Responsive Structures

Chris Wilkinson

Buildings are usually thought of as being static constructions, but they don't have to be. We rate our cars by performance and when we order the latest model we expect it to incorporate the most up-to-date technical features. Car body designs are wind-tunnel tested to achieve the minimum drag coefficient and the engines are constantly being developed to achieve higher performance and fuel efficiency. Internal features include electronic seat adjustment and on-board computers that can help you plan your route, tell you when the next service is required and how efficiently you are driving. Windows open with the press of a button and, with convertible models, the roof can be automatically folded away when the weather is fine.

Buildings should be designed to be more responsive to the environment and to interact with their occupants. All the features available in automotive design are available for buildings, too, and we should be looking to improve their performance. The building envelope could be more responsive and instead of relying on 'mass' for protection against the elements, it would make more sense to use a series of lightweight layers which deal with thermal performance, shading, wind deflection and even power generation. It is well known that wearing a number of thin layers of clothing conserves body temperature better than a single heavy coat. Similarly, the fur on a cat provides the ultimate responsive 'enclosure'; the multiple thin fibres are able to compress or open out to vary the amount of insulation – to keep the skin at the required temperature without adding too much weight. Feathers work in the same way for birds and even the hairs on our own skin respond to temperature in a similarly active way.

The technology is now available to create more 'intelligent building envelopes'. It is theoretically possible not only to achieve zero heat loss/gain through the building skin, but also to collect heat from within the layers and use it to advantage. Curtain-walling has come a long way since the single glazed extruded aluminium systems of the 1950s, but it can be taken much further.

At a recent Architecture conference at IIT in Chicago, Mike Davies described the experience of living in a responsive building of the future:

'Look up at a spectrum-washed envelope whose surface is a map of its instantaneous performance, stealing energy from the air with an iridescent shrug, rippling its photogrids as a cloud runs across the sun, a wall which, as the night chill falls, fluffs up its feathers and turning white on its north face and blue on the south, closes its eyes but not without remembering to pump a little glow down to the night porter, clear a view-patch for the lovers on the southside of level 22 and turn 12 per cent silver just before dawn.'

If this sounds too far fetched, it is worth noting that smart materials which can change colour and transparency already exist and computerised control systems are also available which can respond to time and environmental changes. So what used to be science fiction is now technically possible and could be incorporated in the next generation of buildings.

Arthur C. Clarke once observed that 'any sufficiently advanced technology is indistinguishable from magic.' It is therefore a kind of magic that we are trying to achieve with our 'active glass wall' at Explore at-Bristol. In an attempt to create a constantly changing façade to the street frontages, we have incorporated a number of intelligent glass systems combined with digital art and multiple light sources connected to a sophisticated control system. The façade consists of a conventional outer skin of double-glazed units supported by 600mm-deep glazed fins, which are drilled to receive an inner layer of experimental glazing. This includes: elecrophorretic glass, which changes from transparent to opaque and can be used for back projection; thermochromic films, which are heat-sensitive with a visible reaction to changes in termperature, so they show handprints when touched or could form the basis of thermic art; dichroic film, which refracts light like a prism to create a luminescent colour and works in reverse when seen from a different angle; and lenticular images, which look like holographic forms adhered to the glass. The intention is to show how these 'intelligent glass' systems work and how they might be incorporated in buildings.

Our competition entry for the Royal College of Art extension and new studios experimented with glass in a different way, using areas of reflective fritting, dichroic film and panels of transparency as a pattern on translucent glass, giving interest and complexity to an otherwise plain glazed façade.

The thermal performance of a building is greatly improved if glazed openings are protected from direct sunlight in summer but this doesn't mean that permanent fixed structures are necessary the rest of the time. Shading devices can be folded away and extended outwards automatically when the sun comes out, or can be built into the glazing system. One of the earliest examples of this was the US Pavilion at Expo '67, in which segmental shading devices automatically opened up on the inside of the transparent geodesic dome when the sun came out. Unfortunately, the technology of the day was not quite up to the aspirations of the designer and there were mechanical problems which marred its performance, but the concept was extremely innovative and ahead of its time. Jean Novel progressed this idea further at the Arab Institute in Paris, with integral solar-activated camera lens-type screening to the glazing system.

