• Journal of the Society of Naval Architects of Korea
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• v.49 no.2
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• pp.124-131
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• 2012

This paper provides prediction of ultimate longitudinal strengths of hull girder of a VLCC considering probabilistic damage extents due to collision and grounding accidents based on IMO Guideline(2003). The probability density functions of damage extents are expressed as a function of nondimensional damage variables. The accumulated probability levels of 10%, 30%, 50%, and 70% are taken into account for the damage extent estimation. The ultimate strengths have been calculated using in-house software UMADS (Ultimate Moment Analysis of Damaged Ships) which is based on the progressive collapse method. Damage indices are provided for all heeling angles due to any possible flooding of compartments from $0^{\circ}$ to $180^{\circ}$ which represent from sagging to hogging conditions, respectively. The analysis results reveal that minimum damage indices show different values according to heeling angles and damage levels.

• Structural Engineering and Mechanics
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• v.44 no.4
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• pp.449-463
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• 2012

For buildings subjected to blast loading, structural failure can be categorized into local failure (direct blast effects) and progressive collapse (consequential effects). In direct blast effects, the intensive blast pressures create localized failure of structural elements such as exterior columns and walls. Columns, and their behaviour, play a key role in these situations. Therefore investigating the behaviour of columns under blast loading is very important to estimate the strength, safety and reliability of the whole structure. When a building is subjected to blast loading, it experiences huge loading pressures and undergoes great displacement and plastic behaviour. In order to study the behaviour of an element under blast loading, in addition to elastic properties of materials, plastic and elastic-plastic properties of materials and sections are needed. In this paper, using analytical studies and nonlinear time-history analysis by Ansys software, the effects of shape of column sections and boundary conditions, on behaviour and local failure of steel columns under blast load are studied. This study identifies the importance of elastic-plastic properties of sections and proposes criteria for choosing the best section and boundary conditions for columns to resist blast loading.

• Structural Engineering and Mechanics
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• v.45 no.6
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• pp.803-819
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• 2013

This paper addresses two main issues relevant to the structural assessment of buildings subjected to explosions. The first issue regards the robustness evaluation of steel frame structures: a procedure is provided for computing "robustness curves" and it is applied to a 20-storey steel frame building, describing the residual strength of the (blast) damaged structure under different local damage levels. The second issue regards the precise evaluation of blast pressures acting on structural elements using Computational Fluid Dynamic (CFD) techniques. This last aspect is treated with particular reference to gas explosions, focusing on some critical parameters (room congestion, failure of non-structural walls and ignition point location) which influence the development of the explosion. From the analyses, it can be deduced that, at least for the examined cases, the obtained robustness curves provide a suitable tool that can be used for risk management and assessment purposes. Moreover, the variation of relevant CFD analysis outcomes (e.g., pressure) due to the variation of the analysis parameters is found to be significant.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.3
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• pp.219-226
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• 2012

Columns are the key elements supporting load in structure. Column failure causes the structure to collapse. It is important to evaluate residual strength for damaged columns under blast load for preventing progressive collapse. In this paper, columns were investigated to compare the blast resistance on the change of the number of steel bars within the range of reinforcement ratio. And this study was carried out 4 different analytical models to evaluate effects of aspect ratio. The results indicate that the vertical strain was unaffected by the number of steel bars and aspect ratio. As the number of steel bars facing blast load increase, the blast resisting capacity of the columns was improved in the lateral strain. Also, the analysis results showed that a large moment of inertia of area, as compared to a small one would be superior in residual strength as well as force of restitution.

• Steel and Composite Structures
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• v.11 no.2
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• pp.149-168
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• 2011

This paper presents a computational study of column loss scenarios for typical multi-story steel buildings with perimeter moment frames and composite steel-concrete floors. Two prototype buildings (three-story and ten-story) were represented using three-dimensional nonlinear finite element models and explicit dynamic analysis was used to simulate instantaneous loss of a first-story column. Twelve individual column loss scenarios were investigated in the three-story building and four in the ten-story building. This study provides insight into: three-dimensional load redistribution patterns; demands on the steel deck, concrete slab, connections and members; and the impact of framing configuration, building height and column loss location. In the dynamic simulations, demands were least severe for perimeter columns within a moment frame, but the structures also exhibited significant load redistribution for interior column loss scenarios that had no moment connectivity. Composite action was observed to be an important load redistribution mechanism following column loss and the concrete slab and steel deck were subjected to high localized stresses as a result of the composite action. In general, the steel buildings that were evaluated in this study demonstrated appreciable robustness.

