The most dramatic modern construction in the City of London is 30 st Mary Axe, more commonly known as the Swiss Re Building, The Pine Cone or simply the Gherkin. Prince Charles sees it as symptomatic of a rash of carbuncular towers on the face of London. The architects, Norman Foster and Partners, heralded it as a signature building for the modern age and received the 2004 RIBA Stirling Prize for their creation. It has succeeded in putting the Swiss Re-insurance company in the public eye and has stimulated a wide-ranging debate about the desirability of towers on the traditional horizons and sight-lines of the City of London. Alas while there is an ongoing debate about the aesthetic success of the Gherkin, there is not much doubt that it has been a bit of a commercial disappointment for Swiss Re. The company occupies just the first 15 of the 34 floors, but has never succeeded in renting the other half of the building to another, single, organization. This is not entirely surprising the type of high profile commercial enterprise able to afford such space would recognize that the building has become so totally associated with the name of Swiss Re that it would be forever playing second fiddle and would gain no kudos at all by its presence there. As a result the space has been parceled up into smaller lets.
The most obvious feature of the Gherkin is that it is big : 180 metres high and the creation of a tower on such a scale creates structural and environmental problems. Today, engineers can create sophisticated computer models of a big building that enable them to study its response to wind and heat, its take up of fresh air from the outside, and its effect on passers-by at ground level. Tinkering with one aspect of the design, like the reflectivity of its surface, will have effects in many other areas : changing the internal temperature and AC Requirement, for instance and all the consequences can be seen at once using sophisticated computer simulations of the building. It is no good following a ‘one thing at a time’ approach to designing a complicated structure like a modern building, you have to do a lot of things all at once.
The Gherkin’s elegant curved profile is not just driven by aesthetics or some mad designer’s desire to be spectacular and controversial. The tapering shape , starting narrowest at street level and bulging most at floor 16, before narrowing again steadily towards the top, was chosen in response to the computer models.
Tall buildings funnel winds into narrow channels around them at street level (it’s just like putting your finger partly over the nozzle of a garden hose to make the jet reach further – the increased pressure brought about by the constriction results in a higher velocity of water-flow) and this can have a horrible effect on passers-by and people using the building. They feel as if they are in a wind tunnel. The narrowing of the building at the base reduces these unwanted wind effects because there is less constriction of the airflows. The tapering of the top half also plays an important role. If you stand at ground level beside a conventional un-tapered tower block and look upwards, the building dwarfs you and blots out a large fraction of the sky. A tapering design opens up more of the sky and reduces the dominating effect of the structure because you can’t see the top from close-by on the ground.
The other striking feature of this building’s exterior is that it is round, not square or rectangular. Again, this is advantageous for smoothing and slowing the airflow around the building. It also assists in making the building unusually eco-friendly. Six huge triangular wedges are cut into each floor level from the outside in. They bring light and natural ventilation deep into the heart of the building, reducing the need for so much conventional air conditioning and making the building twice as energy efficient as a typical building of the same scale. These wedges are not set immediately below each other from floor to floor, but are slightly rotated with respect to those the floors above and below. This helps increase the efficiency of the air suction into the interior. It is this slight offsetting of the six wedges from floor to floor that creates the exterior spiral pattern that is so noticeable.
Looking at the rounded exterior from a distance, you might have thought that the individual surface panels are curved – a complicated and expensive manufacturing prospect – but in fact they are not. The panels are small enough, compared with the distance over which the curvature is significant, that a mosaic of flat, four-sided panels is quite sufficient to do the job. The smaller you make them, the better they will be able to approximate the covering of the curved outside surface. All the changes of direction are made at the angles joining different panels.
