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Automatic joinery has become a common technique for the jointing of beams in timber framing and roofing. It has revived traditional, integral joints such as mortise and tenon connections. Similarly, but only recently, the automatic fabrication of traditional cabinetmaking joints has been introduced for the assembly of timber panel shell structures. First prototypes have used such integrated joints for the alignment and assembly of components, while additional adhesive bonding was used for the load-bearing connection. However, glued joints cannot be assembled on site, which results in several design constraints. In this paper, we propose the use of dovetail joints without adhesive bonding, on the case study of a timber folded plate structure. Through their single-degree-of-freedom (1DOF) geometry, these joints block the relative movement of two parts in all but one direction. This presents the opportunity for an interlocking connection of plates, as well as a challenge for the assembly of folded plate shells, where multiple non-parallel edges per plate must be jointed simultaneously.
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Interlocking Folded Plate - Integral Mechanical Attachment for
Structural Wood Panels
Christopher Robeller 1and Yves Weinand 1
1Timber Construction Laboratory IBOIS, EPFL
June 20, 2015
Abstract
Automatic joinery has become a common technique for the jointing of beams in timber framing and
roofing. It has revived traditional, integral joints such as mortise and tenon connections. Similarly,
but only recently, the automatic fabrication of traditional cabinetmaking joints has been introduced
for the assembly of timber panel shell structures. First prototypes have used such integrated joints
for the alignment and assembly of components, while additional adhesive bonding was used for the
load-bearing connection. However, glued joints cannot be assembled on site, which results in several
design constraints.
In this paper, we propose the use of dovetail joints without adhesive bonding, on the case study
of a timber folded plate structure. Through their single-degree-of-freedom (1DOF) geometry, these
joints block the relative movement of two parts in all but one direction. This presents the opportunity
for an interlocking connection of plates, as well as a challenge for the assembly of folded plate shells,
where multiple non-parallel edges per plate must be jointed simultaneously.
1 Introduction
Architectural designs have often been inspired by
folded shapes such as Origami, however the fold-
ing principle can rarely be applied to building
structures directly. Instead, many folded plates
have been cast as concrete thin-shells in the 1960s.
These constructions were labour-intensive and re-
quired elaborate formwork for the in-situ casting.
Prefabricated constructions with discrete ele-
ments made from fiber-reinforced plastics have
been researched in the 1960s. [1]
Folded plates built from laminated timber pan-
els have been presented by C. Schineis [19] (Glu-
lam) and H. Buri [2] (Cross-laminated Timber).
These designs combine the elegant and efficient
shape of folded plate shells with the advantages of
structural timber panels, such as CO2 storage and
a favorable weight-to-strength ratio. However, a
major challenge in the design of a timber folded
plate is presented by the joints: Since timber pan-
els cannot be folded, a large amount of edgewise
joints has to provide two main functions. One
of these functions is the load-bearing behaviour,
where connector features of the joints must pro-
vide a sufficient stiffness and rigidity. The second
main function of the joints is the assembly of the
parts, where locator features of the joints are es-
sential for a precise and fast positioning and align-
ment of the parts.
B. Hahn [5] examined the structural behaviour
of a first timber folded plate shell which was built
from plywood and assembled with screwed miter
joints, concluding that the load-bearing perfor-
mance could be improved significantly with more
resistant connections.
Inspiration for such improvements may be found
in integral mechanical attachment techniques, the
oldest known technique for the jointing of parts,
where the geometry of the parts themselves blocks
their relative movements [13]. Such integrated
joints have recently been re-discovered by the tim-
ber construction industry. Beginning in 1985,
mortise-and tenon joints have been repatriated in
timberframe and roof constructions [7]. Only very
recently, integrated joints have also been proposed
for the edgewise jointing of timber panels. In
the ICD/ITKE Reserach Pavilions 2011 [12] and
1
2013 [11], fingerjoints have been applied to ply-
wood panels and an application of dovetail joints
for cross-laminated timber panels (CLT) was pre-
sented in the IBOIS Curved Folded Wood Pavil-
ion 2013 [18]. In these prototype structures, the
integrated joints have played an important role
for the assembly of the components. They have
also participated in the load-bearing connection
of the parts, but additional adhesive bonding was
needed. With few exceptions [6], such glued joints
cannot be assembled on site, because they require
a curing period with a specific constant tempera-
ture and humidity [15]. Therefore, their applica-
tion is limited to off-site assembly of larger compo-
nents, which complicates both transport and han-
dling while still requiring additional connectors for
the final assembly.
In this paper, we propose the use of dovetail
joints without additional adhesive bonding, on the
case study of a timber folded plate shell. (Figure
1).
Through their single-degree-of-freedom (1DOF)
geometry, these joints block the relative movement
of two parts in all but one direction. This presents
the opportunity for an interlocking connection of
plates, as well as a challenge for the assembly
of folded plate shells, where multiple non-parallel
edges per plate must be jointed simultaneously.
1.1 Dovetail joint geometry and me-
chanical performance
Using polygon mesh processing, we describe an
edgewise joint based on its edge E. From the
mesh connectivity, we obtain the edge vertices p
and qand the adjacent faces F0and F1with their
face normals n0, n1. We use the polygon mesh
to represent the mid-layer of timber panels with
a thickness tand offset F1and F2at ±t
2to ob-
tain the lines L(Figure 2a). From a division of
E, we obtain the points Xjfor a set of refer-
ence frames {u1, u2, u3}, where u1k~pq and u2kn0
(Figure 2b). A finger joint geometry is obtained
from an intersection of planes located at Xj, nor-
mal to u1, with the four lines L.
