Space odyssey.

This colossal (and colossally expensive) new building which is about to open in Tokyo brings a welcome notion of public space to the Japanese capital, which otherwise conspicuously lacks any sense of this dimension. It is likely to be a figure as important to the future of the city as the Sydney Opera House or Big Ben.

The importance of the Tokyo international Forum lies in its contribution to Japanese urban space, its symbolic presence as an icon of the Japanese economic miracle and in the scale and quality of its facilities that are culturally significant, both for Japan itself and for the visitors it will attract from all over the world. Sited close to the imperial Palace Plaza, the Forum is the most sophisticated and the grandest project to emerge in Tokyo this century.

'When a significant spatial experience is shared by a number of people, this is the genesis of a public space.'(1) This Fumihiko Maki 1993 observation accurately identifies both the central idea of the project and the reason for Rafael Vinoly's success in winning the great international competition, the results of which were announced in 1989.

Looking back now at all the short-listed entries, Vinoly's project stands out both because of the new urban space it creates, and for the singular clarity of its plan and section. These elements are locked together in a three-dimensional synthesis of great spatial and functional resolution, eschewing any notions of traditional typology and confronting directly the issue of bigness, inherent in the programmatic requirements of the brief.

In Rafael Vinoly's words, the following crucial considerations arose: 'In a global economic environment which threatens the viability of the public client, the decision of the Tokyo Metropolitan Government to hold this competition presented a unique and open opportunity to rethink fundamental issues related to the civic realm and the making of public space.

'The understanding of the interaction between a site's formal qualities and a critical interpretation of a program is, to me, the substance of the architectural work. The symbolic character of space is what this work is meant to produce ... The interpretation of a site is the first act of design ... We saw the program as a composite of equivalent elements lacking a formal hierarchy ... As a result of this imposed equality, we concluded that the public nature of the architecture had to be expressed, not by a particular arrangement of these elements, but by a shaping of the space between them. The edges of the site were alternatively considered as gateways, barriers, filters, service areas and formal frontal planes, according to the different ways in which the elements were organized.(2)

'The fortuitous viewing of the Pan Am logo with its interlocking curves, unexpectedly suggested taking from the site, the clue to the building's architectural form.'(3)

The site, comprised of two city blocks in the Marunouchi business area, was formerly the location of Tokyo's City Hall and is situated adjacent to the Ginza commercial and entertainment district. The site faces out over two city blocks to the Imperial Palace moat and gardens to the west. On the east it is flanked by the noisy tracks of Japan Railways notably the JR and the Shinkansen bullet train system, terminating at Tokyo Station.

Vinoly's project description goes on to establish certain fundamental decisions. First, the belief that the Great Halls (or Auditoria) of the programme should be an independent group of separated cells, providing fundamental acoustic isolation. Their range and scale could form a stepped plan - form that relates well to the logic of the curving site profile. Next the requirement for a north-south pedestrian route through the block gave the occasion for the creation of special public space - the Plaza, with its associated tree lined garden. In reviewing the section it was possible to augment the scale of the Plaza by elevating and cantilevering the auditoria and carving further public space from the section. Finally the curving eastern edge, against the Shinkansen tracks, suggested a visual and acoustic barrier following that geometry, which when reversed gives rise to the transparent plaza wall of the Glass Hall.

The three elements are thus established; the Great Halls for conference music and drama, the Glass Hall as the principal organisational entry and break-out space for conferences and assemblies, and the mediating Plaza as the public city space that unites these elements. Beneath the Plaza lies the fourth element, the great Exhibition Hall, capable of staging major events, including the first significant gathering to celebrate the completion, in June 1996.

Vinoly has likened the Glass Hall to nineteenth-century public spaces; indeed like arcades: both the Milan Galleria and the Crystal Palace are recalled in this immense, awesome space with its monumental staircases and shimmering bridges and ramps, that are almost Piranesian in scale.

The Plaza itself recalls the scale of other European models like the Piazza Navona in Rome, and the whole ensemble has been compared to the symbolic presence of the Sydney Opera House, or to the grandeur of the Parisian Eiffel Tower.(4)

While these grandiose analogies are all Western (there is no equivalent to the Forum's urban public spaces neither in Tokyo nor in Japan as a whole), the streamlined forms which reach above the surrounding city blocks to capture views of the Imperial Palace and Tokyo Bay, seem particularly appropriate as a shield and background to the arrivals and departures of the heroic Shinkansen - a great symbol of the Japanese economic miracle.

