• Geomechanics and Engineering
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• 제24권5호
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• pp.491-503
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• 2021

Shallow tunnels are vulnerable to earthquakes, and shallow ground is usually inhomogeneous. Based on the limit equilibrium method and variational principle, a solution for the seismic collapse mechanism of shallow tunnel in inhomogeneous ground is presented. And the finite difference method is employed to compare with the analytical solution. It shows that the analytical results are conservative when the horizontal and vertical stresses equal the static earth pressure and zero at vault section, respectively. The safety factor of shallow tunnel changes greatly during an earthquake. Hence, the cyclic loading characteristics should be considered to evaluate tunnel stability. And the curve sliding surface agrees with the numerical simulation and previous studies. To save time and ensure accuracy, the curve sliding surface with 2 undetermined constants is a good choice to analyze shallow tunnel stability. Parameter analysis demonstrates that the horizontal semiaxis, acceleration, ground cohesion and homogeneity affect tunnel stability greatly, and the horizontal semiaxis, vertical semiaxis, tunnel depth and ground homogeneity have obvious influence on tunnel sliding surface. It concludes that the most applicable approaches to enhance tunnel stability are reducing the horizontal semiaxis, strengthening cohesion and setting the tunnel into good ground.

• International Journal of Concrete Structures and Materials
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• 제9권3호
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• pp.345-367
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• 2015

Past earthquakes have signaled the increased collapse vulnerability of mainshock-damaged bridge piers and urgent need of repair interventions prior to subsequent cascading hazard events, such as aftershocks, triggered by the mainshock (MS). The overarching goal of this study is to quantify the collapse vulnerability of mainshock-damaged substandard RC bridge piers rehabilitated with different repair jackets (FRP, conventional thick steel and hybrid jacket) under aftershock (AS) attacks of various intensities. The efficacy of repair jackets on post-MS resilience of repaired bridges is quantified for a prototype two-span single-column bridge bent with lap-splice deficiency at column-footing interface. Extensive number of incremental dynamic time history analyses on numerical finite element bridge models with deteriorating properties under back-to-back MS-AS sequences were utilized to evaluate the efficacy of different repair jackets on the post-repair behavior of RC bridges subjected to AS attacks. Results indicate the dramatic impact of repair jacket application on post-MS resilience of damaged bridge piers-up to 45.5 % increase of structural collapse capacity-subjected to aftershocks of multiple intensities. Besides, the efficacy of repair jackets is found to be proportionate to the intensity of AS attacks. Moreover, the steel jacket exhibited to be the most vulnerable repair intervention compared to CFRP, irrespective of the seismic sequence (severe MS-severe or moderate AS) or earthquake type (near-fault or far-fault).

• 국제초고층학회논문집
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• 제2권1호
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• pp.49-62
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• 2013

Many previous tall building fires demonstrate that despite code compliant construction fires often spread vertically and burn over multiple floors at the same time. The collapses of the WTC complex buildings in 9/11 as well as other partial collapses like the ones of the Windsor Tower in Madrid and of the Technical University of Delft building posed new questions on the stability of tall buildings in fire. These accidents have shown that local or global collapse is possible in multi-floor fires. In most of the previous work involving multi-floor fires all floors were assumed to be heated simultaneously although in reality fires travel from one floor to another. This paper extends previous research by focusing on the collapse mechanisms of tall buildings in fire and performs a parametric study using various travelling rates. The results of the study demonstrate that vertically travelling fires have beneficial impact in terms of the global structural response of tall buildings in comparison to simultaneous fires. Contrary to the beneficial effect of the travelling fires in terms of the global structural response, it was noticed that higher tensile forces were also present in the floors compared to simultaneous multi-floor case. Designers are therefore advised to consider simultaneous multi-floor fire as an upper bound scenario. However, a scenario where a travelling fire is used is also suggested to be examined, as the tensile capacity of connections may be underestimated.

• Earthquakes and Structures
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• 제20권1호
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• pp.1-12
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• 2021

The occurrence of progressive collapse induced by the removal of the vertical load-bearing element in the structure, because of fire or earthquake, has been a significant challenge between structural engineers. Progressive collapse is defined as the complete failure or failure of a part of the structure, initiating with a local rupture in a part of the building and can threaten the stability of the structure. In the current study, the behavior of the structures equipped with a cylindrical friction damper, when the vertical load-bearing elements are eliminated, is considered in two cases: 1-The load-bearing element is removed under the gravity load, and 2-The load-bearing element is removed due to the earthquake lateral forces. In order to obtain a generalized result in the seismic case, 22 pair motions presented in FEMA p 695 are applied to the structures. The study has been conducted using the vertical push down analysis for the case (1), and the nonlinear time-history analysis for the second case using OpenSEES software for 5,10, and 15-story steel frames. Results indicate that, in the first case, the load coefficient, and accordingly the strength of the structure equipped with cylindrical friction dampers are increased considerably. Furthermore, the results from the second case demonstrate that the displacements, and consequently the forces imposed to the structure in the buildings equipped with the cylindrical friction damper substantially was reduced. An optimum slip load is defined in the friction dampers, which permits the damper to start its frictional damping from this threshold load. Therefore, the optimum slip load of the damper is calculated and discussed for both cases.

