• Journal of the Korean Society for Railway
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• v.18 no.3
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• pp.261-269
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• 2015

To overcome the weaknesses of viaduct bridges and the non-economic efficiency of underground LRT, the study of near-surface railway systems is in progress. To apply a box structure to the low depth transit, a connection joint to precast modules are very important when applying precast modular structures to replace temporary structures. In this study, wall to wall connections were applied in diverse cases such as rebar connections, guiding structures that were used to fit the verticality of precast walls during construction, and non-reinforcement structures used only for waterstop. Experimental performance verification was carried out for the bending, shear and splitting of the wall to wall connection. Precision of construction joints between wall to wall was identified as a factor that influenced the structural performance of the precast wall. A structure that can serve as a guide during the vertical insertion of a wall is confirmed for the most suitable case, but it will be necessary to modify this structure for detailed cases.

• Journal of the Korean Society for Railway
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• v.16 no.6
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• pp.466-472
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• 2013

The use of a concrete track is gradually growing in urban and high-speed railways in many part of the world. The resilient pad, which is essentially when concrete tracks are used, plays the important role of relieving the impact caused by train loads. The simple fatigue test[1] to estimate the variable stiffness of resilient pads is usually performed, but it differs depending on the practical conditions of different railways. In this study, the static stiffness levels of used resilient pads according to passing tonnages levels were measured in laboratory tests. Also, the simple fatigue test and the multi-stress accelerated degradation test for new resilient pads were performed in a laboratory. The static stiffness of the used pad was compared with the results of tests of usage times and cycles. The results of the comparison showed that the variable static stiffness levels of the used pad were similar to results of the multi-stress accelerated degradation test considering the fatigue and heat load. With a T-NT equation related to the degree of the multi-stress accelerated degradation, a model of multi-stress accelerated degradation for a resilient pad was devised. It was found through this effort that the total acceleration factor was approximately 2.62. Finally, this study proposes an equation for a multi-stress accelerated degradation model for polyurethane resilient pads.

• Korean Journal of Agricultural Science
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• v.25 no.2
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• pp.260-270
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• 1998

The field tests were performed to suggest the rational method for stability evaluation of soft clay. The behavior of settlement-displacement obtained by field monitoring system was to compare and analyze the results of the observationed method, and to investigate the complex behavior of soft clay with filling height. The results of this study are summarized as follows. 1. The horizontal displacement was suddenly increased when physical properties of soft clay showed maximum values and the part of the turning point. The values of these properties were available to the fundamental data for stability evaluation. The shear deformation appeared that difference of the horizontal displacement was maximum values. 2. Although the stability of embankment by step filling showed the unstable part over the failure standard line, the embankment was confirmed stable. So the evaluation of the stability of embankment is reasonable to use the inclination of curve than failure standard line. 3. The horizontal displacement and relative settlement were increased as same ratio at improvement ground. Estimation of shear deformation using Terzaghi's modified bearing capacity should consider the relations of embankment load and undrained shear strength at nonimprovement ground, and minimum safety factor is recommended to use larger than 1.2. 4. Excess pore water pressure was increased with increasing of filling height and decreased with maintain the filling height. The embankment was unstable when filling height was exceed the evaluation standard line, and the behavior of excess pore water pressure and horizontal displacement could use as a standard of judgement of the filling velocity control because their behavior were agree with each other.

• International Journal of Automotive Technology
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• v.6 no.3
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• pp.221-227
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• 2005

Aim of this study is to investigate an aerodynamic effect of a drag-reducing device on a heavy-duty truck. The vehicle experiences two different kinds of aerodynamic forces such as drag and uplifting force (or downward force) as it is traveling straight forward at constant speed. The drag force on a vehicle may cause an increase of the rate of fuel consumption and driving instability. The rolling resistance of the vehicle may be increased as result of the negative uplifting or downward force on the vehicle. A device named roof-fairing system has been applied to examine the reduction of aerodynamic drag force on a heavy-duty truck. As for a engineering design information, the drag-reducing system should be studied theoretically and experimentally for the best efficiency of the device. Four different types of roof-fairing model were considered in this study to investigate the aerodynamic effect on a model truck. The drag and downward force generated by vehicle has been obtained from numerical calculation conducted in this study. The forces produced on four fairing models considered in this study has been compared each other to evaluate the best fairing model in terms of aerodynamic performance. The result shows that the roof-fairing mounted truck has bigger negative uplifting or downward force than that of non-mounted truck in all speed ranges, and drag force on roof-fairing mounted truck has smaller than that of non-mounted truck. The drag coefficient $(C_D)$ of the roof-fairing mounted truck (Model-3) is reduced up to $41.3\%$ than that of non-mounted trucks (Model-1). A downward force generated by a roof-fairing mounted on a truck is linearly proportional to the rolling resistance force. Therefore, the negative lifting force on a heavy-duty truck is another important factor in aerodynamic design parameter and should be considered in the design of a drag-reducing device of a tractor-trailer. According to the numerical result obtained from present study, the drag force produced by the model-3 has the smallest of all in all speed ranges and has reasonable downward force. The smaller drag force on model-3 with 2/3h in height may results of smallest thickness of boundary layer generated on the topside of the container and the lowest intensity of turbulent kinetic energy occurs at the rear side of the container.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.40 no.3
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• pp.59-65
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• 2017

