Digital Fabrication: Manufacturing Architecture in the Information Age

Section 4 Modeling and Fabrication

Branko Kolarevic University of Pennsylvania, USA

Abstract This paper addresses the recent digital technological advances in design and fabrication and the unprecedented opportunities they created for architectural design and production practices. It investigates the implications of new digital design and fabrication processes enabled by the use of rapid prototyping (RP) and computer-aided manufacturing (CAM) technologies, which offer the production of small-scale models and full-scale building components directly from 3D digital models. It also addresses the development of repetitive non-standardized building systems through digitally controlled variation and serial differentiation, i.e. mass-customization, in contrast to the industrial-age para- digms of prefabrication and mass production. The paper also examines the implications of the recent developments in the architectural application of the latest digital design and fabrication technologies, which offer alternatives to the established understandings of architectural design and production processes and their material and economic constraints. Such critical examination should lead to a revised understanding of the historic relationship between architecture and its means of production. Keywords Digital Fabrication, Computer-Aided Manufacturing, Digital Construction

268 2001: ACADIA Digital Fabrication: Manufacturing Architecture in Branko Kolarevic the Information Age 1 Introduction 2 Fabrication “Integrating computer-aided design with computer-aided The continuous, highly curvilinear surfaces that fabrication and construction [...] fundamentally redefines feature prominently in contemporary architecture the relationship between designing and producing. It elimi- brought to the front the question of how to work nates many geometric constraints imposed by traditional out the spatial and tectonic ramifications of such drawing and production processes—making complex curved non-Euclidean forms. For many architects, shapes much easier to handle, for example, and reducing trained in the certainties of the Euclidean geom- dependence on standard, mass-produced components. [...] It bridges the gap between designing and producing that opened etry, it was the issue of constructability that brought up when designers began to make drawings.” into question the credibility of spatial complexi- ties introduced by the new “digital” avantgarde. - W. Mitchell and M. McCullough in Digital Design Media However, the fact that the topological geometries The Information Age, like the Industrial Age be- are precisely described as NURBS (Non-Uni- fore it, is challenging not only how we design form Rational B-Splines) and thus buildings, but also how we manufacture and con- computationally possible also means that their struct them. In the conceptual realm computa- construction is perfectly attainable by means of tional, digital architectures of topological, non- computer numerically controlled (CNC) fabrica- Euclidean geometric space, kinetic and dynamic tion processes, such as cutting, subtractive, addi- systems, and genetic algorithms, are supplanting tive, and formative fabrication, which are described technological architectures. Digitally driven de- in more detail in this section. sign processes characterized by dynamic, open- ended and unpredictable but consistent transfor- 2.1 2D Fabrication mations of three-dimensional structures are giv- CNC cutting, or 2D fabrication, is the most com- ing rise to new architectonic possibilities monly used fabrication technique. Various cut- (Kolarevic 2000). The generative and creative ting technologies, such as plasma-arc, laser-beam, potential of digital media, together with manu- or water-jet, involve two-axis motion of the sheet facturing advances already attained in automotive material relative to the cutting head and are imple- and airplane industries, is opening up new dimen- mented as a moving cutting head, a moving bed, sions in architectural design. The implications are or a combination of the two. In plasma-arc cut- vast, as “architecture is recasting itself, becoming ting an electric arc is passed through a compressed in part an experimental investigation of topologi- gas jet in the cutting nozzle, heating the gas into cal geometries, partly a computational orchestra- plasma with a very high temperature (25,000F), tion of robotic material production and partly a which converts back into gas as it passes the heat generative, kinematic sculpting of space,” as ob- to the cutting zone (Figure 1). In water-jets, as served by Peter Zellner in “Hybrid Space” (1999). their name suggests, a jet of highly pressurized water is mixed with solid abrasive particles and is It was only within the last few years that the ad- forced through a tiny nozzle in a highly focused vances in computer-aided design (CAD) and com- stream, causing the rapid erosion of the material puter-aided manufacturing (CAM) technologies in its path and producing very clean and accurate have started to have an impact on building design cuts (Figure 2). Laser-cutters use a high-intensity and construction practices. They opened up new focused beam of infrared light in combination opportunities by allowing production and con- with a jet of highly pressurized gas (carbon diox- struction of very complex forms that were until ide) to melt or burn the material that is being cut. recently very difficult and expensive to design, There are, however, large differences between produce, and assemble using traditional construc- these technologies in the kinds of materials or tion technologies. The consequences will be pro- maximum thicknesses that could be cut. While found, as new digitally driven processes of design, laser-cutters can cut only materials that can ab- fabrication and construction are increasingly chal- sorb light energy; water-jets can cut almost any lenging the historic relationship between archi- material. Laser-cutters can cost-effectively cut tecture and its means of production. material up to 5/8”, while water-jets can cut much

