• Smart Structures and Systems
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• v.22 no.5
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• pp.495-508
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• 2018

Shape memory alloys (SMAs) exhibit superelasticity given the ambient temperature is above the austenite finish temperature threshold, the magnitude of which significantly depends on the metal ingredients though. For the monocrystalline CuAlBe SMAs, their superelasticity was found being maintained even when the ambient temperature is down to $-40^{\circ}C$. Thus this makes such SMAs particularly favorable for outdoor seismic applications, such as the framed structures located in cold regions with substantial temperature oscillation. Due to the thermo-mechanical coupling mechanism, the hysteretic properties of SMAs vary with temperature change, primarily including altered material strength and different damping. Thus, this study adopted the monocrystalline CuAlBe SMAs as the kernel component of the SMA braces. To quantify the seismic response characteristics at various temperatures, a wide temperature range from -40 to $40^{\circ}C$ are considered. The middle temperature, $0^{\circ}C$, is artificially selected to be the reference temperature in the performance comparisons, as well the corresponding material properties are used in the seismic design procedure. Both single-degree-of-freedom systems and a six-story braced frame were numerically analyzed by subjecting them to a suite of earthquake ground motions corresponding to the design basis hazard level. To the frame structures, the analytical results show that temperature variation generates minor influence on deformation and energy demands, whereas low temperatures help to reduce acceleration demands. Further, attributed to the excellent superelasticity of the monocrystalline CuAlBe SMAs, the frames successfully maintain recentering capability without leaving residual deformation upon considered earthquakes, even when the temperature is down to $-40^{\circ}C$.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.137-139
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• 2007

To enhance capability on discerning local and regional seismic phases, such as, Pn, Pg, Sn, Rg, etc, within the crust, 2-D numerical forward modeling will be applied to the data obtained from local seismic stations by simulating almost all waves including not only body wave but also surface wave generated without having to explicitly include them under consideration of Q factor. In this study, after getting rid of instrumental response by deconvolution, pseudo-spectral method instead of relying on typical numerical methods, such as, FEM(Finite Element Method) and FDM(Finite Difference Method), will be implemented for 2-D numerical forward modeling by considering velocities of P-wave and S-wave, density, and Q factors. Ultimately, the Power of reaching the enhanced capability on discerning local and regional seismic phases will make it easier for us to identify the seismic source, whether it is originated from man-made explosion or pure earthquake.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.167-167
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• 2011

최근 사회기반 시설물들의 대형화, 고밀도화가 됨에 따라 재해 재난대비에 대한 관심 또한 높아지고 있다. 특히, 화재는 우리 주변에서 지속적으로 발생하는 재난이다. 한편, 지진과 같은 경우에는 중소규모가 한반도내에서 빈번하게 발생하고 있지만 직접적으로 피해를 경험 한 적이 없어, 적극적으로 대비해야하는 재해로는 아직 인식하고 있지 못한다고 할 수 있다. 재난, 재해에 대한 연구는 과거의 피해를 기준으로 미래에 대한 대책을 해결책으로 제시하는 방식으로 많은 연구자들에 의해서 지속적으로 이루어지고 있다. 본 연구에서는 우리사회에 발생 가능한 재난에 대해서 서로 다른 인식 수준을 가지고 있는 지진과 화재의 재난에 대한 시민인식차이를 실증적으로 검토하였다. 화재 및 지진에 대한 설문조사를 실시하고 결과 분석을 통해 나타나는 재난시의 인간행동심리를 Facet이론을 이용하여 범위를 선정하고 분석하였다. 분석방법으로는 통합적 분석 방법으로 각 연령대별로 분류하여 분석하였다. 연령대별로 습득한 지식 및 교육환경 배경이 차이가 있을 것이라는 가정 아래 연령대별 분류를 하였다. 설문조사결과를 바탕으로 Facet이론에 근거하여 분석한 결과, 화재발생시의 통합적 분석의 경우는 [MATTER], [SPACE], [ENERGY]등이 다수 나타났고 지진 발생 시에는 통합적으로 [SPACE], [ENERGY]가 다수 나타났다. 따라서, 지진에 대한 국가적으로 교육시스템을 갖추고 개인적인 지진발생시 행동상황을 숙지하고 연습하는 것이 필요한 것으로 나타났다. 결론적으로 지진과 화재시의 인간행동심리를 비교한 결과, 화재는 우리나라에서 가장 빈번하게 발생하는 재해이기 때문에 비교적 국가적으로나 개인적으로 대비를 하고 있다는 것을 실증적으로 나타내었다. 화재로 인한 재난은 국가적으로 끊임없이 교육(인식전환)을 실시하고 있음에도 불구하고 지속적으로 발생하고 있다. 하지만 지진과 비교해 인위적 과실로 인한 재난임에도 불구하고 사전에 화재발생시 대처하는 행동숙지로 인해 많은 인적 및 재산적 피해를 줄일 수 있다. 최근 우리나라는 지진에 대해서는 건축물의 붕괴로 인한 피해방지에 중점을 두고 건축물의 내진성능에 대한 평가가 점진적으로 추진되고 있다. 하지만, 지진발생시 이와 같은 현재 방재정책과 더불어 국민 스스로 지진에 대한 발생가능성 및 예상위험에 대한 인식수준을 향상시킴으로서 국가적 재난을 효과적으로 대처할 필요가 있음을 실증적으로 나타내었다.

