LAYERED MEDIA.

From modest origins as a cultural centre and library in a provincial town, Toyo Ito's Sendai Mediatheque celebrates and displays its different activities and inventive structure in a dramatic urban shop window.

Sendai is a provincial capital, about 300km north of Tokyo, which was levelled in the Second World War and rebuilt on a spacious grid plan. In 1995, a new mayor decided that this prosperous modern city needed a more appropriate civic symbol than the ruins of its seventeenth-century castle, and invited Arata Isozaki to chair an expert jury to choose a dynamic design for a new arts centre.

Toyo Ito won that competition with a concept that was as audacious as the Pompidou Centre, though smaller and less assertive. Where Rogers and Piano flexed their muscles on the exterior, creating a heroic monument to the Machine Age, Ito proposed a transparent block whose supports would be wrapped in glass and dematerialized. Seven steel floor decks were stacked on 13 hollow columns composed of welded steel tubes. Schematically, it was an updated version of traditional Japanese post and beam construction with movable divisions and permeable boundaries.

Metaphors inspired the structure. Ito thought of the enclosed space as liquid, likened the columns to strands of seaweed drifting through an aquarium, and created sketches of ethereal delicacy. Like the temporary structures that launched his practice, and his computer-synthesized electrographic display in the 1991 Visions of Japan exhibition at the Victoria and Albert Museum (AR November 1991), the Mediatheque was intended to express the fluid dynamics of the modern city in which light and movement are layered atop its physical structure and vibrate around vortexes of energy. For Ito, this was to be a bridge between real and conceptual, a physical embodiment of the electronic labyrinth which many now inhabit--especially the young in Japan.

Two contradictions emerged at the outset. The programme developed to fit into Ito's container fell far short of his vision. Sendai is a conservative city, and librarians anxious to accommodate a growing book collection and local artists seeking display space for academic paintings had no enthusiasm for open plans or virtual reality. Disagreement began the day after the competition winner was announced. The columns had to be beefed up to meet Japan's tough seismic code, and the challenge for structural engineer Mutsuro Sasaki was to retain the poetry while satisfying practical necessities.

Against all odds, much of Ito's concept has survived six years of impassioned debate, and the need for a structure (partly fabricated and welded by shipbuilders) that is more like an ocean liner than an aquarium. From the broad boulevard to the south, it appears as a shimmering rectangle of glass, etched with dots and dashes that animate the double-glazed skin and reduce glare, extending beyond the floor planes. Inside, a forest of canted white tubes (recalling the branches of the zelkova trees that run down the middle of the street), extends through the roof to support a gridded canopy.

At night, the south facade disappears. Only the skeletal structure is visible, animated by a blaze of ceiling lights and tiny accents of colour from furnishings set close to the glass. Though little of the building's activity is apparent above the ground floor, varied ceiling heights and the alternation of transparent, translucent and opaque surfaces on the other three sides of the block hint at its diversity of content. The Mediatheque combats the blandness and visual pollution of a Japanese city (a pachinko parlour formerly occupied the site) by staying cool and enigmatic. Even the graphics, stencilled onto the glass, are reticent. The spacious foyer, shop, and cafe that wrap around an enclosed gallery and service areas in the north-west quadrant reveal the essence of the plan. Four symmetrically-placed corner columns of 240mm diameter tubing carry much of the load and provide the necessary seismic bracing. Nine columns of 160mm diameter tubes are scattered in between; five are straight and contain lifts, the rest are crooked and carry ducts. The hollow columns pull down light from above, and most are clad in glass, adding a further layer of gauzy reflections to those in the polished marble floor and dematerializing the exposed structure. A shiny red plastic reception desk sinuously wraps around one column like a seductive swirl of lipstick, and similar extruded forms in yellow and white anchor the bar and bookshop.

To understand the building's section, take a lift to the top floor. From the glass cab you can see how floor planes have been sliced through, revealing the structural sandwich of steel plates topped with concrete. On a non-stop ascent, the ride gives a fleeting glimpse of each distinctive floor succeeding the next, as though snorkelling up the side of a coral reef. Here, Ito's metaphor of the interior as a fluid medium comes vividly to life. As in the ocean, the colours, the patterns of activity, and intensity of light change with the level.

Ito selected three designers to put their stamp on different floors. Kazuyo Sejima's first floor information department and children's library is a monochromatic composition of white lino tiles, suspended metal channels and a silver-studded black side wall. Sejima, who formerly worked for Ito, designed whimsical grey foam benches that resemble clover leaves, and screened the children's area and staff offices in undulating gauze drapes. Circular reading tables and magazine racks flow around these permeable enclosures. The lofty second-floor library by K. T. Architecture has a more conventional layout: regimented rows of bookstacks to the rear, linear tables in front, and study carrels in a mezzanine gallery. Suspended uplights provide even, diffused illumination off the suspended white ceiling.

Changing exhibitions are presented on the next two levels with their wood-strip floors, demountable white screens, and sculptural seating in vivid colours by Karim Rashid, who also designed the plastic seating in the ground-floor cafe. It is here that you begin to sense the wasted potential of space that would challenge a creative curator to exploit the play of structure and void. Occasional exhibitions may introduce locals to novel ideas, but, as a new arrival that is still gradually winning acceptance, the Mediatheque has to move cautiously. It is too big, arid took too large a bite out of the municipal budget (around [pound]75 million) to ignore its major constituency.

The top floor offers the best marriage of container and content. Ross Lovegrove has designed what he calls 'a garden of knowledge' to house the media library. Biomorphic lime-green plastic chairs, tables and tape racks are deployed like exotic plants on a lime carpet, and video monitors are screened by tensile pods. These occupy the perimeter; at the centre, an undulating glass wall encloses a small theatre, meeting room and offices. Fluorescent tubes are set at angles on a white suspended ceiling, and the sense of detachment from the workaday world is enhanced by glimpses into neighbouring offices where salarymen toil away late into the night, like a Japanese version of Alphaville, where everyone seems to be sealed off in brightly lit capsules.

For Japan, the Mediatheque is extraordinarily informal, with young friendly staff, and it has become a popular local resource; yet the atmosphere is as decorous as a scholars' library. Director Emieko Okuyuma observes: 'When we first announced this project, opponents thought it would be a dangerous monster. In fact, people have responded to the welcoming atmosphere and bright colours. Attendance is larger and younger than we anticipated'. Given time, Ito's original vision may yet be fully realized.

1 At night, Sendai's new Mediatheque pulsates with light and colour like a giant, ethereal aquarium.

2 South facade is wrapped in a clear glass skin. Literal transparency is one means of demystifying the building and encouraging use.

6 Main library on second floor.

7 Arboreal columns animate space. Column cages house lifts and ducts and bring light into the interior.

8 First floor children's library, designed by Kazuyo Sejima.

9 Top floor media library, designed by Ross Lovegrove, one of the more successful marriages of content and container.

MEDIATHEQUE, SENDAI, JAPAN

ARCHITECT

TOYO ITO

Architect Toyo Ito & Associates, Tokyo

Structural engineer Sasaki Structural Consultants

Mechanical engineers Sogo Consultants, ES Associates, Ohtaki E & M Consulting Office

Lighting consultants Lighting Planners Associates