• Structural Engineering and Mechanics
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• v.55 no.6
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• pp.1177-1202
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• 2015

In this paper, a new intensity measure of earthquakes for probabilistic seismic analysis is presented for skewed highway bridges. Three different cases of skewed bridges with different skew angles ($0^{\circ}$, $30^{\circ}$ and $45^{\circ}$) are considered. Well-known intensity measures (e.g., PGA, $S_a$) are evaluated and critically discussed based on sensitivity analysis: efficiency, practically, proficiency and sufficiency of intensity measures are considered in detail. The analyses demonstrated that the intensity measures have to take into account structural acceleration on a wide range of periods so that a new seismic intensity measure is proposed showing that it has less dispersion compared to others. Since the proposed intensity represents the average value of the $S_a$ (between a lower and upper structural period) it has been called Averaged Spectral Acceleration (ASA). Based on performed incremental dynamic analysis (IDA), the seismic analytical fragility curves of typical skewed highway bridges have been evaluated for different states of damage controlling the low dispersion of the ASA index as well as its proficiency and sufficiency.

• Geophysics and Geophysical Exploration
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• v.14 no.1
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• pp.42-49
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• 2011

To locate anomalous features including seepage pathways through the Daeryong earth-fill dam, P and Rayleigh waves were recorded along a 250-m profile on the crest of the dam. Seismic energy was generated using a 5-kg sledgehammer and detected by 24 4.5-Hz vertical-axis geophones installed at 3-m intervals. P-wave and apparent S-wave velocities of the reservoir dam and underlying bedrock were then inverted from first-arrival traveltimes and dispersion curves of Rayleigh waves, respectively. Apparent dynamic Poisson's ratios as high as 0.46 were obtained at the base of the dam near its north-east end, where an outlet conduit occurs, and in the clay core body near the south-west end of the profile where the dam was repeatedly grouted to abate seepage before our survey. These anomalies of higher Poisson's ratios in the upper part of clay core were also associated with effusion of grout on the downstream slope of the dam during post-survey grouting to abate leakage. Combining P-wave traveltime tomography and inversion of Rayleigh wave velocities was very effective in detecting potential pathways for seepage and previous grouted zones in this earthen dam.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.867-874
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• 1994

The complex nature of low flow transport and transformation of nonconservative pollutants in natural streams has been investigated using a numerical solution of a proposed mathematical model that is based on a pair of mass balance equations describing the advection, dispersion, decay and mass exchange mechanisms in streams and in storage zones. In the present study, a mathematical model (named "Storage-Transformation Model") has been developed to predict adequately the non-Fickian nature of mixing and transformation mechanisms for decaying substances in natural streams under low flow conditions. Comparisons of the computed concentration-time curves with the measured data show that the Storage-Transformation Model yields better agreements in general shape, peak concentration and time to peak than the conventional 1-D dispersion model. The proposed model shows significant improvement over the 1-D dispersion model in predicting natural transport and transformation processes in streams through pools and riffles.

• Economic and Environmental Geology
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• v.52 no.6
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• pp.555-560
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• 2019

One-dimensional shear wave velocity structure of North Korea is constrained using short (2-sec) to long period (30-sec) Rayleigh waves generated from four seismic events in China. Rayleigh waves are well recorded at the five broadband seismic stations (BRD, SNU, CHNB, YKB, KSA) which are located near to the border between North and South Korea. Group velocities of fundamental-mode Rayleigh waves are estimated with the Multiple Filter Analysis and refined by using the Phase Matched Filter. Average group velocity dispersion curve ranging from 2.9 to 3.2 km/s, is inverted to constrain the shear wave velocity structures. Relatively low group velocity dispersion curves along the path between the events to BRD at period from 4 to 6 seconds may correspond to the sedimentary sequence of the West Korea Bay Basin (WKBB) in the Yellow Sea. The low velocity zone in deep layers (14-20 km) may be related to the deep sedimentary structure in Pyongnam basin. The fast shear wave velocity structure from the surface to the depth of 14 km is consistent with the existence of metamorphic rocks and igneous bodies in Nangrim massif and Pyongnam basin.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.1
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• pp.34-40
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• 2012

In this study, effects of bonding agent, e.g. epoxy, on the behavior of fundamental guided wave modes propagated in FRP plate bonded on a concrete, are investigated. Global matrix model of multilayered FRP-epoxy-concrete system was constructed to obtain the velocity and attenuation dispersion curves of the fundamental A0 and S0 modes. Two variables, thickness and elastic modulus of epoxy layer, were considered in the dispersion analysis. It was found that both the thickness and the elastic modulus of epoxy layer greatly affect the phase velocity and attenuation of S0 mode while those are negligible for A0 mode. Based on the results, it was concluded that S0 mode is more effective than A0 mode for bonding condition assessment for FRP plate bonded concrete.