• Earthquakes and Structures
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• v.11 no.3
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• pp.517-538
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• 2016

This paper presents a probabilistic fragility analysis for two groups of bridges: simply supported and integral bridges. Comparisons are based on the seismic fragility of the bridges subjected to accelerograms of two seismic sources. Three-dimensional finite-element models of the bridges were created for each set of bridge samples, considering the nonlinear behaviour of critical bridge components. When the seismic hazard in the site is controlled by a few seismic sources, it is important to quantify separately the contribution of each fault to the structure vulnerability. In this study, seismic records come from earthquakes that originated in strike-slip and reverse faulting mechanisms. The influence of the earthquake mechanism on the seismic vulnerability of the bridges was analysed by considering the displacement ductility of the piers. An in-depth parametric study was conducted to evaluate the sensitivity of the bridges' seismic responses to variations of structural parameters. The analysis showed that uncertainties related to the presence of lap splices in columns and superstructure type in terms of integral or simply supported spans should be considered in the fragility analysis of the bridge system. Finally, the fragility curves determine the conditional probabilities that a specific structural demand will reach or exceed the structural capacity by considering peak ground acceleration (PGA) and acceleration spectrum intensity (ASI). The results also show that the simply supported bridges perform consistently better from a seismic perspective than integral bridges and focal mechanism of the earthquakes plays an important role in the seismic fragility analysis of highway bridges.

• Journal of Korea Water Resources Association
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• v.51 no.8
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• pp.643-654
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• 2018

In order to generate the stable tsunami in a numerical wave tank, a two-dimensional numerical model, LES-WASS-2D has been introduced the non-reflected wave generation system for various tsunami waveforms. And then, comparing to existing experimental results it is revealed that computed results of the LES-WASS-2D are in good agreement with the experimental results on spatial and temporal tsunami waveforms in the vicinity of a seawall. It is shown that the applied model in this study is applicable to the numerical simulations on tsunami overtopping and inundation. Using the numerical results, the characteristics of overtopping and inundation on a seawall are also discussed with volume ratio of tsunami and relative tsunami height. The wider the tsunami waveform, tsunami overtopping quantity and inundation distances are linearly increased. Therefore, the hydraulic characteristics is highly likely to be underestimated against the real tsunami if the solitary wave of approximation theory is applied for the overtopping/inundation simulations due to a tsunami.

• Computers and Concrete
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• v.22 no.1
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• pp.123-132
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• 2018

Reinforced concrete (RC) columns which are the main vertical structural members are exposed to several static and dynamic effects such as earthquake and wind. However, impact loading that is sudden impulsive dynamic one is the most effective loading type acting on the RC columns. Impact load is a kind of impulsive dynamic load which is ignored in the design process of RC columns like other structural members. The behavior of reinforced concrete columns under impact loading is an area of research that is still not well understood; however, work in this area continues to be motivated by a broad range of applications. Examples include reinforced concrete structures designed to resist accidental loading scenarios such as falling rock impact; vehicle or ship collisions with buildings, bridges, or offshore facilities; and structures that are used in high-threat or high-hazard applications, such as military fortification structures or nuclear facilities. In this study, free weight falling test setup is developed to investigate the behavior effects on RC columns under impact loading. For this purpose, eight RC column test specimens with 1/3 scale are manufactured. While drop height and mass of the striker are constant, application point of impact loading, stirrup spacing and concrete compression strength are the experimental variables. The time-history of the impact force, the accelerations of two points and the displacement of columns were measured. The crack patterns of RC columns are also observed. In the light of experimental results, low-velocity impact behavior of RC columns were determined and interpreted. Besides, the finite element models of RC columns are generated using ABAQUS software. It is found out that proposed finite element model could be used for evaluation of dynamic responses of RC columns subjected to low-velocity impact load.