• 대한건축학회논문집:구조계
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• 제34권2호
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• pp.19-28
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• 2018

The progressive collapse resistance performance of a steel structure constructed using the moment frame with the WUF-B connection and the composite slabs was evaluated. GSA 2003 was adapted for the evaluation. Additionally the structural robustness and the sensitivity against the progressive collapse were analyzed. In the numerical analysis, a reduced model comprised of the beam and spring elements for WUF-B connection was adapted. The composite slab was modeled using the composite-shell element. Instead of the time-consuming dynamic analysis for the effect of the sudden column removal, the equivalent energy-based static analysis was effectively applied. The analysis results showed that the structure was the most vulnerable to in the case of the internal column removal, however it satisfied the chord rotation criterion of GSA 2003 due to the contribution of the composite slab which improved the stiffness of structure. In the robustness evaluation, the structural performance showed more than 2.5 times of the requirement according to GSA 2003, and the structural sensitivity analysis indicated the decrease of 33% of the initial structural performance.

• Journal of Korea Trade
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• 제24권6호
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• pp.115-134
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• 2020

Purpose - International trade leads to the international division of labor, improving the efficiency of the global economic system. Transport costs are a more serious barrier to international trade than customs tariffs. An increase in competition in the transport sector may thus lead to a reduction in transport costs. However, if a carrier's nationality significantly influences transport costs, simply adding more competing carriers of different nationalities would be ineffective. Therefore, it is necessary to establish national or regional carriers to influence competition and reduce transport costs. This study investigates this "nationality effect" by treating Hanjin Shipping's collapse as a natural experiment. Design/methodology - The theoretical basis of this study is the 3rd-degree price discrimination in container shipping market. By using the monthly data of container freight rates of Korea, China and Japan, this study shows the so-called Korea Premiums, which are the empirical counterparts of nationality effect in Korea container shipping market. For this empirical investigation, the structural model with state-space form is used and the dummy models are also estimated. In addition, because China has been also affected by the Hanjin's collapse, the China premiums are considered too. Findings - Compared with Japan's case, it is shown that there had been the so-called Korea premiums since the collapse of Hanjin Shipping. These results are robust from both the state-space model and dummy models. The time pattern of Korea premiums was consistent with the market evolution, especially the pattern of substitutability in container shipping markets. In addition, this paper shows the magnitude of Korea premiums. Originality/value - The argument of this study that the nationality effect can be interpreted as an extended concept of the home market effect is original, which is expected to evoke future research efforts. Further, the discussion on the shipping industrial policy from both horizontal and vertical aspects will provide the relevant policy makers with solid information, especially for the policy coordination in a global scale.

• 한국지진공학회논문집
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• 제14권5호
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• pp.33-39
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• 2010

본 연구는 Modal Pushover Analysis(MPA)를 기반으로 비탄성 변위비(inelastic displacement ratio, $C_R$)와 붕괴 강도비(collapse strength ratio, $R_C$)를 이용한 간략한 Incremental Dynamic Analysis (IDA) 해석법을 제안해 냈다. 이 해석법은 선형 또는 비선형 동적해석 수행 없이 다자유도 시스템의 응답을 계산하기 때문에 간단하게 IDA곡선을 얻을 수 있다. 제안한 방법의 정확성은 6층, 9층, 20층의 철골 모멘트 골조를 대상으로 44개의 지진데이터를 사용하였으며 본 연구에서 제안하는 MPA를 이용한 $C_R-R_C$ IDA 해석결과와 비선형 동적해석 (Nonlinear Response History Analysis)을 통한 IDA 응답값, 그리고 각 주요모드의 비선형 동적해석을 통한 MPA-IDA 응답 값을 비교하여 타당성을 확인하였다. MPA를 이용한 $C_R-R_C$ IDA 해석법은 반복된 비선형 동적해석 과정이 없기 때문에 계산시 소요시간이 가장 작았으며 비교적 정확한 결과를 나타냈다.