Without additional connectors, finger joints are
a kinematic pair with three degrees of freedom
(3DOF), also called planar joints. They can re-
sist shear forces parallel to the edge and in-plane
compressive forces. However depending on the
plate geometry, thickness and most of all rota-
tional stiffness of the connection detail, bending
moments are also transferred between the plates.
Also, due to the rotation of the plate edge caused
Figure 3: FEM analysis (top view) of a 3x3m,
21mm Kerto-Q folded plate thin shell assuming
fully stiff joints. Distribution of traction (red)
and compression (blue) stresses in the y direction.
Top: gravity load case. Bottom: asymmetric snow
load.
by bending, in-plane traction forces perpendicu-
lar to the edge line appear and their magnitude
increases under asymmetrical loads. Such forces,
which occur as a result of out-of-plane loading,
cannot be supported only by shear and in-plane
compression resistant joints.
On a dovetail joint (Figure 2d,e), the intersec-
tion planes on the points Xjare normal to a ro-
tated vector w1. It is obtained from a rotation
of the reference frame {u1, u2, u3}about u3at an
alternating angle ±θ3. The resulting rotated side
faces reduce the dovetail joints degrees of freedom
to one translation ~w3(1DOF). Simek and Sebera
[20] have suggested θ3= 15for spruce plywood
panels. Such prismatic joints can only be assem-
bled or disassembled along one assembly direction
~v =~w3. In addition to the finger joints resistance
to shear and compressive forces, dovetail joints
can, without adhesive bonding, also resist bend-
ing moments and traction forces which are not
2
Figure 1: Folded thin shell prototype built from 21mm LVL panels, assembled with single-degree-of-
freedom dovetail joints without adhesive bonding. Components interlock with one another
p
q
p
q
p
q
n0n1
w3
F0
F0
F+
F0
F-F1
F1
F+
F1
F-
a. b. c. d. e.
u2u3
u1
Ei
L1
L
L3
LL2
L
L0
L
Xj
j+1
j+2
j+3
j+1
j+2
j+3
j+1
j+2
j+3
v
w1
w2
Figure 2: Joint geometry. a: Basic parameters, b: Intersection planes (grey) normal to ~pq, c: 3DOF
joint, d: Rotated intersection planes (grey) normal to ~wj, e: 1DOF joint
parallel to ~v. Due to the inclination of the side
faces of the joint, resistance to these forces can be
improved significantly. In that way the inclined
faces take over the role that the glue would have
in a finger joint. (Figure4)
1.2 Fabrication Constraints
One of the main reasons for the resurgence of fin-
ger and dovetail joints is the possibility of auto-
matic fabrication. However, the mechanical per-
formance of the joints depends on fabrication pre-
cision. At the same time, fast machine feed rates
are important for a time-efficient production. We
have fabricated such joints with a robot router and
a gantry router, achieving higher precision with
the gantry machine, which is more stiff and pro-
vides a higher repeat accuracy.
The variability of the machine-fabricated joints
is enabled by the 5-axis capability of modern
routers: Although traditional edgewise joints in
cabinetmaking were used for orthogonal assem-
blies, both the finger and dovetail joint can also
be applied for non-orthogonal fold angles, which
was essential for the reference projects mentioned
before. However, there are certain fabrication-
related constraints for machine-fabricated dovetail
joints. In order to integrate the joint fabrication
directly with the panel formatting, we use a side-
cutting technique [8], which is limited to a tool
inclination βmax. We obtain this limit from the
specific geometry of the tool, tool-holder and spin-
dle used for the joint fabrication. (Figure 5)
The parts can be assembled in two ways, as
shown in figure 5, which allows to address a larger
range of dihedral angles ϕ. From this we ob-
tain the fabrication-constrained most acute fold
ϕmin = 90βmax and most obtuse fold ϕmax =
90+βmax. With standard cutting tools, this tech-
nique allows for the jointing of acute folds up to
3
Figure 4: FEM simulation of bending on a dovetail joint connecting two Kerto-Q 21mm LVL panels.
The bending moment applied is transformed into compression, normal and shear forces parallel to the
inclined contact faces.
βmax
φmax
φmin
βmax
βmax
TCP
TCP
TCP
TCP
TCP
TCP
TCP
TCP
TCP
TCP
TCP
TCP
Figure 5: Fabrication Constraints. Side-cutting technique used for the automated fabrication of 1DOF
edgewise joints with common 5-axis CNC routers. The maximum tool inclination βmax results from
the tool and the tool holder geometry. From this we obtain the range of possible dihedral angles ±ϕ
between panels.
ϕ= 50, which is ideal for folded plate structures.
Very obtuse fold angles ϕ140, which might be
required for smooth segmented plate shells, can-
not be fabricated with this method.
1.3 Simultaneous Assembly of Multiple
Edges
The assembly of doubly-corrugated folded plates
requires the simultaneous joining of multiple edges
per component (Figure 1), which has implications
on both the shell and the joint geometry.
For multiple 1DOF-jointed edges, simultaneous
assembly is only possible if the individual assem-
bly directions ~v are parallel. With a normal dove-
tail joint geometry (Figure 7a), this is not the case:
A simultaneous assembly is only possible for par-
allel edges, which allows only for rectangular as-
semblies, such as drawers or a cabinets.
In order to simultaneously join non-parallel
edges, we must rotate the assembly direction vof
the joints to make them parallel. This possibility
is known from Japanese cabinetmaking [9], where
certain joints, like the Nejiri Arigata Joint (Figure
7b), are assembled diagonally, along a vector that
does not lie on either one of the two planes. While
European dovetail form a prism with a single tab,
e1
e2
e1
e0
e2e1
e0
x3
x2
Figure 6: The assembly of a folded plate from dis-
crete elements (left side) requires the simultaneous
assembly of non-parallel edges. (right side) We
rotate the insertion direction of our 1DOF joints,
to make the insertion vectors of simultaneously
jointed edges parallel. We chose a hexagon re-
verse fold pattern which requires only moderate
rotations.