2001: ACADIA 269 Section 4 Modeling and Fabrication thicker materials, for example, up to 15” thick ti- vals, are produced automatically by modeling soft- tanium. ware from a given form and can be used directly The production strategies used in 2D fabrication to articulate structural components of the build- often include contouring, triangulation (or polygo- ing, as was the case in a number of recently com- nal tessellation), use of ruled, developable surfaces, and pleted projects (Figures 3 and 4). unfolding. They all involve extraction of two-di- Complex, curvilinear surface envelopes are often mensional, planar components from geometrically produced by either triangulation (or some other complex surfaces or solids comprising the planar tessellation) or conversion of double-curved into building’s form. Which of these strategies is used ruled surfaces, generated by linear interpolation depends on what is being defined tectonically: between two curves (Figures 5 and 6). Triangu- structure, envelope, a combination of the two, etc. lated or ruled surfaces are then unfolded into pla- In contouring, a sequence of planar sections, often nar strips, which are laid out in some optimal fash- parallel to each other and placed at regular inter- ion as two-dimensional shapes on a sheet (in a process called nesting), which is then used to cut the corresponding pieces of the sheet material using one of the CNC cutting technologies. For example, Frank Gehry’s office used CATIA software in the Experience Music Project in Seattle to “rationalize” the double-curved surfaces by

Figure 1. Plasma-arc CNC cutting of steel supports for masonry walls in Frank Gehry’s Zollhoff Towers in Dusseldorf, Germany (Rempen 1999).

Figure 3. Structural frames in Frank Gehry’s Experience Music Project in Seattle, produced by contouring.

Figure 2. Aluminum space frame for ABB Architects’ BMW Pavilion is cut directly from digital data using CNC water-jet Figure 4. Structural framework for Bernard Franken’s BMW technology. Pavilion produced by bi-directional contouring.

270 2001: ACADIA Digital Fabrication: Manufacturing Architecture in Branko Kolarevic the Information Age converting them into “rule-developable” surfaces, of excessive curvature as there are limits as to how which were then unfolded and fabricated out of much the sheets of metal could be bent in two flat sheets of metal (Linn 2000). directions; the same technique was used on other The surface data could be also used to directly projects by Gehry (Linn 2000). The analysis pro- generate a wireframe abstraction of the building’s duced a colored image that indicated through vari- structural framework, which could be then pro- ous colors the extent of the surface curvature (Fig- cessed by the structural analysis software to gen- ure 7). erate the precise definition of all structural mem- 2.2 Subtractive Fabrication bers. In Gehry’s Bilbao project the contractor used Subtractive fabrication involves removal of speci- a software program from Germany called Bocad fied volume of material from solids (hence the to automatically generate a comprehensive digi- name) using multi-axis milling. In CNC (Com- tal model of the structural steel, including the puter Numerical Control) milling a dedicated brace-framed and secondary steel structures for computer system performs the basic controlling the museum (Stephens 1999). More importantly, functions over the movement of a machine tool that same program was used to automatically pro- using a set of coded instructions (McMahon and duce the fabrication drawings or CNC data to Browne 1998). precisely cut and pre-assemble the various com- Early experiments in using CNC milling ma- ponents (LeCuyer 1997). chines to produce architectural models were car- The surface model could be also used to design, ried out in early 1970s in the United Kingdom. analyze, and fabricate the envelope components Large architectural firms in the United States, from sheet material. In designing the such as Skidmore Owens Merrill’s office in Chi- Guggenheim Museum in Bilbao, Gehry’s office cago, have used CNC milling machines and laser used the Gaussian analysis to determine the areas cutters extensively in the production of architectural models and studies of construction assem- blies. Automated milling machines were used in late 1980s and 1990s to produce construction components (Mitchell and McCullough 1995), such as stones for New York’s Cathedral of Saint John the Divine and columns for Sagrada Familia Church in Barcelona. Frank Gehry’s project for Disney Concert Hall in Los Angeles represents the first comprehensive use of CAD/CAM to pro-

Figure 5. Triangulated complex surfaces in Frank Gehry’s DG Bank Building in Parizer Platz, Berlin, Germany.

