advanced building skins 14 | 15 June 2012 - lamp.tugraz.at - Graz ...

2.2 Geometrical Processing
Advanced Building Skins
The representation of complex geometry with regular elements requires profound understanding of the
surfaces properties. Therefore the recognition of repetitive topologies, patterns and components, as
well as the exact analysis and modelling of the geometry are necessary skills to understand which
possibilities exist to provide a competitive solution. Furthermore it is necessary to enhance the
complete planning process including the development of new production technologies and new
assembly concepts. Traditional conceptions of repeatability and standardisation of individual
constructional components are replaced or adapted. Without further processing and optimisation of a
double curved geometry, the process of rationalization will always lead to warped, twisted or non
developable construction components, which may rule out the full functionality of a building envelope.
The orientation of steel members, the relation of member angle to node orientation, the even
distribution of panel sizes, minimizing gaps between neighbouring elements and improving the
properties of offset are the main goals of the rationalization. Furthermore we deal with aspects of
aesthetics like the fairness of lines, the equal distribution of element sizes and angles between faces,
triangular or quadrangular grids and their orientation on the surface.
Figure 7: From a NURBS surface to a discrete mesh to a full digital model
All these factors of a panelised surface directly influence the properties of glass elements. While many
designs may be approximated by triangular or in some cases flat quadrangular glass panes, there are
cases where the original form and their smoothness have to be preserved either because a solution is
only possible with a significant visual impact or the architect does not allow changes. Assuming there
is a proper budget available for such a project this isn’t a problem at all.
A further approach is the use of cold or thermally bent glass. According to Eigensatz et al [5], pane
types can be classified in flat, cylindrical, toroidal and spherical forms, which differ in material,
fabrication method and costs. Various fabricators have developed proprietary methods and techniques
for manufacturing spherical glass elements. An interesting method to decrease the costs of double
curved glass structures is to simplify the geometry and breakdown the different types into a few
manageable groups. To facilitate the workflow and enable important optimising techniques custom
made software tools were developed by Evolute.
In the past years, researchers have solved various demanding tasks, like the panelisation of a double
curved surface with a rectangular grid consisting of planar quadrangular faces. An additional approach
in contrast to using an existing model is to perform a kind of reverse engineering and to remodel the
complete compliant geometry. A big advantage of doing this is to be able to better understand the
initial design and to create a clean model of the building which satisfies the needs for further
processing. A disadvantage of this new model is that it is just an interpretation of the original
geometry, including deviations and maybe misinterpretation, which we have to keep in mind while
processing the project. The extracted curve network and the resulting mesh out of it is always an
approximation of the original NURBS surface, whereby the nodes of the mesh ideally lie exactly on
the compliant surface. For this reason there are many possible alternatives to interpret the base
geometry, differing in number of members, panes size, aesthetics and costs.
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