• 대한족부족관절학회지
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• 제19권4호
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• pp.161-164
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• 2015

Purpose: The purpose of this study is to define the geographic patterns of partial avascular necrosis (AVN) of the talar body and to determine whether there were any predictors of both the location and occurrence of partial AVN. Materials and Methods: Nineteen patients with fracture of the talar neck treated by open reduction and internal fixation and followed up for more than 1 year were analyzed. The radiographs were examined 6 to 8 weeks after the operation for Hawkins sign and if it was not observed, magnetic resonance scans were performed. The three-dimensional analysis was performed using Mimics 17.0 (Materialise). The incidence of collapse and time to operative intervention was recorded. Results: Partial AVN of the talar body was observed in six out of 19 patients. The avascular segment of the talar body was located predominantly in the anterolateral portion. The average volume of the avascular segment was $289mm^3$, and it occupied 1% of total volume of the talus, and 10% of the talar dome. Collapse occurred in one patient in the area of the avascular process. There were no observable trends with regard to Hawkins classification, incidence of collapse, or time to operative intervention to the location of the avascular segment. Conclusion: Partial AVN can occur after fracture of the talar neck. The predominant location of the avascular segment was the anterolateral portion of the talar body. This information may be helpful to understanding the process of avascular necrosis of the talar body.

• 화약ㆍ발파
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• 제41권3호
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• pp.62-72
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• 2023

1970년대 산업화에 따른 플랜트 구조물이 노후화됨에 따라 구조적 기능을 상실해 발파 해체 공법을 활용한 해체 철거 수요가 증가하고 있다. 발파 해체공법은 기계식 해체공법에 비해 해체 공기가 짧아 환경공해 발생 노출 시간을 최소화할 수 있지만 잘못된 발파 설계 및 시공 계획에 따른 붕괴거동의 실패는 안전성에 매우 큰 위험을 유발한다. 따라서 붕괴거동 모사를 통해 최적의 발파 해체 조건과 이에 따른 영향을 고려하는 것이 중요하다. 본 연구에서는 Finite element method (FEM)와 Discrete element method (DEM)의 장점을 활용해 구축된 3-D Combined finite discrete element method (FDEM) 코드 기반 3-D DFPA 를 적용해 (구)서천화력발전소의 연돌 구조물에 대한 해체 모사를 수행하였으며 실제 구조물의 연돌 구조물 발파해체의 붕괴거동과 비교 분석하였다. 수치 모사 결과, 실제 구조물과 붕괴 거동 및 붕괴 완료 시간이 동일하게 나타났다. 또한, 발파구간 개구부 상부에 위치한 후드부의 크기가 연돌의 붕괴거동에 미치는 영향을 분석하기 위해 후드부의 면적을 조정하여 해체 모사를 수행하고 균열 발생 양상 및 z-방향 변위 곡선을 통해 비교 분석하였다. 분석 결과, 후드부의 면적이 증가함에 따라 하중을 지지하는 면적이 줄어들고 그에 따른 균열 발생 증가 및 전도 시간 감소를 확인하였다.

• 화약ㆍ발파
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• 제31권1호
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• pp.1-10
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• 2013

발파해체 공법은 구조물 형상과 주변현황에 따라 다양한 공법을 적용할 수 있으나, 고종횡비를 가지는 비대칭 구조물을 발파해체 하기 위해서는 사전취약화와 발파지점 및 시차와 주변현황에 따른 발파조건을 고려하여 설계하여야 한다. 본 연구에서는 고종횡비 비대칭 구조물을 안전하게 전도시키기 위해 ELS 소프트웨어를 사용하여 사전취약화 위치와 형상에 따른 모멘트 발생지점을 분석하여 킥백(kick back)을 제어할 수 있는 사전취약화 위치 및 형상에 대한 시뮬레이션을 수행하였으며, 비대칭 구조물의 붕괴 시 전도방향의 좌우로 발생하는 비틀림 모멘트(torsional moment)를 최소화하기 위해 붕괴방향을 제어 할 수 있는 발파 시차 및 위치를 선정하였다. 또한 시뮬레이션상의 사전 취약 및 발파시차를 실 구조물의 전도 붕괴에 적용하여 붕괴 거동에 대한 모션분석을 하였다. 그 결과 시뮬레이션의 붕괴거동에 대한 신뢰성을 확인하였으며, 발파해체 시 사전취약화의 형상 및 위치에 따라 킥백을 제어할 수 있으며, 발파 위치와 시차에 따라 비틀림 모멘트를 제어 할 수 있다는 것을 알 수 있었다.