Solar cell-activated shading devices are no longer cutting-edge technology and are easy to specify. In fact, this technology generally seems to have been advancing so fast that it may have exceeded people's aspirations. In many cases, it makes sense for buildings to be fully enclosed in winter but still have the capacity to open up in good weather, like the Mercedes SLK sports car. You might think that this idea would be taken up by house builders dealing with tight sites but all too often they are still building conventional houses which replicate past styles, rather than looking for innovative solutions.

In this aspect of architecture as with other aspects of life, there are many lessons to be learnt from nature. For example, the hibiscus flower opens during the day but closes up at night to preserve energy, and the sunflower tracks the sun throughout the day. It is always a joy to see a field full of sunflowers all facing in the same direction and it is not a matter of chance. In the same way, solar collectors can be designed to track the sun and now that photovoltaic cells are more efficient, it can make commercial sense to incorporate them into our building structures. The generation of solar power is good for the environment because it saves on CO2 emissions, the by-product of most other kinds of power. It seems particularly relevant to use photovoltaic shading devices because the dual-purpose role of providing shading and the collection of energy from the sun helps to justify the expenditure.

Sustainability is one of the main issues of our time. Lower-energy solutions can be found with natural ventilation systems, which save on instsallation and running costs. With the use of Computer Fluid Dynamic Programmes these systems can now be tested and perfected in the design stages. This doesn't mean that the architecture has to become earthy and low-tech. Our Stratford Station design for the Jubilee Line Extension, for example, uses the 'stack effect' through the structural void between the ceiling and the roof to ventilate the space above the high-level walkway. Here the sun on the outer roof surface and the tapering void space helps to draw air through; so you could call it solar-powered ventilation, with the result that there is no need for any mechanical ventilation plant or ductwork.

In an entirely different way, buildings can also interact with the people using them. We are all familiar with the interactive exhibits used extensively in museum, which have been designed to interest the users, but why shouldn't the building also play its part?

In science centres it is particularly relevant that the building communicates with its occupants and this is an area we have been experimenting with further. At the Challenge of Materials Gallery in London's Science Museum, we collaborated with the sound and light artist Ron Geesin to create an active bridge which spans the atrium and responds to the load variations of people walking across it. The glass deck is supported by a tension structure of fine steel cables and these are strung onto a crescent-shaped stainless-steel plate, which is fixed back to the main building structure through load cells. Each cable and load cell is wired up to a computer that plays sounds which vary according to the superimposed loads. Further sounds are overlaid, triggered by sensors placed under the glass planks of the bridge deck, so that music is produced as you walk on it. The bridge not only looks like a huge stringed instrument but sounds like one. In fact, the cables are tensioned with piano keys and make a deep humming sound when amplified or can be plucked like a harp.

This responsive approach was progressed our fit-out design for the Wellcome Wing at the Science Museum, where interactives have been incorporated into the signage, seating and even the dining tables.

Building structures can also be more responsive and dynamic. At the press launch of our first bridge, completed at Canary Wharf in 1994, there were about 30 people standing on the bridge when, to their surprise, it started to move. The 90m-long, cable-stayed southern half of the bridge is fitted to a slew-bearing pivot mechanism, which enables it to rotate – and we had rather mischievously set it in motion to show how it worked. No one was too alarmed because the slow, controlled movement seemed completely natural. In many ways people are used to technology and have faith in what can be achieved, but sadly the number of innovative projects constructed are still rare.

However, we at WilkinsonEyre are keen on innovation and fired with the experience gained on the rotating South Quay Bridge, we went on to develop the horizontal pivot bridge at Gateshead in which the entire 700-tonne steel-arched structure is mounted on two hydraulic pivot mechanisms, which enable it to open like an eyelid in less than 3 minutes at the press of a button in order to allow ships through. There are many examples of opening bridges and this is by no means the largest, but there are very few examples of this kind of structure being incorporated into buildings. It is only recently that a growing number of sports stadia have incorporated opening roof systems, but for climates such as ours this must surely become the norm.

