Interior view Nagano Olympic Stadium (47k) 

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WOODEN UMBRELLA

Culture plays a large part in design, as MASARU OZAKI of
Kajima Design explains.

There were various reasons for the adoption of Kajima Design's plan not least the fact that the silhouette of the membrane roof echos the Izumo Plane. Also the dome's functionality permits multi-purpose utilisation, and Kajima's plans included specific proposals for operation, maintenance and management after completion.  

The building design uses the wooden construction technique that is so much part of the tradition and culture of Izumo, aiming at the creation of a gentle space that offers warmth, softness, and the fragrance of the bark of a tree. A hybrid frame made of membrane material, laminated timber arch, steel bar bracing and ring cables was adopted to ensure the optimum brightness of the single-layer membrane roof and open out the indoor space to the maximum.  

The three-dimensional tension cable arch structure was used to permit assembly of large membrane panels and allow the self-balancing roof to be lifted lightly on its feet, thereby realising integration of the interior and exterior both visually and functionally. 

The radial skeleton was emphasised as a wooden arch to ensure the centripetality and ascending feeling of the internal space. The fact that the local people get together in the dome whenever they have an event, makes you feel that this large roof is gaining the nature of the "festivity of today". The way the cultural aspect of the architecture is amplified by the adoption of the laminated timber, autonomously assuming symbolic characters and identity, cannot be explained merely by "participation and inheritance of wooden culture," but is deemed to be the charm of the wood itself.  
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Yamabiko Dome   
Shinshu Expo Global Dome (later opened as a multi-purpose sports facility, "Yamabiko Dome") was designed as the main hall of an exhibition held in Matsumoto City. A one hundred metre span dome made of laminated timber from larch trees grown in Nagano Prefecture makes it the first in the 'large dome' class. The arch is assembled with straight small beams (also made of larch) and rafters made of a Japanese cedar which are arranged between the beams, so that the pattern emerges beautifully when lit by the top lights.  

The roof panel was newly devised so that it would play the role not only of ordinary roof sheathing but also as an element to resist horizontal force. The plywood between the rafters is covered with glass wool boards to eliminate the risk of ignition, as well as to effectively contribute to sound absorption and heat insulation. In terms of execution of construction, the roof panels were thoroughly systematised and unitised. 

Such an utterly new idea for roof panels solves various problems of structure, disaster prevention, and control of indoor environment in an integrated manner and is aimed at the creation of general purpose systems that will develop into large wooden spaces in the future. We hope that the development of such a system will revive the use of traditional materials, such as domestic wood, based on new ideas and technology.  
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Nagano Olympic Memorial Arena  
The major design feature of this facility is the integration of the architectural space under an articulated, wooden, suspended roof into a 'linear space system'. This is an unprecedented approach to dome structures.  

The system is longitudinally extendible, giving a "Nagano type" which can vary the space according to the size of teh specific event. The opposing linear fixed stands will be used for American Football games and other large-scale sports events, while a pair of reciprocating semicircular stands will function as "movable walls" that surround the arena to make it smaller for volley-ball and other small-scale sports events and concerts. The running track for lighting and acoustic systems changes its position according to the foci of separated spaces, with separating curtains to help divide up the space. Such facilities are intended to increase the freedom of use by the citizens and the feeling of being involved in an event, as well as to use the space to a maximum extent. These will be essential functions for large public spaces, in order to create local culture on an urban scale. 

It is vital that an ordinary large space can control its light, sound, air, heat and wind, as well as to ensure comfort and improve stage functions in a sustainable manner. Because of the precondition that this facility should be "a speed skate rink and facility for the citizens to use as well",  the requirements of both "open" and "closed" space, is particularly clear in this case.  

In a space underneath a concave ceiling, it is presupposed that the total volume, as well as the air-conditioning load (cooling load), must be reduced, and that the acoustic characteristics (including consideration of the ice rink) must be improved by introducing an irregular reflection shape. Also, in the ceiling system (heat-resistant, anti-sweating, sound-absorbing, and fire-resistant glass wool boards between small beams made of laminated timber) exposed steel parts should be minimised as much as possible.  

The space under the floor of the arena has been made entirely into a parking lot to secure a heat insulation layer between the floor of the arena and floor slabs on the ground. Meanwhile, the large openings in the east-west wind direction have been made into a completely transparent polycarbonate jalousie, looking out onto the Japanese Alps, so that the audience can feel in touch with the season and the place. The overlapping sections of the roof are used for natural lighting and ventilation, functioning as catwalks where the lighting, acoustic and hanging mechanisms are concentrated. The high-side sash allows the ceiling to appear gently under the semi-indirect lighting by the light shelf and diffuses the daylight all over the arena. This section is provided with a damper that controls the wind-response (plate vibration) of the roof, giving a solution to the problem of sophisticated integration/unification for overall control of the indoor environment and of aerodynamic wind.  
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Seating at the Nagano  
Olympic Stadium (30k) 
 
 

Development of each detail was a process of further refining the original geometry. Overlapping sections in the ceiling and inclined walls are separate units, and efforts were made to show cut end-faces clearly. The internally inclined walls are arranged side by side and the barrel-shaped wooden parallel line frame,  (that becomes shorter toward the edge) are overlapped to emphasise the sense of contraction in the cross-sectional direction (short-axis direction) and the sense of energy and openness in the direction of space extension (long-axis direction).  

Meanwhile, the semi-external concourse, with an inclined wall made of plates arranged side by side with each other, is an important buffer zone that connects the arena and the large external grassed area. The effective combination of light, wind and line of sight, create a space that is different from the conventional "concourse".  

Kajima Design have put architectural effort into discovering what the space should be without preconceptions, and have consistently maintained those efforts right down to the smallest detail, including the function, environment and the appearance of interior and exterior, in the attempt to break through to a "new world". Our efforts are part of an overall  process to move away from the conventional "dome architecture".