• Geomechanics and Engineering
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• v.27 no.5
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• pp.465-479
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• 2021

One of the important causes of building and infrastructure failure, such as bridges on pile foundations, is the placement of the piles in liquefiable soil that can become unstable under seismic loads. Therefore, the overarching aim of this study is to investigate the seismic behavior of a soil-pile system in liquefiable soil using three-dimensional numerical FEM analysis, including soil-pile interaction. Effective parameters on concrete pile response, involving the pile diameter, pile length, soil type, and base acceleration, were considered in the framework of finite element non-linear dynamic analysis. The constitutive model of soil was considered as elasto-plastic kinematic-isotropic hardening. First, the finite element model was verified by comparing the variations on the pile response with the measured data from the centrifuge tests, and there was a strong agreement between the numerical and experimental results. Totally 64 non-linear time-history analyses were conducted, and the responses were investigated in terms of the lateral displacement of the pile, the effect of the base acceleration in the pile behavior, the bending moment distribution in the pile body, and the pore pressure. The numerical analysis results demonstrated that the relationship between the pile lateral displacement and the maximum base acceleration is non-linear. Furthermore, increasing the pile diameter results in an increase in the passive pressure of the soil. Also, piles with small and big diameters are subjected to yielding under bending and shear states, respectively. It is concluded that an effective stress-based ground response analysis should be conducted when there is a liquefaction condition in order to determine the maximum bending moment and shear force generated within the pile.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.327-332
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• 2006

In airborne gravimetry, there are two data streams. One is the specific force measured by an air/sea gravimeter or accelerometers, the other is kinematic acceleration measured by DGPS. And the difference of them provides the gravity disturbance information. To satisfy the requirement of most applications, an accuracy of 1mGal $(1mCal=10^{-5}m/s^{2})$ with a spatial resolution of 1km is the aim of current airborne gravimetry. There are two different methods to derive the kinematic acceleration. The generally used method is to differentiate the position twice, and the position can be calculated by commercial DGPS software. The main defect of this method is that integer ambiguities need to be fixed to get the precise position solution, but it's not a trivial thing for long base line. And to fix integer ambiguities, the noisier iono-free measurement is used. When differentiation is applied, noise is amplified and will influence the accuracy of acceleration. The other method is to get carrier phase acceleration by differentiate the carrier phase first, and then using the acceleration of GPS satellite to derive the vehicle acceleration. The main advantages include that fixing integer ambiguities is not needed anymore, position can be relaxed to about 10 meters, and smoother acceleration can be got since iono-free measurement is not needed. In some literatures, it's considered that the dynamic performance of the second method is inferior to that of the first. Through analysis, it is found that the performance degradation in dynamic environment results from the simplification of the GPS carrier phase observable model. And an iterative algorithm is presented to compensate the model error. Using a dynamic GPS data from an aeromagnetic survey, the importance of this compensation is showed at last.

• Earthquakes and Structures
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• v.21 no.5
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• pp.551-562
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• 2021

In this study, the generalized intensity measure (IM) named I_Npg is analyzed. The recently proposed proxy of the spectral shape named N_pg is the base of this intensity measure, which is similar to the traditional N_p based on the spectral shape in terms of pseudo-acceleration; however, in this case the new generalized intensity measure can be defined through other types of spectral shapes such as those obtained with velocity, displacement, input energy, inelastic parameters and so on. It is shown that this IM is able to increase the efficiency in the prediction of nonlinear behavior of structures subjected to earthquake ground motions. For this work, the efficiency of two particular cases (based on acceleration and velocity) of the generalized I_Npg to predict the peak floor acceleration demands on steel frames under 30 earthquake ground motions with respect to the traditional spectral acceleration at first mode of vibration Sa(T₁) is compared. Additionally, a 3D reinforced concrete building and an irregular steel frame is used as a basis for comparison. It is concluded that the use of velocity and acceleration spectral shape increase the efficiency to predict peak floor accelerations in comparison with the traditional and most used around the world spectral acceleration at first mode of vibration.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.2
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• pp.35-42
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• 1992

The effectiveness of the support-isolation system for the equipment mounted on the primary structure is evaluated to reduce its responses under the earthquake load with considering the interaction between the primary structure and the internal equipment in this paper. A computer code (KBISAP) is developed to analyze the above system using the matrix condensation technique and constant average acceleration method. To evaluate the effectiveness of the support-isolation system, three systems are used in this study as follows: i) fixed-base structure with support-fixed equipment, ii) base-isolated structure with support-fixed equipment and iii) fixed-base structure with support-isolated equipment. The results of case study show that the acceleration of equipment with the support-isolation system is less than that of the support-fixed equipment in the base-isolated structure and significantly reduced the response compared with that of the support-fixed equipment in the fixed-base structure with the reduction factor of 8. The support-isolation system used in this study can reduce the response and also increase the safety margin of the important safety-related internal equipments.

