• Physical Therapy Korea
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• v.18 no.3
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• pp.76-84
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• 2011

The purpose of this study was to investigate the correlations between pain intensity, physical impairments, disability, and psychological factors according to the difference in duration of low back pain. This study was a cross-sectional survey of 102 participants with low back pain, divided into two groups equal in number: The first group consisted of patients with acute and subacute low back pain, while the second group consisted of patients suffering from chronic low back pain. The results showed that gender, age, pain intensity, physical impairment, disability and Fear-Avoidance Beliefs (FABs) for work activities were not significantly different between two groups. FABs for physical activities of the first group were significantly more prevalent than in the second group. More than moderate correlations were found between pain intensity, physical impairment, and disability in the first group. Less than moderate correlations were found between pain intensity, physical impairment, disability, FABs, and depression in the second group. These findings suggest that we must consider psychological factors in the treatment of patients with chronic low back pain. Regression analyses revealed that pain intensity and FABs for work activities significantly contributed to the prediction of disability in the first group. Also, pain intensity and FABs for physical activities significantly contributed to the prediction of disability in the second group. Pain intensity was most important predictor of disability in two groups.

• Physical Therapy Korea
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• v.20 no.4
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• pp.22-31
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• 2013

The aim of the present study was to compare measurement precisions of the Oswestry Back Pain Disability Questionnaire (ODQ) and a computer adaptive testing (CAT) method. The ODQ has been regarded as one of the most reliable condition-specific measure for back pain for decades. Cross-sectional study was carried out with two independent convenient samples from two out-patient rehabilitation clinics for back pain ($n_1=42$) and non-back pain group ($n_2=42$). Participants were asked to fill out the ODQ and CAT of International Classification of Functioning, Disability and Health-Activity Measure (ICF-AM). A series of Rasch analyses were performed to calculate person ability measures. The CAT measures had greater relative precision in discriminating the groups than did the ODQ measure in comparisons of the relative precision. The CAT measure appears to be more effective than did the ODQ measure in terms of measurement precision. By administering test items calibrated in a way, CAT measures using item response theory may promise a means with measurement precision as well as efficiency.

• Steel and Composite Structures
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• v.33 no.4
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• pp.595-614
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• 2019

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation on both the welded and screw fastened back-to-back built-up CFS unequal angle sections under axial compression. The load-axial shortening and the load verses lateral displacement behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated FE model was then used for the purpose of a parametric study to investigate the effect of different thicknesses, lengths and, yield stresses of steel on axial strength of back-to-back built-up CFS unequal angle sections. Five different thicknesses and seven different lengths (stub to slender columns) with two different yield stresses were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections.

• Steel and Composite Structures
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• v.42 no.1
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• pp.1-22
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• 2022

In cold-formed steel (CFS) structures, such as trusses, transmission towers and portal frames, the use of back-to-back built-up CFS unequal angle sections are becoming increasingly popular. In such an arrangement, intermediate welds or screw fasteners are required at discrete points along the length, preventing the angle sections from buckling independently. Limited research is available in the literature on axial strength of back-to-back built-up CFS unequal angle sections. The issue is addressed herein. This paper presents an experimental investigation reported by the authors on back-to-back built-up CFS unequal angle sections with intermediate stiffeners under axial compression. The load-axial shortening behaviour along with the deformed shapes at failure are reported. A nonlinear finite element (FE) model was then developed, which includes material non-linearity, geometric imperfections and modelling of intermediate fasteners. The FE model was validated against the experimental test results, which showed good agreement, both in terms of failure loads and deformed shapes at failure. The validated finite element model was then used for the purpose of a parametric study comprising 96 models to investigate the effect of longer to shorter leg ratios, stiffener provided in the longer leg, thicknesses and lengths on axial strength of back-to-back built-up CFS unequal angle sections. Four different thicknesses and seven different lengths (stub to slender columns) with three overall widths to the overall depth (B/D) ratios were investigated in the parametric study. Axial strengths obtained from the experimental tests and FE analyses were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparisons show that the current DSM is conservative by only 7% and 5% on average, while predicting the axial strengths of back-to-back built-up CFS unequal angle sections with and without the stiffener, respectively.

• Transactions of Materials Processing
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• v.33 no.1
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• pp.18-35
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• 2024

In the present work, the evolution rules for the internal variables including continuum damage factors are obtained using the thermodynamic framework, which are in turn facilitated to derive the elastic-plastic constitutive relation for the particulate composites. Using the Mori-Tanaka scheme, the homogenization on state and internal variables such as back-stress and damage factors is carried out to procure the rate independent plasticity relations. Moreover, the degradation of mechanical properties of constituents is depicted by the distinctive damages such that the phase and interfacial damages are treated individually accordingly, whereas the kinematic hardening is depicted by combining the Armstrong-Frederick and Phillips' back-stress evolutions. On the other hand, the present constitutive relation for each phase is expressed in terms of the respective damage-free effective quantities, then, followed by transformation into the damage affected overall nominal relations using the aforementioned homogenization concentration factors. An emphasis is placed on the qualitative analyses for strain localization by observing the perturbation growth instead of the conventional bifurcation analyses. It turns out that the proposed constitutive model offers a wide range of strain localization behavior depending on the evolution of various internal variable descriptions.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.417-424
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• 2005

