by Roma Agrawal
The shape of these bridges reminds me of the basic rope bridges made by our ancient ancestors. Like them, and the bark spider’s bridging line, a stress-ribbon bridge is a catenary. A stress-ribbon bridge is also very light – the concrete planks are quite thin at about 200mm – and the natural curved shape of the steel cables gives them a slender and satisfying aesthetic. And, just as importantly, as far as I’m concerned, these bridges are practical too, being relatively quick to build. Once the foundations are done, the lifting of the pre-made concrete planks onto the cables is a straightforward and speedy procedure, so building them has less of an impact on the surrounding environment.
The curved red ribbon of my Japanese bridge crossed a deep ravine with a small but rapidly flowing stream at its base. As the rain hammered down, I stepped out onto the deck. It was a little bouncy. I walked up and down several times, varying my speed, then jumped on it, to see what that felt like. The movement was disconcerting, and I realised why – even though stress-ribbon bridges look fantastic and are quick to build – some people don’t like them.
Because they are light and rest on cables, there’s a large sag in the middle, and the ends of the bridge have relatively steep slopes which can be tricky for people with buggies or those using wheelchairs. And these bridges can be lively – their lightness and flexibility mean that, as you walk across them, they can feel unstable. Even though they are perfectly safe, stress-ribbon bridges usually move. The sag, combined with the bounciness, can give the impression that these bridges are a little dodgy. People in the three countries I’d already visited loved them, but they were used to their movement. Elsewhere, a misplaced perception of instability, and a lack of strong ground in which to anchor the tendons and keep the structure stable, might be reasons why stress-ribbon bridges haven’t caught on.
By now I was soaked to the skin, but I spent a long time examining the expert engineering (after all, I had travelled nearly 10,000km to see this bridge that was so unusual back home in Britain). When the bridge shook, I clung to a handrail with one hand, trying to keep hold of my umbrella with the other. I found it difficult to stand in the middle for too long, as the valley’s depth, the rapid water gushing through it, and the fact that it moved the most here, unnerved even me.
Nevertheless, like any self-respecting engineer, I made sure that my mum got plenty of snaps of me in situ on the structure, before we raced back to the taxi, where the driver lay asleep in his reclined seat. We drove back to Tokyo, still a little soggy from our visit.
The stress-ribbon structures I studied during my travels have stayed with me: I’m inspired by the fact that the simple rope bridge has evolved to incorporate modern technology and materials – and that despite its modernness, this new form has retained the simplicity and elegance of its forebear. New engineering doesn’t always have to be big and bold; sometimes it can draw on humbler roots.
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Bridges are all very well, but no doubt you’re wondering how things worked out between me and Flirtman. All I can say is that I came to regret emailing my friend to boast that I had got rid of him in three minutes. Four years later, she read that email out loud in front of hundreds of people. During her bridesmaid’s speech. At my wedding.
Yes, dear reader, I married him.
DREAM
Imagine, for a moment, a world without engineers. Abandon Archimedes. Banish Brunelleschi, Bessemer, Brunel and Bazalgette. Forget Fazlur Khan, oust Otis and, yes, get rid of Emily Roebling and Roma Agrawal. What do you see?
More or less nothing.
Of course, there’d be no skyscrapers, no steel, no elevators, no houses and no sewers under London (gross). No Shard. There’d be no phones, no internet and no TV. No cars, nor even carts – which is perhaps just as well since there’d be no roads or bridges either. And we’d be wearing more or less nothing too: there’d be no stitching together of animal skins to make clothes. And no tools for foraging, no fire for safety, no mud huts or log cabins.
Engineering is a big part of what makes us human. Sure, there are crows that can fashion a piece of wire into a hook to retrieve food, and octopuses that carry coconut shells for protection, but – so far at least – we have the edge. Engineering furnished us first with the essentials – food, water, shelter, clothing – and then with the means to cultivate crops, build civilisations and fly to the Moon. Tens of thousands of years of innovation have brought us to where we are today. Human ingenuity is boundless; we will always aspire to manufacture more, to live better, to solve the next problem – and then the next. Engineering has created, in the most literal way, the fabric of our lives; it has shaped the spaces in which we live, work and exist.