The purpose of this study is to investigate the factors and effects of job stress of construction workers on construction accidents and turnover intention in order to improve the field work environment of construction industry which shows higher industrial accidents than other industries. To this end, research models and hypotheses were established based on previous research, and the questionnaire was distributed to 10 construction companies in Daejeon, Sejong, and Chungcheong provinces. The 301 data collected were performed statistical analysis such as basic statistical analysis, factor analysis, reliability analysis, correlation analysis, regression analysis, and logistic regression analysis using the statistical package (IBM SPSS 22). The results of this study are summarized as follows. First, job stress has a significant effect on accident occurrence. Among the sub-factors of job stress, there was positive (+) influence on work culture and relationship conflict between peers, and organizational system had negative influence. Job demands, compensation incompetence, and job instability were not statistically significant. Therefore, it is necessary to concentrate on the factors of work culture, organizational system, and relationship conflict in the construction site. Second, job stress has positive effect on turnover intention. Job stress, inadequacy of compensation, and work culture were positively related to turnover intention. Third, job demands have a slightly greater impact than compensatory inadequacies. The factors that make the job turnover more important are the excessive job burdens such as respect, internal motivation, responsibility rather than expectation non-conformity, time pressure, increase of work load. Therefore, in order to reduce the turnover intention of the construction worker, it is necessary to pay attention to improvement of the job requirement. Fourth, the worker's job stress could overcome by exercise and fatigue elimination, work environment management, and self-opening for others. It is necessary to establish a work environment management system for counseling and intimacy formation to open up the exercise and fatigue relief program of the workers at the construction site and to open themselves between the workers and the supervisors.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.3
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• pp.9-20
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• 1989

It is important to enhance the safety of ship structures as much as possible in order to prevent the disastrous collapse of structures. In fact, the strength problem of structures is closely related with the safety problem of structures. Recently, the direct calculation method using a rational approach based on the first principle is implemented into the structural design process instead of adopting empirical approach based on the rules. The structural designer have shown increased concern with the problem of adequacy of conventional design method based on the safety factor since it does not fully take into account some degree of variability of the applied loads on and the strength of ship structures. To deal with the analysis of structures effectively, it is necessary to have three stages being equally treated. The first one is load analysis, second one response analysis, third one safety analysis. For marine structures, most of research effort has been however put into the first and second stages. The third stage is normally done by simple procedures. Hence, the various probabilistic methods are compared in order to establish the reliability analysis techniques for ship structures. As a result, the advanced level 2 method is selected as a most effective and accurate reliability method. The validity of this method is further demonstrated by comparing the results with the conventional method for the problem of the longitudinal strength of hull girder of Ro-Ro ship.

• Journal of the Ergonomics Society of Korea
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• v.35 no.6
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• pp.503-517
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• 2016

Objective: The aim of this study was to evaluate the effectiveness of 3 dimensional contoured pillow through analyzing contact pressure and to suggest its design guidelines through analyzing the posture of head and neck area. Background: The quality of sleep is a very important factor closely related with human's health. To improve the quality of sleep, the verification of design factors affecting the posture of the head and neck is needed, and a pillow design that can induce proper posture is required. Method: This study measured the contact pressures of the two reference groups (bead and cotton pillows) as a method to evaluate the design effectiveness of the contoured pillow. This study proposed 3-dimensional design guidelines by drawing anthropometry (head length) affecting cervical curvature angle (CCA) through the measurement of the participants' cervical curvature angles. Results: In the design effectiveness evaluation, the contact pressure of cervical region was higher than that of a reference group (cotton pillow), and contract area increased, and contract pressure decreased in the shape distributing the occipital region's body pressure. This study proposed pillow's cervical supporting height by percentile of a head length [head length (%tile) (cervical supporting height) affecting the posture of the head and neck: 14.6cm (5%tile) (6.2cm), 15.5cm (25%tile) (6.7cm), 16.4cm (50%tile) (7.1cm), and 19.3cm (75%tile) (8.9cm)]. Conclusion: This study confirmed the contoured pillow's design effectiveness maintaining cervical angle comfortable to sleep with the shape supporting the cervical vertebrae and by reducing the contact load of the occipital region. Also, this study proposed pillow design guidelines based on the 3-dimensional contoured pillow design effectiveness, through which the study laid the foundation for pillow design in a systematic method. Application: The results of this study are expected to be utilized as the basis data by which the optimum pillow type and pillow design according to main percentile can be standardized.