• Steel and Composite Structures
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• v.13 no.4
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• pp.309-325
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• 2012

The risk of progressive collapse in steel framed buildings under fire conditions is gradually rising due to the increasing use of combustible materials. The fire resistance of such steel framed buildings is evaluated by fire tests. Recently, the application of performance based fire engineering makes it easier to evaluate the fire resistance owing to various engineering techniques and fire science. The fire resistance of steel structural members can be evaluated by the comparison of the limiting temperatures and maximum temperatures of structural steel members. The limiting temperature is derived at the moment that the failure of structural member results from the rise in temperature and the maximum temperature is calculated by using a heat transfer analysis. To obtain the limiting temperatures for structural steel of grades SS400 and SM490 in Korea, tensile strength tests of coupons at high temperature were conducted. The limiting temperatures obtained by the tensile coupon tests were compared with the limiting temperatures reported in the literature and the results of column fire tests under four types of loading with different load ratios. Simple limiting temperature formulas for SS400 and SM490 steel based on the fire tests of the tensile coupons are proposed. The limiting temperature predictions using the proposed formulas were proven to be conservative in comparison with those obtained from H-section and hollow section column fire tests.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.2
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• pp.144-152
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• 2018

This study aims to establish a mathematical formula to provide rapid and safety estimation of the damaged double hull tankers under ship-ship collision. Difference in heights between the striking and struck ships 'h' and penetration depth 'x' were considered as the main parameters. In ship-ship interaction, Large oil tankers are selected as target struck vessels, and they are struck by Very Large Crude-Oil Carrier (VLCC) class oil tanker. The residual strength of damaged ship at several locations and collision scenarios were carried out using Intelligent Supersize Finite Element Method (ISFEM) which considers the progressive collapse behavior of ship hulls strength. Based on these results, satisfactory was achieved and empirical formula was successfully established using the regression analysis method by deploying the height difference 'h' and penetration depth 'x' as the observed parameters.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.1
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• pp.14-26
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• 2014

This paper provides the prediction of ultimate longitudinal strengths of the hull girders of a very large crude carrier considering probabilistic damage extent due to collision and grounding accidents based on IMO Guidelines (2003). The probabilistic density functions of damage extent are expressed as a function of non-dimensional damage variables. The accumulated probabilistic levels of 10%, 30%, 50%, and 70% are taken into account for the estimation of damage extent. The ultimate strengths have been calculated using the in-house software called Ultimate Moment Analysis of Damaged Ships which is based on the progressive collapse method, with a new convergence criterion of force vector equilibrium. Damage indices are provided for several probable heeling angles from $0^{\circ}$ (sagging) to $180^{\circ}$ (hogging) due to collision- and grounding-induced structural failures and consequent flooding of compartments. This paper proves from the residual strength analyses that the second moment of area of a damage section can be a reliable index for the estimation of the residual ultimate strength. A simple polynomial formula is also proposed based on minimum residual ultimate strengths.

• Tuberculosis and Respiratory Diseases
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• v.86 no.4
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• pp.245-250
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• 2023

The healing process of tracheobronchial tuberculosis (TB) results in tracheobronchial fibrosis causing airway stenosis in 11% to 42% of patients. In Korea, where pulmonary TB is still prevalent, post-TB tracheobronchial stenosis (PTTS) is one of the main causes of benign airway stenosis causing progressive dyspnea, hypoxemia, and often life-threatening respiratory insufficiency. The development of rigid bronchoscopy replaced surgical management 30 years ago, and nowadays PTTS is mainly managed by bronchoscopic intervention in Korea. Similar to pulmonary TB, tracheobronchial TB is treated with combination of anti-TB medications. The indication of rigid bronchoscopy is more than American Thoracic Society (ATS) grade 3 dyspnea in PTTS patients. First, the narrowed airway is dilated by multiple techniques including ballooning, laser resection, and bougienation under general anesthesia. Then, most of the patients need silicone stenting to maintain the patency of dilated airway; 1.5 to 2 years after indwelling, the stent could be removed, this has shown a 70% success rate. Acute complications without mortality develop in less than 10% of patients. Subgroup analysis showed successful removal of the stent was significantly associated with male sex, young age, good baseline lung function and absence of complete one lobe collapse. In conclusion, rigid bronchoscopy could be applied to PTTS patients with acceptable efficacy and tolerable safety.

• Structural Engineering and Mechanics
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• v.52 no.3
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• pp.613-632
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• 2014

In the early design stage of ships, the two most important structural analyses are performed to identify the structural capacity and safety. The first step is called global strength analysis (longitudinal strength analysis or hull girder strength analysis) and the second step is local buckling analysis (stiffened panel strength analysis). This paper deals with the ultimate strength performance of Arctic Sea Route-going commercial ships considering the effect of low temperature. In this study, two types of structural analyses are performed in Arctic sea conditions. Three types of ship namely oil tanker, bulk carrier and container ship with four different sizes (in total 12 vessels) are tested in four low temperatures (-20, -40, -60 and $-800^{\circ}C$), which are based on the Arctic environment and room temperature ($20^{\circ}C$). The ultimate strength performance is analysed with ALPS/HULL progressive hull collapse analysis code for ship hulls, then ALPS/ULSAP supersize finite element method for stiffened panels. The obtained results are summarised in terms of temperature, vessel type, vessel size, loading type and other effects. The important insights and outcomes are documented.