4
vv
a. b.
faces across
edge only faces
across edge
faces along
edge +
Figure 7: a. Dovetail Joint, b. Nejiri Arigata Joint
using faces both acrioss and along the edge, the
Nejiri Arigata joints form a prism using multiple,
differently shaped tabs.
We extend this Japanese technique to a vector
subset of possible assembly directions. Figure 8
shows that the rotation about the edge line is con-
strained to 180ϕi. The vector subset is large for
acute and small for obtuse fold angles. This is par-
ticularly important when joining multiple edges
simultaneously, because an intersection must be
found between multiple vector subsets (Fig. 9).
If there is an intersection, the parts can be joined
simultaneously along any direction within the in-
tersection of the subsets.
Finally we extend this concept to a 3-
dimensional rotation (Fig. 10). This is possible
through a second rotation θ2, which is constrained
to a maximum value of ±θ2,max. The limitation
results from multiple other corelated parameters,
such as θ1and βmax. We call the resulting 3D
vector subset rotation window.
With this method, we can search for a joining
solution for the prototype in figure 6. We compute
rotation windows S1,S2,S3for the edges E1,E2,
E3and overlay them at their center point. Fig-
ure 11 shows that there is a common vector sub-
set S1TS2TS3between these three edges, we can
choose our assembly direction within it.
As a result of these limited rotations, the an-
gle between neighbouring, simultaneously joined
edges cannot be very acute. Folded plate pat-
terns like the Herringbone, the Diamond, or the
Hexagon pattern, which we chose for our proto-
types, (Figure 6) work well for our joining tech-
90° 130°50°
"
#
!
!
E34 68344
a.
Figure 8: 2D vector subset
3"3$
3"
3$
E1E2
E1
E2
b.
Figure 9: 2D simultaneous assembly
2, max
1
Figure 10: 3D vector subset
5
S3
S1
E1
E2
S2
v
S1ŀS2ŀS3
E3
3x
Figure 11: 3D simultaneous assembly
nique. Another essential feature provided by these
reverse-folds are the acute fold angles, which eas-
ily satisfies the fabrication-constrained range of
ϕmin = 50to ϕmax = 140.
2 Interlocking Arch Prototype
In an assembly of multiple components (Figure
12), a step-by-step sequence must be planned for
the assembly of the parts. The completed struc-
ture can only be disassembled piecewise in the re-
verse order of assembly. In this way, the elements
interlock with one another like a Burr Puzzle [22].
Each joint consists of two parts, which must be
parallel during assembly. We therefore chose a
folded plate geometry with relatively short edges.
The manual assembly of long edges may be more
difficult but can be simplified with a modified joint
geometry. It is important to know the approxi-
mate direction of insertion for each part, as this is
not easily visible through the joint geometry. De-
formations of the arch during the assembly should
be minimised. We have assembled this first pro-
totype lying on the side. However larger assembly
may require temporary punctual supports. Al-
though the in-plane dimensional stability of the
Kerto-Q panels is very high, panels may be slightly
warped and some force may be necessary during
assembly. While we have simply used a rubber
hammer, more advanced techniques could be ap-
plied.
To understand the mechanical behaviour of the
built prototype, we have applied a vertical load at
mid-span of the arch and measured the vertical de-
0 1 2 3 4 5 6 7
0
200
400
600
800
1000
Load cycle #1
Load cycle #2
Force [N]
Displacement [mm]
Figure 13: Series of 3-point flexural tests on the
small scale interlocking arch prototype built from
Metsawood 12mm birch plywood panels.
flection at the same point. The total load of 821N
was applied in two identical load cycles consist-
ing of four loading/unloading sub-cycles. First, a
vertical load of 117N was applied in seven steps,
after which the load of the last four steps was re-
moved. The loading and unloading of the last four
steps was repeated three more times, after which
the complete load was removed and the residual
deflection was measured. (Figure 13)
Under a vertical load equal to the archs dead
weight of 9.8kg (98N), the deflection measured at
mid-span was 2mm. From this we obtain a span-
to-deflection-ratio of L/750 and the arch’s struc-
tural efficiency which reaches 8.6 when loaded
with 821N (ratio of the maximal load over the
dead weight of the arch).
3 Interlocking Shell Prototype
3.1 Automatic Geometry Processing
Using the RhinoPython application programming
interface, we have developed a computational tool
which lets us instantly generate both the geom-
etry of the individual components and the ma-
chine G-Code required for fabrication. The tool
processes arbitrary polygon meshes, and gener-
ates 1DOF joints for all non-naked edges where
the fold angle ϕis larger than ϕmin and smaller
than ϕmax shown in figure 5(non-smooth meshes).
It also requires an input of edge identifier tuples
identifying those edges which must be jointed si-
multaneously, as well as the thickness of the LVL
panels. Exploiting this geometrical freedom, we
have tested our computational tool on the design
of a folded plate shell prototype with an alter-
6
Figure 12: Folded-plate arch prototype built from 12mm birch plywood (9-layer, I-I-I-I-I). Assembled
without adhesive bonding or metal fasteners. Span 1.65m, self-weight 9.8kg.
nating convex-concave transversal curvature. The
shell spans over 3m at a thickness of 21mm, us-
ing Kerto-Q structural grade LVL panels (7-layer,
I-III-I). (Figure 14)
Comparing this doubly-curved folded plate with
a straight extrusion (as tested by H. Buri [2]), it
can be concluded that the slight double-curvature
proves to be very beneficial when it comes to
global deflections, for example those caused by
wind loads. Deflections for the doubly-curved
shell geometry in the vertical direction are up to
39% smaller and up to 13% smaller in the lateral
direction than the ones for the straight extrusion
one.
