Trans RINA, Vol 154, Part A2, Intl J Maritime Eng, Apr-Jun 2012 NUMERICAL STUDY OF THE EFFECT OF GEOMETRY AND BOUNDARY


CONDITIONS ON THE COLLAPSE BEHAVIOUR OF STOCKY STIFFENED PANELS (DOI No: 10.3940/rina.ijme.2012.a2.221) M C Xu and C Guedes Soares, Centre for Marine Technology & Eng., Instituto Superior Tecnico, Portugal SUMMARY


This study aims at studying different configurations of the stiffened panels in order to identify robust configurations that would not be much sensitive to the imprecision in boundary conditions that can exist in experimental set ups. A numerical study is conducted to analyze the influence of the stiffener’s geometry and boundary conditions on the ultimate strength of stiffened panels under uniaxial compression. The stiffened panels with different combinations of mechanical material properties and geometric configurations are considered. The four types of stiffened panels analysed are made of mild or high tensile steel and have bar, ‘L’ and ‘U’ stiffeners. To understand the effect of finite element modelling on the ultimate strength of the stiffened panels, four types of FE models are investigated in FE analysis including 3 bays, 1/2+1+1/2 bays, 1+1 bays and 1 bay with different boundary conditions.


NOMENCLATURE 


 a


b


B 0 t p


r p yp yp Plate slenderness


Column slenderness Length of plate (mm)


Width of plate (mm)


Width of stiffened panels (mm) Thickness of plate (mm) Radii of gyration


Effective width of plate elements


S , Yield stress of plate (MPa) S u


 E Y


S ,y P x


1.


Ultimate strength of panels (MPa) Column’s Euler stress (MPa) Yield stress (MPa) Pressure


INTRODUCTION


Stiffened panels are very popular structural elements in marine structures and their load carrying capacity is important from the viewpoint of safety and economy. The ratio of strength to weight is an important index to design economical and efficient ship and thus, the thinner plates with high strength steels are adopted. However, thinner


plating raises


buckling strength. FE codes


have been important used to concerns analyse about the the stress


distributions and deformations of very complicated structures with the accuracy demanded in engineering applications under all kinds of loading conditions. They are a suitable tool for assessing the ultimate strength of ship structures. The advanced buckling analysis method is


to be based on nonlinear analysis techniques or


equivalent, which predict the complex behaviour of stiffened and unstiffened panels [1]. Namely, the extent


©2012: The Royal Institution of Naval Architects


of the model used in the buckling assessment is to be sufficient to account for the structure that is surrounding the panel of interest, and to reduce the uncertainties introduced through the boundary conditions. In general, the model is to include more than one stiffener span in the stiffener direction and the portion between two primary support members in the transverse direction to the stiffeners.


Boundary conditions affect the ultimate strength of plates [2, 3] and to prescribe appropriate boundary conditions is a main challenge in modelling plates and stiffened panels in experiments and


in


Because the boundary of stiffened panels is supported by strong members such


as


finite element calculations. longitudinal


girders to zero. and


transverse frames, the restrained boundary condition is often adopted. But the degree of rotational restraints at the panel boundary is not equivalent


It is


important to model the panel edge condition in a relevant way. In order to reproduce adequately the working conditions on ship structures in experimental and numerical models, some of the more important problems are the definition of the boundary conditions on the loaded top edges and unloaded lateral edges of the plate or panel,


the control and measurement of out-of-plane


eccentricity of the load and the continuity of loads and moments in the panels.


The combined load is very common situation in realistic ship structures and results are available for transverse compression [4], lateral pressure [5] and even combined effects [6]. It is also very important to use experimental results to calibrate the numerical analysis. However, before the combined load condition is considered, the uniaxial compression tests considered here are an initial step that


needs to longitudinally panels be are


performed. The used instead of


three bays single-bay


panels in order to properly account for the effect of adjacent plates in the strength of the central one and to avoid boundary conditions problems for the central plates related to eccentricity of load, which was found to be significant by Luís et al. [7, 8].


A-67


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