TALL ORDER.

Days before the cataclysmic destruction of the World Trade Center in New York, architects and developers gathered to discuss the future of tall buildings in Frankfurt.

Today tall buildings are the product of need. Arup's Mohsen Zikri now cites 14 megalopolises with more than 10 million people. By 2015, 28 cities will have more than 10 million and a further 10 cities more than 20 million inhabitants. The cost of land in urban centres and the need for increased density are growing exponentially. To ensure sustainability and environmental friendliness, Arup has developed a simple and effective method to review the design of tall buildings and their contribution to an urban system.

One criterion is transportation, an optimal location being an inner-city transportation node. Piano's 306m high London Bridge Tower gets top marks for being planned next to the city's busiest commuter station, the capacity of which is to be increased from 30 to 40 million passengers a year. Hence the basic rule for the future: tall buildings necessitate the radical regeneration of inner cities and their infrastructure. Developers should help to finance this.

Pride of a city or blot on the skyline

Developers and architects like skyscrapers because they are high profile in every respect. Politicians love them as symbols of civic virility. In clustered CBDs they make the place. But they also cast shadows on public areas and other buildings, affect the cleansing qualities of the wind, causing nasty draughts killing their local streets. For many European cities they are environmental disasters. Paris, Rome, Madrid and Barcelona consequently only allow towers outside their centres.

In Frankfurt, skyscrapers are a major contribution to the City's image as a financial centre. Since 1998 a master plan has coordinated the 4.5 million square metres of new office space expected in the next ten years, including 15 new skyscrapers between 155m and 365m high. These towers are to enhance both the skyline and the quality of the city. They are the result of competitions and will be responsive to their environment. A prime example is Helmut Jahn's 200m tall MAX for Deutsche Grundbesitz, Deutsche Bank's development company. The slick, transparent glass cylinder is also an exercise in architectural branding. It could become Frankfurt's symbol for the twenty-first century. The tower will offer its tenants maximum flexibility at minimum running costs. MAX developer Thomas Norweg hopes MAX's six neighbouring towers (ready to go ahead) will agree to a mutual logistic concept for the construction period.

Record breaking machines

Architecture's Formula One, the present generation of super-tall buildings tries to break records on as many levels as possible. Three record holders presented their extreme machines and ways to deal with the wind as a major factor influencing structural and fire engineering as well as facade design.

Cesar Pelli & Associates' 452m high Petronas Towers is the reigning height champion. For Fred W. Clarke this super-tall building is like 'a president amongst the people'. The towers form both a physical and a symbolic gateway to the new Malaysia. In 2004 they will be overtaken by SOM's 7 South Dearborn, a 108-storey, 472m high tower in Chicago's CBD. The top of the three digital broadcast antennas will reach 609m, making it the world's tallest free-standing structure. The building will include 400 residential units, offices, retail space and 800 parking spaces. The cantilevering of the upper 57 residential floors from the concrete core makes columns unnecessary and provides uninterrupted views in all directions.

Four years ago the construction of the Shanghai World Financial Center was stopped to increase its height from 460m to 500m. William Pedersen (of architects Kohn Pedersen Fox) had to reduce the weight of the building by 10 per cent to use the existing friction piles. The shape of the building changes from floor to floor. The eye-catcher is the huge round hole at the top ('80m of nothingness'). It deals with the wind forces and could become a public attraction with cabins encircling the inner space. Formally, Pedersen mentioned, it relates to the two balls of Shanghai's existing TV tower.

Outlook

The main trends are international. Adrian Smith, of SOM, summed them up:

* Mixed-use programmes of development to spread the investment risk

* Structural innovation to reduce structural and technical systems and increase the speed of construction

* Sustainability: even Chicago is including water and energy conservation as a bonus in their code system.

So hold on tight -- the race to the heavens has only just begun.