• Computers and Concrete
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• v.6 no.4
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• pp.319-341
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• 2009

A new formulation based on lumped plasticity and inelastic hinges is presented in this paper for nonlinear analysis of Reinforced Concrete (RC) frame structures. Inelastic hinge behaviour is described using the principles of Continuum Damage Mechanics (CDM). Member formulation contains provisions to model stiffness degradation due to cracking of concrete and yielding of reinforcing steel. Depending on its nature, cracking is classified as concentrated or distributed. Concentrated cracking is accounted through a damage variable and its growth is defined based on strain energy principles. Presence of distributed flexural cracks in a member is taken care of by modelling it as non-prismatic. Plasticity theory supported by effective stress concept of CDM is applied to describe the post-yield response. Nonlinear quasi-static analysis is carried out on a RC column and a wide two-storey RC frame to verify the formulation. The column is subjected to constant axial load and monotonic lateral load while the frame is subjected to only lateral load. Computed results are compared with those due to experiments or other numerical methods to validate the performance of the formulation and also to highlight the contribution of distributed cracking on global response.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.539-542
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• 2008

Recently, GMP(Glass Molding Press) process is mainly used to produce aspheric glass lenses. Because glass lens is heated at high temperature above Ty (yielding point) for forming glass, the quality of aspheric glass lens is deteriorated by residual stresses which are generated in a aspheric glass lens after forming. Before this study, as a fundamental study to develop forming conditions for progressive GMP process, compression, strain relaxation and thermal conductivity tests were carried out to obtain the visco-rigid plastic, the visco-elastic and thermal properties of K-PBK40 which is newly developed and applied for precision molding glass material, In this study, using the experimental results we obtained, a glass lens forming simulation in progressive GMP process was carried out and we could forecast the shape of deformed glass lenses and residual stresses contribution in the structure of deformed glass lenses after forming.

• Korean Journal of Materials Research
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• v.19 no.7
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• pp.397-402
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• 2009

In this study, Ti powder was fabricated from Ti scrap by the Hydrogenation-Dehydrogenation (HDH) method. Hydrogenation reactions of Ti scrap occurred at near 450 $^{\circ}C$ with a sudden increase in the reaction temperature and the decreasing pressure of hydrogen gas during the hydrogenation process in the furnace. The dehydrogenation process was also carried out at 750 $^{\circ}C$ for 2hrs in a vacuum of $10^{-4}$ torr. After the HDH process, a deoxidation treatment was carried out with the Ca(purity: 99.5) at 700 $^{\circ}C$ for 2hrs in the vacuum system. It was found that the oxidation content of Ti powder that was deoxidized with Ca showed noticeably lower values, compared to the content obtained by HDH process. In order to fabricate Ti compacts, Ti powder was sintered at $1100\sim1400^{\circ}C$ for 2hrs under a vacuum of $10^{-4}$ torr. The relative density of compact was 94.9% at 1300 $^{\circ}C$. After sintering, all of the Ti compacts showed brittle fracture behavior, which occurred in an elastic range with short plastic yielding up to a peak stress.

• Structural Engineering and Mechanics
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• v.27 no.3
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• pp.277-292
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• 2007

Based on the composite finite element simulation and a series of hydrostatic pressure and burst tests, autofrettage effects on strength and deformation of fiber reinforced pressure vessel with metallic liners have been studied in the paper (autofrettage: during the course of one pressure taking effect, the increasing internal stress in metallic liner can surpass the yielding point and the plastic deformation will happen, which result in that when there is no internal pressure, there are press stress in liner while tensile stress in fiber lamination). By making use of a composite finite element Ansys code and a series of experiments, the autofrettage pressure is determined in order to make the aluminium liner be totally in elastic state, under given hydrostatic test pressure. The stress intensity factors of the longitudinal crack in aluminum liner end under internal pressure and thermal loads have been computed and analyzed before and after the autofrettage processing. Through numerical calculation and experiment investigations, it is found that a correct choice for autofrettage pressure can improve the gas-tightness and fatigue strength of FRP vessel.

• Steel and Composite Structures
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• v.29 no.5
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• pp.623-633
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• 2018

A robust element is essential for successful design of steel frames with Direct analysis (DA) method. To this end, an innovative and efficient curved-quartic-function (CQF) beam-column element using the fourth-order polynomial shape function with end-springs in series is proposed for practical applications of DA. The member initial imperfection is explicitly integrated into the element formulation, and, therefore, the P-${\delta}$ effect can be directly captured in the analysis. The series of zero-length springs are placed at the element ends to model the effects of semi-rigid joints and material yielding. One-element-per-member model is adopted for design bringing considerable savings in computer expense. The incremental secant stiffness method allowing for large deflections is used to describe the kinematic motion. Finally, several problems are studied in this paper for examining and validating the accuracy of the present formulations. The proposed element is believed to make DA simpler to use than existing elements, which is essential for its successful and widespread adoption by engineers.

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.6
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• pp.227-235
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• 2022

For a member model in nonlinear structural analysis, a lumped plastic model that idealizes its flexural bending, shear, and axial behaviors by springs with the nonlinear hysteretic model is widely adopted because of its simplicity and transparency compared to the other rigorous finite element methods. On the other hand, a challenging task in its numerical solution is to satisfy the equilibrium condition between nonlinear flexural bending and shear springs connected in series. Since the local forces between flexural and shear springs are not balanced when one or both springs experience stiffness changes (e.g., cracking, yielding, and unloading), the additional unbalanced force due to overshooting or undershooting each spring force is also generated. This paper introduces an iterative scheme for numerical solutions satisfying the equilibrium conditions between flexural bending and shear springs. The effect of equilibrium iteration on analysis results is shown by comparing the results obtained from the proposed method to those from the conventional scheme, where the equilibrium condition is not perfectly satisfied.

