• Journal of the Korean Geotechnical Society
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• v.21 no.9
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• pp.53-64
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• 2005

For geotechnical design in practice, soils are, in general, assumed to behave as a linear elastic or perfect plastic material. More realistic geotechnical design, however, should take into account various factors that affect soil behavior in the field, such as non-linearity of stress-strain response, stress history, and water content. In this study, a series of laboratory tests including triaxial and resonant column tests were peformed with sands of various silt contents, relative densities, stress states, OCR and water contents. This aims at investigating effects of various factors that affect strength and stiffness of sands. From the results in this study, it is found that the effect of OCR is significant for the intermediate stress-strain range from the initial to failure, while it may be ignored for the initial stiffness and peak strength. For the effect of water content, it is observed that the initial elastic modulus decreases with increasing water content at lower confining stress and relative density At higher confining stresses, the effect of water content Is found to become small.

• International Journal of Highway Engineering
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• v.6 no.1 s.19
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• pp.37-45
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• 2004

The characteristics of concrete strength and fracture parameters of recycled aggregate concrete were investigated to apply to the concrete pavements. As the results, the early strength of recycled aggregate concrete showed to be lower than that of natural coarse aggregate concrete, whereas strength at 28 days showed to be similar. Young's modulus of recycled aggregate concrete was lower than that of natural coarse aggregate concrete due to the difference of aggregate strength. And recycled aggregate concrete contained with ground granulated blast furnace slag seemed to have an effect of strength increasing. The critical stress intensity factor of recycled aggregate concrete at the early age was increased, and converged to be similar, compared to natural aggregate concrete at later age. The reliability of two-parameter fracture model was identified by the good correlation between the theoretical value computed by P-CMOD relationship and experimental results for Young's modulus and tensile strength.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.2
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• pp.271-279
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• 2002

This study develops the module to find the lateral stiffness influence matrix of each story and performs the displacement sensitivity analysis by virtual load method for the efficiency of optimal design using lateral stiffness influence matrix. Also, resizing technique based on the estimated lateral stiffness increment factors is developed to apply directly the results of optimal design. To this end, resizing technique is divided into the continuous and discrete section design methods. And then the relationships between section properties and section size are established. Specifically, an initial design under strength constraints is first performed, and then the lateral load resistant system is designed to control lateral displacements yet exceeding the drift criteria. Two types of 45-story three dimensional structures we presented to illustrate the features of the lateral drift control and resizing technique for tall buildings proposed in this study.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.134-142
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• 2003

Autogenous shrinkage, a significant contributor of early-age cracking of high strength concrete (HSC), must be avoided or minimized from an engineering point of view. Therefore, it is necessary to study how to reduce and to predict autogenous shrinkage with respect to tile control of early-age cracking. In this study, autogenous shrinkage of HSC with various water-binder ratio (W/B) ranging from 0.50 to 0.27 and fly ash content of 0, 10, 20, and 30% were investigated. Based on the test results, thereafter, a prediction model for autogenous shrinkage was proposed. Test results show that autogenous shrinkage increased and more rapidly developed with decreasing the W/B. Also, the higher fly ash contents, the smaller autogenous shrinkage. In particular, even if much autogenous shrinkage occurs at very early-ages, stress may not be developed while the stiffness of concrete is low. In order to consider the change of concrete stiffness, the transition time referred as stiffening threshold, was obtained by monitoring of ultrasonic pulse velocity evolution and considered in the autogenous shrinkage model. From a practical point of view, the proposed model can be effectively used to predict autogenous shrinkage and to estimate stress induced by autogenous shrinkage.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.144-152
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• 2016

This paper focuses on the experimental study for investigating the performance for lap splice of hooked or headed reinforcement in beam with different depths. In the experiment, seven specimens, with its variables as the lap length of headed or hooked bar, the existence of stirrups, etc., was manufactured. Bending test was conducted. Lap strengths by test were compared with the theoretical model based on KCI2012. The result showed that the cracks at failure mode occurred along the axial direction to a headed bar. The initial stiffness and the stiffness after initial crack were similar for all specimens. For HS series specimens without stirrups, a 25% increase in lap length was increased 11.8~18.1% maximum strengths. For HH series specimens without stirrups, a increase in lap length did not affect the maximum strengths because of the pryout failure of headed bar. For HS series specimens, the theoretical lap strengths based on KCI2012 considering the B grade lap and the reduction factor for stirrup were evaluated. They are smaller than the test strengths and can ensure the safety in terms of strength capacity. For HH series specimens, the stirrups in the lap zone are needed to prevent the pryout behaviour of headed bar.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.89-96
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• 2017

In this study, CS-H walls with large stiffness were constructed using geosythetics for use in excavation at a depth of 30 m or more in Korea, and in order to construct the CS-H wall suitable for the site conditions, the formulation was examined according to the change in the mixing ratio of the geosythetics and the slump value (slump flow) and as a result, in the target slump 180 mm and the slump flow 500 mm, the formulation was confirmed to meet the mechanical properties such as the initial bending strength, the long-term behavior, and the elastic modulus as well as the economic efficiency. However, in the slump flow 600 mm, the result indicated that the formulation was inappropriate in the mechanical properties such as the initial bending strength, the long-term behavior, and the elastic modulus.

