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Application of Hybrid Glass-Timber Elements
in Architecture
Semi Continuous and Self-generative Glass Layering
Structural System
Philipp Eversmann, Paul Ehret, Christian Louter, and Manuel Santarsiero
Abstract The following paper explores the application of hybrid timber-glass
elements on semi-continuous architectural structures. The use of glass as a structural
material opens multiple fields of investigations. Beyond structural matters and safety
issues, architectural questions as functionality and spatiality are briefly addressed,
since they are paired with the structural layout. Furthermore, the potential of a
glass plate system of overlaying, but yet discontinuous glass elements is addressed
in more depth. Geometrical specifications on the structural glass application are
elaborated on and generalized into a ‘card house’ algorithmic discretization model.
Through the design and fabrication of a ‘case study’, the parallel use and digital
simulation and empirical physical testing are discussed. A further potential use in
the construction industry of the system is debated.
1 Introduction
Spatial liberation of the architectural plan has been an achievement in the use of
reinforced concrete technology. The structural efficiency provided by it enabled the
design of floor plans with the structure and architectonical elements such as a wall
being disconnected.
The use of structural glass, as illustrated for a multitude of new applications by
Henriksen (2012), could aim towards a similar design dialectic. It has implications
on the functionality but also in the perception of space. The rules implied by
the piling of structural glass can determine the spatial arrangement of each floor,
generating a different plan for every level.
P. Eversmann () • P. Ehret • C. Louter • M. Santarsiero
EPF Lausanne - ICOM, GC B3 505, Station 18, CH - 1015 Lausanne, Switzerland
e-mail: philipp.eversmann@epfl.ch;paul.ehret@epfl.ch;christian.louter@epfl.ch;manuel.
santarsiero@epfl.ch
© Springer International Publishing Switzerland 2015
P. Block et al. (eds.), Advances in Architectural Geometry 2014,
DOI 10.1007/978-3-319-11418-7_4
47
48 P. Eversmann et al.
The following sections explain the basic mechanisms of such a system in order
to get an understanding of the constructive feasibility. The main structural principles
constraining the design also reveal the flexibility of the system and show the
possibility to use it as a design driving principle.
2 Structural Glass
In contemporary architecture there is an increasing demand for transparency.
To fulfill this quest for transparency, glass is – besides its common use as a
façade cladding – increasingly applied as a load bearing structural material. Early
applications can be found in the 1980s and 1990s, for example the glass pavilion
for the Sonsbeek art exhibition in Arnhem in the Netherlands in 1986 (Nijsse 2003).
Ever since, structural glass technology has rapidly and significantly evolved, as is
illustrated for instance by Nijsse (2003)andWurm(2007).
Glass can be applied for various load-carrying components (Henriksen 2012).
The most common application of glass as a structural component is its use as a
structural beam, where the glass is loaded in in-plane bending. Other applications
are columns and (shear) wall systems. The latter application is exploited in the
current study. As revealed in Sect. 5, a case study pavilion was constructed based on
a hybrid timber-glass structural system. In this system the glass is placed vertically,
as a wall system, thereby carrying both the vertical and the horizontal forces acting
on the structure. The glass functions both as a vertical column and a horizontal
stiffener and stabilizer, in-between horizontal sheets of timber. Furthermore, the
overall structure is pre-tensioned by means of vertical steel rods, to further enhance
the structural interaction of the timber- glass structure. The cables are placed
according to required maximum distances between the structural members and
maximum heights of each cable.
3 Semi Continuous Structural System
Simple card houses structures are taken as a reference for the structural devel-
opment. If we were to consider this system structurally we would enumerate the
following principles:
• Postulate: the punctual link between two overlapping panels has sufficient
friction to avoid side sliding effect
• One panel needs two points of support to be lifted (Fig. 1)
• Pairing up panels two by two per floors isn’t sufficient to hold: either cross
bracing or the addition of a 3rd panel enables structural integrity of the system
(Fig. 2).
Application of Hybrid Glass-Timber Elements in Architecture 49
Fig. 1 One panel needs two
points of support to be lifted
Fig. 2 Wither cross bracing
or the addition of a 3rd panel
enables structural integrity of
the system
Fig. 3 Floors can stabilize
the supporting panels
• The introduction of floors in which there is a link with the panel stabilizes it: it
does it for the panel below and the one above (Fig. 3).
• This system involves a chain of panels all connected two by two; on each floor
each panel is connected to two panels from the precedent floors, which as a whole
can be considered as continuous (Figs. 4and 5).
• Each floor has at least three panels/walls with at least two different intersections
of their axes for rotational stability (Fig. 6).