3.2 Assembly
Due to the different assembly directions of its 239
joints, the 107 components components in our pro-
totype interlock with one another, similar to a
Burr Puzzle [22]. Figure 15 shows a part of a
so called non-directional blocking graph (NDBG),
which was inroduced by Wilson and Latombe [21].
In such a graph, single arrows indicate that
parts can be removed from the assembly. Two
opposite arrows between parts indicate that the
connection is blocked. In order to remove blocked
parts, the blocking parts must be removed first.
Our graph illustrates a left-to-right assembly. On
the right side, part number 86 is being inserted. It
connects to three other plates and blocks all other
parts in the graph. In such a configuration, the
final part remains removable, it is called the key.
Figure 16 shows the parts from figure 15 in 3D,
demonstrating how the component based on mesh
face F86 is being inserted. Its three edgewise joints
E41,E68 and E89 must be assembled simultane-
ously. The three assembly vectors of the edges
~v41,~v68 and ~v89 have been rotated to be parallel.
The same applies for the adjacent edges on the
left side of the faces F67,F69 ,F88,F103 and F105
(see figure 15). Within the rotation window of the
edge, we can freely rotate ~v for these edges (the
greater the angle between ~v and the main direction
of traction e1, the better).
3.3 Completed Shell Prototype and
Load Test
Figure 17 shows the completed folded plate pro-
totype, with a span of 3m and a shell thickness
of 21mm. Boundary conditions that restrain dis-
placements of the supports in every direction, but
allow rotations, were applied on both sides. A lon-
gitudinal line load was introduced along the top of
the shell and vertical displacement was measured
at center point. (Figure 18)
The prototype structure was also modelled in
7
8889
6869
71
107
87
104
86
70 Blocked
Free
65
98
35
68
89
41
105
106 7
107
90
44
100 91
59
66
36
99
18
Figure 15: Partial connectivity, assembly and blocking graph of the folded plate shell prototype.
(Left-to-right assembly) Large numbers represent mesh faces, small numbers represent mesh edges.
Pi+1
Pi+2
Pi+3 Pi+4
Pi+5
Pi+6
Pi
ni+1
ni+2
ni+3 ni+4
ni+5
CV
1
CC1
CV
2
CV3
CC2
CC3
CC: Concave
CV: Convex
A
B
A
A
B
B
B
A: min length
B: max length
Figure 14: Doubly-curved folded-plate: The ra-
dius (R= 17m) of the transversal curvature is
determined by the folded plates maximum ampli-
tude h[2], which is inversely proportional to the
number of segments mof the cross-section poly-
line (grey). We obtain this polyline from a circular
arc divided into segments of equal length. The in-
terior angle γ= ((m2)180)mof this polyline
is proportional to all fold angles ϕ. The geometry
of our prototype was fabrication-constrained to a
maximum component length B2.5m
FE analysis software (Abaqus) and loaded in the
same way. The plates were modelled using shell el-
ements, where the mid-surface is used to represent
the 3D plate and transverse shearing strains are
neglected. Connections between the plates were
considered as completely rigid in order to obtain
minimal displacements of the structure. By com-
paring the displacements of the structure with in-
finitely stiff joints with the ones measured on the
prototype, we obtained information about the ac-
tual semi-rigidity of the joints. The results ob-
tained from the testing of the large scale prototype
showed that the load of 25kN, that corresponds
to the proportional limit of the load-displacement
curve, causes a vertical displacement of 23mm. In
the FE model, the load applied in the same man-
ner caused a vertical displacement of 2.6mm.
Figure 18: Load-displacement curve of the shell
prototype. A longitudinal line load was intro-
duced along the top of the shell. Vertical displace-
ment was measured at the center point.
8
e3
v41 = v68 = v89
v35 = v65 = v98
v7 = v36
v13 = v42
e2
e1
v7v13
v59
v44
v18 v35 v36
v41 v42
v70
v43
v68
v66
v65
v84
v89
v90
v100
v99 v98
v107
v94
e1
e2
F86
F86
Figure 16: Left-to-right assembly of the Interlocking folded plate shell prototype. Built from Kerto-Q
structural grade LVL panels (7-layer, I-III-I))
9
Figure 17: Folded-plate shell prototype, built from 21mm LVL panels. With a self-weight of 192kg,
the prototype with a span of 3m was tested with a line-load up to 45kN.
4 Conclusion
A timber folded plate shell combines the struc-
tural advantages of timber panels with the effi-
ciency of folded plates. However, in such discrete
element assemblies, a large amount of semi-rigid
joints must provide sufficient support for the ad-
jacent plates in oder to ensure an efficient load-
bearing system. This remains a challenge with
much potential for improvements [5].
Integrated edgewise joints present an interest-
ing addition and an alternative to state-of-the-art
connectors: Compared to adhesive bonding, such
joints can be assembled rapidly on site. Also, com-
pared to costly metal plates and fasteners, which
are typically required in large quantities [14], the
fabrication of integrated joints is not more ex-
pensive. The replacement or reduction of metal
fasteners with an integrated mono-material con-
nection includes advantages such as improved aes-
thetics, ease-of recycling or a homogenous thermal
conductivity of the parts, which can reduce con-
densation and decay. [4] Another particular ad-
vantage is the possibility to join thin panels: The
current technical approval for the Kerto-Q panels
does not permit screwed joints on panels with a
thickness of less than 60mm. [3]
Recent experimental projects, which we intro-
duced in chapter 1, have already demonstrated
first applications of integrated edgewise joints for
timber panels. This paper followed up on these
projects, examining the particular advantages, po-
tential and challenges of 1DOF joints for timber
folded plate shells. We have demonstrated how
this joint geometry helps resisting the forces which
occur in such structures. In addition to the load-
bearing connector features, the joints provide lo-
cator features, which allow for precise positioning
and alignment of the parts through the joint ge-
ometry. This improves both accuracy and ease of
assembly. Furthermore, we have presented a so-
lution for the simultaneous assembly of multiple
edges per panel, which is essential for the applica-
tion of 1DOF joints in a folded plate shell struc-
ture. The per edge ”rotation window” introduced
in section 1.3 integrates the joint constraints re-
lated to assembly and fabrication. It can be pro-
cessed algorithmically and gives instant feedback
on whether or not a set of non-parallel edges can
be jointed simultaneously. This provides a tool for
the exploration of a variety of alternative folded
plate shell geometries.
