The New National Stadium of Japan is more than a large sports facility designed to the highest design specifications and functional requirements. It is a piece of the city’s fabric, and urban connector which enhances and modulates people moving through the site from different directions and points of access. The elevated ground connections govern the flow of people through the site, effectively carving the geometric forms of the building.

The stadium roof defines an iconic silhouette that integrates gently within the cityscape around it. It is an intricate assembly of efficient long-spanning structural ribs which are spanned by a system of lightweight, translucent membranes. This unique structure is a lightweight solution, where the stadium elevation graciously touches the ground, defining a clear approach towards the stadium entrances. The interior of the stadium is also given a clearly identifiable identity through the strong roof structure that contrasts with the lightness of the translucent membrane tensile structures.

The seating bowl has been optimised to suit both Rugby World Cup and Olympic events, with a permanent athletics track to be inserted within the stadium. The design of the bowl will bring spectators as close as possible to the athletics track and jumps, and will not compromise the viewing experience of spectators during football or rugby events.

The seating bowl is adaptable, and has been designed to allow for the scale of the stadium to remain compact. Following the Olympics it is proposed that flexible areas of seating are adapted to enhance the commercial revenue that can be generated by the facility in legacy mode.

The form of the stadium has been driven in response to the functional planning requirements of the stadium and responded closely to the volumetric constraints imposed on this building by the local planning authority requirements.

Design Inspirations; Cultural Resonance

The current design was defined by the client’s brief which is an outcome of their legacy business plan which needs to generate revenue from key stakeholders such as the J League.

For the past two years the clients brief was for a multi-purpose stadium with an adjustable seating bowl which is able to switch sports modes between athletics or football with an operable roof to close the roof opening and allow concerts.

If the government decides to change their brief to a fixed athletic seating bowl of 80,000 seats, it will not be sustainable. If football is watched from the distance of an athletic seating arrangement it’s too far away to create atmosphere and it will not be popular. An athletics formatted bowl is not acceptable to FIFA and will not be acceptable to J League for national football events.

To be sustainable, the investment needs to be focused on long term usage after the Olympics and that means being able to accommodate football which will be the largest user and revenue after the 2020 Games.

There are many options available to achieve this objective but there are certain key parameters to stadium design which we think need to be understood.

HDTV Lighting It’s important to understand that the size and volume of stadium enclosure is not only determined by the seating capacity.

There are other factors that will need to be incorporated in the new stadium regardless of its seating capacity and these factors also determine the size, cost and sustainability of the stadium.

To host the Olympic Summer Games television requires high definition lighting to be able to broadcast.

This requires the stadium to incorporate lighting at a height of 50m surrounding the field of play. It’s a large field of play with many track and field events occurring in different locations. Each of these events needs to be light to the same high standard. The stadium lighting also needs to work for football, which is a different and smaller field of play This requirement means either above or below the roof, an extensive gantry needs to be built at a height all around the field of play. Regardless of seating capacity this lighting is required.

Football Roof Cover The extent of roof cover over the seats is directly related to the amount of seats. Its fundamental purpose is to protect spectators from the weather. In the case of Tokyo 2020 Olympic Games, the weather is hot and humid so the roof should provide as much solar protection as possible to make the spectators comfortable. If the stadium is to work for football, the extent of the roof should be determined to cover all of the seating in football mode. Building a roof once to work for athletics and football will result in the best return on the investment and mean the stadium is sustainable in the long term.

Seats supported by Facilities Any stadium will host a limited number of events in any year and they are difficult to make work as a business. For the new national stadium it was projected it would only host 40 events including 10 concerts in any given year.

There are potentially 80,000 customers at an event so it’s imperative that the stadium design maximises the amount of revenue that it makes at each of these events.

In modern stadium design this means more dining facilities within short travel distances to increase the duration of stay and spend by spectators to any single event.

This means that in addition to the fixed seating there needs to be facilities in close proximity to all seats to ensure revenue is generated.

The current design is designed on this basis and it should be retained to be sustainable not only in terms of usage but also revenue generation.

Site Constraints The site is a very constrained urban island site surrounded by roads on all sides with extensive level differences to navigate and height limitations for any development. The complexity of managing to fit the field of play, seating bowl on the site along with arranging level access in multiple directions means there are very few design options available. Our current design is optimised for this particular site.

Having investigated the site for two years, we have researched and worked to produce the most feasible long term solution for the site. The site area is small so the design has been optimised to create as much external precinct area available as possible for crowd flows by allowing the non-ticketed concourse inwards to create a compact footprint and safer site for crowd management.

Temporary Seating Options We have tested many bowl options including the use of temporary seating. We proposed an option in 2013 to the client to achieve some of the 80,000 by using temporary seating. The option was rejected at the time as the clients brief was and remained to have 80,000 permanent seats in legacy. We know from direct experience in London 2012 that mixing temporary and permanent seating on a constrained site is difficult and it is not a way to save costs. It is a valid option if the long term objective is to achieve a lower permanent seating capacity. This is reasoning behind the success of the London Aquatics Centre which reduced from 17,500 in 2012 to 2,500 after the games.