50 P. Eversmann et al.
Fig. 4 Two supports/panel
Fig. 5 Support points
Fig. 6 Floor layout, axis
configuration
Application of Hybrid Glass-Timber Elements in Architecture 51
4 Algorithmic Design: A Self-generative System
The general concern of this study is to describe surfaces following a stacking
method. For curved geometries, in particular vaults, ‘Trulli’, stacked stone vaults
in southern Italy (Fig. 7), and nineteenth century glass structures (Lauriks 2008)
were taken as a reference.
The goal of the algorithmic modeling is to provide an automated design tool
which can accommodate to various surface types (Fig. 8). The choice of double
curved surfaces was made to ensure that the system accommodatesto a large variety
of surfaces, flat and single curved surfaces being considered as particular cases of
double curvature ones. The aim is to adjust to the curvature changes while leaving
some freedom in the arrangement of the panels for the designer.
The design system takes a reference surface S as an input. The first part consists
in slicing S into a multitude of layers with adjustable heights. The resulting curves
are offset on the same side of S to secure a complete overlapping of the horizontal
panels. These curves can then be fragmented in multiple segments following the
local curvature of the input curve. Starting from the bottom curves every new floor
verifies the consistency with the points announced in the 2nd section, in particular
Fig. 7 Section of traditional ‘Trullo’ (http://www.understandingitaly.com/puglia-content/trulli.
html)
Fig. 8 Stacked dome structure, wall with an inflection point in the generative curve
52 P. Eversmann et al.
one glass panel always having at least two support points (Fig. 4) and the axis
orientation of the panels (Fig. 6). The solution of this problem can obviously have
large number of valid results. For fabrication ease and architectural consistency a
minimum and maximum length of each panel can be defined. The designer has the
flexibility to change the seams of the curve to adjust the start division points and
to correct defects as illustrated in a brick pattern study by Bärtschi and Bonwetsch
(2012).
In the realm of a further study for the elaboration of a building it could also
be imaginable to integrate different user ‘wishes’ for the panel layouts to obtain a
result by a projected functional use of each ‘floor plan’. Each floor can be manually
adjusted and be tested by the verification algorithm. Once all panels are positioned
they can be optimized in different length families.
5 Case Study: The Pavilion ‘Slicing Opacity’
5.1 Architectural Concept
The pavilion Slicing Opacity is the application of the system simplification enun-
ciated in Sect. 3and 4. It is demonstrating the structural efficiency obtained by the
slicing of freeform surfaces into structural planes equally distributed, following a
variation of only two different heights.
It illustrates the new potentialities in the use of structural glass for architecture.
As the scale of the pavilion was closer to urban furniture the idea of organic shapes
was chosen to maximize possibilities of interactions with the visitor (Fig. 9). The
design system explained in Sect. 4has been applied on these freeform surfaces
showing the capacities of the system, despite the drastic curvature changes.
Fig. 9 Case study ‘Slicing Opacity’
Application of Hybrid Glass-Timber Elements in Architecture 53
Fig. 10 (a,b) Fields of maximum principal stress in the glass and timber panels
5.2 Structural Analysis
Preliminary finite element analysis is performed on the structure. Shell rectangular
elements are used to model the vertical laminated glass panels. Solid tetrahedral
elements are used instead to model the timber horizontal plates.
No sliding is allowed between timber and glass components. In order to evaluate
the structure response against lateral load, a horizontal force equal to 0.1 g is applied
to the whole structure. Boundary conditions are given specifying displacements and
rotations equal to zero to the nodes of the base panel. Figure 10 shows the field of
maximum principal stress in the glass plates and timber panels.
Figure 11 shows the field of displacements (displacement scale is 10).
Results indicate that the maximum stresses are located in the glass panels at the
base. This is in agreement to the expectations since the glass panels at the base are
subjected to the maximum shear forces.
5.3 Optimization Form and Structure
The algorithmic design described in Sect. 4is obviously a pure geometric approach
to create the structure, using the structural design assumptions of Sect. 3.Whatif,
the structural analysis could directly inform the geometric pattern and look for a
structural oriented optimization?
For simulating this approach, a parametric model was set up using the software
‘karamba’ (http://www.karamba3d.com/). In the model, a set of parameters was
54 P. Eversmann et al.
Fig. 11 (a,b) Visualization of the field of displacements
Fig. 12 Glass shells position and resulting meshing
defined to be able to rotate all vertical glass elements separately around their central
axis (Fig. 12).
Every position change of the glass shells results in a newly generated mesh
geometry for the horizontal elements.
The overall structural comportment was then calculated using different wind load
cases with the karamba analysis model. Therefore, all the surfaces were projected
into the normal plane of the wind direction to be able to calculate the force per
area of every shell element of the glass structure. The resulting forces can then be
calculated using the karamba solver (Fig. 13).
