Optimal design of tensile fabric structures

The final design of a tensile membrane is achieved when the stress states generated by different and normalised climatic (snow, wind) loadings have been deemed as acceptable by the official control bodies. For this reason, and since in tensile structures the shape and the stress states are strongly related, the whole design may result from a repeated iterative process between the designers, i.e. the firm of architects and the research consultants. This motivates the presentation in this paper of an optimisation tool devoted to fabric structures which could be used to ease the design process in decreasing the number of back-and-forth interactions between all the different participants. First a specific and new shape form finding procedure is proposed; taking into account the usual geometrical constraints or data requirements, but also a desired biaxial (warp and weft) non uniform stress state, an optimal (optimal must be understood in the sense: nearest as possible) initial shape is found Then the climatic loads are applied and the current loaded positions calculated. A Sensitive analysis of these equilibrium positions depending on different parameters such as the positions of the anchorage points and cable tensions, allows one to modify with efficiency the shape and/or the stress state in order to better satisfy the requirements. This optimisation loop is included in a larger one that takes into account possible modifications of the cutting patterns, which is an other way of optimising the stress states. The efficiency of this procedure is demonstrated on an actual example.