• International Journal of Highway Engineering
• /
• v.6 no.4 s.22
• /
• pp.109-121
• /
• 2004

This study was performed to investigate the characteristics of drying shrinkage for concrete slabs as a project for Korean pavement design procedure. According to the volume-surface ratios and aggregate types, the experiments have been executed for 252 days. In order to simulate the volume-surface ratio of a real concrete pavement slab, three-layer epoxy coating and wrapping were used to prevent the evaporation at the part of specimen surfaces. As a result of preliminary test, coating and wrapping method was identified as reliable for three months. According to the volume-surface ratio, the drying shrinkage of the concrete specimen using sandstone was measured 1.32 to 1.8 times higher than that of the limestone specimen. Comparing to the measured drying shrinkage strains and established ACI and CEB-FIP model equations, it turned out that those model equations were underestimated. Finally, considering the age and volume-surface ratios, the prediction equations of the drying shrinkage of concrete specimen were proposed through a multiple nonlinear regression analysis.

• Journal of Labour Economics
• /
• v.30 no.3
• /
• pp.43-75
• /
• 2007

This study reviews the trend of job separation rates for three years from 2002 to 2005 and investigates the various elements which influence this trend, especially the role of the labor unions, by using Korean Labor Panel data. In the basic statistics, the job retention rate of union members were higher by an average of 28.3% points compared to non-union members, but in the results of controlling the observed variables of individual influences in changing jobs, it was estimated that unions increase the job retention rate by 11% to 13% points. To investigate the effect of unions on the job stability of workers in detail, the non-linear decomposition method developed by Fairlie (2003) was used in the analysis. In examining the difference of job separation rates between union members and non-union members through observed variables of workers in explainable parts and unexplainable parts by using the non-linear decomposition technique, the contribution of the explainable part was estimated to be 67% to 74% and the unexplainable part accounted for the rest which was 26% to 33%. This suggests that not only does the union contribute to the job stability of its members, but the propensity to change jobs for a worker who is a union member is on average lower than that of a worker who is not a union member or who works at an establishment that does not have a union. The results of the empirical analysis show that the job stability effect of labor unions is limited within the boundary of a maximum 7% to 9% points. The reason for the effect of labor unions on job stability being so low is due to various reasons such as collective bargaining structure by company, intensified business competition after the financial crisis, and labor market segmentation.

• Journal of Korea Water Resources Association
• /
• v.48 no.7
• /
• pp.567-579
• /
• 2015

This study performed the non-stationary flood frequency analysis considering time-varying parameters of a probability density function. Also, return period and risk under non-stationary condition were estimated. A stationary model and three non-stationary models using Generalized Extreme Value(GEV) were developed. The only location parameter was assumed as time-varying parameter in the first model. In second model, the only scale parameter was assumed as time-varying parameter. Finally, the both parameters were assumed as time varying parameter in the last model. Relative likelihood ratio test and Akaike information criterion were used to select appropriate model. The suggested procedure in this study was applied to eight multipurpose dams in South Korea. Using relative likelihood ratio test and Akaike information criterion it is shown that the inflow into the Hapcheon dam and the Seomjingang dam were suitable for non-stationary GEV model but the other six dams were suitable for stationary GEV model. Also, it is shown that the estimated return period under non-stationary condition was shorter than those estimated under stationary condition.

• Science of Emotion and Sensibility
• /
• v.17 no.4
• /
• pp.71-78
• /
• 2014

Composite draw textured yarns(DTY) and air jet textured yarns(ATY) with hollow PET filament have been used for making high emotional fabrics including light weight sports wear garments. This study investigated effect of hollow composite yarns and fabric structural parameters to the comfort properties related to the moisture and thermal transport phenomena for the composite fabrics made of DTY and ATY with hollow PET filament. Wicking property of hollow composite fabric was superior at the high pore size fabric and was not influenced by fabric cover factor. Wicking property of the fabric with ATY was better than that of the fabric with DTY. On the other hand, drying rate of fine pore sized fabric was shorter than that of large pore sized fabric and drying rate of high multi yarn fabric with low cover factor and small pore size was superior than that of hollow composite fabric. The pore size of the fabric was dominant factor in the air permeability and thermal conductivity of hollow composite fabric. High pore sized fabric showed high air permeability and thermal conductivity of hollow composite fabric was nonlinearly inversely proportional to pore size of the fabric.

