On progressive failure study of composite hypar shell roofs

Abstract

Hyperbolic paraboloid (hypar) shell bounded by straight edges, an aesthetically appealing doubly curved anticlastic surface, which is easy to fabricate being doubly ruled, and is preferred as roofing units in many practical situations demanding large column free spaces. The skewed hypar shells are architecturally beautiful, easy to cast and are often preferred as roofing units. Laminated composite shells are frequently used in various engineering applications including aerospace, mechanical, marine and automotive engineering. Laminated composites gained popularity in civil engineering structures as use of these materials results in reduced mass and mass induced forces like seismic forces. Failure study of these materials is necessary, which includes the load value (first ply failure load) at which failure initiates and the failure propagation location and the ultimate load carrying capacity. The present article aims to study a comparative failure propagation of uniformly loaded simply supported hypar shells of different stacking orders using finite element method. An eight noded curved quadratic isoparametric shell element is used to develop the finite element program and validated through solution of benchmark problems. Well accepted failure criteria are used to evaluate the failure loads and failure propagation from engineering standpoint. While obtaining the failure loads, each lamina is considered to be under plane stress condition i.e. no transverse stresses are considered to act on any lamina. The results are analysed thoroughly and the paper ends with a number of conclusions of design significance.