• Journal of the Korean Society of Safety
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• v.27 no.1
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• pp.44-48
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• 2012

The seismic safety of long-period cable-stayed bridges is assessed by probabilistic finite element analysis and reliability analysis under NFE. The structural response of critical members of cable-stayed bridges is evaluated using the developed probabilistic analysis algorithm. In this study, the real earthquake recording(Chi-Chi Earthquake; 1997) was selected as the input NFE earthquake for investigating response characteristics. The probabilistic response and reliability index shows the different aspect comparing the result from FFE earthquake. Therefore, the probabilistic seismic safety assessment on NFE earthquakes should be performed for the exact evaluation of long-period cable-stayed bridges and the earthquake resistant design criteria should be complemented.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.4
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• pp.49-60
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• 2010

The actual hysteretic behavior of structural elements and systems is smooth. Smooth hysteretic behavior is more representative of actual behavior than bi-linear or piece-wise linear stiffness degrading models. The strength reduction factor in seismic design is used to reduce the elastic strength demand to design levels. In this study, the effect of smoothness on the strength reduction factor is evaluated for several smooth hysteretic systems subjected to near-fault and far-fault earthquakes. For design purposes, a simple expression of the strength reduction factor considering hysteretic smoothness and earthquake characteristics, represented as near-fault and far-fault earthquakes, is proposed. The strength reduction factors calculated by the proposed simple formulation are more similar to the factors directly obtained from inelastic response spectrum analyses than those calculated by several existing formulas.

• Earthquakes and Structures
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• v.9 no.1
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• pp.93-109
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• 2015

Based on the reconnaissance of buildings in Dujiangyan City during 2008 Wenchuan earthquake, China, structural damage characteristics and the spatial distribution of structural damage are investigated, and the possible reasons for the extraordinary features are discussed with consideration of the influence of urban historical evolution and spatial variation of earthquake motions. Firstly, the urban plan and typical characteristics of structural seismic damage are briefly presented and summarized. Spatial distribution of structural damage is then comparatively analyzed by classifying all surveyed buildings in accordance with different construction age, considering the influence of seismic design code on urban buildings. Finally, the influences of evolution of seismic design code, topographic condition, local site and distance from fault rupture on spatial distribution of structural damage are comprehensively discussed. It is concluded that spatial variation of earthquake motions, resulting from topography, local site effect and fault rupture, are very important factor leading to the extraordinary spatial distribution of building damage except the evolution of seismic design codes. It is necessary that the spatial distribution of earthquake motions should be considered in seismic design of structures located in complicated topography area and near active faults.

• Nuclear Engineering and Technology
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• v.43 no.5
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• pp.437-446
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• 2011

Siting criteria for nuclear power plants require that faults be characterized as to their potential for generating earthquakes, or that the absence of the potential for these occurrences be demonstrated. Because the definition of active faults in Korea has been applied by the deterministic method, which depends on the numerical age of fault movement, the possibility of inherent uncertainties exists in determining the maximum earthquake from the fault sources for seismic design. In an attempt to overcome these problems this study suggests new criteria and a probabilistic quantitative diagnostic procedure that could estimate whether a fault is capable of generating earthquakes in the near future.

• Structural Engineering and Mechanics
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• v.86 no.5
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• pp.589-605
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• 2023

This paper investigates the ductility demands of steel frames equipped with self-centring fuses under near-fault earthquake motions considering multiple yielding stages. The study is commenced by verifying a trilinear self-centring hysteretic model accounting for multiple yielding stages of steel frames equipped with self-centring fuses. Then, the seismic response of single-degree-of-freedom (SDOF) systems following the validated trilinear self-centring hysteretic law is examined by a parametric study using a near-fault earthquake ground motion database composed of 200 earthquake records as input excitations. Based on a statistical investigation of more than fifty-two (52) million inelastic spectral analyses, the effect of the post-yield stiffness ratios, energy dissipation coefficient and yielding displacement ratio on the mean ductility demand of the system is examined in detail. The analysis results indicate that the increase of post-yield stiffness ratios, energy dissipation coefficient and yielding displacement ratio reduces the ductility demands of the self-centring oscillators responding in multiple yielding stages. A set of empirical expressions for quantifying the ductility demands of trilinear self-centring hysteretic oscillators are developed using nonlinear regression analysis of the analysis result database. The proposed regression model may offer a practical tool for designers to estimate the ductility demand of a low-to-medium rise self-centring steel frame equipped with self-centring fuses progressing in the ultimate stage under near-fault earthquake motions in design and evaluation.

• Journal of Korean Society of Steel Construction
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• v.19 no.5
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• pp.435-454
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• 2007

In this study, we demonstrated the characteristics of the near-fault ground motion thatwas not considered in the domestic seismic design code and how the effect of the near-fault ground motion affects the response of cable-stayed bridges. Afterselecting the actual measurement records of the typical near- and far-fault ground motion, the characteristics of ground motion is analyzed using the elastic and inelastic response spectrum. Analyzing the response regarding the earthquake's characteristics on cable-stayed bridges by the typical three-type cable-stayed bridges and the actual cable-stayed bridge, the characteristics of responses about main members are compared and analyzed. Moreover,reliability analysis is accomplished using the results of the seismic response analysis, and the seismic safety of the cable-stayed bridges is evaluated quantitatively as a reliability index and probability of failure. According to the results of the response spectrum, the earthquake response analysis and the reliability analysis, because the effect of the near fault ground motion against the response of cable-stayed bridges is different from the effect of the existing far-fault ground motion, it should be considered as an important factor when designing cable-stayed bridges.