• Nuclear Engineering and Technology
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• v.52 no.1
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• pp.192-205
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• 2020

Seismic design practices and seismic response analyses of civil structures and nuclear power plants (NPPs) have conventionally used the peak ground acceleration (PGA) or spectral acceleration (S_a) as an intensity measure (IM) of an earthquake. However, there are many other earthquake IMs that were proposed by various researchers. The aim of this study is to investigate the correlation between seismic responses of NPP components and 23 earthquake IMs and identify the best IMs for correlating with damage of NPP structures. Particularly, low- and high-frequency ground motion records are separately accounted in correlation analyses. An advanced power reactor NPP in Korea, APR1400, is selected for numerical analyses where containment and auxiliary buildings are modeled using SAP2000. Floor displacements and accelerations are monitored for the non- and base-isolated NPP structures while shear deformations of the base isolator are additionally monitored for the base-isolated NPP. A series of Pearson's correlation coefficients are calculated to recognize the correlation between each of the 23 earthquake IMs and responses of NPP structures. The numerical results demonstrate that there is a significant difference in the correlation between earthquake IMs and seismic responses of non-isolated NPP structures considering low- and high-frequency ground motion groups. Meanwhile, a trivial discrepancy of the correlation is observed in the case of the base-isolated NPP subjected to the two groups of ground motions. Moreover, a selection of PGA or S_a for seismic response analyses of NPP structures in the high-frequency seismic regions may not be the best option. Additionally, a set of fragility curves are thereafter developed for the base-isolated NPP based on the shear deformation of lead rubber bearing (LRB) with respect to the strongly correlated IMs. The results reveal that the probability of damage to the structure is higher for low-frequency earthquakes compared with that of high-frequency ground motions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.4
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• pp.415-422
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• 2016

When shock acceleration is applied to a mechanical system, it may cause malfunctioning and damage to the system. Hence, to prevent these problems when developing a gimbal structure system for observation reconnaissance, the MIL-STD-810G shock standard must be satisfied as a design specification. Rubber vibration isolators are generally assembled on the base of the system in order to reduce the shock transferred from the aircraft. It is difficult to analyze the transient behavior of the system accurately, because rubber has a nonlinear load-deformation curve. To treat the nonlinear characteristic of the rubber, bilinear approximation was introduced. Using this assumption, transient responses of the system under base shock acceleration were calculated by the finite element method. In addition, experiments with a true prototype were performed using the same conditions as the analytical model. Compared with experimental data, the proposed numerical method is useful for the transient analysis of gimbal structure systems, including rubber vibration isolators with nonlinear stiffness and damping.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.4
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• pp.86-92
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• 2008

This paper is to investigate the behavior of linear static structure stress, the fatigue and experimental shock fracture far engine base in the Auxiliary Power Unit to resolve its restricted electrical power problem. The shock fracture test was experimentally made under MIL standard criteria. The numerical results by finite element method had a good agreement with those from the shock test. The design data of predicting the fracture at the initial crack and the damage behavior of structure with shock and vibration load in the battle field can be obtained from shock test. In the functional shock test, the crack at the side parts of the engine base was found at peak acceleration of 40g.

• Smart Structures and Systems
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• v.31 no.5
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• pp.531-543
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• 2023

Base isolation is one of the most widely implemented and well-known technique to reduce structural vibration and damages during an earthquake. However, while the base-isolated structure reduces storey drift significantly, it also increases the base drifts causing many practical problems. This study proposes the use of Shape Memory Alloys (SMA) wires for the reduction in base drift while controlling the overall structure vibrations. A multi-degree-of-freedom (MDOF) structure along with base isolators and Shape-Memory-Alloys (SMA) wires in diagonal is tested experimentally and analytically. The isolation bearing considered in this study consists of laminates of steel and silicon rubber. The performance of the proposed structure is evaluated and studied under different loadings including harmonic loading and seismic excitation. To assess the seismic performance of the proposed structure, shake table tests are conducted on base-isolated MDOF frame structure incorporating SMA wires, which is subjected to incremental harmonic and historic seismic loadings. Root mean square acceleration, displacement and drift are analyzed and discussed in detail for each story. To better understand the structure response, the percentage reduction of displacement is also determined for each story. The result shows that the reduction in the response of the proposed structure is much better than conventional base-isolated structure.

• Smart Structures and Systems
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• v.20 no.1
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• pp.35-42
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• 2017

Recently, compressive sensing based data loss recovery techniques have become popular for Structural Health Monitoring (SHM) applications. These techniques involve an encoding process which is onerous to sensor node because of random sensing matrices used in compressive sensing. In this paper, we are presenting a model where the sampled raw acceleration data is directly transmitted to base station/receiver without performing any type of encoding at transmitter. The received incomplete acceleration data after data losses can be reconstructed faithfully using compressive sensing based reconstruction techniques. An in-depth simulated analysis is presented on how random losses and continuous losses affects the reconstruction of acceleration signals (obtained from a real bridge). Along with performance analysis for different simulated data losses (from 10 to 50%), advantages of performing interleaving before transmission are also presented.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.487-494
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• 2005

In this study, a set of artificial earthquake time histories, which can be used for the earthquake-resistant design of seismically isolated highway bridges, was presented. In addition, adequateness of the generated ground accelerations was investigated. These were performed based on the seismic design standard for seismically isolated bridges. Total of 22 acceleration time histories were generated for each soil condition by the spectral method. The time histories were verified to meet the code provisions including (1) mean response spectrum at control frequencies, (2) EPGA (effective peak ground acceleration), and (3) correlation coefficient. Finally, the maximum response corresponding to four time histories and the mean response associated with seven time histories were computed using the generated acceleration time histories, which shows validity of the proposed artificial earthquake time histories.