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Topo-facade: envelope design and fabrication planning using Topological mesh representations

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Computational design tools based on Autodesk’s DesignScript language have been used with geometry and topology modelling techniques in the design of a climatised free-form building envelope. This project involves structural and performance analysis tools applied to structural engineering, façade engineering and fabrication planning. The project has progressed from concept through tender phases. The particular geometry presented unique conditions that required non-standard solutions to be used; to this end DesignScript was introduced to allow the design and engineering team to build a number of scripted topological façade models that explored alternative façade configurations. This paper combines a discussion about the specific fabrication project with a more generalised discussion of the role of computational tools in design and fabrication. The main interest is to explore the two-way relationship between practice and tool building by considering how computation can contribute to a practical fabrication project and equally important, how computational tools can be tested and refined by being used in practice on demanding projects.
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
Fi. 1: Carrier frame fabrication concept.

-
 
  

Gustav FaGerström, Buro H appold, erik verBoon, Buro Happold, roBert aisH
uni ver sity oF BatH
Computational desin tools based on Autodesk’s DesinScript lanuae have been used with eometry and topoloy modellin
techniques in the desin of a climatised free-form buildin envelope. This project involves structural and performance analysis tools
applied to structural enineerin, façade enineerin and fabrication plannin. The project has proressed from concept throuh
tender phases. The particular eometry presented unique conditions that required non-standard solutions to be used; to this end
DesinScript was introduced to allow the desin and enineerin team to build a number of scripted topoloical façade models that
explored alternative façade confiurations. This paper combines a discussion about the specific fabrication project with a more
eneralised discussion of the role of computational tools in desin and fabrication. The main interest is to explore the two-way
relationship between practice and tool buildin by considerin how computation can contribute to a practical fabrication project and
equally important, how computational tools can be tested and refined by bein used in practice on demandin projects.
introduction
 
The architectural concept used in this paper is based on a
sculptural approach in which lass joints alternate between
uniquely anled concave and convex relationships between
adjacent panels (fi. 2).
The self-weiht of the lare insulated lass units (IGU) de-
mands a support stratey where the ede of each panel should
be continuously supported. This requires that a strict eomet-
ric relationship be maintained between the lass and the sup-
port structure. Furthermore, the eometric conditions around
each node are unique, bein the simultaneous meetin point
for both concave and convex lass panels. Consequently, each
node, while based on a common topoloical principle, has a
unique eometric confiuration, and therefore requires the
development of a unique fabrication eometry.
As a base constraint, the architect had instructed that a
point-supported approach was undesirable and expressed a
preference for the use of rectanular or plate primary struc-
tural elements as opposed to the more traditional round hol-
low section and spherical node approach often found in struc-
tures of this type. The subsequent studies looked at both
structural approaches as a system that was offset from the Fi.2: Site Context. (Imae courtesy of Robert A. M. Stern Architects)
lazin line. The method for supportin the lass to the pri-
mary structure utilised continuous anles, or ‘carrier frames’
that followed and were structurally attached to the lass ed-
es via structural silicone sealant. Periodic steel plates struc-
turally linked the lass to the primary structure, while also ad-

dressin the chanin distance and anle between the two
systems. The multiple anled relationships between lass pan-
els required that the IGU’s have steppin or cantilevered inner
or outer lihts in order to maintain a consistent external joint
width.