In addition, the project affirms the status of the Japanese economy as a major global economic force. Vinoly's response, after all, is to the programme of the Tokyo Metropolitan Government, who requested some 145 000 square metres of space at a project cost of about a billion and a half US dollars. In itself, an awesome brief to be appointed to execute, in just five years.

The building complex is coded by differing levels of transparency and natural light. The solid form of the elevated Auditoria - the Great Halls, lining the Metropolitan Road 402 are clad in vast walls of Brazilian granite, with the elevations facing the Plaza in metallic grey aluminium panels. Internally the halls are fitted out with a fabulous range of materials including exotic hardwoods. Conversely, the Glass Hall is an astringent skin of laminated glazing to both the Plaza and aloft, with protective walls of Brazilian granite on precast concrete and aluminium panelling, shielding the great space within from the noise of the trains, on the outrigged eastern flank. The Plaza itself is a vast area of Cambrian Black Granite, containing Zelkova trees, and lined with cafes, shops and galleries. Its three outer edges are separated by toughened glass margins from the peripheral public pavements that are formed in Impala Black Granite, with special curbs and bollards. The Plaza contains access to several subways, which occur on three sides of the site and the principal access to the Yurakucho line is signalled by a spectacular structural-glass entrance canopy.(5)

The subdivision of the forms into clear programmatic elements - Great Halls, Glass Hall and subterranean Exhibition Hall - has given rise to a corresponding range of separate structural forms. The Great Halls are a heavy structure of concrete and steel, essential to the nature of the oversailing cantilevered shells of the overhead Auditoria containers. The Glass Hall incorporates a two-column support for a mega-truss using cast, forged and plate metal construction - this awesome perforated, transparent tour de force, the result of much experimentation, testing and collaboration, involves technology usually associated with major bridge construction. The Exhibition Hall supports the deep transfer floor-plate of the Plaza with a series of quadripartite strutted trees, rotated on to the diagonal axis.

The stories of the construction processes are many, complex and exhilarating, often involving original innovative methods. The whole saga is underwritten with an exemplary record of collaboration between the design team and the vast range of contractors brought together to construct the project. Two qualities in particular stand out. First, the tremendous tenacity and fluid talent of Vinoly the architect, whose freehand sketches controlled every option and detail. Equally impressive has been the dedication of Vinoly's principal architect collaborators, and the contribution of some outstanding consultants. Their five-year commitment and collaboration with all the craftsmen has resulted in a building of rare tectonic quality.

In his 1989 competition report Vinoly described the architectural treatment: '... The general approach to the architectural expression of this building is based on a vocabulary which uses the tectonics of the different construction methods as the basis for an aesthetic discourse. The development of the design is guided by the pursuit of controlled elegance through technological expression.

'Architecturally, the building counterpoints two types of volumes which are contained by neutral linear elements. These two spaces, the Glass Hall and the Great Halls, are differentiated by their relative degrees of transparency'.(6)

In addition to the structures that house the main Halls and Exhibition space, there are spaces for conferences. Also included are restaurants, retail and information centres, parking and offices. The paved and planted Plaza unites and links all the facilities visually, while the Glass Hall and its bridge links to the Auditoria, organise the main pedestrian movement within the complex.

The external Plaza, or Urban Garden, brings together and controls all entry points to both the Glass Hall, whose portals slide open at each tip, and to the Great Halls whose upper Lobby level is accessible from six major points served by escalator on the the Road 402 frontage, all within the framework of the Plaza floor-plane. The most significant street entry, serving Hall B, the Rehearsal Room and the largest Reception Hall, is also positioned on an axis of a minor street whose vista allows an urban window - a huge glazed structural element within the major masonry facade - to take views directly into the garden of the Imperial Palace. This vista celebrates the major vertical circulation node of the Halls complex, whose space is sliced by the flashing silver stainless metal of the escalators.

The main Lobby level of the Great Halls, at 2nd floor level, contains an array of counter cafes and, with Hall A, a special cafe and Terrace with views out over the Plaza and its predominant wide entrance marked by five spectacular stainless-steel flagpoles. Above at 3rd floor level are the main Auditoria support spaces and dressing rooms.

Level 4 contains the major stage platform areas to Halls A and C, the Rehearsal Room and further dressing rooms and other back-up spaces, the VIP and Green Room and the first tiered levels of the two principal Auditoria. At this level the first bridge link serves across the Plaza to unite the Glass Hall and its first major level of smaller conference break-out spaces.

