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TRANSPARENCY, MINIMALISM AND COMPLEX GEOMETRY IN GLASS

Hugh DuttonArchitect

HDAFrance

This paper will review three recent popular architectural themes:Transparency, minimalism and complex geometry as they arise in severalrecent projects in our HDA office in Paris. Concepts in cable structureengineering are discussed in the context of the continuing search forephemeral structure. Projects involving complex surfaces using curvedglass are presented with discussion on the industrys response to this newchallenge. The computer is ever-present throughout the process, from thegeneration of complex surfaces, to its use in engineering analysis as wellas in the sophistication of industrial techniques.

Design and Fabrication Process

The design begins with the architectural concept or idea. In our owndesign office the process begins by developing a corresponding technicalconcept that is compatible with this initial architectural concept and triesto express the architectural idea in its very own technical resolution.

Product research, engineering and analysis follows to optimise structuraland technical performance. Detailed drawings and specifications are thenproduced to define the work package to be realised by the contractor.

Computers are an essential tool in this process. To begin, they are usedfor graphic representations and definition of the geometry of the project.Recent software packages enable architects to conceive and representcomplex shapes and surfaces. For engineering, computers can beexploited non-linear and finite element analysis of problems that were notpreviously solvable with traditional methods. CAD software can be usedfor complex geometry previously unmanageable by hand. Recentsoftware also permits simulation of thermal performance of facades aswell as scientific representation of solar exposure and aerodynamicsimulations. These highly useful and practical electronic tools howevershould never be considered as an alternative to the designers intuitiveunderstanding of the design. Indeed the risk of losing control of theprocess is of critical importance in a world of ever increasing dependenceon the machine.

In the future we remain hopeful however that the use of electronic datacan allow a smoother transition between the designer and the fabricationprocess as more and more of the industrys tools use numerically-operated systems.

Structure and glass components are integrated as far as possible tooptimise materials and transparency. At the conception phases of theproject development the critical issues of structural performance, safety,user well-being, energy conservation, durability, and maintenance are

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integrated into the design. Work package specifications are developed todefine clear and realisable guidelines for the quality realisation of thework and specify particular quality control procedures for criticalcomponents or fabrication procedures.

TRANSPARENCY

Transparency has always been an important concept in Modernarchitecture with the notably famous Bauhaus transparent corner byGropius as a classic and highly publicised example of this ambition.

Fig.1

Transparency was the principle theme of architect Adrien Fainsilber inour work on the La Villette Bioclimatic Greenhouses project with PeterRice at RFR in the early eighties. Rice proposed the use of the first cabletrusses as wind bracing for glass to remove visually heavy bendingstructures from the facade plane. Specific articulated bolts weredeveloped to adapt to the deflection movements of the cables. Otherprojects at RFR continued to develop the idea of cable structures usingthe articulated bolt system and amongst these the 50 Avenue Montaigne24m high by 16m wide suspended glass plane in 1993 is a significantexample.

Fig.1 Bauhaus

Architect : Walter Gropius

Fig.2

Fig.2 Bioclimatic Facade

Architect : Adrien FainsilberEngineer/ Facade Concultants :RFR / Contractor : CFEM (nowEiffel

Fig.3

The technology of transparency involves exploiting the structuralcapacity of glass through tempering as well as inventive engineering forcable structures using non-linear analysis methods. Both designers andthe industry are adapting themselves to these new techniques.

Fig.3 Avenue Montaigne

Architect : Epstein GlaimanVidal/ Contractor : Eiffel

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The recent Cartier Foundation building in Paris by Jean Nouvel includeslarge extensions of the glass facade beyond the building volume whosesole raison detre is visual effect as they serve no structural purpose.

Fig.4

Fig.4 La Fondation Cartier

Architect : Jean Nouvel/Engineers : Ove Arup

The transparent image is finding a new justification in recent years as apotential demonstration of energy conservation through the use of doubleskins. They are employed to exploit solar radiation created in the voidbetween the two glass skins resulting from the greenhouse effect. Thetechniques involve using a void between two glass skins as a buffer zoneto decrease heat loss. It is also possible to trap energy that can be drawnoff to contribute to lowering heating demands. In the hot seasons the voidis used as a location for shading devices that are protected from pollutionand wind damage. The stack effect of air in the void is permits heat to bedrawn away from the internal glass surface thereby reducing coolingloads for the building air conditioning systems.

