• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.4
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• pp.1-11
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• 2007

This paper verifies the difference of the seismic behavior and seismic damage of the neighboring two reinforced concrete piers damaged by the 1995 Hyogoken Nanbu earthquake. The two piers were almost the same size, carrying slightly different dead load, and were provided with the same reinforcement arrangement except the amount of longitudinal reinforcement at the bottom portion of the piers. The pier with more reinforcement was completely collapsed due to this near field earthquake by shear failure at the longitudinal reinforcement cut-off while the other was only damaged at the bottom by flexure even though the longitudinal reinforcement cut-off was also existed at the mid height of the pier. According to the results of the pseudo dynamic test, the seismic damage was recognized to be greatly dependent on the ground motion characteristics even though the employed ground motions had the same peak acceleration. The severe damage was observed when the test employed the seismic wave that had strong influence to the longer period range compared to the initial natural period of the pier. On the other hand, based on the similar model experiment, the defect of gas-pressure welded splice of longitudinal reinforcement was revealed to save the piers against collapse due to the so-called fail-safe mechanism contrary to the intuitive opinion of some researchers. It was concluded that the primary cause of the collapse of the pier was the extremely strong intensity and peculiar characteristics of the earthquake motion according to both the site-specific and the structure-specific effects.

• Journal of the Korean Geotechnical Society
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• v.32 no.7
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• pp.35-45
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• 2016

Estimation of vertical bearing capacity is critical in the design of bucket foundation used to support offshore structure. Empirical formula and closed form solutions for bucket foundations in uniform sand or clay profiles have been extensively studied. However, the vertical bearing capacity of bucket foundations in alternating layers of sand overlying clay is not well defined. We performed a series of two-dimensional axisymmetric finite element analyses on bucket foundations in sand overlying clay soil, using elasto-plastic soil model. The load transfer mechanism is investigated for various conditions. Performing the parametric study for the friction angles, undrained shear strengths, thickness of sand layer, and aspect ratios of foundation, we present the predictive charts for determining the vertical bearing capacities of bucket foundations in sand overlying clay layer. In addition, after comparing with the finite element analysis results, it is found that linear interpolation between the design charts give acceptable values in these ranges of parameters.

• Applied Chemistry for Engineering
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• v.26 no.4
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• pp.406-412
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• 2015

Unidirectional carbon/carbon (C/C) composites were manufactured using phenolic resins as a precursor of the carbonized matrix throughout a one-step manufacturing process. Also, molybdenum oxide ($MoO_3$) and binder pitches were impregnated with phenolic resins to improve the bulk density and mechanical property of the C/C composites. In this study, the influence of $MoO_3$ and binder pitches on mechanical properties of the C/C composites were investigated by measuring flexural strength (${\sigma}_f$) and interlaminar shear strength (ILSS). The results show that the enhancement of interfacial adhesions between the fibers and matrix resins of the C/C composites with $MoO_3$ and binder pitches which led to the improvement of mechanical properties of the C/C composites. This indicates that the presence of $MoO_3$ and binder pitches in C/C composites can develop the graphite structure and increase the bulk density.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.627-634
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• 2004

The purpose of this study is to investigate seismic performance of a bearing wall system for apartment buildings. An 1/3 scale three-story specimen was constructed and tested under cyclic lateral loads. The specimen was consisted of pierced walls and coupling elements as well as floor slabs. The bearing wall system is considered to have a adequate deformation capacity up to $2.0\%$ of roof drift ratio, and the experimental results showed the ductile load-deformation characteristics even though some walls were failed in shear Nonlinear analysis was peformed to compare the load-deformation curve obtained from the experimental program. The result of nonlinear analysis could be useful to predict the actual behavior characteristics of the bearing wall system subjected to lateral loads.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.67-74
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• 2007

We perform an experimental study of concrete beam with pultruded fiber reinforced polymer(FRP) plank using as a permanent formwork and the tensile reinforcement. A satisfactory bond at the interface between the smooth surface of the pultruded plank and the concrete must be developed for the FRP plank and the concrete to act as a composite structural member. Two kinds of aggregate were bonded to the FRP plank using a commercially available epoxy. No additional flexural or shear reinforcement was provided in the beams. For comparison we test two types of control specimen. One control did not have any aggregate bonded to the FRP plank and the other control had infernal steel reinforcing bars instead of the FRP plank. The beams were loaded by central patch load to their ultimate capacity. The experimental results were compared to current ACI 318 (2005) and ACI 440 (2006) code predictions. This study demonstrates that the FRP plank has the potential to serve as formwork and reinforcing for concrete structures.