And it’ll shape our future, too. Already, I can see certain trends in engineering – irregular geometry, technology such as robotics and 3D printing, a quest for more sustainability, the merging of different disciplines (such as in biomedical engineering), a mimicking of Nature – that will once again change the way our landscape looks and feels, and the ways in which we inhabit the planet. Even if some of these seem the stuff of science fiction at the moment.
Computing capacity has made it possible for us to draw complicated, cambering shapes, such as the flowing surfaces of the Spanish Pavilion at 2010’s World Expo, the undulating Guggenheim Museum in Bilbao, and the Heydar Aliyev Center in Azerbaijan, which is as intricately shaped as a conch shell. This move towards the geometrically complex takes us away from the traditional square or rectangular building and towards more natural forms. At present, creating these shapes is still expensive because it involves curving steel and shaping it into bespoke contours, or building intricate moulds for concrete. Interestingly, these moulds can account for up to 60 per cent of the total construction budget of a project – only to be binned once the concrete has hardened. In fact, to date, keeping the cost of the moulds (or formwork) down is one of the reasons why our columns, walls and beams tend to be rectangular: it’s cheap and easy to buy rectilinear pieces of plywood.
So with this emergence of curvy shapes, we need to think smartly about how we’re going to build them. (Concrete is a good option since its liquid origin makes it ideal for transforming into any shape.) One way is to use large polystyrene blocks, painstakingly carved by hand or by machine, against which concrete can be poured. But this creates much waste, because the blocks are useless once the concrete has hardened. An exciting idea – which has been around since the 1950s but has so far only been used sparingly – is the flexible membrane mould. Almost any material, ranging from hessian or burlap to light sheets of plastic made from polyethylene (PE) or polypropylene (PP), can be used. These fabrics start off slack and shapeless – but introduce some wet concrete and we’re quickly reminded of what a responsive and sensory material it is: concrete interacts with the fabric, stretching and moving it to create a final shape. Two seemingly disparate materials come together in a symbiotic relationship of pressure and restraint.
Spanish architect Miguel Fisac designed the MUPAG Rehabilitation Center in Madrid (opened in 1969), using this technique to create a façade that looks cushion-like and bouncy. At one of the entrances to the Heartlands Project in Cornwall is a wall that looks like a flowing piece of silk suspended from the sky; touch it, however, and you feel solid concrete. I’m sure we’re going to see more structures like this, including many on a much larger scale, because using PE or PP sheets as formwork eliminates a huge amount of waste; plus they don’t tear easily – and if they do, the tears don’t propagate. Moreover, nothing – including concrete – sticks to them, so they can be used multiple times. The internal steel reinforcement skeleton doesn’t need to change much; neither does the concrete mix itself. But the challenge so far has been that we’re simply not used to working this way. It completely changes the aesthetics of structures: architects and engineers need to catch up, as do the logistics and procurement of construction. But they will, and I bet you that when they do, I won’t be the only one caught stroking concrete in public.
Talking about stroking materials: at the University of California, Berkeley, I once got my hands on some 3D printed modules (which ranged in size from my palm to a dinner plate) that could be assembled to make small installations, walls, facades and shelters. The modules were in a range of colours, and when I asked why I was gobsmacked by the answer. The white ones were salt. The black ones, recycled rubber tyres. The brown and the grey ones were more familiar materials – clay and concrete, respectively – but the purple ones were made of grape skins. That’s right: grape skins. A research team led by Ronald Rael is investigating the use of unusual materials (mixed with resins to create a printable paste) to build stuff. I love the fact that, as well as working with traditional materials in a futuristic way – from geometric concrete blocks with irregular perforations to small gorgeously patterned hexagonal clay tiles for use on facades – they are also experimenting with waste materials, including those from the local wine industry. Some of their designs are self-supporting and don’t require any additional structure. It got me to thinking about how 3D printing, along with exciting new combinations of materials, could lead to a future where we print these pieces and then assemble our own homes.
