chris wise engineer

The birth of London’s Millennium Bridge

A few January’s ago, I was standing in the middle of Cornwall on a very cold, but very sunny afternoon. It was so cold that the ground was frozen, which is a rare event for those parts. There is a ridge running down the middle of the county, which lifts the fields high above the sea which flanks the peninsula on both sides. As I stood up there I found myself profoundly moved by the situation and, in particular, the quality of the light, which seemed to come from all around me. In the distance the ground was covered with a tracery of mist, but close up the blues, yellows, greens and browns were more intense than a Van Gogh painting, and the coldness made every shadow appear as if it had been etched out of solid air. I realised that the setting sun was being reflected back up off the sea so that you felt as if you were on a bridge walking through light. I had a tremendous sense of connection with the place, and I felt part of that visceral landscape.

In attempting to find a design for the Millennium Bridge, we were trying to capture the same vital clarity, and the same sense of place. We wanted to do something that would lift the spirit, and we knew that if we succeeded it would be an intense experience. What follows are my recollections of the intuitions and feelings behind the birth of the design of London’s first new river crossing since Tower Bridge. To some extent they are offered as an antidote to the process-gurus who believe design is a system, in which humanity is a side-line.

As a Londoner for the past two decades, I feel part of the London landscape, and I care deeply about it. To attempt to design a bridge for London is to try to design the landscape of the city itself. A bridge connects people together…in fact it makes new connections where previously there were none.  It is a gift to the people…something that everyone can enjoy and use. It gives you the opportunity to pause high above the river and see London’s skyline from a new perspective. Our bridge was also to be a bridge across time, linking three centuries from St. Paul’s Cathedral to the new Tate Modern at Bankside, each of which is an towering icon, a regeneration project and a symbol of its age, and connecting even further back to the Celts and the Romans who both crossed the Thames near our site.  Symbolically, it was to link the City and Southwark, among the richest and poorest parts of London. And it was to be a pedestrian bridge, totally in tune with the need to give London back to its people, and entirely sustainable.

In that context the feelings that arise are profound…among them humility, privilege, and a sense of our place here for  short time as we look after London for our children and grand-children. You want to find a design that is pure, distilled, and will stand the test of time. At such a site, it is unbecoming to try to compete for attention with St. Paul’s and the Tate, with the River, or with London itself.  You hope to be able to do something that is in harmony with its place, and with its time, something of which our generation can be proud. A bridge is normally designed to last 120 years, or 6 generations, but we all hope it will last longer.  We found ourselves wanting to do the “perfect” project, knowing that we wouldn’t be able to, but believing it was worth the attempt.

And there was the small matter of having to win an open competition with more than 200 entries just to get the commission.  We almost didn’t enter at all because we felt the odds were too long to justify the soul-searching needed to do the project justice. I was telephoned at Arup’s by Sir Norman Foster who asked me to work with him and Sir Anthony Caro on an entry. I worried that I as I wasn’t a knight too our team would be a little unbalanced, but the problem was solved when I asked my long-time mentor and friend Sir Jack Zunz if he would like to help us and he gladly agreed.  Jack is a wonderfully pragmatic critic and later proved to be a wise counsel for the whole team.

We all knew the site very well, and arranged to meet at Tony Caro’s studio to share our first thoughts on the project.  The night before the meeting, I went out with my fellow engineer Roger Ridsdill Smith to a wine bar called Zelda’s in Charlotte Street.  Roger has some of the qualities of an artist-engineer in the old sense…he can draw beautifully but understands the technology of building too. We spent the evening at Zelda’s, and talked about London, the bridge, and what it could be like. We knew that the bridge would land high up on the bank on the St. Paul’s side, and probably low down on the Tate side. We knew that we had to span nearly 150 metres clear across the middle of the river so that up to 500 ships a day could move up and down safely. And we knew that we would like everyone to be able to use the bridge, old and young, walkers and wheel-chairs, businessmen and lovers alike. With the right alignment, the bridge would open up a magnificent new view of St. Paul’s, through the break in the riverside buildings and up Peter’s Hill to the portico. Sir Christopher Wren had to watch his new cathedral rise from the ashes of the Great Fire from his house on the opposite bank near the Globe Theatre, but the bridge would allow us and the residents of Southwark to walk back and forth, joining visitors to the cathedral and the Tate and helping to regenerate the river front and its hinterland. How Wren must have wished for a bridge when, as an old man, he was rowed across Sweete Thames each day to visit his construction site.