10
The prototypes presented in this paper already
suggest possible patterns and demonstrate the re-
ciprocal relationship between the geometry of the
plates and the joints. Two built structures allowed
us to test and verify the proposed methods for fab-
rication and assembly while providing valuable in-
formation about the load-bearing capacity of the
integrated joints.
For the application in a large-scale building
structure, further research is required to deter-
mine if the integrated joints can replace additional
connectors entirely or reduce their amount. A pos-
sible combination of integrated joints with addi-
tional metal fasteners has been demonstrated re-
cently in the LaGa Exhibition Hall [10]. Another
possibility would be a combination of the 1DOF
joints with integrated elastic interlocks. [17]
Acknowledgments
We would like to thank Andrea Stitic and Paul
Mayencourt for their support with the finite ele-
ment models and load testing of the prototypes,
as well as Gabriel Tschanz and Francois Perrin
for assisting with the fabrication and assembly of
prototypes. We also thank Jouni Hakkarainen and
the Metsa Group for the supply of information and
materials.
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... The origami-inspired designs have shown advantages in reconfigurations for multifunctionality and enhanced adaptability. In the field of architecture and construction, novel origami-inspired adaptive structures have been proposed such as foldable building facades, canopies, and rapidly deployable bridges [5,[7][8][9][10][11][12][13][14]. ...
... On the other hand, prefabrication and modular construction have improved efficiency in building time compared to traditional onsite fabrication. The combined use of visual coding, lasercut fabrication, and industrial robotic arms allowed for the rapid and low-cost production of scale prototypes [11,37,38]. However, the construction of origami structures at the architectural scale remains challenging and the success of integrating origami structures in the future depends on the definition of a suitable design model, the actual sizing of structural elements, and thickness-accommodation techniques [39]. ...
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The search for efficient and elegant geometric forms is always the center of structural design. With advances in parametric modeling, countless geometric forms can be generated for architects and engineers. This powerful digital tool is applicable to the design of many structural systems, in particular modular structures. This technical note develops and implements a general framework of the design, parametric modeling, and manufacturing for modular structures based on the modification of a classic Miura origami pattern. Guided by the geometric analysis, we compared three modified Miura origami units and tessellations. A representative origami-based canopy with varying angles in the Hcircumferential direction was designed through the proposed framework and numerically simulated to evaluate the kinematic and structural behavior. Finally, a meter-scale canopy prototype was constructed with digitally fabricated modular thick panels and assembled rapidly on the site. We envision that the proposed framework using parametric modeling can enable diverse designs and applications of origami-inspired deployable structures that can be later integrated into the development of adaptive and responsive structures in the future.
... Automatically generated joinery has been an active topic in the recent decades (Robeller and Weinand, 2015), leading to the resurgence of traditional joint systems (Robeller, 2019) in such a way that they can be computationally generated, evaluated, and optimized for the multi-objective performances in timber structures. Despite a variety of the custom joint system which has been applied to the wood construction, only recently, algorithmically generated joint systems have been applied to a segmented CLT shell demonstrator where additional mechanical connectors like form-fitting wedge fasteners and glued wood dowels are used for transferring loads between the CLT plates (Robeller and Von Haaren. ...
... In addition, joints determine the quality of rapid and precise assembly. Customization of the form-and forcefitting finger joint system is already a common design method for the realization the of the geometrically complex segmented timber structures like, among others, ICD/ITKE Research Pavilions 2011 (La Magna et al, 2013), foldedplate arch prototype (Robeller and Weinand, 2015), Landesgartenschau Exhibition Hall , and Buga pavilion (Bechert et al, 2021), expanding a new horizon into geometric manipulation of the interlocking timber connections. ...
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The paper presents an algorithmic modeling tool for segmented timber shell structures made of glued wave-edge CLT plates. The goal is to provide a larger bonding area and thereby higher adhesive strength between plates, especially where a higher tension-resistant capacity is required. In addition to a number of contemporary research for exploring stereotomic modules, the inspiration is taken from the long history of the traditional glued finger joints in carpentry where they are used for providing higher interlocking capacity and adhesive strength. The structural performance of regular and glued finger joints is directly proportional to the bonding area between adjoining elements where they are interlocked and glued. Hence, expanding the shared faces would intrinsically magnify the structural performance of the glued finger joints. The paper presents the modeling method of a material-efficient, grain-informed, and structurally-optimized wedge edge joint system for the multi-shaped shell structures where the wave pattern is chosen for generating smoother fabrication toolpaths compared to any sharp-cornered pattern. The algorithm developed by the authors can efficiently maximize the glue bond by optimizing the wave-edge properties dynamically with respect to the geometric design, material system, and structural analysis within a feedback loop. The wave-edge properties directly affect the material waste and fabrication time and cost; therefore, the production parameters could be directly considered and controlled within the design process. The algorithm is able to produce the structural data model for the direct RFEM structural analysis, and fabrication data for automated production of a plenty of elements. The paper argues the application possibilities and limitations of the joint system for multi-shaped timber plate shells made of a multitude of geometrically-differentiated timber plates. Keywords: Algorithmic Design, Wave-edge Joint System, CLT, Shell Structure, Timber Prefabrication.
