• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.6
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• pp.556-562
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• 2007

This paper presents the use of a novel fiber optic accelerometer system to monitor ambient vibration (both wind-induced one and vehicle-induced) of a real bridge structure. This sensor system integrates the $Moir\'{e}$ fringe phenomenon with fiber optics to achieve accurate and reliable measurements. A low-cost signal processing unit implements unique algorithms to further enhance the resolution and increase the dynamic bandwidth of the sensors. The fiber optic accelerometer has two major benefits in using this fiber optic accelerometer system for monitoring civil engineering structures. One is its immunity to electromagnetic (EM) interference making it suitable for difficult applications in such environments involving strong EM fields, electrical spark-induced explosion risks, and cabling problems, prohibiting the use of conventional electromagnetic accelerometers. The other is its ability to measure both low- and high-amplitude vibrations with a constantly high resolution without pre-setting a gain level, as usually required in a conventional accelerometer. The second benefit makes the sensor system particularly useful for real-time measurement of both ambient vibration (that is often used for structural health monitoring) and strong motion such as earthquake. Especially, the semi-strong motion and the small ambient one are successfully simulated and measured by using the new fiber optic accelerometer in the experiment of the structural health monitoring of a real bridge.

• Journal of the Korean Mathematical Society
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• v.44 no.2
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• pp.443-453
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• 2007

We study the equation of a membrane with strong viscosity. Based on the variational formulation corresponding to the suitable function space setting, we have proved the fundamental results on existence, uniqueness and continuous dependence on data of weak solutions.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1250-1257
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• 2009

Due to the improvement of the seismic hazard analysis method and the design code, dynamic analysis method is widely used. To conduct dynamic analysis, various coefficients should be designated. The time history acceleration is one of the most essential factor. However, strong earthquake motion data from the outside of the country have been used to conduct dynamic analysis without considering of the ground motion parameters. In this study, the methodology to choose appropriate input motion is developed by using time domain design spectrum matching procedure. Two examples are applied to verify the methodology. The Result shows that the methodology satisfies seismic circumstances and the design code.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.4
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• pp.320-329
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• 2016

An implicit method of solving the six degree-of-freedom rigid body motion equations based on the second order Adams-Bashforth-Moulten method was utilised as an improvement over the leapfrog scheme by making modifications to the rigid body motion solver libraries directly. The implementation will depend on predictor-corrector steps still residing within the hybrid Pressure Implicit with Splitting of Operators - Semi-Implicit Method for Pressure Linked Equations (PIMPLE) outer corrector loops to ensure strong coupling between fluid and motion. Aitken's under-relaxation is also introduced in this study to optimise the convergence rate and stability of the coupled solver. The resulting coupled solver ran on a free floating object tutorial test case when converged matches the original solver. It further allows a varying 70%-80% reduction in simulation times compared using a fixed under-relaxation to achieve the required stability.

• Journal of the Korea Concrete Institute
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• v.20 no.4
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• pp.451-458
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• 2008

The near-fault ground motion (NFGM) is characterized by a single long period velocity pulse of large magnitude. NFGM's have been observed in recent strong earthquakes, Izmit Turkey (1999), Kobe Japan (1995), Northridge USA (1994), etc. These strong earthquakes have caused considerable damage to infrastructures because the epicenter was close to the urban area, called as NFGM. Extensive research for the near-fault ground motion (NFGM) have been carried out in strong seismic region, but limited research have been done for NFGM in low or moderate seismic regions because of very few records. The purpose of this study is to investigate and analyze the effect of near-fault ground motions on reinforced concrete (RC) bridge piers with lap-spliced longitudinal reinforcing steels. The seismic performance of four RC bridge piers under near-fault ground motions was investigated on the shake table. In addition, a RC bridge pier is subjected to pseudo-dynamic loadings. Test results showed that large residual displacements were observed in RC bridge piers under NFGM. RC specimens on the shake table failed at relatively low displacement ductility, compared with the displacement ductility of RC bridge pier subjected to pseudo-dynamic loadings.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.09a
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• pp.3-10
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• 2002

