a. b. SNAP-FIT JOINTS CNC-FABRICATED, INTEGRATED MECHANICAL ATTACHMENT FOR STRUCTURAL WOOD PANELS P deflection h tip y l h base F mating ABSTRACT

Transcription

1 SNAP-FIT JOINTS CNC-FABRICATED, INTEGRATED MECHANICAL ATTACHMENT FOR STRUCTURAL WOOD PANELS Christopher Robeller Paul Mayencourt Yes Weinand Swiss Federal Institute o Technology Lausanne EPFL a. b. b P delection h tip y l h base F mating α Female Male Basic Cantileer Hook Nomenclature: (a) Geometrical parameters o the two parts. (b) Mating orce F mating in relation to the insertion angle α and the delection orce P delection ABSTRACT This paper describes the design and potential applications o CNC-abricated snap-it joints or cross-laminated eneer lumber panels (LVL). These joints are new to the building construction sector, but commonly used in other domains such as the automotie or consumer electronics industry. We explain our application o existing knowledge about the design and dimensioning o such joints, as well as seeral adaptations that we hae made in order to optimize the connectors or the jointing o structural wood panels. This was necessary due to the materials and abrication processes in timber construction, which are dierent rom those in the sectors o origin o the snap-it joints. We propose applications, including two case studies with physical prototypes:. A box girder prototype on which we introduce the combination o snap-it joints with shear-resistant tab-and-slot joints and test the mechanical perormance o the joints. : A double-layer arch prototype with non-orthogonal, 5-axis CNC-abricated joints. 89

2 INTRODUCTION In 00 the building sector was responsible or nearly a third (3 per cent) o global inal energy use. The embodied energy in buildings can be signiicantly reduced with materials which require less energy in their production, such as wood products (IPPC 03). Typical building certiied spruce laminated eneer lumber (LVL) panels are made rom more than 90 per cent renewable materials and store 450 g o carbon per kg. Following the combustion conditions proided by the manuacturer, these panels can be recycled into energy production. Generally, due to its low weight-to-strength ratio, timber is an ideal material or the production o preabricated building components, where ease-o-transport, handling and assembly hae a great impact on the construction ootprint, cost and timespan. In this context, LVL panels oer particular adantages: Compared to cross-laminated timber panels (CLT), thinner cross-sections are possible with the more homogenous and mechanically strong peeled-eneer laminate components, such as the Kerto RIPA rib or box elements (MetsäWood 04). In the context o shell and spatial structures, timber panels machine easily into irregular shapes, and preabrication simpliies the use o adanced techniques and technology. Howeer, while LVL panels oer numerous adantages or such constructions, design constraints result rom limitations in the edgewise jointing o the thin panels. Geometrically simple, orthogonal components such as the Kerto RIPA elements can be preabricated with glued butt joints. On site, metal plates or asteners are used or the inal assembly. Gluing is not possible due to a lack o constant conditions or the curing o the adhesie. For more complex timber panel assemblies, such as olded plate structures (Buri 00), the assembly o large amounts o angular edgewise joints becomes ery challenging with state-o-the-art metal asteners. Preious studies hae also demonstrated that the structural perormance o such designs could be increased considerably through improed joints (Hahn 009). Inspiration or improements can be taken rom Integral mechanical attachment, the oldest known method o joining (Messler 006). Rigid interlocks orm one category o this general concept, including connections like mortise-and-tenon, doetail or inger-joints, which were common handcrated joining techniques in traditional carpentry and cabinetmaking. Howeer, with industrialization and its prolieration o machine-tool-technology (Schindler 009), these joints were widely replaced by mass-produced metal plate connectors and asteners. Only recently, the increasing use o inormation-tool-technology in timber construction companies and Application Programing Interaces or the algorithmic