The Millennium Bridge Projects - Case Study Example

The Millennium Bridge Over the centuries from the Romans onwards there have been bridges over the Thames. The first one was wooden, possibly built on pontoons and in two parts leading to an island in the river. It was roughly in the position of the present London Bridge and connected Watling Street ( The present A3, and the main road to the south coast ports and so on to the larger continent and Rome itself. Although repaired and replaced many times ( Hence the famous rhyme ‘London Bridge is falling down’) this was the position more or less of the only fixed crossing of the river near the City of London until the building of Putney Bridge as late as 1729. Instead boat men conveyed people back and forth. From that time of the building of Putney Bridge however bridges proliferated, especially with the coming of the industrial revolution and the railways. There had however been no new purely pedestrian bridge for more than a century. The Millennium Bridge Opposite the City of London there was huge development in the late 20th century. The new Shakespeare’s Globe theatre, long planned, was rebuilt on the shores of the South Bank and opened in 1997. This was and is a huge tourist attraction, even to those who only want to stand and stare at its thatched roof, contrasting as it does so thoroughly with the other buildings around it. Also the old Bankside Power Station site has become the Tate Modern, again a huge attraction with thousands of visitors each day, especially as so much of it is free and the coffee is excellent. Opened in May 2000 it attracted 5,000,000 visitors in its first 5 years, many of them crossing on foot from the city, having arrived via Tube ( Blackfriars, St Paul’s and Mansion House) rail ( Blackfriars) and bus. Then there are the longer established attractions of the Southbank – from markets to theatres and restaurants. The London Millennium Footbridge The London Millennium footbridge was an idea waiting to happen. Made of concrete, steel and aluminium, it is 325 metres long and crosses the Thames from near St Paul’s Cathedral in the City of London to the Tate Modern art gallery on the South Bank. It began as an idea from the Financial Times, many of whose readers would of course be users of London bridges, whether rail, road and foot, which held an international competition. This was done in conjunction with the Royal Institute of British Architects and the London Borough of Southwark, as described on the web site ‘themilllenniumbridge’. The idea was to provide a footbridge between the Southwark and Blackfriars bridges, both road bridges. One wonders why the City of London was not also involved at this stage. It was decided that it should be a long span bridge, a piece of public architecture as much as an engineering project. The fact that it is for pedestrians only means that users have a unique, traffic free view of the sights. The result was an unusual collaboration between the firm of Arup Engineers, the sculptor Sir Anthony Caro and architects Foster and Partners. The bridge was finally opened by her majesty the Queen, with huge publicity in June 2000. 80,000 people crossed the bridge on the first day according to the BBC In depth report. Others, such as Arup themselves, think there could have been as many as 100,000 individuals. The Risks This bridge was innovative in its design and any new engineering project always carries something of a risk. The people involved did however do all they felt possible in order that their project would be a success. It was a highly publicised project, especially because it was right in the heart of London and had the Queen herself to open it. It could have all fallen very flat. It proved to at the very least an embarrassment to the Queen, the government, and the companies involved. Risks were minimized by in the first instance closing the bridge on the 12th of June and then looking at various possible options, and finally making necessary adjustments. As it is the original disaster has, over time, become a long term triumph. Survey of Opinion Opinions are almost entirely positive. The bridge of course wobbles. Not as much as it did at first though, but enough to notice if you try. To some extent it made the builders, designers, and in particular Tony Blair’s New Labour Government, look very foolish. Some see even this as a positive. There were lots of Millennium projects, but this was one of the most visible ones, not least because of its position, and it apparently didn’t work very well as the newspapers and other media quickly made clear. One opinion is that they created a three dimensional bridge using a two dimensional model. That was ten years ago. Now it is accepted as a British triumph according to a survey of some twenty people, all of whom have walked across. It is fun. ‘No one remembers a bridge that stays still’ was one opinion from a happy and frequent user. It is also convenient – there are more tube stations and bus services near to the north bank of the Thames than the south and the bridge provides a convenient , safe link that is also a very positive experience, although it can be more than a little chilly in winter, something tourists from warmer countries have been heard to complain about. Yes, it does wobble, just a little – but this is taken as a lovely example of British eccentricity, as are the bales of straw that hang from the superstructure as a traditional warning to any ships that might pass underneath. And you never know who you will see taking this pleasant short cut - London lawyers with their silken bags, politicians, some you even recognise, parties of Japanese tourists following the uplifted umbrella of their guide , couples on honeymoon with arms entwined, Andrew Marr rushing to an interview, a crocodile of school girls or a star of the Shakespearean stage going to rehearsal. The large Globe Education project which opened in 2010 means even more people will need to cross the river safely, easily and quickly. The bridge is a perfect solution. No one who was surveyed thinks it should not have been built, though they do tend to think the extreme problems involved should have been more easily anticipated by the engineers. That it wasn’t seems to be generally considered to be because all bridges are unique. Their success depends not just on design, but such things as popularity, the weather conditions, the prevailing geography and a whole lot of other variables. Problems The first reaction of Tony Fitzpatrick of Arup, the project director, as seen on the video ‘London Millennium Bridge Opening’ was that ’All bridges move a little’. His next reaction, when he had actually seen what was occurring was ‘This isn’t real. This isn’t happening.’ The builders, despite all their research into such things as the foundations, cables, wind, vertical vibration and the bridge building codes, has not anticipated any such problem. The possibility was known to seismic engineers, but this information hadn’t reached bridge engineers, despite the fact that the same thing happened in Auckland in 1975 as described by the BBC In depth report, although this, it must be said, has a totally different plan and structure. The Auckland problem was a phenomenon which Arup describe as not known at the time to ‘practicing bridge engineers.’. This was a whole generation before the present problems emerged. What was happening in 2000 was that because of the wobble people began to widen their stance in order to maintain their balance, creating a sideways rather than a vertical vibration. The central section of the bridge was moving by up to 70mm. People were picking up the slight vibration of the bridge and ‘locking’ i.e. all fitting into a particular pattern of movement rather than moving randomly. It was more comfortable and felt safer and steadier to move with the same frequency as the movements of the bridge. Pat Dallard the project consultant explains how they thought they understood very well how such a bridge would perform when full of pedestrians and yet here it was doing something entirely unanticipated. It has long been known that if soldiers march in formation over as bridge this can create a repetitive vertical force which can be dangerous. For this reason soldiers are ordered to break step when crossing. A sign on the Albert Bridge up river stills warns about this possibility. A report on YouTube by Elsie Harris describes how this could not have been foreseen by the designers and engineers, and how, over time, reports came in from other bridges, one in Japan and one in Paris, where similar problems had been experienced when the crown syncronises its movements to the natural movement of the bridge. The immediate reaction was to limit the number of people crossing at one time, but this was not found to be a valid solution, and then within days the bridge had to be closed . The bridge had been heralded as ‘a blade of light’ across the Thames and as an ‘absolute statement of our capabilities at the beginning of the 21st century.’ as quoted by the BBC in depth report. The Science 2.0 web page report of 2008 says ‘Engineering Absolved – London Bridge ‘Wobble’ Happened Because People Walked Wrong’, in other words not the way the engineers expected them to perform. The problem wasn’t directly in the design, but by human behaviour. The people were, as they struggled to maintain their balance, unintentionally and unknowingly feeding energy in to the bridge vibrations, increasing rather than damping them. The Scientific Blogging web page quotes Dr John Macdonald, a senior Lecturer in Civil Engineering, who said in 2008: "It is clear that the motion of the bridge affects the force from the pedestrian, rather than the pedestrian simply applying an external force.” The Arup web page explains the forces generated. When people walk, as well as their body weight, a repetative pattern of forces is created as the body mass rises and falls with each step. With each step there is a flucuating verticla force of some 250 Newtons i.e. about 55 pounds. Also, because there is a sideways distance between the feet this causes a sway - a force of around 25 Newtons ( 5 lbs 8 oz) which is directed from side to side as weight is moved from the left to the right foot and back again. Solution The bridge was not designed to cope with great horizontal vibration modes but only vertical. The problem was solved by installing dampers at the points of support. At first the engineers proposed a stiffening of structures. Then they decided to limit numbers by using bollards and barriers. Both options were soon forgotten. Tests were carried out in the summer of 2000. The results indicated the validity of the original ideas, the assumptions made and the resultant model. Experts in the field from several countries who knew a great deal about bridges and vibrations were asked to provide further advice A database was built up of other possibly similar occurrences worldwide. A series of scientific tests using moving platforms were carried out at Southampton University and at London’s Imperial College. This was in order to determine the forces