Levels 5 and 6 are the most interconnected and important events above grade. Level 5 is the piano nobile of the whole complex revealing the full amphitheatres of Hall A - the great 5000 seat multi-purpose auditorium, and Hall C - the 1500 seat multi-use Theatre. The Reception Hall mediates between these two huge auditoria and two floors above, on level 7, is topped by Hall B, a flexible cubic subdivisible volume. It is also at level 7, that the smallest 'black-box' theatre occurs, Hall D, terminating the range of auditoria. All these major spaces can be adapted for several uses, particularly conferences.

Levels 5 and 6, the principal levels of Halls A and C, are connected by V form bridges to the Glass Hall, its galleria and transparent ramp and the attendant smaller conference rooms, whose wall of accommodation shields the whole complex from the Shinkansen track-curvature. Both the Reception Hall and the Large Conference Room, at level 5, are finished with exotic materials and floored with designer carpets. The Reception Hall relates, on its east-west axis, to the Glass Hall and the Urban Window, while the volume of the room is partly encircled by an eroded cylinder finished in a Japanese-green coating. Similarly the spectacular Lobby to Hall A, at level 6, contains planar screen walls of red and green Iranian travertine. This limited use of colour is an essential relief to both the scale and austerity of the overall interior volumes and their neutral surfaces.

The 7th level of the complex is the culmination of all the major spaces - the galleries of Halls A and C, and the main floors of Halls B and D that occur between the two essential auditoria volumes. In the Glass Hall, the floor of the Galleria is voided at each tip to form an open space with outrigged glass roof incidents fastened on to the masonry bulk of the outer wall mass. These glazed conservatory spaces have balcony edges that lock on to the cast centres of the two macro-columns, that in turn support the vast ribcage of steel and glass roof, hovering over the whole lens-plan enclosure.

The interior volumes of Halls A and C, the two principal auditoria, have received special detail design work. Hall A is a 5000 seat Theatre which can be used for conferences. For classical concerts, and other similar functions, the auditorium is equipped with an electronic architecture system (AFC/reverberation reinforcement), capable of creating symphonic concert hall sound associated with smaller, more intimate halls. Within the proscenium, a demountable shell of Japanese maple walls and hood adds a further blending facility for the projection of the orchestral sound, through the full frequency spectrum.

In contrast, the 1500 seat Theatre (Hall C) is lined with splayed and stepped panelling made from a beautiful selection of Indonesian quince-wood, and topped with inward projecting wooden overhangs that define intimate side galleries on each side of the double-galleried amphitheatre. The surface design and volume yields a natural acoustic response suitable for a range of events, from lectures through to all forms of theatrical installations and musical concerts.

The crystalline Glass Hall is at once the icon of the project and its singular spatial and structural grand gesture. Rafael Vinoly comments: '... the Glass Hall structure was always a truss-like element, transparent ... to minimise its shadow over the garden ... the tectonics of the building result from the conscious manipulation of the route of main forces to the foundation, and the controlled expression of these routes'.

The roof held up on just two massive columns also led to the idea that the glass walls could be supported independently from the roof structure at the base, allowing the rocking of the roof under earthquake forces to be taken up by a sliding joint between the walls and the roof itself. In turn the great glass walls to the Plaza are stiffened by two arches - one in the form of a linear ascending ramp, while horizontal wind load is taken by cable stay trusses. The glass wall itself, an amalgam of laminated HS glass, housed in a plated unitised framing system, is able to shunt and slide, plate against plate, in the event of an earthquake. These and numerous other refinements of fixing, casting, cable stiffening and sectional smoke venting, together with an insulated glass membrane roof over the whole elliptical Hall, combine into an awesome tectonic frame and skin, enclosing a breathtaking spatial volume.

It is perhaps the illuminated spectacle of the Glass Hall, at night, that symbolises and signals a futuristic Japanese culture and reasserts Tokyo as a world city. It is a monumental gesture of the late twentieth century, intended to herald the Japanese entry into the next millennium.

1 See Tokyo International Forum: A Work in Progress, Rafael Vinoly Architects, essay by Fumihiko Maki 'The Birth of a new Public Place', New York 1993.

2 Ibid. Essay by Rafael Vinoly 'Making a Building: Notes on an Architectural Process'.

3 Ibid. Rafael Vinoly's sketches on a First Class Menu from a Pan Am flight, reveal the double curvilinear geometry in the logo, that reversed, produce the lens shaped plan-form of the Glass Hall.

4 Ibid. Essay by Kenneth Frampton 'A Forum for Tokyo'.

5 The spectacular Yurakucho Subway structural glass canopy was designed by Rafael Vinoly Architects with Dewhurst MacFarlane of London, as structural consultants.

6 Report of the jury, Tokyo Forum Design Competition, Tokyo, Japan 1991. A document describing the winner and all short-listed entries.