generation, analysis o integrated joints, has caused a resurgence o integral mechanical attachment techniques. First examples o integrated line-joints or wood panels hae been demonstrated on the ICD/ITKE Research Pailion 0 (la Magna et al. 03) and the Cured-olded CLT Pailion (Robeller et al. 04), as well as the recent ICD/ITKE LaGa Exhibition Hall (ICD/ITKE 04). In these projects, orm-itting joints integrate locator eatures or the ast and precise positioning o elements, which enables and simpliies complex assemblies. Simultaneously, the joints participate in the load-bearing connection o the components through their connector eatures. Additional metal asteners or adhesie bonding are necessary to receie orces and to retain elements in their remaining degrees o reedom. A possible solution or the jointing o structural wood panels without additional asteners or adhesie bonding may be ound in elastic interlocks, another category o integral mechanical attachment techniques. So-called snap-it joints proide an integrated locking eature to connect the parts. While snap-it joints are a common attachment technique in the consumer electronics or automotie industry, possible applications or the jointing o timber panel structures hae yet to be studied. CONCEPT Snap-it joints are widely used in the industry as a simple, economical and quick way o connecting two parts. The joints consist o one male and one emale part. The temporary bending o the cantileer hook allows the it o two pieces, using the material s elasticity property. Ater the joining operation, the pieces return to a stress-ree state. The geometrical parameters o the parts deine the orce needed to assemble or disassemble it and the separable or inseparable characters o the joints. The joint is mainly designed according to the mechanical load during assembly and its corresponding assembly orce (Figure ). GENERAL JOINT DESIGN Rudimentary design is proided by the snap-it manuacturers such as BASF (BASF 00) or Bayer (Bayer MaterialScience LLC 000). Based on the assumption o the Euler-Bernoulli beam theory, the design ariables or the joints are the ollowing: Height o the cantileer beam h, Length o the cantileer l, Width o the cantileer b, Undercut y. FABRICATION AGENCY ACADIA 04 DESIGN AGENCY 90

3 Gien the maximal permissible strain o the material ε, the maximal delection or a cantileer with rectangular and constant cross section is: y max = 0.6 (εl ) / h base For a cantileer snap joint with decreasing height to one-hal at the tip oer the length the 0.6 actor becomes.09. During the assembly, the delection orce P at the tip o the cantileer at y max is gien by: P delection = (bh /6) (Eε/l) Retention Force Diagram (Courtesy o A. Luscher) Where E is the E-modulus o the material and b the width o cantileer. More inormation on the design o cantileer snap joint with other geometry such as trapezoid section can be ound at (BASF 00) or deried rom the beam theory o a cantileer beam with point load at the tip (Figure ). A B Protruding Snap (Section) Protruding J Snap E (Section) I J H E G F G F D D Non-protruding Snap (Section) Non-protruding Snap (Section) The orce necessary to assemble the joint, called mating orce, depends on the riction coeicient o the material μ, the insertion angle and the delection orce. Both the delection and riction orce hae to be oercome by the mating orce: F mating =P [μ+tan(α)] / [-μtan(α)] A I H B C C H The same equation can be used to determine the separation orce o the joint where the insertion angle alpha has to be replaced by the retention angle beta. A alue o 90 or the retention angle gies the maximal retention orce. Assembly Protruding Snap H (Eleation) Protruding Snap (Eleation) Assembly Locate Insert Lock Assembly Locate Insert Lock Non-protruding Snap (Eleation) Non-protruding Snap (Eleation) Disassembly Unlock Disassembly Disassembly Unlock Detach Detach Furthermore, a study rom Luscher (Luscher 995) shows that the retention orce not only depends on the retention angle but on the Percentage o Engagement (PE) as well. The engagement is the depth o insertion in the undercut o the mating part. A hook ully in contact with its mating part would hae a PE o 00 per cent. The PE deines the ailure mode and thus the maximal retention orce. (Figure ) shows that