Using space vertically.

In their designs for towers, Buro Happold has been in the vanguard of exploring new environmental control systems, passive and active, to cope with a great variety of climates.

The potential of integrating innovative structural engineering solutions with sustainability was explored in a joint competition entry with Christoph Ingenhoven (of Ingenhoven Overdiek Kahlen & Partner) for the Commerzbank in Frankfurt (AR May 1992). The entry came second (first prize was won by Norman Foster and Partners -- AR] July 1997). The concept was a cylindrical glass tower with a double glass skin which allowed natural ventilation to the adjacent offices and enclosed internal gardens. The ideas, in a modified form, were put into practice shortly after, when the Ingenhoven team won a competition to design an office tower in Essen, Germany, for the headquarters of RWE (AR July 1997).The 30-storey tower, a 32m diameter glazed cylinder, I 30m high, has a semi-detached glass lift tower beside it. It is one of the first high-rise corporate buildings in which contemporary methods of environmental control --thermal mass, displacement and night ventilation -- are applied.

Wedge-shaped offices form the perimeter of a standard office floor, reached by a circular corridor. The glazed external skin of the offices comprises a breathing wall -- with sun-screening blinds between and slots for natural through-ventilation. The whole facade was built in floor-height prefabricated components. Floors are 250mm thin flat concrete slabs which taper to a row of circular columns at the perimeter and rest on ring beams supported on circular columns on the outside corridor line.

A 260m tapering tower in an extreme climate is part of a new joint venture with Foster and Partners. The Al Faisaliah Centre is set in the heart of Riyadh, one of the hottest capitals of the world where in summer outside air temperatures regularly exceed 45 degrees Celsius. The tower, which will be one of the first high-rise buildings in the city, is part of a project which includes a 224-bedroom luxury hotel, apartment buildings, and a shopping mall set round a lushly planted open plaza which has a large banqueting hall beneath it.

Square in plan, the tower tapers upwards in a curie, clad in silver anodized aluminium panels, to a finial-like lattice communications mast. It has a compact concrete core in the centre and four concrete columns at the corners which define the upward curve. Ground, 12th, 21st and 30th floors are open decks, acting as viewing galleries for visitors, which are framed by exposed storey-height concrete K-braces. The braces collect forces from intermediate concrete floors and transfer them to corner columns, allowing more slender columns to be used. To control distorting deflections, the K-braces incorporate tie-beams which were sequentially post-tensioned as construction proceeded upwards. The Al Faisaliah facade is of clear glass protected from the glare and solar gain of the sun by deep aerofoil-shaped aluminium blades fixed to it with projecting brackets.

Designed to accommodate up to 2000 people, the exhibition and banqueting hall is a 63 x 8lm column-free space, its roof formed of eight pairs of wishbone-shaped concrete bow-string arches. These, braced by a series of steel tendons, taper towards the apex of the roof. Secondary beams 400mm wide rest on the arches to support the concrete ground slab. Spaces between arch and beam structure have been designed to integrate ceiling, lighting and air diffuser systems.

The whole project is energy efficient and easily maintained. For example, to reduce peak electrical load on the grid, the building incorporates thermal ice storage. Ice created overnight is stored in a rock chamber below the shopping mall and used to cool interior spaces during the heat of the afternoon.

Ingenhoven Overdiek Kahlen & Partner and ECADI have recently completed another high-rise project, the Wang Xian International Plaza in Shanghai, a 55-storey, 288m high tower with a public square and gallery. Triangular on plan, the exoskeletal-braced structure of the glazed tower acts with the internal lift cores to resist typhoon and seismic loads. The facade consists of a double-glazed outer layer of clear glass, a ventilated cavity fitted with blinds, and double-glazed inner layer of clear glass. Cooled return air is drawn from the room and through the cavity, passing over the blinds to remove solar energy at source.

A tower on a smaller scale, but with unique requirements, stands in the main square of Basildon. England; 27m high and octagonal in plan, the tower contains a full peal of eight bells on its third floor. It has frameless glass walls which allow bell ringers and bells to be seen in action.

Designing a slender tower with 2.6 tonnes of bells swinging 17m above its base posed a unique problem. The worst case is when the tenor bell - the largest bell weighing a tonne - and the smaller bell opposite it are moving in the same direction at the same time. To dynamic forces generated by bell ringing had to be added worst-case wind load. The structure was analyzed using ETABS, a structural analysis package for tall buildings which gives dynamic modelling. It was clear that a conventional frame could not give the stiffness required. The solution was to use, instead of a single column at each of the eight corners of the tower, a triple column consisting of three 139mm diameter steel tubes tied together at floor levels by 20mm thick Y-shaped steel brackets acting with cross bracing set between the columns. One column sits within the frameless glass panels and is connected to a tubular ring beam. Tubular beams which support the floors radiate from this to an inner ring beam. The steel brackets stiffen the c olumn structure and hide the glass corner joints.