• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1318-1326
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• 2020

Structural modification in the electrical cabinet is investigated by a proposed procedure that comprises of an experimental, analytical and numerical solution. This research emphasizes the linear dynamic analysis of the cabinet that is studied under the seismic excitation to demonstrate the real behavior of the cabinets in NPP. To this end, an actual electric cabinet is experimentally tested using an impact hammer test which reveals the fundamental parameters of the cabinet. The Frequency-domain decomposition (FDD) method is used to extract the dynamic properties of the cabinet from the experiment which is then used for numerical modeling. To validate the dynamic properties of the cabinet an analytical solution is suggested. The calibrated model is analyzed under the floor response obtained from the Connecticut nuclear power plant structure excited by Tabas 1978 (Mw 7.4) earthquake. Eventually, the grouping effect of the cabinets is proposed which represents the influence on the dynamic modification. This grouping of the cabinets is described more sophisticatedly by the theoretical understating, which results in a significant change in the seismic response. Considering the grouping effects will be helpful in the assessment of the real seismic behavior, design, and performance of cabinets.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.3
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• pp.503-515
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• 2017

Underground structures that have recently become larger are required to be stable not only during normal times but also during earthquakes. Especially, it is very important to maintain the stability of the subsea tunnels during the earthquake. The objective of this paper is to verify the effectiveness of the flexible segment, which is one of the breakthrough facilities to maintain the stability of the subsea tunnel during the earthquake using the shaking table test. Another goal of this paper is to propose the optimum position of the flexible segment through 3D dynamic numerical analysis based on the verified results from shaking table tests. The 1g shaking table test considering the similarity ratio (1:100) to the cross section of the selected artificial subsea tunnel was carried out considering the Geongju and Artificial seismic waves, longitudinal and lateral wave, and with/without flexible segments eight times or more. As a result of the shaking table test, it was confirmed that the flexible segment is effective in improving the seismic performance of the undersea tunnel in all the experimental results. In addition, 3D dynamic numerical analysis was performed to select the optimum position of the flexible segment which is effective for improving seismic performance. As a result, it was confirmed that the seismic acceleration is attenuated when the flexible segment is installed adjacent to the branch section in subsea tunnel.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2A
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• pp.119-130
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• 2009

Seismic fragility curves of a structure represent the probability of exceeding the prescribed structural damage state for a given various levels of ground motion intensity such as peak ground acceleration (PGA), spectral acceleration ($S_a$) and spectral displacement ($S_d$). So those are very essential to evaluate the structural seismic performance and seismic risk. The purpose of this paper is to develop seismic fragility curves for PSC box girder bridges. In order to construct numerical fragility curve of bridge structure using nonlinear time history analysis, a set of ground motions corresponding to design spectrum are artificially generated. Assuming a lognormal distribution, the fragility curve is estimated by using the methodology proposed by Shinozuka et al. PGA is simple and generally used parameter in fragility curve as ground motion intensity. However, the PGA has not good relationship with the inelastic structural behavior. So, $S_a$ and $S_d$ with more direct relationship for structural damage are used in fragility analysis as more useful intensity measures instead of PGA. The numerical fragility curves based on nonlinear time history analysis are compared with those obtained from simple method suggested in HAZUS program.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.177-178
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• 2018

Unlike the projects that the government has implemented recently to develop new cities under the New Deal project, Saeddeul Village projects to improve the environment of the city are gaining attention. The problem has been found to be that many of the buildings in Saeddeul Village are still not earthquake-proof by using drones to review the state of the town. It also revealed that after two years of earthquakes, Pilotis structures are the most vulnerable to earthquakes. However, it is suitable for small spaces in the city because it provides parking spaces as well as residential spaces. Accordingly, the focus should be on repair and reinforcement rather than reconstruction. In this study, a concrete-based seismic design and construction method is developed in the columns of the existing pylotis structure.

• Smart Structures and Systems
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• v.25 no.2
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• pp.241-254
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• 2020

Using confined shape memory alloy (SMA) bar or plate, this study proposes an innovative self-centering damper. The damper is essentially properly machined SMA core, i.e., bar or plate, that encased in buckling-restrained device. To prove the design concept, cyclic loading tests were carried out. According to the test results, the damper exhibited desired flag-shape hysteretic behaviors upon both tension and compression actions, although asymmetric behavior is noted. Based on the experimental data, the hysteretic parameters that interested by seismic applications, such as the strength, stiffness, equivalent damping ratio and recentering capacity, are quantified. Processed in the Matlab/Simulink environment, a preliminary evaluation of the seismic control effect for this damper was conducted. The proposed damper was placed at the first story of a multi-story frame and then the original and controlled structures were subjected to earthquake excitations. The numerical outcome indicated the damper is effective in controlling seismic deformation demands. Besides, a companion SMA damper which represents a popular type in previous studies is also introduced in the analysis to further reveal the seismic control characteristics of the newly proposed damper. In current case, it was found that although the current SMA damper shows asymmetric tension-compression behavior, it successfully contributes comparable seismic control effect as those having symmetrical cyclic behavior. Additionally, the proposed damper even shows better global performance in controlling acceleration demands. Thus, this paper reduces the concern of using SMA dampers with asymmetric cyclic behavior to a certain degree.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.225-233
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• 2003

