In this paper, a constructional problem related to grid-shells design is approached as an optimisation problem and an evolutionary solution technique is proposed. The construction of glass grid-shells, when only four sides cladding elements are used, requires to check the planarity of each element, it means that the four corner points have to belong to the same plane. This requirement can be satisfied by generating the grid surface in specific ways, but when the design involves truly free form shapes, a procedure of optimisation able to reduce the non planarity of each element can be applied. The proposed one is based on the use of a genetic algorithm and has been applied to a benchmark and to a real case, in order to evaluate the efficiency of the procedure and the goodness of the solution.

In this paper, a computational morphogenesis process is applied to the design and the optimization of the shell roof of a large music hall. The architectural concept is based on the folded plate technique: a set of reinforced concrete plates, connected to each other on the edges, forms the global shape of the roof. The dimensions of each plate are different, so that the structure is not regular; moreover each plate is not plane but slightly curved to form hypars. Starting from the geometric concept of the roof, a process of optimization and form finding has been applied, in order to obtain the best acoustic performance, in terms of distribution of the acoustic pressure level in the hall. The folded plate surface has been described mathematically by using a NURBS representation and the control point positions has been assumed as the design variables. The acoustic performance has been evaluated by means of an algorithm able to calculate the acoustic pressure level in all the points of the hall, considering the reflection of the roof. The uniformity of acoustic pressure level in all the points of the hall has been assumed as the target of the optimization process. A genetic algorithm, i.e. an evolutionary iterative population-based scheme, has been adopted in the optimization procedure. The evolution of the shape towards the optimal solution is controlled interactively by the designer, in order to avoid the convergence to unexpected configurations.