• 한국지반공학회논문집
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• 제33권12호
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• pp.141-150
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• 2017

해상처분장 건설시 폐기물 내부에 생성되는 침출수 및 기타 오염물질을 차폐하기 위하여 토목섬유를 활용하는 것이 일반적이며, 이러한 토목섬유 포설시 필연적으로 토목섬유-흙 접촉면이 생성되게 된다. 본 연구에서는 토목섬유-흙 접촉면이 포함된 해상처분장에 지진하중 재하시 동적 전단거동을 수치해석적으로 파악하였다. 해상처분장은 호안형식에 따라 경사식 및 중력식으로 구분할 수 있으며 각각의 형식에 대하여 2차원 동적수치해석을 수행하여 그 거동을 분석하였다. 수치해석시 지중 간극수압의 분포를 고려한 유효응력해석을 수행하였으며 호안형식에 따른 토목섬유-흙 접촉면의 변형율 및 축력 발생경향을 지진파 주기 특성에 따라 비교하였다. 그 결과, 중력식 호안형식을 적용시 액상화에 대하여 보다 안정한 것으로 판단되고, 토목섬유 축력 및 접촉면 전단변형에 유리한 것으로 나타났다.

• Geomechanics and Engineering
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• 제20권2호
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• pp.131-146
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• 2020

Evaluation of earthquake impacts in settlements with a high risk of earthquake occurrence is important for the determination of site-specific dynamic soil parameters and earthquake-resistant structural planning. In this study, dynamic soil properties of Karliova (Bingol) city center, located near to the intersection point of the North Anatolian Fault Zone and the East Anatolian Fault Zone and therefore having a high earthquake risk, were investigated by one-dimensional equivalent linear site response analysis. From ground response analyses, peak ground acceleration, predominant site period, 0.2-sec and 1-sec spectral accelerations and soil amplification maps of the study area were obtained for both near-field and far-field earthquake effects. The average acceleration spectrum obtained from analysis, for a near-field earthquake scenario, was found to exceed the design spectra of the Turkish Earthquake Code and Eurocode 8. Yet, the average acceleration spectrum was found to remain below the respective design spectra of the two codes for the far-field earthquake scenario. According to both near- and far-field earthquake scenarios in the study area, the low-rise buildings with low modal vibration durations are expected to be exposed to high spectral acceleration values and high-rise buildings with high modal vibration durations will be exposed to lower spectral accelerations. While high amplification ratios are observed in the north of the study area for the near-distance earthquake scenario, high amplification ratios are observed in the south of the study area for the long-distance earthquake scenario.

• 한국지진공학회논문집
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• 제25권3호
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• pp.103-110
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• 2021

A shake table test is conducted for the three-story reinforced concrete building structure using 0.28 g, 0.5 g, 0.75 g, and 1.0 g of seismic input motions based on the Gyeongju earthquake. Computational efforts are made in parallel to explore the mechanical details in the structure. For engineering practice, the elastic modulus of concrete and rebar in the dynamic analysis is reduced to 38% and 50%, respectively, to calibrate the structure's natural frequencies. The engineering approach to the reduced modulus of elasticity is believed to be due to the inability to specify the flexibility of the actual boundary conditions. This aspect may lead to disadvantages of nonlinear dynamic analysis that can distort local stress and strain relationships. The initial elastic modulus can be applied directly without the so-called engineering adjustment with infinite element models with spring and spring-dashpot boundary conditions. This has the advantage of imposing the system flexibility of the structure on the sub-boundary conditions of springs and damping devices to control its sensitivity in a serial arrangement. This can reflect the flexibility of realistic boundary conditions and the effects of system damping (such as the gap between a concrete footing and shake table, loosening of steel anchors, etc.) in scalar quantities. However, these spring and dashpot coefficients can only be coordinated based on experimental results, making it challenging to select the coefficients in-prior to perform an experimental test.

