• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1603-1611
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• 2004

The validity of 'modified overlay model' to describe the cyclic behavior of annealed 316L stainless steel at room temperature was investigated. Material parameters(~f$_{i}$, m$_{i}$b, η, E) fur the model were obtained through constant strain amplitude test. The strain amplitude dependency of elastic limit and cyclic hardening, which were the characteristics of this model, were considered. Eight subelements were used to describe the nonlinearity of the hysteresis loops. The calculated hysteresis curve in each condition (0.5％, 0.7％, 0.9％ train amplitude test) was very close to the experimental one. Two tests, incremental step test and 5-step test, ere performed to check the validity of 'modified overlay model'. The elastic limit was saturated to the one of the highest strain amplitudes of the block in the incremental step test, so it seemed to be Masing material at the stabilized block. Cyclic hardening was successfully described in the increasing sequence of the strain amplitude in 5-step test. But, the slight cyclic softening followed by higher strain amplitude would not be able to simulate by'modified overlay model'. However, the discrepancy induced was very small between the calculated hystereses and the experimental ones. In conclusion,'Modified overlay model'was proved to be appropriate in strain range of 0.35％~ 1.0％..0％.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.87-98
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• 1999

Consolidation settlements on soft clay are often greatly and potentially damaging to structures. Currently, large-scale projects are in planning or progressing in Korea. These structures will be constructed on both thick and soft clay layers, and so the accurate evaluation of magnitude of settlement is required at every step in design and construction. Especially, secondary compression may play an important role in consolidation settlements of soft clay. Generally, the magnitudes of secondary compression are evaluated by laboratory and in-situ consolidation tests. The empirical $C_a/C_c$ may be economical, fast and powerful tool in estimating secondary consolidation settlement. However, the databases of the $C_a/C_c$ at construction site in Korea are insufficient. The purpose of this study is to investigate the relationship of $C_a/C_c$ on marine clay near the southern sea in Korea. A series of incremental loading consolidation tests (measuring base pore water pressure) is peformed. It was found that the $C_a/C_c$ on undisturbed marine clay is 0.0397.

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.6
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• pp.2317-2322
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• 2015

Background: Despite the increasing number of screening examinations performed for cervical cancer utilizing the Papanicolaou smear test (Pap test), few studies have examined whether this strategy is cost-effective in Korea. Objective: This study was conducted to evaluate the cost-effectiveness of cervical cancer screening strategies incorporating the Pap test based on age at the start and end of screening as well as screening interval. Materials and Methods: We designed four alternative screening strategies based on patient age when screening was started (20 or 30 years) and discontinued (lifetime, 79 years). Each strategy was assessed at screening intervals of 1, 2, 3, or 5 years. A Markov model was developed to determine the cost-effectiveness of the 16 possible cervical cancer screening strategies, and this was evaluated from a societal perspective. The main outcome measures were average lifetime cost, incremental quality-adjusted life-years (QALYs), and incremental cost-effectiveness ratio (ICER). Results: Compared with various strategies comprising younger starting age, discontinuation age, and longer screening intervals, strategies employing annual screening for cervical cancer starting at a target age of 30 years and above were the most cost-effective, with an ICER of 21,012.98 dollars per QALY gained (with a Korean threshold of 30,000,000 KRW or US$27,272). Conclusions: We found that annual screening for cervical cancer beginning at a target age of 30 years and above is most cost-effective screening strategy. Considering the potential economic advantages, more intense screening policies for cervical cancer might be favorable among countries with high rates of cervical cancer and relatively low screening costs.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.10
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• pp.5125-5129
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• 2012

