• Steel and Composite Structures
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• 제47권1호
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• pp.121-134
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• 2023

This paper tested 11 concrete-encased concrete-filled steel tube (CFST) composite columns and one reinforced concrete column under combined axial compression and lateral loads. The primary parameters, including the loading system, axial compression ratio, volume stirrup ratio, diameter-to-thickness ratio of the steel tube, and stirrup form, were varied. The influence of the parameters on the failure mode, strength, ductility, energy dissipation, strength degradation, and damage evolution of the composite columns were revealed. Moreover, a two-parameter nonlinear seismic damage model for composite columns was established, which can reflect the degree and development process of the seismic damage. In addition, the relationships among the inter-story drift ratio, damage index and seismic performance level of composite columns were established to provide a theoretical basis for seismic performance design and damage assessments.

• Smart Structures and Systems
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• 제25권3호
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• pp.311-322
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• 2020

This paper studies the influence of parameters of a novel SMA helical spring energy dissipation brace on the seismic resistance of a frame structure. The force-displacement relationship of the SMA springs is established mathematically based on a multilinear constitutive model of the SMA material. Four SMA helical springs are fabricated, and the force-displacement relationship curves of the SMA springs are obtained via tension tests. A numerical dynamic model of a two-floor frame with spring energy dissipation braces is constructed and evaluated via vibration table tests. Then, two spring parameters, namely, the ratio of the helical spring diameter to the wire diameter and the pre-stretch length, are selected to investigate their influences on the seismic responses of the frame structure. The simulation results demonstrate that the optimal ratio of the helical spring diameter to the wire diameter can be found to minimize the absolute acceleration and the relative displacement of the frame structure. Meanwhile, if the pre-stretch length is assigned a suitable value, excellent vibration reduction performance can be realized. Compared with the frame structure without braces, the frames with spring braces exhibit highly satisfactory seismic resistance performance under various earthquake waves. However, it is necessary to select an SMA spring with optimal parameters for realizing optimal vibration reduction performance.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2010년도 학술대회 초록집
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• pp.27-27
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• 2010

There have been several studies about empirical relation between seismic source parameters(e.g., focal mechanisms, depths, magnitudes, etc.) and T-wave observation. In order to delineate the relation, numerical and theoretical approaches to figure out T-wave excitation mechanism are required. In an attempt to investigate source radiation and wave scattering effects in the oceanic crust on T-wave envelopes, we perform three-dimensional numerical modeling to synthesize T-wave envelopes. We first calculate seismic P- and SV-wave energy on the seafloor using the Direct Simulation Monte Carlo based on the Radiative Transfer Theory, which enables us to take into account both realistic seismic source parameters and wave scattering in heterogeneous media, and then estimate excited T-wave energy by normal mode computation. The numerical simulation has been carried out considering the following different conditions: source types (strike and normal faults), source depths (shallow and deep), and wave propagation through homogeneous and heterogeneous Earth media. From the results of numerical modeling, we confirmed that T-wave envelopes vary according to spatial seismic energy distributions on the seafloor for the various input parameters. Furthermore, the synthesized T-wave envelopes show directional patterns due to anisotropic source radiation, and the slope change of T-wave envelopes caused by focal depth. Seismic wave scattering in the oceanic crust is likely to control the shape of envelopes.

• Structural Engineering and Mechanics
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• 제84권1호
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• pp.85-100
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• 2022

The updated Turkish Building Earthquake Code has been significantly renovated and expanded compared to previous seismic design codes. The use of earthquake ground motion levels with different probabilities of exceedance is one of the major advances in structural mechanics with the current code. This study aims to investigate the earthquake performance of steel structure in settlements with different seismic hazards for various earthquake ground motion levels. It is focused on earthquake and structural parameters for four different ground motion levels with different probabilities of exceedance calculated according to the location of the structure by the updated Turkish Hazard Map. For this purpose, each of the seven different geographical regions of Turkey which has the same seismic zone in the previous earthquake hazard map has been considered. Earthquake parameters, horizontal design elastic spectra obtained and comparisons were made for all different ground motion levels for the seven different locations, respectively. Structural analyzes for a sample steel structure were carried out using pushover analysis by using the obtained design spectra. It has been determined that the different ground motion levels significantly affect the expected target displacements of the structure for performance criteria. It is noted that the different locations of the same earthquake zone in the previous code with the same earthquake-building parameters show significant variations due to the micro zoning properties of the updated seismic design code. In addition, the main innovations of the updated code were discussed.