• Earthquakes and Structures
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• 제21권5호
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• pp.515-530
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• 2021

In a tall reinforced concrete (RC) core wall system subjected to strong ground motions, inelastic behavior near the base as well as mid-height of the wall is possible. Generally, the formation of plastic hinge in a core wall system may lead to extensive damage and significant repairing cost. A new configuration of core structures consisting of buckling restrained braced frames (BRBFs) and RC walls is an interesting idea in tall building seismic design. This concept can be used in the plan configuration of tall core wall systems. In this study, tall buildings with different configurations of combined core systems were designed and analyzed. Nonlinear time history analysis at severe earthquake level was performed and the results were compared for different configurations. The results demonstrate that using enough BRBFs can reduce the large curvature ductility demand at the base and mid-height of RC core wall systems and also can reduce the maximum inter-story drift ratio. For a better investigation of the structural behavior, the probabilistic approach can lead to in-depth insight. Therefore, incremental dynamic analysis (IDA) curves were calculated to assess the performance. Fragility curves at different limit states were then extracted and compared. Mean IDA curves demonstrate better behavior for a combined system, compared with conventional RC core wall systems. Collapse margin ratio for a RC core wall only system and RC core with enough BRBFs were almost 1.05 and 1.92 respectively. Therefore, it appears that using one RC core wall combined with enough BRBF core is an effective idea to achieve more confidence against tall building collapse and the results demonstrated the potential of the proposed system.

• 한국지반신소재학회논문집
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• 제23권2호
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• pp.29-42
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• 2024

2017년 포항지진으로 인해 액상화 현상에 의한 안벽구조물에 피해가 발생하였다. 액상화는 지진 시 과잉간극수압 증가로 인해 유효응력이 소실되어 발생하게 된다. 이에 따른 잔교식 안벽의 피해 발생 부분을 규명하며 액상화로 인한 피해를 분석하였다. 또한 개량지반의 경우 연암층과 강성차이로 인해 하부 Sand 층의 액상화 현상으로 인해 피해가 발생하여, 비액상화 지반으로 가정하고 추가적인 수치해석을 수행하였다. 과잉간극수압비의 증가에 영향을 주는 요인으로는 지반의 상대밀도 및 입력 지진가속도의 크기 등 여러 가지 원인이 있다. 따라서 본 연구는 입력가속도의 크기를 증가시켜 Case 1~3에 대해 수치해석을 수행하였고, 개량지반의 경우 하부 Sand층의 액상화 현상으로 인한 피해가 발생하여 비액상화지반으로 가정하여 분석을 수행하였다. 결과적으로, 개량지반은 하부 액상화지반이 있을 경우 추가적인 보강이 필요하며, 잔교식 안벽 말뚝의 수평변위가 약 2배 감소하는 현상이 나타났다.

• 한국지진공학회논문집
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• 제5권4호
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• pp.27-38
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• 2001

반무한 호소의 동적 모델링을 위한 역학적 집중변수모델을 제안하였다. 깊이가 일정한 2차원 반무한 호소의 전달경계의 정해를 구하였다. 정해의 거동특성을 주파수 영역과 시간 영역에서 조사하였다. 고유진동수와 합성곱 적분의 핵함수인 베셀 함수의 모양 등과 같은 해의 주요 특성이 변하지 않도록 질량, 감쇠기, 스프링 계수를 구한다. 최종 집중 변수 모델은 각각의 고유값에 대해 2개의 질량, 1개의 스프링, 2개의 감쇠기로 구성된다. 적용 예제를 통하여 새로운 집중변수모델이 댐-호소계의 시간 영역 해석에 효율적으로 사용될 수 있음을 확인하였다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 추계 학술발표회논문집
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• pp.191-198
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• 2003

Flat slab system has been adopted in many buildings constructed recently because of the advantage of reduced floor heights to meet the economical and architectural demands. Structural engineers commonly use the equivalent frame method(EFM) with equivalent beams proposed by Jacob S. Grossman in practical engineering for the analysis of flat slab structures. However, in many cases, when it is difficult to use the EFM, it is necessary to use a refined finite element model for an accurate analysis. But it would take significant amount of computational time and memory if the entire building structure were subdivided into a finer mesh. An efficient analytical method is proposed in this study to obtain accurate results in significantly reduced computational time. The proposed method employs super elements developed using the matrix condensation technique and fictitious beams are used in the development of super elements to enforce the compatibility at the interfaces of super elements. The stiffness degradation of flat slab system considered in the EFM was taken into account by reducing the elastic modulus of floor slabs in this study. Static and dynamic analyses of example structures were peformed and the efficiency and accuracy of the proposed method were verified by comparing the results with those of the refined finite element model and the EFM.