• Journal of the Korean Society for Railway
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• v.12 no.3
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• pp.396-404
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• 2009

With developing the next generation high speed railway, there need to be plans to make sure of running safety though researchs on the crack and break of rail by rolling contact fatigue. Therefore, this study performed the parametric analysis effecting on the fatigue life of rail using simplified equations. It analyzed the internal stress of rail according to the track quality, train velocity, wheel radius, track stiffness, sleeper space, wheel load. For the more, via the finite element method, it analyzed shear force on the rail head which could be changed by the early length of crack, angle of crack and temperature. As a result, this study continued the main parameter effecting on the fatigue life of rail.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.6
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• pp.80-87
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• 1998

In this study, the effects of residual shaft bow and flexible bearings of a single disk rotor are investigated. The stiffness coefficients of a shaft with initial deflection are different from those of a straight shaft. The stiffness coefficients are calculated using Castigliano theorem considering initial deflections. The stiffness coefficients, which are obtained in this study, are in good agreement with FEM results. The speed which causes zero amplitude is shown to be the square root of the ratio of residual bow amplitude to unbalance eccentricity in the case of rigid bearings and isotropic flexible bearings, but not in anisotropic bearings.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.4
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• pp.276-282
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• 2013

The reclaimed water has been highlighted as a representative alternative to solve the lacking water resources. This study examined the reduction of residual free chlorine by temperature (5, 15, $25^{\circ}C$) and initial injection concentration (1, 2, 4, 6 mg/L) in the reclaimed water and carried out propose on the calculating method of the optimal chlorine dosage. As the reclaimed water showed a very fast reaction with chlorine at the intial time comparing to that of drinking water, the existing general first-order decay model ($C_t=C_o(e^{-k_bt})$) was not suitable for use. Accordingly, the reduction of residual free chlorine could be estimated in a more accurate way as a result of applying the exponential first-order decay model ($C_t=a+b(e^{-k_bt})$). ($r^2$=0.872~0.988). As a result of calculating the bulk decay constant, it showed the highest result at 653 $day^{-1}$ under the condition of 1 mg/L, $25^{\circ}C$ for the initial injection whereas it showed the lowest result at 3.42 $day^{-1}$ under the condition of 6 mg/L, $5^{\circ}C$ for the initial injection. The bulk decay constant tends to increase as temperature increases, whereas the bulk decay constant tends to decrease as the initial injection concentration increases. More accurate calculation for optimal chlorine dosage could be done by using the experimental results for 30~5,040 min, after the entire response time is classified into 0~30 min and 30~5,040 min to calculate the optimal chlorine dosage. In addition, as a result of calculating the optimal chlorine dosage by temperature, the relationships of initial chlorine demand (y) by temperature (x) could be obtained such as y=1.409+0.450x to maintain 0.2 mg/L of residual free chlorine at the time after 4 hours from the chlorine injection.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4D
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• pp.539-546
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• 2011

Traffic accident collision interpretation is composed of various shapes, and speed variations working to the vehicle during collision are utilized as a very important factor in evaluating collision degrees between vehicles and safety of passengers who got in the vehicle. So, methods of interpreting results on speed variations utilizing simulation programs on the collision interpretation become necessary. By the way, reliability evaluation on each program is being required because various collision interpretations simulations are spread widely. This study utilized collision interpretation programs such as EDSMAC and PC-CRASH adopting completely different physical approaches, and then carried out collision experiments of one-dimensional front and two-dimensional right angle while changing values of a lot of collision factors such as vehicle's weight, center of gravity, rolling resistance, stiffness coefficient, and braking forces among early input conditions. Also, the study recognized effects of collision factors to speed variations as output results during crashing. As a result of this research, two simulation programs showed same speed variations together on the vehicle's weight, center of gravity, and braking forces. Stiffness coefficient of the vehicle reacted to EDSMAC only, and rolling resistance coefficient did not affect any particular influences on speed variations. However, there appeared a bit comparative differences from the speed variation's values, and this is interpreted as responding outcomes by applying fixed properties values to each simulation program plainly. Therefore, reliability on analysis of traffic accident collisions shall be improved by doing speed analysis after taking the fixed value of simulation programs into consideration.