• Journal of Korea Soil Environment Society
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• v.2 no.2
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• pp.81-94
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• 1997

In many solute transport studies, either flux or resident concentration has been used. Choice of the concentration mode was dependent on the monitoring device in solute displacement experiments. It has been accepted that no priority exists in the selection of concentration mode in the study of solute transport. It would be questionable, however, to accept the equivalency in the solute transport parameters between flux and resident concentrations in structured soils exhibiting preferential movement of solute. In this study, we investigate how they differ in the monitored breakthrough curves (BTCs) and transport parameters for a given boundary and flow condition by performing solute displacement experiments on a number of undisturbed soil columns. Both flux and resident concentrations have been simultaneously obtained by monitoring the effluent and resistance of the horizontally-positioned TDR probes. Two different solute transport models namely, convection-dispersion equation (CDE) and convective lognormal transfer function (CLT) models, were fitted to the observed breakthrough data in order to quantify the difference between two concentration modes. The study reveals that soil columns having relatively high flux densities exhibited great differences in the degree of peak concentration and travel time of peak between flux and resident concentrations. The peak concentration in flux mode was several times higher than that in resident one. Accordingly, the estimated parameters of flux mode differed greatly from those of resident mode and the difference was more pronounced in CDE than CLT model. Especially in CDE model, the parameters of flux mode were much higher than those of resident mode. This was mainly due to the bypassing of solute through soil macropores and failure of the equilibrium CDE model to adequate description of solute transport in studied soils. In the domain of the relationship between the ratio of hydrodynamic dispersion to molecular diffusion and the peclet number, both concentrations fall on a zone of predominant mechanical dispersion. However, it appears that more molecular diffusion contributes to the solute spreading in the matrix region than the macropore region due to the nonliearity present in the pore water velocity and dispersion coefficient relationship.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4C
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• pp.231-238
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• 2008

A column testing device capable of measuring the electrical resistivity of soil at 3 different locations was developed to verify applicability of bulk electrical conductivity (BEC) breakthrough curves in monitoring contaminant transport. Tracer injection tests were conducted with three different types of saturated sands to obtain average linear velocities and longitudinal hydrodynamic dispersion coefficients based on BEC breakthrough curves and effluent solute breakthrough curves. Comparative analysis of transport parameters obtained from curve fitting the results into the analytical solutions confirmed the validity of resistance measurements in estimating time-continuous resident solute concentration. Under the assumption that a linear relationship exists between ${\sigma}_{sat}-{\sigma}_w-C$, the BEC breakthrough curves are able to effectively reduce the laborious and time-consuming processes involved in the conventional method of sampling and analysis. In order to reduce possible uncertainties in analyzing the BEC breakthrough curves, it was recommended that resistance measurements take place nearby the effluent boundary. In addition, a sufficient electrical contrast or difference in the electrical conductivity of the influent and the saturating solution is required to conduct reliable analysis.

• Interaction and multiscale mechanics
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• v.5 no.1
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• pp.13-26
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• 2012

In this paper, the wave propagation in a generalized thermo elastic plate embedded in an elastic medium (Winkler model) is studied based on the Lord-Schulman (LS) and Green-Lindsay (GL) generalized two dimensional theory of thermo elasticity. Two displacement potential functions are introduced to uncouple the equations of motion. The frequency equations that include the interaction between the plate and foundation are obtained by the traction free boundary conditions using the Bessel function solutions. The numerical calculations are carried out for the material Zinc and the computed non-dimensional frequency and attenuation coefficient are plotted as the dispersion curves for the plate with thermally insulated and isothermal boundaries. The wave characteristics are found to be more stable and realistic in the presence of thermal relaxation times and the foundation parameter. A comparison of the results for the case with no thermal effects shows well agreement with those by the membrane theory.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.1
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• pp.15-20
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• 1993

This study describes ultrasonic reflection at a water/fiber reinforced polymer composite/water interface. Theoretical predictions of reflected beam amplitudes are also presented. Four different polymer composite laminates are investigated : T300/5208 graphite/epoxy $[0]_{31T},\;[45/90/-45/0]_{3S},\;[45/-45]_{2S}$, and S-2 glass/epoxy $[0/90]_{4S}$. The analytical leaky plate wave dispersion curves for the unidirectional laminate and other three laminates can be obtained by searching for the minimum magnitude of the reflection coefficient.

• Journal of the Korean Ceramic Society
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• v.27 no.1
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• pp.13-22
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• 1990

The magnetite ferrofluids of which solvents are water or kerosene have been prepared by making surfactant absorbed on the surface of the magnetite which have been synthesized by air oxidation of Fe(OH)2 at pH 11 and 75$^{\circ}C$, and their basic properties have been measured by XRD, SEM, DTA, TG, viscometer, magnetometer and B-H tracer. The results are as follows ; 1) The shape of magnetite prepared by air oxidation is found to be sphere-like shape and its particle size is smaller than 200A. 2) The maximum amount of sodium oleate adsorbed on the surface of magnetite is about 20% in the weight of the magnetite including the adsorbed sodium oleate. And when magnetite is well dispersed into solvent, R(the weight ratio of the added sodium oleate to Fe3O4) is 0.40-0.48. 3) The dispersion ratio, the viscosity and the magnetization of magnetite ferrofluid are constant regardless of the added amount of sodium oleate above R=0.40-0.48. 4) The magnetic hysteresis curves of magnetite ferrofluid show superparamagnetism-like behavior.