a Percentage o Engagement o 00 per cent or higher is preerable. Finally, the stress concentration at the root o the cantileer should be reduced by adding a illet radius. Locate Insert Lock Unlock Detach ADAPTATION TO FABRICATION AND MATERIALS IN TIMBER CONSTRUCTION 3 CNC abricated Snap-it Joint or LVL Panels - Protrusion (A), panel thickness (B), cantileer length (C), insertion angle (D), cantileer height (E), cantileer spacing (F), mating cutout (G), illet radius (H), lateral pressure zone (I), undercut (J). Top right shows a ersion o the joint without hook protrusion. Bottom shows a schematic time-lapse assembly and disassembly. (Figure ) shows our design or a CNC-abricated snap-it joint. For the production o our prototypes, we hae used a MAKA MMs 5-axis router equipped with a cemented carbide shank-type cutter with a radius o 6mm, operated at a eed rate o 6-8m per minute and a rotational speed o,000 reolutions per minute. 9 ROBELLER, WEINAND, MAYENCOURT SNAP-FIT JOINTS

4 .. The elasticity o the wood allows to design a cantileering hook or the jointing o two panels o wood. For a gien panel thickness t and an undercut y the cantileer length l and height h can be chosen to correspond to the material s limits: 4 Box Girder Specimen or the Mechanical Analysis o Combined Snap-it and Tab-and-slot Joints - A combination o the snap-it joint with shear-resistant taband-slot joints allows or a mechanical behaiour equialent to a screwed joint Maximal permissible elastic strain in the bending direction. Maximal compressie strength at the hook contact to aoid iber crushing. During the joining operation, the hook will be bent. This implies bending moment at the base o the cantileer and a delection orce against the mating panel. For a gien undercut, the length and height o the cantileer hae been chosen to limit the strain at the base in its elastic range and to aoid the crushing o the ibers at the tip o the hook and the top layer o the mating part, due to the delection orce. The undercut is the displacement constraint imposed to the hook during insertion. A smaller height gies a larger lexibility o the cantileer, smaller strain at the base (h) and a smaller delection orce (h ). In case o the use o the retention resistance and an engagement o the hook higher than 00 per cent, the section o the cantileer hae to be sized suiciently or the disassembly tensile orce. COMBINATION WITH TAB-AND-SLOT JOINTS While Snap-it joints can resist a certain retention orce, they do not proide any shear resistance. In order to use this joint as a load-bearing connection or building components, we combine the snap-it joint with prismatic tab-and-slot joints, which receie the majority o the orces. Generally, we consider the snap-it-joint as a special type o tab-and-slot-joint, with an integrated retention eature. This combination o integrated joints allows us to achiee a mechanical behaior equialent to a screwed joint. The speciic shear-resistance o such a joint combination depends on the indiidual length and oerall amount o the tabs. We hae irst tested this behaior on a simple box girder prototype (Figure 4). FABRICATION AGENCY ACADIA 04 DESIGN AGENCY 9

5 5 FEM Simulation o a 3-point Flexural Test with the Box Girder Specimen Geometry the image shows compression on the taband-slot joints on side o the specimen. The FEM results were subsequently compared with a series o physical load tests. FABRICATION AND ASSEMBLY The geometry o the joint is parameterized in a Rhino3D Python script. The geometry o the snapit joint is automatically generated based on the panel thickness and the beore mentioned calculations. The G-Code or a CNC milling machine is also generated automatically at the same step. The assembly o a snap-it jointed beam is carried out by clipping the two webs to the bottom panel and inally connecting the top panel. This is done ery quickly and no ixation is needed to get the precise geometry. The time o cutting is gained back with the simplicity o assembly o the beam. Moreoer, the beam can be assembled and disassembled at any time. This means that the panels could be transported lat and then put together only when needed. The transportation olume or a beam with equialent static height is greatly reduced. MECHANICAL PERFORMANCE In order to ealuate the