DESIGN STRATEGIES OF HYBRID BENDING-ACTIVE SYSTEMS BASED ON GRAPHIC STATICS AND A CONSTRAINED FORCE DENSITY METHOD

摘要

In the design of bending-active structures, the shaping of actively bent elements can be achieved either by means of additional restraining systems such as membranes and cable nets, or by a controlled variation of the bending stiffness along their length. Combining both approaches, this paper proposes a novel method for the design of hybrid bending-active structures composed of flexible linear elements with non constant stiffness, actively bent into in-plane shapes by cable nets. The actively bent elements and the tensile cable nets are considered successively: first, the bent geometry of the splines is set, as a design input, and, in a second step, compatible equilibrium cable nets are form-found. The proposed method utilizes a graphical method for the modelling of the in-plane bent splines and a constrained force density method for the form-finding of the cable nets. First, it is shown how the use of a force diagram enables the calculation of a non constant distribution of bending stiffness along an in-plane spline to reach a target bent geometry under given loads. Then, an extension of the force density method under the constrains of equilibrium between the splines and the restraining systems is presented. Finally, as the different design strategies are explained, their potential is illustrated through design case studies.