Observed field behaviors are frequently different from the behaviors predicted in the design state due to several uncertainties involved in soil properties, numerical modelling, and error of measuring system even though a sophisticated numerical analysis technique is applied to solve the consolidation behavior of drainage-installed soft deposits. In this study, genetic algorithms are applied to back-analyze the soil properties using the observed behavior of soft clay deposit composed of multi layers that shows complex consolidation characteristics. Utilizing the program, one might be able to appropriately predict the subsequent consolidation behavior from the measured data in an early stage of consolidation of multi layered soft deposits. Example analyses for drainage-installed multi-layered soft deposits are performed to examine the applicability of proposed back-analysis method.

• Journal of the Korean Operations Research and Management Science Society
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• v.35 no.4
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• pp.17-31
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• 2010

This study investigates two-stage return policy and recycling issues in an e-marketplace supply chain consisting of consumers, a retailer and a manufacturer. The manufacturer, a focal company in the e-marketplace supply chain, considers the recycling of commercial returns so offers the retailer a buy-back contract of which transfer payment consists of a wholesale price and a buy-back price. Then, under the given contract offer, the retailer determines a selling price and a return policy to control consumers' demand and return requests. We consider the retailer's opportunistic behavior and supply chain coordination issues based on the principal-agent paradigm. We compare the first-best and second-best optima and conduct comparative static analyses to evaluate the performance results of the buy-back contract and provide important managerial implications.

• Transactions of Materials Processing
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• v.17 no.3
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• pp.161-169
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• 2008

In the present work, the two-back stress model is proposed and continuum damage mechanics (CDM) is incorporated into the plastic constitutive relation in order to describe the plastic deformation localization and the damage evolution in a deforming continuum body. Coupling between damage mechanics and isothermal rate independent plasticity is performed using the kinematic hardening rule, which in turn is formulated by combining the nonlinear Armstrong-Frederick rule and the Phillips rule. The numerical analyses are carried out within h deformation theory. It is noted that the damage evolution within a work piece accelerates the plastic deformation localization such that the material with lower hardening exponent results in a rapid shear band formation. Moreover, the results from the numerical analysis reflected closely with the micro-structures around the fractured regime. The effects of the various hardening parameters on deformation localization are also investigated. As the nonlinear strain rate description in the back stress evolution becomes dominant, the strain localization becomes intensified as well as the damage evolution.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.10
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• pp.16-23
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• 2020

Vehicle seats provide a comfortable ride for passengers by properly absorbing vibrations and shocks transmitted during driving. Vibration analyses on three models with different shapes were carried with the same material properties and constraint conditions. By varying the height of the seat-back, models 1, 2, and 3 were designed according to the inclined angle of the seat-back frame. Models 1, 2, and 3 were modeled with relatively simple designs using CATIA. The areas touching the buttocks of passengers show the most deformation. This work shows that seat durability and stability can vary depending on the shape of the seat design.

• Journal of the Ergonomics Society of Korea
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• v.30 no.6
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• pp.695-703
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• 2011

Objective: This study was to investigate the effects of coordinated upper-limb body postures on the subjective discomfort rating, heart rate, and muscle activities. Background: Although generally many checklists such as OWAS, RULA, and REBA were applied to evaluate various body postures, the body postures were might be overestimated or underestimated because each body part(i.e., back, shoulder, and elbow etc.) was evaluated separately, and then added all rates of individual body parts to assess an overall risk level for the body posture in these methodologies. Methods: A total of 20 participants maintained 14 postures which were combinations of back, shoulder, and elbow flexion angles and then muscle activities, subjective discomfort, and heart rates were collected every three minute during a sustained 15 minute and 0.5kg weight holding task. Four muscle groups were investigated: erector spine, anterior deltoid, upper trapezius, triceps brachii. Results: Results showed that subjective discomfort was the lowest when the angle of back and shoulder were both $0^{\circ}s$, while the body posture with $45^{\circ}$ of back angle and $45^{\circ}$ shoulder angle was rated as the most subjective discomfort posture. In general, the subjective discomfort ratings increased as back and shoulder flexion angles increased. It was noted that, however, the subjective discomfort of body posture with a $45^{\circ}$ back angle and $45^{\circ}$ shoulder flexion angle was lower than that of body posture with a $0^{\circ}$ back and $45^{\circ}$ shoulder flexion angle. The research findings of heart rates and muscle activities showed similar results for the analyses of subjective discomfort ratings. Conclusions: The possible limitations of the current ergonomics evaluation techniques which assessing a body posture with summing all body part score after individually analyzed in this study. Based on the analyses of subjective discomfort, heart rate, and muscle activities, it was recommended that a use of effects of coordinated upper-limb body postures would be considered when one evaluates work-load for various working postures. Application: These findings can be used for developing a more accurate assessment checklist for working posture as well as preventing musculoskeletal disorders of workers in workplaces.