• Bulletin of the Society of Naval Architects of Korea
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• v.25 no.4
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• pp.47-57
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• 1988

A new discrete method using idealized rigid body-spring model is introduced. This rigid element method is known to be more efficient and accurate than the finite element method in the inelastic range of structural analysis owing to simplified stress-strain and strain-displacement relations This kind of physical concept using idealized rigid model has been already applied among structural engineers to some problems such as rigid-plastic analysis or plastic design considering rigid bodies and plastic hinges. However the most rigorous and systematic research has been recently performed by T. Kawai et al.[1]. In this paper, an attempt is made to analyze the collapse behavior of stiffened plates under lateral loading by some modification and expansion of Kawai's rigid element approach to the collapse of plates without stiffener. Stiffened plates are treated as orthotropic plates which have equivalent bending rigidities. By employing Morley's plate element resubdivision technique, variety is given to mesh-division styles which have greate effect on the accuracy of numerical results. Some examples are shown to verify the validity of applying rigid element method to the ultimate strength analysis of stiffened plates. It is clarified that lateral deflections and detailed collapse patterns up to the ultimate state of stiffened plates can be easily obtained by the present approach.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.12
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• pp.947-955
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• 2003

This research analyzes the dynamic stability of stiffened plates on elastic foundations using the finite element method. For analyzing the stiffened plates, both the Mindlin plate theory and Timoshenko beam-column theory were applied. In application of the finite element method, 8-nodes serendipity element system and 3-nodes finite element system were used for plate and beam elements, respectively Elastic foundations were modeled as the Pasternak foundations in which the continuity effect of foundation is considered. In order to verify the theory of this study, solutions obtained by this analysis were compared with the classical solutions in open literature and experimental solutions. The dynamic stability legions of stiffened plates on Pasternak foundations were determined according to changes of in-plane stresses, foundation parameters and dimensions of stiffener.

• Journal of Korean Society of Steel Construction
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• v.22 no.3
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• pp.219-228
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• 2010

This paper describes an experimental research on the structural behavior and the ultimate strength of longitudinally stiffened plates subjected to local, distortional, or mixed-mode buckling under compression. The stiffened plate undergoes local, distortional, or interactive local-distortional buckling according to the flexural rigidity of the plate's longitudinal stiffeners and the width-thickness ratios of the sub-panels of the stiffened plate. A significant post-buckling strength in the local and distortional modes affects the ultimate strength of the longitudinally stiffened plate. Compression tests were conducted on stiffened plates that were fabricated from 4mm-thick SM400 steel plates with a nominal yield stress of 235MPa. A simple strength formula for the Direct Strength Method based on the test results was proposed. This paper proves that the Direct Strength Method can properly predict the ultimate strength of stiffened plates when the local buckling and distortional buckling occur simultaneously or nearly simultaneously.

• Bulletin of the Society of Naval Architects of Korea
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• v.17 no.2
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• pp.11-16
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• 1980

For vibration analysis of stiffened plates the orthotropic plate analogy is commonly accepted. As to stiffened plates in contact with water, however, there is still much uncertainty in estimation of the added mass because of the lack of direct methods. The authors, considering that for added mass of plates there are many reliable data derived theoretically or experimentally available, suggest a method to estimate the added mass of a stiffened plate by combining the mass increase factor, $\beta$, of an equivalent orthotropic plate and the correction factor, $\kappa$, for the effects of stiffeners. The latter is to be derived from systematic experimental investigations. Then, the natural frequency in water, f', can be calculated from that in air, f, by the equation $f'=f/\sqrt{1+\kappa\beta}$. To investigate practical applicability of this method, a systematic experiment was carried out with five uniaxially stiffened plates. Each of them had a plate of same size, $600mm{\times}600mm{\times}3.2mm$, but stiffeners of different size in the web-depth, 41.6mm, 51.2mm or 66.8mm and of different spacing 75mm, 100mm, or 150mm. Natural frequencies were measured under simply supported-edge conditions in both air and water, and corresponding $\kappa$ values derived. In spite of wide variations of web-depth and spcae of stiffeners, the experimental results show that the diversity of $\kappa$ values is not remarkable; mean values of $\kappa$ are 1.31 with standard deviation of 0.025 for the first modes and 1.27 with that 0.077 for the second modes. Hence, the authors concluded that the above $\kappa$ values can be used generally for the cases of uniaxially stiffened plates both sides of which contact with water, and that $\kappa$ values of general use for the cases of cross-stiffened plates may also be obtainable from similar experiments.