mechanical behaior o the Snap-it joints, a set o three beams hae been tested with a three point lexural test, loaded at mid-span. The results were alidated with a Finite Element numerical model (Figure 5). The perormance o the snap-it beam is then compared to a beam with screwed connection. Finally, an optimized snap-it beam is proposed with the conclusion o the analysis. PHYSICAL LOAD TESTS The snap-it beam specimens hae been built with spruce Kerto-Q panels with a nominal thickness o [mm]. The panels consist o seen laminated layers ( - - ), ie o them in the main grain direction and two in the perpendicular direction (Technical Research Centre o Finland 009). Kerto-Q has the adantage o being ery dimensionally stable to humidity changes with good structural characteristics. The beam spans 0.5 mm or a total length o the beam o 43.6 mm. The size was constraint by the maximal dimension o the CNC milling machine.5 m. The displacements were both measured with Linear Variable Dierential Transormer (LVDT) sensors on the top lange and with the stereo correlation technique on the bottom lange. 93 ROBELLER, WEINAND, MAYENCOURT SNAP-FIT JOINTS

6 NUMERICAL MODEL Using the Finite Element Sotware Abaqus, the snap-it joint beam was numerically simulated. The ollowing material alues were taken rom the national technical approal certiicate (VTT) o the panel manuacturer: VARIABLES VALUES FROM VTT FOR KERTO-Q [MM] Density ρ mean =50[kg/m 3 ] E E 0,mean = 0,000 [N/mm ] E E 90,edge =,400 [N/mm ] E 3 E 90,lat = 30 [N/mm ] ν 0.09 ν ν G G 0,edge, mean = 600 [N/mm ] G 3 G 0,lat, mean = 60 [N/mm ] G 3 G 90,lat, mean = [N/mm ] The Kerto-Q material was modeled as perectly linear elasti Linear brick 8-nodes elements with reduced integration (C3D8R) were used or the mesh. Attention was paid to reine the mesh at the contact zones. The contact is modeled with the general contact unction o Abaqus. Its interaction property has two eatures: a tangential behaior deined by a riction coeicient µ = 0:4 (Technical Research Centre o Finland, 009) and a normal behaior deined as hard contact. Contact constraints are enorced or both with the penalty method. Separation ater contact is allowed. RESULTS This section presents the results o the experimental tests and the numerical model. The results o the test are consistent with the numerical results. A inal delection at mid-span o 35 [mm] was reached or the ailure load o 6000N. The ailure occurred in the panel. The numerical model gies a delection o 3 mm or the same load. As we can see rom the results in Abaqus (Figure 4), the snap-it hook is not participating to the shear connection. Its stiness is much lower than the tab connection as it was designed to be easily bent or the joining operation. OPTIMIZATION OF THE SNAP-FIT CONNECTION FOR THE BEAM Looking at the result o the irst snap-it beam, the design o the beam could be improed or optimized by changing the hook geometry and the number o hooks. In the case o the beam, the snap-it does not need to take any traction orces when the beam is loaded. The snap-it is only necessary to keep the pieces together during construction. This means that the hooks do not need to be designed or high traction orces but should only be able to retain the our panels rom going apart. The snap-it cantileer can then be slender designed to make it more lexible, which would reduce the risk o iber crushing during insertion. Moreoer, as the hook is not participating in the resistance o the shear connection, ewer snapits are needed and could be replaced by more tap joints to improe the shear capacity o the shear connection. Furthermore, it is not necessary to hae the hook pointing in two directions. As it can be seen on the deormed shape o the beam in (Figure 4), the hooks pointing in the direction opposite o the shear stresses are losing contact as soon as the beam deorms and are then unnecessary. Less snap-it hook will considerably reduce the cutting time with the CNC and improe the competitieness o the technique oer the glued or screwed connection. Finally, in order to hae lat suraces, the height o hooks and taps can be trimmed to the panel surace. The analysis o the optimized beam gies a delection o 5 mm at mid-span or the same load o 6000N. COMPARISON WITH SCREWED CONNECTIONS Metal asteners