• Structural Engineering and Mechanics
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• 제81권6호
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• pp.677-689
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• 2022

Generally, the goal of seismic retrofit design of an existing structure using energy dissipation devices is to determine the optimum design parameters of a retrofit device to satisfy a specified limit state with minimum cost. However, the presence of multiple parameters to be optimized and the computational complexity of performing non-linear analysis make it difficult to find the optimal design parameters in the realistic 3D structure. In this study, genetic algorithm-based optimal seismic retrofit methods for determining the required number, yield strength, and location of steel slit dampers are proposed to retrofit an asymmetric soft first-story structure. These methods use a multi-objective and single-objective evolutionary algorithms, each of which varies in computational complexity and incorporates nonlinear time-history analysis to determine seismic performance. Pareto-optimal solutions of the multi-objective optimization are found using a non-dominated sorting genetic algorithm (NSGA-II). It is demonstrated that the developed multi-objective optimization methods can determine the optimum number, yield strength, and location of dampers that satisfy the given limit state of a three-dimensional asymmetric soft first-story structure. It is also shown that the single-objective distribution method based on minimizing plan-wise stiffness eccentricity turns out to produce similar number of dampers in optimum locations without time consuming nonlinear dynamic analysis.

• Earthquakes and Structures
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• 제25권5호
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• pp.325-342
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• 2023

The damping modification factor (DMF) is used to modify the 5%-damped response spectrum to produce spectral values that correspond to other necessary damping ratios for seismic design. The DMF has been the subject of numerous studies, and it has been discovered that seismological parameters like magnitude and distance can have an impact on it. However, DMF formulations incorporating these seismological parameters cannot be directly applied to seismic design because these parameters are not specified in the present seismic codes. The goal of this study is to develop a formulation for the DMF that can be directly applied in seismic design and that takes the effects of magnitude, distance, and site conditions into account. To achieve this goal, 16660 ground motions with magnitudes ranging from 4 to 9 and epicentral distances ranging from 10 to 200 km are used to systematically study the effects of magnitude, distance, and site conditions on the DMF. Furthermore, according to the knowledge that magnitude and distance affect the DMF primarily by changing the spectral shape, a spectral shape factor is adopted to reflect influences of magnitude and distance, and a new formulation for the DMF incorporating the spectral shape factor is developed. In comparison to the current formulations, the proposed formulation provides a more accurate prediction of the DMF and can be employed directly in seismic design.

• 한국음향학회지
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• 제28권3호
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• pp.251-259
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• 2009

본 논문에서는 하이드로폰으로 측정한 지진음 데이터를 가지고 20 MSVQ 알고리즘을 이용하여 자연지진음과 인공지진음을 식별하였다. 지진음 식별을 위한 특징 파라미터로는 스펙트럼 대역별 에너지, MFCC를 사용하였으며, 실험을 통하여 식별에 적합한 특징 파라미터 차수를 결정하였다. 2개의 특징 파라미터를 가지고 20 MSVQ 알고리즘으로 식별한 결과 MFCC를 사용하였을 경우에 99.9%, 스펙트럼 에너지 파라미터는 83.9%의 식별결과를 얻었다. 본 논문에서 제안한 파라미터와 알고리즘을 사용하여 지진음을 식별한 결과 성능이 매우 우수함을 확인하였다.