• Journal of Korean Society of Steel Construction
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• v.26 no.4
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• pp.277-288
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• 2014

In this study, the local displacement and moment characteristics of a plate stiffened with closed ribs are analyzed according to the dimensions of stiffened plates. The analyzed results of various stiffened plates under square distributed load show that the effect of the loading panel width to the local behavior is dominant but that of the next panel width is very small. And the local behavior of reference stiffened plates can be expressed by the angle between the plate and the rib, and that of other stiffened plates can be obtained by multiplying ratio functions of the loading panel width, plate thickness, rib thickness, rib height and next panel width and they give good results. Applying ratio functions to other loading sizes shows that the applicability of ratio functions except for the loading panel width is proved and the modified ratio functions of the loading panel width improve error ratios. Therefore, the local displacement and moments of a plate stiffened with closed ribs can easily achieve proper results regardless of the dimensions using ratio functions proposed in this study.

• Journal of Ocean Engineering and Technology
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• v.34 no.1
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• pp.37-45
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• 2020

Unstiffened and stiffened cylindrically curved plates are often used in ship structures. For example, they can be found on a deck with a camber, a side shell at the fore and aft parts, and the circular bilge part of a ship structure. It is believed that such cylindrically curved plates can be fundamentally modelled using a portion of a circular cylinder. From estimations using cylindrically curved plate models, it is known that the curvature generally increases the buckling strength compared to a flat plate under axial compression. The existence of curvature is also expected to increase both the ultimate and buckling strengths. In the present study, a series of finite element analyses were conducted on stiffened curved plates with several varying parameters such as the curvature, panel slenderness ratio, and web height and type of stiffener applied. The results of numerical calculations on stiffened and unstiffened curved plates were examined to clarify the influences of such parameters on the characteristics of their buckling/plastic collapse behavior and strength under an axial compression.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.174-180
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• 1985

A new measuring technique for the rigidities of stiffened plated is presented. The equations relating the rigidities of stiffened plates and the natural frequencies of a cantilever plate are derived and the rigidities are determined using the measured natural frequencies of the plate. The static deflection tests are conducted for checking the validity of this method. For unstiffened plates the measured rigidities are good agreement with the theoretical values and the experimental results of deflection tests. In the case of stiffened plates the measured rigidities closely matched with the results of deflection tests. It has been also demonstrated that this measuring technique can be utilized in determining the rigidities of arbitrarily stiffened plates.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.1A
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• pp.191-203
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• 2006

The vibration characteristics of composite stiffened laminated plates with stiffener is presented using the assumed natural strain 9-node shell element. To compare with previous research, the stiffened plates are composed of carbon-epoxy composite laminate with a symmetric stacking sequence. Also, the result of the present shell model for the stiffener made of composite material is compared with that of the beam model. In the case of torsionally weak stiffener, a local buckling occurs in the stiffener. In this case, the stiffener should be idealized by using the shell elements. The current investigation concentrates upon the vibration analysis of rectangular stiffened and unstiffened composite plates when subjected to the in-plane compression and shear loads. The in-plane compression affect the natural frequencies and mode shapes of the stiffened laminated composite plates and the increase in magnitude of the in-plane compressive load reduces the natural frequencies, which will become zero when the in-plane load is equal to the critical buckling load of the plate. The natural frequencies of composite stiffened plates with shear loads exhibit the higher values than the case of without shear loads. Also, the intersection, between the curves of frequencies against in-plane loads, interchanges the sequence of some of the mode shapes as a result of the increase in the inplane compressive load. The results are compared with those available in the literature and this result shows that the present shell model for the stiffened plate gives more accurate results. Therefore, the magnitude, direction type of the in-plane shear and compressive loads in laminated composite stiffened plates should be selected properly to control the specific frequency and mode shape. The Lanczos method is employed to solve the eigenvalue problems.

• Bulletin of the Society of Naval Architects of Korea
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• v.24 no.3
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• pp.35-42
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• 1987

For the analysis of natural vibrations of a rectangular stiffened plate with inner cutouts, an application of the Rayleigh-Ritz method is investigated. In construction of the trial function for the Rayleigh quotient, only the outer boundary conditions are satisfied with combination of Euler beam functions. As to the modeling of stiffened plates for the energy calculations, a lumping stiffener-effects method and the orthotropic plate analogy are considered for the purpose of comparison. Some numerical results obtained by the Rayleigh-Ritz method are compared with results by experiments and the finite element method. The following are major conclusions; (1) With the lumping stiffener-effects modeling the Rayleigh-Ritz method gives good results of both natural frequencies and mode shapes. The orthotropic plate analogy in cases of regularly stiffened plates is of restrictive use i.e. acceptable for a small cutout. (2) The natural frequency of a stiffened plate with inner cutouts between stiffeners is higher than that of without cutouts and increase as the hole area ratio increases as long as there are no discontinuous stiffeners due to the cutout.