Failure of laminated composite shell roofs

Abstract

The aesthetically appealing shell roofs have gained wide popularity in civil engineering applications due to their ability to cover large column free unsupported areas with lesser thicknesses compared to those required for plates. In several civil engineering projects, apart from regular shell geometries (cylindrical and spherical), complicated shell forms like elliptic paraboloids, skewed hypars and conoids have been preferred by the practicing engineers. In recent years, the laminated composite shell structures have achieved immense popularity in aerospace, offshore, mechanical and especially in civil engineering applications. It is observed from the detailed review of literature that the first ply failure strengths of industrially preferred and aesthetically appealing doubly curved synclastic spherical and doubly ruled anticlastic skewed hypar shell forms have not been studied in depth by the researchers. Thus, it is felt that failure characteristics of these forms with different laminations need to be studied in details to apply them efficiently as roofing units and to popularize their use further in the industry. In the present work, the finite element method is employed to study the first ply failure behaviour of laminated composite shell roofs considering geometrically linear and nonlinear strains using an eight noded curved quadratic Serendipity element having five degrees of freedom at each node. Different well-established failure criteria are used to obtain the linear and nonlinear first ply failure load values. The finite element code developed for assessing the first ply failure load is validated through solutions of benchmark problems before applying it to generate new results. Furthermore, a set of author’s own problems are taken up with different parametric variations to arrive at some meaningful conclusions regarding the first ply failure behaviour of laminated composite spherical and skewed hypar shell roofs. Apart from failure criteria governed by strength, the author also studies the failure characteristics of composite shells employing the serviceability criterion of deflection. Failure modes or tendencies, failed plies and failure zones are furnished in different chapters of this thesis.