The strong ground motion data recorded in the Sino-Korea Craton are analysed toobtain attenuation relations valid for 5 < M < 8, r < 400 km applicable to the Korean Peninsula. The result is logA : -1.83+0.386M- log${\gamma}$-0.0015${\gamma}$ where A is peak horizontal acceleration in g, M is surface-wave magnitude, and r is hypocentral distance in km. Our result is compared with the existing attenuation relations of Western North America and Eastern North America and the prior predictive equations for the Southern part of Korean Peninsula. Our result compares better with those of North America than those of the Southern part of the Korean Peninsula. More theoretical and empirical studies are required for better attenuation relations appropriate for the Korean Peninsula.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.04a
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• pp.57-60
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• 1999

Amplification factor spectrum using the observed strong ground motions database in the Korean Peninsula has been obtained and compared with Standard Rpectrum which wa suggested by United States Nuclear Regulatory Committee. The observed ground motions from the Yongwol and the Kyoungju Earthquakes respectively which are supposed to represent domestic seismotectonic characteristics such as seismic source attenuation of the propagation meium and site specific effect are used for the analysis of amplification factor spectrum,. The database are slightly different from the those of the second study. Amplification factors have been calculated by comparing the observed peak ground motions with results from responses to the observed horizontal na vertical ground motions. The comparison have shown that the amplification factors resultant from this study exceeds those of Standard Response Spectrum The results suggest that the characteristics of seismic strong ground motion which are supposed to represent the domestic seismotectonic characteristics differs from those of Standard Response Spectrum especially at higher frequencies. The results from the 2nd study are similar to those of 1st analysis.

• Structural Engineering and Mechanics
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• v.54 no.6
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• pp.1111-1133
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• 2015

Rebar corrosion in concrete is one of the main causes of reduction of service life of reinforced concrete buildings. This paper presents the influence of rebar corrosion on the structural behavior of reinforced concrete (RC) buildings subjected to strong earthquake ground motion. Different levels of rebar corrosion scenarios were applied on a typical four story RC frame. The deteriorated conditions as a result of these scenarios include loss in cross-sectional area and loss of mechanical properties of the reinforcement bars, loss in bond strength, and loss in concrete strength and its modulus of elasticity. Dynamic analyses of the frame with different corrosion scenarios are performed with selected strong earthquake ground motion records. The influences of degradation in both concrete and reinforcement on structural behavior are investigated by comparing the various parameters of the frame under different corrosion scenarios with respect to each other. The results show that the progressive deterioration of the frame due to rebar corrosion causes serious structural behavior changes such as change in failure mode. The intensity, propagation time, and extensity of rebar corrosion have very important effects on the level of degradation of steel and concrete, as well as on the earthquake behavior of the structure.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.04a
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• pp.190-195
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• 2001

In the present paper computational simulation of a concrete dam is performed to determine the effect of vertical ground motions on earthquake response of concrete dams. Cyclic and dynamic versions of the plastic-damage model proposed by Lee and Fenves are used to represent micro-crack development and crack opening/closing, which is important mechanism in nonlinear damage analysis of concrete structures subject to strong earthquake loading. The result shows that the vertical component of ground motion effects on final crack patterns and consequently, on displacement response.

• Earthquakes and Structures
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• v.27 no.1
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• pp.41-55
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• 2024

There are obvious differences between the characteristics of offshore ground motion and onshore ground motion in current studies, and factors such as water layer and site conditions have great influence on the characteristics of offshore ground motion. In addition, unlike seismic response analysis of offshore superstructures such as sea-crossing bridges, tunnels are affected by offshore soil constraints, so it is necessary to consider the dynamic interaction between structure and offshore soil layer. Therefore, a seismic response analysis model considering the seawater, soil layer and tunnel structure coupling is established. Firstly, the measured offshore and different soil layers onshore ground records are input respectively, and the difference of seismic response under different types of ground motions is analyzed. Then, the models of different site conditions were input into the measured onshore bedrock strong ground motion records to study the influence of seawater layer and silt soft soil layer on the seabed and tunnel structure. The results show that the overall seismic response between the seabed and the tunnel structure is more significant when the offshore ground motion is input. The seawater layer can suppression the vertical seismic response of seabed and tunnel structure, while the slit soft soil layer can amplify the horizontal seismic response. The results will help to promote seismic wave selection of marine structures and provide reference for improving the accuracy of seismic design of immersed tunnels.