That night in Zelda’s, Roger and I tried everything to capture the essence of the site and to respond to it with as much grace as we could muster. My sketchbook from that evening shows we tried a cable stayed bridge, rejected because it was too tall and egotistical for the site. We didn’t even consider a suspension bridge (for the same reason). We tried a flat arch (still too strong for the site), and an even flatter truss (too clumsy and heavy), and we explored paired sloping arches (which would become rapidly dated). We looked at a cable truss (too fussy). But sometimes late at night your mind has an ability to focus on just one thing in great depth, and as the evening wore on we tried to strip away everything that was superfluous. In that mood, Roger and I decided that we should just try to make the structure from cables stretched as tightly as possible between the two banks, and then walk on them.  Surprisingly, given the lateness of the hour, we even did some very rough calculations to see if the idea could work.

Looking at them now I am amazed that we got reasonably close to the eventual  answer…0.5m sag of the central span (actually 0.75m), total cable forces of 1600 tonnes (actually 2000 tonnes), a natural period of about 2 seconds (actually 2.5 seconds).  We went home that night tremendously excited about the purity of the diagram, and petrified that the bridge might shake itself to bits like the Tacoma Narrows unless we could find a neat way of providing some rotational stiffness and damping.  Our thoughts that first night involved putting the cables outside the deck, so that they would act as outriggers to give some measure of torsional stability, and eventually this matured through three generations of wind-tunnel tests into the use of the same supporting cables as aerodynamic dampers.  Mies van der Rohe’s “less is more” distilled into high-strength steel.

The next morning we went to Caro’s studio and met Tony and Norman. Everyone talked about the site and the project, and Tony showed us some sculptural ideas for the bridge developed from his series of long steel table sculptures. As sculptures they were beautiful, as a bridge a little harder to imagine and even harder to walk across, but they were a fascinating glimpse into the way a sculptor approaches a design compared to an architect or an engineer. When we showed Tony and Norman our ideas for the taut flat cables upon which you could walk, they both became very reflective and simply said: “Yes, that’s what we should do”. Norman later did a beautiful sketch which showed how our bridge would sit in the site, and together we won the competition. At night-time he imagined it as a “blade of light”, echoing my Cornish experience of a few months earlier. For the next two years we tested, refined, consulted, and honed the project, trying all the time to maintain the simplicity of those first sketches to which we all had such a strong intuitive response.  As in all projects, the Bridge has been a team activity, with a supportive client, and the team has worked well because everyone believes so much in the project. Perhaps this was exemplified nearly two years into the project, at 12pm one Sunday night, when Sophie le Bourva of Arup was putting the finishing touches to the final tender package. Although she was very tired, and had been working long hours and weekends for many weeks, she was humming contentedly and smiling to herself, because she was very happy about what she was doing.

The Millennium Bridge is something that everyone can enjoy and use. For the designers and now the contractors, it is a privilege to be entrusted with such a project in the heart of our own city. From 2000 it will become as much a part of the walking fabric of London as any other footway. One small question arises…..totally tuned to the drive to get us out of our cars and onto our feet, it is tempting to ask John Prescott why even a bridge like this is only half-funded by the Millennium Commission and would not have happened at all if it relied on government funding. Perhaps for the moment it is enough to enjoy the slender product of a unique collaboration between public and private funding, sculptor, engineer and architect, the world’s flattest suspension bridge and the first new bridge in London for over 100 years.

Client:                                                                London Borough of Southwark
Engineer and Lead Consultant:                        Ove Arup and Partners
Architect:                                                           Foster and Partners
Sculptor:                                                            Sir Anthony Caro
Lighting:                                                             Claud Engle
Contractor:                                                         Sir Robert McAlpine/Monberg Thorsen J.V.
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