• Steel and Composite Structures
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• v.51 no.3
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• pp.325-335
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• 2024

Yielding dampers exhibit varying cyclic behavior based on their geometry. These dampers not only increase the energy dissipation of the structure but also increase the strength and stiffness of the structure. In this study, parametric investigations were carried out to explore the impact of angled U-shape damper (AUSD) dimensions on its cyclic behavior. Initially, the numerical model was calibrated using the experimental specimen. Subsequently, analytical equations were presented to calculate the yield strength and elastic stiffness, which agreed with the experimental results. The outcomes of the parametric studies encompassed ultimate strength, effective stiffness, energy dissipation, and equivalent viscous damper ratio (EVDR). These output parameters were compared with similar dampers. Also, the magnitude of the effect of damper dimensions on the results was investigated. The results of parametric studies showed that the yield strength is independent of the damper width. The length and thickness of the damper have the greatest effect on the elastic stiffness. Reducing length and width resulted in increased energy dissipation, effective stiffness, and ultimate strength. Damper width had a more significant effect on EVDR than its length. On average, every 5 mm increase in damper thickness resulted in a 3.6 times increase in energy dissipation, 3 times the effective stiffness, and 3 times the ultimate strength of the model. Every 15 mm reduction in damper width and length increased energy dissipation by 14% and 24%, respectively.

• Tunnel and Underground Space
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• v.19 no.6
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• pp.498-506
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• 2009

The stability assessment of a concrete liner of a compressed air storage tunnel should be performed by an approach which is different from that commonly used for the liners of road tunnels, since the liner is exposed to high air pressure. In this study, the stability analysis method for the liner of compressed air storage tunnel is proposed based on the elastic and elasto-plastic solutions of the thick-walled cylinder problem. In case of elastic analysis, the yield initiation condition at the inner boundary is considered as the failure condition of the liner, while the condition which results in the extension of yielding zone to a certain depth is taken as a failure indicator of the liner in the elasto-plastic analysis taking Mohr-Coulomb criterion. The application of the proposed method revealed that the influence of the relative magnitude of boundary loads on the stability of liner is considerable. In particular, noting that the estimation of the outer boundary load may be relatively difficult, it is thought that the precise prediction of outer boundary load is very important in the analysis. Accordingly, the emphasis is put on the selection of the liner installation time, which may govern the magnitude of outer boundary load.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6C
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• pp.267-275
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• 2009

The steel pipe of steel-concrete composite piles increases the pile strength and induces the ductile failure by constraining the deformation of the inner concrete. In this research, the load-movement relations and the reinforcement effect by the outer steel pipe in the steel-concrete composite pile were analyzed by performing three-dimensional numerical analyses, which can simulate the yielding behavior of the pile material and the elasto-plastic behavior of soils. The parameters analyzed in the study include three pile materials of steel, concrete and composite, pile diameter and loading direction. As the results, the axial capacity of the composite pile was 1.9 times larger than that of the steel pipe pile and similar with that of the concrete pile. At the allowable movement criteria, the horizontal capacity of the composite pile was 1.46 times larger than that of the steel pile and 1.25 times larger than that of the concrete pile. In addition, the horizontal movement at the pile head of the composite pile was about 78% of that of the steel pile and about 53% of that of the concrete pile, which showed that the movement reduction effect of the composite pile was significant and enables the economical design of drilled shafts.

• Korean Journal of Soil Science and Fertilizer
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• v.33 no.1
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• pp.1-7
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• 2000

Management of phosphorus availability in the plastic film house soils in Korea merits attention because salts have been accumulated for last decades due to the heavy application of fertilizers and intensive cropping practices. In an attempt to characterize the P availability, available phosphorus contents and electrical conductivity of the saturated extracts ($EC_e$) were measured for soils collected from the 169 plastic film houses in Kangwon-do. Soil phosphorus contents were analyzed by methods of Lancaster, Bray No. 1, Olsen, Truog, water extractable and saturation extracts. Phosphorus concentrations in the saturated extracts of the plastic film house soils ranged from 0.02 to $34mg\;L^{-1}$, with the average of $8mg\;L^{-1}$. The available $P_2O_5$ of the soils ranged from 136 to $3,689mg\;Kg^{-1}$, with the average of $1,261mg\;Kg^{-1}$. The water soluble $P_2O_5$ ranged from 2 to $118mg\;L^{-1}$, with the average of $39mg\;L^{-1}$. A significant correlation existed between saturation extract P (Y) and available $P_2O_5$ (X) [Y = -5.075 + 0.018X, $r=0.662^{***}$] indicating $1.0mg\;P\;L^{-1}$ of in the saturated extract was equivalent to $337mg\;Kg^{-1}$ of the available $P_2O_5$ by Lancaster method. Electrical conductivity of the saturated pastes ($EC_e$) was highly significantly correlated with EC (1:5), yielding the slope of 12.2 for the coarse textured plastic film house soils. Results of higher concentrations of available P in soil solution and dilution factor of 12.2 for $EC_e$ demonstrate that a special care must be taken in terms of fertilizer management and data interpretation for soils under this specific condition.