• Computers and Concrete
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• v.33 no.3
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• pp.301-308
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• 2024

This paper proposes a numerically-based methodology to implicitly model irreversible deformations in concrete through a damage model. Plasticity theory is not explicitly employed, although resemblances are still present. A scalar isotropic damage model is adopted and the damage variable is split in two: one contributing for stiffness degradation (cracking) and other contributing for irreversible deformations (plasticity). The proposed methodology is thermodynamically consistent as it consists in a damage model rewritten in different terms. Its Finite Element coding is presented, indicating that minor changes are necessary. It is also demonstrated that nonlinear algorithms are unnecessary to model concrete cracking and plasticity. Experimental data from direct tension and four-point bending tests under cyclic loading are compared to the proposed methodology. A numerical case study of a low-cycle fatigue is also presented. It can be concluded that the model is simple, feasible and capable to capture the essentials concerning cracking and plasticity.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3176-3183
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• 2010

A multi-scale fatigue life prediction methodology of composite pressure vessels subjected to multi-axial loading has been proposed in this paper. The multi-scale approach starts from the constituents, fiber, matrix and interface, leading to predict behavior of ply, laminates and eventually the composite structures. The multi-scale fatigue life prediction methodology is composed of two steps: macro stress analysis and micro mechanics of failure based on fatigue analysis. In the macro stress analysis, multi-axial fatigue loading acting at laminate is determined from finite element analysis of composite pressure vessel, and ply stresses are computed using a classical laminate theory. The micro stresses are calculated in each constituent from ply stresses using a micromechanical model. Three methods are employed in predicting fatigue life of each constituent, i.e. a maximum stress method for fiber, an equivalent stress method for multi-axially loaded matrix, and a critical plane method for the interface. A modified Goodman diagram is used to take into account the generic mean stresses. Damages from each loading cycle are accumulated using Miner's rule. Monte Carlo simulation has been performed to predict the overall fatigue life of a composite pressure vessel considering statistical distribution of material properties of each constituent, fiber volume fraction and manufacturing winding angle.

• Land and Housing Review
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• v.8 no.4
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• pp.249-256
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• 2017

Urbanization can be remarkable affected flood, pollutant loading, ecological system, and green infrastructure by distortion of hydrologic cycle. In order to mitigate these problems in urban, Low Impact Development(LID) technique has been introduced and applied in the world. SWMM model was calibrated with sets of field monitoring data and applied for calculation of runoff and pollutant loading in Asan-tangjung LID city under 2016 rainfall. Runoff reduction of watershed and catchment basins were showed efficiency 12.2% and 62.0%, respectively. Reduction of COD and TP loading also high efficiency in catchment basins were evaluated 74.9 and 71.4%. The results of this study can be used effectively in decision making processes of urban development project by comparing watershed runoff and pollutant reduction by designs of sort of LID technique, LID volume and location.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.589-597
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• 2009

High Performance Fiber-reinforced Cement Composite (HPFRCC) shows the multiple crack and damage tolerance capacity due to the interfacial bonding of the fibers to the cement matrix. For practical application, it is needed to investigate the fractural behavior of HPFRCC and understand the micro-mechanism of cement matrix with reinforcing fiber. This study is devoted to the investigation of the AE signals in HPFRCC under monotonic and cyclic uniaxial compressive loading, and total four series were tested. The major experimental parameters include the type and volume fraction of fiber (PE, PVA, SC), the hybrid type and loading pattern. The test results showed that the damage progress by compressive behavior of the HPFRCC is a characteristic for the hybrid fiber type and volume fraction. It is found from acoustic emission (AE) parameter value, that the second and third compressive load cycles resulted in successive decrease of the amplitude as compared with the first compressive load cycle. Also, the AE Kaiser effect existed in HPFRCC specimens up to 80% of its ultimate strength. These observations suggested that the AE Kaiser effect has good potential to be used as a new tool to monitor the loading history of HPFRCC.

• The Journal of Engineering Geology
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• v.16 no.3 s.49
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• pp.235-244
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• 2006

Granite cores were sampled within Korea Atomic Energy Research Institute and cyclic loadings up to 1550 cycles were applied. Microcrack development in samples due to cyclic loading was estimated using Acoustic Emission(AE) method. AE showed two different types depending on numbers of cycle. Type 1 appeared at low cycles and had low energy and diverse frequencies, while type 2 appeared at high cycles and had high energy and uniform frequency. AE property of type 1 indicates voids and pre-existing microcracks in samples may close or propagate up to certain length. Microcracks may be sheared or closed during loading and are recovered from shear or opened during unloading when AE of type 2 were measured. P wave velocities and Felicity ratios were measured at 50, 150, 350, 750, 1550 cycles. P wave velocities were almost the same regardless of number of cycles applied. However, Felicity ratios were much lower than 0.9, indicating that microcracks were developed within samples. This result indicates that Felicity ratio is a better tool than P wave velocity to estimate the damage of rock.

• Korean Journal of Agricultural Science
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• v.13 no.2
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• pp.255-264
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• 1986

The objectives of this study were to examine the viscoelastic behaviour of stem samples of rice in force-relaxation and rheological model to represent its relaxation behaviour, and to study the effects of rate of deformation and initial deformation on the relaxation time. The results were as follows; 1. In the process of loading and unloading, there is any plastic deformation so called elasto-plastic hysterisis. 2. Loading and unloading of stem of rice for several cycles has also shown the reduction of plastic or residual deformation and work hardening. 3. The relaxation behaviour of stem of rice in compression may be described by a generalized Maxwell model consisting of three Maxwell units in parallel. The rheological equation of such a model is given as $$F(t)=C_1e^{{-t/{\tau}}_1}+C_2e^{{-t/{\tau}}_2}+C_3e^{{-t/{\tau}}_3}$$ 4. Force relaxation always increased with increasing rates of deformation and initial deformation.