... Another important joint classification is rigid and elastic joints. In existing examples of complex timber plate structures, there are several interlocking joint types that were used to connect the plates as shown in Fig. 3. Three rigid joints were used; finger joints in ICD/ITKE 2011 research pavilion and Landesgartenschau exhibition hall, dovetail joint in IBOIS folded plate structure prototypes (Robeller and Weinand 2015) and rigid spline mitered butt joints in Kobra Pavilion (Manahl et al. 2012). One elastic snap-fit joint was utilized in single-folded double-layer arch prototype (Robeller et al. 2014). ...
... Rigid interlocks have a designed-in and pre-fabricated geometry of two opposing complementary shapes that can be joined with each other with some simple motion in some direction (Robeller and Weinand 2015). In elastic interlocks, one of the two opposing shapes is explicitly designed to deflect elastically and once the two parts are joined the deflected feature elastically recovers to cause interference, interlocking, and joining (Messler 2011: 40), thus allowing for the assembly and disassembly of the parts for multiple times. ...
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Interlocking wooden joints are a material driven traditional structural method that is used in complex wooden structures. Nowadays they are frequently used in computationally designed and digitally fabricated structures and pavilions. The present research contributes to the understanding of advanced technologies’ impact in revitalizing the use of traditional practices and contemporary applications of an established craftsmanship in a digital environment where the interlocking wood joinery is the main connection type. An explorative case study was defined to develop elastic wood joint for complex geometries of plate components using parametric modeling. The goal was to fabricate a physical prototype from wood to test the applicability of the developed elastic joint. The result led to the development of digital and physical prototypes of a wooden shell pavilion with a parametric interlocking elastic wooden plate joint.
... Indeed, several studies have explored bioinspired structures made of wood, given that this natural composite can be used as a self-forming material to generate double curvature shapes [110,111] and interlocking pieces to form folded plates. [112] It is also possible to obtain bilayer wood sheets that bend with temperature or humidity changes due to their anisotropic nature. [113,114] As a natural composite, wood offers multiple advantages thanks to its microfibril structure and highly anisotropic behavior. ...
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This research review discusses several examples of plant movements, either depending on the direction of the triggering stimuli (tropisms) or not (nastic responses), which have served as inspiration to develop smart biomimetic actuators. In addition, it presents an overview of the multiple approaches for the development of autonomous actuators based on synthetic materials, as well as of their advantages and disadvantages, applicability, and limitations. The classification is based on structural and conformational characteristics (mono‐, bi‐, or multimaterial assemblies, their orientation, chemical structures, and geometrical configurations). Additionally, this review presents an alternative formulation and extension of the pioneering Timoshenko's model, which provides an understanding of the underlying mechanical principle of bilayer bending actuation. Finally, upscaled applications of this actuation principle are described, focusing mainly on biomimetic architecture. Attention is given to previously reported real‐life applications based on bio‐based materials and material systems. Furthermore, this review discusses the multiple challenges for synthetic materials when an upscaling perspective is intended. In this sense, key aspects such as time responsiveness and mechanical amplification, in terms of speed, displacement, and load‐bearing capability, are discussed.
... The utilisation of small-scale CLT elements has been a subject of continuous exploration in recent years. When working with small scale building elements, a prevalent strand of inquiry is into geometrically complex shell structures, such as ICD/ITKE Research Pavilion 2011 (Knippers et al., 2015), folded-plate arch prototype (Robeller et al., 2015), Landesgartenschau Exhibition Hall , or Buga pavilion (Bechert et al., 2021). Mostly these projects abide by the digital industry ideology of mass customisation, neglecting the economy of scale. ...
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The ELEMENTerial research project focuses on the development of an innovative design and construction system for Cross-Laminated Timber (CLT) offcuts. CLT construction, while offering advantages for automation, raises concerns about offcut waste, which constitute 5-10% of the material production in Estonian CLT timber industry. This research highlights the importance of aligning timber construction with circular economy principles by effectively utilising offcuts. The study focuses on the development of a design method, creating a versatile and holistic construction system that breaks away from traditional orthogonal designs. Algorithmic tools are employed to streamline the design process and to help manage the complexities of working with smaller elements. The outcomes include a geometric strategy, offering variable configurations for assembly in walls, floors, ceilings and openings. The research demonstrates the potential to automate and pre-rationalise the design process, providing design freedom beyond orthogonal constraints and shell structures. The applications range from shelters to facade systems, building extensions to potentially large-scale construction systems. This study offers environmental benefits and design flexibility in the construction industry. It holds a potential to guide the sector towards reduced waste and increased material efficiency, fostering sustainability and economic value from waste materials. The prospects for future research include further automation, refinement of connection details, and efficiency in production and material usage.
... There are several precedents of folded or segmented timber plate structures (Stitic and Weinand, 2015;Robeller et al., 2016;Tagliaboschi, 2020;Shah et al., 2022). Most structures either consist of interlocking plates (Henriques, 2012;Foged, Pasold and Jensen, 2014;Gatóo et al., 2022;Robeller et al., 2015;Bechert et al., 2018), and tenon joints (Robeller and Weinand, 2016;Rezaei Rad, Burton and Weinand, 2020) or comprise of individual panels that are connected with cleats (Schimek, Meisel and Bogenperger, 2010;Ruffo, Schimek and Wiltsche, 2011;Manahl, Stavric and Wiltsche, 2012). An interesting method and tool is Wood Frame grammar that connects plywood panels either with studs or with the help of structural connections, such as dog bones connectors (Sass, 2005). ...
