• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.175-182
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• 1998

An analytical study to trace the nonlinear structural behavior of composite beams is undertaken to include the nonlinear material properties of steel sheeting, reinforcing steel bar and concrete. To trace Moment-curvature relations, sectioning analysis method and two simple formulas are developed. A simple power model which has been originally used to expect the flexural capacity of the beam to column connections is proposed and the second formula is composed of two experimental functions to express the Moment-curvature relation in the elastic and plastic range separately. The load-deflection behavior of the beams has been simulated by the step-by-step numerical integration method and is compared with the test results available.

• Geotechnical Engineering
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• v.4 no.3
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• pp.53-62
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• 1988

When a ground soil is under the constant continuous stress less than the failure strength of that soil, its deformation, in some cases, will increase continuously as time goes on due to creep phenomena. Deformation of soil caused by creep behavior will appear in various types depending on the elastic, plastic, viscous properties of soil. Therefore in this study, visco-plastic characteristics of grouted soil was studied by analysing the result of uniaxial creep test on the grouted soil. As a result of this research, it was found that the rheological model of grouted soil can be decided as Vyalov model and the visco-plastic properties of grouted soil is influenced by the content of silicate in grout.

• Geomechanics and Engineering
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• v.16 no.2
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• pp.205-215
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• 2018

Strain-based criteria are known as a direct method in determining the stability of the geomechanical structures. In spite of the widely use of Sakurai critical strain criterion, it is so conservative to make use of them in rocks with initial plastic deformation on account of the considerable difference between the failure and critical strains. In this study, a new criterion has been developed on the basis of the failure strain to attain more reasonable results in determining the stability status of the tunnels excavated in the rocks mostly characterized by plastic-elastic/plastic behavior. Firstly, the stress-strain curve was obtained having conducted uniaxial compression strength tests on 91 samples of eight rock types. Then, the initial plastic deformation was omitted making use of axis translation technique and the criterion was presented allowing for the modified secant modulus and by use of the failure strain. The results depicted that the use of failure strain criterion in such rocks not only decreases the conservativeness of the critical strain criterion up to 42%, but also it determines the stability status of the tunnel more accurately.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.12
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• pp.73-85
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• 1997

The rolling force and roll deformation behavior in the twin roll type strip continuous casting process has been computed to estimate the thermal charcteristics of a caster roll. To calculation of rolling force, the relationship between flow stress and strain for a roll material and casting alloy are assumed as a function of strain-rate and temperature because mechanical properties of a casting materials depends on tempera- ture. The three dimensional thermal dlastic-plastic analysis of a cooling roll has also been carried out to obtain a roll stress and plastic strain distributions with the commercial finite element analysis package of ANSYS. Temperature fields data of caster roll which are provided by authors were used to estimated of roll deformation. Roll life considering thermal cycle is calculated by using thermal elastic-plastic analysis results. Roll life is proposed as a terms of a roll revolution in the caster roll with and without fine failure model on the roll surface. To obtain of plastic strain distributions of caster roll, thermomechan- ical properties of roll sleeve with a copper alloy is obtained by uniaxial tensile test for variation of temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1031-1036
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• 2000

In this study, a numerical simulation that can effectively predict the strengthening effect of repaired aged RC structures is developed using the axial deformation link elements. In repaired structures, concrete and interface are modeled as quasi-brittle materials. An elastic-perfectly plastic constitutive relationship is introduced for reinforcing bars. Also, a linear-elastic relationship for repair materials such as FRP or CFS. Structural deterioration in terms of corrosion of steel rebar is considered. The interfacial property between steel and concrete which is reduced by corrosion of steel rebar is obtained by comparing numerical results with experimental results of pull out tests. Obtained values are used in repaired reinforced concrete structures under flexural loading conditions. To investigate strengthening effect of the structures repaired with carbon fiber sheet(CFS), repaired and unrepaired RC structures are analyzed numerically. From analysis, rip-off, debonding and rupture failure mechanisms of interface between substrate and CFS can be determined. Finally, strengthening effect according to the variation of interfacial material properties is investigated, and it is shown that interfacial material properties have influence on the mechanical behavior of repaired structure systems Therefore, the developed numerical method using axial deformation link elements can use for determining the strengthening effects and failure mechanism of repaired aged RC structure.

