International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056 Volume: 02 Issue: 04 | July-2015 www.irjet.net p-ISSN: 2395-0072 © 2015, IRJET.NET- All Rights Reserved Page 1650 Analysis of Stiffened Plates using FEM – A Parametric Study Deepak Kumar Singh 1 , S K Duggal 2 , P Pal 3 1 Research Scholar, Civil Engineering Department, MNNIT Allahabad, U.P., India 2 Professor, Civil Engineering Department, MNNIT Allahabad, U.P., India 3 Assistant Professor, Civil Engineering Department, MNNIT Allahabad, U.P., India ---------------------------------------------------------------------***--------------------------------------------------------------------- Abstract - This paper deals with the behavior of stiffened plates subjected to different loading conditions. Finite element method is used for modelling and analysis of the stiffened plates. The maximum deflection at the center of bare plate is verified with the reported results. A parametric study is carried out to estimate the maximum deflection and stress in the isotropic plates by varying the geometry of stiffener keeping the constant volume of material. Key Words: Thin plate, Stiffener, Finite element method, ANSYS workbench 15. 1. INTRODUCTION A plate is a flat structural element in which the thickness is very small compared to the surface dimensions. A plate is characterised based on its thickness as very thin if width to thickness ratio is greater than 100, moderately thin if ratio fall between 20 to 100, thick if fall between 3 to 20 and very thick if less than 3 [1] . Of the available plate theories, following two are widely accepted and used [2] ,  The Kirchhoff–Love theory of plates (classical plate theory)  The Mindlin–Reissner theory of plates (first-order shear plate theory) Although thick-plate formulation is recommended in general because it tends to be more accurate. For thin- plate bending problems in which shear deformation is truly negligible, the use of thick plate formulation is in practice because of its easy application. However, the accuracy of thick-plate formulation is sensitive to mesh distortion and large aspect ratios, and therefore should not be used in such cases when shear deformation is known to be small. The economical design of plate can be obtained by using stiffeners instead of increasing the thickness of plate. Stiffeners are secondary plates or sections used to stiffen the primary element or member. Stiffened plates are widely used in different fields of engineering viz. ships, aircrafts, airframes, chemical industry structures etc. The stiffened plates are needed to avoid the use of thick plates that produce high weight for the structures. Stiffened plates are light weight, high-strength structural elements [3] . The stiffeners enhance the rigidity of base structures by increasing their cross sectional moment of inertia [4] . The configuration of the stiffeners should be consistent with the natural modes likely to be excited by the service loads, so as to arrive at a design with a high strength-to-weight ratio [5] . The optimum locations of the ribs or stiffeners for a given set of design constraints were studied by Hasan [6] . The authors found the best design of stiffened plates when stiffeners were used on either side of square plate. The stiffened clamped plate subjected to a pressure was studied by Yousif et al. [3] . The investigation carried out to find out the optimum height which was found to be in between 40 and 50mm. The relationship between the deflections of a clamped plate subjected to pressure was studied by Pedatzur [7] . The stiffened plates for various types of loadings and stiffeners shape were investigated by Virag [8] . Author concluded that the trapezoidal stiffener is the most economic one. The cost saving can be 69% when compared with various ribs. Paykani et. al. [9] investigated the bending of an isotropic rectangular plate for various boundary conditions using MATLAB code and ANSYS. Classical plate theory (CPT) and plane stress assumption were used. 2. THEORETICAL FORMULATION The Kirchoff-Love and Reissner-Mindlin FSDT are well known in literature. The descriptions for these formulations are circumvented here in for the sake of conciseness of this paper. Only the Finite element modeling is presented in the next section, for completeness of the paper and convenience of the reader. 3. FINITE ELEMENT MODELLING Finite element modeling consists of four steps: creating the geometry of the model, generating a mesh for the solid mesh (i.e. dividing the model into elements), applying boundary conditions and loadings, and final is solution. A number of finite element based computer programs (NASTRAN, PATRAN, MARC, CATIA, ANSYS etc.) may be used for the analysis of stiffened plates. ANSYS Workbench 15 is used in the present investigation. A square plate of size 1000×1000×10mm, shown in Fig- 1(a), is consider in the present study and the different dimensions of stiffeners are used to attach with the plate by keeping the constant volume of material (10320000 mm 3 ) throughout which is presented in Table-2. Although a many shapes of stiffeners may be used to strengthen the plates to increase the stiffness of the structures like flat, L-