such as screws allow or a ast and conenient assembly o wood components on site. Unlike adhesies, constant climatic conditions are not required or their assembly. Howeer, or the edgewise jointing o structural wood panels with screws with a shat diameter d, a lateral distance must be respected. For the Kerto Panels, the minimum distance is deined as 5*d, while the minimum screw shat diameter d is 6mm (Deutsches Institut ür Bautechnik 0). From this, we obtain a minimum lateral distance o 30 mm and a minimum panel thickness o 60 mm. Following these regulations, screwed edgewise joints cannot be used on thin LVL panels. Furthermore, large amounts o asteners are necessary or load-bearing joints and additional locator eatures are necessary to improe precision and ease o assembly. The combination o integrated connectors presented in this paper supports loads not with additional asteners but with the parametric geometry o the joints, which can automatically be optimized depending on the speciic material characteristics and actual local load-bearing requirements. Elements can be transported to the construction site lat-packed and put together on site. This reduces the necessary transportation olume. Moreoer, they can be quickly put together or disassembled i needed. Finally, the snap-it connection is a mono-material connection, including adantages such as aesthetics, ease-o recycling or a homogenous thermal conductiity o the parts, which can reduce condensation and decay (Graubner and Wolram 986). FABRICATION AGENCY ACADIA 04 DESIGN AGENCY 94

7 β max A B β e 3 e e TCP 6 Side-cutting Fabrication o a Non-orthogonal Snap-it Joint with a 5-axis CNC Router The illustration at the top let shows the main abrication constraint o the side-cutting technique, which is the maximum tool inclination bmax. It is determined by the geometry o the tool and the tool holder. From this angle, we obtain the most obtuse (A) and the most acute angle (B) or the non-orthogonal snap-it joint. The blue line (TCP) shows the tool center point path, generated with our RhinoPython script. Note the automatic height compensation or inclined aces Sandwich Element with Inclined Vertical Connectors The snap-it joint allows or a simple, precise and quick assembly o non-orthogonal connections. There is no dierence between the abrication and assembly o a 90 joint and a 0 joint. This can be exploited or the assembly o corrugated sandwich components Cassette Shear block Direct Cassette Shear block Direct Shear block Direct 8 Prototype or a Snap-it Jointed, Double-layered Corner (90 and 0 old) built rom mm plywood, 5mm spacing. Note the double-snap-it- element, which has a hook or the irst layer and another hook or the second layer. The snap-it joint in the middle is used as a spacer element. This technique can be used or structural improement as well as or the itting o (locked) insulation materials 95 ROBELLER, WEINAND, MAYENCOURT SNAP-FIT JOINTS

8 a. m m m b. m m d. e. 9 Assembly o Multiple Double-layer Components in one Direction (a) and (b) show two possible male (m)/emale () connector conigurations and the resulting insertion directions o the panels. (a) requires spacer elements only on one interior panel, while (b) requires spacers on both interior panels. (c) and (d) show this method applied to an arch prototype. (e) shows additional snap-itted shear block elements or this single-olded structure 0 Physical Prototype o the Single-olded Double-layer Arch. - The prototype was built rom Kerto-Q mm panels and spans oer.5m APPLICATIONS AND FEATURES: 5-AXIS FABRICATION OF NON-ORTHOGONAL JOINTS As one o the most important eatures, 5-axis cutting allows us to abricate the snap-it joint not only at 90, but also or a abrication-constrained range o non-orthogonal joints (Figure 6). Such angular joints can be used or the design o structurally eicient timber olded-plates. In an assembly with multiple components, additional elements can be added to a naked edge where both the exterior and the interior layer are itted with either male or emale connectors (Figure 9) and (Figure 0). This assembly constraint results rom the act that panels with snap-it joints must be inserted along a ector that lies on the plane o the male part o the connection. DOUBLE-LAYER STRUCTURES As mentioned in our