• Earthquakes and Structures
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• v.3 no.3_4
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• pp.315-340
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• 2012

There are many types of seismic isolation devices that are being used today for structural control of earthquake response in buildings. The most commonly used are sliding bearings and elastomeric bearings, the latter with or without lead core. An alternative solution is the use of steel springs combined with viscoelastic fluid dampers, which is the case discussed in this paper. An analytical study of a three-story building supported on helical steel springs and viscoelastic fluid dampers, GERB Control System (GCS), subjected to near-fault earthquakes is presented. Several earthquakes records have been obtained by the acceleration network installed in the isolated building and in its non-isolated twin since they were finished. These experimental results are analysed and discussed. The aim is to show that the spring-based system can be an alternative for base isolation of small building located near active faults.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.101-111
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• 2006

This paper proposes a method for modeling new fault ground motion due to moderate size earthquakes in Stable Continental Regions (SCRs) for the first time. The near fault ground motion is characterized by a single long period velocity pulse of large amplitude. In order to model the velocity pulse, its period and peak amplitude need be determined in terms of earthquake magnitude and distance from the causative fault. Because there have been observed very few new fault ground motions, it is difficult to derive the model directly from the recorded data in SCRs. Instead an indirect approach is adopted in this work. The two parameters, the period and peak amplitude of the velocity pulse, are known to be functions of the rise time and the slip velocity. For Western United States (WUS) that belongs active tectonic regions, there art empirical formulas for these functions. The relations of rise time and slip velocity on the magnitude in SCRs are derived by comparing related data between Western United States and Central-Eastern United States that belongs to SCRs. From these relations, the functions of these pulse parameters for NFGM in SCRs can be expressed in terms of earthquake magnitude and distance. A time history of near fault ground motion of moderate magnitude earthquake in stable continental regions is synthesized by superposing the velocity pulse on the for field ground motion that is generated by stochastic method. As an demonstrative application, the response of a single degree of freedom elasto-plastic system is studied.

• Earthquakes and Structures
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• v.16 no.2
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• pp.221-234
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• 2019

Today, many important concrete face rockfill dams (CFRDs) have been built on the world, and some of these important structures are located on the strong seismic regions. In this reason, examination and monitoring of these water construction's seismic behaviour is very important for the safety and future of these dams. In this study, the nonlinear seismic behaviour of Ilısu CFR dam which was built in Turkey in 2017, is investigated for various reservoir water heights taking into account 1995 Kobe near-fault and far-fault ground motions. Three dimensional (3D) finite difference model of the dam is created using the FLAC3D software that is based on the finite difference method. The most suitable mesh range for the 3D model is chosen to achieve the realistic numerical results. Mohr-Coulomb nonlinear material model is used for the rockfill materials and foundation in the seismic analyses. Moreover, Drucker-Prager nonlinear material model is considered for the concrete slab to represent the nonlinearity of the concrete. The dam body, foundation and concrete slab constantly interact during the lifetime of the CFRDs. Therefore, the special interface elements are defined between the dam body-concrete slab and dam body-foundation due to represent the interaction condition in the 3D model. Free field boundary condition that was used rarely for the nonlinear seismic analyses, is considered for the lateral boundaries of the model. In addition, quiet artificial boundary condition that is special boundary condition for the rigid foundation in the earthquake analyses, is used for the bottom of the foundation. The hysteric damping coefficients are separately calculated for all of the materials. These special damping values is defined to the FLAC3D software using the special fish functions to capture the effects of the variation of the modulus and damping ratio with the dynamic shear-strain magnitude. Total 4 different reservoir water heights are taken into account in the seismic analyses. These water heights are empty reservoir, 50 m, 100 m and 130 m (full reservoir), respectively. In the nonlinear seismic analyses, near-fault and far-fault ground motions of 1995 Kobe earthquake are used. According to the numerical analyses, horizontal displacements, vertical displacements and principal stresses for 4 various reservoir water heights are evaluated in detail. Moreover, these results are compared for the near-fault and far-faults earthquakes. The nonlinear seismic analysis results indicate that as the reservoir height increases, the nonlinear seismic behaviour of the dam clearly changes. Each water height has different seismic effects on the earthquake behaviour of Ilısu CFR dam. In addition, it is obviously seen that near-fault earthquakes and far field earthquakes create different nonlinear seismic damages on the nonlinear earthquake behaviour of the dam.

• Journal of the Earthquake Engineering Society of Korea
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• v.28 no.3
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• pp.159-164
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• 2024

Recent earthquakes in Korea, like Gyeongju and Pohang, have highlighted the need for accurate seismic hazard assessment. The lack of substantial ground motion data necessitates stochastic simulation methods, traditionally used with a simplistic point-source assumption. However, as earthquake magnitude increases, the influence of finite faults grows, demanding the adoption of finite faults in simulations for accurate ground motion estimates. We analyzed variations in simulated ground motions with and without the finite fault method for earthquakes with magnitude (Mw) ranging from 5.0 to 7.0, comparing pseudo-spectral acceleration. We also studied how slip distribution and hypocenter location affect simulations for a virtual earthquake that mimics the Gyeongju earthquake with Mw 5.4. Our findings reveal that finite fault effects become significant at magnitudes above Mw 5.8, particularly at high frequencies. Notably, near the hypocenter, the virtual earthquake's ground motion significantly changes using a finite fault model, especially with heterogeneous slip distribution. Therefore, applying finite fault models is crucial for simulating ground motions of large earthquakes (Mw ≥ 5.8 magnitude). Moreover, for accurate simulations of actual earthquakes with complex rupture processes having strong localized slips, incorporating finite faults is essential even for more minor earthquakes.