• Structural Engineering and Mechanics
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• 제69권4호
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• pp.383-397
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• 2019

More than one longitudinal web stiffener may be economical in the design of plate girders that have considerably high width-to-thickness ratio of webs. In this study, the bend-buckling strength of relatively deep webs with two horizontal lines of flat plate-shaped single-sided stiffeners was numerically investigated. Linear eigenvalue buckling analyses were conducted for specially selected hypothetical models of stiffened web panels, in which top and bottom junctions of a web with flanges were assumed to have simply supported boundary conditions. Major parameters in the analyses were the locations of two longitudinal stiffeners, stress ratios in the web, slenderness ratios and aspect ratios of web panels. Based on the application of assumptions on the combined locations of the two longitudinal web stiffeners, simplified equations were proposed for the bend-buckling coefficients and compared to the case of one longitudinal stiffener. It was found that bend-buckling coefficients can be doubled by adopting two longitudinal stiffeners instead of one longitudinal stiffener. For practical design purposes, additional equations were proposed for the required bending rigidity of the longitudinal stiffeners arranged in two horizontal lines on a web.

• 한국안전학회지
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• 제24권6호
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• pp.93-102
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• 2009

Because steel girder bridge has big slenderness ratio, buckling is very important in design. Local buckling of plate girders having two longitudinal stiffeners in different positions under various load conditions is investigated. Various parametric study according to the change of web height, transverse stiffeners and load conditions are examined. These parametric studies are performed by numerical simulation utilizing finite element method. The objective of this study is to present the rational reinforcement location of two longitudinal stiffeners. The results of analysis are compared to that recommended by korean specifications for road bridges(2003).

• Structural Engineering and Mechanics
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• 제69권2호
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• pp.193-204
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• 2019

This paper presents results from experimental and numerical studies on the response of steel-concrete composite box bridge girders under certain localized fire exposure conditions. Two composite box bridge girders, a simply supported girder and a continuous girder respectively, were tested under simultaneous loading and fire exposure. The simply supported girder was exposed to fire over 40% of its span length in the middle zone, and the two-span continuous girder was exposed to fire over 38% of its length of the first span and full length of the second span. A measurement method based on comparative rate of deflection was provided to predict the failure time in the hogging moment zone of continuous composite box bridge girders under certain localized fire exposure condition. Parameters including transverse and longitudinal stiffeners and fire scenarios were introduced to investigate fire resistance of the composite box bridge girders. Test results show that failure of the simply supported girder is governed by the deflection limit state, whereas failure of the continuous girder occurs through bending buckling of the web and bottom slab in the hogging moment zone. Deflection based criterion may not be reliable in evaluating failure of continuous composite box bridge girder under certain fire exposure condition. The fire resistance (failure time) of the continuous girder is higher than that of the simply supported girder. Data from fire tests is successfully utilized to validate a finite element based numerical model for further investigating the response of composite box bridge girders exposed to localized fire. Results from numerical analysis show that fire resistance of composite box bridge girders can be highly influenced by the spacing of longitudinal stiffeners and fire severity. The continuous composite box bridge girder with closer longitudinal stiffeners has better fire resistance than the simply composite box bridge girder. It is concluded that the fire resistance of continuous composite box bridge girders can be significantly enhanced by preventing the hogging moment zone from exposure to fire. Longitudinal stiffeners with closer spacing can enhance fire resistance of composite box bridge girders. The increase of transverse stiffeners has no significant effect on fire resistance of composite box bridge girders.

• Journal of Ship and Ocean Technology
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• 제1권1호
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• pp.1-14
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• 1997

Hydroelastic slamming against the wetdeck of a multihull vessel is studied numerically and experimentally. The beam equations and a two-dimensional flow model are used to find the dynamic stresses in longitudinal stiffeners between two transverse stiffeners. The largest stresses in the structure occur in the time scale of the lowest wet natural period of the beam. A simple relation between the maximum stress, the local geometry and the impact velocity of the wetdeck is established. The stresses in the wetdeck are neither sensitive to the radius of curvature of the waves nor where the waves initially hit the wetdeck. It is concluded that the maximum impact pressure should not be used to find maximum bending stresses during wetdeck slamming.

• Steel and Composite Structures
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• 제35권4호
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• pp.509-525
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• 2020

Steel-concrete composite slabs with profiled steel sheeting are widely used in the execution of floors in steel and composite buildings. The rapid construction process, the elimination of conventional replaceable shuttering and the reduction of temporary support are, in general, considered the main advantages of this structural system. In slabs with the spans currently used, the longitudinal shear resistance commonly provided by the embossments along the steel sheet tends to be the governing design mode. This paper presents an innovative reinforcing system that increases the longitudinal shear capacity of composite slabs. The system is constituted by a set of transversal reinforcing bars crossing longitudinal stiffeners executed along the upper flanges of the steel sheet profiles. This type of reinforcement takes advantage of the high bending resistance of the composite slabs and increases the slab's ductility. Two experimental programmes were carried out: a small-scale test programme - to study the resistance provided by the reinforcing system in detail - and a full-scale test programme to test simply supported and continuous composite slabs - to assess the efficacy of the proposed reinforcing system on the global behaviour of the slabs. Based on the results of the small-scale tests, an equation to predict the resistance provided by the proposed reinforcing system was established. The present study concludes that the resistance and the ductility of composite slabs using the reinforcing system proposed here are significantly increased.