• 한국지진공학회논문집
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• 제14권2호
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• pp.75-84
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• 2010

원자력발전소에 설치되는 주요 전기기기들의 내부 부품을 내진검증하기 위해서는 캐비닛내부응답스펙트럼이 필요하고, 이는 캐비닛의 각 위치에서 정확한 지진응답을 구한 후에 생성이 가능하다. 반면에 대부분의 전기기기는 질량과 강성 분포가 복잡하기 때문에 해석적 방법에 의해 동적 분석을 수행하는 것이 어렵다. 이러한 여건을 감안하여 이 연구에서는 해석과 시험을 조합하여 기기의 지진응답을 예측하는 간편한 절차를 제안하였다. 제안된 절차는 먼저 충격시험을 통하여 규명된 실험모드특성을 이용하여 독립된 모드방정식을 구성하고, 이로부터 모드응답을 계산한 다음, 각 모드응답을 중첩함으로써 구조물의 지진응답을 예측한다. 제안된 절차의 신뢰성을 검증하기 위해서, 별도로 제작된 단순 강재 프레임 시편에 제안된 절차를 적용하여 지진응답을 예측하고, 이를 실제 진동대시험을 통하여 계측한 결과와 비교하였다. 이 연구를 통하여 충격시험에 의해 얻어진 실험모드특성을 이용하여 구조물의 지진응답을 비교적 정확하게 예측할 수 있음을 확인하였다.

• Structural Engineering and Mechanics
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• 제83권2호
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• pp.207-227
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• 2022

In general, the interaction conditions between the discrete stones are not taken into account by structural engineers during the modeling and analyzing of historical stone bridges. However, many structural damages in the stone bridges occur due to ignoring the interaction conditions between discrete stones. In this study, it is aimed to examine the seismic behavior of a historical stone bridge by considering the interaction stiffness parameters between stone elements. For this purpose, Tokatli historical stone arch bridge was built in 1179 in Karabük-Turkey, is chosen for three-dimensional (3D) seismic analyses. Firstly, the 3D finite-difference model of the Tokatli stone bridge is created using the FLAC3D software. During the modeling processes, the Burger-Creep material model which was not used to examine the seismic behavior of historical stone bridges in the past is utilized. Furthermore, the free-field and quiet non-reflecting boundary conditions are defined to the lateral and bottom boundaries of the bridge. Thanks to these boundary conditions, earthquake waves do not reflect in the 3D model. After each stone element is modeled separately, stiffness elements are defined between the stone elements. Three situations of the stiffness elements are considered in the seismic analyses; a) for only normal direction b) for only shear direction c) for both normal and shear directions. The earthquake analyses of the bridge are performed for these three different situations of the bridge. The far-fault and near-fault conditions of 1989 Loma Prieta earthquake are taken into account during the earthquake analyses. According to the seismic analysis results, the directions of the stiffness parameters seriously changed the earthquake behavior of the Tokatli bridge. Moreover, the most critical stiffness parameter is determined for seismic analyses of historical stone arch bridges.

• Earthquakes and Structures
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• 제3권2호
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• pp.117-140
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• 2012

The proposed research includes a comprehensive study on the seismic vulnerability assessment of typical building types, representative of the structural materials, the seismic codes and the construction techniques of Southern Europe. A damage database is created after the elaboration of the results of the observational data obtained from post-earthquake surveys carried out in the area struck by the September 7, 1999 Athens earthquake, a near field seismic event in an extended urban region. The observational database comprises 180.945 buildings which developed damage of varying degree, type and extent. The dataset is elaborated in order to gather useful information about the structural parameters influence on the seismic vulnerability and their correlation to the type and degree of building damages in near field earthquakes. The damage calibration of the observational data was based on label - damage provided by Earthquake Planning and Protection Organization (EPPO) in Greece and referred to the qualitative characterization for the recording of damage in post-earthquake surveys. Important conclusions are drawn on the parameters that influence the seismic response based on the wide homogeneous database which adds to the reliability of the collected information and reduces the scatter on the produced results.