The Sydney Olympic Stadium used 30,000 temporary seats. Although conceived as temporary they were built to similar standards to a permanent stand to achieve compliance with code. They took a significant percentage of the overall construction budget and took longer than anticipated to convert to the legacy stadium format after the Games. We should learn from London and previous Olympics on the use of temporary seating. The reasons for choosing this option need to be determined not to save costs or time, but to satisfy the long term business plan after the games. The option remains possible with the current design and the keel arches of the current design are similar to the structure designed for the same purposes in Sydney.

Design Benefits; Compact Bowl We have developed the design to turn the requirements of the brief and site into benefits for the the local community, Tokyo, and the nation as its national stadium. To start, and given the site constraints of the site in size and height, we have produced the most compact bowl footprint possible for a multipurpose stadium design. Using Arup Sports’ experience of previous Olympic stadium design, the design achieves a more compact design to fit the site, allow more space for safe passage on the precinct whilst achieving better proximity to the field of play and better quality of view for all spectators by comparison to the previous Olympic stadiums of Beijing in 2008 and London in 2012.

The compactness of the design has brought spectators significantly closer to the action in both athletics and football formats, and provided them with an enhanced quality of view (elevation + proximity) when compared to London and Beijing. The result is a very efficient sports focused stadium design which has been optimised for this specific site.

Design Benefits; Saddle Bowl We have been aware since our competition submission in 2012 of the sensitivity of the site location with respect to the size of the stadium. This is the reason why we have proposed a ‘saddle’ seating bowl as opposed to a flat top bowl. A saddle seating bowl is shaped like a saddle which means it has got a varying height. Its benefits are twofold. The first is that it allows the majority of seats to be positioned in the most popular location along the middle of the field of play and requires less seats at the ends. The result is more seats that are easier to sell.

The second advantage of the saddle bowl is that externally the pedestrian perception of the stadium is much reduced where the inclined elevation of the stadium comes down as low as 24m and rising to a height of 44m where from most viewpoints will look and feel like its lower. By comparison a flat top bowl would be a constant height of approx. 40m which from all viewpoints will look and feel like a wall 40m high.

Design Benefits; Skybridge, Extension of Park

The saddle bowl profile allowed the development of a unique additional public feature, the skybridge. This feature of the design is not essential to the stadium functionality but it’s a gift to the public realm of Gaien. The skybridge is an elevated walkway following the saddle bowl profile. Its allows the daily usage of the stadium with elevated views and it connects it into the daily walk or runs of the public in the Gaien area. The skybridge would be open every day creating more direct access with the stadium than its event schedule. It was intended to allow the stadium to become more used part of the city fabric on a daily basis and more integrated into the promenade culture of the Gaien area.

Design Benefits; Arch & Construction Time With our experience of previous Olympic deadlines, it was clear that the stadium design should have advantages in saving construction time. We proposed keel arches, which span the longitudinal direction of the field of play, create column free views and rest on the ground. As they rest on the ground, it means the arches can be built in parallel to the seating bowl. We believe this approach will save 3 months in construction time compared to a sequential build of bowl first and then the roof supported off the bowl. This time saving can be critical in achieving a fixed deadline and it should have cost saving benefits as well. This design benefit did not materialise in the joint venture bid but it remains possible under a new bidding process.

The efficiency and cost of the keel arch design is possible to measure by comparing its tonnage to other stadium roof constructions of similar span lengths and seismic conditions as Tokyo. We undertook these studies and the keel arch is an efficient and cost effective solution with many benefits.

Design Benefits; Arch & Construction Time Before defining a new budget for the stadium, the current price submitted by the contractors should be better understood. It was not the price of the design as we have just described, it was a price based on considerable omissions from that design. The price of JPY 252 billion did not include for the operable roof, nor the moving seating tiers and only a partial enclosure of concourses. It was therefore already the market price of a fixed athletic stadium of 80,000 permanent seating. Save for the skybridge, 252 Billion Yen is the current price in Tokyo for a fairly basic 80,000 capacity stadium on that site.

A new process needs to change the market conditions in Tokyo, not the design. It should also be understood that immovable deadlines such as the Olympics combined with limited competition in the marketplace create inflated prices. The determining factor in the price is the market and the demand on materials and labour. The design is not the determining factor in these circumstances. Rather the design should be seen as the only way to achieve value for money in the market. Without a design as a contractual commitment as much as time and cost, there will be considerable risk to achieving value and return on the investment. The current design can be redesigned to achieve a lower budget but it should be retained in principle so the Japanese public achieve this value from the market and they get a long term return on the investment.