Economic decision models are being increasingly used to assess medical interventions. Advances in this field are mainly due to enhanced processing capacity of computers, availability of specific software to perform the necessary tasks, and refined mathematical techniques. We here estimated the incremental cost-effectiveness of ten strategies for colon cancer screening, as well as no screening, incorporating quality of life, noncompliance and data on the costs and profit of chemotherapy in Iran. We used a Markov model to measure the costs and quality-adjusted life expectancy of a 50-year-old average-risk Iranian without screening and with screening by each test. In this paper, we tested the model with data from the Ministry of Health and published literature. We considered costs from the perspective of a health insurance organization, with inflation to 2011, the Iranian Rial being converted into US dollars. We focused on three tests for the 10 strategies considered currently being used for population screening in some Iranians provinces (Kerman, Golestan Mazandaran, Ardabil, and Tehran): low-sensitivity guaiac fecal occult blood test, performed annually; fecal immunochemical test, performed annually; and colonoscopy, performed every 10 years. These strategies reduced the incidence of colorectal cancer by 39%, 60% and 76%, and mortality by 50%, 69% and 78%, respectively, compared with no screening. These approaches generated ICER (incremental cost-effectiveness ratios) of $9067, $654 and $8700 per QALY (quality-adjusted life year), respectively. Sensitivity analyses were conducted to assess the influence of various scales on the economic evaluation of screening. The results were sensitive to probabilistic sensitivity analysis. Colonoscopy every ten years yielded the greatest net health value. Screening for colon cancer is economical and cost-effective over conventional levels of WTP8.

• Tunnel and Underground Space
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• v.11 no.3
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• pp.225-236
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• 2001

The roughness of rock joint is one of the most important parameters in developing the shear resistance and the tendency of dilation. Due to the damage accumulated with shearing displacement, the roughness angle is lowered continuously. It is known that dilation, shear strength hardening, and softening are directly related to the degradation of asperities. Much effort has been directed to incorporate the complicated damage mechanism of asperities into a constitutive model fur rock joints. This study presents an elasto-plastic formulation of joint behavior including elastic deformability, dilatancy and asperity surface damage. It is postulated that the plastic portion of incremental displacement 7an be decomposed into contributions from both sliding along the asperity surface and damage of asperity. Numerical cyclic shear tests are presented to illustrate th? performance of the derived incremental stress-displacement relation. A laboratory cyclic shear test is also simulated. Numerical examples reveal that the elasto-plastic joints model is promising.

• Steel and Composite Structures
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• v.35 no.4
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• pp.599-609
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• 2020

The tension-only braced frames (TOBFs) are widely used as a lateral force resisting system (LFRS) in low-rise steel buildings due to their simplicity and economic advantage. However, the system has poor seismic energy dissipation capacity and pinched hysteresis behavior caused by early buckling of slender bracing members. The main concern in utilizing the TOBF system is the determination of appropriate performance factors for seismic design. A formalized approach to quantify the seismic performance factor (SPF) based on determining an acceptable margin of safety against collapse is introduced by FEMA P695. The methodology is applied in this paper to assess the SPFs of the TOBF systems. For this purpose, a trial value of the R factor was first employed to design and model a set of TOBF archetype structures. Afterwards, the level of safety against collapse provided by the assumed R factor was investigated by using the non-linear analysis procedure of FEMA P695 comprising incremental dynamic analysis (IDA) under a set of prescribed ground motions. It was found that the R factor of 3.0 is appropriate for safe design of TOBFs. Also, the system overstrength factor (Ω₀) was estimated as 2.0 by performing non-linear static analyses.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.3
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• pp.259-266
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• 2012

In this paper the seismic performance of a flat plate wall system structure was evaluated based on the ATC-63 approach, and the results were compared with those of a wall slab structure having the same size. As analysis model structures, a twelve story flat plate wall structure and a wall slab structure were designed based on the KBC-2009, and their seismic performances and collapse behaviors were evaluated by nonlinear static and incremental dynamic analyses(IDA). It was observed that the flat plate wall structure was designed with smaller amount of reinforced concrete, and showed slightly larger displacement response compared with those of the wall slab structure. The collapse margin ratios of the two structures obtained from the incremental dynamic analyses satisfied the limit states specified in the ATC-63, and the structures turned out to have enough capacity to resist the design level seismic load.

