Numerical Study on Failure of Thin Composite Conoidal Shell Roofs Considering Geometric Nonlinearity

Kaustav Bakshi,Dipankar Chakravorty 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.3

Thin laminated composite conoidal shell roofs are popular among civil engineers due to its stiff, singly ruled and aesthetically appealing geometry. Such surfaces may undergo large displacements under transverse static overloading. Since no researchers reported failure of laminated conoids using nonlinear strains the authors aim to fill the void in the literature. A finite element code is proposed considering von-Karman nonlinearity. The study of linear and nonlinear failure loads clearly indicates that the linear formulation wrongly overestimates the failure loads and hence, not acceptable from practical engineering standpoint. Moreover, displacements at failure, the coordinate locations from where the failure initiates and the lamina stress initiating failure in the shell are also studied.

Nonlinear first ply failure analysis of composite skewed hypar shells using FEM

Ghosh, Arghya,Chakravorty, Dipankar Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.1

This paper uses the finite element method (FEM) considering geometrically nonlinear strains to study the first ply failure of laminated composite skewed hypar shell roofs through well-established failure criteria along with the serviceability criterion of deflection. Apart from validating the approach through solution of benchmark problems, skewed hypars with different practical parametric variations are studied for failure loads and tendencies. First ply failure zones are also identified to suggest design and non-destructive monitoring guidelines to the practising engineers. Recommendation tables regarding the design approaches to be adopted in specific cases and factor of safety values needed to be imposed on first ply failure load values for varying shell curvatures are also suggested in this paper. Providing practical inputs to design engineers is the main achievement of the present study.

Nonlinear first ply failure analysis of composite skewed hypar shells using FEM

Arghya Ghosh,Dipankar Chakravorty 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.1

This paper uses the finite element method (FEM) considering geometrically nonlinear strains to study the first ply failure of laminated composite skewed hypar shell roofs through well-established failure criteria along with the serviceability criterion of deflection. Apart from validating the approach through solution of benchmark problems, skewed hypars with different practical parametric variations are studied for failure loads and tendencies. First ply failure zones are also identified to suggest design and non-destructive monitoring guidelines to the practising engineers. Recommendation tables regarding the design approaches to be adopted in specific cases and factor of safety values needed to be imposed on first ply failure load values for varying shell curvatures are also suggested in this paper. Providing practical inputs to design engineers is the main achievement of the present study.

Application of FEM on first ply failure of composite hypar shells with various edge conditions

Arghya Ghosh,Dipankar Chakravorty 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.32 No.4

This study aims to accurately predict the first ply failure loads of laminated composite hypar shell roofs with different boundary conditions. The geometrically nonlinear finite element method (FEM) is used to analyse different symmetric and anti-symmetric, cross and angle ply shells. The first ply failure loads are obtained through different well-established failure criteria including Puck’s criterion along with the serviceability criterion of deflection. The close agreement of the published and present results for different validation problems proves the correctness of the finite element model used in the present study. The effects of edge conditions on first ply failure behavior are discussed critically from practical engineering point of view. Factor of safety values and failure zones are also reported to suggest design and non-destructive monitoring guidelines to practicing engineers. Apart from these, the present study indicates the rank wise relative performances of different shell options. The study establishes that the angle ply laminates in general perform better than the cross ply ones. Among the stacking sequences considered here, three layered symmetric angle ply laminates offer the highest first ply failure load. The probable failure zones on the different shell surfaces, identified in this paper, are the areas where non-destructive health monitoring may be restricted to. The contributions made through this paper are expected to serve as important design aids to engineers engaged in composite hypar shell design and construction.

Relative static and dynamic performances of composite conoidal shell roofs

Kaustav Bakshi,Dipankar Chakravorty 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.15 No.4

Conoidal shells are doubly curved stiff surfaces which are easy to cast and fabricate due to their singly ruled property. Application of laminated composites in fabrication of conoidal shells reduces gravity forces and mass induced forces compared to the isotropic constructions due to the high strength to weight ratio of the material. These light weight shells are preferred in the industry to cover large column free open spaces. To ensure design reliability under service conditions, detailed knowledge about different behavioral aspects of conoidal shell is necessary. Hence, in this paper, static bending, free and forced vibration responses of composite conoidal shells are studied. Lagrange's equation of motion is used in conjunction with Hamilton's principle to derive governing equations of the shell. A finite element code using eight noded curved quadratic isoparametric elements is developed to get the solutions. Uniformly distributed load for static bending analysis and three different load time histories for solution of forced vibration problems are considered. Eight different stacking sequences of graphite-epoxy composite and two different boundary conditions are taken up in the present study. The study shows that relative performances of different shell combinations in terms of static behaviour cannot provide an idea about how they will relatively behave under dynamic loads and also the fact that the points of occurrence of maximum static and dynamic displacement may not be same on a shell surface.

Application of FEM in nonlinear progressive failure of composite skew plates with practical non-uniform edge conditions

Dona Chatterjee,Arghya Ghosh,Dipankar Chakravorty 국제구조공학회 2024 Structural Engineering and Mechanics, An Int'l Jou Vol.90 No.3

Composite skew plates are aesthetically appealing light weight structural units finding wide applications in floors and roofs of commercial buildings. Although bending and vibration characteristics of these units have received attention from researchers but the domain of first and progressive failure has not been explored. Confident use of these plates necessitates comprehensive understanding of their failure behavior. With this objective, the present paper uses an eight noded isoparametric finite element together with von-Kármán’s approach of nonlinear strains to study first ply and progressive failure up to ultimate damage of skew plates being subjected to uniform surface pressure. Parameters like skew angles, laminations and boundary conditions are varied and the results are practically analyzed. The novelty of the paper lies in the fact that the stiffness matrix of the damaged plate is calculated by considering material degradation locally only at failed points at each stage of first and progressive failure and as a result, the present outputs are so close to experimental findings. Interpretation of results from practical angles and proposing the relative performances of the different plate combinations in terms of ranks will be of much help to practicing engineers in selecting the best suited plate option among many combinations.