comparison with screwed joints, the combination o snap-it joints and tab-and-slot-joints allows or the edgewise jointing o thin LVL panels (or example Kerto-Q,, 3 mm). We can thereore, instead o a single layer o thick panels, design double-layer structures, where we achiee a large static height at a low sel-weight and take adantage o the compressie and tensile strength o the panels at the top and bottom (Figure ). Another adantage o such double-layer structures is the preab-integration o insulation materials, which are protected rom mechanical damage inside the components during transportation. Finally, this assembly technique can also be applied to olded plate shells corrugated in two directions, allowing or the design o doubly-cured and ree-orm shell structures (Trautz, Martin et al. 009; Falk, Andreas et al. 0). In such structures, multiple edges must be jointed simultaneously, which has, depending on the chosen assembly technique (Figure 9a) or (Figure 9b), certain implications on the geometry o the olded plate shell (Figure ). This prototype also demonstrates a possible combination o snap-it joints with doetail joints on the exterior panels o a old. While perorming similarly to the tab-and-slot joints, the doetails do not require a protrusion on the panel with emale connectors. A particular structural adantage o the snap-it and tab-and-slot joints on such double-layer assemblies is the possibility to establish a direct edgewise connection between all our layers o a old (Figure 8). With longer snap-it connectors, the interior panels o a old can irst cross through each other like a mortise-and-tenon joint, and then snap into the exterior layers aboe. The interior panels now double-lock the exterior panels in place, and the two additional line-joints per edge improe the oerall stiness and rigidity o the connection. CONCLUSIONS AND OUTLOOK This irst study on a snap-it connection or structural wood panels clearly shows the potential o its application. Numerical parameterized geometry and CNC cutting technology enable the production o the joint. Few restrictions on the design need to be taken into account due to the wood s material properties. The behaior o the irst application on a box-beam o the beam was satisactory but showed that improements o the connection are still possible. FABRICATION AGENCY ACADIA 04 DESIGN AGENCY 96

9 a. b. a. a. b. b. a. b. F F F F FF F F F F F F F F F4 upper F4 upper F4 upper d. e. 8 9 d. e d. e. Assembly o a Double-layer Folded Plate Shell (a.) Two edges o one panel (F4lower) simultaneously connect panels on two layers (Flower / Fupper) and (lower / upper) ia their our edges. The direction may be chosen within the plane o (F4). (b) shows the insertion o the upper panel (F4upper) with emale connectors. Here, the 3 line 9 o insertion must lie on all planes the panel will be attached to (F and ). For only two edges, a solution will always be ound at the intersection line o the two planes. This constraint does not apply to the technique shown in (Figure 9b). (c) shows the interior iew o the double layer assembly. Joints will only be isible on the mountain olds. The drawings (d) and (e) show two possible old patterns which are corrugated in two directions and their order o assembly. The illustrated Herringbone (d) and diamond patterns (e) require only a small deiation () o 4the snap-it 8 joints 4 insertion direction 4 rom 8 a line 4 perpendicular to the edge to be jointed. 8 9 Finally, the construct-ability o more complex joint geometries was shown on the last part, taking adantage o the ability to join thin panels, which was used or the jointing o double-layer prototypes. The possibility o disassembling the parts at any time and transporting them unassembled opens a wide range o uture applications such as temporary or modular structures. ACKNOWLEDGEMENTS We would like to thank Andrea Stitic and Stéphane Nicolas Roche or the discussions and the conduction o the three-point lexural tests on the box beam specimen, as well as Jouni Hakkarainen and the Metsä Group or the supply o inormation and materials. REFERENCES BASF The Chemical Company. 00. Snap-it Design Manual. BASF Corporation, Engineering Plastics, Florham Park, New Jersey. Bayer MaterialScience LLC Snap-it Joints or Plastics A Design Guide. Bayer Polycarbonates Business Unit, Pittsburgh, Pennsylania. Buri, Hans Ulrich. 