• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.3
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• pp.509-525
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• 2015

Predicting residual strength of corroded plates is of crucial importance for service life estimation of aged structures. A series of nonlinear finite element method is employed for ultimate strength analysis of stiffened plates with pitting corrosion. Influential parameters, including plate thickness, type and size of stiffeners, pit depth and degree of pitting are varied and more than 208 finite element models are analyzed. It is found that ultimate strength is reduced by increasing pit depth to thickness ratio. Thin and intermediate plates have minimum and maximum reduction of ultimate strength with stronger stiffeners, respectively. In weak stiffener, reduction of ultimate strength in thin and intermediate plates depends on DOP. Reduction of ultimate strength in thick plates depends on thickness of plate and DOP. For intermediate plates, reduction for all stiffeners regardless of shape and size are the same.

• Journal of Welding and Joining
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• v.8 no.4
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• pp.69-75
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• 1990

In this paper, ultimate compressive strength of TMCP 50HT steel plates (yield stress .sigma.$_{o}$=36kg/mm$^{2}$) with HAZ softening is studied. Finite element method formulated by the author is applied to analyze the elasto-plastic large deflection behaviour of the plates. The influence of HAZ softening breadth, welding direction and slenderness ratio on the ultimate compressive strength is investigated. The results obtained are summarized as 1) With the increasing of the HAZ softening breadth, early plasticity on the plates is formed and then the ultimate compressive strength is decreased, in which about 8% of the ultimate strength for the plate with h/t=4(h: HAZ softening breadth, t: plate thickness) was reduced comparing with no HAZ softening. 2) The large decrease of the ultimate strength for the case that the welding direction is normal to the loading direction is occurred than the case that the welding direction is parallel to the loading direction. 3) The influence of HAZ softening on the ultimate compressive strength is serious for thick plates, while it may be negligible for thin plates.s.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.3
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• pp.447-456
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• 2021

Methods for predicting the ultimate/buckling strength of ship structures have been extensively improved in terms of design formulas and analytical solutions. In recent years, the design strategy of ships and offshore structures has tended to emphasize lighter builds and improve operational safety. Therefore, the corresponding geometrical changes in design necessitate the use of high-tensile steel and thin plates. However, the existing design formulas were mainly developed for thick plates and mild steels. Therefore, the calculation methods require appropriate modification for new designs beased on high-tensile steel and thin plates. In this study, a modified formula was developed to predict the ultimate strength of thin steel plates subjected to compressive and shear loads. Based on the numerical results, the effects of the yield stress, slenderness ratio, and loading condition on the buckling/ultimate strength of steel plates were examined, and a newly modified double-beta parameter formula was developed. The results were used to derive and modify existing closed-form expressions and empirical formulas to predict the ultimate strength of thin-walled steel structures.

• Journal of Ship and Ocean Technology
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• v.7 no.1
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• pp.1-12
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• 2003

Stiffened plates are among the most popular structural elements for marine structures like ships or offshore platforms. Many researchers have performed and reported the results of structural tests on stiffened plates in the open literature. However, the behaviour of stiffened plates in post-ultimate regime has not been fully reported. This paper reports the results of twenty-one axial compression tests including the initial imperfections and material properties of the test models. In aiming to investigate the post-ultimate behaviour of stiffened panels, the axial shortenings were increased up to far beyond the ultimate state. The results obtained from these tests can be utilized in substantiating design formulae in predicting the post-ultimate behaviour of stiffened plates.

• Journal of Korean Port Research
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• v.14 no.3
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• pp.331-340
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• 2000

For the rational and economic design of the structural elements of ships which is built using welding, the ultimate strength analyses of the plates having initial imperfections, such as welding residual stresses and strains, are needful. The welding deformation usually relied on approximative equations or based on expert's experience. But in this paper, for the thermal elasto-plastic analysis of plates, the finite element analysis was performed, based on initial strain method. In formulating the incremental analysis, unbalanced force terns were included. In the plastic domain during the incremental process, the 2nd order terns stress increment and yield stress increment were considered, so that time increment could be controlled for a more stable solution. The ultimate strength analysis program of the plates having initial imperfections was made. The ultimate strength analysis was carried out based on the results of the welding deformations of this paper. In the ultimate strength analysis the Rayleigh-Ritz method based on the minimum potential theory was used.