• Korean Journal of Construction Engineering and Management
• /
• v.10 no.4
• /
• pp.87-100
• /
• 2009

The quality of early cost estimates is critical to the feasibility analysis and budget allocation decisions for public capital projects. Various researches have been attempted to develop cost prediction models in the early stage of a construction project. However, existing studies are limited on its applicability to actual projects because they focus primarily on a specific phase as well as utilize restricted information while the amount of information collectable differs from one another along with the project stages. This research aims to develop two-staged cost estimation model for the schematic planning and preliminary design process of a construction projects, considering the available information of each phase. In the schematic planning stage where outlined information of a project is only available, the Case-Based Reasoning model is used for easy and rapid elicitation of a project cost based on the extensive database of more than 90 actual highway construction projects. Then, the representing quantity-based model is proposed for the preliminary design stage where more information on the quantities and unit costs are collectable based on the alternative routes and cross-sections of a highway project. Real case studies are used to demonstrate and validate the benefits of the proposed approach. Through the two-stage cost estimation system, users are able to hold a timely prospect to presume the final cost within the budge such that feasibility study as well as budget allocation decisions are made on effectively and competitively.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.15 no.2
• /
• pp.69-80
• /
• 2013

This study evaluates the seismic performance of road tunnels designed before the provisions for seismic design of tunnels were first established in 1999. Extensive design data and site investigation reports are investigated to select tunnels sections that are considered to be most susceptible to seismically induced damage under earthquake loading. Detailed analyses are performed on selected tunnels. The methods used are method of displacement and dynamic analysis. In performing the method of displacement, which is a type of pseudo-static analysis method used for underground structures, full domain and reduced domain modeling were used. The dynamic analyses are performed using finite difference method and using nonlinear constitutive model. Comparisons show that the reduced domain method of displacement match very closely with the dynamic analysis, demonstrating that it is the most suitable method for evaluating the seismic performance of road tunnels built in rocks. It is also shown that road tunnels, for which seismic design were not applied, are safe under the seismic risks corresponding to an earthquake with a return period 1000 years. It is concluded that additional seismic retrofit of tunnels is not necessary.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.7 no.3
• /
• pp.31-38
• /
• 2003

Lap splices were located in the plastic hinge region of most bridge piers that were constructed before the adoption of the seismic design provision of Korea Highway Design Specification on 1992. But sudden brittle failure of lap splices may occur under inelastic cyclic loading. The purpose of this study is to analytically predict nonlinear hysteretic behavior and ductility capacity of reinforced concrete bridge piers with lap splices under cyclic loading. For this purpose, a nonlinear analysis program, RCAHEST(Reinforced Concrete Analysis in Higher Evaluation System Technology) is used. Lap spliced bar element is developed to predict behaviors of lap spliced bar. Maximum bar stress and slip of lap spliced bar is also considered, The proposed numerical method for seismic performance evaluation of reinforced concrete bridge piers with lap splices is verified by comparison with reliable experimental results.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.2C
• /
• pp.238-246
• /
• 2004

In this paper, an estimator that take advantages of time and frequency correlation within an OFDM symbol is investigated. OFDM systems using the proposed estimator can be very effective in detecting signals under non-sampled space and time-varying channels. Also, under same complexity, the proposed estimator outperforms the previously proposed estimator. Since even if there are no assumption about channel correlation, the linear interpolation method instead of optimal interpolation using correct channel correlation is proposed in case the receiver does not know the channel correlation function in time domain. Therefore the proposed channel estimator help improving the performance of OFDM systems under non-sampled spaced and fast time-varying channels.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.20 no.6
• /
• pp.719-730
• /
• 2007

This study presents a thin-walled space frame element based on the classical Timoshenko beam theory. The element is derived according to the assumed strain field in order to resolve the shear-locking phenomenon. The shape function is developed in accordance with the strain field which is assumed to be constant at a 2-noded straight frame element. In this study, the geometrically nonlinear analysis applies the Corotational procedure in order to evaluate unbalanced loads. The bowing effect is also considered faithfully. Two numerical examples are given; monosymmetric curved and nonsymmetric straight cantilever. When these example structures behave lateral-torsional bucking, the critical loads are obtained by this study and ABAQUS shell elements. Also, the post-buckling behavior is examined. The results give good agreement between this study and ABAQUS shell.

• Korean Journal of Remote Sensing
• /
• v.25 no.4
• /
• pp.321-338
• /
• 2009

The objective of this paper is to compare spatial prediction capabilities of univariate kriging algorithms for generating GIS-based thematic maps from ground survey data with asymmetric distributions. Four univariate kriging algorithms including traditional ordinary kriging, three non-linear transform-based kriging algorithms such as log-normal kriging, multi-Gaussian kriging and indicator kriging are applied for spatial interpolation of geochemical As and Pb elements. Cross validation based on a leave-one-out approach is applied and then prediction errors are computed. The impact of the sampling density of the ground survey data on the prediction errors are also investigated. Through the case study, indicator kriging showed the smallest prediction errors and superior prediction capabilities of very low and very high values. Other non-linear transform based kriging algorithms yielded better prediction capabilities than traditional ordinary kriging. Log-normal kriging which has been widely applied, however, produced biased estimation results (overall, overestimation). It is expected that such quantitative comparison results would be effectively used for the selection of an optimal kriging algorithm for spatial interpolation of ground survey data with asymmetric distributions.