Fig.5a/b

Fig.5a & 5b

Dusseldorfer Stadttor

Architects : Petzinka Pink &Partners

The recent competition-winning design by architect Bernard Tschumi forthe New York African Arts Museum involves a giant clear glass boxenvelope around the museum itself. In this case the glass box is alsojustified as an energy recuperation device.

Fig.6

Fig.6 African Arts Museum

Architect : Bernard Tschumi/Engineers : Ove Arup/ FacadeConsultants : Israel Berger

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Fig.7

Architectural design concept: Architect Paul Andreu established a cleararchitectural concept of a transparent hemispherical shell that was to givethe users of the museum the feeling of being in a maritime environmentwhilst sheltered from the elements and also to create a strong visualsymbol for the city at the port gates to the harbour.

Technical concept The shell structure theory combining a lamellalozenge geometry with the necessary diagonal bracing for triangulationalso used for glazing support. Solar shading is provided by perforatedsheeting integrated into the laminate of the bolted glass panels withvarying degrees of transparency as a response to the solar exposure of thedome.

A single layer structure is achievable with this lattice shell structureconcept: triangulate a four sided planar lozenge. The dome geometry,again in comparison to the geodesic, is a Lamella geometry of everdiminishing lozenges from equator to pole instead of the varyingtriangles of the geodesic. This geometry was selected for the pleasingspiralling effect achieved by the crossing over of the continuousstructural members. The glass is fixed to the dome structure around theperimeter of each structural lozenge as well as the central cross-overpoint of the tension X bracing. The dimensions of each structurallozenge, beginning at the equator, were determined by a maximum ofwhat could be achieved with four pieces of glass, with their internalcorners positioned on the tension bracing cross-over point.

Fig.8

The dome glass is a sandwich of tempered and heat strengthened glasswith perforated metal sheet between them. The perforated holes varyingsize according to the amount of solar protection required. A pattern ofcontours representing the sun energy projected onto the dome throughouta year was plotted on the surface. Each contour was made with an everincreasing amount and size of penetrations. The areas of the domereceiving most radiation, beginning with the summit have only 10%holes, the next with 20%, then 40%, 60% and clear glass on the northface and the equator, thereby optimising protection and transparency. Theproduct employed was based on a product of Asahi glass used on earlierprojects under the trade name Lamimetal.

Fig.7 Osaka Maritime Museumdome

Architect : Paul Andreu/Engineers : Tohata & Ove Arup/Technical Design Assistance :HDA

Fig.8 Osaka Maritime Museumdome

( Internal View )

Fig.9

Fig.9 Osaka Maritime Museumdome

(Computer-generated domecontours by HDA)

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Each lozenge of four glass panels is individually fixed to the dome,independently of the adjacent lozenges, such that they behave like scaleson a fish capable of adapting to the movements of the steel shell inearthquake conditions, thermal expansion, deflection in wind or any otherdisplacement of the steel. The panels are suspended at two upper pointswith all other attachments capable of lateral movements using hingedconnections. The bolt attachment is the articulated countersunk boltdeveloped at La Villette .

Fig.10

Fig.10 Osaka Maritime Museumdome

( by Day & Night )

MINIMALISM

Minimalism, with economy and simplicity too have long been importantthemes in modern architecture. The architectural expression is found inthe simple quality of the materials employed, presented with minimaldetailing. These qualities are found historically in Japanese architecture,and a notable example is the traditional Shoji screen walls that createsubtle light filters and space dividers.

Fig.11

Fig.11 Traditional JapaneseShoji Screen

( The From of JapaneseWindows- Nakamura Ayako )

Many recent projects return to this simplicity and often it is the simpleglass box with minimally detailed glass such as the recent PorteAudermer civic centre by Jakob and Macfarlane which uses simplealternation of laminate and clear glass, that displays timeless elegance.

