• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.1
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• pp.36-42
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• 2018

This paper considers the Marine Traffic Risk Assessment for fixed and moving targets, which threaten officers during a voyage. The Collision Risk Assessment Formula was calculated based on a dynamic ship domain considering the length, speed and maneuvering capability of a vessel. In particular, the Navigation Risk Assessment Model that is used to quantitatively index the effect of a ship's size, speed, etc. has been reviewed and improved using a hybrid combination of a vessel's dynamic area and the Collision Risk Assessment Formula. Accordingly, a new type of Marine Traffic Risk Assessment Model has been suggested giving consideration to the Speed Length Ratio, which was not sufficiently reflected in the existing Risk Assessment Model. The larger the Speed Length Ratio (dimensionless speed), the higher the CJ value. That is, the CJ value is presented well by the Speed Length Ratio. When the Speed Length Ratio is large, states ranging from [Caution], [Warning], [Dangerous] or [Very Dangerous] are presented from a greater distance than when the Speed Length Ratio is small. The results of this study, can be used for route and port development, including dangerous route avoidance, optimum route planning, breakwater width, bridge span, etc. as well as the development of costal navigation safety charts. This research is also applicable for the selection of optimum ship routing and the prevention of collisions for smart ships such as autonomous vessels.

• Journal of the Korean Geotechnical Society
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• v.16 no.4
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• pp.141-148
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• 2000

For the construction of 4.8km long Multi-Purpose Jamuna Bridge in Bangladesh, 2 or 3 large diameter open-ended steel pipe piles were used for the foundation of piers. A total of 123 piles were driven for 50 piers and 2 test piles from the river bed through the normally-consolidated upper sand layer and rested n top of gravel layer. Two types of piles, having 3.15 or 2.50m diameter and variable wall thickness in the range of 40 to 60mm, were driven to the depths of 69 to 74m with the rake of 6:1 by connecting 2 or 3 pieces of short piles. Dynamic pile tests were performed on 24 selected piles during pile driving and soil plug length inside the pile was also measured after driving of each short section.These piles were plugged with soil to, though slightly affected by pile diameters, about 75% of total length of pile driven. Active plug at the tip of pile contributed substantial amount of inner skin friction to the total capacity. Piles soon after driving showed a skin-friction dominant pile behaviour, tat is, 90% of total capacity being developed by skin resistance. Quakes values and Smith damping factors were almost constant regardless of pile diameters. This result reflects the influence of uniform soil condition at the site.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.61-69
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• 2004

The bridge piers under service suffered a brittle failure due to the deterioration of lap-spliced longitudinal reinforcement without developing its flexural capacity or ductility. The earthquake induced lateral force results in tension which causes bond-slip failure at the lap-spliced region in circular bridge piers. In this case, such a brittle failure can be controlled by the seismic retrofit using FRP laminated circular tube. The retrofitted piers using FRP laminated circular tube showed significant improvement in seismic performance due to FRP's confinement effect. This paper presents the analytical results on the seismic strengthening effect of circular bridge piers with poor lap-splice details and strengthened with FRP laminated circular tube. FRP's confinement effect is predicted by the classical elasticity solution for the laminated circular tube manufactured with several layers. The FRP laminated circular tube induces the flexural failure instead of a bond-slip failure of the circular reinforced concrete piers under seismic induced lateral forces. To investigate the correctness and effectiveness of analytical solution derived in this study, the analytical results were compared with the experimental data and it was confirmed that the results were correlated well each other, The effects on the confinement of FRP laminated circular tube, such as the number of layers, the fiber orientations, and the mechanical properties, were investigated. From the parametric study, it was found that the number of layers, the fiber orientations, and the major Young's modulus (E11) of the FRP laminated circular tube were the dominant parameters affecting the confinement of reinforced concrete circular bridge piers.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.197-208
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• 2003

This paper is to determine the possibility of re-using waste concrete from Incheon city area. The strength test was conducted with five aggregate compounds which was replaced a natural aggregate with recycled aggregate. After checking the physical characteristics of recycled aggregate compounds, the mix design of recycled concrete was conducted. For the relatively comparison between natural and recycled compounds, while the unit aggregate weight was changed, other conditions were fixed. The freezing and thawing test which included fly-ash and super-plastezer were performed to check the durability and workability when recycling waste concrete. In the physical characteristics of recycled aggregate, it was found that the specific gravity of recycled coarse aggregate and recycled fine aggregate satisfied the first grade of recycle specification(KS), and all compounds of recycled aggregate also satisfied the second grade of absorption specification, Especially up to the 50% substitution of recycled aggregate is equal to or a bit lower than that of convention aggregate. In comparison with conventional concrete, the recycled concrete is lower than maximum by 7% in compressive strength decreasing rate after freezing-thawing test. From now, although most of recycled concrete was used to the building lot, subgrade, asphalt admixture, through the result. It was proved that possibility of re-using recycled aggregate as the substructure of bridge, retaining wall, tunnel lining and concrete structure which is not attacked the drying shrinkage severely.

• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.697-704
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• 2008

This paper presents an analytical prediction of Nonlinear characteristics of prestressed concrete bridges by strengthened of externally tendon considering construction sequence, using unbonded tendon element and beam-column element based on flexibility method. Unbonded tendon model can represent unbounded tendon behavior in concrete of PSC structures and it can deal with the prestressing transfer of posttensioned structures and calculate prestressed concrete structures more efficiently. This tendon model made up the several nodes and segment, therefore a real tendon of same geometry in the prestressed concrete structure can be simulated the one element. The beam-column element was developed with reinforced concrete material nonlinearities which are based on the smeared crack concept. The fiber hysteresis rule of beam-column element is derived from the uniaxial constitutive relations of concrete and reinforcing steel fibers. The formulation of beam-column element is based on flexibility. Beam-column element and unbonded tendon element were be involved in A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), that were used the analysis of RC and PSC structures. The proposed numerical method for prestressed concrete structures by strengthened of externally tendon is verified by comparison with reliable experimental results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.3
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• pp.1778-1785
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• 2014

In order to construct offshore structures safely, geotechnical investigation should be carried out with high accuracy. Up to now, onshore geotechnical investigation equipments installed on the barge are used for offshore geotechnical investigation. In this case, many limitations can be confronted such as deep water depth, high wave, strong current, severe wind and so on. For the safe and economic offshore geotechnical investigation with high precision, a seabed type unmanned automated site investigation equipment is developed. It can be operated remotely underwater conditions with 100m water depth and can explore the ground depth of 50m. Also, the standard penetration test (SPT), soil boring, soil sampling and rock coring can be possible using the equipment. Numerical analysis was conducted to secure the stability of the equipment against current of 4 knot. Energy efficiency of SPT apparatus which is attached to the equipment shows 78% in average.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.747-754
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• 2014

In spite of its usefulness for health monitoring of structures on steady external load, the statistical pattern recognition technology (SPRT), based on Mahalanobis distance theory (MDT), is not good enough for the health monitoring of structures on large variability external load like earthquake. Damage is usually determined by the difference between the average measured value of undamaged structure and the measure value of damaged one. So when external variability gets larger, the difference gets bigger along, which is thus easily mistaken for a damage. This paper aims to overcome the problem and develop an improved Mahalanobis distance theory (IMDT), that is, a SPRT with revised MDT in order to decrease external variability so that we will be able to continue to monitor the structure on uncertain external variability. This method is experimentally tested to see if it precisely evaluates the health of a cable-stayed bridge on each general random load and earthquake load. As a result, the IMDT is found to be valid in locating structural damage made by damaged cables by means of data from undamaged cables. So it is proved to be effectively applicable to the health monitoring of bridges on external load of variability.

• International Journal of Highway Engineering
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• v.5 no.3 s.17
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• pp.11-20
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• 2003

Concrete structures such as bridges, pavement, and offshore structures are normally subjected to repeated load. Because highway and airfield pavements are to resist tension in bending, fatigue failure behavior is very important the fatigue life of materials. Therefore, in this paper was carried according to the fatigue test method and experiment variables for pavement concrete. The fatigue tests were applied split tension($150{\times}75$ in size) and flexural($150mm{\times}150mm{\times}550mm$ in size) beam fatigue test method. Major experimental variable in the fatigue tests in order to consideration of fatigue life were conducted loading frequency of 1, 5, 10, 20Hz and loading shape of block, sine, triangle and moisture condition of dry and wet condition and curing age of 28day and 56day. The test results show that the effect of loading frequency increasing the frequency increased fatigue life, decreased significant at frequencies below 200 cycles. The effect of loading wave form on fatigue life show that a block decreased, triangular increased in comparison with sine. The effect of moisture condition decreased in wet condition in comparison with dry condition. The effect of curing age increased in 564ays in comparison with 28day.

• Journal of Korea Water Resources Association
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• v.41 no.2
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• pp.197-212
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• 2008

Recently, stream flow analysis has been accomplished by one or two dimensional equations and was applied by simple momentum equations and fixed energy conservations which contain many condition limits. In this study, FLOW-3D using CFD (Computational Fluid Dynamics) was applied to stream flow analysis which can solve three dimensional RANS (Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behaviors and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as ${\kappa}-{\varepsilon}$, RNG (Renormalized Group) ${\kappa}-{\varepsilon}$ and LES (Large Eddy Simulation). Numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow, water level pressure and eddy flows around the piers and transverse overflow type structures. These results will be able to used by basis data that catch hold of effects on long-term bed elevation changes, sediment accumulations, scours and water aggravations by removal of obsolete transverse over flow type structures in urban stream.

• Korean Journal of Construction Engineering and Management
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• v.21 no.3
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• pp.39-47
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• 2020

There are two kinds of cost estimate system in construction in china. Quota valuation model is a traditional cost estimate system under the unity of quantity and price, which is easier and has been used for decades. But the Quota valuation model becomes increasingly unsuited to the needs of society with the development of market economy. To meet the needs of China's market economy development and construction works in the field of international cooperation, the Bill of Quantities valuation model was introduced in 2003. However, there are still many shortcomings and deficiencies in the course of implementation of Bill of Quantities valuation model. In addition, interest in the Chinese construction market continues to increase in Korea due to the recent new North Korean policy and China's the Belt and Road policy. This paper aims to examine the cost estimate system of public construction works in China, and to provide basic data for deriving future improvement plans by comparing and analyzing it with standard cost estimate system in Korea.