Figure 6. Use of ruled surfaces in the Water Pavilion by NOX in the Netherlands. Figure 7. Gaussian analysis of the surface curvature.

2001: ACADIA 271 Section 4 Modeling and Fabrication duce architectural stonework: for the initial 1:1 2.3 Additive Fabrication scale model the stone panels with double-curved Additive fabrication involved incremental forming geometry were CNC milled in Italy and then by adding material in a layer-by-layer fashion, in shipped to Los Angeles, where they were posi- a process converse of milling. It is often referred tioned and fixed in place on steel frames (Mitchell to as layered manufacturing, solid freeform fabrica- and McCullough 1995). Gehry’s office used this tion, rapid prototyping, or desktop manufacturing. All same fabrication technique for the stone cladding additive fabrication technologies share the same in the Bilbao project. principle in that the digital (solid) model is sliced into two-dimensional layers. The information of The CNC milling has recently been applied in each layer is then transferred to the processing new ways in building industry – to produce the head of the manufacturing machine and the physi- formwork (molds) for the off-site and on-site cast- cal product is incrementally generated in a layer- ing of concrete elements with double-curved ge- by-layer fashion (Jacobs 1992). ometry, as in one of the Gehry’s office buildings in Dusseldorf, Germany, and for the production Since the first commercial system based on of the laminated glass panels with complex curvi- stereolithography was introduced by 3D Systems linear surfaces, as in Gehry’s Conde Nast Cafete- in 1988, a number of competing technologies now ria project and Bernard Franken’s BMW pavilion exist on the market, utilizing a variety of materi- (Figure 8). als and a range of curing processes based on light, heat, or chemicals (Kochan 1993, Chua and In Gehry’s project in Dusseldorf (Zollhof tow- Leong 1997). Stereolithography (SLA) is based on ers) the undulated forms of the load-bearing ex- liquid polymers that solidify when exposed to la- ternal wall panels, made of reinforced concrete, ser light. In Selective Laser Sintering (SLS) laser were produced using blocks of lightweight poly- beam melts a layer by layer of metal powder to styrene (Styrofoam), which were shaped in CATIA create solid objects. In 3D Printing (3DP) layers and CNC milled (Figure 9) to produce 355 dif- of ceramic powder are glued to form objects. ferent curved molds that became the forms for Sheets of material (paper, plastic), either precut the casting of the concrete (Rempen 1999, Slessor or on a roll, are glued (laminated) together and 2000). laser cut in the Laminated Object Manufacture (LOM) process. In Fused Deposition Modeling (FDM) each cross section is produced by melting

Figure 9. Milling of Styrofoam molds for the casting of rein- Figure 8. Milling of molds for the production of double-curved forced concrete panels for Gehry’s Zollhof Towers in Dusseldorf, acrylic glass panels for Bernard Franken’s BMW pavilion. Germany (Rempen 1999).

272 2001: ACADIA Digital Fabrication: Manufacturing Architecture in Branko Kolarevic the Information Age a plastic filament that solidifies upon cooling. tion pavilions designed by Bernhard Franken Multi-jet manufacture (MJM) uses a modified (ABB Architekten) for BMW. printing head to deposit melted thermoplastic/ 2.5 Assembly wax material in very thin layers, one layer at a After the components are digitally fabricated, their time, to create three-dimensional solids. assembly on site can be augmented with digital Because of the limited size of the objects that could technology. Digital three-dimensional models can be produced, costly equipment, and lengthy pro- be used to determine the location of each com- duction times, the additive fabrication processes ponent, to move each component to its location, have a rather limited application in building de- and finally, to fix each component in its proper sign and production. In design they are mainly place. used for the fabrication of (massing) models with Traditionally, builders took dimensions and co- complex, curvilinear geometries (Novitski 2000). ordinates from paper drawings and used tape In construction, they are used to produce com- measures, plumb-bobs, and other devices to lo- ponents in series, such as steel elements in light cate the building components on site. New digi- truss structures, by creating patterns that are then tally-driven technologies, such as electronic survey- used in investment casting (Figure 10). Recently, ing and laser positioning, are increasingly being used however, several experimental techniques based on construction sites around the world to pre- on sprayed concrete were introduced to manu- cisely determine the location of building compo- facture large-scale building components directly nents. For example, as described by Annette from digital data (Khoshnevis 1998). LeCuyer (1997), Frank Gehry’s Guggenheim 2.4 Formative Fabrication Museum in Bilbao “was built without any tape In formative fabrication mechanical forces, restrict- measures. During fabrication, each structural ing forms, heat, or steam are applied on a mate- component was bar coded and marked with the rial so as to form it into the desired shape through nodes of intersection with adjacent layers of struc- reshaping or deformation, which can be axially ture. On site bar codes were swiped to reveal the or surface constrained. For example, the reshaped coordinates of each piece in the CATIA model. material may be deformed permanently by such Laser surveying equipment linked to CATIA en- processes as stressing metal past the elastic limit, abled each piece to be precisely placed in its posi- heating metal then bending it while it is in a soft- tion as defined by the computer model.” Similar ened state, steam-bending boards, etc. Double- processes were used on Gehry’s project in Seattle curved, compound surfaces can be approximated (Figure 11). As LeCuyer notes in her article, this by arrays of height-adjustable, numerically-con- processes are common practice in the aerospace trolled pins, which could be used for the produc- industry, but relatively new to building. tion of molded glass and plastic sheets and for curved stamped metal. Plane curves can be fabricated by numerically-controlled bending of thin rods, tubes, or strips of elastic material, such as steel or wood, as was done for one of the exhibi-