• Geotechnical Engineering
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• v.9 no.1
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• pp.7-20
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• 1993

The first Korean earthquake resistant design code was enacted in 1988. In the code, the soil factor which takes into account both the soil amplification factor and the soil -structare interaction effect is divided into three groups : soil factor, 5 : 1.0, 1.2 and 1.5. In order to assist in choosing the soil factors appropriately in the earthquake resistant design, the local site effects on the based shear force induced by earthquakes are considered in depth for typical soil conditions in Korea. The depth of the alluvial and/or weathered zone is usually not deep and the fresh rock is found at depth shallower than 20 meters, and even at about 10 meters around Seoul. One dimensional wave propagation theory and the elastic half space method are used to obtain the soil -structure interaction effect as well as the soil amplification effect. The kinematic interaction effect due to scattering of waves by pile foundation is also considered. Finally, the soil factor is recommended for each soil condition from loose state to dense, and also from shallow soil depth to deep, so that the designer can choose the factor with-out difficulty.

• Journal of the Korean Geotechnical Society
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• v.31 no.2
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• pp.65-73
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• 2015

The bank revetment work which is conducted on the slope of river bank to protect against flowing water as a geotechnical structure has been applied as an average value of critical tractive force based on domestic and international standard design. Currently, an appropriate evaluation is needed for the hydraulic stability and geotechnical behavior analysis of bank revetments because of the effects of climate change and ambiguous design criterion. This study has compared the critical tractive forces of soil improvement material and conventional materials used for the bank revetment work. Through various experiments, the shear strength of mixtures with soil improvement material was investigated by curing time and mixture ratio. It was found that the critical tractive force of the mixture obtained from a scour test is suitable to the reinforcement of the slope of river bank which has problems such as seepage erosion and scour.

• Journal of Hydrogen and New Energy
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• v.31 no.3
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• pp.328-336
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• 2020

In the Francis turbine, the leakage flow through the runner gaps which are between the runner and the stator structure influences the internal flow and hydraulic performance. Thus, the investigation for the flow characteristics induced by the runner gaps is important. However, the runner gaps are often disregarded by considering the time and cost of the numerical analysis. Therefore, in this study, the flow characteristics according to runner gaps of the Francis turbine model were investigated including the leakage flow of the runner cone. The three-dimensional unsteady Reynolds-averaged Navier-Stokes analyses were conducted using a scale-adaptive simulation shear stress transport as a turbulence model for observing the influence of the leakage flow on the internal flow and hydraulic performance. The efficiencies were decreased slightly with runner gaps; and the complicated flows were captured in the gaps.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.83-92
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• 1987

Fatigue fracture of reinforced concrete structures are characterized by considerably larger strains and microcracking as compared to fracture of R.C. structures under static loading. The strain of stirrup is increased suddenly by the occuring of inclined crack and the average strain ${\epsilon}_{\omega}$ of all stirrups in a structure at maximum load increase approximately in proportion to log N. The structures critical in longitudinal reinforcement seemed to have an endurance limit of 60~70 percent of static ultimate strengths for 1,000,000 cycles. In this test, the average fatigue strength at 1,000,000 cycles for all structures tested was approximately 65 percent of the static ultimate strength.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.309-314
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• 2012

Flame flickering occurs mainly because of the buoyancy force for pool fires under ambient air. The cup-burner flame was used for experimental investigation of the effect of the oxidizer velocity on the gravitational instability. The results showed that the flickering frequency decreased with increasing oxidizer velocity. The frequency-buoyancy relation with nondimensional variables coincided with that of the buoyant flume and pool fires when the characteristic velocity was defined as the difference between the fuel and oxidizer velocities, which implies that the origin of the gravitational instability is the Kelvin-Helmholtz instability in the shear layer. The effect of the oxidizer composition on the instability was also examined through nitrogen dilution in the oxidizer stream. As the concentration of inert gas increased, the length of the blue flame increased and lift-off behavior was observed. The oscillation frequency was independent of the dilution ratio, but was related to the local flame structure.