, material property changes of composites were successfully shown according to temperatures and we confirmed that fiber Bragg grating sensor is very appropriate to strain measurement of composites under high temperature.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.6
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• pp.589-596
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• 2014

Joints, fasteners or connected parts frequently have a significant effect on the dynamical behavior of assembled mechanical structures. Therefore, the analytical prediction of structural responses depends on the accuracy of joint modeling. This paper deals with the formulation and analysis of dynamic mechanism for joint flexibilities whose relevant magnitudes of stiffnesses are investigated by using linear and torsional springs. The equation of motion is derived by using a generic joint in the middle of clamped-clamped beam. A reanalysis due to changes in magnitudes of joint stiffnesses is based on the reduced analysis where the binomial series terms are used as basis vectors. The solution procedures are straightforward and the method can be readily used with a general finite element method. The computational effort needed by this approach is usually much smaller than the effort needed for complete vibration analysis. Two numerical examples show that accurate results are obtained efficiently by reducing the number of degree in the reduced model.

• Structural Engineering and Mechanics
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• v.52 no.5
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• pp.1019-1032
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• 2014

Rails are key elements in railway superstructure since these elements receive directly the train load transmitted by the wheels. Simultaneously, rails must provide effective stress transference to the rest of the track elements. This track element often deteriorates as a consequence of the vehicle passing or manufacturing imperfections that cause in rail several defects. Among these rail defects, transverse cracks highlights and are considered a severe pathology because they can suddenly trigger the rail failure. This study is focused on UIC-60 rails with transverse cracks. A 3-D FEM model is developed in ANSYS for the flawless rail in which conditions simulating the crack presence are implemented. To account for the inertia loss of the rail as a consequence of the cracking, a reduction of the bending stiffness of the rail is considered. The numerical models have been calibrated using the first four bending vibration modes in terms of frequencies. These vibration frequencies have been obtained using the Experimental Modal Analysis technique, studying the changes in the modal parameters of the rails induced by the crack and comparing the results obtained by the model with experimental results. Finally, the calibrated and validated models for the single rail have been implemented in a complete railway ballasted track FEM model in order to study the static influence of the cracks on the rail deflection caused by a load passing.

• Computers and Concrete
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• v.24 no.6
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• pp.541-553
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• 2019

Alkali-silica reaction (ASR) in concrete can induce degradation in its mechanical properties, leading to compromised serviceability and even loss in load capacity of concrete structures. Compared to other properties, ASR often affects the modulus of elasticity more significantly. Several empirical models have thus been established to estimate elastic modulus reduction based on the ASR expansion only for condition assessment and capacity evaluation of the distressed structures. However, it has been observed from experimental studies in the literature that for any given level of ASR expansion, there are significant variations on the measured modulus of elasticity. In fact, many other factors, such as cement content, reactive aggregate type, exposure condition, additional alkali and concrete strength, have been commonly known in contribution to changes of concrete elastic modulus due to ASR. In this study, an artificial intelligent model using artificial neural network (ANN) is proposed for the first time to provide an innovative approach for evaluation of the elastic modulus of ASR-affected concrete, which is able to take into account contribution of several influence factors. By intelligently fusing multiple information, the proposed ANN model can provide an accurate estimation of the modulus of elasticity, which shows a significant improvement from empirical based models used in current practice. The results also indicate that expansion due to ASR is not the only factor contributing to the stiffness change, and various factors have to be included during the evaluation.

• Journal of the Korean Geophysical Society
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• v.6 no.4
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• pp.277-294
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• 2003

Structures show the phenomena of deformation and lowering of function with time-lapse by artificial environments and changes of geotechnical conditions or accumulation of initial deformation elements. This study aims the structural assessment of cultural property, Chum-Sung-Dae, located in Kyeongjucity, Korea. It was built about 1,300 years ago, and has undergone deformation and ground-subsidence with time-lapse. Non-destructive evaluation techniques were applied to the Chum-Sung-Dae, to protect it from survey. Because of this reason, 3D precise laser scanning surveying system was applied to measure the exact size of Chum-Sung-Dae, displacement and declining angles. Geophysical exploration also was applied to study the subsurface distribution of geotechnical parameters or physical properties. Natural frequencies were measured from real and model of Chum-Sung-Dae to study the dynamic characteristics of vibration and/or earthquake load and stiffness of structures.

• Elastomers and Composites
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• v.42 no.3
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• pp.143-150
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• 2007

Hardness of rubbery materials, which is important for dimensional stability and product performance, was investigated upon temperature change in this study. A newly developed IRHD (International Rubber Hardness Degree) tester was used to measure the hardness changes of NR and SBR specimens at various temperatures and the hardness values were compared with the Young's modulus. The harness and Young's modulus of NR and SBR showed an abrupt change near the glass transition temperatures. The hardness and Young's modulus were increased by increasing temperature due to the increased random chain conformation of molecules. The effect of temperature on hardness and Young's modulus of NR and SBR specimens filled with carbon black and silica was decreased by increasing filler content.