Figure 10. Trypiramid, a fabricator in New York, used rapid Figure 11. Global Positioning System (GPS) technology was used prototyping to manufacture truss elements for Polshek’s Rose Cen- on Gehry’s Experience Music Project in Seattle to verify the loca- ter for Earth and Sciences in New York. tion of components (Linn 2000).

2001: ACADIA 273 Section 4 Modeling and Fabrication In Japan, a number of robotic devices for moving digital data is increasingly passed directly from and fixing of components was developed, such as an architect to a fabricator, so will the building Shimizu’s Mighty Jack for heavy steel beam posi- design and construction processes become more tioning, Kajima’s Reinforcing Bar Arranging Ro- efficient. By some estimates, there is a potential bot, Obayashi-Gumi’s Concrete Placer for pouring for building construction to become 28–40 per- concrete into forms, Takenaka’s Self-Climbing In- cent more efficient through better (digital) infor- spection Machine, Taisei’s Pillar Coating Robot for mation and coordination (Cramer 2000). But for painting, and Shimizu’s Insulation Spray Robot. that process to begin, the AEC legal framework, 3 Implications in which the drawings establish the grounds of The digital design and production techniques liability, would have to change. In other words, based on CAD/CAM technologies were widely the 19th century AEC practices would have to adopted over the past two decades in many fields, change for architects to work directly with fabri- such as product design, automotive, aerospace and cators, i.e., subcontractors; this shipbuilding industries. The impact was profound “disintermediation” (Cramer 2000) should bring – there was a complete reinvention of how prod- new efficiencies. As observed by James Cramer, ucts in those respective industries were designed Chairman/CEO of Greenway Consulting, “de- and made. Boeing 777, “the first 100% digitally signers and contractors will no longer be the cus- designed aircraft,” is probably one of the best- todians of traditional assets but the creators of new known examples. value in a new industry.” According to Cramer, architects will find themselves “moving from lin- While the CAD/CAM technological advances and ear to non-linear changes – from information that the resulting changes in design and production is shared by teams, rather than individuals, and techniques had an enormous impact on other in- communication that is continuous, rather than dustries, there has yet to be a similarly significant formal and fragmented.” and industry-wide impact in the world of building design and construction. The opportunities 3.1 New Materiality As new digital processes of conception and pro- for the architecture, engineering, and construc- duction begin to permeate building design and tion (AEC) industries are there and the benefits production, there is an increasing interest in were already manifested in related fields. “new” materials, well known in other production By integrating design, analysis, manufacture and fields and only recently discovered by architects. assembly of buildings around digital technologies, Much of the interest among architects in new architects, engineers, and builders have the op- materials stems from the new geometric complexi- portunity to reinvent the role of a “master- ties. In dealing with tectonic ramifications of non- builder” and reintegrate the currently separate Euclidean forms a particular challenge is how to disciplines of architecture, engineering and con- avoid the usual translation into structural bays, struction into a relatively seamless digital collabo- often done by contouring, described in the pre- rative enterprise, thus bridging “the gap between vious section. This had lead to a renewed interest designing and producing that opened up when in surface or shell structures, or monocoque or semi- designers began to make drawings,” as observed monocoque constructions in which the skin absorbs by Mitchell and McCullough (1995). all or most of the stresses. The principal idea is to The legal framework within which AEC profes- conflate the structure and the skin into one ele- sionals operate still requires drawings, often tens ment thus creating self-supporting forms that re- of thousands of them for a project of medium size quire no armature. That in turn prompted a search and complexity. As new synergies in architecture, for “new” materials, such as high-temperature engineering, and construction are emerging, the foams, rubbers, plastics, and composites, which need to externalize representations of design, i.e., were until recently rarely used in building indus- produce drawings, is bound to wane. As produc- try. As observed by Giovannini (2000b), “the idea tion of (unnecessary) drawings declines, i.e., as of a structural skin not only implies a new mate-