• Computers and Concrete
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• v.22 no.2
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• pp.227-237
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• 2018

Today, the modeling of concrete as a material within finite element simulations is predominantly done through nonlinear material models of concrete. In current sophisticated computational systems, there are a number of complex concrete material models which are based on theory of plasticity, damage mechanics, linear or nonlinear fracture mechanics or combinations of those theories. These models often include very complex constitutive relations which are suitable for the modeling of practically any continuum mechanics tasks. However, the usability of these models is very often limited by their parameters, whose values must be defined for the proper realization of appropriate constitutive relations. Determination of the material parameter values is very complicated in most material models. This is mainly due to the non-physical nature of most parameters, and also the large number of them that are frequently involved. In such cases, the designer cannot make practical use of the models without having to employ the complex inverse parameter identification process. In continuum mechanics, however, there are also constitutive relations that require the definition of a relatively small number of parameters which are predominantly of a physical nature and which describe the behavior of concrete very well within a particular task. This paper presents an example of such constitutive relations which have the potential for implementation and application in finite element systems. Specifically, constitutive relations for modeling the plane stress state of concrete are presented and subsequently tested and evaluated in this paper. The relations are based on the incremental theory of elastic strain-hardening plasticity in which a non-associated flow rule is used. The calculation result for the case of concrete under uniaxial compression is compared with the experimental data for the purpose of the validation of the constitutive relations used.

• Computers and Concrete
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• v.10 no.1
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• pp.1-18
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• 2012

This paper presents the details of studies conducted on hollow concrete block masonry (HCBM) units and wall panels. This study includes, compressive strength of unit block, ungrouted and grouted HCB prisms, flexural strength evaluation, testing of HCBM panels with and without opening. Non-linear finite element (FE) analysis of HCBM panels with and without opening has been carried out by simulating the actual test conditions. Constant vertical load is applied on the top of the wall panel and then lateral load is applied in incremental manner. The in-plane deformation is recorded under each incremental lateral load. Displacement ductility factors and response reduction factors have been evaluated based on experimental results. From the study, it is observed that fully grouted and partially reinforced HCBM panel without opening performed well compared to other types of wall panels in lateral load resistance and displacement ductility. In all the wall panels, shear cracks originated at loading point and moved towards the compression toe of the wall. The force reduction factor of a wall panel with opening is much less when compared with fully reinforced wall panel with no opening. The displacement values obtained by non-linear FE analysis are found to be in good agreement with the corresponding experimental values. The influence of mortar joint has been included in the stress-strain behaviour as a monolith with HCBM and not considered separately. The derived response reduction factors will be useful for the design of reinforced HCBM wall panels subjected to lateral forces generated due to earthquakes.

• Structural Engineering and Mechanics
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• v.68 no.6
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• pp.747-760
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• 2018

In the present study, a methodology for developing fragilities of arch concrete dams to assess their performance against seismic hazards is introduced. Firstly, the probability risk and fragility curves are presented, followed by implementation and representation of the way this method is used. Amirkabir arch concrete dam was subjected to non-linear dynamic analyses. A modified three dimensional rotating smeared crack model was used to take the nonlinear behavior of mass concrete into account. The proposed model considers major characteristics of mass concrete. These characteristics are pre-softening behavior, softening initiation criteria, fracture energy conservation, suitable damping mechanism and strain rate effect. In the present analysis, complete fluid-structure interaction is included to account for appropriate fluid compressibility and absorptive reservoir boundary conditions. In this study, the Amirkabir arch concrete dam is subjected to a set of 8 three-component earthquakes each scaled to 10 increasing intensity levels. Using proposed nonlinear smeared crack model, nonlinear analysis is performed where the structure is subjected to a large set of scaled and un-scaled ground motions and the maximum responses are extracted for each one and plotted. Based on the results, fragility curves were plotted according to various and possible damages indexes. Discrete damage probabilities were calculated using statistical methods for each considered performance level and incremental nonlinear analysis. Then, fragility curves were constructed based on the lognormal distribution assumption. Two damage indexes were introduced and compared to one another. The results indicate that the dam has a proper stability under earthquake conditions at MCE level. Moreover, displacement damages index is more conservative and impractical in the fragility analysis than tensional damage index.