... The high level of precision and the ability to articulate every single joint according to its structural and geometric need is achievable through the digital process and the robotic fabrication. (Robeller & Weinand, 2015) ...
Technical Report
EDITED BY Pedro Palma and Gerhard Fink (list of authors in pages 3-4) FOREWORD Working Group (WG) 1 of COST Action CA 20139 HELEN deals with aspects related to design for robustness, adaptability, disassembly and reuse, and repairability in taller timber buildings. As of October 2022, WG 1 has 102 registered members from 40 different countries. About 80% of the members are also members of other WGs, 35% of which are also members of WG 4 and 25% are members of all other WGs. This shows the broad scope and interdisciplinary nature of the topics addressed in WG 1. After the 1st WG 1 meeting in Izola (SI), on 24-25.05.2022, WG 1 was organised into one Sub-Group (SG) on robustness and disproportionate damages: - SG Robustness, coordinated by Pedro Palma (Empa, Switzerland) and Maria Felicita (TU Delft, The Netherlands) and three subgroups (SG) related to the circular economy: - SG Adaptability, coordinated by Kristina Kröll (University of Wuppertal, Germany), Lisa-Mareike Ottenhaus (The University of Queensland, Australia), and Felipe Riola-Parada (City University of Applied Sciences Bremen, Germany); - DG Design for disassembly and reuse, coordinated by Gerhard Fink (Aalto University, Finland) and José Manuel Cabrero (Navarra University, Spain); - SG Repairability and maintenance, coordianted by Robert Jockwer (Chalmers University, Sweden). The documents collated in this publication were written within the scope of the various SGs and were revised based on comments received during and after the 2nd CA 20139 Plenary Meeting in Gothenburg (SE), on 04-05.10.2022. COPYRIGHT NOTICE The copyrights remain with the authors of the documents. CITING THE REPORT OR SPECIFIC CONTRIBUTIONS If you wish to reuse this document or any part of it, contact the corresponding author(s) and editor(s) for permission. The various contributions included in this document can be cited as Author 1, Author 2, Author n, 2022. “Title.” Design for robustness, adaptability, disassembly and reuse, and repairability of taller timber buildings: a state of the art report. COST Action CA 20139 Holistic design of taller timber buildings (HELEN). The report can be cited as: Palma, P., and G. Fink (Eds.) 2022. Design for robustness, adaptability, disassembly and reuse, and repairability of taller timber buildings: a state of the art report. COST Action CA 20139 Holistic design of taller timber buildings (HELEN).
... Robot-oriented designs can involve robotic machining, robotic assembly, or both. Robeller and Weinand [25] are interested in 1DOF dovetail machining by a 5-axis CNC router. It is necessary to consider the maximum inclination of the tool holder and the spindle to the wooden panel. ...
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Full-text available
Due to its many technical advantages and environmental properties, engineered wood products (EWPs) have been increasingly used in the construction industry. With the standardization of the industry, adhesives and metal fasteners are often used as joints in EWPs of modern wooden buildings to replace traditional wooden joints. Using adhesive is one of the key solutions, making the structure strong and light and preventing the wood material from shrinking and expanding due to moisture. However, the use of adhesives raises concerns about recyclability, further processing, and wider environmental effects of glulam products. Despite continuous progress in this research area, critical views on bio-based adhesives still exist. Metal fasteners are also important for EWPs, but they also reduce the recyclability and disposal of EWPs. Environmentally friendly wood construction would use a pure – adhesive- and metal-fastener-free – massive wood solution based on one of the oldest traditional joining methods, i.e., the dovetail joining technique (DJT). There have been many studies in the literature on the technological aspects of EWPs with different construction solutions. In contrast, there is only a limited amount of research on DJT, based on several structural analyzes and model testing, and not so much on the structural performance evaluation of such wood products. This prevents us from understanding the potential of DJT, particularly in terms of environmental impact and recyclability. DoMWoB project (Dovetailed Massive Wood Board Elements for Multi-Story Buildings) researches and develops massive wood board elements assembled with the traditional dovetail joining technique, where no adhesive or metal fasteners are used. Within the scope of the 2-year project (01 August 2021 - 31 July 2023) with a budget of (202,680.96 + 93,000 €), fire performance, structural bending, air permeance, sound insulation tests were carried out at Tamper University, Finland.
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This article investigates the application of a multi-robotic platform to the fabrication of complex “free-form” timber structures. A concept of “smart factory”, with a 13-DOF robotic cell combining robotic mobility with fixed workstations, is proposed. A computational workflow was implemented to allow for fast iterations during the early design stage. The robotic cell design and design workflow are implemented in practical experiments conducted in the framework of intensive workshops. A productivity assessment is performed on a 50 m2 pavilion pre-fabricated with the proposed robotic cell.
Chapter
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The prototype presented in this chapter utilizes the technique of curved folding for the design of a thin-shell structure built from curved cross-laminated timber panels (CLT). The curved-folded geometry allows for a span of 13.5 m, at a shell thickness of only 77 mm. The construction requires curved line CLT joints, which are difficult to address with state-of-the-art jointing techniques for CLT. Inspired by traditional woodworking joinery, we have designed connections for the integrated attachment of curved CLT panels, utilizing digital geometry processing tools to combine the advantages of traditional joinery techniques with those of modern automation technology.