Even though a lot of advanced researches on analysis, design, and performance evaluation of reinforced concrete (RC) under seismic action have been carried out, there has been only a few study on seismic analysis of underground RC structures surrounding soil medium. Since the underground RC structures interact with surrounding soil medium, a path-dependent soil model which can predict the soil response is necessary for analyzing behavior of the structure inside soil medium. The behavior of interfacial zone between the RC structure and the surrounding medium should be also considered for more accurate seismic analysis of the RC structure. In this paper, an averaged constitutive model of concrete and reinforcing bars for RC structure and path-dependent Ohsaki's model for soil are applied, and an elasto-plastic interface model having thickness is proposed for seismic analysis of underground RC structures. A finite element analysis technique is developed by applying aforementioned constitutive equations and is verified by predicting both static and dynamic behaviors of RC structures. Then, failure mechanisms of underground RC structure under seismic action are numerically derived through seismic analysis of underground RC station structure under different seismic forces. Finally, the changes of failure mode and the damage level of the structures are also analytically derived for different design cases of underground RC structures.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.425-434
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• 2019

It is important to ensure the seismic safety of pile-bent bridges constructed in areas with thick soft ground consisting of various soil layers against seismic motion in these layers. In this study, several synthetic seismic waves that are compatible with the seismic design spectrum for rock sites were generated, and the ground acceleration history of each soil layer was obtained based on ground analyses. Using these acceleration histories, each soil layer was modeled using equivalent linear springs, and multi-support excitation analyses were performed using the input motion obtained at each soil layer. Due to the nonlinear behavior of the soft soil layers, the intensity of the input ground motion was not amplified, which resulted in the elastic behavior of the bridge. In addition, inputting the acceleration history obtained from a particular layer simultaneously into all the ground springs reduced the response. Therefore, the seismic performance of this type of bridge might be overestimated if multi-excitation analysis is not performed.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.4
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• pp.83-94
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• 1999

High-strength concrete has demonstrated characteristics of both increased strength and enhanced durability; hence its use has become more and more widespread. But, due to the lack of experimental evidance on the seismic performance of frame members constructed with high-strength concrete, the current codes of their design provisions are based on normal concrete test. The purpose of this study is to compare the response of the high-strength concrete beam-column-slab subassemblies with the response of a normal-strength concrete specimens. Four assemblies $(f_c'=240kg/\textrm{cm}^2, f_c'=700kg/\textrm{cm}^2)$ with 2/3 scale were designed and tested to investigate seismic behavior.

• Structural Engineering and Mechanics
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• v.61 no.4
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• pp.483-496
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• 2017

Earthquake excitations may induce important amount of seismic energy into structures. Current design philosophy mainly deals with the plastic deformations of replaceable energy dissipating devices rather than damages accumulated on structural members. Since earthquake damage is substantially concentrated on these devices they could be replaced after severe earthquakes. In this study, the efficiency of steel cushion (SC) on seismic improvement of a vulnerable reinforced concrete (RC) frame is determined by means of several numerical simulations. The cyclic shear behaviors of SCs were determined by performing quasi-static tests. The test results were the main basis of the theoretical model of SCs which were used in the numerical analysis. These analyses were performed on three types of RC frames namely bare frame (BF), full-braced frame (F-BF) and semi-braced frame (S-BF). According to analysis results; implementation of SCs has considerable effects in reducing the storey shear forces and storey drifts. Moreover plastic energy demands of structural elements were reduced which indicates a significant improvement in seismic behavior of the RC frame preventing damage accumulation on structural elements. Full-braced frame having SCs with the thickness of 25 mm has better performance than semi-braced frame interms of energy dissipation. However, global energy dissipation demand of S-BF and F-BF having SCs with the thickness of 18 mm are almost similar.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.795-800
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• 2007

In the previous study, a simple but effective analysis procedure, named as an Improved Modal Pushover Analysis (IMPA) was proposed to estimates the seismic capacities of multi-span continuous bridge structures, on the basis of the modal pushover analysis which considers all the dynamic modes of a structure. Differently from other previous studies, IMPA maintains the simplicity of the capacity-demand curve method and also gives a better estimation of the maximum dynamic response of a structure. Nevertheless, its applicability has never been approved for multi-span continuous bridges with large differences in the length of their adjacent piers. This paper, accordingly, concentrates on a parametric study to verify the efficiency and limitation in application of IMPA through a correlation study between various analytical models including the Equivalent Single Degree Of Freedom (ESDOF) and Modal Pushover Analysis (MPA) usually used in the seismic design of structures. Based on the obtained numerical results, this paper introduces a practical guidance and/or limitation for using IMPA to predict the seismic response of a bridge effectively.