And 3D printing is not only being used on a modular scale – in fact, the world’s first 3D-printed footbridge was opened in Madrid in December 2016. At 12m long, it was analysed to find out exactly where the forces were being channelled; material was then deposited only in those sections – meaning minimal material, less waste and a lighter end product. Robots are also being designed to lay bricks and pour concrete on site: manufacturing embraced this trend decades ago, and now its the turn of the construction industry to catch up.
Taking the return to nature in form and material another step further is biomimicry, whereby not only do you mimic the shape of beehives, bamboo or termite mounds, but also their function. A famous example of this technique is the burdock burr that inspired Velcro: we copied its hooks, and its ability to stick to other surfaces. Nature builds simply and with as little material as possible, and we can reflect this principle in our structures. The skulls of birds, for example, have two layers of bone between which is a complex web of truss-like connections separated by large air pockets – in fact, bone tissue forms naturally around the cells that experience high pressure, leaving voids elsewhere. London-based architect Andres Harris conceptualised a curving canopy using a web of cushions around which a structure, similar to the birds’ skulls, can be cast. Similarly, the Landesgartenschau Exhibition Hall in Stuttgart gets its inspiration from the sea urchin, which has a skeleton made from interlocking plates or ossicles, each of which is sponge-like and lightweight. The exhibition centre is made from 50mm-thick plywood sheets, analysed carefully by software and then fabricated robotically and assembled. If you magically expanded an egg to be the same size as this structure, the plywood would be thinner than the egg’s shell.
Nature also heals itself: the human body can detect when something is wrong (often making us feel pain) and then, through a series of steps, fixes the problem. So far, with structures, we have had to intervene and perform repairs – or surgery – when things go amiss. However, a team led by Phil Purnell of the University of Leeds is designing robots that can travel – like white blood cells – through pipes in the road to diagnose defects which can then be fixed before they lead to erosion and collapse. The Institute of Making’s Mark Miodownik is leading a team developing 3D printing technology that can be carried by drones to repair potholes and other road defects so we won’t need to close down roads to repair them, saving money and easing traffic – the end of roadworks, perhaps? And a team at the Cambridge Centre for Smart Infrastructure and Construction is looking at adding nervous systems to new structures. A single fibre optic cable, tens of kilometres long, with continuous sensing elements, can measure the strain and temperature inside piles, tunnels, walls, slopes and bridges. Data that has never been available before can be collected, and will not only help engineers learn from these designs, but also warn them of impending problems.
If I try and imagine what the world of the future will look like, I imagine these biological forms interspersed with pencil-thin towers and conserved historical structures. Already, towers such as 432 Park Avenue in Manhattan boast of their slenderness ratio (it’s 14 times taller than it is wide). A challenge for stability and sway, these ultra-thin skyscrapers usually have dampers. I expect we will see more and more such structures combining offices, apartments, shops and public areas as the battle for space in congested cities intensifies. Many of our historical structures are starting to underperform as time goes on: their water and drainage pipes are often inadequate; lots of heat is lost as they were never well insulated; and beams and floors can be seen to sag. Walk around London and you will notice ornate old facades shooting up into the sky seemingly unaided because the buildings behind them have been demolished. But these facades are being surreptitiously supported by a network of beams and columns that hold them steady until a new building is put in place. Using technology such as lasers to create detailed 3D maps will make it easier for engineers to understand the old and combine it with the new.
And if I really think into the future far beyond my lifetime, I imagine my descendants living underwater in pods made from paper-thin glass that cannot be shattered. Our bridges could span ten times the distance they do today because they’ll be made from graphene, the ‘super-material’ of our future. Perhaps we will even ‘grow’ our homes from biological material that can be shaped and modified to suit our needs.
But for now, I arrive home every night to the welcoming arms of my old, rectangular, solid-brick Victorian flat. As I turn out the lights (still holding my rather more haggard stuffed-toy cat from New York) and begin to doze, I wonder what the Vitruvius and the Emily Roebling of the future will create. The possibilities are limited only by our imaginations – for whatever we can dream up, engineers can make real.