Application of Hybrid Glass-Timber Elements in Architecture 55
Fig. 13 Max displacement of the shell elements in karamba
Using the genetic algorithm ‘galapagos’ in grasshopper, multiples of variations
of the orientation of the panels could be calculated, using the maximal deflection of
the whole structure as a fitness criteria.
The movement of all panels or selected ones can be constrained to only certain
movements to ensure the architectural integrity of the project.
5.4 Fabrication
The idea of the fabrication was to keep the process simple for the wood cutting,
which was done at our university’s own laboratory, whereas the glass panels
were produced by a local glass contractor to ensure quality control and safety
requirements are held throughout a manufacturing process which needs very specific
tooling and knowledge. Every glass panel is composed of two float glass panels
of only 4 mm thickness, laminated with a Polyvinylbutyral film to panels of 11
different lengths and two height families with a total of around 400 panels. In order
to gain stiffness and meet the security requirements every single border has been
edge treated (Fig. 14).
Physical tests were previously effectuated in order to understand the relationship
between the geometry of the glass panels and the structural behavior. The test
objects were constructed in real scale and were then structurally evaluated. This
56 P. Eversmann et al.
Fig. 14 Tower fabrication model
d
Inlay pockets
Glass Thickness
Steel cable
Fig. 15 Physical test objects, glass-timber interaction
method of empirical testing proved a fast way to approach the structural feasibility
of the project and to get reliable figures needed for structural evaluation.
A major problem was to accommodate the tolerances of the different glass
thicknesses due to the lamination process to the pocketing of the wood panels in
a way to provide sufficient holding of the panels on side loads. If the cuts were too
large in the tested prototypes, the whole structure became slippery since the wood
panels had too much possibility of movement (Fig. 15). If on the other side cuts
Application of Hybrid Glass-Timber Elements in Architecture 57
N
α < 45°
α
α > 45°
α
Fig. 16 Classification of surfaces on angles for direction of milling operations
were too thin, it was impossible to insert easily the glass into the wood without
extra pressure on its edge, risking unnecessary stress on it.
Since this parameter was neglected in the structural simulation, we chose to
pretension the whole system with cables to get more friction between the elements,
preventing them from slipping. All wood elements could be cut out of 21 panels of
Sperracolor© 1.5 m 3.5 m plates, a dense plywood with a serigraphy coating for
weather protection.
The production consists of only three different processes: drilling for fixation and
cable holes and two sided inlay pockets (Fig. 15) to define the inserts for the glass
panels for the vertical assembly. Then in order to get the overall shape closer to the
original reference surface S the wood edges were chamfered with an angle following
the local tangent to S at every single point of the curve C. Due to the machine head
size it was cut using the five axis following two different positions (Fig. 16).
6 Architectural Application
The material capacities of reinforced glass as a primary structural material coupled
with the proposed stacking system offer new potentials for a maximum of trans-
parency as well as a functional generation of floor plan layouts.
The system can be imagined in a multitude of scales, daylighting can be
modulated through the variation of the stacking geometry (Fig. 17).
Though the case study prototype (Fig. 16) could be only effectuated on a
relatively reduced scale, structural reinforcement of the glass panels by laminated
58 P. Eversmann et al.
Fig. 17 Scale: inhabitable object – full scale floor heights
Fig. 18 Case study house
Fig. 19 Case study house
tension elements in the base parts of the panels makes a much larger scale
imaginable (Louter 2007). If we were to take “Slicing Opacity” as a mockup of
what a new generation building could be, we could pursue towards a functional
optimization of floor plan layouts within the limits of certain shape types. Once
the user typologies are identified in adequacy with the corresponding floor plan
typology and proportions the plans and the structural layout could be generated
(Figs. 18 and 19).
Application of Hybrid Glass-Timber Elements in Architecture 59
Conclusion
This paper presents a system of hybrid timber-glass elements which can be
applied on semi-continuous architectural structures. A fabrication case study
project shows the algorithmic generation, structural analysis and fabrication
detailing in the scale of urban furniture. Following current research in glass
reinforcement, the system is applied on bigger scale structures to show future
possibilities in an architectural application. The more complex detailing and
structural simulation involved in the application on larger structures was not
part of this paper, but should be subject to further investigation.
Within its own set of rules this logic opens new fields of investigation
for the designer. The glass structural constrains are stretching the modern
language (column/beam) to a semi continuous logic as it is explained in the
earlier chapters. Further studies could explore the repercussion of this new
dialectic of the floor occupation: functional matters as well as visual and
perception questions could be addressed, based on the fact that the structural
module is transparent.
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