DesinScript (as the interation of lanuae, eometry, topol-
oy and plu-ins) allowed the enineerin team to assess the
eometric feasibility of the architectural concept by buildin a
number of alteratively scripted topoloical façade models. This
approach enables the team to model the correspondence be-
tween the façade topoloy and the physical components of the
facade: lass panels as topoloical faces, structural members
as topoloical edes and node connectors as topoloical verti-
ces. DesinScript topoloy classes reveal the underlyin func-
tionality of the Autodesk Shape Manaers (ASM) via its API ¹
(Aish, 2012).
The sinle topoloical mesh model allows each of the con-
stituent components (face, ede or vertex) to make topoloi-
cal and eometric queries to the adjacent components, for ex-
ample, the computation of averae vertex normals, and ede
bisectors. Additionally, DesinScript is interated with Robot
Structural analysis and Performative Desin and reveals us-
er-oriented API’s directly to the enineers usin DesinScript.
This allows the sinle topoloical mesh model to be direct-
ly analysed both structurally and environmentally, while the
mesh also forms the basis for related fabrication models.
application: ca se study
Typically, facades are modelled as meshes usin the architect-
established desin surfaces (here represented by the front of
lass (FOG). The structural support system is typically defined
as an offset mesh from this definin mesh. The resultin struc-
ture is more easily realised if the definin mesh has ‘torsion-
free’ nodes. This means that the vertex normals at the end of
each ede are coplanar and the ede members are planar.
In some cases, a mesh with non-torsion-free nodes can be
optimised by movin the vertex positions ² (Wallner and Pott-
mann, 2011). This approach is more appropriate where the
mesh represents a smooth surface and the chanes in vertex
position (and hence the shape of the façade panels) is not visu-
ally apparent. However, the desin intention for this façade is
to create a very specific faceted confiuration, which could not
be optimised in this way.
In a non-torsion-free facade, the ede normal (as the bi-
sector of the ede’s adjacent faces) and the vertex normals at
either end of the ede are not coplanar. If the ede members
are planar and based on their respective ede normal, then
the ede members meetin at a common vertex will not in-
tersect alon a common vector (fi. 3). Alternatively, if it is re-
quired that all ede members intersect at a common vector at
each vertex, then the structural system has to resolve the twist
alon the ede members.
 
A carrier frame and offset structure was considered. If the off-
set structure is based on a uniform offset from the face of the
definin façade, then the edes of the offset may not lay on the
face bisectors, and the relationship between the carrier frame
and the offset structure may have to be desined to accommo-
date such deviations.
  
While these 2D studies were conceptually useful, a 3D ap-
proach was necessary to address the multiple unique condi-
tions imposed by the eometry. Buildin on this exploratory
work, a scripted approach was developed, harnessin mesh to-
poloy and allowin for the automated creation of panels from
mesh faces, structural members from mesh edes and connec-
tor nodes from mesh vertices (fi. 4).
B2
B1
B3
B4
B5
B6
N2
N1
N3
N4
N6
N5
N0 - Average normal
Separate intersection
point, >2’
B - Bisectors
N - Normals
Fi. 3: Characteristics of non-torsion-free eometry,
averae node vertex normal principle and ede face bisectors.

Fi. 4: Desin eometry expressed as topoloy mesh.
Fi. 5: The mesh topoloy used to define the façade.
Orane lines: the edes of the primary façade mesh
(front of lass)
Red lines: the averae vertex normals
Cyan lines: the weihted averae vertex normals
(weihed by the face areas)
Maenta lines: the offset mesh (used to define
the offset structure) (based on offsettin the vertices
of the primary mesh alon the weihted averae
vertex normals)

 
The ede-based structural system has to support one or two
planar sheets of lass and the twist between the vertices at
its ends. The question remains: Should there be a sinle ede
member that combines all these roles or a carrier frame to sup-
port the planar lass linked to a separate structural member to
accommodate the twist?
Four structural hypotheses were considered:
Carrier Frame and Plate oriented alon the ede normal (fi. 6)
Carrier Frame and Plate twistin to accommodate both end
points’ vertex normals (fi. 7)
Chamfered tube with chamfer axis usin the averae vertex
normal (fi. 8)
– Offset structure and carrier frame, with offset node con-
nectors based on the averae vertex normal (fis. 9– 10)
Fi. 6: Structural Hypothesis 1 – Carrier frame and plate, with the plate
oriented alon ede normal.
Fi. 7: Structural Hypothesis 2 – Carrier frame and Plate, with the plate
twisted between end points’ non co-planar vertex normals.
Fi. 8: Structural Hypothesis 3 – Chamfered tube with chamfer axis usin
the averae vertex normal
Fi. 9: Structural Hypothesis 4 – Offset structure and carrier frame,
with the offset node connectors based on the averae vertex normal.
    
The different test models were built on a simple hand-coded
test mesh (fis. 5–8). DesinScript allowed the test mesh to be
swapped out for the full mesh in order to build the complete
facade (f is. 9–10).

Fis. 10–12: Desin development model with offset structure
and carrier frame fabrication concept.