• The Journal of Advanced Prosthodontics
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• v.1 no.2
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• pp.85-90
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• 2009

STATEMENT OF PROBLEM. Over the years, resin-bonded fixed partial dentures (RBFPDs) have gone through substantial development and refinement. Several studies examined the biomechanics of tooth preparation and framework design in relation to the success rate of RBFPDs and considered retention and resistance form essential for increase of clinical retention. However, these criteria required preparations to be more invasive, which violates not only the original intentions of the RBFPD, but may also have an adverse effect on retention due to loss of enamel, an important factor in bonding. PURPOSE. The object of this in vitro study was to compare the dislodgement resistance of the new types of RBFPDs, the conventional three-unit fixed partial denture, and conventional design of RBFPD (Maryland bridge). MATERIAL AND METHODS. Fifty resin mandibular left second premolars and second molars were prepared on dentiforms, according to the RBFPD design. After model fabrication (five group, n = 10), prostheses were fabricated and cemented with zinc phosphate cement. After cementation, the specimens were subjected to tensile loading at a cross head speed of 4 mm/min in a universal testing machine. The separation load was recorded and analyzed statistically using one-way analysis of variance followed by Duncan's multiple range test. RESULTS. Group V, the pin-retained RBFPDs, had the highest mean dislodgement resistance, whereas specimens of group II, the conventional RBFPDs, exhibited a significantly lower mean dislodgement resistance compared to the other 4 groups (P <.05). There were no significant differences between group I, III, and IV in terms of dislodgement resistance (P>.05). Group V had the highest mean MPa (N/$mm^2$) (P <.05). There was no significant difference between groups I, II, III and IV (P > .05). CONCLUSION. Within the limits of the design of this in vitro study, it was concluded that: 1. The modified RBFPDs which utilizes the original tooth undercuts and requires no tooth preparation, compared with the conventional design of RBFPDs, has significantly high dislodgement resistance (P < .05). 2. The modified RBFPDs which utilizes the original tooth undercuts and requires minimal tooth preparation, compared with the conventional FPDs, has significantly no difference in retention and dislodgement resistance)(P>.05). 3. The pin-retained FPDs showed a high dislodgement resistance compared to the conventional three-unit FPDs (P<.05).

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.187-194
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• 2013

Fiber reinforced polymer (FRP) has been gathering interest from designers and engineers for its possible usage as a replacement reinforcement of a steel reinforcing bar due to its advantageous characteristics such as high tensile strength, non-corrosive material, etc. Since it is manufactured with various contents ratios, fiber types, and shapes without any general specification, test results for concrete members reinforced with these FRP reinforcing bars could not be systematically used. Moreover, since investigations for FRP reinforced members have mainly focused on short-term behavior, the purpose of this study is to evaluate long-term behaviors of glass FRP (GFRP) reinforcing bar and concrete beams reinforced with GFRP. In this paper, test results of tensile and bond performance of GFRP reinforcing bar and creep behavior are presented. In the creep tests, results showed that 100 years of service time can be secured when sustained load level is below 55% of tensile strength of GFRP reinforcing bar. A modification factor of 0.73 used to calculate long-term deflection of GFRP reinforced beams was acquired from the creep tests for GFRP reinforced concrete beams. It is expected that these test results would give more useful information for design of FRP reinforced members.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.3
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• pp.1-12
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• 2004

Due to the 1989 Loma Prieta, 1995 Hyogoken Nambu earthquakes, etc, a number of bridge columns  were collapsed in flexure-shear failures as a consequence of the premature termination of the column longitudinal reinforcement. Nevertheless, previous researches for the performance of bridge columns were concentrated on the flexural failure mode. It is well understood that the seismic behaviour of RC bridge piers was dependent on the performance of the plastic hinge of RC bridge piers, the ductility of which was desirable to be computed on the basis of the curvature. Experimental investigation was made to evaluate the variation of the curvature of the plastic hinge  region for the seismic performance of earthquake-damaged RC columns in flexure-shear failure mode. Seven test specimens in the aspect ratio of 2.5 were made with test parameters: confinement ratios, lap splices, and retrofitting FRP materials. They were damaged under series of artificial earthquakes that could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading under a constant axial load, $P=0.1f_{ck}A_g$. Residual seismic capacity of damaged specimens was evaluated by analzying the moment-curvature hysteresis and the curvature ductility. Test results show that the biggest curvature was developed around 15cm above the footing, which induced the column failure. It was observed that RC bridge specimens with lap-spliced longitudinal steels appeared to fail at low curvature ductility but significant improvement was made in the curvature ductility of RC specimens with FRP straps wrapped around the plastic hinge region. Based on the experimental variation of the curvature of RC specimens, new equivalent length of the plastic hinge region was proposed by considering the lateral confinement in this study. The analytical and experimental relationship between the displacement and the curvature ductility were compared based on this proposal, which gave excellent result.