engleski

Experimental Shape Approximation of Cable-net Structures

Tensile structures, like cable-nets and textile membranes are, because of their lightness and technological features, in recent years very often used for roof covering of permanent and temporary wide-span buildings (stadiums, exhibition and sport halls...). Since are these structures exclusively tensile resistant, they are characterized by self-forming process, where the form of the structure will be result of boundary conditions and prestressing forces. This is the reason why the form finding of these structures appears as the special engineering problem, where satisfying conditions of equilibrium and structural safety, as well as the architects intentions, shape of the structure is to be determined. This procedure usually involve numerical solving of highly nonlinear equations of equilibrium which requires starting approximation. Applying linearised equations, the force-density method is the most convenient for approximation of the shape. Dealing with first stage of tensile structures design process, architects usually use simple physical models, which always satisfy equilibrium conditions and offer excelled visualization. Possibility to measure the 3-D geometry of the model, getting digital results suitable as approximation for the further numerical analysis would significantly increase the efficiency of the design process. The main goal of this work is to develop such procedure of experimental shape approximation, and to evaluate results achieved by this method. For this purpose, highly automatised digital topometric equipment ATOS has been used to determine shape of convenient, stretch-fabric architectural model built for the purpose of investigation. The method is tested on simple boundary condition task of minimal net (such configuration where the whole cable length is minimal). Results achieved by this method are compared with the results of traditional force-density approximation method, and idealized, numerically calculated minimal net knot coordinates. There is shown that quality of experimental approximation is equal and in some cases even better than the numerical one.

tensile structures; design; 3D shape digitisation; optical measurement

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