Fig.12 Fig.12 Porte Auderner(Orange Box )

Architects : Jakob & Macfarlane

The cable net concept is a recent development of transparent point-fixedglass systems in this similar minimal tendency. As an alternative to theexpression of highly visible spatial cable structures this concept wasdeveloped Helmut Jahn and Jorg Schlaich at the Kimpinsky Hotel inMunich with stunning recent developments by Jan Stormer and WernerSobek at the Bremen University entrance hall or Vignoly and DewhurstMacfarlane at the Kimmel Centre in Philadelphia. Wind loads areresisted by pure tension in simple planar nets of highly stressed cablesworking in a similar way to a tennis racket. The cable wind bracingstructures in these projects have little more visual presence than thewaterproofing joints between the glass panels.

Fig.13

Fig.13 Kimpinsky Hotel

Architects : Helmut Jahn/Engineer : Jorg Schlaich

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Singapore Changi International Airport Terminal 3 Facades

Fig.14

Architectural Concept: The architects PWD Airport DevelopmentDivision in collaboration with SOM proposal for the main building of thenew terminal is a simple rectangular volume whose roof and walls are assimple and ephemeral as possible with a capacity to adapt themselvessubtly to varying light conditions.

Technical conceptMinimal structural support systems using tension components tominimise visible structure, either as a cable net or as bowstring assistedtraditional mullions. A homogeneous grid of glazing framing is achievedin both cases. Solar radiation and glare protection is provided eitherthrough high performance coatings on the glass, fritting or shadinglouvers, whose support is provided by the bowstring tension system.

The cable net design is a hierarchical two way grid of primary cablestensioned between the roof and the concrete slab in the vertical directionand secondary ones tensioned between columns in the horizontaldirection. Visible deflection of the system is a major concern and thehorizontal cables provide assist the vertical ones limiting it to less than1/50th the span. Though the facade is close to 300m long, the cablesystem is conceived in distinct and individual bays each 15 wide and 18mhigh. The cable system is isolated from local support deformations usingsprings at the anchors. Specific adaptations are made for wide dooropenings.

Fig.14 Singapore ChangiInternational Airport T3

Architects : PWD & SOM/Facade Consultants : HDA

The glass panels are heat strengthened laminated glass with solarprotection fritting to reduce glare in a similar approach the Osakamaritime museum discussed above. The glass is clipped to the cable gridat the cable clamps using a specific and individual casting design.

Fig.15

Fig.15 Singapore ChangiInternational Airport T3

( HDA Cable Clamp design )

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The other facades of the building are double-glazed in response to thelocal OTTV regulations and consist of a homogeneous grid of rectangulartubes with stiffening tension rods to form bowstring mullions for theprinciple vertical spans. As these spans vary, the rod configuration varies.In-plane bracing is achieved with alternating bays of the facade used asVierendeel ladder frames. Glass panels are fit into unitised frames onadjustable fixings to the steel frame. Each bowstring mullion is in facttwo back to back half Vierendeels with the tubular frame spine workingin compression and the rods in tension.

Fig.16 Fig.16 Singapore ChangiInternational Airport T3

( HDA Vierendeel ladder frames& Frit Glass Configuratiion )

Particular attention is paid to the spreader penetrations at the glass nodes.The tension system is exploited to support the shading louvers.

Fig.17

Fig.17 Singapore ChangiInternational Airport

( HDA Sun-shading device )

This bowstring system is similar to one realised for the recently openedInchon International Airport in Seoul Korea as far as detailing isconcerned.

Fig.18

Fig.17 Singapore ChangiInternational Airport

( HDA Bowstring mullionsystem )

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Fig.19

Fig.19 Inchon InternationalAirport

Architects : KACI with KurtFentress/ Facade Design : HDA

COMPLEX GEOMETRY

Complex geometry is another architectural theme of considerable recentpopularity. Architecture has always been particularly attracted by thebeauty of complex and curved shapes. A personal historical favourite inthe glass field is the Bicton palm house where the delicate glass skincontributes to the structural stability through shell action.

