An Extended Force Density Method for the Form Finding of Suspended Pedestrian Bridges

In cable supported systems it is not possible to separate the moment of the form conception from that of the structural analysis. In fact, the cables have not bending stiffness and the distribution of the axial forces is directly related to the structural shape. This intimate relationship between form and stress state determines the need for a first phase, concerning the determination of the equilibrium shape, through which the feasible set of internal forces and structural geometry are found. This process is called form finding. During last years there has been a growing development of form finding techniques, addressed also to the study of self-stressed systems. Among others, a versatile method is the Force Density Method, which operates on cable nets without requiring any assumption neither on the geometry, nor on the material properties. In this paper an approach focused to extend the force density method to the mixed systems is proposed. In particular, a new form finding technique able to determine the particular equilibrium shape (geometry and associated prestress) of a system of cables and of an elastic system under a specific load condition, is presented. Some examples will show the efficiency of the proposed method.