• Steel and Composite Structures
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• v.43 no.4
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• pp.511-522
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• 2022

An experimental investigation to study the behaviour of connections between cold-formed steel (CFS) joist and plywood structural panel is presented in this paper. Material testing on CFS and plywood was carried out to assess their mechanical properties and behaviour. Push-out tests were conducted to determine the slip modulus and failure modes of three different shear connection types. The employed shear connectors in the study were; size 14 (6mm diameter) self-drilling screw, M12 coach screw, and M12 nut and bolt. The effective bending stiffness of composite cold-formed steel and plywood T-beam assembly is calculated based on the slip modulus values computed from push-out tests. The effective bending stiffness was increased by 25.5%, 18% and 30.2% for self-drilling screw, coach screw, nut and bolt, respectively, over the stiffness of cold-formed steel joist alone. This finding suggests the potential to enhance the structural performance of composite cold-formed steel and timber flooring system by mobilisation of composite action present between timber sheathing and CFS joist.

• Journal of the Korean Wood Science and Technology
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• v.32 no.3
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• pp.33-41
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• 2004

In ancient wooden structures, the mechanical properties of the structural members have been reduced by time-dependent degradations such as fatigue or creep. Also, the external and internal deterioration was caused by environmental condition, fungi, bacteria, or insect, and then reduced the quality of structural members. However, the previous methods for evaluating the deterioration have been mainly depended on the visual inspection. In this study, therefore, ultrasonic stress wave test, accelerometer stress wave test were used to evaluate the deterioration of structural wood members in ancient wooden structures. Based on the results, the quantitative criteria of stress wave transmitted velocity were proposed to evaluate the deterioration of structural member. The proposed criteria were related to the degree of deterioration. In accelerometer stress wave, the criteria of deterioration of wave reciprocal velocity was below 1800 ㎲/m at incipient deterioration (below 12% ratio of deterioration), between 1800 and 2200 ㎲/m at moderate deterioration (12~17%) and above 2200 ㎲/m at severe deterioration (above 17%). The ultrasonic stress wave, the criteria of deterioration were 800 and 950 ㎲/m at below 8% and above 15% of the degree of deterioration respectively.

• Smart Structures and Systems
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• v.29 no.3
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• pp.475-484
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• 2022

The loss of cable tension for civil infrastructure reduces structural bearing capacity and causes harmful deformation of structures. Currently, most of the structural health monitoring (SHM) approaches for cables rely on contact transducers. This paper proposes a cable tension identification technology using percussion sound, which provides a fast determination of steel cable tension without physical contact between cables and sensors. Notably, inspired by the concept of tensioning strings for piano tuning, this proposed technology predicts cable tension value by deep learning assisted classification of "percussion" sound from tapping a steel cable. To simulate the non-linear mapping of human ears to sound and to better quantify the minor changes in the high-frequency bands of the sound spectrum generated by percussions, Mel-frequency cepstral coefficients (MFCCs) were extracted as acoustic features to train the deep learning network. A convolutional neural network (CNN) with four convolutional layers and two global pooling layers was employed to identify the cable tension in a certain designed range. Moreover, theoretical and finite element methods (FEM) were conducted to prove the feasibility of the proposed technology. Finally, the identification performance of the proposed technology was experimentally investigated. Overall, results show that the proposed percussion-based technology has great potentials for estimating cable tension for in-situ structural safety assessment.

• Journal of the Korean Society for Advanced Composite Structures
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• v.2 no.1
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• pp.15-22
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• 2011

Pultruded fiber reinforced polymeric plastic (PFRP) structural members may be one of attractive alternatives of the structural members in the civil engineering applications because of its many advantageous mechanical properties. However, they have relatively low modulus of elasticity and also cross-sections of structural shapes are composed of thin plate components such as flange and web. Therefore, structural stability is an important issue in the design of pultruded structural compression members. For the design of pultruded structural member under compression, buckling and post-buckling strengths of plate components may be taken into account. In the structural steel design following AISC/LRFD, in addition to the buckling strength, the nonuniform stress distribution in the section is incorporated with a form factor. In this paper, the form factor for the design of PFRP structural member under compression is investigated through the analytical study. Furthermore, the process for the determination of the form factor is suggested.

• Journal of Labour Economics
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• v.29 no.2
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• pp.29-66
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• 2006

This study investigates the structural change of wage determination within internal labor market that have occurred around the financial crisis in 1997 by using the personnel data(1996~2000) of a Korean large firm. We take the effect of performance-based pay system to apply on wage determination of workers using Mincerian earnings function estimation. After introducing the annual salary system in the firm, we did not find the fact that the wage effect of seniority decreases, but we found the wage effect of relative evaluation ratings increases. Then, this study identifies the importance of the reward strategy of firm in Korean internal labor market. Finally, we have concluded that although the firm acknowledged the positive effects of performance-based HRM practices, we have not obtained enough evidence on the transformation into such practices because the seniority-based HRM has been traditionally prevalent in the Korean internal labor market.