274 2001: ACADIA Digital Fabrication: Manufacturing Architecture in Branko Kolarevic the Information Age rial, but also geometries, such as curves and folds as to produce 1000 identical ones). Mass- that would enable the continuous skin to act struc- customization, sometimes referred to as system- turally, obviating an independent static system: atic customization, can be defined as mass produc- The skin alone does the heavy lifting.” Thus an tion of individually customized goods and services interesting reciprocal relationship is established (Pine 1993), thus offering a tremendous increase between the new geometries and new materiali- in variety and customization without a corre- ties: new geometries opened up a quest for new sponding increase in costs. It was anticipated as a materials and vice versa. Kolatan and MacDonald’s technological capability in 1970 by Alvin Toffler house addition project in Connecticut nicely il- in Future Shock and delineated (as well as named) lustrates that reciprocity: the building is made of in 1987 by Stan Davis in Future Perfect (Pine 1993). polyurethane foam sprayed over an egg-crate ply- In addition to “mass-customization,” the CNC- wood armature that was CNC-cut, thus forming driven production processes, which afford the fab- a monocoque structure that is structurally self- rication of non-standardized repetitive compo- sufficient without the egg-crate, which will re- nents directly from digital data, have also intro- main captured within the monocoque form (Fig- duced into architectural discourse the new “log- ure 12). ics of seriality,” i.e., the local variation and differ- The implications of the “new” materiality are sig- entiation in series. It is now possible to produce nificant, as noted by Giovannini (2000b), as “new” “series-manufactured, mathematically coherent materiality promises a radical departure from but differentiated objects, as well as elaborate, Modernism’s ideals: precise and relatively cheap one-off components,” “In some ways the search for a material and form according to Peter Zellner (1999), who argues that that unifies structure and skin is a counterrevolu- in the process the “architecture is becoming like tion to Le Corbusier’s Domino House, in which ‘firmware,’ the digital building of software space the master separated structure from skin. The new inscribed in the hardwares of construction.” That conflation is a return to the bearing wall, but one is precisely what Greg Lynn’s “Embryologic with freedoms that Corb never imagined possible. Houses” manifest: “mass-customized” individual Architects could build many more exciting build- house designs produced by differentiation ings on the Statue of Liberty paradigm, but com- achieved through parametric variation in non-lin- plex surfaces with integrated structures promise a ear dynamic processes. quantum leap of engineering elegance and intel- The implications of mass-customization are pro- lectual satisfaction.” found. As Catherine Slessor (1997) observed, “the 3.2 Mass Customization notion that uniqueness is now as economic and The ability to mass-produce irregular building easy to achieve as repetition, challenges the sim- components with the same facility as standard- plifying assumptions of Modernism and suggests ized parts introduced the notion of mass- the potential of a new, post-industrial paradigm customization into building design and production based on the enhanced, creative capabilities of (it is just as easy and cost-effective for a CNC electronics rather than mechanics.” In the Mod- milling machine to produce 1000 unique objects ernist aesthetic, the house was to be considered a manufactured item (“machine for living”), drawing upon the engineering logic for the design to be clarified and reduced to the essential. Mass production of the house would bring the best to a wide market and design would not cater to the elite (Le Corbusier 1931). At the start of the twenty-first century the goal remains, although reinterpreted, with the process inverted. No longer does factory production mean mass pro- Figure 12. Kolatan and Macdonald’s house addition in Connecti- duction of a standard item to fit all purposes, i.e., cut.

