Millennium Bridge - Medium and value

Medium

The Millennium bridge is a suspension bridge, made exclusively for pedestrians, located over the Thames, in London. First bridge built since the Southwark bridge, in 1921, it has an architecture and a structure very different from its colleagues. It is made of steel, of course, like most modern bridges. One of its particularities comes from the fact that the city of London gave Norman Foster and his partners for this project restrictions on height, and also from the beautiful view on Saint paul cathedral that a low bridge offers on this place: indeed, supporting cables are below the deck level, thus giving this very thin profile. It was built on two big piers, which are on the Thames and cut the Millennium Bridge in three main sections: from North to South, the first one of 81m, the second one of 144m, and the last one of 108m. That gives us a total length of....... 325m, according to official data, which seems impossible when you calculate but... That's how it is... However, regardless of those three sections, the bridge, when seen from above, consists of 2 “Y” frames. But a bridge is meant to be crossed, therefore there is a 4m wide lightweight aluminium deck. The 8 supporting cable pull with a force of 2000 tons against the structures set on each bank. That represents 2400 twingos ! Anyway, that also represents a virtual capacity of 5000 people walking on the bridge at the same time. I'd like to conclude this part by saying that Mr Foster's partner Arup, who was responsible of the engineering part, did quite a bad job, as a phenomenon of resonant structural response, which caused the bridge to move when too much people crossed it. What was identified as a Synchronous lateral excitation was later fixed.

Value

Now let's take a look at the value of the Millennium Bridge. Its initial budget was 18,2million £, but, as always in such project, there was a delay and there were extra costs: it is eventually worth more than 20million £. As it does not use revolutionary techniques or scarce materials, this is not incredibly expensive for a bridge. However, I explained in the Medium part that a phenomenon of resonant structural response affected the structure. Given the famous incident of the Tacoma Bridge, in 1941, engineers took the wise decision of doing something, as a disaster involving innocent citizens drowning in the center of London would NOT be a good advertisement. Modifications lasted 6 months and were successful, but they raised the expenditures linked to the Millennium Bridge: that was an extra 5million £ to spend. Nevertheless, even though I don't want to spoil the rest of our presentation, let's just say that the view on Saint Paul Cathedrale and the presence of old and famous neighbours, such as the London Bridge, the Millenium Bridge, has a very important value that can't be measured with cash.