Thesis
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Timber folded plate Structures combine the advantages of timber as a construction material, such as its carbon-dioxide storage, low energy production and favorable weight-to-strength ratio, with the structural efficiency and elegance of folded surface structures. The construction of such surface-active structure systems with timber is a relatively new development, driven by an increasing awareness for sustainable building constructions, and enabled by new engineered wood products. However, these constructions require a large amount of edgewise joints between the thin timber plates, which are difficult to address with state-of-the-art connection techniques. Instead of using mass-produced mechanical fasteners for these connections, this thesis investigates the use of customized Integral Mechanical Attachment techniques, which use geometrical features of the parts to establish connections, rather than additional fasteners. Integral joints were common in traditional woodworking, but their manual crafting became infeasible during the industrialization. However, new computer-controlled fabrication technology, which is already available in the timber prefabrication industry, allows for an efficient, automatic production of integral joints. The advantages of such joints have already been demonstrated in framing constructions, where timber beams are used as the primary structural components. The proliferation of automatic joinery machines has repatriated customizable single-degree-of-freedom (1DOF) joints, which allow for the fast and precise assembly of prefabricated components. The objective of this thesis is to transfer these advantages to the construction of timber folded plate structures. Inspiration is taken from traditional cabinetmaking joints from Europe and Asia, as well as other industry sectors, where mass-produced integral joints are commonly used. The thesis will demonstrate several adaptations which have been made for the application of the joints on cross-laminated wood panels, for their automatic fabrication and for the customized purposes in the jointing timber folded plate structures. The geometry, fabrication and assembly of these new joints is being implemented and tested through the development of algorithmic tools. This is followed up by a verification of the proposed methods through large- and small scale physical prototypes. In its three peer-reviewed core chapters, the thesis presents investigations ranging from an initial hybrid approach, where integral joints are combined with adhesive bonding, towards a completely integral mechanical attachment solution. After a first application of the joints on a surface which is folded in one direction, the integral attachment of bidirectionally folded surfaces will be demonstrated. This is achieved through a new technique, which allows for the simultaneous jointing of multiple non-parallel edges, with single-degree-of-freedom joints. Algorithms will be presented, which allow for the automatic processing and the automatic fabrication of the joints. The automation of these processes will then be used for the construction of a doubly-curved, bidirectionally-folded surface, which obtains its structurally beneficial double-curvature through incremental changes in the geometry of the plates. [...]
Chapter
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The HygroSkin project explores a novel mode of climate responsive architecture based on the combination and interrelationships of material inherent behaviour, computational morphogenesis and robotic manufacturing. The dimensional instability of wood in relation to moisture content is employed to develop a meteorosensitive architectural skin that opens and closes in response to climate changes with no need for any technical equipment or a supply of external energy. Embedded within robotically fabricated, lightweight structural components made of elastically bent plywood panels, the responsive wood-composite apertures adjust the envelope’s porosity in direct feedback to changes in ambient relative humidity. The HygroSkin Pavilion was commissioned by the Fonds Régional d’Art Contemporain du Centre and now forms part of the permanent collection of the FRAC Centre in Orleans.
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The objective of the paper is the parametrization and the finite element analysis of mechanical properties of a through dovetail joint made with the use of a specific procedure by a 3-axis CNC machine. This corner joint was used for the simulation of the bending load of the joint in the angle plane - by compression, i.e. by pressing the joint together. The deformation fields, the stress distribution, the stiffness and the bending moment of the joints were evaluated. The finite element system ANSYS was used to create two parametric numerical models of the joint. The first one represents an ideally stiff joint - both joint parts have been glued together. The second model includes the contact between the joined parts. This numerical model was used to monitor the response of the joint stiffness to the change of the static friction coefficient. The results of both models were compared both with each other and with similar analyses conducted within the research into ready-to-assemble furniture joints. The results can be employed in the designing of more complex furniture products with higher demands concerning stiffness characteristics, such as furniture for sitting. However, this assumption depends on the correction of the created parametric models by experimental testing.
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Conference Paper
The research presented in this paper pursues the development and construction of a robotically fabricated, lightweight timber plate system through a biologically informed, integrative computational design method. In the first part of the paper, the authors give an overview of their approach starting with the description of the biological role model and its technical abstraction, moving on to discuss the computational modelling approach that integrates relevant aspects of biomimetics, robotic fabrication and structural design. As part of the validation of the research, a full-scale, fully enclosed, insulated and waterproof building prototype has been developed and realized: The first building featuring a robotically fabricated primary structure made of beech plywood. Subsequently, the methods and results of a geodetic evaluation of the fabrication process are presented. Finally, as the close collaboration between architects, structural and geodetic engineers, and timber fabricators is integral to the process, the architectural and structural potentials of such integrative design processes are discussed.
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Integral Mechanical Attachment, highlights on one of the world's oldest technologies and makes it new again. Think of buttons and toggles updated to innovative snaps, hooks, and interlocking industrial parts. Mechanical fasteners have been around as long as mankind, but manufacturers of late have been re-discovering their quick, efficient and fail proof advantages when using them as interlocking individual components as compared with such traditional means of joining materials like welding, soldering, gluing and using nuts bolts, rivets and other similar devices. For many years, it has been virtually impossible to find a single-source reference that provides an overview of the various categories of fastening systems and their various applications. Design engineers should find this book to be an invaluable source of detailed, illustrated information on how such fasteners work, and how they can save time and money. Students, too, will find this book to be extremely useful for courses in mechanical design, machine design, product development and other related areas where fastening and joining subjects are taught. This will be the first reference book to come along in many years that will fully illustrate the major classes of integral mechanical fasteners, replete with examples of typical assembly and ideas and suggestions for further research. * Covers all major techniques for integral mechanical attachment within the context of other types of joining including chemical (adhesive) bonding, melting and solidification (welding, soldering, brazing), and mechanical joining (fasteners and part features) * Includes specific chapters for particular attachment considerations by materials type, including metals, plastics, ceramics, glass, wood, and masonry * Provides unique coverage of mechanical/electrical connections for reliable contact and use.