2001: ACADIA 275 Section 4 Modeling and Fabrication one size fits all. Instead, we now strive for mass Bibliography customization, bringing the benefits of factory Chua, C. K. and Leong K. F. (1997). Rapid prototyping: production to the creation of a unique compo- principles & applications in manufacturing. New York: Wiley. nent or series of similar elements differentiated through digitally controlled variation (Kvan and Cramer, J. (2000). http://www.greenwayconsulting.com/. Kolarevic 2001). Davis, S. M. (1987). Mass Customizing. In Future Perfect, 138-190. Reading, Massachusetts: Addison-Wesley. 4 Conclusions Giovannini, J. (1997). Fred and Ginger Dance in Prague. The paradigm shifts currently at play in contem- In Architecture 86(2): 52-62. porary architectural design are fundamental and Giovannini, J. (2000a). Experience Music Project. In Ar- inevitable, displacing many of the well-established chitecture 89(8): 78-89. conventions. In a digitally-mediated design, as Giovannini, J. (2000b). Building a Better Blob. In Architec- manifested in Gehry’s buildings and projects of ture 89(9): 126-128. the “digital avantgarde,” the practices of the past Jacobs, P. (1992). Rapid Prototyping and Manufacturing: Ad- suddenly appear irrational. Models of design ca- vanced Rapid Prototyping. Dearborn, Michigan: Society of pable of consistent, continual and dynamic trans- Manufacturing Engineers (SME). formation are replacing the static norms of con- Khoshnevis, B. (1998). Innovative Rapid Prototyping. In Material Technology 13(2), p. 53- 56. ventional processes. The predictable relationships between the design and representations are aban- Kochan, D. (1993). Solid Freeform Manufacturing: Advanced Rapid Prototyping. Amsterdam: Elsevier. doned in favor of computationally generated com- Kolarevic, B. (2000). Digital Architectures. In Proceedings plexities. The topological, curvilinear geometries of the ACADIA 2000 Conference, eds. M. Clayton and G. are produced with the same ease as Euclidean Vasquez. Washington, DC: Catholic University of geometries of planar shapes and cylindrical, America. spherical, or conical forms. Plan no longer “gen- Kvan, T. and B. Kolarevic. (2001). “Rapid Prototyping and erates” the design; sections attain a purely ana- Its Application in Architectural Design. In Automation in lytical role. Grids, repetitions, and symmetries lose Construction (forthcoming). Amsterdam: Elsevier. their past raison d’etre as infinite variability be- Le Corbusier. (1931). Towards a new architecture, tr. F. comes as feasible as modularity and as mass- Etchells, New York : Dover. customization offers alternatives to mass-produc- LeCuyer, A. (1997). Building Bilbao. In Architectural Re- view 102(1210): 43-45. tion. Linn, C. (2000). Creating Sleek Metal Skins for Buildings. As architects find themselves increasingly work- In Architectural Record, October 2000: 173-178. ing across the disciplines of architecture, mate- McMahon, C. and J. Browne. (1998). CADCAM: Principles, rial science, and computer-aided manufacturing, Practice and Manufacturing Management, 2nd ed. Read- the historic relationship between architecture and ing, Massachusetts: Addison-Wesley. its means of production is increasingly being chal- Mitchell, W. and M. McCullough. (1995). Prototyping (Ch. lenged by the emerging digitally driven processes 18). In Digital Design Media, 2nd ed., 417-440. New York, Van Nostrand Reinhold. of design, fabrication and construction. The amal- gamation of what were until recently separate Novitski, B.J. (2000). Scale Models from Thin Air. In Ar- chitecture Week, 2 August 2000. (Online at http:// enterprises has already transformed other indus- www.architectureweek.com/2000/0802/tools_1-1.html) tries such as aerospace, automotive, and ship Pine, B. J. (1993). Mass Customization: The New Frontier in building, but there has yet to be a similarly sig- Business Competition. Boston: Harvard Business School nificant and industry-wide impact in the world of Press. building design and construction. That change, Rempen, T. (1999). Frank O. Gehry: der Neue Zollhof however, has already started, and is inevitable and Düsseldorf. Essen, Germany: Bottrop. unavoidable. Rotheroe, K. C. (2000). Manufacturing Freeform Archi- tecture. In Architecture Week, 18 October 2000. (Online at http://www.architectureweek.com/2000/1018/tools_2- 1.html) Russell, J. S. (2000). The Experience Music Project. In Ar- chitectural Record, August 2000: 126-137.

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