pedestrians create and the influence lateral movements have on these. Having obtained these results it was felt that the only way to replicate more precisely the conditions posed by large numbers of people of walking on the Millennium Bridge was to carry out crowd tests on the actual bridge. One hundred people were involved, some with sensors that detected how and where they put their feet. There were also devices fixed to the actual bridge to measure the amounts and types of movements. A second test was carried out 5 months later in December 2000 using 275 people. The final solution was the use of damping mechanisms to absorb the energy created by the movement of so many people at once. Stiffening of structures meant that the frequency of footsteps and movements of the bridge would no longer match so exactly. Gigantic shock absorbers were needed to limit the way the bridge responded to the forces placed upon it. This is a solution that has been tried in many other places, especially in areas susceptible to earth movements. They are a good solution because they are under the structure or otherwise out of sight so don’t affect the amazing view from the bridge. Two types of dampers, some similar to car shock absorbers, were used, some to counter quite small movements and others much larger ones. Costs The BBC in depth report on the Millenium Bridge, ‘What happened’ gives very prescise measurements and descriptions of the bridge, with its innovative lateral suspension system. They give the cost as £18,000,000 plus a further £5,000,000 in order to help fix the embarrassing problems. £7,000,000 of the original cost came from the Millenium Commission. Sustainability The bridge was finally reopened in February 2002 and is there toi stay. At the time of ther re-opening the weather conditions were not brilliant and pictures of the time show umbrellas galore as shown on the web page ‘Millenium Bridge Reopens’ from Urban 75 . Did the engineers fully take into account the effect of wind on so many umbrellas? But still the people came. Although relatively new the ‘wobbly’ bridge today is as much part of the London scene as the Houses of Parliament or the London Eye. The ‘bad’ publicity has resulted in the bridge itself becoming a major tourist attraction. It is listed on the ‘London Landmarks’ web site which considers it to be an ‘A list’ attraction. With the bridge cables below thin wafer of aluminium deck level views are totally unimpeded on the long central section, except for snow, sleet and rain. The cost of the bridge was enormous, especially with the necessary adjustments, but thousands of happy tourists cross it every day – and each one of them needs food, accomodation and all the rest. All these things mean more and more money pouring onto the coffers. London is a great city for walkers with everything within a relatively small area. It is especially great for those who walk across this very special bridge. Conclusion There are of course two or more ‘Millennium bridges - the other best known one linking Gateshead and Newcastle, but that is in the far north and most visitors arrive in the south. When American tourist stake a photo from the Millennium Bridge it is St Paul’s Cathedral they tend to have in their view finder rather than the Newcastle water front or Gateshead’s Sage Centre. Millennium Bridge looking towards St Paul’s Cathedral, London Landmarks. Millennium projects have varied in their success and their acceptability by the public. Some, not least the Millennium Dome, much of which has since been demolished, have been seen as irrelevant and a waste of money. The numbers of visitors was often lower than anticipated. In the case of the bridge, just as few imagined the original problems, few today can imagine how so much money can have been spent, with such a poor ( at first ) result. The public cannot understand how expert engineers could not have anticipated the chaos that resulted. They of course speak from a position of little or no knowledge. Today however, ten years on, the London Millennium Bridge is accepted as a permanent feature and as a necessity and a convenience and even loved, except perhaps in the depths of a British winter. Despite the often draughty passage it is used and used and re- used, wobble or not. References DALLARD, P. speaking on London Millenium Bridge Opening, available from http://www.youtube.com/watch?v=gQK21572oSU ( accessed 12th October 2010) SCIENTIFIC BLOGGING, 16th December 2008, Engineering absolved, - London Millennium Bridge ‘wobble’ happened because people walk wrong, available from http://www.science20.com/news_releases/engineering_absolved_london_millenium_bridge_wobble_happened_because_people_walk_wrong ( accessed 12th October 2010) FITZPATRICK.T. speaking on London Millenium Bridge Opening, available from http://www.youtube.com/watch?v=gQK21572oSU ( accessed 12th October 2010) HARRIS, E., London Millenium Bridge Opening, available from http://www.youtube.com/watch?v=gQK21572oSU ( accessed 12th October 2010) MILLENIUM BRIDGE, BBC In depth, available from http://news.bbc.co.uk/hi/english/static/in_depth/uk/2000/millennium_bridge/default.stm ( acessed 12th October 2010) MILLENIUM BRIDGE , LONDON, London Landmarks, available from http://www.urban75.org/london/millennium.html ( accessed 10th October 2010) MILLENIUM BRIDGE REOPENS, February 2002, Urban75, available from http://www.urban75.org/photos/london/lon182.html ( accessed 10th October 2010) THEMILLENNIUMBRIDGE, Arup, available from http://www.arup.com/MillenniumBridge/ ( accessed 12th October 2010) Read More