00. Origami Folded Plate Structures. EPFL Doctoral Thesis No. 44, École polytechnique édérale de Lausanne. Deutsches Institut ür Bautechnik. 0. Allgemeine bauausichtliche Zulassung Kerto-Q Z Paragraph 4. and Attachment No, Table Falk, Andreas et al. 0. Form Exploration o Folded Plate Timber Structures based on Perormance Criteria. Taller, Longer, Lighter: 0 meeting growing demand with limited resources : IABSE-IASS 3 9 Symposium 0. London: Hemming Group Ltd., 0. Graubner, Wolram Holzerbindungen,Gegenüberstellung 3 6 on Holzerbindungen Holz in Holz und mit Metallteilen. Deutsche Verlags-Anstalt Stuttgart, 9. Hahn, Benjamin Analyse und Beschreibung eines raumlichen Tragwerks aus Massiholzplatten. EPFL Master Thesis, École polytechnique édérale de Lausanne. IPCC. 04. Intergoernmental Panel on Climate Change Kollar, Lajos Some Problems o Static Analysis o Folded Plate Structures. Periodica Polytechnica Ser. Ciil Eng. 3: 6 0. La Magna, Riccardo et al. 03. From Nature to Fabrication: Biomimetic Design Principles or the Production o Complex Spatial Structures. International Journal o Spatial Structures 8 (): 40. Luscher, Anthony An Inestigation Into the Perormance o Cantileer Hook-type Integral Attachment Features. Department o Mechanical Engineering, Rensselaer Polytechnic Institute. ICD/ITKE. 04. LaGa Exhibition Hall. de/?p=3. Messler Jr., Robert W. (006). Integral Mechanical Attachment: A. Resurgence o the Oldest Method o Joining. Butterworth Heinemann. MetsäWood. 04. Kerto-ripa. products. 3 d. e ROBELLER, WEINAND, MAYENCOURT SNAP-FIT JOINTS

10 d. d. e. e. d. d. e. d. e Robeller, Christopher et al. (04). Design and Fabrication o Robotmanuactured Joints or a Cured-olded Thin-shell Structure made rom CLT. Robotic Fabrication in Architecture, Art and Design 04. Schindler, Christoph Ein architektonisches Periodisierungsmodell anhand ertigungstechnischer Kriterien, dargestellt am Beispiel des Holzbaus. Dissertation. ETH Nr Technical Research Center Finland VTT Certiicate No 84/03, reised. Trautz, Martin et al The Application o Folded Plate Principles on Spatial Structures with Regular, Irregular and Free-orm Geometries. Presented at the IASS Eolution and Trends in Design, Analysis and Construction o Shell and Spatial Structures, Valencia. IMAGE CREDITS Figure. With permission. From Luscher, A. (995), An Inestigation o Cantileer Hook Type Integral Attachment Features, Department o Mechanical Engineering, Rensselaer Polytechnic Institute Figure -. Image credit to Authors (04). CHRISTOPHER ROBELLER receied his Proessional Diploma in Architecture with Distinction rom London Metropolitan Uniersity. He has worked as a Research Associate or the Institute or Computational Design (ICD) at the Uniersity o Stuttgart and is currently working as a PhD Candidate at the Timber Construction Laboratory IBOIS at the Swiss Federal Institute o Technology in Lausanne (EPFL). His research at the intersection o architecture, ciil engineering and digital geometry processing is ocused on the deelopment o integrated, machine-abricated jointing techniques or timber panel structures. PAUL MAYENCOURT receied his Bachelor Degree rom the Swiss Federal Institute o Technology in Lausanne (EPFL) and his Master Degree in Structural and Geotechnical Engineering rom the Swiss Federal Institute o Technology in Zurich in 03 (ETHZ). He worked at the Timber Construction Laboratory IBOIS at EPFL as a research assistant and is currently working as a bridge engineer in Zurich. YVES WEINAND, born 963, Belgian, architect and engineer. Ater an architecture diploma at the Institut supérieur d architecture Saint-Luc, Liège/Belgium, he worked as an architect in Helsinki, Finland; New York; and Brussels, Belgium. Ciil engineering studies at the Swiss Federal Institute o Technology in Lausanne (EPFL) were ollowed by a PhD-thesis Sichtbare Spannungen at the RWTH Aachen Uniersity, Germany. Owner since 996 o the Bureau d Etudes Weinand, in Liège, Belgium, he was proessor at the Institute o Structures at the Faculty o Architecture at Graz Uniersity o Technology in Austria, beore joining the EPFL as a proessor and head o the Timber Construction Laboratory IBOIS in 004. FABRICATION AGENCY ACADIA 04 DESIGN AGENCY 98