• Journal of the Korean Wood Science and Technology
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• v.43 no.1
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• pp.25-35
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• 2015

The goal of this study was to review the visual grading and allowable stress determination methodologies for the domestic softwood. Previous studies used different grading (KFRI 1995-27, KFRI 2000-39, KFRI 2007-3, KFRI 2009-1) and allowable stress determination methodologies (ASTM D 245, KS F 2152, JAS 1990). The results of the visual grading were different by each researcher. Compared to the $1^{st}$ grade proportion from the previous studies using the previous specification on visual grading (KFRI 1995-2007), a higher $1^{st}$ grade proportion was found from the studies using the current specification (KFRI 2009). Compared to the allowable stress values from the small clear sample, the higher allowable stress values from the structural size were found. The results indicated that the strength reduction factor used in small clear sample was too conservative for the different grades. To obtain consistent results for the grade, it is required to have experts in visual grading and authorized organizations. An official standard methodology for the allowable stress value determination needs to be defined for the reliable stress value.

• Journal of the Korea Society of Computer and Information
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• v.23 no.10
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• pp.143-149
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• 2018

The purpose of this study was to construct and validate a middle - aged exercise adherence model. The model was designed based on self - determination theory. Participants were 215 middle-aged men and women aged 40-60 who had been exercising for more than six months. Data was collected from four big cities of Seoul, Busan, Gwangju and Daejeon in Korea, using a questionnaire consisting of basic psychological needs, intrinsic motivation, social support, and exercise adherence. Data were analyzed with SPSS 19.0 and AMOS 20.0. Social support and exercise adherence of the questionnaire were partially revised and verified by confirmatory factor analysis. The results of the study were as follows. The model's fit indices: GFI = .938, AGFI) = .915, NFI = .912, CFI = .941, and RMSEA = 0.041. The model satisfied the model fit of the structural model equation. This study model based on self - determination theory was confirmed that basic psychological needs, intrinsic motivation, and social support were important factors for the middle - aged's exercise adherence. Basic psychological need and intrinsic motivation had a direct influence on the adherence of exercise, and social support indirectly influenced the exercise adherence through intrinsic motivation. Both basic psychological needs and social support directly affected internal motivation. The most influential factor in the middle - aged's exercise adherence was intrinsic motivation. In conclusion, it was found that intrinsic motivation such as interest and fun is important for the middle - aged to continue the exercise. Also, the basic psychological needs were important for middle aged's exercise adherence. The results of this study will provide basic data for restoring or maintaining health by continuing exercise. Strategies that enhance intrinsic motivation are needed when a chronic ill person needs to continue long-term exercising.

• Structural Engineering and Mechanics
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• v.58 no.5
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• pp.757-781
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• 2016

The results of diagnostics and analysis of an industrial hall located on the premises of a thermal power plant severely damaged by fire are presented in the paper. The comprehensive failure-related diagnostics, non-destructive and destructive tests of steel and concrete materials, geodetic surveying of selected structural members, numerical modelling, static analysis and reliability assessment were focused on two basic goals: The determination of the current technical condition of the load bearing structure and the assessment of its post fire resistance as well as assessing the degree of damage and subsequent design of reconstruction measures and arrangements which would enable the safe and reliable use of the building. The current mechanical properties of the steel material obtained from the tests and measured geometric characteristics of the structural members with imperfections were employed in finite element models to study the post-fire behaviour of the structure. In order to compare the behaviour of the numerically modelled steel roof truss, subjected to the effects of fire, with the real post-fire response of the damaged structure theoretically obtained resistance, critical temperature and the time at which the structure no longer meets the required reliability criteria under its given loading are compared with real values. A very good agreement between the simulated results and real characteristics of the structure after the fire was observed.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3427-3429
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• 2012

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.891-896
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• 2001

As composite materials, the addition of steel fiber in concrete significantly improves the engineering properties of structural members, notably shear strength and ductility, In this study, shear capacity evaluation method according to steel fiber contents was proposed from the literature surveys and member tests. For this, previously proposed five shear strength equation were examined and evaluated by maximum shear strength and shear capacity ratio. From the parametric study and regression analysis, following conclusion can be made; the maximum shear strength of steel fiber reinforced column will be estimated by relative shear capacity ratio.