Fig.20

Fig.20 Bicton Palm House

Architects : H & D.Bailey

In recent years, the computer has enabled architects to manage themassive information required to define and represent complex shapeswith examples such as the outstanding Guggenheim Museum in Bilbaoby Gehry or the British Museum of Norman Foster with Buro Happold.

Fig.21

Fig.21 Bilbao Museum

Architect : Frank O Gehry

Fig.22

Fig.22 British Museum

Architect : Norman Foster

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Hammerson Lattice Grid Atrium Roof

Architectural concept:The architect Brauns intention was a delicate Cubist interplay,overlapping and interlocking of surfaces and spaces.

Technical concept was the determination of a geometry that responded tothe building surface planes and inclined entry direction creating atriangulated surface that could then exploit shell action by transformingitself into a complex surface where structural performance was required.

The atrium enters the building on a diagonal axis beginning with a streetopening then passing under the main floor plate to terminate in acourtyard. The lattice roof structure consists of a grid of steel tubeswhose plan directions follow the facade planes of the courtyard with adiagonal stiffening cable in the diagonal direction. This triangulatedlattice grid is transformed into a three dimensional shape where it is opento the sky and requires structural capacity for snow loads and large spans.In the courtyard, the free edge is supported by a tied arch, causing thelattice to be warped into an anticlastic shape that is then refined bystructural analysis form-finding..

Fig.23

A laminated glass covering is fitted to the lattice in triangular panes, sothat the rigid planes of glass could follow the three dimensional surface.In the cases of exposed roof area, the panels are in insulated glass, and inprotected area like the ceiling it is a translucent laminate.

Fig.23 Hammerson LatticeGrid Atrium Roof

Architect : F. Braun

(HDA Atrium roof study model )

Fig.24

Fig.24 Hammerson LatticeGrid Atrium Roof

Architect : F. Braun

( Cleints Internal Perspective )

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Fig.25

Fig.25 Hammerson LatticeGrid Atrium Roof

Architect : F. Braun

(HDA Structural/ perfomanceanalysis of lattice grid )

Drugstore Publicis

Fig.26

Architectural Concept: Fluid movement of transparent skins of glass infront of an existing 70s mirror glass facade, giving the building a newimage through a complex series of curved glass screens that revitalise theexisting facade.

Technical concept Making it possible through a rigorous mathematicaldefinition of the geometry of the glass/support interface. The supportingstructure is in symbiosis with the glass surfaces and designed tocompatible curves that are then exploited for their structural capacity.Curved glass too is exploited for structural capacity of its shape.

Fig.26 Drugstore Publicis

Architect : Building Inc. LAFacade Design Consultants &Engineers : HDA

Fig. 27

Fig.27 Drugstore Publicis

( HDA Theoretical Geometryanalysis of Curved Glass Form )

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A primary structure of sinuous tubes are fixed to the columns of theexisting building so as not to interfere with the existing facade. The glassis fixed to extruded stainless steel profiles with structural silicone. Theglass itself is curved to developable and mathematically definable shapessuch as cylinders, cones and simple tores. The project depends on theprecise dimensional control of structural design. The architectural limitfor this project is defined by the industrial limit of curved glass and wehope to exploit new developments in the glass industry where thetraditional and time consuming artisanal method of curving glass to hand-made moulds might be replaced with computer controlled alternatives.

Fig. 28

Fig.28 Drugstore Publicis

( HDA Primary & Secondarystructures for supporting glass )

Fig. 29

INDUSTRYS RESPONSE

Development in laminated glass, tempered glass, curving glass,translucent and coloured interlayers as reviewed by other speakers in thisconference are the response of the industry to these architecturalintentions.

It is the responsibility of the designers to understand the industry andwhat the industrys capabilities and limitations are. It is also theindustrys responsibility to respond to the architectural ambitions and bydeveloping new techniques that make the architectural ambition feasible.

Fig.29 Drugstore Publicis

( HDA on-site Glass Mock-up )