• 대한조선학회 특별논문집
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• 대한조선학회 2009년도 특별논문집
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• pp.123-129
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• 2009

Ship painting procedures can be divided into two categories; Out-shell plate painting of the hull and the interior painting of each double gull blocks. It is really hard to apply standardized and automated operations to the latter because the double hull blocks contains a variety of complicated supportive materials and pipes to strengthen the ship structure. In addition their poor working conditions cause painting workers to avoid working in them, resulting in the waste of paints and additional pollution issues. So this research, successfully focused on overcoming the difficulties in working in the complicated blocks and the tough working conditions introduces the main details of automatic equipment systems and their transfer algorism which show how the equipment paints the inner sides of a longitudinal stiffener and moves to another automatically.

• 대한조선학회논문집
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• 제54권4호
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• pp.335-343
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• 2017

The Newman-Raju formula and contour integral-based finite element analyses(FEAs) have been widely used to assess crack growth rates and residual lives at crack locations in ships or offshore structures, but the Newman-Raju formula is known to be less accurate for the complicated weld details and the conventional FEA-based contour integral approach needs concentrated efforts to construct FEA models. Recently, an extended finite element method(XFEM) has been proposed to reduce those modeling efforts with reliable accuracy. Stress intensity factors(SIFs) from the approaches such as the Newman-Raju formula, conventional FEA-based J-integral, and XFEM-based J-integral were compared for an infinitely long plate with a propagating elliptic crack. It was concluded that the XFEM approach was far reliable in terms of prediction ability of SIFs. Assuming a 25 year-aged coast guard patrol ship had the prescribed cracks at the bracket toes attached to longitudinal stiffeners in way of deck and bottom, SIFs were derived based on the three approaches. To obtain axial tension loads acting on the longitudinal stiffeners, long term hull girder bending moments were assumed to obey Weibull distribution of which two parameters were decided from a reference (DNV, 2014). For the complicated weld details, it was concluded that the XFEM approach could cost-effectively and accurately estimate the crack growth rates and residual lives of ship structures.

• Steel and Composite Structures
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• 제18권4호
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• pp.811-831
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• 2015

This paper focuses on the strengthening methods used for improving the compression behaviors of perforated box-section walls as provided in the anchorage zones of steel pylons. Rectangular plates containing double-row continuous elliptical holes are investigated by employing the boundary condition of simple supporting on four edges in the out-of-plane direction of plate. Two types of strengthening stiffeners, named flat stiffener (FS) and longitudinal stiffener (LS), are considered. Uniaxial compression tests are first conducted for 18 specimens, of which 5 are unstrengthened plates and 13 are strengthened plates. The mechanical behaviors such as stress concentration, out-of-plane deformation, failure pattern, and elasto-plastic ultimate strength are experimentally investigated. Finite element (FE) models are also developed to predict the ultimate strengths of plates with various dimensions. The results of FE analysis are validated by test data. The influences of non-dimensional parameters including plate aspect ratio, hole spacing, hole width, stiffener slenderness ratio, as well as stiffener thickness on the ultimate strengths are illustrated on the basis of numerous parametric studies. Comparison of strengthening efficiency shows that the continuous longitudinal stiffener is the best strengthening method for such perforated plates. The simplified formulas used for estimating the compression strengths of strengthened plates are finally proposed.

• Journal of Ship and Ocean Technology
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• 제3권1호
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• pp.27-41
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• 1999

The objective of the paper is to study the impact of changing the traditional hull design of bulk carriers by providing them with a double hull while keeping the same deadweight. It is demonstrated that by introducing the double hull the structural reliability is increased throughout the entire life and also the extend of the needed repair is reduced. The results are obtained with recently developed mathematical tools for the reliability assessment of ship hulls subjected to the existence of multiple cracks both in the stiffeners and in the plating and it models the crack growth process. The effect of corrosion is represented as time dependent. The long-term stress range acting on the elements is defined as a function of the local transverse pressure of the internal cargo and outside sea water combined with the stresses resulting from the longitudinal bending of the hull, which is a combined with the stresses resulting from the longitudinal bending of the hull, which is a combineation of horizontal and vertical bending moments. The effect of maintenance actions is modelled as a stochastic process. The results show that a different design of the midship section improves the structural safety and also the economy with respect to structural repair of bulk carriers.

• 동력기계공학회지
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• 제9권2호
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• pp.106-111
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• 2005

After many casualties of conventional bulk carriers in recent years, a double hull bulk carrier was proposed to enhance the structural safety of a side shell and a transverse bulkhead. In this paper, two alternative structural designs of a double hull bulk carrier were carried out based on the Lloyd's rule. One has the double sided hull with longitudinal stiffeners and the other has that with a girder. The final structural design was examined in comparison with an existing single hull bulk carrier from the viewpoints of cargo hold capacity and the increases of weight and construction cost. Generally, the construction cost of a ship consists of the costs of material, labor and overhead cost. But, in this study, the relative construction cost concept was introduced to compare the economical validity more precisely. In this concept, fixed overhead cost is excluded in the assessment of construction cost, and only the variable overhead cost is added up to labor cost. As the result of this study, a double hull bulk carrier can be constructed within 1% increase of weight and construction cost.