STABILITY ANALYSIS OF STIFFENED PANELS SUBJECTED TO INPLANE. SHEAR AND COMPRESSION

Abstract

Stiffened panels are generic structural elements in weight sensitive structural systems such as long span box girders, aerospace structures, ship deck hulls and super structure of offshore oil platforms. These panels are becoming increasingly used in structural applications because of their high specific stiffness (stiffness/unit weight) and their high specific strengths (failure stress/unit weight). Being a thin walled structure the design of stiffened panels is governed by stability criterion. In all cases of buckling of the plates, the critical loads are proportional to the flexural rigidity of the plates. Increasing the thickness of the, plate always can increase the stability of plate, but such a design will not be economical in respect of the materials used. A more economical solution is obtained by keeping the thickness of the plate as small as possible and increasing the stability by introducing stiffeners. As in the case of any plate the presence of inplane loading may cause buckling of stiffened panels. The accurate knowledge of critical buckling load and mode shapes are essential for reliable and light weight structural design. Steel serves as an ideal and reliable material for construction due to its high strength, stiffness, ductility and uniform quality. In addition to this, steel offers considerable flexibility in design, construction as well as ease in fabrication of structural systems. Composite materials are non-homogeneous, anisotropic and difficult to characterise but at the same time offers the possibility to curtail their properties as per requirements. Due to this, many laminated stiffened composite panels have developed which are very efficient when compared with other materials used structurally, and are being adopted increasingly in design. The present work attempts to compare two analysis approaches available for the stability analysis of stiffened panels namely smeared stiffener solution and finite element solution. Smeared stiffener solution is obtained by averaging or smearing the stiffeness of the stiffeners of the panel. FEM software ANSYS 5.4 version is used for the buckling iii analysis and the models are validated for the literature. The buckling results presented in the literature indicate that the smeared stiffener solution should be used only with caution. Thus, both the compression and inplane shear are taken for stability analysis of panels that are simply supported. In addition to this literature review reveals that buckling behaviour of laminated composite stiffened panels is a live research area and yet there has been a need to fill the gaps in this area as the exact buckling behaviour needs to be still understood to fully exploit the advantages of laminated composite constructions. The work attempts to examine the validity of smeared stiffener solution with the help of finite element solution, These two approaches are compared for the metal stiffened panels and laminated composite stiffened panels with the aim to identify the range of application of smeared stiffener solution in predicting the shear-buckling load. Numerical studies by changing the parameters like D1/D2, number of stiffeners, a/b ratios were done and different buckling mode shapes were presented to get a clear understanding of the buckling behaviour of the stiffened panels. iv