• Magazine of the Korea Concrete Institute
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• v.4 no.1
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• pp.135-145
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• 1992

With the increasing tendency to construct high rise reinforced concrete building~i, it is required to use high strength materIals, smaller member sections, and larger reinforcing bars, I t is generally recognized that under severe seismic loads beam column jomts may become more critical structural components than other structural elements. In a ductile momentresistmg reinforced concrete frame, the connection of bearncolumn must be capable of resistll1g the large lateral forces caused by seismic actions, The purpose of this experimental study is to evaluate and ll1vestigate the earthquake resistant perform ance of beam-colurrm subassemblies constructed with high-strength concrete cast by the concrete of com¬pressive strength of 700kg / cm2 subjected to reversed cyclic loadings. New approaches for moving the plastic hinging zone away from the column face and preventing the di¬agonal crack in the joint region are adopted to advance the earthquake-resistant performance of beam-column subassemblies using high-strengh concrete under severe earthquake-type loading. Exper¬imental results indicate that the modified new details which are introduced by intermediate reinforcement in the beam over a specific beam length adjacent to the joint are able to attain the stable hysteretic behavior and the enhancement of earthquake-resistant performance. Keywords: high strength concrete: beam-column Joints; seirnic loads(reversed cyclic loading) : earth¬quake-resistant performance; plastic hinge zone: diagonal crack: intermediate reinforce¬ment ; closed strirrup: hysteretic behavior: enhancement .

• Journal of the Korean Geotechnical Society
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• v.35 no.6
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• pp.39-48
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• 2019

This study investigated the lateral behavior of monopile embedded in the dry sand through cyclic lateral loading test using a centrifuge test. The sand sample for the experiment was the dry Jumunjin standard sand at 80% relative density and the friction angle of $38^{\circ}$. In the experimental procedure, firstly, it was determined the static lateral bearing capacity by performing the static lateral loading test to decide the cyclic load. This derived static lateral bearing capacity values of 30%, 50%, 80%, 120% were determined as the cyclic lateral load, and the number of cycle was performed 100 times. Through the results, the experiment cyclic p-y curve was calculated, and the cyclic p-y backbone curve by depth was derived using the derived maximum soil resistance point by the load. The initial slope at the same depth was underestimated than API (1987) p-y curves, and the ultimate soil resistance was overestimated than API (1987) p-y curves. In addition, the result of the comparison with the suggested dynamic p-y curve was that the suggested dynamic p-y curve was overestimated than the cyclic p-y backbone curve on the initial slope and soil resistance at the same depth. It is considered that the p-y curve should be applied differently depending on the loading conditions of the pile.

• The Journal of Korean Academy of Prosthodontics
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• v.59 no.4
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• pp.379-394
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• 2021

Purpose. In our previous studies, application of trichloroacetic acid (TCA) to gingival fibroblasts or to canine palatal soft tissue was verified to alter the expression of several genes responsible for cell cycle progression. In order to confirm this effect in a system allowing sequential release of TCA and epidermal growth factor (EGF), expression of various cell cycle genes following the application of the agents, using hydrophobically modified glycol chitosan (HGC)-based nano-controlled release system, was explored in this study. Materials and methods. HGC-based nano-controlled release system was developed followed by loading TCA and EGF. The groups were defined as the control (CON); TCA-loaded nano-controlled release system (EXP1); TCA- and EGF- individually loaded nano-controlled release system (EXP2). At 24- and 48 hr culture, expression of 37 cell cycle genes was analyzed in human gingival fibroblasts. Correlations and the influential genes were also analyzed. Results. Numerous genes such as cyclins (CCNDs), cell division cycles (CDCs), cyclin-dependent kinases (CDKs), E2F transcription factors (E2Fs), extracellular signal-regulated kinases (ERKs) and other cell cycle genes were significantly up-regulated in EXP1 and EXP2. Also, cell cycle arrest genes of E2F4, E2F5, and GADD45G were up-regulated but another cell cycle arrest gene SMAD4 was down-regulated. From the multiple regression analysis, CCNA2, CDK4, and ANAPC4 were determined as the most influential factors on the expression of ERK genes. Conclusion. Application of TCA and EGF, using the HGC-based nano-controlled sequential release system significantly up-regulated various cell cycle progression genes, leading to the possibility of regenerating oral soft tissue via application of the proposed system.

• Journal of the Korean Electrochemical Society
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• v.21 no.3
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• pp.47-54
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• 2018

To maximize the areal capacity($mAh\;cm^{-2}$) of $LiNi_{0.5}Co_{0.2}Mn_{0.3}O_2$(NCM523) electrode with the same loading level of $15mg\;cm^{-2}$, three NCM523 electrodes with 4, 2, and 1 wt% poly(vinylidene fluoride)(PVdF) binder content are fabricated. Due to the delamination issue of electrode composite at the edge during punching process, the 1 wt% electrode is excluded for further evaluation. When the PVdF binder content decreases from 4 to 2 wt%, both adhesion strength and shear stress decrease from 0.4846 to $0.2627kN\;m^{-1}$ by -46% and from 3.847 to 2.013 MPa by -48%, respectively. Regardless of these substantial decline of mechanical properties, their initial electrochemical properties such as initial coulombic efficiency and voltage profile are almost the same. However, owing to high loading level, the 2 wt% electrode not only exhibits worse cycle performance than the 4 wt% electrode, but also cannot maintain its mechanical integrity only after 80 cycles. Therefore, if the binder content is reduced to increase the area capacity, the mechanical properties as well as the cycle performance must be carefully evaluated.