There are many other opportunities for kinetic building structures and it is heartening to see the results of Chuck Hoberman's research into what he calls 'unfolding structures'. This young American engineer/sculptor, who invented the popular Hoberman Sphere Toy (a collapsible skeletal ball made of brightly coloured plastic), has been working on the design of building structures which expand from a small kit of parts into an enclosing form. Hoberman has taken the engineering discipline of deployable structures to a new level with his expanding geodesic and iris dome structures and we are looking to collaborate with him on building structures in the future.

Engineers involved with the design of buildings are usually terrified of creating structural mechanisms; yet this would seem to be an area ripe for future advances. It now seems feasible to accommodate in buildings load-shifting mechanisms that respond to applied forces, like muscles in our bodies, and help reduce the weight of structure. In fact, the human body provides an excellent example for architectural structures. Donald E. Ingber, in his article 'The Architecture of Life' (Scientific American, January 1998) compares the human body to a tensegrity structure:

'The principles of tensegrity apply at essentially every detectable size scale in the body. At the macroscopic level the 206 bones that constitute our skeleton are pulled up against the force of gravity and stabilized in a vertical form by the pull of tensile muscles, tendons and ligaments. In other words, in the complex tensegrity structure inside every one of us, bones are the compression struts and muscles, tendons and ligaments are the tension-bearing members. At the other end of the scale, proteins and other key molecules in the body also stabilize themselves through the principles of tensegrity.'

He defines tensegrity as 'an architectural system in which structures stabilize themselves by balancing the counteracting forces of compression and tension' and compares cell composition to Kenneth Snelson sculptures and to Buckminster Fuller geodesic domes.

As architects, we are attracted to tensegrity structures for their visual lightness and their efficiency. They offer the maximum strength for a given amount of material, which keeps the member sizes slender and light. This is particularly relevant to bridges, where long spans can be achieved with slender suspension structures, such as our Metsovitikos Bridge in northern Greece. Cable structures have movement and life, which adds to their appeal. When a bridge structure moves in response to your weight as you cross it, you know that it has been designed for efficiency. A certain amount of movement in structures is generally a good thing, so long as it is controlled within defined limits.

In racing yachts, where the sail structures are designed for performance and the materials are pushed to the limits, rigs are actively tuned, manipulating tensions and deflections to optimize performance. No one would suggest that bridges and building structures should be pushed that far, but dead loads should be kept to the minimum. More use could be made of dynamic dampening. For some time now, hydraulic load dampers have been used on the top of skyscrapers in the United States to reduce the effects of windload on the structure and thereby save on the weight and cost of the building structure. It is a principle which could be applied to more situations in the interest of improved efficiency and performance.

In a modest way, dynamic dampening was used on a small project of ours to reduce deflections on our camera arm structures at the heritage Northern Line Stations for London Underground. We wanted the structure to be light and elegant but the client's performance requirement for minimum movement deflections for the cameras, mounted at the end of the structural arm, called for a stiff bulky structure. Bryn Bird, our structural engineer on the project, solved the problem by using a sprung mass damper to soak up vibrations. It was something of a relief, when the prototype was tested, to find that this inventive solution succeeded in dampening the structural movement and vibration to within the permitted tolerances. They are now installed at more than 20 stations on the line.

Architecture is steeped in history but it has always been inextricably linked with technology. Today we have the opportunity to explore completely new fields and we must look to creating more efficient and more intelligent buildings, which respond more actively to the environment and attend to the needs of the user. We should welcome innovation so that we can enjoy increased sustainability and a new genre of responsive structures.

Chris Wilkinson

This essay originally appeared in the practice monograph 'Bridging Art and Science' (Booth –Clibborn Editions, 2001).