• Journal of Korean Tunnelling and Underground Space Association
• /
• v.25 no.4
• /
• pp.305-330
• /
• 2023

Unlike NATM tunnels, Shield TBM tunnels have split linings. Therefore, the stress distribution of the lining is different even if the lining is under the same load. Representative methods for analyzing the stress generated in lining in Shield TBM tunnels include Non-joint Mode that does not consider connections and a 2-ring beam-spring model that considers ring-to-ring joints and segment connections. This study is an analysis method by Break-joint Mode. However, we do not consider the structural role of segment lining connections. The effectiveness of the modeling is verified by analyzing behavioral characteristics against vibration loads by modeling with segment connection interfaces to which vertical stiffness and shear stiffness, which are friction components, are applied. Unlike the Non-joint mode, where the greatest stress occurs on the crown for static loads such as earth pressure, the stress distribution caused by contact between segment lining and friction stiffness produced the smallest stress in the crown key segment where segment connections were concentrated. The stress distribution was clearly distinguished based on segment connections. The results of static analysis by earth pressure, etc., produced up to seven times the stress generated in Non-joint mode compared to the stress generated by Break-joint Mode. This result is consistent with the stress distribution pattern of the 2-ring beam-spring model. However, as for the stress value for the train vibration load, the stress of Break-joint Mode was greater than that of Non-joint mode. This is a different result from the static mechanics concept that a segment ring consisting of a combination of short members is integrated in the circumferential direction, resulting in a smaller stress than Non-joint mode with a relatively longer member length.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.21 no.2
• /
• pp.279-299
• /
• 2019

Recently occurred earthquake Gyeongju and Pohang served as a momentum to remind that Korean peninsular is not a safety zone from earthquake anymore. The importance of seismic design, therefore, have been realized and researches regarding design response spectrum have been actively carried out by many researchers and engineers. Current tunnel seismic design method is conducted to check safety of tunnel structure by dynamic numerical analysis with condition of completed lining installation, so, it is impossible to consider safety of tunnel behavior under construction. In this study, therefore, dynamic numerical analysis considering seismic wave propagations has been performed after back analysis using results from field monitoring of tunnel under construction in fractured zone and 1st reinforcement (shotcrete, rockbolt) behaviour are analyzed. Waves are classified by period characteristic (short and long). As a result, the difference depending on period characteristic is minor, and increasements of displacement are obtained at crown displacement due to seismic wave is 28~31%, 14~16% at left side of tunnel in the fractured zone, 13~27% at right side of tunnel in the bed rock, respectively. In case of shotcrete axial force is increased 113~115% at tunnel crown, 102% at left side, 106~110% at right side, respectively. Displacement and axial force of rockbolts which are selected by type of anchored grounds (only fractured zone, fractured zone and bed rock, only bedrock) are analyzed, as a result, rockbolt which is anchored to fractured zone and bed rock at the same time are weaker than any other case.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.28 no.3
• /
• pp.132-145
• /
• 2016

In case of the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure will be generated significantly due to pore volume change associated with rearrangement soil grains. This effect will lead a seabed liquefaction around and under structures as a result from decrease in the effective stress. Under the seabed liquefaction occurred and developed, the possibility of structure failure will be increased eventually. In this study, to evaluate the liquefaction potential on the seabed quantitatively, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank model and the finite element elasto-plastic model. Under the condition of the regular wave field, the time and spatial series of the deformation of submerged breakwater, the pore water pressure (oscillatory and residual components) and pore water pressure ratio in the seabed were estimated.

• Journal of the Korean GEO-environmental Society
• /
• v.18 no.4
• /
• pp.31-40
• /
• 2017

In this study, a simple method to evaluate the seismic vulnerability of river levees was examined considering the structural characteristic of river levee, that is long, and the functional characteristic of river levee that performs temporary function against flood but is a permanent structure in the ordinary way. Considering the fact that one of the main failure modes of the levee during the earthquake are the settlement due to the strength reduction of the ground caused by the increase of the excess pore pressure in the levee body and foundation and the settlement due to liquefaction, the 2-dimensional section of the levee was regarded as the 1-dimensional section and the liquefaction potential index (LPI) for the regarded section was estimated. The estimated LPI was correlated with the seismic vulnerability of river levees. The relationship between the displacement of the levee crest caused by the earthquake and the seismic vulnerability of the levees was obtained from the results of previous researches and the correlation between the displacements of the levee crest computed by 2-dimensional dynamic coupled analyses and LPIs based on the results of 1-dimensional seismic response analyses was investigated. In connection with this correlation, as a result of examination of the correlation between LPI and the seismic vulnerability of the levee, it was concluded that the method for evaluation of the seismic vulnerability of the Korean river levee using LPI is applicable.

• Journal of the Korean Geosynthetics Society
• /
• v.13 no.1
• /
• pp.71-83
• /
• 2014

Busan is located at the mouth of Nakdong River and if an earthquake occurs, it is very likely that the damage by the earthquake will be worse as liquefaction can happen in the sand layer, builtup soil, and landfill ground due to amplification in the lower sedimentary layer that is well developed in the river mouth. Therefore, this study first examined the possibility of liquefaction in the replaced sand layer under breakwater using 14 earthquakes in 5.6-7.9 scale and artificial earthquakes including the seismic wave suggested in the standard specifications for seismic design of ports and fishing port facilities to evaluate the stability of breakwater which is the primary protective structure for port facilities against earthquakes. Second, analysis on characteristics of the seismic energy and acceleration response spectrum by size of earthquake was performed to suggest the most appropriate size of seismic wave for the condition in Korea. Third, finite element analysis was performed using the suggested seismic wave to study the characteristics of earthquake by finding the dynamic lateral displacement of breakwater and verifying the stability of structure and the displacement and forces occurring at geotextile. Results of the study showed that the possibility of liquefaction in the landfill and replaced sand layer, the dynamic lateral displacement of breakwater, and changes of geotextile are greatly affected by the subsurface ground (replaced sand layer).