ACKNOWLEDGEMENTS
Thank you:
Steph Ebdon, who planted the seed of writing a book in my mind, even though I laughed and said it would never happen. I’m ecstatic that it did.
Patrick Walsh, agent extraordinaire, who believed in me and my idea, taught me how to add texture to text, and supported me through every step of the process. Leo Hollis for his support, and that timely introduction to Patrick.
Natalie Bellos, brilliant editor, who saw something in my proposal and guided me through its years of development. Her insights, dedication (even while on leave) and attention to detail are unparalleled. Lisa Pendreigh and Lena Hall for turning it into a real object, for getting it over the finish line. Pascal Cariss for making my ‘sentences sizzle’ – you breathed life into my words. Ben Sumner for his impeccable copy-editing. The global Bloomsbury team, for nurturing my baby and making it the book it is today.
The brilliant Mexican engineers I met: Dr Efraín Ovando-Shelley (Instituto de Ingenieria, UNAM), who showed me the Metropolitan Cathedral; and Dr Edgar Tapia-Hernández, Dr Luciano Fernández-Sola, Dr Tiziano Perea and Dr Hugón Juárez-García (Universidad Autónoma Metropolitana – Azcapotzalco), who explained the challenges of the ground and earthquakes. The British Council, for organising a very memorable trip to Mexico City.
Phil Stride of Tideway; Karl Ratzko, Neil Poulton, Simon Driscoll of WSP; Ronald Rael of the University of California, Berkeley: for their time and interviews aiding my research. Robert Hulse at the Brunel Museum for his insight.
Rob Thomas, fountain of book-related knowledge at the Institution of Structural Engineers’ library, who found the most obscure sources for me and was always available to listen to my ramblings. Debra Francis of the Institution of Civil Engineers’ library for her help.
Mark Miodownik, whose book Stuff Matters is my inspiration (it’s still on my bed-stand): the nicest guy you could ever meet, you’ve done so much for me. Timandra Harkness for her support, and her introduction to my wonderful writing friends at NeuWrite, who commented an
d critiqued.
John Parker, Dean Ricks, Ron Slade; everyone on ‘The Shard Team’; the directors at WSP: for an amazing decade of learning and growing. David Holmes and Gordon Kew at Interserve; John Priestland, Mike Burton, Peter Sutcliffe and Darran Leaver at AECOM: all my superbly supportive employers – I know I am an ‘unusual’ employee.
David Maundrill, Joe Harris, May Chiu, Dr Christina Burr, James Dickson, Pooja Agrawal, Niri Arambepola, Emma Bowes, Chris Gosden, Jeremy Parker, Karl Ratzko and Chris Christofi, dear friends and colleagues (and sister) who read chapters, fact-checked and helped me.
The engineers and scientists, organisations and institutions out there that have inspired me to go out and tell people about what we do. For giving me a platform to speak and write. I am optimistic about the future of our collective profession – its innovation, its impact, its inclusivity.
My family, the whole extended worldwide clan – my grandparents, aunts, uncles, cousins, nieces and nephews, and my mother-in-law – who have always been my cheerleaders, and who waited patiently for this huge project to be finished. My friends, whom I haven’t seen much of recently – I will be back. You were always there. My loved ones who are no longer here, I miss you.
My parents, Hem and Lynette Agrawal; my sister, Pooja Agrawal: where do I start? For always telling me I could achieve everything I wanted through ‘hard work’, for inspiring me with Lego, science and our worldwide travels, for giving me the best education, for challenging and questioning me, for all your love.
And finally, my Flirtman, aka Badri Wadawadigi, who has navigated me – sometimes kicking and screaming – through four years of writing, for reading the words more times than anyone else, for reminding me that I can do it when I didn’t believe I could, for telling me off when I procrastinated, for intelligent feedback, for naming the book, for encouraging and pushing me to achieve more than my dreams, and for your love. Let there be many more Bridges of the Day.