• Earthquakes and Structures
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• v.17 no.6
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• pp.557-566
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• 2019

The evaluation of the seismic hazard for a given site is to estimate the seismic ground motion at the surface. This is the result of the combination of the action of the seismic source, which generates seismic waves, the propagation of these waves between the source and the site, and site local conditions. The aim of this work is to evaluate the sensitivity of dynamic response of extended structures to spatial variable ground motions (SVGM). All factors of spatial variability of ground motion are considered, especially local site effect. In this paper, a method is presented to simulate spatially varying earthquake ground motions. The scheme for generating spatially varying ground motions is established for spatial locations on the ground surface with varying site conditions. In this proposed method, two steps are necessary. Firstly, the base rock motions are assumed to have the same intensity and are modelled with a filtered Tajimi-Kanai power spectral density function. An empirical coherency loss model is used to define spatial variable seismic ground motions at the base rock. In the second step, power spectral density function of ground motion on surface is derived by considering site amplification effect based on the one dimensional seismic wave propagation theory. Several dynamics analysis of a curved viaduct to various cases of spatially varying seismic ground motions are performed. For comparison, responses to uniform ground motion, to spatial ground motions without considering local site effect, to spatial ground motions with considering coherency loss, phase delay and local site effects are also calculated. The results showed that the generated seismic signals are strongly conditioned by the local site effect. In the same sense, the dynamic response of the viaduct is very sensitive of the variation of local geological conditions of the site. The effect of neglecting local site effect in dynamic analysis gives rise to a significant underestimation of the seismic demand of the structure.

• Journal of Korean Society of Steel Construction
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• v.18 no.5
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• pp.585-596
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• 2006

This study focuses on the seismic behavior of 3-, 9-, and 20-story steel moment resisting frame (MRF) structures designed in accordance with the 2000 International Building Code using different Response Modification factors (R factors), i.e., 8, 9, 10, 11, and 12. For a detailed case study, 30 different structures were evaluated for 20 ground motions representing the hazard level, which is equal to a 2% probability in 50 years (2% in 50 years). The results showed that the current R factors provide conservative designs for the 3- and 9-story buildings for the Collapse Prevention performance objective. the 20-story buildings, which were designed without using the minimum requirement of spectral acceleration CS prescribed in IBC 2000, did not satisfy the seismic performance for Collapse Prevention performance.

• Earthquakes and Structures
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• v.9 no.3
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• pp.603-623
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• 2015

The scale and nature of the recent earthquakes in the world and the related earthquake disaster index coerce the concerned community to become anxious about it. Therefore, it is crucial that seismic lateral load effect will be appropriately considered in structural design. Application of seismic isolation system stands as a consistent alternative against this hazard. The objective of the study is to evaluate the structural and economic feasibility of reinforced concrete (RC) buildings with base isolation located in medium risk seismic region. Linear and nonlinear dynamic analyses as well as linear static analysis under site-specific bi-directional seismic excitation have been carried out for both fixed based (FB) and base isolated (BI) buildings in the present study. The superstructure and base of buildings are modeled in a 3D finite element model by consistent mass approach having six degrees of freedom at each node. The floor slabs are simulated as rigid diaphragms. Lead rubber bearing (LRB) and High damping rubber bearing (HDRB) are used as isolation device. Change of structural behaviors and savings in construction costing are evaluated. The study shows that for low to medium rise buildings, isolators can reduce muscular amount of base shears, base moments and floor accelerations for building at soft to medium stiff soil. Allowable higher horizontal displacement induces structural flexibility. Though incorporating isolator increases the outlay, overall structural cost may be reduced. The application of base isolation system confirms a potential to be used as a viable solution in economic building design.

• Earthquakes and Structures
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• v.17 no.5
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• pp.511-519
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• 2019

The concrete gravity dam is one of the most important parts of the nation's infrastructure. Besides the benefits, the dam also has some potentially catastrophic disasters related to the life of citizens directly. During the lifetime of service, some degradations in a dam may occur as consequences of operating conditions, environmental aspects and deterioration in materials from natural causes, especially from dynamic loads. Cumulative Absolute Velocity (CAV) plays a key role to assess the operational condition of a structure under seismic hazard. In previous researches, CAV is normally used in Nuclear Power Plant (NPP) fields, but there are no particular criteria or studies that have been made on dam structure. This paper presents a method to calculate the limitation of CAV for the Bohyeonsan Dam in Korea, where the critical Peak Ground Acceleration (PGA) is estimated from twelve sets of selected earthquakes based on High Confidence of Low Probability of Failure (HCLPF). HCLPF point denotes 5% damage probability with 95% confidence level in the fragility curve, and the corresponding PGA expresses the crucial acceleration of this dam. For determining the status of the dam, a 2D finite element model is simulated by ABAQUS. At first, the dam's parameters are optimized by the Minitab tool using the method of Central Composite Design (CCD) for increasing model reliability. Then the Response Surface Methodology (RSM) is used for updating the model and the optimization is implemented from the selected model parameters. Finally, the recorded response of the concrete gravity dam is compared against the results obtained from solving the numerical model for identifying the physical condition of the structure.