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.26 no.5
• /
• pp.437-444
• /
• 2020

This study was focused on the stabilization of surge motions of a moored vessel under irregular head seas. A two-point moored vessel shows strong non-linearity even in regular sea, owing to its inherent non-linear restoring force. A long-crested irregular wave is subjected to the vessel system, resulting in more complex nonlinear behavior of the displacement and velocities than in the case of regular waves. Sliding mode control (SMC) is implemented in the moored vessel to control both surge displacement and surge velocity. The SMC can provide a closed-loop system with performance and robustness against parameter uncertainties and disturbances; however, chattering is the main drawback for implementing SMC. The goal of minimizing the chattering and state convergence with accuracy is achieved using a quasi-sliding mode that approximates the discontinuous function via a continuous sigmoid function. Numerical simulations were conducted to validate the effectiveness of the proposed control algorithm.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.22 no.1
• /
• pp.137-146
• /
• 2018

On September 12, 2016, the Gyeongju District was strongly shaken with M=5.8, which was the largest one since measured by the actual seismometer in Korea, and some buildings were damaged. The field survey of reinforced concrete school buildings in the affected area was carried out, and their residual seismic capacities(R) were estimated based on the Japanese Standard for post-earthquake damage evaluation. In this study, the M school, which was greatly damaged by the 2016 Gyeongju Earthquake, was selected, and its damage level was evaluated on the basis of the Japanese Standard. The seismic capacity of the M school was also evaluated using the nonlinear dynamic analysis, and relationships between its damage level and seismic capacity was also conducted to investigate causes of earthquake damage. The damage level of M school was classified into light with R=88.2%. The result of the dynamic analysis agreed reasonably well with the damage of M school sustained by the 2016 Gyeongju earthquake. This will provide fundamental data for earthquake preparedness measures, such as the seismic rehabilitation of low-rise reinforced concrete buildings in Korea.

• Applied Chemistry for Engineering
• /
• v.16 no.4
• /
• pp.527-532
• /
• 2005

Ionic polymer metal composites (IPMC) are soft polymeric smart materials having large displacement at low voltage in air and water. The polymeric electrolyte actuator consists of a thin and porous membrane and metal electrodes plated on both faces, in impregnation electro-plating method. The response and actuation of actuator are governed. Among many factors governing the activation and response of IPMC actuator, the surface electrode plays an important role. In this study, the well-designed modification of electrode surface was carried out in order to improve the chemical stability well as electromechanical characteristics of the IPMC actuator. We employed Ion Beam Assisted Deposition (IBAD) method to prepare the topologically homogeneous thin surface electrode. After roughing the surface of Nafion membrane in order to get a larger surface area, the IPMC was prepared by impregnation for electro-plating and re- coating on the surface through traditional chemical deposition, followed by an additional surface treatment with high conductive metals with IBAD. It was observed that our IPMC specimen shows the enhanced surface electrical properties as well as the improved actuation and response characteristics under applied electric field.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.31 no.2
• /
• pp.87-95
• /
• 2018

This paper introduces a new explicit spectral element method for the simulation of SH-waves in semi-infinite domains. To simulate the wave motion in unbounded domains, it is necessary to reduce the infinite extent to a finite computational domain of interest. To prevent the wave reflection from the trunctated boundaries, perfectly matched layer(PML) wave-absorbing boundary is introduced. The forward problem for simulating SH-waves in PML-truncated domains can be formulated as second-order PDEs. The second-order semi-discrete form of the governing PDEs is constructed by using a mixed spectral elements with Legendre-gauss-Lobatto quadrature method, which results in a diagonalized mass matrix. Then the second-order semi-discrete form is transformed to a first-order, whose solutions are calculated by the fourth-order Runge-Kutta method. Numerical examples showed that solutions of SH-wave in the two-dimensional analysis domain resulted in stable and accurate, and reflections from truncated boundaries could be reduced by using PML boundaries. Elastic wave propagation analysis using explicit time integration method may be apt for solving larger domain problems such as three-dimensional elastic wave problem more efficiently.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.21 no.6
• /
• pp.64-72
• /
• 2017

The longitudinal dynamic instability which can occur in the fueling process of a space launch vehicle is called pogo. It is caused by coupling between the fuselage and propulsion system and they would be formed as a closed-loop system. so that the amplitude of the response may increase or decrease. In this paper, a mathematical model which is applicable to the systematic pogo analysis of a general launch vehicle is developed for an example of space shuttle. The formulations are composed of the linearized second-order differential equation for the propulsion system, and of the pressure, weight displacement, and generalized displacement. Those are important parameters for pogo analysis, are derived through eigenvalue analysis. By the formulation suggested in this paper, it is expected that mathematical modeling method of the pogo system can be obtained and systematic pogo stability analysis for any launch vehicle will be enabled.