• Earthquakes and Structures
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• 제17권5호
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• pp.463-475
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• 2019

In this paper, a procedure to develop fragility curves of structures equipped with semi-active tuned mass dampers (SATMDs) considering multiple failure criteria has been presented while accounting for the uncertainties of the input excitation, structure and control device parameters. In this procedure, Latin hypercube sampling (LHS) method has been employed to generate 30 random SATMD-structure systems and nonlinear incremental dynamic analysis (IDA) has been conducted under 20 earthquakes to determine the structural responses, where failure probabilities in each intensity level have been evaluated using Monte Carlo simulation (MCS) method. For numerical analysis, an eight-story nonlinear shear building frame with bilinear hysteresis material behavior has been used. Fragility curves for the structure equipped with optimal SATMDs have been developed considering single and multiple failure criteria for different performance levels and compared with that of uncontrolled structure as well as structure controlled using passive tuned mass damper (TMD). Numerical analysis has shown the capability of SATMDs in significant enhancement of the seismic fragility of the nonlinear structure. Also, considering multiple failure criteria has led to increasing the fragility of the structure. Moreover, it is observed that the influence of the uncertainty of input excitation with respect to the other uncertainties is considerable.

• Geomechanics and Engineering
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• 제11권6호
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• pp.821-845
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• 2016

Extensive researches on distribution of earthquake induced damages in different regions have shown that geological and geotechnical conditions of the local soils significantly influence behavior of alluvial areas under seismic loading. In this article, the site of Babol city which is formed up of saturated fine alluvial soils is considered as a case study. In order to reduce the uncertainties associated with earthquake resistant design of structures in this area (Babol city), the required design parameters have been evaluated with consideration of site's dynamic effects. The utilized methodology combines experimental ground ambient noise analysis, expressed in terms of horizontal to vertical (H/V) spectral ratio, with numerical one-dimensional response analysis of soil columns using DEEPSOIL software. The H/V spectral analysis was performed at 60 points, experimentally, for the region in order to estimate both the fundamental period and its corresponding amplification for the ground vibration. The investigation resulted in amplification ratios that were greater than one in all areas. A good agreement between the proposed ranges of natural periods and alluvial amplification ratios obtained through the analytical model and the experimental microtremor studies verifies the analytical model to provide a good engineering reflection of the subterraneous alluviums.

• Structural Engineering and Mechanics
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• 제69권3호
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• pp.243-255
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• 2019

Utilization of fiber beam-column element has gained considerable attention in recent years due mainly to its ability to model distributed plasticity over the length of the element through a number of integration points. However, the relatively high sensitivity of the method to modeling parameters as well as material behavior models can pose a significant challenge. Residual drift is one of the seismic demands which is highly sensitive to modeling parameters and material behavior models. Permanent deformations play a prominent role in the post-earthquake evaluation of serviceability of bridges affected by a near-fault ground shaking. In this research, the influence of distributed plasticity modeling parameters using both force-based and displacement-based fiber elements in the prediction of internal forces obtained from the nonlinear static analysis is studied. Having chosen suitable type and size of elements and number of integration points, the authors take the next step by investigating the influence of material behavioral model employed for the prediction of permanent deformations in the nonlinear dynamic analysis. The result shows that the choice of element type and size, number of integration points, modification of cyclic concrete behavior model and reloading strain of concrete significantly influence the fidelity of fiber element method for the prediction of permanent deformations.