Reverse engineering of free form shell structures: From point cloud to finite element model

Many free form shell structures that have been designed and build in previous decades are fascinating structures. We can learn from these structures by analysing them and studying their structural behaviour. However, in some cases the geometry of these structures is not available; most notably the shapes of shell structures designed and build by Heinz Isler, who has built over 1400 shells. The geometry of many of his scale models and build structures have been obtained by the authors by making use of 3D laser scanners which create point clouds.This paper presents a method for reverse engineering of free form shell structures from point cloud to finite element model. Since shape and force interact, special attention is given to the geometric accuracy. Every model must be sufficiently accurate. The method has been applied to data obtained by scanning Isler’s shells. Important aspects that influence the quality of the resulting finite element model are described.Structural Design & Mechanic

Scanning in 3D and analysing the models of Heinz Isler, the preliminary results

During his live Heinz Isler built around 1400 shell structures, until he deceased in 2009. Heinz Isler is part of a Swizz tradition of structural art in the 20th century, which includes engineers such as Robert Maillart, Othmar Ammann und Christian Menn [1]. During his live Heinz Isler developed several methods for physical form finding of his shell structures [2, 3]. Methods such as hanging models, inflated membranes etc. The physical scale model where used for determining the strains and stresses in the shell structure. This was done by loading the scale models and measuring the strains and consequently calculating the stresses. The geometry of the scale models was used for the actually build shell structures by precisely measuring the scale models and scaling these up to the real size shell. Analysing Isler’s shells has always been impossible because Isler never published the precise geometry of his shell structures. Isler’s model where scanned for the first time ever in 2011, the results where used to construct NURBS (Non Uniform Rational B-spline) surfaces which describe the exact geometry of Isler’s scale models. The results are used for all kinds of analysis, such as finite element (FEM) calculations, curvature analysis etc. This means that for the first time a qualitative investigation can be made of Isler’s shell structures. This paper will present the first results. Hopefully it will give us a greater insight in the relation between geometry and the structural behaviour of shell structures.Architectural Engineering +TechnologyArchitecture and The Built Environmen

Structural analysis of Heinz Isler’s bubble shell

This paper presents a detailed structural analysis of a bubble shell engineered by Heinz Isler. Through 3D scanning the geometry of this shell structure has become available to the authors. Structural analysis has not been possible before since the geometry of the shell was not available. The bubble shell was Isler’s most built type of shell. In the paperfirst the process of reverse engineering the geometry of the shell is described. Second, the effect of pre-stress in the edge beams is described. Third, the load distribution throughout the shell and the membrane behaviour relative to bending behaviour is assessed.Accepted Author ManuscriptStructural Design & Mechanic