   
DesinScript provides a familiar ‘data flow’ approach to desin
computation and makes the creation and execution of desin
loic accessible to desiners with little or no prorammin ex-
perience. In this project, data from the input nodes in the top
left part of the raph ‘flows’ via intermediate mesh modelin
nodes to create the facade in the bottom riht part of the raph
(f i. 1 4).
The ‘data flow’ approach works well with simple models.
However, usability issues bein to emere when the problem
bein addressed ets more complex and there are many more
nodes to consider. This issue is addressed throuh the ‘node to
code’ functionality in DesinScript which automatically trans-
lates the user’s data flow diaram into an associative script
(fi. 12). DesinScript also includes support for reular impera-
tive scriptin usin conventional ‘for’ loops (for iteration) and
if’ statements (for conditionals) ³ (Aish 2013).
Bracketlength Carrierangle Position
7.204577 112 A111
9.277795 114 A112
8.996179 140 A113
8.973133 52 B71
6.642246 83 B72
8.632262 22 B73
6.056679 85 B21
6.814823 154 B22
7.22186 40 B23
8.648544 131 A91
8.918658 71 A92
6.064782 47 A93
6.664838 152 A81
7.675841 37 A82
6.426951 102 A83
9.645642 48 T21
6.832239 26 T22
7.152264 133 T23
7.25188 126 T91
7.055309 43 T92
6.64823 27 T93
7.916496 46 T21
8.305637 40 T22
9.694806 18 T23
8.837067 52 C51
6.535089 78 C52
6.896258 133 C53
8.967901 42 D51
7.42581 114 D52
8.955504 141 D53
Fi. 14: Diaram outlinin DesinScript data flow raph used as a visual prorammin interface (top)
as well as its ‘node to code’ functionality (bottom) allowin the desiner to selectively replace all
or part of a raph node diaram with the correspondin code, thus makin it possible to reduce visual
clutter and proress to a more succinct form of desin computation.
Fi. 13: umerical output complementin or replacin
traditional shop drawins.
 
Movin forward into fabrication plannin with hypothesis4
(above), the process was reversed with respect to that out-
lined in fi. 4. The topoloically represented structure is now
the source of an additional level of information describin the
carrier brackets’ lenth, shape, anle and position within the
overall assembly. The resultin information packae (fi. 13)
can be used in conjunction with – or entirely in lieu of – tradi-
tional shop drawins.

conclusions
This project demonstrates that script-driven topoloy can be
used as the central representation for eometric assessment,
structural analysis, performative analysis, fabrication plan-
nin and component enineerin, ultimately providin an ef-
fective way to realise a challenin façade.
More enerally, it is reconised that computation is drivin
more aspects of contemporary architectural and enineerin
practice. The contribution of DesinScript is to unify compu-
tation, eometry and topoloy with alternative prorammin
interfaces (both visual and textual) and thereby support differ-
ent levels of computational skill.
It is important to reflect on the results of this work. At one
level, it is the physical buildin. At another level, it is the op-
portunity this project provided to test and refine a new en-
eration of computational desin tools. But maybe the most im-
portant result is the acquisition of knowlede and skills made
by the practitioners. All three results have the potential to con-
tribute to even more challenin projects.

DesinScript Development Team, Autodesk Sinapore Research
Development Centre
Andrew Marsh for the Performative Desin plu-in for DesinScript
Al Fisher and Buro Happold Bath for the Autodesk Robot Structural
Analysis plu-in for DesinScript
Buro Happold ew York Structures and Facades roups
Robert A.M. Stern Architects
DesinScript is available at Autodesk Labs, http://labs.autodesk.com/
utilities/desinscript/
Additional information and plu-ins for DesinScript are available at
http://www.desinscript.or/

1 Robert Aish and Aparajit Pratap, ‘Spatial Information Modelin of
Buildins usin on-Manifold Topoloy with ASM and DesinScript’,
in Proceedings of Advances in Architectural Geometry (Paris:
Spriner 2012), pp. 25–36.
2 Johannes Wallner and Helmut Pottman, ‘Geometric Computin
for Freeform Architecture’, Journal of Mathematics in Industry 1,
no. 4 (2011).
3 Robert Aish, ‘DesinScript: A Learnin Enviroment for Desin
Computation’, in Proceedings of the Design Modelling Symposium
(Berlin: Spriner, 2013).
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