• Journal of Welding and Joining
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• v.9 no.2
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• pp.44-50
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• 1991

The use of high tensile steel plates is increasing in the fabrication of ship and offshore structures. The softening region which has lower yield stress than base metal is located to prevent cracking in the conventional high tensile steel. Also, thermo mechanical control process(TMCP) steel with low carbon equivalent has the softening region which occurs in the heat affected zone when high heat input weld is carried out. The softening region in the high tensile steel gives rise to serious effect on structural strength such as tensile strength, fatigue strength and ultimate strength. In order to make a reliable structural design using high tensile steel plates, the influence of the softening on plate strength should be evaluated in advance. In the previous paper, the authors discussed the ultimate compressive strength of 50HT steel square plates with softening region. In this paper, the ultimate compressive strength with varying the yield stress of softening region and the aspect ratio of the plate is investigated by using the elasto-plastic large deformation finite element method.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2004.10a
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• pp.101-109
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• 2004

Ship structures is thin-walled structures and she has lots of curved platings. In these days, lots different kinds of closed-formulas are development for ultimate strength of flat plate but for curved panels, there are not enough study or papers for this field. In this study, the ultimate strength characteristics for ship curved plates are studied. The ship plating is generally subjected to combined in-plane and lateral pressure loads. In-plane loads included biaxial compression/tension and edge shear. This is first report about the developing of ultimate compressive strength for ship curved plating. A closed-form formula for predicting the ultimate compressive strength of curved plates are empirically derived by curve fitting based on the computed results. The results and insights developed in the present study will be useful for damage tolerant design of curved plated structures.

• Bulletin of the Society of Naval Architects of Korea
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• v.20 no.1
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• pp.11-20
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• 1983

In this paper elastic-plastic large deflection analysis of ship structural members, plates, stiffened plates and cylindrical shallow shell, are performed by the finite element method. And for the consideration of the yielded propagation through the depth of the member, the layered element approach is employed. The present method is justified by comparing its results with those of experiment and others. As results, the nonlinear behavior and the ultimate strength curves are shown, which can be used in the design of the plates and the stiffened plates under compression, and the applicability to the shell structures is suggested. The analysis results are as followings. (1) The results of the approximate equations as well as those of buckling analysis may not guarantee precisely the safety of the structures in some cases and the optimum in other cases. Therefore they may not show the design criteria for the optimal design. (2) As the initial deflection increases, its effects on the ultimate strength of the structure generally increases, and the ultimate load, therefore, decreases. (3) This approach can be applied to the shell type structures. (4) The present method can be applied to the various structures composed of plate and beam members, for example, plates with hole and the stiffened plates with hole stiffened by spigot, doubler and/or stiffener, for the optimal design.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.20-29
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• 1995

When structures are constructed by welding, structural elements are always accompained by welding residual stress and deformation. Therefore, when the rigidity and strength of the welded structures is considered, it is very important to have sufficient information about the effect of initial deflection and welding residual stress on them. In this paper, the square plates with welding residual stress under compression are dealt with; First, heat conduction and thermal elastic-plastic problems are analyzed by finite element method using 4-node isoparametric elements for assessment on the ultimate strength of welding joint. Later, the ultimate strength of welding joint is assessed by examining the effect of changed type of loading. The specimens are 500{\times}$500mm(a/b=1) and 750{\times}$500mm(a/b=1.5) rectangular plates of whichthicknesses is 9.0mm and simply supported plates getting axiul load in each direction.

• Journal of Ocean Engineering and Technology
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• v.21 no.4
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• pp.34-37
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• 2007

The safety of ships is one of the most important concerns in terms of the environment and human life. A ship in bad condition is likely to be subject to accidents, such as collision and grounding. When a ship has minor collision damages in the form of circle or ellipse, its ultimate strength will be reduced. It is important to evaluate the reduction ratio of a ship's ultimate strength that results from damages. The strength reduction of a plate with a cutout in the form of hole has been treated by many researchers. A closed-form formula for the reduction of ultimate strength of a plate, considering the effect of several forms of cutout, has been suggested. However, the structure of ships is composed of plates and stiffeners so-called stiffened plates and it is likely that plates and stiffeners will be damaged together in collisions. This paper investigates the effect of minor collision damages on the ultimate strength of a stiffened plate by using numerical analysis. For this study, the deformed shape of minor collision damages on a stiffened plate was made by using a contact algorithm and was used as the initial shape for ultimate stress analysis. Then, a series of nonlinear FE analyses was conducted to investigate the reduction effects on the ultimate strength of the stiffened plate. The boundary conditions were simply supported at all boundaries, and the tripping of stiffener was neglected. The results are presented in the form of reduction ratio between the ultimate strength of an original, intact stiffened plate and that of a damaged stiffened plate.