Méndez Echenagucia T. and Block P.
Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2015
Funicular shell structures are usually associated to synclastic shapes, which are concave towards the inside. The use of these shapes as sound reflective ceilings in auditoria is generally avoided as they can cause undesirable sound concentrations. These are the source of acoustical defects, such as echoes and colouration, and tend to have a negative subjective impression by the audience. Existing concert spaces built with synclastic shapes thus typically had to be altered by invasive sound reflectivesurfaces and treatments that significantly influence their spatial quality. Previous research on the use of Multi-Objective Genetic Algorithms (MOGAs) for the shape optimization of concert spaces shows the acoustic potential of freeform, continuous surfaces with both convex and concave areas, and the difficulty of achieving high standards with synclastic shapes. Thrust Network Analysis (TNA) is capable of generating compression-only shapes that go beyond synclastic surfaces, thus presenting an opportunity for the use of funicular structures for concert auditoria. This paper presents the use of Multi-Objective Genetic Algorithms (MOGAs) for the acoustical optimization of compression-only shell structures. The MOGA combines ray-tracing simulation for the study of the acoustical quality of the spaces with TNA for the generation of freeform funicular shapes. The method is exemplified in the case study of a multi-purpose room in Barranquilla, Colombia. The MOGA employed in this paper uses the independent force densities in the TNA framework as design parameters to control the shape of the ceiling. In other words, the geometry is not controlled with a parametric model that moves control points to modify the shape, but by modifying the force distribution and boundary conditions of a TNA model. In doing so, the MOGA generates shapes that are all compression only.
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