• Journal of Surface Science and Engineering
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• v.54 no.3
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• pp.139-143
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• 2021

Cr-Al-N coatings were deposited onto WC-Co substrates using a cathodic arc evaporation (CAE) system. CAE technique is recognized to be a very useful process for hard coatings because it has many advantages such as high packing density and good adhesion to metallic substrates. In this study, the influence of deposition temperature as a key process parameter on film growth behavior and mechanical properties of Cr-Al-N coatings were systematically investigated and correlated with microstructural changes. From various analyses, the Cr-Al-N coatings prepared at deposition temperature of 450℃ in the CAE process showed excellent mechanical properties with higher deposition rate. The Cr-Al-N coatings with deposition temperature around 450℃ exhibited the highest hardness of about 35 GPa and elastic modulus of 442 GPa. The resistance to elastic strain to failure (H/E ratio) and the index of plastic deformation (H³/E² ratio) were also good values of 0.079 and 0.221 GPa, respectively, at the deposition temperature of 450℃. Based on the XRD, SEM and TEM analyses, the Cr-Al-N coatings exhibited a dense columnar structure with f.c.c. (Cr,Al)N multi-oriented phases in which crystallites showed irregular shapes (50~100nm in size) with many edge dislocations and lattice mismatches.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.1 no.1
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• pp.53-68
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• 1981

Most clays under sustained load exhibit time-dependent deformation because of creep movement of soil particles and many investigators have attempted to relate their findings to the creep behavior of natural ground and to the long-term stability of slopes. Since the creep behavior of clays may assume a variety of forms depending on such factors as soil plasticity, activity and water content, it is difficult and complicated to analyse the creep behavior of clays. Rheological models composed of linear springs in combination with linear or nonlinear dashpots and sliders, are generally used for the mathematical description of the time-dependent behavior of soils. Most rheological models, however, have been proposed to simulate the behavior of secondary compression for saturated clays and few definitive data exist that can evaluate the behavior of non-saturated clays under the action of sustained stress. The clays change gradually from a solid state through plastic state to a liquid state with increasing water content, therefore, the rheological models also change. On the other hand, creep is time-dependent, and also the effect of thixotropy is time-function. Consequently, there may be certain correlations between creep behavior and the effects of thixotropy in compacted clays. In addition, the states of clay depend on water content and hence the height of the specimen under drained conditions. Futhermore, based on present and past studies, because immediate elastic deformation occurs instantly after the pressure increment without time-delayed behavior, the factor representing immediate elastic deformations in the rheological model is necessary. The investigation described in this paper, based on rheological model, is designed to identify the immediate elastic deformations and the effects of thixotropy and height of clay specimens with varing water content and stress level on creep deformations. For these purposes, the uniaxial drain-type creep tests were performed. Test results and data for three compacted clays have shown that a linear top spring is needed to account for immediate elastic deformations in the rheological model, and at lower water content below the visco-plastic limit, the effects of thixotropy and height of clay specimens can be represented by the proposed rheological model not considering the effects. Therefore, the rheological model does not necessitate the other factors representing these effects. On the other hand, at water content higher than the visco-plastic limit, although the state behavior of clays is visco-plastic or viscous flow at the beginning of the test, the state behavior, in the case of the lower height sample, does not represent the same behavior during the process of the test, because of rapid drainage. In these cases, the rheological model does not coincide with the model in the case of the higher specimens.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.2
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• pp.315-327
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• 2002

The main objective of this study is to develop an discrete optimization algorithm of plane steel frames with rigid using second-order-elastic-plastic hinge analysis which is considering panel zone. Conventional analyses of steel frame are usually tarried out without considering the effect of panel zone deformation on frame behavior The validity of this model is established by comparison without panel zone on joint models is analyzed numerically to demonstrate the importance of using realistic models in steel frame analysis. The objective function is taken as Weight of steel frames and the constraints we formulated based on AISC-LRFD(1994). The validity of the developed algorithm we demonstrate by comparing the result with those of SAP2000. The result of the study indicates that the optimal design algorithm considering of panel zone behavior more economic design than simple steel frame design methods.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.465-471
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• 2006

To describe hysteretic behavior of steel structures under dynamic loading such as earthquake, the dynamic cyclic plasticity model considering stress-strain relationship and characteristics of used steel materials under static-dynamic deforming is required. In this paper, mechanical characteristics and stress-strain relationship of SM490 was clarified by carrying out static-dynamic monotonic and cyclic loading test. A dynamic cyclic plasticity model of SM490 was proposed based on the test results and applied 3-dimensional finite element analysis using finite deformation theory. An analytical method developed by the authors was verified validity and accuracy by comparing both analysis and test results. The comparison result shows that the analytical method developed by the authors can predict static-dynamic hysteretic behavior of steel structures with accuracy.

• Steel and Composite Structures
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• v.21 no.5
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• pp.1121-1144
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• 2016

This paper presents a displacement-based finite element procedure for second-order distributed plasticity analysis of planar steel frames with semi-rigid beam-to-column connections under static loadings. A partially strain-hardening elastic-plastic beam-column element, which directly takes into account geometric nonlinearity, gradual yielding of material, and flexibility of semi-rigid connections, is proposed. The second-order effects and distributed plasticity are considered by dividing the member into several sub-elements and meshing the cross-section into several fibers. A new nonlinear solution procedure based on the combination of the Newton-Raphson equilibrium iterative algorithm and the constant work method for adjusting the incremental load factor is proposed for solving nonlinear equilibrium equations. The nonlinear inelastic behavior predicted by the proposed program compares well with previous studies. Coupling effects of three primary sources of nonlinearity, geometric imperfections, and residual stress are investigated and discussed in this paper.